Auto merge of #112026 - saethlin:misaligned-addrof, r=pnkfelix

Don't check for misaligned raw pointer derefs inside Rvalue::AddressOf

From https://github.com/rust-lang/rust/pull/112026#issuecomment-1565686697:

rustc 1.70 (stable next week) added a Mir pass to add pointer alignment checks in debug mode. Adding these checks caused some crates to break, but that was expected, since they contain broken code (https://github.com/rust-lang/rust/issues/111487) for tracking that.

However, the checks added are slightly more aggressive than they should have been. Specifically, they also check the place in an `addr_of!` expression. Whether lack of alignment there is or isn't UB is unclear. This PR modifies the pass to not affect those cases.

I spot checked the crater regressions and the ones I saw were not the case that this PR is modifying. It still seems good to not land anything overaggressive though

1 files changed, 8 insertions, 0 deletions

diff --git a/compiler/rustc_mir_transform/src/check_alignment.rs b/compiler/rustc_mir_transform/src/check_alignment.rs
index d60184e0ebe..1fe8ea07892 100644
--- a/compiler/rustc_mir_transform/src/check_alignment.rs
+++ b/compiler/rustc_mir_transform/src/check_alignment.rs
@@ -75,6 +75,14 @@ struct PointerFinder<'tcx, 'a> {
 }
 
 impl<'tcx, 'a> Visitor<'tcx> for PointerFinder<'tcx, 'a> {
+    fn visit_rvalue(&mut self, rvalue: &Rvalue<'tcx>, location: Location) {
+        if let Rvalue::AddressOf(..) = rvalue {
+            // Ignore dereferences inside of an AddressOf
+            return;
+        }
+        self.super_rvalue(rvalue, location);
+    }
+
     fn visit_place(&mut self, place: &Place<'tcx>, context: PlaceContext, _location: Location) {
         if let PlaceContext::NonUse(_) = context {
             return;