Rollup merge of #105317 - RalfJung:retag-rework, r=oli-obk

make retagging work even with 'unstable' places

This is based on top of https://github.com/rust-lang/rust/pull/105301. Only the last two commits are new.

While investigating https://github.com/rust-lang/unsafe-code-guidelines/issues/381 I realized that we would have caught this issue much earlier if the add_retag pass wouldn't bail out on assignments of the form `*ptr = ...`.

So this PR changes our retag strategy:
- When a new reference is created via `Rvalue::Ref` (or a raw ptr via `Rvalue::AddressOf`), we do the retagging as part of just executing that address-taking operation.
- For everything else, we still insert retags -- these retags basically serve to ensure that references stored in local variables (and their fields) are always freshly tagged, so skipping this for assignments like `*ptr = ...` is less egregious.
r? ```@oli-obk```

1 files changed, 0 insertions, 10 deletions

diff --git a/compiler/rustc_mir_transform/src/generator.rs b/compiler/rustc_mir_transform/src/generator.rs
index 8922298ecaf..69f96fe48ea 100644
--- a/compiler/rustc_mir_transform/src/generator.rs
+++ b/compiler/rustc_mir_transform/src/generator.rs
@@ -985,16 +985,6 @@ fn create_generator_drop_shim<'tcx>(
         tcx.mk_ptr(ty::TypeAndMut { ty: gen_ty, mutbl: hir::Mutability::Mut }),
         source_info,
     );
-    if tcx.sess.opts.unstable_opts.mir_emit_retag {
-        // Alias tracking must know we changed the type
-        body.basic_blocks_mut()[START_BLOCK].statements.insert(
-            0,
-            Statement {
-                source_info,
-                kind: StatementKind::Retag(RetagKind::Raw, Box::new(Place::from(SELF_ARG))),
-            },
-        )
-    }
 
     // Make sure we remove dead blocks to remove
     // unrelated code from the resume part of the function