Disable SimplifyBranchSame optimization for now

Author: FabianWolff

compiler/rustc_mir_transform/src/simplify_try.rs

@@ -544,6 +544,12 @@ pub struct SimplifyBranchSame;
 
 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();