Auto merge of #100043 - RalfJung:scalar-always-init, r=RalfJung

interpret: remove support for uninitialized scalars

With Miri no longer supporting `-Zmiri-allow-uninit-numbers`, we no longer need to support storing uninit data in a `Scalar`. We anyway already only use this representation for types with *initialized* `Scalar` layout (and we have to, due to partial initialization), so let's get rid of the `ScalarMaybeUninit` type entirely.

I tried to stage this into meaningful commits, but the one that changes `read_immediate` to always trigger UB on uninit is the largest chunk of the PR and I don't see how it could be subdivided.

Fixes https://github.com/rust-lang/miri/issues/2187
r? `@oli-obk`

35 files changed, 282 insertions, 429 deletions

diff --git a/src/test/ui/const-generics/min_const_generics/invalid-patterns.32bit.stderr b/src/test/ui/const-generics/min_const_generics/invalid-patterns.32bit.stderr
index f5396b8381a..be92429e3ab 100644
--- a/src/test/ui/const-generics/min_const_generics/invalid-patterns.32bit.stderr
+++ b/src/test/ui/const-generics/min_const_generics/invalid-patterns.32bit.stderr
@@ -22,19 +22,14 @@ error[E0308]: mismatched types
 LL |   get_flag::<42, 0x5ad>();
    |                  ^^^^^ expected `char`, found `u8`
 
-error[E0080]: it is undefined behavior to use this value
-  --> $DIR/invalid-patterns.rs:38:21
+error[E0080]: evaluation of constant value failed
+  --> $DIR/invalid-patterns.rs:38:32
    |
 LL |   get_flag::<false, { unsafe { char_raw.character } }>();
-   |                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value: encountered uninitialized bytes, but expected a valid unicode scalar value (in `0..=0x10FFFF` but not in `0xD800..=0xDFFF`)
-   |
-   = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rustc repository if you believe it should not be considered undefined behavior.
-   = note: the raw bytes of the constant (size: 4, align: 4) {
-               __ __ __ __                                     │ ░░░░
-           }
+   |                                ^^^^^^^^^^^^^^^^^^ using uninitialized data, but this operation requires initialized memory
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/invalid-patterns.rs:40:14
+  --> $DIR/invalid-patterns.rs:41:14
    |
 LL |   get_flag::<{ unsafe { bool_raw.boolean } }, 'z'>();
    |              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value: encountered 0x42, but expected a boolean
@@ -45,7 +40,7 @@ LL |   get_flag::<{ unsafe { bool_raw.boolean } }, 'z'>();
            }
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/invalid-patterns.rs:42:14
+  --> $DIR/invalid-patterns.rs:43:14
    |
 LL |   get_flag::<{ unsafe { bool_raw.boolean } }, { unsafe { char_raw.character } }>();
    |              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value: encountered 0x42, but expected a boolean
@@ -55,16 +50,11 @@ LL |   get_flag::<{ unsafe { bool_raw.boolean } }, { unsafe { char_raw.character
                42                                              │ B
            }
 
-error[E0080]: it is undefined behavior to use this value
-  --> $DIR/invalid-patterns.rs:42:47
+error[E0080]: evaluation of constant value failed
+  --> $DIR/invalid-patterns.rs:43:58
    |
 LL |   get_flag::<{ unsafe { bool_raw.boolean } }, { unsafe { char_raw.character } }>();
-   |                                               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value: encountered uninitialized bytes, but expected a valid unicode scalar value (in `0..=0x10FFFF` but not in `0xD800..=0xDFFF`)
-   |
-   = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rustc repository if you believe it should not be considered undefined behavior.
-   = note: the raw bytes of the constant (size: 4, align: 4) {
-               __ __ __ __                                     │ ░░░░
-           }
+   |                                                          ^^^^^^^^^^^^^^^^^^ using uninitialized data, but this operation requires initialized memory
 
 error: aborting due to 8 previous errors
 
diff --git a/src/test/ui/const-generics/min_const_generics/invalid-patterns.64bit.stderr b/src/test/ui/const-generics/min_const_generics/invalid-patterns.64bit.stderr
index f5396b8381a..be92429e3ab 100644
--- a/src/test/ui/const-generics/min_const_generics/invalid-patterns.64bit.stderr
+++ b/src/test/ui/const-generics/min_const_generics/invalid-patterns.64bit.stderr
@@ -22,19 +22,14 @@ error[E0308]: mismatched types
 LL |   get_flag::<42, 0x5ad>();
    |                  ^^^^^ expected `char`, found `u8`
 
-error[E0080]: it is undefined behavior to use this value
-  --> $DIR/invalid-patterns.rs:38:21
+error[E0080]: evaluation of constant value failed
+  --> $DIR/invalid-patterns.rs:38:32
    |
 LL |   get_flag::<false, { unsafe { char_raw.character } }>();
-   |                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value: encountered uninitialized bytes, but expected a valid unicode scalar value (in `0..=0x10FFFF` but not in `0xD800..=0xDFFF`)
-   |
-   = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rustc repository if you believe it should not be considered undefined behavior.
-   = note: the raw bytes of the constant (size: 4, align: 4) {
-               __ __ __ __                                     │ ░░░░
-           }
+   |                                ^^^^^^^^^^^^^^^^^^ using uninitialized data, but this operation requires initialized memory
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/invalid-patterns.rs:40:14
+  --> $DIR/invalid-patterns.rs:41:14
    |
 LL |   get_flag::<{ unsafe { bool_raw.boolean } }, 'z'>();
    |              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value: encountered 0x42, but expected a boolean
@@ -45,7 +40,7 @@ LL |   get_flag::<{ unsafe { bool_raw.boolean } }, 'z'>();
            }
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/invalid-patterns.rs:42:14
+  --> $DIR/invalid-patterns.rs:43:14
    |
 LL |   get_flag::<{ unsafe { bool_raw.boolean } }, { unsafe { char_raw.character } }>();
    |              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value: encountered 0x42, but expected a boolean
@@ -55,16 +50,11 @@ LL |   get_flag::<{ unsafe { bool_raw.boolean } }, { unsafe { char_raw.character
                42                                              │ B
            }
 
-error[E0080]: it is undefined behavior to use this value
-  --> $DIR/invalid-patterns.rs:42:47
+error[E0080]: evaluation of constant value failed
+  --> $DIR/invalid-patterns.rs:43:58
    |
 LL |   get_flag::<{ unsafe { bool_raw.boolean } }, { unsafe { char_raw.character } }>();
-   |                                               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value: encountered uninitialized bytes, but expected a valid unicode scalar value (in `0..=0x10FFFF` but not in `0xD800..=0xDFFF`)
-   |
-   = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rustc repository if you believe it should not be considered undefined behavior.
-   = note: the raw bytes of the constant (size: 4, align: 4) {
-               __ __ __ __                                     │ ░░░░
-           }
+   |                                                          ^^^^^^^^^^^^^^^^^^ using uninitialized data, but this operation requires initialized memory
 
 error: aborting due to 8 previous errors
 
diff --git a/src/test/ui/const-generics/min_const_generics/invalid-patterns.rs b/src/test/ui/const-generics/min_const_generics/invalid-patterns.rs
index 682e0eced9d..13b2cca2f24 100644
--- a/src/test/ui/const-generics/min_const_generics/invalid-patterns.rs
+++ b/src/test/ui/const-generics/min_const_generics/invalid-patterns.rs
@@ -36,10 +36,12 @@ fn main() {
 
 
   get_flag::<false, { unsafe { char_raw.character } }>();
-  //~^ ERROR it is undefined behavior
+  //~^ ERROR evaluation of constant value failed
+  //~| uninitialized
   get_flag::<{ unsafe { bool_raw.boolean } }, 'z'>();
   //~^ ERROR it is undefined behavior
   get_flag::<{ unsafe { bool_raw.boolean } }, { unsafe { char_raw.character } }>();
-  //~^ ERROR it is undefined behavior
+  //~^ ERROR evaluation of constant value failed
+  //~| uninitialized
   //~| ERROR it is undefined behavior
 }
diff --git a/src/test/ui/consts/const-err4.32bit.stderr b/src/test/ui/consts/const-err4.32bit.stderr
index a553847833a..1cbf78173a7 100644
--- a/src/test/ui/consts/const-err4.32bit.stderr
+++ b/src/test/ui/consts/const-err4.32bit.stderr
@@ -1,13 +1,8 @@
-error[E0080]: it is undefined behavior to use this value
-  --> $DIR/const-err4.rs:9:11
+error[E0080]: evaluation of constant value failed
+  --> $DIR/const-err4.rs:9:21
    |
 LL |     Boo = [unsafe { Foo { b: () }.a }; 4][3],
-   |           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value: encountered uninitialized bytes, but expected initialized bytes
-   |
-   = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rustc repository if you believe it should not be considered undefined behavior.
-   = note: the raw bytes of the constant (size: 4, align: 4) {
-               __ __ __ __                                     │ ░░░░
-           }
+   |                     ^^^^^^^^^^^^^^^ using uninitialized data, but this operation requires initialized memory
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/consts/const-err4.64bit.stderr b/src/test/ui/consts/const-err4.64bit.stderr
index 66bfc30c3a8..1cbf78173a7 100644
--- a/src/test/ui/consts/const-err4.64bit.stderr
+++ b/src/test/ui/consts/const-err4.64bit.stderr
@@ -1,13 +1,8 @@
-error[E0080]: it is undefined behavior to use this value
-  --> $DIR/const-err4.rs:9:11
+error[E0080]: evaluation of constant value failed
+  --> $DIR/const-err4.rs:9:21
    |
 LL |     Boo = [unsafe { Foo { b: () }.a }; 4][3],
-   |           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value: encountered uninitialized bytes, but expected initialized bytes
-   |
-   = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rustc repository if you believe it should not be considered undefined behavior.
-   = note: the raw bytes of the constant (size: 8, align: 8) {
-               __ __ __ __ __ __ __ __                         │ ░░░░░░░░
-           }
+   |                     ^^^^^^^^^^^^^^^ using uninitialized data, but this operation requires initialized memory
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/consts/const-err4.rs b/src/test/ui/consts/const-err4.rs
index f0625faa801..107dc3f8234 100644
--- a/src/test/ui/consts/const-err4.rs
+++ b/src/test/ui/consts/const-err4.rs
@@ -7,7 +7,8 @@ union Foo {
 
 enum Bar {
     Boo = [unsafe { Foo { b: () }.a }; 4][3],
-    //~^ ERROR it is undefined behavior to use this value
+    //~^ ERROR evaluation of constant value failed
+    //~| uninitialized
 }
 
 fn main() {
diff --git a/src/test/ui/consts/const-eval/const-pointer-values-in-various-types.64bit.stderr b/src/test/ui/consts/const-eval/const-pointer-values-in-various-types.64bit.stderr
index 655a7d52054..82afa70309d 100644
--- a/src/test/ui/consts/const-eval/const-pointer-values-in-various-types.64bit.stderr
+++ b/src/test/ui/consts/const-eval/const-pointer-values-in-various-types.64bit.stderr
@@ -44,19 +44,14 @@ LL |     const I32_REF_U64_UNION: u64 = unsafe { Nonsense { int_32_ref: &3 }.uin
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
    = note: for more information, see issue #71800 <https://github.com/rust-lang/rust/issues/71800>
 
-error[E0080]: it is undefined behavior to use this value
-  --> $DIR/const-pointer-values-in-various-types.rs:46:5
+error[E0080]: evaluation of constant value failed
+  --> $DIR/const-pointer-values-in-various-types.rs:46:47
    |
 LL |     const I32_REF_U128_UNION: u128 = unsafe { Nonsense { int_32_ref: &3 }.uint_128 };
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value: encountered uninitialized bytes, but expected initialized bytes
-   |
-   = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rustc repository if you believe it should not be considered undefined behavior.
-   = note: the raw bytes of the constant (size: 16, align: 8) {
-               __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ │ ░░░░░░░░░░░░░░░░
-           }
+   |                                               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ using uninitialized data, but this operation requires initialized memory
 
 error: any use of this value will cause an error
-  --> $DIR/const-pointer-values-in-various-types.rs:49:43
+  --> $DIR/const-pointer-values-in-various-types.rs:50:43
    |
 LL |     const I32_REF_I8_UNION: i8 = unsafe { Nonsense { int_32_ref: &3 }.int_8 };
    |     --------------------------            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unable to turn pointer into raw bytes
@@ -65,7 +60,7 @@ LL |     const I32_REF_I8_UNION: i8 = unsafe { Nonsense { int_32_ref: &3 }.int_8
    = note: for more information, see issue #71800 <https://github.com/rust-lang/rust/issues/71800>
 
 error: any use of this value will cause an error
-  --> $DIR/const-pointer-values-in-various-types.rs:53:45
+  --> $DIR/const-pointer-values-in-various-types.rs:54:45
    |
 LL |     const I32_REF_I16_UNION: i16 = unsafe { Nonsense { int_32_ref: &3 }.int_16 };
    |     ----------------------------            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unable to turn pointer into raw bytes
@@ -74,7 +69,7 @@ LL |     const I32_REF_I16_UNION: i16 = unsafe { Nonsense { int_32_ref: &3 }.int
    = note: for more information, see issue #71800 <https://github.com/rust-lang/rust/issues/71800>
 
 error: any use of this value will cause an error
-  --> $DIR/const-pointer-values-in-various-types.rs:57:45
+  --> $DIR/const-pointer-values-in-various-types.rs:58:45
    |
 LL |     const I32_REF_I32_UNION: i32 = unsafe { Nonsense { int_32_ref: &3 }.int_32 };
    |     ----------------------------            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unable to turn pointer into raw bytes
@@ -83,7 +78,7 @@ LL |     const I32_REF_I32_UNION: i32 = unsafe { Nonsense { int_32_ref: &3 }.int
    = note: for more information, see issue #71800 <https://github.com/rust-lang/rust/issues/71800>
 
 error: any use of this value will cause an error
-  --> $DIR/const-pointer-values-in-various-types.rs:61:45
+  --> $DIR/const-pointer-values-in-various-types.rs:62:45
    |
 LL |     const I32_REF_I64_UNION: i64 = unsafe { Nonsense { int_32_ref: &3 }.int_64 };
    |     ----------------------------            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unable to turn pointer into raw bytes
@@ -91,19 +86,14 @@ LL |     const I32_REF_I64_UNION: i64 = unsafe { Nonsense { int_32_ref: &3 }.int
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
    = note: for more information, see issue #71800 <https://github.com/rust-lang/rust/issues/71800>
 
-error[E0080]: it is undefined behavior to use this value
-  --> $DIR/const-pointer-values-in-various-types.rs:65:5
+error[E0080]: evaluation of constant value failed
+  --> $DIR/const-pointer-values-in-various-types.rs:66:47
    |
 LL |     const I32_REF_I128_UNION: i128 = unsafe { Nonsense { int_32_ref: &3 }.int_128 };
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value: encountered uninitialized bytes, but expected initialized bytes
-   |
-   = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rustc repository if you believe it should not be considered undefined behavior.
-   = note: the raw bytes of the constant (size: 16, align: 8) {
-               __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ │ ░░░░░░░░░░░░░░░░
-           }
+   |                                               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ using uninitialized data, but this operation requires initialized memory
 
 error: any use of this value will cause an error
-  --> $DIR/const-pointer-values-in-various-types.rs:68:45
+  --> $DIR/const-pointer-values-in-various-types.rs:70:45
    |
 LL |     const I32_REF_F32_UNION: f32 = unsafe { Nonsense { int_32_ref: &3 }.float_32 };
    |     ----------------------------            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unable to turn pointer into raw bytes
@@ -112,7 +102,7 @@ LL |     const I32_REF_F32_UNION: f32 = unsafe { Nonsense { int_32_ref: &3 }.flo
    = note: for more information, see issue #71800 <https://github.com/rust-lang/rust/issues/71800>
 
 error: any use of this value will cause an error
-  --> $DIR/const-pointer-values-in-various-types.rs:72:45
+  --> $DIR/const-pointer-values-in-various-types.rs:74:45
    |
 LL |     const I32_REF_F64_UNION: f64 = unsafe { Nonsense { int_32_ref: &3 }.float_64 };
    |     ----------------------------            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unable to turn pointer into raw bytes
@@ -121,7 +111,7 @@ LL |     const I32_REF_F64_UNION: f64 = unsafe { Nonsense { int_32_ref: &3 }.flo
    = note: for more information, see issue #71800 <https://github.com/rust-lang/rust/issues/71800>
 
 error: any use of this value will cause an error
-  --> $DIR/const-pointer-values-in-various-types.rs:76:47
+  --> $DIR/const-pointer-values-in-various-types.rs:78:47
    |
 LL |     const I32_REF_BOOL_UNION: bool = unsafe { Nonsense { int_32_ref: &3 }.truthy_falsey };
    |     ------------------------------            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unable to turn pointer into raw bytes
@@ -130,7 +120,7 @@ LL |     const I32_REF_BOOL_UNION: bool = unsafe { Nonsense { int_32_ref: &3 }.t
    = note: for more information, see issue #71800 <https://github.com/rust-lang/rust/issues/71800>
 
 error: any use of this value will cause an error
-  --> $DIR/const-pointer-values-in-various-types.rs:80:47
+  --> $DIR/const-pointer-values-in-various-types.rs:82:47
    |
 LL |     const I32_REF_CHAR_UNION: char = unsafe { Nonsense { int_32_ref: &3 }.character };
    |     ------------------------------            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unable to turn pointer into raw bytes
@@ -139,7 +129,7 @@ LL |     const I32_REF_CHAR_UNION: char = unsafe { Nonsense { int_32_ref: &3 }.c
    = note: for more information, see issue #71800 <https://github.com/rust-lang/rust/issues/71800>
 
 error: any use of this value will cause an error
-  --> $DIR/const-pointer-values-in-various-types.rs:84:39
+  --> $DIR/const-pointer-values-in-various-types.rs:86:39
    |
 LL |     const STR_U8_UNION: u8 = unsafe { Nonsense { stringy: "3" }.uint_8 };
    |     ----------------------            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unable to turn pointer into raw bytes
@@ -148,7 +138,7 @@ LL |     const STR_U8_UNION: u8 = unsafe { Nonsense { stringy: "3" }.uint_8 };
    = note: for more information, see issue #71800 <https://github.com/rust-lang/rust/issues/71800>
 
 error: any use of this value will cause an error
-  --> $DIR/const-pointer-values-in-various-types.rs:88:41
+  --> $DIR/const-pointer-values-in-various-types.rs:90:41
    |
 LL |     const STR_U16_UNION: u16 = unsafe { Nonsense { stringy: "3" }.uint_16 };
    |     ------------------------            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unable to turn pointer into raw bytes
@@ -157,7 +147,7 @@ LL |     const STR_U16_UNION: u16 = unsafe { Nonsense { stringy: "3" }.uint_16 }
    = note: for more information, see issue #71800 <https://github.com/rust-lang/rust/issues/71800>
 
 error: any use of this value will cause an error
-  --> $DIR/const-pointer-values-in-various-types.rs:92:41
+  --> $DIR/const-pointer-values-in-various-types.rs:94:41
    |
 LL |     const STR_U32_UNION: u32 = unsafe { Nonsense { stringy: "3" }.uint_32 };
    |     ------------------------            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unable to turn pointer into raw bytes
@@ -166,7 +156,7 @@ LL |     const STR_U32_UNION: u32 = unsafe { Nonsense { stringy: "3" }.uint_32 }
    = note: for more information, see issue #71800 <https://github.com/rust-lang/rust/issues/71800>
 
 error: any use of this value will cause an error
-  --> $DIR/const-pointer-values-in-various-types.rs:96:41
+  --> $DIR/const-pointer-values-in-various-types.rs:98:41
    |
 LL |     const STR_U64_UNION: u64 = unsafe { Nonsense { stringy: "3" }.uint_64 };
    |     ------------------------            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unable to turn pointer into raw bytes
@@ -175,7 +165,7 @@ LL |     const STR_U64_UNION: u64 = unsafe { Nonsense { stringy: "3" }.uint_64 }
    = note: for more information, see issue #71800 <https://github.com/rust-lang/rust/issues/71800>
 
 error: any use of this value will cause an error
-  --> $DIR/const-pointer-values-in-various-types.rs:100:43
+  --> $DIR/const-pointer-values-in-various-types.rs:102:43
    |
 LL |     const STR_U128_UNION: u128 = unsafe { Nonsense { stringy: "3" }.uint_128 };
    |     --------------------------            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unable to turn pointer into raw bytes
@@ -184,7 +174,7 @@ LL |     const STR_U128_UNION: u128 = unsafe { Nonsense { stringy: "3" }.uint_12
    = note: for more information, see issue #71800 <https://github.com/rust-lang/rust/issues/71800>
 
 error: any use of this value will cause an error
-  --> $DIR/const-pointer-values-in-various-types.rs:104:39
+  --> $DIR/const-pointer-values-in-various-types.rs:106:39
    |
 LL |     const STR_I8_UNION: i8 = unsafe { Nonsense { stringy: "3" }.int_8 };
    |     ----------------------            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unable to turn pointer into raw bytes
@@ -193,7 +183,7 @@ LL |     const STR_I8_UNION: i8 = unsafe { Nonsense { stringy: "3" }.int_8 };
    = note: for more information, see issue #71800 <https://github.com/rust-lang/rust/issues/71800>
 
 error: any use of this value will cause an error
-  --> $DIR/const-pointer-values-in-various-types.rs:108:41
+  --> $DIR/const-pointer-values-in-various-types.rs:110:41
    |
 LL |     const STR_I16_UNION: i16 = unsafe { Nonsense { stringy: "3" }.int_16 };
    |     ------------------------            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unable to turn pointer into raw bytes
@@ -202,7 +192,7 @@ LL |     const STR_I16_UNION: i16 = unsafe { Nonsense { stringy: "3" }.int_16 };
    = note: for more information, see issue #71800 <https://github.com/rust-lang/rust/issues/71800>
 
 error: any use of this value will cause an error
-  --> $DIR/const-pointer-values-in-various-types.rs:112:41
+  --> $DIR/const-pointer-values-in-various-types.rs:114:41
    |
 LL |     const STR_I32_UNION: i32 = unsafe { Nonsense { stringy: "3" }.int_32 };
    |     ------------------------            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unable to turn pointer into raw bytes
@@ -211,7 +201,7 @@ LL |     const STR_I32_UNION: i32 = unsafe { Nonsense { stringy: "3" }.int_32 };
    = note: for more information, see issue #71800 <https://github.com/rust-lang/rust/issues/71800>
 
 error: any use of this value will cause an error
-  --> $DIR/const-pointer-values-in-various-types.rs:116:41
+  --> $DIR/const-pointer-values-in-various-types.rs:118:41
    |
 LL |     const STR_I64_UNION: i64 = unsafe { Nonsense { stringy: "3" }.int_64 };
    |     ------------------------            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unable to turn pointer into raw bytes
@@ -220,7 +210,7 @@ LL |     const STR_I64_UNION: i64 = unsafe { Nonsense { stringy: "3" }.int_64 };
    = note: for more information, see issue #71800 <https://github.com/rust-lang/rust/issues/71800>
 
 error: any use of this value will cause an error
-  --> $DIR/const-pointer-values-in-various-types.rs:120:43
+  --> $DIR/const-pointer-values-in-various-types.rs:122:43
    |
 LL |     const STR_I128_UNION: i128 = unsafe { Nonsense { stringy: "3" }.int_128 };
    |     --------------------------            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unable to turn pointer into raw bytes
@@ -229,7 +219,7 @@ LL |     const STR_I128_UNION: i128 = unsafe { Nonsense { stringy: "3" }.int_128
    = note: for more information, see issue #71800 <https://github.com/rust-lang/rust/issues/71800>
 
 error: any use of this value will cause an error
-  --> $DIR/const-pointer-values-in-various-types.rs:124:41
+  --> $DIR/const-pointer-values-in-various-types.rs:126:41
    |
 LL |     const STR_F32_UNION: f32 = unsafe { Nonsense { stringy: "3" }.float_32 };
    |     ------------------------            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unable to turn pointer into raw bytes
@@ -238,7 +228,7 @@ LL |     const STR_F32_UNION: f32 = unsafe { Nonsense { stringy: "3" }.float_32
    = note: for more information, see issue #71800 <https://github.com/rust-lang/rust/issues/71800>
 
 error: any use of this value will cause an error
-  --> $DIR/const-pointer-values-in-various-types.rs:128:41
+  --> $DIR/const-pointer-values-in-various-types.rs:130:41
    |
 LL |     const STR_F64_UNION: f64 = unsafe { Nonsense { stringy: "3" }.float_64 };
    |     ------------------------            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unable to turn pointer into raw bytes
@@ -247,7 +237,7 @@ LL |     const STR_F64_UNION: f64 = unsafe { Nonsense { stringy: "3" }.float_64
    = note: for more information, see issue #71800 <https://github.com/rust-lang/rust/issues/71800>
 
 error: any use of this value will cause an error
-  --> $DIR/const-pointer-values-in-various-types.rs:132:43
+  --> $DIR/const-pointer-values-in-various-types.rs:134:43
    |
 LL |     const STR_BOOL_UNION: bool = unsafe { Nonsense { stringy: "3" }.truthy_falsey };
    |     --------------------------            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unable to turn pointer into raw bytes
@@ -256,7 +246,7 @@ LL |     const STR_BOOL_UNION: bool = unsafe { Nonsense { stringy: "3" }.truthy_
    = note: for more information, see issue #71800 <https://github.com/rust-lang/rust/issues/71800>
 
 error: any use of this value will cause an error
-  --> $DIR/const-pointer-values-in-various-types.rs:136:43
+  --> $DIR/const-pointer-values-in-various-types.rs:138:43
    |
 LL |     const STR_CHAR_UNION: char = unsafe { Nonsense { stringy: "3" }.character };
    |     --------------------------            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unable to turn pointer into raw bytes
@@ -324,7 +314,7 @@ LL |     const I32_REF_U64_UNION: u64 = unsafe { Nonsense { int_32_ref: &3 }.uin
 
 Future breakage diagnostic:
 error: any use of this value will cause an error
-  --> $DIR/const-pointer-values-in-various-types.rs:49:43
+  --> $DIR/const-pointer-values-in-various-types.rs:50:43
    |
 LL |     const I32_REF_I8_UNION: i8 = unsafe { Nonsense { int_32_ref: &3 }.int_8 };
    |     --------------------------            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unable to turn pointer into raw bytes
@@ -335,7 +325,7 @@ LL |     const I32_REF_I8_UNION: i8 = unsafe { Nonsense { int_32_ref: &3 }.int_8
 
 Future breakage diagnostic:
 error: any use of this value will cause an error
-  --> $DIR/const-pointer-values-in-various-types.rs:53:45
+  --> $DIR/const-pointer-values-in-various-types.rs:54:45
    |
 LL |     const I32_REF_I16_UNION: i16 = unsafe { Nonsense { int_32_ref: &3 }.int_16 };
    |     ----------------------------            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unable to turn pointer into raw bytes
@@ -346,7 +336,7 @@ LL |     const I32_REF_I16_UNION: i16 = unsafe { Nonsense { int_32_ref: &3 }.int
 
 Future breakage diagnostic:
 error: any use of this value will cause an error
-  --> $DIR/const-pointer-values-in-various-types.rs:57:45
+  --> $DIR/const-pointer-values-in-various-types.rs:58:45
    |
 LL |     const I32_REF_I32_UNION: i32 = unsafe { Nonsense { int_32_ref: &3 }.int_32 };
    |     ----------------------------            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unable to turn pointer into raw bytes
@@ -357,7 +347,7 @@ LL |     const I32_REF_I32_UNION: i32 = unsafe { Nonsense { int_32_ref: &3 }.int
 
 Future breakage diagnostic:
 error: any use of this value will cause an error
-  --> $DIR/const-pointer-values-in-various-types.rs:61:45
+  --> $DIR/const-pointer-values-in-various-types.rs:62:45
    |
 LL |     const I32_REF_I64_UNION: i64 = unsafe { Nonsense { int_32_ref: &3 }.int_64 };
    |     ----------------------------            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unable to turn pointer into raw bytes
@@ -368,7 +358,7 @@ LL |     const I32_REF_I64_UNION: i64 = unsafe { Nonsense { int_32_ref: &3 }.int
 
 Future breakage diagnostic:
 error: any use of this value will cause an error
-  --> $DIR/const-pointer-values-in-various-types.rs:68:45
+  --> $DIR/const-pointer-values-in-various-types.rs:70:45
    |
 LL |     const I32_REF_F32_UNION: f32 = unsafe { Nonsense { int_32_ref: &3 }.float_32 };
    |     ----------------------------            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unable to turn pointer into raw bytes
@@ -379,7 +369,7 @@ LL |     const I32_REF_F32_UNION: f32 = unsafe { Nonsense { int_32_ref: &3 }.flo
 
 Future breakage diagnostic:
 error: any use of this value will cause an error
-  --> $DIR/const-pointer-values-in-various-types.rs:72:45
+  --> $DIR/const-pointer-values-in-various-types.rs:74:45
    |
 LL |     const I32_REF_F64_UNION: f64 = unsafe { Nonsense { int_32_ref: &3 }.float_64 };
    |     ----------------------------            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unable to turn pointer into raw bytes
@@ -390,7 +380,7 @@ LL |     const I32_REF_F64_UNION: f64 = unsafe { Nonsense { int_32_ref: &3 }.flo
 
 Future breakage diagnostic:
 error: any use of this value will cause an error
-  --> $DIR/const-pointer-values-in-various-types.rs:76:47
+  --> $DIR/const-pointer-values-in-various-types.rs:78:47
    |
 LL |     const I32_REF_BOOL_UNION: bool = unsafe { Nonsense { int_32_ref: &3 }.truthy_falsey };
    |     ------------------------------            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unable to turn pointer into raw bytes
@@ -401,7 +391,7 @@ LL |     const I32_REF_BOOL_UNION: bool = unsafe { Nonsense { int_32_ref: &3 }.t
 
 Future breakage diagnostic:
 error: any use of this value will cause an error
-  --> $DIR/const-pointer-values-in-various-types.rs:80:47
+  --> $DIR/const-pointer-values-in-various-types.rs:82:47
    |
 LL |     const I32_REF_CHAR_UNION: char = unsafe { Nonsense { int_32_ref: &3 }.character };
    |     ------------------------------            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unable to turn pointer into raw bytes
@@ -412,7 +402,7 @@ LL |     const I32_REF_CHAR_UNION: char = unsafe { Nonsense { int_32_ref: &3 }.c
 
 Future breakage diagnostic:
 error: any use of this value will cause an error
-  --> $DIR/const-pointer-values-in-various-types.rs:84:39
+  --> $DIR/const-pointer-values-in-various-types.rs:86:39
    |
 LL |     const STR_U8_UNION: u8 = unsafe { Nonsense { stringy: "3" }.uint_8 };
    |     ----------------------            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unable to turn pointer into raw bytes
@@ -423,7 +413,7 @@ LL |     const STR_U8_UNION: u8 = unsafe { Nonsense { stringy: "3" }.uint_8 };
 
 Future breakage diagnostic:
 error: any use of this value will cause an error
-  --> $DIR/const-pointer-values-in-various-types.rs:88:41
+  --> $DIR/const-pointer-values-in-various-types.rs:90:41
    |
 LL |     const STR_U16_UNION: u16 = unsafe { Nonsense { stringy: "3" }.uint_16 };
    |     ------------------------            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unable to turn pointer into raw bytes
@@ -434,7 +424,7 @@ LL |     const STR_U16_UNION: u16 = unsafe { Nonsense { stringy: "3" }.uint_16 }
 
 Future breakage diagnostic:
 error: any use of this value will cause an error
-  --> $DIR/const-pointer-values-in-various-types.rs:92:41
+  --> $DIR/const-pointer-values-in-various-types.rs:94:41
    |
 LL |     const STR_U32_UNION: u32 = unsafe { Nonsense { stringy: "3" }.uint_32 };
    |     ------------------------            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unable to turn pointer into raw bytes
@@ -445,7 +435,7 @@ LL |     const STR_U32_UNION: u32 = unsafe { Nonsense { stringy: "3" }.uint_32 }
 
 Future breakage diagnostic:
 error: any use of this value will cause an error
-  --> $DIR/const-pointer-values-in-various-types.rs:96:41
+  --> $DIR/const-pointer-values-in-various-types.rs:98:41
    |
 LL |     const STR_U64_UNION: u64 = unsafe { Nonsense { stringy: "3" }.uint_64 };
    |     ------------------------            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unable to turn pointer into raw bytes
@@ -456,7 +446,7 @@ LL |     const STR_U64_UNION: u64 = unsafe { Nonsense { stringy: "3" }.uint_64 }
 
 Future breakage diagnostic:
 error: any use of this value will cause an error
-  --> $DIR/const-pointer-values-in-various-types.rs:100:43
+  --> $DIR/const-pointer-values-in-various-types.rs:102:43
    |
 LL |     const STR_U128_UNION: u128 = unsafe { Nonsense { stringy: "3" }.uint_128 };
    |     --------------------------            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unable to turn pointer into raw bytes
@@ -467,7 +457,7 @@ LL |     const STR_U128_UNION: u128 = unsafe { Nonsense { stringy: "3" }.uint_12
 
 Future breakage diagnostic:
 error: any use of this value will cause an error
-  --> $DIR/const-pointer-values-in-various-types.rs:104:39
+  --> $DIR/const-pointer-values-in-various-types.rs:106:39
    |
 LL |     const STR_I8_UNION: i8 = unsafe { Nonsense { stringy: "3" }.int_8 };
    |     ----------------------            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unable to turn pointer into raw bytes
@@ -478,7 +468,7 @@ LL |     const STR_I8_UNION: i8 = unsafe { Nonsense { stringy: "3" }.int_8 };
 
 Future breakage diagnostic:
 error: any use of this value will cause an error
-  --> $DIR/const-pointer-values-in-various-types.rs:108:41
+  --> $DIR/const-pointer-values-in-various-types.rs:110:41
    |
 LL |     const STR_I16_UNION: i16 = unsafe { Nonsense { stringy: "3" }.int_16 };
    |     ------------------------            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unable to turn pointer into raw bytes
@@ -489,7 +479,7 @@ LL |     const STR_I16_UNION: i16 = unsafe { Nonsense { stringy: "3" }.int_16 };
 
 Future breakage diagnostic:
 error: any use of this value will cause an error
-  --> $DIR/const-pointer-values-in-various-types.rs:112:41
+  --> $DIR/const-pointer-values-in-various-types.rs:114:41
    |
 LL |     const STR_I32_UNION: i32 = unsafe { Nonsense { stringy: "3" }.int_32 };
    |     ------------------------            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unable to turn pointer into raw bytes
@@ -500,7 +490,7 @@ LL |     const STR_I32_UNION: i32 = unsafe { Nonsense { stringy: "3" }.int_32 };
 
 Future breakage diagnostic:
 error: any use of this value will cause an error
-  --> $DIR/const-pointer-values-in-various-types.rs:116:41
+  --> $DIR/const-pointer-values-in-various-types.rs:118:41
    |
 LL |     const STR_I64_UNION: i64 = unsafe { Nonsense { stringy: "3" }.int_64 };
    |     ------------------------            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unable to turn pointer into raw bytes
@@ -511,7 +501,7 @@ LL |     const STR_I64_UNION: i64 = unsafe { Nonsense { stringy: "3" }.int_64 };
 
 Future breakage diagnostic:
 error: any use of this value will cause an error
-  --> $DIR/const-pointer-values-in-various-types.rs:120:43
+  --> $DIR/const-pointer-values-in-various-types.rs:122:43
    |
 LL |     const STR_I128_UNION: i128 = unsafe { Nonsense { stringy: "3" }.int_128 };
    |     --------------------------            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unable to turn pointer into raw bytes
@@ -522,7 +512,7 @@ LL |     const STR_I128_UNION: i128 = unsafe { Nonsense { stringy: "3" }.int_128
 
 Future breakage diagnostic:
 error: any use of this value will cause an error
-  --> $DIR/const-pointer-values-in-various-types.rs:124:41
+  --> $DIR/const-pointer-values-in-various-types.rs:126:41
    |
 LL |     const STR_F32_UNION: f32 = unsafe { Nonsense { stringy: "3" }.float_32 };
    |     ------------------------            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unable to turn pointer into raw bytes
@@ -533,7 +523,7 @@ LL |     const STR_F32_UNION: f32 = unsafe { Nonsense { stringy: "3" }.float_32
 
 Future breakage diagnostic:
 error: any use of this value will cause an error
-  --> $DIR/const-pointer-values-in-various-types.rs:128:41
+  --> $DIR/const-pointer-values-in-various-types.rs:130:41
    |
 LL |     const STR_F64_UNION: f64 = unsafe { Nonsense { stringy: "3" }.float_64 };
    |     ------------------------            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unable to turn pointer into raw bytes
@@ -544,7 +534,7 @@ LL |     const STR_F64_UNION: f64 = unsafe { Nonsense { stringy: "3" }.float_64
 
 Future breakage diagnostic:
 error: any use of this value will cause an error
-  --> $DIR/const-pointer-values-in-various-types.rs:132:43
+  --> $DIR/const-pointer-values-in-various-types.rs:134:43
    |
 LL |     const STR_BOOL_UNION: bool = unsafe { Nonsense { stringy: "3" }.truthy_falsey };
    |     --------------------------            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unable to turn pointer into raw bytes
@@ -555,7 +545,7 @@ LL |     const STR_BOOL_UNION: bool = unsafe { Nonsense { stringy: "3" }.truthy_
 
 Future breakage diagnostic:
 error: any use of this value will cause an error
-  --> $DIR/const-pointer-values-in-various-types.rs:136:43
+  --> $DIR/const-pointer-values-in-various-types.rs:138:43
    |
 LL |     const STR_CHAR_UNION: char = unsafe { Nonsense { stringy: "3" }.character };
    |     --------------------------            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unable to turn pointer into raw bytes
diff --git a/src/test/ui/consts/const-eval/const-pointer-values-in-various-types.rs b/src/test/ui/consts/const-eval/const-pointer-values-in-various-types.rs
index f10a67392e8..f6a5e4d3c2b 100644
--- a/src/test/ui/consts/const-eval/const-pointer-values-in-various-types.rs
+++ b/src/test/ui/consts/const-eval/const-pointer-values-in-various-types.rs
@@ -44,7 +44,8 @@ fn main() {
     //~| WARN this was previously accepted by the compiler but is being phased out
 
     const I32_REF_U128_UNION: u128 = unsafe { Nonsense { int_32_ref: &3 }.uint_128 };
-    //~^ ERROR it is undefined behavior to use this value
+    //~^ ERROR evaluation of constant value failed
+    //~| uninitialized
 
     const I32_REF_I8_UNION: i8 = unsafe { Nonsense { int_32_ref: &3 }.int_8 };
     //~^ ERROR any use of this value will cause an error
@@ -63,7 +64,8 @@ fn main() {
     //~| WARN this was previously accepted by the compiler but is being phased out
 
     const I32_REF_I128_UNION: i128 = unsafe { Nonsense { int_32_ref: &3 }.int_128 };
-    //~^ ERROR it is undefined behavior to use this value
+    //~^ ERROR evaluation of constant value failed
+    //~| uninitialized
 
     const I32_REF_F32_UNION: f32 = unsafe { Nonsense { int_32_ref: &3 }.float_32 };
     //~^ ERROR any use of this value will cause an error
diff --git a/src/test/ui/consts/const-eval/heap/alloc_intrinsic_uninit.32bit.stderr b/src/test/ui/consts/const-eval/heap/alloc_intrinsic_uninit.32bit.stderr
index f1a780926e7..a0f4519eaad 100644
--- a/src/test/ui/consts/const-eval/heap/alloc_intrinsic_uninit.32bit.stderr
+++ b/src/test/ui/consts/const-eval/heap/alloc_intrinsic_uninit.32bit.stderr
@@ -2,7 +2,7 @@ error[E0080]: it is undefined behavior to use this value
   --> $DIR/alloc_intrinsic_uninit.rs:8:1
    |
 LL | const BAR: &i32 = unsafe { &*(intrinsics::const_allocate(4, 4) as *mut i32) };
-   | ^^^^^^^^^^^^^^^ constructing invalid value at .<deref>: encountered uninitialized bytes, but expected initialized bytes
+   | ^^^^^^^^^^^^^^^ constructing invalid value at .<deref>: encountered uninitialized memory, but expected an integer
    |
    = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rustc repository if you believe it should not be considered undefined behavior.
    = note: the raw bytes of the constant (size: 4, align: 4) {
diff --git a/src/test/ui/consts/const-eval/heap/alloc_intrinsic_uninit.64bit.stderr b/src/test/ui/consts/const-eval/heap/alloc_intrinsic_uninit.64bit.stderr
index 2eb401226f8..d2bffa42561 100644
--- a/src/test/ui/consts/const-eval/heap/alloc_intrinsic_uninit.64bit.stderr
+++ b/src/test/ui/consts/const-eval/heap/alloc_intrinsic_uninit.64bit.stderr
@@ -2,7 +2,7 @@ error[E0080]: it is undefined behavior to use this value
   --> $DIR/alloc_intrinsic_uninit.rs:8:1
    |
 LL | const BAR: &i32 = unsafe { &*(intrinsics::const_allocate(4, 4) as *mut i32) };
-   | ^^^^^^^^^^^^^^^ constructing invalid value at .<deref>: encountered uninitialized bytes, but expected initialized bytes
+   | ^^^^^^^^^^^^^^^ constructing invalid value at .<deref>: encountered uninitialized memory, but expected an integer
    |
    = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rustc repository if you believe it should not be considered undefined behavior.
    = note: the raw bytes of the constant (size: 8, align: 8) {
diff --git a/src/test/ui/consts/const-eval/ub-enum-overwrite.rs b/src/test/ui/consts/const-eval/ub-enum-overwrite.rs
index c5677849229..086a1001d11 100644
--- a/src/test/ui/consts/const-eval/ub-enum-overwrite.rs
+++ b/src/test/ui/consts/const-eval/ub-enum-overwrite.rs
@@ -6,12 +6,13 @@ enum E {
 }
 
 const _: u8 = {
-    //~^ ERROR is undefined behavior
     let mut e = E::A(1);
     let p = if let E::A(x) = &mut e { x as *mut u8 } else { unreachable!() };
     // Make sure overwriting `e` uninitializes other bytes
     e = E::B;
     unsafe { *p }
+    //~^ ERROR evaluation of constant value failed
+    //~| uninitialized
 };
 
 fn main() {}
diff --git a/src/test/ui/consts/const-eval/ub-enum-overwrite.stderr b/src/test/ui/consts/const-eval/ub-enum-overwrite.stderr
index 8560112ae3b..5750212b44c 100644
--- a/src/test/ui/consts/const-eval/ub-enum-overwrite.stderr
+++ b/src/test/ui/consts/const-eval/ub-enum-overwrite.stderr
@@ -1,13 +1,8 @@
-error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-enum-overwrite.rs:8:1
+error[E0080]: evaluation of constant value failed
+  --> $DIR/ub-enum-overwrite.rs:13:14
    |
-LL | const _: u8 = {
-   | ^^^^^^^^^^^ constructing invalid value: encountered uninitialized bytes, but expected initialized bytes
-   |
-   = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rustc repository if you believe it should not be considered undefined behavior.
-   = note: the raw bytes of the constant (size: 1, align: 1) {
-               __                                              │ ░
-           }
+LL |     unsafe { *p }
+   |              ^^ using uninitialized data, but this operation requires initialized memory
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/consts/const-eval/ub-enum.32bit.stderr b/src/test/ui/consts/const-eval/ub-enum.32bit.stderr
index 2f8b44da0fc..1e80dd7c765 100644
--- a/src/test/ui/consts/const-eval/ub-enum.32bit.stderr
+++ b/src/test/ui/consts/const-eval/ub-enum.32bit.stderr
@@ -57,19 +57,14 @@ LL | const BAD_ENUM2_WRAPPED: Wrap<Enum2> = unsafe { mem::transmute(&0) };
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
    = note: for more information, see issue #71800 <https://github.com/rust-lang/rust/issues/71800>
 
-error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-enum.rs:59:1
+error[E0080]: evaluation of constant value failed
+  --> $DIR/ub-enum.rs:59:42
    |
 LL | const BAD_ENUM2_UNDEF : Enum2 = unsafe { MaybeUninit { uninit: () }.init };
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value at .<enum-tag>: encountered uninitialized bytes, but expected initialized bytes
-   |
-   = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rustc repository if you believe it should not be considered undefined behavior.
-   = note: the raw bytes of the constant (size: 4, align: 4) {
-               __ __ __ __                                     │ ░░░░
-           }
+   |                                          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ using uninitialized data, but this operation requires initialized memory
 
 error: any use of this value will cause an error
-  --> $DIR/ub-enum.rs:63:1
+  --> $DIR/ub-enum.rs:64:1
    |
 LL | const BAD_ENUM2_OPTION_PTR: Option<Enum2> = unsafe { mem::transmute(&0) };
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unable to turn pointer into raw bytes
@@ -78,7 +73,7 @@ LL | const BAD_ENUM2_OPTION_PTR: Option<Enum2> = unsafe { mem::transmute(&0) };
    = note: for more information, see issue #71800 <https://github.com/rust-lang/rust/issues/71800>
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-enum.rs:81:1
+  --> $DIR/ub-enum.rs:82:1
    |
 LL | const BAD_UNINHABITED_VARIANT1: UninhDiscriminant = unsafe { mem::transmute(1u8) };
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value at .<enum-variant(B)>.0: encountered a value of the never type `!`
@@ -89,7 +84,7 @@ LL | const BAD_UNINHABITED_VARIANT1: UninhDiscriminant = unsafe { mem::transmute
            }
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-enum.rs:83:1
+  --> $DIR/ub-enum.rs:84:1
    |
 LL | const BAD_UNINHABITED_VARIANT2: UninhDiscriminant = unsafe { mem::transmute(3u8) };
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value at .<enum-variant(D)>.0: encountered a value of uninhabited type Never
@@ -100,7 +95,7 @@ LL | const BAD_UNINHABITED_VARIANT2: UninhDiscriminant = unsafe { mem::transmute
            }
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-enum.rs:91:1
+  --> $DIR/ub-enum.rs:92:1
    |
 LL | const BAD_OPTION_CHAR: Option<(char, char)> = Some(('x', unsafe { mem::transmute(!0u32) }));
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value at .<enum-variant(Some)>.0.1: encountered 0xffffffff, but expected a valid unicode scalar value (in `0..=0x10FFFF` but not in `0xD800..=0xDFFF`)
@@ -111,13 +106,13 @@ LL | const BAD_OPTION_CHAR: Option<(char, char)> = Some(('x', unsafe { mem::tran
            }
 
 error[E0080]: evaluation of constant value failed
-  --> $DIR/ub-enum.rs:96:77
+  --> $DIR/ub-enum.rs:97:77
    |
 LL | const BAD_UNINHABITED_WITH_DATA1: Result<(i32, Never), (i32, !)> = unsafe { mem::transmute(0u64) };
    |                                                                             ^^^^^^^^^^^^^^^^^^^^ transmuting to uninhabited type
 
 error[E0080]: evaluation of constant value failed
-  --> $DIR/ub-enum.rs:98:77
+  --> $DIR/ub-enum.rs:99:77
    |
 LL | const BAD_UNINHABITED_WITH_DATA2: Result<(i32, !), (i32, Never)> = unsafe { mem::transmute(0u64) };
    |                                                                             ^^^^^^^^^^^^^^^^^^^^ transmuting to uninhabited type
@@ -171,7 +166,7 @@ LL | const BAD_ENUM2_WRAPPED: Wrap<Enum2> = unsafe { mem::transmute(&0) };
 
 Future breakage diagnostic:
 error: any use of this value will cause an error
-  --> $DIR/ub-enum.rs:63:1
+  --> $DIR/ub-enum.rs:64:1
    |
 LL | const BAD_ENUM2_OPTION_PTR: Option<Enum2> = unsafe { mem::transmute(&0) };
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unable to turn pointer into raw bytes
diff --git a/src/test/ui/consts/const-eval/ub-enum.64bit.stderr b/src/test/ui/consts/const-eval/ub-enum.64bit.stderr
index 3a05a5150f1..a6208f30c22 100644
--- a/src/test/ui/consts/const-eval/ub-enum.64bit.stderr
+++ b/src/test/ui/consts/const-eval/ub-enum.64bit.stderr
@@ -57,19 +57,14 @@ LL | const BAD_ENUM2_WRAPPED: Wrap<Enum2> = unsafe { mem::transmute(&0) };
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
    = note: for more information, see issue #71800 <https://github.com/rust-lang/rust/issues/71800>
 
-error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-enum.rs:59:1
+error[E0080]: evaluation of constant value failed
+  --> $DIR/ub-enum.rs:59:42
    |
 LL | const BAD_ENUM2_UNDEF : Enum2 = unsafe { MaybeUninit { uninit: () }.init };
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value at .<enum-tag>: encountered uninitialized bytes, but expected initialized bytes
-   |
-   = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rustc repository if you believe it should not be considered undefined behavior.
-   = note: the raw bytes of the constant (size: 8, align: 8) {
-               __ __ __ __ __ __ __ __                         │ ░░░░░░░░
-           }
+   |                                          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ using uninitialized data, but this operation requires initialized memory
 
 error: any use of this value will cause an error
-  --> $DIR/ub-enum.rs:63:1
+  --> $DIR/ub-enum.rs:64:1
    |
 LL | const BAD_ENUM2_OPTION_PTR: Option<Enum2> = unsafe { mem::transmute(&0) };
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unable to turn pointer into raw bytes
@@ -78,7 +73,7 @@ LL | const BAD_ENUM2_OPTION_PTR: Option<Enum2> = unsafe { mem::transmute(&0) };
    = note: for more information, see issue #71800 <https://github.com/rust-lang/rust/issues/71800>
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-enum.rs:81:1
+  --> $DIR/ub-enum.rs:82:1
    |
 LL | const BAD_UNINHABITED_VARIANT1: UninhDiscriminant = unsafe { mem::transmute(1u8) };
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value at .<enum-variant(B)>.0: encountered a value of the never type `!`
@@ -89,7 +84,7 @@ LL | const BAD_UNINHABITED_VARIANT1: UninhDiscriminant = unsafe { mem::transmute
            }
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-enum.rs:83:1
+  --> $DIR/ub-enum.rs:84:1
    |
 LL | const BAD_UNINHABITED_VARIANT2: UninhDiscriminant = unsafe { mem::transmute(3u8) };
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value at .<enum-variant(D)>.0: encountered a value of uninhabited type Never
@@ -100,7 +95,7 @@ LL | const BAD_UNINHABITED_VARIANT2: UninhDiscriminant = unsafe { mem::transmute
            }
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-enum.rs:91:1
+  --> $DIR/ub-enum.rs:92:1
    |
 LL | const BAD_OPTION_CHAR: Option<(char, char)> = Some(('x', unsafe { mem::transmute(!0u32) }));
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value at .<enum-variant(Some)>.0.1: encountered 0xffffffff, but expected a valid unicode scalar value (in `0..=0x10FFFF` but not in `0xD800..=0xDFFF`)
@@ -111,13 +106,13 @@ LL | const BAD_OPTION_CHAR: Option<(char, char)> = Some(('x', unsafe { mem::tran
            }
 
 error[E0080]: evaluation of constant value failed
-  --> $DIR/ub-enum.rs:96:77
+  --> $DIR/ub-enum.rs:97:77
    |
 LL | const BAD_UNINHABITED_WITH_DATA1: Result<(i32, Never), (i32, !)> = unsafe { mem::transmute(0u64) };
    |                                                                             ^^^^^^^^^^^^^^^^^^^^ transmuting to uninhabited type
 
 error[E0080]: evaluation of constant value failed
-  --> $DIR/ub-enum.rs:98:77
+  --> $DIR/ub-enum.rs:99:77
    |
 LL | const BAD_UNINHABITED_WITH_DATA2: Result<(i32, !), (i32, Never)> = unsafe { mem::transmute(0u64) };
    |                                                                             ^^^^^^^^^^^^^^^^^^^^ transmuting to uninhabited type
@@ -171,7 +166,7 @@ LL | const BAD_ENUM2_WRAPPED: Wrap<Enum2> = unsafe { mem::transmute(&0) };
 
 Future breakage diagnostic:
 error: any use of this value will cause an error
-  --> $DIR/ub-enum.rs:63:1
+  --> $DIR/ub-enum.rs:64:1
    |
 LL | const BAD_ENUM2_OPTION_PTR: Option<Enum2> = unsafe { mem::transmute(&0) };
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unable to turn pointer into raw bytes
diff --git a/src/test/ui/consts/const-eval/ub-enum.rs b/src/test/ui/consts/const-eval/ub-enum.rs
index d8d2a499b1d..0e8744e790f 100644
--- a/src/test/ui/consts/const-eval/ub-enum.rs
+++ b/src/test/ui/consts/const-eval/ub-enum.rs
@@ -57,7 +57,8 @@ union MaybeUninit<T: Copy> {
     init: T,
 }
 const BAD_ENUM2_UNDEF : Enum2 = unsafe { MaybeUninit { uninit: () }.init };
-//~^ ERROR is undefined behavior
+//~^ ERROR evaluation of constant value failed
+//~| uninitialized
 
 // Pointer value in an enum with a niche that is not just 0.
 const BAD_ENUM2_OPTION_PTR: Option<Enum2> = unsafe { mem::transmute(&0) };
diff --git a/src/test/ui/consts/const-eval/ub-int-array.32bit.stderr b/src/test/ui/consts/const-eval/ub-int-array.32bit.stderr
index 8eece9e30e4..6100a98d161 100644
--- a/src/test/ui/consts/const-eval/ub-int-array.32bit.stderr
+++ b/src/test/ui/consts/const-eval/ub-int-array.32bit.stderr
@@ -1,35 +1,20 @@
-error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-int-array.rs:14:1
+error[E0080]: evaluation of constant value failed
+  --> $DIR/ub-int-array.rs:16:9
    |
-LL | const UNINIT_INT_0: [u32; 3] = unsafe {
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value at [0]: encountered uninitialized bytes
-   |
-   = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rustc repository if you believe it should not be considered undefined behavior.
-   = note: the raw bytes of the constant (size: 12, align: 4) {
-               __ __ __ __ 01 00 00 00 02 00 00 00             │ ░░░░........
-           }
+LL |         MaybeUninit { uninit: () }.init,
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ using uninitialized data, but this operation requires initialized memory
 
-error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-int-array.rs:23:1
-   |
-LL | const UNINIT_INT_1: [u32; 3] = unsafe {
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value at [1]: encountered uninitialized bytes
+error[E0080]: evaluation of constant value failed
+  --> $DIR/ub-int-array.rs:31:13
    |
-   = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rustc repository if you believe it should not be considered undefined behavior.
-   = note: the raw bytes of the constant (size: 12, align: 4) {
-               00 00 00 00 01 __ 01 01 02 02 __ 02             │ .....░....░.
-           }
+LL |             MaybeUninit { uninit: () }.init,
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ using uninitialized data, but this operation requires initialized memory
 
-error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-int-array.rs:43:1
-   |
-LL | const UNINIT_INT_2: [u32; 3] = unsafe {
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value at [2]: encountered uninitialized bytes
+error[E0080]: evaluation of constant value failed
+  --> $DIR/ub-int-array.rs:57:13
    |
-   = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rustc repository if you believe it should not be considered undefined behavior.
-   = note: the raw bytes of the constant (size: 12, align: 4) {
-               00 00 00 00 01 01 01 01 02 02 02 __             │ ...........░
-           }
+LL |             MaybeUninit { uninit: () }.init,
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ using uninitialized data, but this operation requires initialized memory
 
 error: aborting due to 3 previous errors
 
diff --git a/src/test/ui/consts/const-eval/ub-int-array.64bit.stderr b/src/test/ui/consts/const-eval/ub-int-array.64bit.stderr
index 8eece9e30e4..6100a98d161 100644
--- a/src/test/ui/consts/const-eval/ub-int-array.64bit.stderr
+++ b/src/test/ui/consts/const-eval/ub-int-array.64bit.stderr
@@ -1,35 +1,20 @@
-error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-int-array.rs:14:1
+error[E0080]: evaluation of constant value failed
+  --> $DIR/ub-int-array.rs:16:9
    |
-LL | const UNINIT_INT_0: [u32; 3] = unsafe {
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value at [0]: encountered uninitialized bytes
-   |
-   = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rustc repository if you believe it should not be considered undefined behavior.
-   = note: the raw bytes of the constant (size: 12, align: 4) {
-               __ __ __ __ 01 00 00 00 02 00 00 00             │ ░░░░........
-           }
+LL |         MaybeUninit { uninit: () }.init,
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ using uninitialized data, but this operation requires initialized memory
 
-error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-int-array.rs:23:1
-   |
-LL | const UNINIT_INT_1: [u32; 3] = unsafe {
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value at [1]: encountered uninitialized bytes
+error[E0080]: evaluation of constant value failed
+  --> $DIR/ub-int-array.rs:31:13
    |
-   = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rustc repository if you believe it should not be considered undefined behavior.
-   = note: the raw bytes of the constant (size: 12, align: 4) {
-               00 00 00 00 01 __ 01 01 02 02 __ 02             │ .....░....░.
-           }
+LL |             MaybeUninit { uninit: () }.init,
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ using uninitialized data, but this operation requires initialized memory
 
-error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-int-array.rs:43:1
-   |
-LL | const UNINIT_INT_2: [u32; 3] = unsafe {
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value at [2]: encountered uninitialized bytes
+error[E0080]: evaluation of constant value failed
+  --> $DIR/ub-int-array.rs:57:13
    |
-   = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rustc repository if you believe it should not be considered undefined behavior.
-   = note: the raw bytes of the constant (size: 12, align: 4) {
-               00 00 00 00 01 01 01 01 02 02 02 __             │ ...........░
-           }
+LL |             MaybeUninit { uninit: () }.init,
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ using uninitialized data, but this operation requires initialized memory
 
 error: aborting due to 3 previous errors
 
diff --git a/src/test/ui/consts/const-eval/ub-int-array.rs b/src/test/ui/consts/const-eval/ub-int-array.rs
index 1221f71d1e5..cb85e3b016a 100644
--- a/src/test/ui/consts/const-eval/ub-int-array.rs
+++ b/src/test/ui/consts/const-eval/ub-int-array.rs
@@ -12,17 +12,15 @@ union MaybeUninit<T: Copy> {
 }
 
 const UNINIT_INT_0: [u32; 3] = unsafe {
-//~^ ERROR it is undefined behavior to use this value
-//~| constructing invalid value at [0]: encountered uninitialized bytes
     [
         MaybeUninit { uninit: () }.init,
+        //~^ ERROR evaluation of constant value failed
+        //~| uninitialized
         1,
         2,
     ]
 };
 const UNINIT_INT_1: [u32; 3] = unsafe {
-//~^ ERROR it is undefined behavior to use this value
-//~| constructing invalid value at [1]: encountered uninitialized bytes
     mem::transmute(
         [
             0u8,
@@ -31,6 +29,8 @@ const UNINIT_INT_1: [u32; 3] = unsafe {
             0u8,
             1u8,
             MaybeUninit { uninit: () }.init,
+            //~^ ERROR evaluation of constant value failed
+            //~| uninitialized
             1u8,
             1u8,
             2u8,
@@ -41,8 +41,6 @@ const UNINIT_INT_1: [u32; 3] = unsafe {
     )
 };
 const UNINIT_INT_2: [u32; 3] = unsafe {
-//~^ ERROR it is undefined behavior to use this value
-//~| constructing invalid value at [2]: encountered uninitialized bytes
     mem::transmute(
         [
             0u8,
@@ -57,6 +55,8 @@ const UNINIT_INT_2: [u32; 3] = unsafe {
             2u8,
             2u8,
             MaybeUninit { uninit: () }.init,
+            //~^ ERROR evaluation of constant value failed
+            //~| uninitialized
         ]
     )
 };
diff --git a/src/test/ui/consts/const-eval/ub-nonnull.32bit.stderr b/src/test/ui/consts/const-eval/ub-nonnull.32bit.stderr
index d450a814cfa..693c0e99bfd 100644
--- a/src/test/ui/consts/const-eval/ub-nonnull.32bit.stderr
+++ b/src/test/ui/consts/const-eval/ub-nonnull.32bit.stderr
@@ -37,19 +37,14 @@ LL | const NULL_USIZE: NonZeroUsize = unsafe { mem::transmute(0usize) };
                00 00 00 00                                     │ ....
            }
 
-error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-nonnull.rs:33:1
+error[E0080]: evaluation of constant value failed
+  --> $DIR/ub-nonnull.rs:33:36
    |
 LL | const UNINIT: NonZeroU8 = unsafe { MaybeUninit { uninit: () }.init };
-   | ^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value at .0: encountered uninitialized bytes, but expected initialized bytes
-   |
-   = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rustc repository if you believe it should not be considered undefined behavior.
-   = note: the raw bytes of the constant (size: 1, align: 1) {
-               __                                              │ ░
-           }
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ using uninitialized data, but this operation requires initialized memory
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-nonnull.rs:41:1
+  --> $DIR/ub-nonnull.rs:42:1
    |
 LL | const BAD_RANGE1: RestrictedRange1 = unsafe { RestrictedRange1(42) };
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value: encountered 42, but expected something in the range 10..=30
@@ -60,7 +55,7 @@ LL | const BAD_RANGE1: RestrictedRange1 = unsafe { RestrictedRange1(42) };
            }
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-nonnull.rs:47:1
+  --> $DIR/ub-nonnull.rs:48:1
    |
 LL | const BAD_RANGE2: RestrictedRange2 = unsafe { RestrictedRange2(20) };
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value: encountered 20, but expected something less or equal to 10, or greater or equal to 30
diff --git a/src/test/ui/consts/const-eval/ub-nonnull.64bit.stderr b/src/test/ui/consts/const-eval/ub-nonnull.64bit.stderr
index ed0d91aabd3..d22191213ac 100644
--- a/src/test/ui/consts/const-eval/ub-nonnull.64bit.stderr
+++ b/src/test/ui/consts/const-eval/ub-nonnull.64bit.stderr
@@ -37,19 +37,14 @@ LL | const NULL_USIZE: NonZeroUsize = unsafe { mem::transmute(0usize) };
                00 00 00 00 00 00 00 00                         │ ........
            }
 
-error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-nonnull.rs:33:1
+error[E0080]: evaluation of constant value failed
+  --> $DIR/ub-nonnull.rs:33:36
    |
 LL | const UNINIT: NonZeroU8 = unsafe { MaybeUninit { uninit: () }.init };
-   | ^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value at .0: encountered uninitialized bytes, but expected initialized bytes
-   |
-   = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rustc repository if you believe it should not be considered undefined behavior.
-   = note: the raw bytes of the constant (size: 1, align: 1) {
-               __                                              │ ░
-           }
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ using uninitialized data, but this operation requires initialized memory
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-nonnull.rs:41:1
+  --> $DIR/ub-nonnull.rs:42:1
    |
 LL | const BAD_RANGE1: RestrictedRange1 = unsafe { RestrictedRange1(42) };
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value: encountered 42, but expected something in the range 10..=30
@@ -60,7 +55,7 @@ LL | const BAD_RANGE1: RestrictedRange1 = unsafe { RestrictedRange1(42) };
            }
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-nonnull.rs:47:1
+  --> $DIR/ub-nonnull.rs:48:1
    |
 LL | const BAD_RANGE2: RestrictedRange2 = unsafe { RestrictedRange2(20) };
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value: encountered 20, but expected something less or equal to 10, or greater or equal to 30
diff --git a/src/test/ui/consts/const-eval/ub-nonnull.rs b/src/test/ui/consts/const-eval/ub-nonnull.rs
index 259707b8028..777c6d9880e 100644
--- a/src/test/ui/consts/const-eval/ub-nonnull.rs
+++ b/src/test/ui/consts/const-eval/ub-nonnull.rs
@@ -31,7 +31,8 @@ union MaybeUninit<T: Copy> {
     init: T,
 }
 const UNINIT: NonZeroU8 = unsafe { MaybeUninit { uninit: () }.init };
-//~^ ERROR it is undefined behavior to use this value
+//~^ ERROR evaluation of constant value failed
+//~| uninitialized
 
 // Also test other uses of rustc_layout_scalar_valid_range_start
 
diff --git a/src/test/ui/consts/const-eval/ub-ref-ptr.32bit.stderr b/src/test/ui/consts/const-eval/ub-ref-ptr.32bit.stderr
index ae114233c0f..25560d8003d 100644
--- a/src/test/ui/consts/const-eval/ub-ref-ptr.32bit.stderr
+++ b/src/test/ui/consts/const-eval/ub-ref-ptr.32bit.stderr
@@ -110,19 +110,14 @@ LL | const USIZE_AS_BOX: Box<u8> = unsafe { mem::transmute(1337usize) };
                39 05 00 00                                     │ 9...
            }
 
-error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-ref-ptr.rs:53:1
+error[E0080]: evaluation of constant value failed
+  --> $DIR/ub-ref-ptr.rs:53:41
    |
 LL | const UNINIT_PTR: *const i32 = unsafe { MaybeUninit { uninit: () }.init };
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value: encountered uninitialized raw pointer
-   |
-   = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rustc repository if you believe it should not be considered undefined behavior.
-   = note: the raw bytes of the constant (size: 4, align: 4) {
-               __ __ __ __                                     │ ░░░░
-           }
+   |                                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ using uninitialized data, but this operation requires initialized memory
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-ref-ptr.rs:56:1
+  --> $DIR/ub-ref-ptr.rs:57:1
    |
 LL | const NULL_FN_PTR: fn() = unsafe { mem::transmute(0usize) };
    | ^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value: encountered null pointer, but expected a function pointer
@@ -132,19 +127,14 @@ LL | const NULL_FN_PTR: fn() = unsafe { mem::transmute(0usize) };
                00 00 00 00                                     │ ....
            }
 
-error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-ref-ptr.rs:58:1
+error[E0080]: evaluation of constant value failed
+  --> $DIR/ub-ref-ptr.rs:59:38
    |
 LL | const UNINIT_FN_PTR: fn() = unsafe { MaybeUninit { uninit: () }.init };
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value: encountered uninitialized bytes, but expected a proper pointer or integer value
-   |
-   = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rustc repository if you believe it should not be considered undefined behavior.
-   = note: the raw bytes of the constant (size: 4, align: 4) {
-               __ __ __ __                                     │ ░░░░
-           }
+   |                                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ using uninitialized data, but this operation requires initialized memory
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-ref-ptr.rs:60:1
+  --> $DIR/ub-ref-ptr.rs:62:1
    |
 LL | const DANGLING_FN_PTR: fn() = unsafe { mem::transmute(13usize) };
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value: encountered 0xd[noalloc], but expected a function pointer
@@ -155,7 +145,7 @@ LL | const DANGLING_FN_PTR: fn() = unsafe { mem::transmute(13usize) };
            }
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-ref-ptr.rs:62:1
+  --> $DIR/ub-ref-ptr.rs:64:1
    |
 LL | const DATA_FN_PTR: fn() = unsafe { mem::transmute(&13) };
    | ^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value: encountered alloc41, but expected a function pointer
diff --git a/src/test/ui/consts/const-eval/ub-ref-ptr.64bit.stderr b/src/test/ui/consts/const-eval/ub-ref-ptr.64bit.stderr
index 1b93a869c0d..8c86ddbfa5f 100644
--- a/src/test/ui/consts/const-eval/ub-ref-ptr.64bit.stderr
+++ b/src/test/ui/consts/const-eval/ub-ref-ptr.64bit.stderr
@@ -110,19 +110,14 @@ LL | const USIZE_AS_BOX: Box<u8> = unsafe { mem::transmute(1337usize) };
                39 05 00 00 00 00 00 00                         │ 9.......
            }
 
-error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-ref-ptr.rs:53:1
+error[E0080]: evaluation of constant value failed
+  --> $DIR/ub-ref-ptr.rs:53:41
    |
 LL | const UNINIT_PTR: *const i32 = unsafe { MaybeUninit { uninit: () }.init };
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value: encountered uninitialized raw pointer
-   |
-   = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rustc repository if you believe it should not be considered undefined behavior.
-   = note: the raw bytes of the constant (size: 8, align: 8) {
-               __ __ __ __ __ __ __ __                         │ ░░░░░░░░
-           }
+   |                                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ using uninitialized data, but this operation requires initialized memory
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-ref-ptr.rs:56:1
+  --> $DIR/ub-ref-ptr.rs:57:1
    |
 LL | const NULL_FN_PTR: fn() = unsafe { mem::transmute(0usize) };
    | ^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value: encountered null pointer, but expected a function pointer
@@ -132,19 +127,14 @@ LL | const NULL_FN_PTR: fn() = unsafe { mem::transmute(0usize) };
                00 00 00 00 00 00 00 00                         │ ........
            }
 
-error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-ref-ptr.rs:58:1
+error[E0080]: evaluation of constant value failed
+  --> $DIR/ub-ref-ptr.rs:59:38
    |
 LL | const UNINIT_FN_PTR: fn() = unsafe { MaybeUninit { uninit: () }.init };
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value: encountered uninitialized bytes, but expected a proper pointer or integer value
-   |
-   = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rustc repository if you believe it should not be considered undefined behavior.
-   = note: the raw bytes of the constant (size: 8, align: 8) {
-               __ __ __ __ __ __ __ __                         │ ░░░░░░░░
-           }
+   |                                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ using uninitialized data, but this operation requires initialized memory
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-ref-ptr.rs:60:1
+  --> $DIR/ub-ref-ptr.rs:62:1
    |
 LL | const DANGLING_FN_PTR: fn() = unsafe { mem::transmute(13usize) };
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value: encountered 0xd[noalloc], but expected a function pointer
@@ -155,7 +145,7 @@ LL | const DANGLING_FN_PTR: fn() = unsafe { mem::transmute(13usize) };
            }
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-ref-ptr.rs:62:1
+  --> $DIR/ub-ref-ptr.rs:64:1
    |
 LL | const DATA_FN_PTR: fn() = unsafe { mem::transmute(&13) };
    | ^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value: encountered alloc41, but expected a function pointer
diff --git a/src/test/ui/consts/const-eval/ub-ref-ptr.rs b/src/test/ui/consts/const-eval/ub-ref-ptr.rs
index d0216f74668..c62848f70db 100644
--- a/src/test/ui/consts/const-eval/ub-ref-ptr.rs
+++ b/src/test/ui/consts/const-eval/ub-ref-ptr.rs
@@ -51,12 +51,14 @@ const USIZE_AS_BOX: Box<u8> = unsafe { mem::transmute(1337usize) };
 //~^ ERROR it is undefined behavior to use this value
 
 const UNINIT_PTR: *const i32 = unsafe { MaybeUninit { uninit: () }.init };
-//~^ ERROR it is undefined behavior to use this value
+//~^ ERROR evaluation of constant value failed
+//~| uninitialized
 
 const NULL_FN_PTR: fn() = unsafe { mem::transmute(0usize) };
 //~^ ERROR it is undefined behavior to use this value
 const UNINIT_FN_PTR: fn() = unsafe { MaybeUninit { uninit: () }.init };
-//~^ ERROR it is undefined behavior to use this value
+//~^ ERROR evaluation of constant value failed
+//~| uninitialized
 const DANGLING_FN_PTR: fn() = unsafe { mem::transmute(13usize) };
 //~^ ERROR it is undefined behavior to use this value
 const DATA_FN_PTR: fn() = unsafe { mem::transmute(&13) };
diff --git a/src/test/ui/consts/const-eval/ub-wide-ptr.32bit.stderr b/src/test/ui/consts/const-eval/ub-wide-ptr.32bit.stderr
index 9431fb33c53..09a877400d0 100644
--- a/src/test/ui/consts/const-eval/ub-wide-ptr.32bit.stderr
+++ b/src/test/ui/consts/const-eval/ub-wide-ptr.32bit.stderr
@@ -72,19 +72,14 @@ LL | const MYSTR_NO_INIT: &MyStr = unsafe { mem::transmute::<&[_], _>(&[MaybeUni
                ╾─allocN─╼ 01 00 00 00                         │ ╾──╼....
            }
 
-error[E0080]: it is undefined behavior to use this value
+error[E0080]: evaluation of constant value failed
   --> $DIR/ub-wide-ptr.rs:63:1
    |
 LL | const SLICE_LENGTH_UNINIT: &[u8] = unsafe {
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value: encountered uninitialized reference
-   |
-   = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rustc repository if you believe it should not be considered undefined behavior.
-   = note: the raw bytes of the constant (size: 8, align: 4) {
-               2a 00 00 00 __ __ __ __                         │ *...░░░░
-           }
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ using uninitialized data, but this operation requires initialized memory
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-wide-ptr.rs:69:1
+  --> $DIR/ub-wide-ptr.rs:70:1
    |
 LL | const SLICE_TOO_LONG: &[u8] = unsafe { mem::transmute((&42u8, 999usize)) };
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value: encountered a dangling reference (going beyond the bounds of its allocation)
@@ -95,7 +90,7 @@ LL | const SLICE_TOO_LONG: &[u8] = unsafe { mem::transmute((&42u8, 999usize)) };
            }
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-wide-ptr.rs:72:1
+  --> $DIR/ub-wide-ptr.rs:73:1
    |
 LL | const SLICE_TOO_LONG_OVERFLOW: &[u32] = unsafe { mem::transmute((&42u32, isize::MAX)) };
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value: encountered invalid reference metadata: slice is bigger than largest supported object
@@ -106,7 +101,7 @@ LL | const SLICE_TOO_LONG_OVERFLOW: &[u32] = unsafe { mem::transmute((&42u32, is
            }
 
 error: any use of this value will cause an error
-  --> $DIR/ub-wide-ptr.rs:75:1
+  --> $DIR/ub-wide-ptr.rs:76:1
    |
 LL | const SLICE_LENGTH_PTR: &[u8] = unsafe { mem::transmute((&42u8, &3)) };
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unable to turn pointer into raw bytes
@@ -115,7 +110,7 @@ LL | const SLICE_LENGTH_PTR: &[u8] = unsafe { mem::transmute((&42u8, &3)) };
    = note: for more information, see issue #71800 <https://github.com/rust-lang/rust/issues/71800>
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-wide-ptr.rs:79:1
+  --> $DIR/ub-wide-ptr.rs:80:1
    |
 LL | const SLICE_TOO_LONG_BOX: Box<[u8]> = unsafe { mem::transmute((&42u8, 999usize)) };
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value: encountered a dangling box (going beyond the bounds of its allocation)
@@ -126,7 +121,7 @@ LL | const SLICE_TOO_LONG_BOX: Box<[u8]> = unsafe { mem::transmute((&42u8, 999us
            }
 
 error: any use of this value will cause an error
-  --> $DIR/ub-wide-ptr.rs:82:1
+  --> $DIR/ub-wide-ptr.rs:83:1
    |
 LL | const SLICE_LENGTH_PTR_BOX: Box<[u8]> = unsafe { mem::transmute((&42u8, &3)) };
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unable to turn pointer into raw bytes
@@ -135,7 +130,7 @@ LL | const SLICE_LENGTH_PTR_BOX: Box<[u8]> = unsafe { mem::transmute((&42u8, &3)
    = note: for more information, see issue #71800 <https://github.com/rust-lang/rust/issues/71800>
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-wide-ptr.rs:87:1
+  --> $DIR/ub-wide-ptr.rs:88:1
    |
 LL | const SLICE_CONTENT_INVALID: &[bool] = &[unsafe { mem::transmute(3u8) }];
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value at .<deref>[0]: encountered 0x03, but expected a boolean
@@ -146,7 +141,7 @@ LL | const SLICE_CONTENT_INVALID: &[bool] = &[unsafe { mem::transmute(3u8) }];
            }
 
 error: any use of this value will cause an error
-  --> $DIR/ub-wide-ptr.rs:87:40
+  --> $DIR/ub-wide-ptr.rs:88:40
    |
 LL | const SLICE_CONTENT_INVALID: &[bool] = &[unsafe { mem::transmute(3u8) }];
    | ------------------------------------   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ referenced constant has errors
@@ -155,7 +150,7 @@ LL | const SLICE_CONTENT_INVALID: &[bool] = &[unsafe { mem::transmute(3u8) }];
    = note: for more information, see issue #71800 <https://github.com/rust-lang/rust/issues/71800>
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-wide-ptr.rs:95:1
+  --> $DIR/ub-wide-ptr.rs:96:1
    |
 LL | const MYSLICE_PREFIX_BAD: &MySliceBool = &MySlice(unsafe { mem::transmute(3u8) }, [false]);
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value at .<deref>.0: encountered 0x03, but expected a boolean
@@ -166,7 +161,7 @@ LL | const MYSLICE_PREFIX_BAD: &MySliceBool = &MySlice(unsafe { mem::transmute(3
            }
 
 error: any use of this value will cause an error
-  --> $DIR/ub-wide-ptr.rs:95:42
+  --> $DIR/ub-wide-ptr.rs:96:42
    |
 LL | const MYSLICE_PREFIX_BAD: &MySliceBool = &MySlice(unsafe { mem::transmute(3u8) }, [false]);
    | --------------------------------------   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ referenced constant has errors
@@ -175,7 +170,7 @@ LL | const MYSLICE_PREFIX_BAD: &MySliceBool = &MySlice(unsafe { mem::transmute(3
    = note: for more information, see issue #71800 <https://github.com/rust-lang/rust/issues/71800>
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-wide-ptr.rs:100:1
+  --> $DIR/ub-wide-ptr.rs:101:1
    |
 LL | const MYSLICE_SUFFIX_BAD: &MySliceBool = &MySlice(true, [unsafe { mem::transmute(3u8) }]);
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value at .<deref>.1[0]: encountered 0x03, but expected a boolean
@@ -186,7 +181,7 @@ LL | const MYSLICE_SUFFIX_BAD: &MySliceBool = &MySlice(true, [unsafe { mem::tran
            }
 
 error: any use of this value will cause an error
-  --> $DIR/ub-wide-ptr.rs:100:42
+  --> $DIR/ub-wide-ptr.rs:101:42
    |
 LL | const MYSLICE_SUFFIX_BAD: &MySliceBool = &MySlice(true, [unsafe { mem::transmute(3u8) }]);
    | --------------------------------------   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ referenced constant has errors
@@ -194,19 +189,14 @@ LL | const MYSLICE_SUFFIX_BAD: &MySliceBool = &MySlice(true, [unsafe { mem::tran
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
    = note: for more information, see issue #71800 <https://github.com/rust-lang/rust/issues/71800>
 
-error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-wide-ptr.rs:109:1
+error[E0080]: evaluation of constant value failed
+  --> $DIR/ub-wide-ptr.rs:110:1
    |
 LL | const RAW_SLICE_LENGTH_UNINIT: *const [u8] = unsafe {
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value: encountered uninitialized raw pointer
-   |
-   = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rustc repository if you believe it should not be considered undefined behavior.
-   = note: the raw bytes of the constant (size: 8, align: 4) {
-               2a 00 00 00 __ __ __ __                         │ *...░░░░
-           }
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ using uninitialized data, but this operation requires initialized memory
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-wide-ptr.rs:117:1
+  --> $DIR/ub-wide-ptr.rs:119:1
    |
 LL | const TRAIT_OBJ_SHORT_VTABLE_1: W<&dyn Trait> = unsafe { mem::transmute(W((&92u8, &3u8))) };
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value at .0: encountered allocN, but expected a vtable pointer
@@ -217,7 +207,7 @@ LL | const TRAIT_OBJ_SHORT_VTABLE_1: W<&dyn Trait> = unsafe { mem::transmute(W((
            }
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-wide-ptr.rs:121:1
+  --> $DIR/ub-wide-ptr.rs:123:1
    |
 LL | const TRAIT_OBJ_SHORT_VTABLE_2: W<&dyn Trait> = unsafe { mem::transmute(W((&92u8, &3u64))) };
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value at .0: encountered allocN, but expected a vtable pointer
@@ -228,7 +218,7 @@ LL | const TRAIT_OBJ_SHORT_VTABLE_2: W<&dyn Trait> = unsafe { mem::transmute(W((
            }
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-wide-ptr.rs:125:1
+  --> $DIR/ub-wide-ptr.rs:127:1
    |
 LL | const TRAIT_OBJ_INT_VTABLE: W<&dyn Trait> = unsafe { mem::transmute(W((&92u8, 4usize))) };
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value at .0: encountered 0x4[noalloc], but expected a vtable pointer
@@ -239,25 +229,25 @@ LL | const TRAIT_OBJ_INT_VTABLE: W<&dyn Trait> = unsafe { mem::transmute(W((&92u
            }
 
 error[E0080]: evaluation of constant value failed
-  --> $DIR/ub-wide-ptr.rs:128:57
+  --> $DIR/ub-wide-ptr.rs:130:57
    |
 LL | const TRAIT_OBJ_UNALIGNED_VTABLE: &dyn Trait = unsafe { mem::transmute((&92u8, &[0u8; 128])) };
    |                                                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ using allocN as vtable pointer but it does not point to a vtable
 
 error[E0080]: evaluation of constant value failed
-  --> $DIR/ub-wide-ptr.rs:131:57
+  --> $DIR/ub-wide-ptr.rs:133:57
    |
 LL | const TRAIT_OBJ_BAD_DROP_FN_NULL: &dyn Trait = unsafe { mem::transmute((&92u8, &[0usize; 8])) };
    |                                                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ using allocN as vtable pointer but it does not point to a vtable
 
 error[E0080]: evaluation of constant value failed
-  --> $DIR/ub-wide-ptr.rs:134:56
+  --> $DIR/ub-wide-ptr.rs:136:56
    |
 LL | const TRAIT_OBJ_BAD_DROP_FN_INT: &dyn Trait = unsafe { mem::transmute((&92u8, &[1usize; 8])) };
    |                                                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ using allocN as vtable pointer but it does not point to a vtable
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-wide-ptr.rs:137:1
+  --> $DIR/ub-wide-ptr.rs:139:1
    |
 LL | const TRAIT_OBJ_BAD_DROP_FN_NOT_FN_PTR: W<&dyn Trait> = unsafe { mem::transmute(W((&92u8, &[&42u8; 8]))) };
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value at .0: encountered allocN, but expected a vtable pointer
@@ -268,7 +258,7 @@ LL | const TRAIT_OBJ_BAD_DROP_FN_NOT_FN_PTR: W<&dyn Trait> = unsafe { mem::trans
            }
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-wide-ptr.rs:142:1
+  --> $DIR/ub-wide-ptr.rs:144:1
    |
 LL | const TRAIT_OBJ_CONTENT_INVALID: &dyn Trait = unsafe { mem::transmute::<_, &bool>(&3u8) };
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value at .<deref>.<dyn-downcast>: encountered 0x03, but expected a boolean
@@ -279,7 +269,7 @@ LL | const TRAIT_OBJ_CONTENT_INVALID: &dyn Trait = unsafe { mem::transmute::<_,
            }
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-wide-ptr.rs:147:1
+  --> $DIR/ub-wide-ptr.rs:149:1
    |
 LL | const RAW_TRAIT_OBJ_VTABLE_NULL: *const dyn Trait = unsafe { mem::transmute((&92u8, 0usize)) };
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value: encountered null pointer, but expected a vtable pointer
@@ -290,7 +280,7 @@ LL | const RAW_TRAIT_OBJ_VTABLE_NULL: *const dyn Trait = unsafe { mem::transmute
            }
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-wide-ptr.rs:149:1
+  --> $DIR/ub-wide-ptr.rs:151:1
    |
 LL | const RAW_TRAIT_OBJ_VTABLE_INVALID: *const dyn Trait = unsafe { mem::transmute((&92u8, &3u64)) };
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value: encountered allocN, but expected a vtable pointer
@@ -301,13 +291,13 @@ LL | const RAW_TRAIT_OBJ_VTABLE_INVALID: *const dyn Trait = unsafe { mem::transm
            }
 
 error[E0080]: could not evaluate static initializer
-  --> $DIR/ub-wide-ptr.rs:155:5
+  --> $DIR/ub-wide-ptr.rs:157:5
    |
 LL |     mem::transmute::<_, &dyn Trait>((&92u8, 0usize))
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ out-of-bounds pointer use: null pointer is a dangling pointer (it has no provenance)
 
 error[E0080]: could not evaluate static initializer
-  --> $DIR/ub-wide-ptr.rs:159:5
+  --> $DIR/ub-wide-ptr.rs:161:5
    |
 LL |     mem::transmute::<_, &dyn Trait>((&92u8, &3u64))
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ using allocN as vtable pointer but it does not point to a vtable
@@ -339,7 +329,7 @@ LL | const MY_STR_LENGTH_PTR: &MyStr = unsafe { mem::transmute((&42u8, &3)) };
 
 Future breakage diagnostic:
 error: any use of this value will cause an error
-  --> $DIR/ub-wide-ptr.rs:75:1
+  --> $DIR/ub-wide-ptr.rs:76:1
    |
 LL | const SLICE_LENGTH_PTR: &[u8] = unsafe { mem::transmute((&42u8, &3)) };
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unable to turn pointer into raw bytes
@@ -350,7 +340,7 @@ LL | const SLICE_LENGTH_PTR: &[u8] = unsafe { mem::transmute((&42u8, &3)) };
 
 Future breakage diagnostic:
 error: any use of this value will cause an error
-  --> $DIR/ub-wide-ptr.rs:82:1
+  --> $DIR/ub-wide-ptr.rs:83:1
    |
 LL | const SLICE_LENGTH_PTR_BOX: Box<[u8]> = unsafe { mem::transmute((&42u8, &3)) };
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unable to turn pointer into raw bytes
@@ -361,7 +351,7 @@ LL | const SLICE_LENGTH_PTR_BOX: Box<[u8]> = unsafe { mem::transmute((&42u8, &3)
 
 Future breakage diagnostic:
 error: any use of this value will cause an error
-  --> $DIR/ub-wide-ptr.rs:87:40
+  --> $DIR/ub-wide-ptr.rs:88:40
    |
 LL | const SLICE_CONTENT_INVALID: &[bool] = &[unsafe { mem::transmute(3u8) }];
    | ------------------------------------   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ referenced constant has errors
@@ -372,7 +362,7 @@ LL | const SLICE_CONTENT_INVALID: &[bool] = &[unsafe { mem::transmute(3u8) }];
 
 Future breakage diagnostic:
 error: any use of this value will cause an error
-  --> $DIR/ub-wide-ptr.rs:95:42
+  --> $DIR/ub-wide-ptr.rs:96:42
    |
 LL | const MYSLICE_PREFIX_BAD: &MySliceBool = &MySlice(unsafe { mem::transmute(3u8) }, [false]);
    | --------------------------------------   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ referenced constant has errors
@@ -383,7 +373,7 @@ LL | const MYSLICE_PREFIX_BAD: &MySliceBool = &MySlice(unsafe { mem::transmute(3
 
 Future breakage diagnostic:
 error: any use of this value will cause an error
-  --> $DIR/ub-wide-ptr.rs:100:42
+  --> $DIR/ub-wide-ptr.rs:101:42
    |
 LL | const MYSLICE_SUFFIX_BAD: &MySliceBool = &MySlice(true, [unsafe { mem::transmute(3u8) }]);
    | --------------------------------------   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ referenced constant has errors
diff --git a/src/test/ui/consts/const-eval/ub-wide-ptr.64bit.stderr b/src/test/ui/consts/const-eval/ub-wide-ptr.64bit.stderr
index 15ef703024a..79fa7a83e84 100644
--- a/src/test/ui/consts/const-eval/ub-wide-ptr.64bit.stderr
+++ b/src/test/ui/consts/const-eval/ub-wide-ptr.64bit.stderr
@@ -72,19 +72,14 @@ LL | const MYSTR_NO_INIT: &MyStr = unsafe { mem::transmute::<&[_], _>(&[MaybeUni
                ╾───────allocN───────╼ 01 00 00 00 00 00 00 00 │ ╾──────╼........
            }
 
-error[E0080]: it is undefined behavior to use this value
+error[E0080]: evaluation of constant value failed
   --> $DIR/ub-wide-ptr.rs:63:1
    |
 LL | const SLICE_LENGTH_UNINIT: &[u8] = unsafe {
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value: encountered uninitialized reference
-   |
-   = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rustc repository if you believe it should not be considered undefined behavior.
-   = note: the raw bytes of the constant (size: 16, align: 8) {
-               __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ │ ░░░░░░░░░░░░░░░░
-           }
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ using uninitialized data, but this operation requires initialized memory
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-wide-ptr.rs:69:1
+  --> $DIR/ub-wide-ptr.rs:70:1
    |
 LL | const SLICE_TOO_LONG: &[u8] = unsafe { mem::transmute((&42u8, 999usize)) };
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value: encountered a dangling reference (going beyond the bounds of its allocation)
@@ -95,7 +90,7 @@ LL | const SLICE_TOO_LONG: &[u8] = unsafe { mem::transmute((&42u8, 999usize)) };
            }
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-wide-ptr.rs:72:1
+  --> $DIR/ub-wide-ptr.rs:73:1
    |
 LL | const SLICE_TOO_LONG_OVERFLOW: &[u32] = unsafe { mem::transmute((&42u32, isize::MAX)) };
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value: encountered invalid reference metadata: slice is bigger than largest supported object
@@ -106,7 +101,7 @@ LL | const SLICE_TOO_LONG_OVERFLOW: &[u32] = unsafe { mem::transmute((&42u32, is
            }
 
 error: any use of this value will cause an error
-  --> $DIR/ub-wide-ptr.rs:75:1
+  --> $DIR/ub-wide-ptr.rs:76:1
    |
 LL | const SLICE_LENGTH_PTR: &[u8] = unsafe { mem::transmute((&42u8, &3)) };
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unable to turn pointer into raw bytes
@@ -115,7 +110,7 @@ LL | const SLICE_LENGTH_PTR: &[u8] = unsafe { mem::transmute((&42u8, &3)) };
    = note: for more information, see issue #71800 <https://github.com/rust-lang/rust/issues/71800>
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-wide-ptr.rs:79:1
+  --> $DIR/ub-wide-ptr.rs:80:1
    |
 LL | const SLICE_TOO_LONG_BOX: Box<[u8]> = unsafe { mem::transmute((&42u8, 999usize)) };
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value: encountered a dangling box (going beyond the bounds of its allocation)
@@ -126,7 +121,7 @@ LL | const SLICE_TOO_LONG_BOX: Box<[u8]> = unsafe { mem::transmute((&42u8, 999us
            }
 
 error: any use of this value will cause an error
-  --> $DIR/ub-wide-ptr.rs:82:1
+  --> $DIR/ub-wide-ptr.rs:83:1
    |
 LL | const SLICE_LENGTH_PTR_BOX: Box<[u8]> = unsafe { mem::transmute((&42u8, &3)) };
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unable to turn pointer into raw bytes
@@ -135,7 +130,7 @@ LL | const SLICE_LENGTH_PTR_BOX: Box<[u8]> = unsafe { mem::transmute((&42u8, &3)
    = note: for more information, see issue #71800 <https://github.com/rust-lang/rust/issues/71800>
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-wide-ptr.rs:87:1
+  --> $DIR/ub-wide-ptr.rs:88:1
    |
 LL | const SLICE_CONTENT_INVALID: &[bool] = &[unsafe { mem::transmute(3u8) }];
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value at .<deref>[0]: encountered 0x03, but expected a boolean
@@ -146,7 +141,7 @@ LL | const SLICE_CONTENT_INVALID: &[bool] = &[unsafe { mem::transmute(3u8) }];
            }
 
 error: any use of this value will cause an error
-  --> $DIR/ub-wide-ptr.rs:87:40
+  --> $DIR/ub-wide-ptr.rs:88:40
    |
 LL | const SLICE_CONTENT_INVALID: &[bool] = &[unsafe { mem::transmute(3u8) }];
    | ------------------------------------   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ referenced constant has errors
@@ -155,7 +150,7 @@ LL | const SLICE_CONTENT_INVALID: &[bool] = &[unsafe { mem::transmute(3u8) }];
    = note: for more information, see issue #71800 <https://github.com/rust-lang/rust/issues/71800>
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-wide-ptr.rs:95:1
+  --> $DIR/ub-wide-ptr.rs:96:1
    |
 LL | const MYSLICE_PREFIX_BAD: &MySliceBool = &MySlice(unsafe { mem::transmute(3u8) }, [false]);
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value at .<deref>.0: encountered 0x03, but expected a boolean
@@ -166,7 +161,7 @@ LL | const MYSLICE_PREFIX_BAD: &MySliceBool = &MySlice(unsafe { mem::transmute(3
            }
 
 error: any use of this value will cause an error
-  --> $DIR/ub-wide-ptr.rs:95:42
+  --> $DIR/ub-wide-ptr.rs:96:42
    |
 LL | const MYSLICE_PREFIX_BAD: &MySliceBool = &MySlice(unsafe { mem::transmute(3u8) }, [false]);
    | --------------------------------------   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ referenced constant has errors
@@ -175,7 +170,7 @@ LL | const MYSLICE_PREFIX_BAD: &MySliceBool = &MySlice(unsafe { mem::transmute(3
    = note: for more information, see issue #71800 <https://github.com/rust-lang/rust/issues/71800>
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-wide-ptr.rs:100:1
+  --> $DIR/ub-wide-ptr.rs:101:1
    |
 LL | const MYSLICE_SUFFIX_BAD: &MySliceBool = &MySlice(true, [unsafe { mem::transmute(3u8) }]);
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value at .<deref>.1[0]: encountered 0x03, but expected a boolean
@@ -186,7 +181,7 @@ LL | const MYSLICE_SUFFIX_BAD: &MySliceBool = &MySlice(true, [unsafe { mem::tran
            }
 
 error: any use of this value will cause an error
-  --> $DIR/ub-wide-ptr.rs:100:42
+  --> $DIR/ub-wide-ptr.rs:101:42
    |
 LL | const MYSLICE_SUFFIX_BAD: &MySliceBool = &MySlice(true, [unsafe { mem::transmute(3u8) }]);
    | --------------------------------------   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ referenced constant has errors
@@ -194,19 +189,14 @@ LL | const MYSLICE_SUFFIX_BAD: &MySliceBool = &MySlice(true, [unsafe { mem::tran
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
    = note: for more information, see issue #71800 <https://github.com/rust-lang/rust/issues/71800>
 
-error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-wide-ptr.rs:109:1
+error[E0080]: evaluation of constant value failed
+  --> $DIR/ub-wide-ptr.rs:110:1
    |
 LL | const RAW_SLICE_LENGTH_UNINIT: *const [u8] = unsafe {
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value: encountered uninitialized raw pointer
-   |
-   = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rustc repository if you believe it should not be considered undefined behavior.
-   = note: the raw bytes of the constant (size: 16, align: 8) {
-               __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ │ ░░░░░░░░░░░░░░░░
-           }
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ using uninitialized data, but this operation requires initialized memory
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-wide-ptr.rs:117:1
+  --> $DIR/ub-wide-ptr.rs:119:1
    |
 LL | const TRAIT_OBJ_SHORT_VTABLE_1: W<&dyn Trait> = unsafe { mem::transmute(W((&92u8, &3u8))) };
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value at .0: encountered allocN, but expected a vtable pointer
@@ -217,7 +207,7 @@ LL | const TRAIT_OBJ_SHORT_VTABLE_1: W<&dyn Trait> = unsafe { mem::transmute(W((
            }
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-wide-ptr.rs:121:1
+  --> $DIR/ub-wide-ptr.rs:123:1
    |
 LL | const TRAIT_OBJ_SHORT_VTABLE_2: W<&dyn Trait> = unsafe { mem::transmute(W((&92u8, &3u64))) };
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value at .0: encountered allocN, but expected a vtable pointer
@@ -228,7 +218,7 @@ LL | const TRAIT_OBJ_SHORT_VTABLE_2: W<&dyn Trait> = unsafe { mem::transmute(W((
            }
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-wide-ptr.rs:125:1
+  --> $DIR/ub-wide-ptr.rs:127:1
    |
 LL | const TRAIT_OBJ_INT_VTABLE: W<&dyn Trait> = unsafe { mem::transmute(W((&92u8, 4usize))) };
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value at .0: encountered 0x4[noalloc], but expected a vtable pointer
@@ -239,25 +229,25 @@ LL | const TRAIT_OBJ_INT_VTABLE: W<&dyn Trait> = unsafe { mem::transmute(W((&92u
            }
 
 error[E0080]: evaluation of constant value failed
-  --> $DIR/ub-wide-ptr.rs:128:57
+  --> $DIR/ub-wide-ptr.rs:130:57
    |
 LL | const TRAIT_OBJ_UNALIGNED_VTABLE: &dyn Trait = unsafe { mem::transmute((&92u8, &[0u8; 128])) };
    |                                                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ using allocN as vtable pointer but it does not point to a vtable
 
 error[E0080]: evaluation of constant value failed
-  --> $DIR/ub-wide-ptr.rs:131:57
+  --> $DIR/ub-wide-ptr.rs:133:57
    |
 LL | const TRAIT_OBJ_BAD_DROP_FN_NULL: &dyn Trait = unsafe { mem::transmute((&92u8, &[0usize; 8])) };
    |                                                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ using allocN as vtable pointer but it does not point to a vtable
 
 error[E0080]: evaluation of constant value failed
-  --> $DIR/ub-wide-ptr.rs:134:56
+  --> $DIR/ub-wide-ptr.rs:136:56
    |
 LL | const TRAIT_OBJ_BAD_DROP_FN_INT: &dyn Trait = unsafe { mem::transmute((&92u8, &[1usize; 8])) };
    |                                                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ using allocN as vtable pointer but it does not point to a vtable
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-wide-ptr.rs:137:1
+  --> $DIR/ub-wide-ptr.rs:139:1
    |
 LL | const TRAIT_OBJ_BAD_DROP_FN_NOT_FN_PTR: W<&dyn Trait> = unsafe { mem::transmute(W((&92u8, &[&42u8; 8]))) };
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value at .0: encountered allocN, but expected a vtable pointer
@@ -268,7 +258,7 @@ LL | const TRAIT_OBJ_BAD_DROP_FN_NOT_FN_PTR: W<&dyn Trait> = unsafe { mem::trans
            }
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-wide-ptr.rs:142:1
+  --> $DIR/ub-wide-ptr.rs:144:1
    |
 LL | const TRAIT_OBJ_CONTENT_INVALID: &dyn Trait = unsafe { mem::transmute::<_, &bool>(&3u8) };
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value at .<deref>.<dyn-downcast>: encountered 0x03, but expected a boolean
@@ -279,7 +269,7 @@ LL | const TRAIT_OBJ_CONTENT_INVALID: &dyn Trait = unsafe { mem::transmute::<_,
            }
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-wide-ptr.rs:147:1
+  --> $DIR/ub-wide-ptr.rs:149:1
    |
 LL | const RAW_TRAIT_OBJ_VTABLE_NULL: *const dyn Trait = unsafe { mem::transmute((&92u8, 0usize)) };
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value: encountered null pointer, but expected a vtable pointer
@@ -290,7 +280,7 @@ LL | const RAW_TRAIT_OBJ_VTABLE_NULL: *const dyn Trait = unsafe { mem::transmute
            }
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-wide-ptr.rs:149:1
+  --> $DIR/ub-wide-ptr.rs:151:1
    |
 LL | const RAW_TRAIT_OBJ_VTABLE_INVALID: *const dyn Trait = unsafe { mem::transmute((&92u8, &3u64)) };
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value: encountered allocN, but expected a vtable pointer
@@ -301,13 +291,13 @@ LL | const RAW_TRAIT_OBJ_VTABLE_INVALID: *const dyn Trait = unsafe { mem::transm
            }
 
 error[E0080]: could not evaluate static initializer
-  --> $DIR/ub-wide-ptr.rs:155:5
+  --> $DIR/ub-wide-ptr.rs:157:5
    |
 LL |     mem::transmute::<_, &dyn Trait>((&92u8, 0usize))
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ out-of-bounds pointer use: null pointer is a dangling pointer (it has no provenance)
 
 error[E0080]: could not evaluate static initializer
-  --> $DIR/ub-wide-ptr.rs:159:5
+  --> $DIR/ub-wide-ptr.rs:161:5
    |
 LL |     mem::transmute::<_, &dyn Trait>((&92u8, &3u64))
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ using allocN as vtable pointer but it does not point to a vtable
@@ -339,7 +329,7 @@ LL | const MY_STR_LENGTH_PTR: &MyStr = unsafe { mem::transmute((&42u8, &3)) };
 
 Future breakage diagnostic:
 error: any use of this value will cause an error
-  --> $DIR/ub-wide-ptr.rs:75:1
+  --> $DIR/ub-wide-ptr.rs:76:1
    |
 LL | const SLICE_LENGTH_PTR: &[u8] = unsafe { mem::transmute((&42u8, &3)) };
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unable to turn pointer into raw bytes
@@ -350,7 +340,7 @@ LL | const SLICE_LENGTH_PTR: &[u8] = unsafe { mem::transmute((&42u8, &3)) };
 
 Future breakage diagnostic:
 error: any use of this value will cause an error
-  --> $DIR/ub-wide-ptr.rs:82:1
+  --> $DIR/ub-wide-ptr.rs:83:1
    |
 LL | const SLICE_LENGTH_PTR_BOX: Box<[u8]> = unsafe { mem::transmute((&42u8, &3)) };
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unable to turn pointer into raw bytes
@@ -361,7 +351,7 @@ LL | const SLICE_LENGTH_PTR_BOX: Box<[u8]> = unsafe { mem::transmute((&42u8, &3)
 
 Future breakage diagnostic:
 error: any use of this value will cause an error
-  --> $DIR/ub-wide-ptr.rs:87:40
+  --> $DIR/ub-wide-ptr.rs:88:40
    |
 LL | const SLICE_CONTENT_INVALID: &[bool] = &[unsafe { mem::transmute(3u8) }];
    | ------------------------------------   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ referenced constant has errors
@@ -372,7 +362,7 @@ LL | const SLICE_CONTENT_INVALID: &[bool] = &[unsafe { mem::transmute(3u8) }];
 
 Future breakage diagnostic:
 error: any use of this value will cause an error
-  --> $DIR/ub-wide-ptr.rs:95:42
+  --> $DIR/ub-wide-ptr.rs:96:42
    |
 LL | const MYSLICE_PREFIX_BAD: &MySliceBool = &MySlice(unsafe { mem::transmute(3u8) }, [false]);
    | --------------------------------------   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ referenced constant has errors
@@ -383,7 +373,7 @@ LL | const MYSLICE_PREFIX_BAD: &MySliceBool = &MySlice(unsafe { mem::transmute(3
 
 Future breakage diagnostic:
 error: any use of this value will cause an error
-  --> $DIR/ub-wide-ptr.rs:100:42
+  --> $DIR/ub-wide-ptr.rs:101:42
    |
 LL | const MYSLICE_SUFFIX_BAD: &MySliceBool = &MySlice(true, [unsafe { mem::transmute(3u8) }]);
    | --------------------------------------   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ referenced constant has errors
diff --git a/src/test/ui/consts/const-eval/ub-wide-ptr.rs b/src/test/ui/consts/const-eval/ub-wide-ptr.rs
index 2da694a8bc4..788403a6df6 100644
--- a/src/test/ui/consts/const-eval/ub-wide-ptr.rs
+++ b/src/test/ui/consts/const-eval/ub-wide-ptr.rs
@@ -61,7 +61,8 @@ const MYSTR_NO_INIT: &MyStr = unsafe { mem::transmute::<&[_], _>(&[MaybeUninit::
 const SLICE_VALID: &[u8] = unsafe { mem::transmute((&42u8, 1usize)) };
 // bad slice: length uninit
 const SLICE_LENGTH_UNINIT: &[u8] = unsafe {
-//~^ ERROR it is undefined behavior to use this value
+//~^ ERROR evaluation of constant value failed
+//~| uninitialized
     let uninit_len = MaybeUninit::<usize> { uninit: () };
     mem::transmute((42, uninit_len))
 };
@@ -107,7 +108,8 @@ const RAW_SLICE_VALID: *const [u8] = unsafe { mem::transmute((&42u8, 1usize)) };
 const RAW_SLICE_TOO_LONG: *const [u8] = unsafe { mem::transmute((&42u8, 999usize)) }; // ok because raw
 const RAW_SLICE_MUCH_TOO_LONG: *const [u8] = unsafe { mem::transmute((&42u8, usize::MAX)) }; // ok because raw
 const RAW_SLICE_LENGTH_UNINIT: *const [u8] = unsafe {
-//~^ ERROR it is undefined behavior to use this value
+//~^ ERROR evaluation of constant value failed
+//~| uninitialized
     let uninit_len = MaybeUninit::<usize> { uninit: () };
     mem::transmute((42, uninit_len))
 };
diff --git a/src/test/ui/consts/const-eval/union-const-eval-field.rs b/src/test/ui/consts/const-eval/union-const-eval-field.rs
index a1e48cac4fa..d88bf2a8479 100644
--- a/src/test/ui/consts/const-eval/union-const-eval-field.rs
+++ b/src/test/ui/consts/const-eval/union-const-eval-field.rs
@@ -26,7 +26,8 @@ const fn read_field2() -> Field2 {
 
 const fn read_field3() -> Field3 {
     const FIELD3: Field3 = unsafe { UNION.field3 };
-    //~^ ERROR it is undefined behavior to use this value
+    //~^ ERROR evaluation of constant value failed
+    //~| uninitialized
     FIELD3
     //~^ ERROR erroneous constant used [E0080]
 }
diff --git a/src/test/ui/consts/const-eval/union-const-eval-field.stderr b/src/test/ui/consts/const-eval/union-const-eval-field.stderr
index c512e682504..00964489e04 100644
--- a/src/test/ui/consts/const-eval/union-const-eval-field.stderr
+++ b/src/test/ui/consts/const-eval/union-const-eval-field.stderr
@@ -1,16 +1,11 @@
-error[E0080]: it is undefined behavior to use this value
-  --> $DIR/union-const-eval-field.rs:28:5
+error[E0080]: evaluation of constant value failed
+  --> $DIR/union-const-eval-field.rs:28:37
    |
 LL |     const FIELD3: Field3 = unsafe { UNION.field3 };
-   |     ^^^^^^^^^^^^^^^^^^^^ constructing invalid value: encountered uninitialized bytes, but expected initialized bytes
-   |
-   = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rustc repository if you believe it should not be considered undefined behavior.
-   = note: the raw bytes of the constant (size: 8, align: 8) {
-               __ __ __ __ __ __ __ __                         │ ░░░░░░░░
-           }
+   |                                     ^^^^^^^^^^^^ using uninitialized data, but this operation requires initialized memory
 
 error[E0080]: erroneous constant used
-  --> $DIR/union-const-eval-field.rs:30:5
+  --> $DIR/union-const-eval-field.rs:31:5
    |
 LL |     FIELD3
    |     ^^^^^^ referenced constant has errors
diff --git a/src/test/ui/consts/const-eval/union-ice.rs b/src/test/ui/consts/const-eval/union-ice.rs
index 4189619b2aa..dd970a35562 100644
--- a/src/test/ui/consts/const-eval/union-ice.rs
+++ b/src/test/ui/consts/const-eval/union-ice.rs
@@ -11,11 +11,15 @@ union DummyUnion {
 
 const UNION: DummyUnion = DummyUnion { field1: 1065353216 };
 
-const FIELD3: Field3 = unsafe { UNION.field3 }; //~ ERROR it is undefined behavior to use this value
+const FIELD3: Field3 = unsafe { UNION.field3 };
+//~^ ERROR evaluation of constant value failed
+//~| uninitialized
 
-const FIELD_PATH: Struct = Struct { //~ ERROR it is undefined behavior to use this value
+const FIELD_PATH: Struct = Struct {
     a: 42,
     b: unsafe { UNION.field3 },
+    //~^ ERROR evaluation of constant value failed
+    //~| uninitialized
 };
 
 struct Struct {
@@ -23,10 +27,12 @@ struct Struct {
     b: Field3,
 }
 
-const FIELD_PATH2: Struct2 = Struct2 { //~ ERROR it is undefined behavior to use this value
+const FIELD_PATH2: Struct2 = Struct2 {
     b: [
         21,
         unsafe { UNION.field3 },
+        //~^ ERROR evaluation of constant value failed
+        //~| uninitialized
         23,
         24,
     ],
diff --git a/src/test/ui/consts/const-eval/union-ice.stderr b/src/test/ui/consts/const-eval/union-ice.stderr
index 21a54550900..bd39a05510b 100644
--- a/src/test/ui/consts/const-eval/union-ice.stderr
+++ b/src/test/ui/consts/const-eval/union-ice.stderr
@@ -1,37 +1,20 @@
-error[E0080]: it is undefined behavior to use this value
-  --> $DIR/union-ice.rs:14:1
+error[E0080]: evaluation of constant value failed
+  --> $DIR/union-ice.rs:14:33
    |
 LL | const FIELD3: Field3 = unsafe { UNION.field3 };
-   | ^^^^^^^^^^^^^^^^^^^^ constructing invalid value: encountered uninitialized bytes, but expected initialized bytes
-   |
-   = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rustc repository if you believe it should not be considered undefined behavior.
-   = note: the raw bytes of the constant (size: 8, align: 8) {
-               __ __ __ __ __ __ __ __                         │ ░░░░░░░░
-           }
+   |                                 ^^^^^^^^^^^^ using uninitialized data, but this operation requires initialized memory
 
-error[E0080]: it is undefined behavior to use this value
-  --> $DIR/union-ice.rs:16:1
-   |
-LL | const FIELD_PATH: Struct = Struct {
-   | ^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value at .b: encountered uninitialized bytes, but expected initialized bytes
+error[E0080]: evaluation of constant value failed
+  --> $DIR/union-ice.rs:20:17
    |
-   = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rustc repository if you believe it should not be considered undefined behavior.
-   = note: the raw bytes of the constant (size: 16, align: 8) {
-               __ __ __ __ __ __ __ __ 2a __ __ __ __ __ __ __ │ ░░░░░░░░*░░░░░░░
-           }
+LL |     b: unsafe { UNION.field3 },
+   |                 ^^^^^^^^^^^^ using uninitialized data, but this operation requires initialized memory
 
-error[E0080]: it is undefined behavior to use this value
-  --> $DIR/union-ice.rs:26:1
-   |
-LL | const FIELD_PATH2: Struct2 = Struct2 {
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value at .b[1]: encountered uninitialized bytes
+error[E0080]: evaluation of constant value failed
+  --> $DIR/union-ice.rs:33:18
    |
-   = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rustc repository if you believe it should not be considered undefined behavior.
-   = note: the raw bytes of the constant (size: 40, align: 8) {
-               0x00 │ 15 00 00 00 00 00 00 00 __ __ __ __ __ __ __ __ │ ........░░░░░░░░
-               0x10 │ 17 00 00 00 00 00 00 00 18 00 00 00 00 00 00 00 │ ................
-               0x20 │ 2a __ __ __ __ __ __ __                         │ *░░░░░░░
-           }
+LL |         unsafe { UNION.field3 },
+   |                  ^^^^^^^^^^^^ using uninitialized data, but this operation requires initialized memory
 
 error: aborting due to 3 previous errors
 
diff --git a/src/test/ui/consts/const-eval/union-ub.32bit.stderr b/src/test/ui/consts/const-eval/union-ub.32bit.stderr
index baf68259660..38ded4d65cf 100644
--- a/src/test/ui/consts/const-eval/union-ub.32bit.stderr
+++ b/src/test/ui/consts/const-eval/union-ub.32bit.stderr
@@ -9,16 +9,11 @@ LL | const BAD_BOOL: bool = unsafe { DummyUnion { u8: 42 }.bool};
                2a                                              │ *
            }
 
-error[E0080]: it is undefined behavior to use this value
-  --> $DIR/union-ub.rs:35:1
+error[E0080]: evaluation of constant value failed
+  --> $DIR/union-ub.rs:35:36
    |
 LL | const UNINIT_BOOL: bool = unsafe { DummyUnion { unit: () }.bool};
-   | ^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value: encountered uninitialized bytes, but expected a boolean
-   |
-   = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rustc repository if you believe it should not be considered undefined behavior.
-   = note: the raw bytes of the constant (size: 1, align: 1) {
-               __                                              │ ░
-           }
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ using uninitialized data, but this operation requires initialized memory
 
 error: aborting due to 2 previous errors
 
diff --git a/src/test/ui/consts/const-eval/union-ub.64bit.stderr b/src/test/ui/consts/const-eval/union-ub.64bit.stderr
index baf68259660..38ded4d65cf 100644
--- a/src/test/ui/consts/const-eval/union-ub.64bit.stderr
+++ b/src/test/ui/consts/const-eval/union-ub.64bit.stderr
@@ -9,16 +9,11 @@ LL | const BAD_BOOL: bool = unsafe { DummyUnion { u8: 42 }.bool};
                2a                                              │ *
            }
 
-error[E0080]: it is undefined behavior to use this value
-  --> $DIR/union-ub.rs:35:1
+error[E0080]: evaluation of constant value failed
+  --> $DIR/union-ub.rs:35:36
    |
 LL | const UNINIT_BOOL: bool = unsafe { DummyUnion { unit: () }.bool};
-   | ^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value: encountered uninitialized bytes, but expected a boolean
-   |
-   = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rustc repository if you believe it should not be considered undefined behavior.
-   = note: the raw bytes of the constant (size: 1, align: 1) {
-               __                                              │ ░
-           }
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ using uninitialized data, but this operation requires initialized memory
 
 error: aborting due to 2 previous errors
 
diff --git a/src/test/ui/consts/const-eval/union-ub.rs b/src/test/ui/consts/const-eval/union-ub.rs
index c1bfe69a706..bb29edcf8b0 100644
--- a/src/test/ui/consts/const-eval/union-ub.rs
+++ b/src/test/ui/consts/const-eval/union-ub.rs
@@ -33,7 +33,8 @@ union Bar {
 const BAD_BOOL: bool = unsafe { DummyUnion { u8: 42 }.bool};
 //~^ ERROR it is undefined behavior to use this value
 const UNINIT_BOOL: bool = unsafe { DummyUnion { unit: () }.bool};
-//~^ ERROR it is undefined behavior to use this value
+//~^ ERROR evaluation of constant value failed
+//~| uninitialized
 
 // The value is not valid for any union variant, but that's fine
 // unions are just a convenient way to transmute bits around
diff --git a/src/test/ui/consts/extra-const-ub/detect-extra-ub.with_flag.stderr b/src/test/ui/consts/extra-const-ub/detect-extra-ub.with_flag.stderr
index 1706db7ac43..b940a77f8a5 100644
--- a/src/test/ui/consts/extra-const-ub/detect-extra-ub.with_flag.stderr
+++ b/src/test/ui/consts/extra-const-ub/detect-extra-ub.with_flag.stderr
@@ -8,13 +8,13 @@ error[E0080]: evaluation of constant value failed
   --> $DIR/detect-extra-ub.rs:15:21
    |
 LL |     let _x: usize = transmute(&3u8);
-   |                     ^^^^^^^^^^^^^^^ constructing invalid value: encountered (potentially part of) a pointer, but expected plain (non-pointer) bytes
+   |                     ^^^^^^^^^^^^^^^ constructing invalid value: encountered (potentially part of) a pointer, but expected an integer
 
 error[E0080]: evaluation of constant value failed
   --> $DIR/detect-extra-ub.rs:22:30
    |
 LL |     let _x: (usize, usize) = transmute(x);
-   |                              ^^^^^^^^^^^^ constructing invalid value at .0: encountered (potentially part of) a pointer, but expected plain (non-pointer) bytes
+   |                              ^^^^^^^^^^^^ constructing invalid value at .0: encountered (potentially part of) a pointer, but expected an integer
 
 error[E0080]: evaluation of constant value failed
   --> $DIR/detect-extra-ub.rs:28:20