From ff54f71c8e30b7fc36992e87396c8027e1b585f8 Mon Sep 17 00:00:00 2001
From: Fabian Wolff <fabian.wolff@alumni.ethz.ch>
Date: Sun, 3 Oct 2021 22:58:24 +0200
Subject: [PATCH] Disable `SimplifyBranchSame` optimization for now

(cherry picked from commit dd9b4763a4805e508cafd9aa49eebda27e5298c0)
---
 compiler/rustc_mir/src/transform/simplify_try.rs | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/compiler/rustc_mir/src/transform/simplify_try.rs b/compiler/rustc_mir/src/transform/simplify_try.rs
index 4277754724f0..9c3055c6796d 100644
--- a/compiler/rustc_mir/src/transform/simplify_try.rs
+++ b/compiler/rustc_mir/src/transform/simplify_try.rs
@@ -544,6 +544,12 @@ fn match_variant_field_place<'tcx>(place: Place<'tcx>) -> Option<(Local, VarFiel
 
 impl<'tcx> MirPass<'tcx> for SimplifyBranchSame {
     fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
+        // This optimization is disabled by default for now due to
+        // soundness concerns; see issue #89485 and PR #89489.
+        if !tcx.sess.opts.debugging_opts.unsound_mir_opts {
+            return;
+        }
+
         trace!("Running SimplifyBranchSame on {:?}", body.source);
         let finder = SimplifyBranchSameOptimizationFinder { body, tcx };
         let opts = finder.find();