From d58061e6131f6141985faadb6794af540f81b1db Mon Sep 17 00:00:00 2001
From: Camille Gillot <gillot.camille@gmail.com>
Date: Tue, 16 Sep 2025 01:22:10 +0000
Subject: [PATCH] Restrict simple assignment condition.

---
 compiler/rustc_mir_transform/src/dest_prop.rs | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/compiler/rustc_mir_transform/src/dest_prop.rs b/compiler/rustc_mir_transform/src/dest_prop.rs
index b9ab0a9feee..c57483a6811 100644
--- a/compiler/rustc_mir_transform/src/dest_prop.rs
+++ b/compiler/rustc_mir_transform/src/dest_prop.rs
@@ -596,8 +596,14 @@ fn save_as_intervals<'tcx>(
             // as behaving so by default.
             // We make an exception for simple assignments `_a.stuff = {copy|move} _b.stuff`,
             // as marking `_b` live here would prevent unification.
-            let is_simple_assignment =
-                matches!(stmt.kind, StatementKind::Assign(box (_, Rvalue::Use(_))));
+            let is_simple_assignment = match stmt.kind {
+                StatementKind::Assign(box (
+                    lhs,
+                    Rvalue::CopyForDeref(rhs)
+                    | Rvalue::Use(Operand::Copy(rhs) | Operand::Move(rhs)),
+                )) => lhs.projection == rhs.projection,
+                _ => false,
+            };
             VisitPlacesWith(|place: Place<'tcx>, ctxt| {
                 if let Some(relevant) = relevant.shrink[place.local] {
                     match DefUse::for_place(place, ctxt) {