Auto merge of #92686 - saethlin:unsafe-debug-asserts, r=Amanieu

Add debug assertions to some unsafe functions

As suggested by https://github.com/rust-lang/rust/issues/51713

~~Some similar code calls `abort()` instead of `panic!()` but aborting doesn't work in a `const fn`, and the intrinsic for doing dispatch based on whether execution is in a const is unstable.~~

This picked up some invalid uses of `get_unchecked` in the compiler, and fixes them.

I can confirm that they do in fact pick up invalid uses of `get_unchecked` in the wild, though the user experience is less-than-awesome:
```
     Running unittests (target/x86_64-unknown-linux-gnu/debug/deps/rle_decode_fast-04b7918da2001b50)

running 6 tests
error: test failed, to rerun pass '--lib'

Caused by:
  process didn't exit successfully: `/home/ben/rle-decode-helper/target/x86_64-unknown-linux-gnu/debug/deps/rle_decode_fast-04b7918da2001b50` (signal: 4, SIGILL: illegal instruction)
```

~~As best I can tell these changes produce a 6% regression in the runtime of `./x.py test` when `[rust] debug = true` is set.~~
Latest commit (https://github.com/rust-lang/rust/pull/92686/commits/6894d559bdb4365243b3f4bf73f18e4b1bed04d1) brings the additional overhead from this PR down to 0.5%, while also adding a few more assertions. I think this actually covers all the places in `core` that it is reasonable to check for safety requirements at runtime.

Thoughts?

1 files changed, 4 insertions, 4 deletions

diff --git a/compiler/rustc_data_structures/src/map_in_place.rs b/compiler/rustc_data_structures/src/map_in_place.rs
index 5dd9fc6e8bc..874de03d37a 100644
--- a/compiler/rustc_data_structures/src/map_in_place.rs
+++ b/compiler/rustc_data_structures/src/map_in_place.rs
@@ -30,13 +30,13 @@ impl<T> MapInPlace<T> for Vec<T> {
             while read_i < old_len {
                 // move the read_i'th item out of the vector and map it
                 // to an iterator
-                let e = ptr::read(self.get_unchecked(read_i));
+                let e = ptr::read(self.as_ptr().add(read_i));
                 let iter = f(e).into_iter();
                 read_i += 1;
 
                 for e in iter {
                     if write_i < read_i {
-                        ptr::write(self.get_unchecked_mut(write_i), e);
+                        ptr::write(self.as_mut_ptr().add(write_i), e);
                         write_i += 1;
                     } else {
                         // If this is reached we ran out of space
@@ -76,13 +76,13 @@ impl<T, A: Array<Item = T>> MapInPlace<T> for SmallVec<A> {
             while read_i < old_len {
                 // move the read_i'th item out of the vector and map it
                 // to an iterator
-                let e = ptr::read(self.get_unchecked(read_i));
+                let e = ptr::read(self.as_ptr().add(read_i));
                 let iter = f(e).into_iter();
                 read_i += 1;
 
                 for e in iter {
                     if write_i < read_i {
-                        ptr::write(self.get_unchecked_mut(write_i), e);
+                        ptr::write(self.as_mut_ptr().add(write_i), e);
                         write_i += 1;
                     } else {
                         // If this is reached we ran out of space