Auto merge of #64026 - Centril:rollup-le667lp, r=Centril

Rollup of 7 pull requests

Successful merges:

 - #62957 (Match the loop examples)
 - #63600 (Merge oli-obk mail addresses)
 - #63684 (Constify LinkedList new function)
 - #63847 ([rustdoc] Fix system theme detection)
 - #63999 (Add missing links on AsRef trait)
 - #64014 ( miri: detect too large dynamically sized objects )
 - #64015 (some const-eval test tweaks)

Failed merges:

r? @ghost

45 files changed, 222 insertions, 141 deletions

diff --git a/.mailmap b/.mailmap
index 72c76006f7c..da8044de405 100644
--- a/.mailmap
+++ b/.mailmap
@@ -184,12 +184,19 @@ Neil Pankey <npankey@gmail.com> <neil@wire.im>
 Nick Platt <platt.nicholas@gmail.com>
 Nicole Mazzuca <npmazzuca@gmail.com>
 Nif Ward <nif.ward@gmail.com>
-Oliver Schneider <oliver.schneider@kit.edu> oli-obk <github6541940@oli-obk.de>
-Oliver Schneider <oliver.schneider@kit.edu> Oliver 'ker' Schneider <rust19446194516@oli-obk.de>
-Oliver Schneider <oliver.schneider@kit.edu> Oliver Schneider <git-spam-no-reply9815368754983@oli-obk.de>
-Oliver Schneider <oliver.schneider@kit.edu> Oliver Schneider <git-spam9815368754983@oli-obk.de>
-Oliver Schneider <oliver.schneider@kit.edu> Oliver Schneider <github333195615777966@oli-obk.de>
-Oliver Schneider <oliver.schneider@kit.edu> Oliver Schneider <github6541940@oli-obk.de>
+Oliver Scherer <oliver.schneider@kit.edu> <git-spam-no-reply9815368754983@oli-obk.de>
+Oliver Scherer <oliver.schneider@kit.edu> <git-spam9815368754983@oli-obk.de>
+Oliver Scherer <oliver.schneider@kit.edu> <github333195615777966@oli-obk.de>
+Oliver Scherer <oliver.schneider@kit.edu> <github6541940@oli-obk.de>
+Oliver Scherer <oliver.schneider@kit.edu> <rust19446194516@oli-obk.de>
+Oliver Scherer <oliver.schneider@kit.edu> <git-no-reply-9879165716479413131@oli-obk.de>
+Oliver Scherer <oliver.schneider@kit.edu> <git1984941651981@oli-obk.de>
+Oliver Scherer <oliver.schneider@kit.edu> <github35764891676564198441@oli-obk.de>
+Oliver Scherer <oliver.schneider@kit.edu> <github6541940@oli-obk.de>
+Oliver Scherer <oliver.schneider@kit.edu> <oli-obk@users.noreply.github.com>
+Oliver Scherer <oliver.schneider@kit.edu> <public.oliver.schneider@kit.edu>
+Oliver Scherer <oliver.schneider@kit.edu> <obk8176014uqher834@olio-obk.de>
+Oliver Scherer <oliver.schneider@kit.edu>
 Ožbolt Menegatti <ozbolt.menegatti@gmail.com> gareins <ozbolt.menegatti@gmail.com>
 Paul Faria <paul_faria@ultimatesoftware.com> Paul Faria <Nashenas88@gmail.com>
 Peer Aramillo Irizar <peer.aramillo.irizar@gmail.com> parir <peer.aramillo.irizar@gmail.com>
diff --git a/src/liballoc/collections/linked_list.rs b/src/liballoc/collections/linked_list.rs
index a14a3fe9994..816a71f2557 100644
--- a/src/liballoc/collections/linked_list.rs
+++ b/src/liballoc/collections/linked_list.rs
@@ -276,7 +276,7 @@ impl<T> LinkedList<T> {
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
-    pub fn new() -> Self {
+    pub const fn new() -> Self {
         LinkedList {
             head: None,
             tail: None,
diff --git a/src/libcore/convert.rs b/src/libcore/convert.rs
index 641621f492b..402a7b2c95a 100644
--- a/src/libcore/convert.rs
+++ b/src/libcore/convert.rs
@@ -104,22 +104,17 @@ pub const fn identity<T>(x: T) -> T { x }
 /// If you need to do a costly conversion it is better to implement [`From`] with type
 /// `&T` or write a custom function.
 ///
-/// `AsRef` has the same signature as [`Borrow`], but `Borrow` is different in few aspects:
+/// `AsRef` has the same signature as [`Borrow`], but [`Borrow`] is different in few aspects:
 ///
-/// - Unlike `AsRef`, `Borrow` has a blanket impl for any `T`, and can be used to accept either
+/// - Unlike `AsRef`, [`Borrow`] has a blanket impl for any `T`, and can be used to accept either
 ///   a reference or a value.
-/// - `Borrow` also requires that `Hash`, `Eq` and `Ord` for borrowed value are
+/// - [`Borrow`] also requires that [`Hash`], [`Eq`] and [`Ord`] for borrowed value are
 ///   equivalent to those of the owned value. For this reason, if you want to
-///   borrow only a single field of a struct you can implement `AsRef`, but not `Borrow`.
-///
-/// [`Borrow`]: ../../std/borrow/trait.Borrow.html
+///   borrow only a single field of a struct you can implement `AsRef`, but not [`Borrow`].
 ///
 /// **Note: This trait must not fail**. If the conversion can fail, use a
 /// dedicated method which returns an [`Option<T>`] or a [`Result<T, E>`].
 ///
-/// [`Option<T>`]: ../../std/option/enum.Option.html
-/// [`Result<T, E>`]: ../../std/result/enum.Result.html
-///
 /// # Generic Implementations
 ///
 /// - `AsRef` auto-dereferences if the inner type is a reference or a mutable
@@ -132,9 +127,16 @@ pub const fn identity<T>(x: T) -> T { x }
 /// converted to the specified type `T`.
 ///
 /// For example: By creating a generic function that takes an `AsRef<str>` we express that we
-/// want to accept all references that can be converted to `&str` as an argument.
-/// Since both [`String`] and `&str` implement `AsRef<str>` we can accept both as input argument.
+/// want to accept all references that can be converted to [`&str`] as an argument.
+/// Since both [`String`] and [`&str`] implement `AsRef<str>` we can accept both as input argument.
 ///
+/// [`Option<T>`]: ../../std/option/enum.Option.html
+/// [`Result<T, E>`]: ../../std/result/enum.Result.html
+/// [`Borrow`]: ../../std/borrow/trait.Borrow.html
+/// [`Hash`]: ../../std/hash/trait.Hash.html
+/// [`Eq`]: ../../std/cmp/trait.Eq.html
+/// [`Ord`]: ../../std/cmp/trait.Ord.html
+/// [`&str`]: ../../std/primitive.str.html
 /// [`String`]: ../../std/string/struct.String.html
 ///
 /// ```
diff --git a/src/librustc_mir/interpret/eval_context.rs b/src/librustc_mir/interpret/eval_context.rs
index ac01d436bdc..054b65f0e1a 100644
--- a/src/librustc_mir/interpret/eval_context.rs
+++ b/src/librustc_mir/interpret/eval_context.rs
@@ -442,27 +442,30 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
 
                 // Issue #27023: must add any necessary padding to `size`
                 // (to make it a multiple of `align`) before returning it.
-                //
-                // Namely, the returned size should be, in C notation:
-                //
-                //   `size + ((size & (align-1)) ? align : 0)`
-                //
-                // emulated via the semi-standard fast bit trick:
-                //
-                //   `(size + (align-1)) & -align`
-
-                Ok(Some((size.align_to(align), align)))
+                let size = size.align_to(align);
+
+                // Check if this brought us over the size limit.
+                if size.bytes() >= self.tcx.data_layout().obj_size_bound() {
+                    throw_ub_format!("wide pointer metadata contains invalid information: \
+                        total size is bigger than largest supported object");
+                }
+                Ok(Some((size, align)))
             }
             ty::Dynamic(..) => {
                 let vtable = metadata.expect("dyn trait fat ptr must have vtable");
-                // the second entry in the vtable is the dynamic size of the object.
+                // Read size and align from vtable (already checks size).
                 Ok(Some(self.read_size_and_align_from_vtable(vtable)?))
             }
 
             ty::Slice(_) | ty::Str => {
                 let len = metadata.expect("slice fat ptr must have vtable").to_usize(self)?;
                 let elem = layout.field(self, 0)?;
-                Ok(Some((elem.size * len, elem.align.abi)))
+
+                // Make sure the slice is not too big.
+                let size = elem.size.checked_mul(len, &*self.tcx)
+                    .ok_or_else(|| err_ub_format!("invalid slice: \
+                        total size is bigger than largest supported object"))?;
+                Ok(Some((size, elem.align.abi)))
             }
 
             ty::Foreign(_) => {
diff --git a/src/librustc_mir/interpret/traits.rs b/src/librustc_mir/interpret/traits.rs
index 34a10de7de7..10b767ebba1 100644
--- a/src/librustc_mir/interpret/traits.rs
+++ b/src/librustc_mir/interpret/traits.rs
@@ -1,5 +1,5 @@
 use rustc::ty::{self, Ty, Instance, TypeFoldable};
-use rustc::ty::layout::{Size, Align, LayoutOf};
+use rustc::ty::layout::{Size, Align, LayoutOf, HasDataLayout};
 use rustc::mir::interpret::{Scalar, Pointer, InterpResult, PointerArithmetic,};
 
 use super::{InterpCx, Machine, MemoryKind, FnVal};
@@ -151,6 +151,11 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
             vtable.offset(pointer_size * 2, self)?,
         )?.not_undef()?;
         let align = self.force_bits(align, pointer_size)? as u64;
+
+        if size >= self.tcx.data_layout().obj_size_bound() {
+            throw_ub_format!("invalid vtable: \
+                size is bigger than largest supported object");
+        }
         Ok((Size::from_bytes(size), Align::from_bytes(align).unwrap()))
     }
 }
diff --git a/src/librustc_mir/interpret/validity.rs b/src/librustc_mir/interpret/validity.rs
index c2505547c5b..3e14ba3efcc 100644
--- a/src/librustc_mir/interpret/validity.rs
+++ b/src/librustc_mir/interpret/validity.rs
@@ -1,3 +1,9 @@
+//! Check the validity invariant of a given value, and tell the user
+//! where in the value it got violated.
+//! In const context, this goes even further and tries to approximate const safety.
+//! That's useful because it means other passes (e.g. promotion) can rely on `const`s
+//! to be const-safe.
+
 use std::fmt::Write;
 use std::ops::RangeInclusive;
 
diff --git a/src/librustdoc/html/static/storage.js b/src/librustdoc/html/static/storage.js
index 9d30e7ee79b..40a6a156972 100644
--- a/src/librustdoc/html/static/storage.js
+++ b/src/librustdoc/html/static/storage.js
@@ -118,7 +118,8 @@ function switchTheme(styleElem, mainStyleElem, newTheme, saveTheme) {
 }
 
 function getSystemValue() {
-    return getComputedStyle(document.documentElement).getPropertyValue('content');
+    var property = getComputedStyle(document.documentElement).getPropertyValue('content');
+    return property.replace(/\"\'/g, "");
 }
 
 switchTheme(currentTheme, mainTheme,
diff --git a/src/libstd/keyword_docs.rs b/src/libstd/keyword_docs.rs
index 85a9dea09ed..a8dfe924fdf 100644
--- a/src/libstd/keyword_docs.rs
+++ b/src/libstd/keyword_docs.rs
@@ -681,14 +681,15 @@ mod while_keyword { }
 ///     # break;
 /// }
 ///
-/// let mut i = 0;
+/// let mut i = 1;
 /// loop {
 ///     println!("i is {}", i);
-///     if i > 10 {
+///     if i > 100 {
 ///         break;
 ///     }
-///     i += 1;
+///     i *= 2;
 /// }
+/// assert_eq!(i, 128);
 /// ```
 ///
 /// Unlike the other kinds of loops in Rust (`while`, `while let`, and `for`), loops can be used as
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 cc5ddb44016..a2196db780c 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
@@ -1,5 +1,6 @@
 // only-x86_64
 
+#[repr(C)]
 union Nonsense {
     u: usize,
     int_32_ref: &'static i32,
diff --git a/src/test/ui/consts/const-eval/const-pointer-values-in-various-types.stderr b/src/test/ui/consts/const-eval/const-pointer-values-in-various-types.stderr
index 73aca911531..3333ffac4c9 100644
--- a/src/test/ui/consts/const-eval/const-pointer-values-in-various-types.stderr
+++ b/src/test/ui/consts/const-eval/const-pointer-values-in-various-types.stderr
@@ -1,5 +1,5 @@
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/const-pointer-values-in-various-types.rs:24:5
+  --> $DIR/const-pointer-values-in-various-types.rs:25:5
    |
 LL |     const I32_REF_USIZE_UNION: usize = unsafe { Nonsense { int_32_ref: &3 }.u };
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered a pointer, but expected initialized plain (non-pointer) bytes
@@ -7,7 +7,7 @@ LL |     const I32_REF_USIZE_UNION: usize = unsafe { Nonsense { int_32_ref: &3 }
    = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
 
 error: any use of this value will cause an error
-  --> $DIR/const-pointer-values-in-various-types.rs:27:43
+  --> $DIR/const-pointer-values-in-various-types.rs:28:43
    |
 LL |     const I32_REF_U8_UNION: u8 = unsafe { Nonsense { int_32_ref: &3 }.uint_8 };
    |     --------------------------------------^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^---
@@ -17,7 +17,7 @@ LL |     const I32_REF_U8_UNION: u8 = unsafe { Nonsense { int_32_ref: &3 }.uint_
    = note: `#[deny(const_err)]` on by default
 
 error: any use of this value will cause an error
-  --> $DIR/const-pointer-values-in-various-types.rs:30:45
+  --> $DIR/const-pointer-values-in-various-types.rs:31:45
    |
 LL |     const I32_REF_U16_UNION: u16 = unsafe { Nonsense { int_32_ref: &3 }.uint_16 };
    |     ----------------------------------------^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^---
@@ -25,7 +25,7 @@ LL |     const I32_REF_U16_UNION: u16 = unsafe { Nonsense { int_32_ref: &3 }.uin
    |                                             a raw memory access tried to access part of a pointer value as raw bytes
 
 error: any use of this value will cause an error
-  --> $DIR/const-pointer-values-in-various-types.rs:33:45
+  --> $DIR/const-pointer-values-in-various-types.rs:34:45
    |
 LL |     const I32_REF_U32_UNION: u32 = unsafe { Nonsense { int_32_ref: &3 }.uint_32 };
    |     ----------------------------------------^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^---
@@ -33,7 +33,7 @@ LL |     const I32_REF_U32_UNION: u32 = unsafe { Nonsense { int_32_ref: &3 }.uin
    |                                             a raw memory access tried to access part of a pointer value as raw bytes
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/const-pointer-values-in-various-types.rs:36:5
+  --> $DIR/const-pointer-values-in-various-types.rs:37:5
    |
 LL |     const I32_REF_U64_UNION: u64 = unsafe { Nonsense { int_32_ref: &3 }.uint_64 };
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered a pointer, but expected initialized plain (non-pointer) bytes
@@ -41,7 +41,7 @@ LL |     const I32_REF_U64_UNION: u64 = unsafe { Nonsense { int_32_ref: &3 }.uin
    = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/const-pointer-values-in-various-types.rs:39:5
+  --> $DIR/const-pointer-values-in-various-types.rs:40:5
    |
 LL |     const I32_REF_U128_UNION: u128 = unsafe { Nonsense { int_32_ref: &3 }.uint_128 };
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered uninitialized bytes, but expected initialized plain (non-pointer) bytes
@@ -49,7 +49,7 @@ LL |     const I32_REF_U128_UNION: u128 = unsafe { Nonsense { int_32_ref: &3 }.u
    = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
 
 error: any use of this value will cause an error
-  --> $DIR/const-pointer-values-in-various-types.rs:42:43
+  --> $DIR/const-pointer-values-in-various-types.rs:43:43
    |
 LL |     const I32_REF_I8_UNION: i8 = unsafe { Nonsense { int_32_ref: &3 }.int_8 };
    |     --------------------------------------^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^---
@@ -57,7 +57,7 @@ LL |     const I32_REF_I8_UNION: i8 = unsafe { Nonsense { int_32_ref: &3 }.int_8
    |                                           a raw memory access tried to access part of a pointer value as raw bytes
 
 error: any use of this value will cause an error
-  --> $DIR/const-pointer-values-in-various-types.rs:45:45
+  --> $DIR/const-pointer-values-in-various-types.rs:46:45
    |
 LL |     const I32_REF_I16_UNION: i16 = unsafe { Nonsense { int_32_ref: &3 }.int_16 };
    |     ----------------------------------------^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^---
@@ -65,7 +65,7 @@ LL |     const I32_REF_I16_UNION: i16 = unsafe { Nonsense { int_32_ref: &3 }.int
    |                                             a raw memory access tried to access part of a pointer value as raw bytes
 
 error: any use of this value will cause an error
-  --> $DIR/const-pointer-values-in-various-types.rs:48:45
+  --> $DIR/const-pointer-values-in-various-types.rs:49:45
    |
 LL |     const I32_REF_I32_UNION: i32 = unsafe { Nonsense { int_32_ref: &3 }.int_32 };
    |     ----------------------------------------^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^---
@@ -73,7 +73,7 @@ LL |     const I32_REF_I32_UNION: i32 = unsafe { Nonsense { int_32_ref: &3 }.int
    |                                             a raw memory access tried to access part of a pointer value as raw bytes
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/const-pointer-values-in-various-types.rs:51:5
+  --> $DIR/const-pointer-values-in-various-types.rs:52:5
    |
 LL |     const I32_REF_I64_UNION: i64 = unsafe { Nonsense { int_32_ref: &3 }.int_64 };
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered a pointer, but expected initialized plain (non-pointer) bytes
@@ -81,7 +81,7 @@ LL |     const I32_REF_I64_UNION: i64 = unsafe { Nonsense { int_32_ref: &3 }.int
    = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/const-pointer-values-in-various-types.rs:54:5
+  --> $DIR/const-pointer-values-in-various-types.rs:55:5
    |
 LL |     const I32_REF_I128_UNION: i128 = unsafe { Nonsense { int_32_ref: &3 }.int_128 };
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered uninitialized bytes, but expected initialized plain (non-pointer) bytes
@@ -89,7 +89,7 @@ LL |     const I32_REF_I128_UNION: i128 = unsafe { Nonsense { int_32_ref: &3 }.i
    = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
 
 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_F32_UNION: f32 = unsafe { Nonsense { int_32_ref: &3 }.float_32 };
    |     ----------------------------------------^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^---
@@ -97,7 +97,7 @@ LL |     const I32_REF_F32_UNION: f32 = unsafe { Nonsense { int_32_ref: &3 }.flo
    |                                             a raw memory access tried to access part of a pointer value as raw bytes
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/const-pointer-values-in-various-types.rs:60:5
+  --> $DIR/const-pointer-values-in-various-types.rs:61:5
    |
 LL |     const I32_REF_F64_UNION: f64 = unsafe { Nonsense { int_32_ref: &3 }.float_64 };
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered a pointer, but expected initialized plain (non-pointer) bytes
@@ -105,7 +105,7 @@ LL |     const I32_REF_F64_UNION: f64 = unsafe { Nonsense { int_32_ref: &3 }.flo
    = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
 
 error: any use of this value will cause an error
-  --> $DIR/const-pointer-values-in-various-types.rs:63:47
+  --> $DIR/const-pointer-values-in-various-types.rs:64:47
    |
 LL |     const I32_REF_BOOL_UNION: bool = unsafe { Nonsense { int_32_ref: &3 }.truthy_falsey };
    |     ------------------------------------------^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^---
@@ -113,7 +113,7 @@ LL |     const I32_REF_BOOL_UNION: bool = unsafe { Nonsense { int_32_ref: &3 }.t
    |                                               a raw memory access tried to access part of a pointer value as raw bytes
 
 error: any use of this value will cause an error
-  --> $DIR/const-pointer-values-in-various-types.rs:66:47
+  --> $DIR/const-pointer-values-in-various-types.rs:67:47
    |
 LL |     const I32_REF_CHAR_UNION: char = unsafe { Nonsense { int_32_ref: &3 }.character };
    |     ------------------------------------------^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^---
@@ -121,7 +121,7 @@ LL |     const I32_REF_CHAR_UNION: char = unsafe { Nonsense { int_32_ref: &3 }.c
    |                                               a raw memory access tried to access part of a pointer value as raw bytes
 
 error: any use of this value will cause an error
-  --> $DIR/const-pointer-values-in-various-types.rs:69:39
+  --> $DIR/const-pointer-values-in-various-types.rs:70:39
    |
 LL |     const STR_U8_UNION: u8 = unsafe { Nonsense { stringy: "3" }.uint_8 };
    |     ----------------------------------^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^---
@@ -129,7 +129,7 @@ LL |     const STR_U8_UNION: u8 = unsafe { Nonsense { stringy: "3" }.uint_8 };
    |                                       a raw memory access tried to access part of a pointer value as raw bytes
 
 error: any use of this value will cause an error
-  --> $DIR/const-pointer-values-in-various-types.rs:72:41
+  --> $DIR/const-pointer-values-in-various-types.rs:73:41
    |
 LL |     const STR_U16_UNION: u16 = unsafe { Nonsense { stringy: "3" }.uint_16 };
    |     ------------------------------------^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^---
@@ -137,7 +137,7 @@ LL |     const STR_U16_UNION: u16 = unsafe { Nonsense { stringy: "3" }.uint_16 }
    |                                         a raw memory access tried to access part of a pointer value as raw bytes
 
 error: any use of this value will cause an error
-  --> $DIR/const-pointer-values-in-various-types.rs:75:41
+  --> $DIR/const-pointer-values-in-various-types.rs:76:41
    |
 LL |     const STR_U32_UNION: u32 = unsafe { Nonsense { stringy: "3" }.uint_32 };
    |     ------------------------------------^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^---
@@ -145,7 +145,7 @@ LL |     const STR_U32_UNION: u32 = unsafe { Nonsense { stringy: "3" }.uint_32 }
    |                                         a raw memory access tried to access part of a pointer value as raw bytes
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/const-pointer-values-in-various-types.rs:78:5
+  --> $DIR/const-pointer-values-in-various-types.rs:79:5
    |
 LL |     const STR_U64_UNION: u64 = unsafe { Nonsense { stringy: "3" }.uint_64 };
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered a pointer, but expected initialized plain (non-pointer) bytes
@@ -153,7 +153,7 @@ LL |     const STR_U64_UNION: u64 = unsafe { Nonsense { stringy: "3" }.uint_64 }
    = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
 
 error: any use of this value will cause an error
-  --> $DIR/const-pointer-values-in-various-types.rs:81:43
+  --> $DIR/const-pointer-values-in-various-types.rs:82:43
    |
 LL |     const STR_U128_UNION: u128 = unsafe { Nonsense { stringy: "3" }.uint_128 };
    |     --------------------------------------^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^---
@@ -161,7 +161,7 @@ LL |     const STR_U128_UNION: u128 = unsafe { Nonsense { stringy: "3" }.uint_12
    |                                           a raw memory access tried to access part of a pointer value as raw bytes
 
 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:85:39
    |
 LL |     const STR_I8_UNION: i8 = unsafe { Nonsense { stringy: "3" }.int_8 };
    |     ----------------------------------^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^---
@@ -169,7 +169,7 @@ LL |     const STR_I8_UNION: i8 = unsafe { Nonsense { stringy: "3" }.int_8 };
    |                                       a raw memory access tried to access part of a pointer value as raw bytes
 
 error: any use of this value will cause an error
-  --> $DIR/const-pointer-values-in-various-types.rs:87:41
+  --> $DIR/const-pointer-values-in-various-types.rs:88:41
    |
 LL |     const STR_I16_UNION: i16 = unsafe { Nonsense { stringy: "3" }.int_16 };
    |     ------------------------------------^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^---
@@ -177,7 +177,7 @@ LL |     const STR_I16_UNION: i16 = unsafe { Nonsense { stringy: "3" }.int_16 };
    |                                         a raw memory access tried to access part of a pointer value as raw bytes
 
 error: any use of this value will cause an error
-  --> $DIR/const-pointer-values-in-various-types.rs:90:41
+  --> $DIR/const-pointer-values-in-various-types.rs:91:41
    |
 LL |     const STR_I32_UNION: i32 = unsafe { Nonsense { stringy: "3" }.int_32 };
    |     ------------------------------------^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^---
@@ -185,7 +185,7 @@ LL |     const STR_I32_UNION: i32 = unsafe { Nonsense { stringy: "3" }.int_32 };
    |                                         a raw memory access tried to access part of a pointer value as raw bytes
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/const-pointer-values-in-various-types.rs:93:5
+  --> $DIR/const-pointer-values-in-various-types.rs:94:5
    |
 LL |     const STR_I64_UNION: i64 = unsafe { Nonsense { stringy: "3" }.int_64 };
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered a pointer, but expected initialized plain (non-pointer) bytes
@@ -193,7 +193,7 @@ LL |     const STR_I64_UNION: i64 = unsafe { Nonsense { stringy: "3" }.int_64 };
    = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
 
 error: any use of this value will cause an error
-  --> $DIR/const-pointer-values-in-various-types.rs:96:43
+  --> $DIR/const-pointer-values-in-various-types.rs:97:43
    |
 LL |     const STR_I128_UNION: i128 = unsafe { Nonsense { stringy: "3" }.int_128 };
    |     --------------------------------------^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^---
@@ -201,7 +201,7 @@ LL |     const STR_I128_UNION: i128 = unsafe { Nonsense { stringy: "3" }.int_128
    |                                           a raw memory access tried to access part of a pointer value as raw bytes
 
 error: any use of this value will cause an error
-  --> $DIR/const-pointer-values-in-various-types.rs:99:41
+  --> $DIR/const-pointer-values-in-various-types.rs:100:41
    |
 LL |     const STR_F32_UNION: f32 = unsafe { Nonsense { stringy: "3" }.float_32 };
    |     ------------------------------------^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^---
@@ -209,7 +209,7 @@ LL |     const STR_F32_UNION: f32 = unsafe { Nonsense { stringy: "3" }.float_32
    |                                         a raw memory access tried to access part of a pointer value as raw bytes
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/const-pointer-values-in-various-types.rs:102:5
+  --> $DIR/const-pointer-values-in-various-types.rs:103:5
    |
 LL |     const STR_F64_UNION: f64 = unsafe { Nonsense { stringy: "3" }.float_64 };
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered a pointer, but expected initialized plain (non-pointer) bytes
@@ -217,7 +217,7 @@ LL |     const STR_F64_UNION: f64 = unsafe { Nonsense { stringy: "3" }.float_64
    = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
 
 error: any use of this value will cause an error
-  --> $DIR/const-pointer-values-in-various-types.rs:105:43
+  --> $DIR/const-pointer-values-in-various-types.rs:106:43
    |
 LL |     const STR_BOOL_UNION: bool = unsafe { Nonsense { stringy: "3" }.truthy_falsey };
    |     --------------------------------------^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^---
@@ -225,7 +225,7 @@ LL |     const STR_BOOL_UNION: bool = unsafe { Nonsense { stringy: "3" }.truthy_
    |                                           a raw memory access tried to access part of a pointer value as raw bytes
 
 error: any use of this value will cause an error
-  --> $DIR/const-pointer-values-in-various-types.rs:108:43
+  --> $DIR/const-pointer-values-in-various-types.rs:109:43
    |
 LL |     const STR_CHAR_UNION: char = unsafe { Nonsense { stringy: "3" }.character };
    |     --------------------------------------^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^---
diff --git a/src/test/ui/consts/const-eval/const_transmute.rs b/src/test/ui/consts/const-eval/const_transmute.rs
index 0e0e003dcf4..4a7d8490ef2 100644
--- a/src/test/ui/consts/const-eval/const_transmute.rs
+++ b/src/test/ui/consts/const-eval/const_transmute.rs
@@ -2,6 +2,7 @@
 
 #![feature(const_fn_union)]
 
+#[repr(C)]
 union Transmute<T: Copy, U: Copy> {
     t: T,
     u: U,
diff --git a/src/test/ui/consts/const-eval/dangling.rs b/src/test/ui/consts/const-eval/dangling.rs
new file mode 100644
index 00000000000..b5d72d46f28
--- /dev/null
+++ b/src/test/ui/consts/const-eval/dangling.rs
@@ -0,0 +1,13 @@
+#![feature(const_transmute, const_raw_ptr_deref)]
+
+use std::{mem, usize};
+
+// Make sure we error with the right kind of error on a too large slice.
+const TEST: () = { unsafe { //~ NOTE
+    let slice: *const [u8] = mem::transmute((1usize, usize::MAX));
+    let _val = &*slice; //~ ERROR: any use of this value will cause an error
+    //~^ NOTE: total size is bigger than largest supported object
+    //~^^ on by default
+} };
+
+fn main() {}
diff --git a/src/test/ui/consts/const-eval/dangling.stderr b/src/test/ui/consts/const-eval/dangling.stderr
new file mode 100644
index 00000000000..286de080097
--- /dev/null
+++ b/src/test/ui/consts/const-eval/dangling.stderr
@@ -0,0 +1,16 @@
+error: any use of this value will cause an error
+  --> $DIR/dangling.rs:8:16
+   |
+LL | / const TEST: () = { unsafe {
+LL | |     let slice: *const [u8] = mem::transmute((1usize, usize::MAX));
+LL | |     let _val = &*slice;
+   | |                ^^^^^^^ invalid slice: total size is bigger than largest supported object
+LL | |
+LL | |
+LL | | } };
+   | |____-
+   |
+   = note: `#[deny(const_err)]` on by default
+
+error: aborting due to previous error
+
diff --git a/src/test/ui/consts/const-eval/double_check.rs b/src/test/ui/consts/const-eval/double_check.rs
index 2cf6a5494dd..ff2fff7fb79 100644
--- a/src/test/ui/consts/const-eval/double_check.rs
+++ b/src/test/ui/consts/const-eval/double_check.rs
@@ -8,6 +8,7 @@ enum Bar {
     C = 42,
     D = 99,
 }
+#[repr(C)]
 union Union {
     foo: &'static Foo,
     bar: &'static Bar,
diff --git a/src/test/ui/consts/const-eval/double_check2.rs b/src/test/ui/consts/const-eval/double_check2.rs
index dc2b58faf92..7c222b113cd 100644
--- a/src/test/ui/consts/const-eval/double_check2.rs
+++ b/src/test/ui/consts/const-eval/double_check2.rs
@@ -6,6 +6,7 @@ enum Bar {
     C = 42,
     D = 99,
 }
+#[repr(C)]
 union Union {
     foo: &'static Foo,
     bar: &'static Bar,
diff --git a/src/test/ui/consts/const-eval/double_check2.stderr b/src/test/ui/consts/const-eval/double_check2.stderr
index 2b61d33852c..9c56f199520 100644
--- a/src/test/ui/consts/const-eval/double_check2.stderr
+++ b/src/test/ui/consts/const-eval/double_check2.stderr
@@ -1,5 +1,5 @@
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/double_check2.rs:15:1
+  --> $DIR/double_check2.rs:16:1
    |
 LL | / static FOO: (&Foo, &Bar) = unsafe {(
 LL | |     Union { u8: &BAR }.foo,
diff --git a/src/test/ui/consts/const-eval/feature-gate-const_fn_union.rs b/src/test/ui/consts/const-eval/feature-gate-const_fn_union.rs
index b0ae746ace5..3f7bab06586 100644
--- a/src/test/ui/consts/const-eval/feature-gate-const_fn_union.rs
+++ b/src/test/ui/consts/const-eval/feature-gate-const_fn_union.rs
@@ -2,6 +2,7 @@
 
 fn main() {}
 
+#[repr(C)]
 union Foo {
     u: u32,
     i: i32,
diff --git a/src/test/ui/consts/const-eval/feature-gate-const_fn_union.stderr b/src/test/ui/consts/const-eval/feature-gate-const_fn_union.stderr
index 5bf43cb8b6a..6899b7b82c5 100644
--- a/src/test/ui/consts/const-eval/feature-gate-const_fn_union.stderr
+++ b/src/test/ui/consts/const-eval/feature-gate-const_fn_union.stderr
@@ -1,5 +1,5 @@
 error[E0658]: unions in const fn are unstable
-  --> $DIR/feature-gate-const_fn_union.rs:11:5
+  --> $DIR/feature-gate-const_fn_union.rs:12:5
    |
 LL |     Foo { u }.i
    |     ^^^^^^^^^^^
diff --git a/src/test/ui/consts/const-eval/issue-49296.rs b/src/test/ui/consts/const-eval/issue-49296.rs
index a7c3c5318d4..c6caeeffd22 100644
--- a/src/test/ui/consts/const-eval/issue-49296.rs
+++ b/src/test/ui/consts/const-eval/issue-49296.rs
@@ -4,6 +4,7 @@
 #![feature(const_fn_union)]
 
 const unsafe fn transmute<T: Copy, U: Copy>(t: T) -> U {
+    #[repr(C)]
     union Transmute<T: Copy, U: Copy> {
         from: T,
         to: U,
diff --git a/src/test/ui/consts/const-eval/issue-49296.stderr b/src/test/ui/consts/const-eval/issue-49296.stderr
index 7a4bba8daa7..48809e0ae64 100644
--- a/src/test/ui/consts/const-eval/issue-49296.stderr
+++ b/src/test/ui/consts/const-eval/issue-49296.stderr
@@ -1,5 +1,5 @@
 error: any use of this value will cause an error
-  --> $DIR/issue-49296.rs:18:16
+  --> $DIR/issue-49296.rs:19:16
    |
 LL | const X: u64 = *wat(42);
    | ---------------^^^^^^^^-
diff --git a/src/test/ui/consts/const-eval/promoted_const_fn_fail.rs b/src/test/ui/consts/const-eval/promoted_const_fn_fail.rs
index 88181cb8610..3edd4e08686 100644
--- a/src/test/ui/consts/const-eval/promoted_const_fn_fail.rs
+++ b/src/test/ui/consts/const-eval/promoted_const_fn_fail.rs
@@ -2,6 +2,7 @@
 
 #![allow(const_err)]
 
+#[repr(C)]
 union Bar {
     a: &'static u8,
     b: usize,
diff --git a/src/test/ui/consts/const-eval/promoted_const_fn_fail.stderr b/src/test/ui/consts/const-eval/promoted_const_fn_fail.stderr
index 519ba7d84b0..6618f1cd1c0 100644
--- a/src/test/ui/consts/const-eval/promoted_const_fn_fail.stderr
+++ b/src/test/ui/consts/const-eval/promoted_const_fn_fail.stderr
@@ -1,5 +1,5 @@
 error[E0716]: temporary value dropped while borrowed
-  --> $DIR/promoted_const_fn_fail.rs:20:27
+  --> $DIR/promoted_const_fn_fail.rs:21:27
    |
 LL |     let x: &'static u8 = &(bar() + 1);
    |            -----------    ^^^^^^^^^^^ creates a temporary which is freed while still in use
diff --git a/src/test/ui/consts/const-eval/promoted_const_fn_fail_deny_const_err.rs b/src/test/ui/consts/const-eval/promoted_const_fn_fail_deny_const_err.rs
index 061ab7eeb02..7887e426534 100644
--- a/src/test/ui/consts/const-eval/promoted_const_fn_fail_deny_const_err.rs
+++ b/src/test/ui/consts/const-eval/promoted_const_fn_fail_deny_const_err.rs
@@ -2,6 +2,7 @@
 
 #![deny(const_err)]
 
+#[repr(C)]
 union Bar {
     a: &'static u8,
     b: usize,
diff --git a/src/test/ui/consts/const-eval/promoted_const_fn_fail_deny_const_err.stderr b/src/test/ui/consts/const-eval/promoted_const_fn_fail_deny_const_err.stderr
index 987d2304ae8..5f9f3bda87b 100644
--- a/src/test/ui/consts/const-eval/promoted_const_fn_fail_deny_const_err.stderr
+++ b/src/test/ui/consts/const-eval/promoted_const_fn_fail_deny_const_err.stderr
@@ -1,5 +1,5 @@
 error[E0716]: temporary value dropped while borrowed
-  --> $DIR/promoted_const_fn_fail_deny_const_err.rs:21:27
+  --> $DIR/promoted_const_fn_fail_deny_const_err.rs:22:27
    |
 LL |     let x: &'static u8 = &(bar() + 1);
    |            -----------    ^^^^^^^^^^^ creates a temporary which is freed while still in use
diff --git a/src/test/ui/consts/const-eval/ref_to_int_match.rs b/src/test/ui/consts/const-eval/ref_to_int_match.rs
index b6a2ed1f9bc..45ce040fb9e 100644
--- a/src/test/ui/consts/const-eval/ref_to_int_match.rs
+++ b/src/test/ui/consts/const-eval/ref_to_int_match.rs
@@ -9,6 +9,7 @@ fn main() {
     }
 }
 
+#[repr(C)]
 union Foo {
     f: Int,
     r: &'static u32,
diff --git a/src/test/ui/consts/const-eval/ref_to_int_match.stderr b/src/test/ui/consts/const-eval/ref_to_int_match.stderr
index f8eafed68e4..0be82e34341 100644
--- a/src/test/ui/consts/const-eval/ref_to_int_match.stderr
+++ b/src/test/ui/consts/const-eval/ref_to_int_match.stderr
@@ -1,5 +1,5 @@
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ref_to_int_match.rs:23:1
+  --> $DIR/ref_to_int_match.rs:24:1
    |
 LL | const BAR: Int = unsafe { Foo { r: &42 }.f };
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered a pointer, but expected initialized plain (non-pointer) bytes
diff --git a/src/test/ui/consts/const-eval/ub-enum.rs b/src/test/ui/consts/const-eval/ub-enum.rs
index d4b22206951..483285aa4e1 100644
--- a/src/test/ui/consts/const-eval/ub-enum.rs
+++ b/src/test/ui/consts/const-eval/ub-enum.rs
@@ -10,6 +10,7 @@ struct Wrap<T>(T);
 enum Enum {
     A = 0,
 }
+#[repr(C)]
 union TransmuteEnum {
     in1: &'static u8,
     in2: usize,
@@ -35,6 +36,7 @@ enum Enum2 {
     A = 2,
 }
 
+#[repr(C)]
 union TransmuteEnum2 {
     in1: usize,
     in2: &'static u8,
@@ -60,6 +62,7 @@ const BAD_ENUM2_OPTION_PTR: Option<Enum2> = unsafe { TransmuteEnum2 { in2: &0 }.
 
 // Invalid enum field content (mostly to test printing of paths for enum tuple
 // variants and tuples).
+#[repr(C)]
 union TransmuteChar {
     a: u32,
     b: char,
diff --git a/src/test/ui/consts/const-eval/ub-enum.stderr b/src/test/ui/consts/const-eval/ub-enum.stderr
index 8ecb1aabdd0..30dd86592d4 100644
--- a/src/test/ui/consts/const-eval/ub-enum.stderr
+++ b/src/test/ui/consts/const-eval/ub-enum.stderr
@@ -1,5 +1,5 @@
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-enum.rs:22:1
+  --> $DIR/ub-enum.rs:23:1
    |
 LL | const BAD_ENUM: Enum = unsafe { TransmuteEnum { in2: 1 }.out1 };
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered 1, but expected a valid enum discriminant
@@ -7,7 +7,7 @@ LL | const BAD_ENUM: Enum = unsafe { TransmuteEnum { in2: 1 }.out1 };
    = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-enum.rs:25:1
+  --> $DIR/ub-enum.rs:26:1
    |
 LL | const BAD_ENUM_PTR: Enum = unsafe { TransmuteEnum { in1: &1 }.out1 };
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered a pointer, but expected a valid enum discriminant
@@ -15,7 +15,7 @@ LL | const BAD_ENUM_PTR: Enum = unsafe { TransmuteEnum { in1: &1 }.out1 };
    = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-enum.rs:28:1
+  --> $DIR/ub-enum.rs:29:1
    |
 LL | const BAD_ENUM_WRAPPED: Wrap<Enum> = unsafe { TransmuteEnum { in1: &1 }.out2 };
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered a pointer, but expected something that cannot possibly fail to be equal to 0
@@ -23,7 +23,7 @@ LL | const BAD_ENUM_WRAPPED: Wrap<Enum> = unsafe { TransmuteEnum { in1: &1 }.out
    = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-enum.rs:46:1
+  --> $DIR/ub-enum.rs:48:1
    |
 LL | const BAD_ENUM2: Enum2 = unsafe { TransmuteEnum2 { in1: 0 }.out1 };
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered 0, but expected a valid enum discriminant
@@ -31,7 +31,7 @@ LL | const BAD_ENUM2: Enum2 = unsafe { TransmuteEnum2 { in1: 0 }.out1 };
    = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-enum.rs:48:1
+  --> $DIR/ub-enum.rs:50:1
    |
 LL | const BAD_ENUM2_PTR: Enum2 = unsafe { TransmuteEnum2 { in2: &0 }.out1 };
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered a pointer, but expected a valid enum discriminant
@@ -39,7 +39,7 @@ LL | const BAD_ENUM2_PTR: Enum2 = unsafe { TransmuteEnum2 { in2: &0 }.out1 };
    = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-enum.rs:50:1
+  --> $DIR/ub-enum.rs:52:1
    |
 LL | const BAD_ENUM2_WRAPPED: Wrap<Enum2> = unsafe { TransmuteEnum2 { in2: &0 }.out2 };
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered a pointer, but expected something that cannot possibly fail to be equal to 2
@@ -47,7 +47,7 @@ LL | const BAD_ENUM2_WRAPPED: Wrap<Enum2> = unsafe { TransmuteEnum2 { in2: &0 }.
    = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-enum.rs:54:1
+  --> $DIR/ub-enum.rs:56:1
    |
 LL | const BAD_ENUM2_UNDEF : Enum2 = unsafe { TransmuteEnum2 { in3: () }.out1 };
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered uninitialized bytes, but expected a valid enum discriminant
@@ -55,7 +55,7 @@ LL | const BAD_ENUM2_UNDEF : Enum2 = unsafe { TransmuteEnum2 { in3: () }.out1 };
    = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-enum.rs:58:1
+  --> $DIR/ub-enum.rs:60:1
    |
 LL | const BAD_ENUM2_OPTION_PTR: Option<Enum2> = unsafe { TransmuteEnum2 { in2: &0 }.out3 };
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered a pointer, but expected a valid enum discriminant
@@ -63,7 +63,7 @@ LL | const BAD_ENUM2_OPTION_PTR: Option<Enum2> = unsafe { TransmuteEnum2 { in2:
    = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-enum.rs:68:1
+  --> $DIR/ub-enum.rs:71:1
    |
 LL | const BAD_OPTION_CHAR: Option<(char, char)> = Some(('x', unsafe { TransmuteChar { a: !0 }.b }));
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered 4294967295 at .<downcast-variant(Some)>.0.1, but expected something less or equal to 1114111
diff --git a/src/test/ui/consts/const-eval/ub-nonnull.rs b/src/test/ui/consts/const-eval/ub-nonnull.rs
index 9edae1965ce..8ce64ced7df 100644
--- a/src/test/ui/consts/const-eval/ub-nonnull.rs
+++ b/src/test/ui/consts/const-eval/ub-nonnull.rs
@@ -24,6 +24,7 @@ const NULL_U8: NonZeroU8 = unsafe { mem::transmute(0u8) };
 const NULL_USIZE: NonZeroUsize = unsafe { mem::transmute(0usize) };
 //~^ ERROR it is undefined behavior to use this value
 
+#[repr(C)]
 union Transmute {
     uninit: (),
     out: NonZeroU8,
diff --git a/src/test/ui/consts/const-eval/ub-nonnull.stderr b/src/test/ui/consts/const-eval/ub-nonnull.stderr
index 7b3c97e5fbf..de20c3d0b8c 100644
--- a/src/test/ui/consts/const-eval/ub-nonnull.stderr
+++ b/src/test/ui/consts/const-eval/ub-nonnull.stderr
@@ -41,7 +41,7 @@ LL | const NULL_USIZE: NonZeroUsize = unsafe { mem::transmute(0usize) };
    = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-nonnull.rs:31:1
+  --> $DIR/ub-nonnull.rs:32:1
    |
 LL | const UNINIT: NonZeroU8 = unsafe { Transmute { uninit: () }.out };
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered uninitialized bytes, but expected something greater or equal to 1
@@ -49,7 +49,7 @@ LL | const UNINIT: NonZeroU8 = unsafe { Transmute { uninit: () }.out };
    = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-nonnull.rs:39:1
+  --> $DIR/ub-nonnull.rs:40:1
    |
 LL | const BAD_RANGE1: RestrictedRange1 = unsafe { RestrictedRange1(42) };
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered 42, but expected something in the range 10..=30
@@ -57,7 +57,7 @@ LL | const BAD_RANGE1: RestrictedRange1 = unsafe { RestrictedRange1(42) };
    = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-nonnull.rs:45:1
+  --> $DIR/ub-nonnull.rs:46:1
    |
 LL | const BAD_RANGE2: RestrictedRange2 = unsafe { RestrictedRange2(20) };
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: 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-ref.rs b/src/test/ui/consts/const-eval/ub-ref.rs
index bbab85c2121..03ac12c8b1a 100644
--- a/src/test/ui/consts/const-eval/ub-ref.rs
+++ b/src/test/ui/consts/const-eval/ub-ref.rs
@@ -11,6 +11,9 @@ const UNALIGNED: &u16 = unsafe { mem::transmute(&[0u8; 4]) };
 const NULL: &u16 = unsafe { mem::transmute(0usize) };
 //~^ ERROR it is undefined behavior to use this value
 
+// It is very important that we reject this: We do promote `&(4 * REF_AS_USIZE)`,
+// but that would fail to compile; so we ended up breaking user code that would
+// have worked fine had we not promoted.
 const REF_AS_USIZE: usize = unsafe { mem::transmute(&0) };
 //~^ ERROR it is undefined behavior to use this value
 
diff --git a/src/test/ui/consts/const-eval/ub-ref.stderr b/src/test/ui/consts/const-eval/ub-ref.stderr
index f1702955ed7..cd3cc38467c 100644
--- a/src/test/ui/consts/const-eval/ub-ref.stderr
+++ b/src/test/ui/consts/const-eval/ub-ref.stderr
@@ -15,7 +15,7 @@ LL | const NULL: &u16 = unsafe { mem::transmute(0usize) };
    = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-ref.rs:14:1
+  --> $DIR/ub-ref.rs:17:1
    |
 LL | const REF_AS_USIZE: usize = unsafe { mem::transmute(&0) };
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered a pointer, but expected initialized plain (non-pointer) bytes
@@ -23,7 +23,7 @@ LL | const REF_AS_USIZE: usize = unsafe { mem::transmute(&0) };
    = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-ref.rs:17:1
+  --> $DIR/ub-ref.rs:20:1
    |
 LL | const REF_AS_USIZE_SLICE: &[usize] = &[unsafe { mem::transmute(&0) }];
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered a pointer at .<deref>, but expected plain (non-pointer) bytes
@@ -31,7 +31,7 @@ LL | const REF_AS_USIZE_SLICE: &[usize] = &[unsafe { mem::transmute(&0) }];
    = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-ref.rs:20:1
+  --> $DIR/ub-ref.rs:23:1
    |
 LL | const USIZE_AS_REF: &'static u8 = unsafe { mem::transmute(1337usize) };
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered dangling reference (created from integer)
diff --git a/src/test/ui/consts/const-eval/ub-uninhabit.rs b/src/test/ui/consts/const-eval/ub-uninhabit.rs
index 42cba02f579..d2745d71bdb 100644
--- a/src/test/ui/consts/const-eval/ub-uninhabit.rs
+++ b/src/test/ui/consts/const-eval/ub-uninhabit.rs
@@ -6,6 +6,7 @@ use std::mem;
 #[derive(Copy, Clone)]
 enum Bar {}
 
+#[repr(C)]
 union TransmuteUnion<A: Clone + Copy, B: Clone + Copy> {
     a: A,
     b: B,
diff --git a/src/test/ui/consts/const-eval/ub-uninhabit.stderr b/src/test/ui/consts/const-eval/ub-uninhabit.stderr
index c8842ecc23c..43d91483797 100644
--- a/src/test/ui/consts/const-eval/ub-uninhabit.stderr
+++ b/src/test/ui/consts/const-eval/ub-uninhabit.stderr
@@ -1,5 +1,5 @@
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-uninhabit.rs:14:1
+  --> $DIR/ub-uninhabit.rs:15:1
    |
 LL | const BAD_BAD_BAD: Bar = unsafe { (TransmuteUnion::<(), Bar> { a: () }).b };
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered a value of an uninhabited type
@@ -7,7 +7,7 @@ LL | const BAD_BAD_BAD: Bar = unsafe { (TransmuteUnion::<(), Bar> { a: () }).b }
    = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-uninhabit.rs:17:1
+  --> $DIR/ub-uninhabit.rs:18:1
    |
 LL | const BAD_BAD_REF: &Bar = unsafe { mem::transmute(1usize) };
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered a value of an uninhabited type at .<deref>
@@ -15,7 +15,7 @@ LL | const BAD_BAD_REF: &Bar = unsafe { mem::transmute(1usize) };
    = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-uninhabit.rs:20:1
+  --> $DIR/ub-uninhabit.rs:21:1
    |
 LL | const BAD_BAD_ARRAY: [Bar; 1] = unsafe { (TransmuteUnion::<(), [Bar; 1]> { a: () }).b };
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered a value of an uninhabited type
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 765ed60ee97..1f810c40572 100644
--- a/src/test/ui/consts/const-eval/ub-wide-ptr.rs
+++ b/src/test/ui/consts/const-eval/ub-wide-ptr.rs
@@ -7,6 +7,7 @@
 // normalize-stderr-test "allocation \d+" -> "allocation N"
 // normalize-stderr-test "size \d+" -> "size N"
 
+#[repr(C)]
 union BoolTransmute {
   val: u8,
   bl: bool,
@@ -26,6 +27,7 @@ struct BadSliceRepr {
     len: &'static u8,
 }
 
+#[repr(C)]
 union SliceTransmute {
     repr: SliceRepr,
     bad: BadSliceRepr,
@@ -58,6 +60,7 @@ struct BadDynRepr {
     vtable: usize,
 }
 
+#[repr(C)]
 union DynTransmute {
     repr: DynRepr,
     repr2: DynRepr2,
@@ -91,10 +94,10 @@ const MY_STR_LENGTH_PTR: &MyStr = unsafe { SliceTransmute { bad: BadSliceRepr {
 //~^ ERROR it is undefined behavior to use this value
 
 // invalid UTF-8
-const J1: &str = unsafe { SliceTransmute { slice: &[0xFF] }.str };
+const STR_NO_UTF8: &str = unsafe { SliceTransmute { slice: &[0xFF] }.str };
 //~^ ERROR it is undefined behavior to use this value
 // invalid UTF-8 in user-defined str-like
-const J2: &MyStr = unsafe { SliceTransmute { slice: &[0xFF] }.my_str };
+const MYSTR_NO_UTF8: &MyStr = unsafe { SliceTransmute { slice: &[0xFF] }.my_str };
 //~^ ERROR it is undefined behavior to use this value
 
 // # slice
@@ -111,16 +114,16 @@ const SLICE_LENGTH_PTR: &[u8] = unsafe { SliceTransmute { bad: BadSliceRepr { pt
 //~^ ERROR it is undefined behavior to use this value
 
 // bad data *inside* the slice
-const H: &[bool] = &[unsafe { BoolTransmute { val: 3 }.bl }];
+const SLICE_CONTENT_INVALID: &[bool] = &[unsafe { BoolTransmute { val: 3 }.bl }];
 //~^ ERROR it is undefined behavior to use this value
 
 // good MySliceBool
-const I1: &MySliceBool = &MySlice(true, [false]);
+const MYSLICE_GOOD: &MySliceBool = &MySlice(true, [false]);
 // bad: sized field is not okay
-const I2: &MySliceBool = &MySlice(unsafe { BoolTransmute { val: 3 }.bl }, [false]);
+const MYSLICE_PREFIX_BAD: &MySliceBool = &MySlice(unsafe { BoolTransmute { val: 3 }.bl }, [false]);
 //~^ ERROR it is undefined behavior to use this value
 // bad: unsized part is not okay
-const I3: &MySliceBool = &MySlice(true, [unsafe { BoolTransmute { val: 3 }.bl }]);
+const MYSLICE_SUFFIX_BAD: &MySliceBool = &MySlice(true, [unsafe { BoolTransmute { val: 3 }.bl }]);
 //~^ ERROR it is undefined behavior to use this value
 
 // # raw slice
@@ -132,17 +135,17 @@ const RAW_SLICE_LENGTH_UNINIT: *const [u8] = unsafe { SliceTransmute { addr: 42
 
 // # trait object
 // bad trait object
-const D: &dyn Trait = unsafe { DynTransmute { repr: DynRepr { ptr: &92, vtable: &3 } }.rust};
+const TRAIT_OBJ_SHORT_VTABLE_1: &dyn Trait = unsafe { DynTransmute { repr: DynRepr { ptr: &92, vtable: &3 } }.rust};
 //~^ ERROR it is undefined behavior to use this value
 // bad trait object
-const E: &dyn Trait = unsafe { DynTransmute { repr2: DynRepr2 { ptr: &92, vtable: &3 } }.rust};
+const TRAIT_OBJ_SHORT_VTABLE_2: &dyn Trait = unsafe { DynTransmute { repr2: DynRepr2 { ptr: &92, vtable: &3 } }.rust};
 //~^ ERROR it is undefined behavior to use this value
 // bad trait object
-const F: &dyn Trait = unsafe { DynTransmute { bad: BadDynRepr { ptr: &92, vtable: 3 } }.rust};
+const TRAIT_OBJ_INT_VTABLE: &dyn Trait = unsafe { DynTransmute { bad: BadDynRepr { ptr: &92, vtable: 3 } }.rust};
 //~^ ERROR it is undefined behavior to use this value
 
 // bad data *inside* the trait object
-const G: &dyn Trait = &unsafe { BoolTransmute { val: 3 }.bl };
+const TRAIT_OBJ_CONTENT_INVALID: &dyn Trait = &unsafe { BoolTransmute { val: 3 }.bl };
 //~^ ERROR it is undefined behavior to use this value
 
 // # raw trait object
diff --git a/src/test/ui/consts/const-eval/ub-wide-ptr.stderr b/src/test/ui/consts/const-eval/ub-wide-ptr.stderr
index 88d8af80261..aadabc323fb 100644
--- a/src/test/ui/consts/const-eval/ub-wide-ptr.stderr
+++ b/src/test/ui/consts/const-eval/ub-wide-ptr.stderr
@@ -1,5 +1,5 @@
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-wide-ptr.rs:84:1
+  --> $DIR/ub-wide-ptr.rs:87:1
    |
 LL | const STR_TOO_LONG: &str = unsafe { SliceTransmute { repr: SliceRepr { ptr: &42, len: 999 } }.str};
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered dangling reference (not entirely in bounds)
@@ -7,7 +7,7 @@ LL | const STR_TOO_LONG: &str = unsafe { SliceTransmute { repr: SliceRepr { ptr:
    = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-wide-ptr.rs:87:1
+  --> $DIR/ub-wide-ptr.rs:90:1
    |
 LL | const STR_LENGTH_PTR: &str = unsafe { SliceTransmute { bad: BadSliceRepr { ptr: &42, len: &3 } }.str};
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered non-integer slice length in wide pointer
@@ -15,7 +15,7 @@ LL | const STR_LENGTH_PTR: &str = unsafe { SliceTransmute { bad: BadSliceRepr {
    = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-wide-ptr.rs:90:1
+  --> $DIR/ub-wide-ptr.rs:93:1
    |
 LL | const MY_STR_LENGTH_PTR: &MyStr = unsafe { SliceTransmute { bad: BadSliceRepr { ptr: &42, len: &3 } }.my_str};
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered non-integer slice length in wide pointer
@@ -23,23 +23,23 @@ LL | const MY_STR_LENGTH_PTR: &MyStr = unsafe { SliceTransmute { bad: BadSliceRe
    = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-wide-ptr.rs:94:1
+  --> $DIR/ub-wide-ptr.rs:97:1
    |
-LL | const J1: &str = unsafe { SliceTransmute { slice: &[0xFF] }.str };
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered uninitialized or non-UTF-8 data in str at .<deref>
+LL | const STR_NO_UTF8: &str = unsafe { SliceTransmute { slice: &[0xFF] }.str };
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered uninitialized or non-UTF-8 data in str at .<deref>
    |
    = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-wide-ptr.rs:97:1
+  --> $DIR/ub-wide-ptr.rs:100:1
    |
-LL | const J2: &MyStr = unsafe { SliceTransmute { slice: &[0xFF] }.my_str };
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered uninitialized or non-UTF-8 data in str at .<deref>.0
+LL | const MYSTR_NO_UTF8: &MyStr = unsafe { SliceTransmute { slice: &[0xFF] }.my_str };
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered uninitialized or non-UTF-8 data in str at .<deref>.0
    |
    = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-wide-ptr.rs:104:1
+  --> $DIR/ub-wide-ptr.rs:107:1
    |
 LL | const SLICE_LENGTH_UNINIT: &[u8] = unsafe { SliceTransmute { addr: 42 }.slice};
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered uninitialized data in wide pointer metadata
@@ -47,7 +47,7 @@ LL | const SLICE_LENGTH_UNINIT: &[u8] = unsafe { SliceTransmute { addr: 42 }.sli
    = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-wide-ptr.rs:107:1
+  --> $DIR/ub-wide-ptr.rs:110:1
    |
 LL | const SLICE_TOO_LONG: &[u8] = unsafe { SliceTransmute { repr: SliceRepr { ptr: &42, len: 999 } }.slice};
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered dangling reference (not entirely in bounds)
@@ -55,7 +55,7 @@ LL | const SLICE_TOO_LONG: &[u8] = unsafe { SliceTransmute { repr: SliceRepr { p
    = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-wide-ptr.rs:110:1
+  --> $DIR/ub-wide-ptr.rs:113:1
    |
 LL | const SLICE_LENGTH_PTR: &[u8] = unsafe { SliceTransmute { bad: BadSliceRepr { ptr: &42, len: &3 } }.slice};
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered non-integer slice length in wide pointer
@@ -63,31 +63,31 @@ LL | const SLICE_LENGTH_PTR: &[u8] = unsafe { SliceTransmute { bad: BadSliceRepr
    = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-wide-ptr.rs:114:1
+  --> $DIR/ub-wide-ptr.rs:117:1
    |
-LL | const H: &[bool] = &[unsafe { BoolTransmute { val: 3 }.bl }];
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered 3 at .<deref>[0], but expected something less or equal to 1
+LL | const SLICE_CONTENT_INVALID: &[bool] = &[unsafe { BoolTransmute { val: 3 }.bl }];
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered 3 at .<deref>[0], but expected something less or equal to 1
    |
    = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-wide-ptr.rs:120:1
+  --> $DIR/ub-wide-ptr.rs:123:1
    |
-LL | const I2: &MySliceBool = &MySlice(unsafe { BoolTransmute { val: 3 }.bl }, [false]);
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered 3 at .<deref>.0, but expected something less or equal to 1
+LL | const MYSLICE_PREFIX_BAD: &MySliceBool = &MySlice(unsafe { BoolTransmute { val: 3 }.bl }, [false]);
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered 3 at .<deref>.0, but expected something less or equal to 1
    |
    = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-wide-ptr.rs:123:1
+  --> $DIR/ub-wide-ptr.rs:126:1
    |
-LL | const I3: &MySliceBool = &MySlice(true, [unsafe { BoolTransmute { val: 3 }.bl }]);
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered 3 at .<deref>.1[0], but expected something less or equal to 1
+LL | const MYSLICE_SUFFIX_BAD: &MySliceBool = &MySlice(true, [unsafe { BoolTransmute { val: 3 }.bl }]);
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered 3 at .<deref>.1[0], but expected something less or equal to 1
    |
    = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-wide-ptr.rs:130:1
+  --> $DIR/ub-wide-ptr.rs:133:1
    |
 LL | const RAW_SLICE_LENGTH_UNINIT: *const [u8] = unsafe { SliceTransmute { addr: 42 }.raw_slice};
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered uninitialized data in wide pointer metadata
@@ -95,39 +95,39 @@ LL | const RAW_SLICE_LENGTH_UNINIT: *const [u8] = unsafe { SliceTransmute { addr
    = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-wide-ptr.rs:135:1
+  --> $DIR/ub-wide-ptr.rs:138:1
    |
-LL | const D: &dyn Trait = unsafe { DynTransmute { repr: DynRepr { ptr: &92, vtable: &3 } }.rust};
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered dangling or unaligned vtable pointer in wide pointer or too small vtable
+LL | const TRAIT_OBJ_SHORT_VTABLE_1: &dyn Trait = unsafe { DynTransmute { repr: DynRepr { ptr: &92, vtable: &3 } }.rust};
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered dangling or unaligned vtable pointer in wide pointer or too small vtable
    |
    = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-wide-ptr.rs:138:1
+  --> $DIR/ub-wide-ptr.rs:141:1
    |
-LL | const E: &dyn Trait = unsafe { DynTransmute { repr2: DynRepr2 { ptr: &92, vtable: &3 } }.rust};
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered dangling or unaligned vtable pointer in wide pointer or too small vtable
+LL | const TRAIT_OBJ_SHORT_VTABLE_2: &dyn Trait = unsafe { DynTransmute { repr2: DynRepr2 { ptr: &92, vtable: &3 } }.rust};
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered dangling or unaligned vtable pointer in wide pointer or too small vtable
    |
    = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-wide-ptr.rs:141:1
+  --> $DIR/ub-wide-ptr.rs:144:1
    |
-LL | const F: &dyn Trait = unsafe { DynTransmute { bad: BadDynRepr { ptr: &92, vtable: 3 } }.rust};
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered dangling or unaligned vtable pointer in wide pointer or too small vtable
+LL | const TRAIT_OBJ_INT_VTABLE: &dyn Trait = unsafe { DynTransmute { bad: BadDynRepr { ptr: &92, vtable: 3 } }.rust};
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered dangling or unaligned vtable pointer in wide pointer or too small vtable
    |
    = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-wide-ptr.rs:145:1
+  --> $DIR/ub-wide-ptr.rs:148:1
    |
-LL | const G: &dyn Trait = &unsafe { BoolTransmute { val: 3 }.bl };
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered 3 at .<deref>.<dyn-downcast>, but expected something less or equal to 1
+LL | const TRAIT_OBJ_CONTENT_INVALID: &dyn Trait = &unsafe { BoolTransmute { val: 3 }.bl };
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered 3 at .<deref>.<dyn-downcast>, but expected something less or equal to 1
    |
    = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-wide-ptr.rs:149:1
+  --> $DIR/ub-wide-ptr.rs:152:1
    |
 LL | const RAW_TRAIT_OBJ_VTABLE_NULL: *const dyn Trait = unsafe { DynTransmute { bad: BadDynRepr { ptr: &92, vtable: 0 } }.rust};
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered dangling or unaligned vtable pointer in wide pointer or too small vtable
@@ -135,7 +135,7 @@ LL | const RAW_TRAIT_OBJ_VTABLE_NULL: *const dyn Trait = unsafe { DynTransmute {
    = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-wide-ptr.rs:151:1
+  --> $DIR/ub-wide-ptr.rs:154:1
    |
 LL | const RAW_TRAIT_OBJ_VTABLE_INVALID: *const dyn Trait = unsafe { DynTransmute { repr2: DynRepr2 { ptr: &92, vtable: &3 } }.raw_rust};
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered dangling or unaligned vtable pointer in wide pointer or too small vtable
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 56f3ef3db25..7f29a5bc24e 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
@@ -4,6 +4,7 @@ type Field1 = i32;
 type Field2 = f32;
 type Field3 = i64;
 
+#[repr(C)]
 union DummyUnion {
     field1: Field1,
     field2: Field2,
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 4a53337341e..4d008a0e02a 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
@@ -1,5 +1,5 @@
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/union-const-eval-field.rs:27:5
+  --> $DIR/union-const-eval-field.rs:28:5
    |
 LL |     const FIELD3: Field3 = unsafe { UNION.field3 };
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered uninitialized bytes, but expected initialized plain (non-pointer) bytes
diff --git a/src/test/ui/consts/const-eval/union-ice.rs b/src/test/ui/consts/const-eval/union-ice.rs
index 33736b360d3..5a14c7fd993 100644
--- a/src/test/ui/consts/const-eval/union-ice.rs
+++ b/src/test/ui/consts/const-eval/union-ice.rs
@@ -3,6 +3,7 @@
 type Field1 = i32;
 type Field3 = i64;
 
+#[repr(C)]
 union DummyUnion {
     field1: Field1,
     field3: Field3,
diff --git a/src/test/ui/consts/const-eval/union-ice.stderr b/src/test/ui/consts/const-eval/union-ice.stderr
index b25cb8c5aa0..8d950e86d27 100644
--- a/src/test/ui/consts/const-eval/union-ice.stderr
+++ b/src/test/ui/consts/const-eval/union-ice.stderr
@@ -1,5 +1,5 @@
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/union-ice.rs:13:1
+  --> $DIR/union-ice.rs:14:1
    |
 LL | const FIELD3: Field3 = unsafe { UNION.field3 };
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered uninitialized bytes, but expected initialized plain (non-pointer) bytes
@@ -7,7 +7,7 @@ LL | const FIELD3: Field3 = unsafe { UNION.field3 };
    = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/union-ice.rs:15:1
+  --> $DIR/union-ice.rs:16:1
    |
 LL | / const FIELD_PATH: Struct = Struct {
 LL | |     a: 42,
@@ -18,7 +18,7 @@ LL | | };
    = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/union-ice.rs:25:1
+  --> $DIR/union-ice.rs:26:1
    |
 LL | / const FIELD_PATH2: Struct2 = Struct2 {
 LL | |     b: [
diff --git a/src/test/ui/consts/const-eval/union-ub.rs b/src/test/ui/consts/const-eval/union-ub.rs
index cf436141c5a..848826e6ef7 100644
--- a/src/test/ui/consts/const-eval/union-ub.rs
+++ b/src/test/ui/consts/const-eval/union-ub.rs
@@ -1,5 +1,6 @@
 #![allow(const_err)] // make sure we cannot allow away the errors tested here
 
+#[repr(C)]
 union DummyUnion {
     u8: u8,
     bool: bool,
@@ -14,11 +15,13 @@ enum Enum {
 }
 
 #[derive(Copy, Clone)]
+#[repr(C)]
 union Foo {
     a: bool,
     b: Enum,
 }
 
+#[repr(C)]
 union Bar {
     foo: Foo,
     u8: u8,
diff --git a/src/test/ui/consts/const-eval/union-ub.stderr b/src/test/ui/consts/const-eval/union-ub.stderr
index 7baa55be6e1..6a3a397585c 100644
--- a/src/test/ui/consts/const-eval/union-ub.stderr
+++ b/src/test/ui/consts/const-eval/union-ub.stderr
@@ -1,5 +1,5 @@
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/union-ub.rs:28:1
+  --> $DIR/union-ub.rs:31:1
    |
 LL | const BAD_BOOL: bool = unsafe { DummyUnion { u8: 42 }.bool};
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered 42, but expected something less or equal to 1
diff --git a/src/test/ui/consts/const-eval/union_promotion.rs b/src/test/ui/consts/const-eval/union_promotion.rs
index d3566511ef8..7167f88a118 100644
--- a/src/test/ui/consts/const-eval/union_promotion.rs
+++ b/src/test/ui/consts/const-eval/union_promotion.rs
@@ -1,5 +1,6 @@
 #![allow(const_err)]
 
+#[repr(C)]
 union Foo {
     a: &'static u32,
     b: usize,
diff --git a/src/test/ui/consts/const-eval/union_promotion.stderr b/src/test/ui/consts/const-eval/union_promotion.stderr
index b530c02f2fb..ed186e3ebd2 100644
--- a/src/test/ui/consts/const-eval/union_promotion.stderr
+++ b/src/test/ui/consts/const-eval/union_promotion.stderr
@@ -1,5 +1,5 @@
 error[E0716]: temporary value dropped while borrowed
-  --> $DIR/union_promotion.rs:9:29
+  --> $DIR/union_promotion.rs:10:29
    |
 LL |       let x: &'static bool = &unsafe {
    |  ____________-------------____^
diff --git a/src/test/ui/consts/const-eval/valid-const.rs b/src/test/ui/consts/const-eval/valid-const.rs
index 30bd4721923..65c642d750b 100644
--- a/src/test/ui/consts/const-eval/valid-const.rs
+++ b/src/test/ui/consts/const-eval/valid-const.rs
@@ -1,7 +1,8 @@
-// build-pass (FIXME(62277): could be check-pass?)
+// check-pass
 
 // Some constants that *are* valid
 #![feature(const_transmute)]
+#![deny(const_err)]
 
 use std::mem;
 use std::ptr::NonNull;