Auto merge of #101483 - oli-obk:guaranteed_opt, r=fee1-dead

The `<*const T>::guaranteed_*` methods now return an option for the unknown case

cc https://github.com/rust-lang/rust/issues/53020#issuecomment-1236932443

I chose `0` for "not equal" and `1` for "equal" and left `2` for the unknown case so backends can just forward to raw pointer equality and it works ✨

r? `@fee1-dead` or `@lcnr`

cc `@rust-lang/wg-const-eval`

3 files changed, 19 insertions, 31 deletions

diff --git a/src/test/ui/consts/miri_unleashed/slice_eq.rs b/src/test/ui/consts/miri_unleashed/slice_eq.rs
index fd843105daf..83e10bf1213 100644
--- a/src/test/ui/consts/miri_unleashed/slice_eq.rs
+++ b/src/test/ui/consts/miri_unleashed/slice_eq.rs
@@ -4,14 +4,10 @@
 #![feature(const_raw_ptr_comparison)]
 
 const EMPTY_SLICE: &[i32] = &[];
-const EMPTY_EQ: bool = EMPTY_SLICE.as_ptr().guaranteed_eq(&[] as *const _);
-const EMPTY_EQ2: bool = EMPTY_SLICE.as_ptr().guaranteed_ne(&[] as *const _);
-const EMPTY_NE: bool = EMPTY_SLICE.as_ptr().guaranteed_ne(&[1] as *const _);
-const EMPTY_NE2: bool = EMPTY_SLICE.as_ptr().guaranteed_eq(&[1] as *const _);
+const EMPTY_EQ: Option<bool> = EMPTY_SLICE.as_ptr().guaranteed_eq(&[] as *const _);
+const EMPTY_EQ2: Option<bool> = EMPTY_SLICE.as_ptr().guaranteed_eq(&[1] as *const _);
 
 fn main() {
-    assert!(!EMPTY_EQ);
-    assert!(!EMPTY_EQ2);
-    assert!(!EMPTY_NE);
-    assert!(!EMPTY_NE2);
+    assert!(EMPTY_EQ.is_none());
+    assert!(EMPTY_EQ2.is_none());
 }
diff --git a/src/test/ui/consts/ptr_comparisons.rs b/src/test/ui/consts/ptr_comparisons.rs
index 20233db09c9..0a3c2d4bedc 100644
--- a/src/test/ui/consts/ptr_comparisons.rs
+++ b/src/test/ui/consts/ptr_comparisons.rs
@@ -14,38 +14,30 @@ const FOO: &usize = &42;
 macro_rules! check {
     (eq, $a:expr, $b:expr) => {
         pub const _: () =
-            assert!(std::intrinsics::ptr_guaranteed_eq($a as *const u8, $b as *const u8));
+            assert!(std::intrinsics::ptr_guaranteed_cmp($a as *const u8, $b as *const u8) == 1);
     };
     (ne, $a:expr, $b:expr) => {
         pub const _: () =
-            assert!(std::intrinsics::ptr_guaranteed_ne($a as *const u8, $b as *const u8));
+            assert!(std::intrinsics::ptr_guaranteed_cmp($a as *const u8, $b as *const u8) == 0);
     };
-    (!eq, $a:expr, $b:expr) => {
+    (!, $a:expr, $b:expr) => {
         pub const _: () =
-            assert!(!std::intrinsics::ptr_guaranteed_eq($a as *const u8, $b as *const u8));
-    };
-    (!ne, $a:expr, $b:expr) => {
-        pub const _: () =
-            assert!(!std::intrinsics::ptr_guaranteed_ne($a as *const u8, $b as *const u8));
+            assert!(std::intrinsics::ptr_guaranteed_cmp($a as *const u8, $b as *const u8) == 2);
     };
 }
 
 check!(eq, 0, 0);
 check!(ne, 0, 1);
-check!(!eq, 0, 1);
-check!(!ne, 0, 0);
 check!(ne, FOO as *const _, 0);
-check!(!eq, FOO as *const _, 0);
+check!(ne, unsafe { (FOO as *const usize).offset(1) }, 0);
+check!(ne, unsafe { (FOO as *const usize as *const u8).offset(3) }, 0);
+
 // We want pointers to be equal to themselves, but aren't checking this yet because
 // there are some open questions (e.g. whether function pointers to the same function
 // compare equal, they don't necessarily at runtime).
 // The case tested here should work eventually, but does not work yet.
-check!(!eq, FOO as *const _, FOO as *const _);
-check!(ne, unsafe { (FOO as *const usize).offset(1) }, 0);
-check!(!eq, unsafe { (FOO as *const usize).offset(1) }, 0);
+check!(!, FOO as *const _, FOO as *const _);
 
-check!(ne, unsafe { (FOO as *const usize as *const u8).offset(3) }, 0);
-check!(!eq, unsafe { (FOO as *const usize as *const u8).offset(3) }, 0);
 
 ///////////////////////////////////////////////////////////////////////////////
 // If any of the below start compiling, make sure to add a `check` test for it.
diff --git a/src/test/ui/consts/ptr_comparisons.stderr b/src/test/ui/consts/ptr_comparisons.stderr
index 1d47f243f01..3de2aba5b05 100644
--- a/src/test/ui/consts/ptr_comparisons.stderr
+++ b/src/test/ui/consts/ptr_comparisons.stderr
@@ -7,19 +7,19 @@ LL |         unsafe { intrinsics::offset(self, count) }
    |                  out-of-bounds pointer arithmetic: alloc3 has size $WORD, so pointer to $TWO_WORDS bytes starting at offset 0 is out-of-bounds
    |                  inside `ptr::const_ptr::<impl *const usize>::offset` at $SRC_DIR/core/src/ptr/const_ptr.rs:LL:COL
    |
-  ::: $DIR/ptr_comparisons.rs:58:34
+  ::: $DIR/ptr_comparisons.rs:50:34
    |
 LL | const _: *const usize = unsafe { (FOO as *const usize).offset(2) };
-   |                                  ------------------------------- inside `_` at $DIR/ptr_comparisons.rs:58:34
+   |                                  ------------------------------- inside `_` at $DIR/ptr_comparisons.rs:50:34
 
 error[E0080]: evaluation of constant value failed
-  --> $DIR/ptr_comparisons.rs:61:33
+  --> $DIR/ptr_comparisons.rs:53:33
    |
 LL |     unsafe { std::ptr::addr_of!((*(FOO as *const usize as *const [u8; 1000]))[999]) };
    |                                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ dereferencing pointer failed: alloc3 has size $WORD, so pointer to 1000 bytes starting at offset 0 is out-of-bounds
 
 error: any use of this value will cause an error
-  --> $DIR/ptr_comparisons.rs:65:27
+  --> $DIR/ptr_comparisons.rs:57:27
    |
 LL | const _: usize = unsafe { std::mem::transmute::<*const usize, usize>(FOO) + 4 };
    | --------------            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unable to turn pointer into raw bytes
@@ -31,7 +31,7 @@ LL | const _: usize = unsafe { std::mem::transmute::<*const usize, usize>(FOO) +
    = help: the absolute address of a pointer is not known at compile-time, so such operations are not supported
 
 error: any use of this value will cause an error
-  --> $DIR/ptr_comparisons.rs:70:27
+  --> $DIR/ptr_comparisons.rs:62:27
    |
 LL | const _: usize = unsafe { *std::mem::transmute::<&&usize, &usize>(&FOO) + 4 };
    | --------------            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unable to turn pointer into raw bytes
@@ -46,7 +46,7 @@ error: aborting due to 4 previous errors
 For more information about this error, try `rustc --explain E0080`.
 Future incompatibility report: Future breakage diagnostic:
 error: any use of this value will cause an error
-  --> $DIR/ptr_comparisons.rs:65:27
+  --> $DIR/ptr_comparisons.rs:57:27
    |
 LL | const _: usize = unsafe { std::mem::transmute::<*const usize, usize>(FOO) + 4 };
    | --------------            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unable to turn pointer into raw bytes
@@ -59,7 +59,7 @@ LL | const _: usize = unsafe { std::mem::transmute::<*const usize, usize>(FOO) +
 
 Future breakage diagnostic:
 error: any use of this value will cause an error
-  --> $DIR/ptr_comparisons.rs:70:27
+  --> $DIR/ptr_comparisons.rs:62:27
    |
 LL | const _: usize = unsafe { *std::mem::transmute::<&&usize, &usize>(&FOO) + 4 };
    | --------------            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unable to turn pointer into raw bytes