Re-enable SimplifyToExp in match_branches.

Author: dianqk

Diff for: compiler/rustc_mir_transform/src/match_branches.rs

@@ -44,10 +44,7 @@ impl<'tcx> MirPass<'tcx> for MatchBranchSimplification {
                 should_cleanup = true;
                 continue;
             }
-            // unsound: https://github.com/rust-lang/rust/issues/124150
-            if tcx.sess.opts.unstable_opts.unsound_mir_opts
-                && SimplifyToExp::default().simplify(tcx, body, bb_idx, param_env).is_some()
-            {
+            if SimplifyToExp::default().simplify(tcx, body, bb_idx, param_env).is_some() {
                 should_cleanup = true;
                 continue;
             }

Diff for: tests/mir-opt/matches_reduce_branches.rs

@@ -1,5 +1,4 @@
 //@ test-mir-pass: MatchBranchSimplification
-//@ compile-flags: -Zunsound-mir-opts
 
 #![feature(repr128)]
 #![feature(core_intrinsics)]

Diff for: tests/mir-opt/matches_u8.rs

@@ -1,6 +1,5 @@
 // skip-filecheck
 //@ test-mir-pass: MatchBranchSimplification
-//@ compile-flags: -Zunsound-mir-opts
 
 // EMIT_MIR matches_u8.exhaustive_match.MatchBranchSimplification.diff
 // EMIT_MIR matches_u8.exhaustive_match_i8.MatchBranchSimplification.diff