Disable the SimplifyArmIdentity mir-opt

The optimization still has some bugs that need to be worked out
such as #77359.

We can try re-enabling this again after the known issues are resolved.

compiler/rustc_mir/src/transform/simplify_try.rs

@@ -367,7 +367,12 @@ fn optimization_applies<'tcx>(
 }
 
 impl<'tcx> MirPass<'tcx> for SimplifyArmIdentity {
-    fn run_pass(&self, _tcx: TyCtxt<'tcx>, source: MirSource<'tcx>, body: &mut Body<'tcx>) {
+    fn run_pass(&self, tcx: TyCtxt<'tcx>, source: MirSource<'tcx>, body: &mut Body<'tcx>) {
+        // FIXME(77359): This optimization can result in unsoundness.
+        if !tcx.sess.opts.debugging_opts.unsound_mir_opts {
+            return;
+        }
+
         trace!("running SimplifyArmIdentity on {:?}", source);
         let local_uses = LocalUseCounter::get_local_uses(body);
         let (basic_blocks, local_decls, debug_info) =

src/test/codegen/try_identity.rs

@@ -1,4 +1,4 @@
-// compile-flags: -C no-prepopulate-passes -Z mir-opt-level=2
+// compile-flags: -C no-prepopulate-passes -Z mir-opt-level=2 -Zunsound-mir-opts
 
 // Ensure that `x?` has no overhead on `Result<T, E>` due to identity `match`es in lowering.
 // This requires inlining to trigger the MIR optimizations in `SimplifyArmIdentity`.

src/test/mir-opt/simplify-arm.rs

@@ -1,4 +1,4 @@
-// compile-flags: -Z mir-opt-level=2
+// compile-flags: -Z mir-opt-level=2 -Zunsound-mir-opts
 // EMIT_MIR simplify_arm.id.SimplifyArmIdentity.diff
 // EMIT_MIR simplify_arm.id.SimplifyBranchSame.diff
 // EMIT_MIR simplify_arm.id_result.SimplifyArmIdentity.diff

src/test/mir-opt/simplify-locals-removes-unused-discriminant-reads.rs

@@ -1,3 +1,5 @@
+// compile-flags: -Zunsound-mir-opts
+
 fn map(x: Option<Box<()>>) -> Option<Box<()>> {
     match x {
         None => None,

src/test/mir-opt/simplify_locals_removes_unused_discriminant_reads.map.SimplifyLocals.32bit.diff

@@ -2,25 +2,25 @@
 + // MIR for `map` after SimplifyLocals
 
   fn map(_1: Option<Box<()>>) -> Option<Box<()>> {
-      debug x => _1;                       // in scope 0 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:1:8: 1:9
-      let mut _0: std::option::Option<std::boxed::Box<()>>; // return place in scope 0 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:1:31: 1:46
--     let mut _2: isize;                   // in scope 0 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:3:9: 3:13
--     let _3: std::boxed::Box<()>;         // in scope 0 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:4:14: 4:15
--     let mut _4: std::boxed::Box<()>;     // in scope 0 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:4:25: 4:26
--     let mut _5: bool;                    // in scope 0 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:6:1: 6:2
--     let mut _6: isize;                   // in scope 0 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:6:1: 6:2
--     let mut _7: isize;                   // in scope 0 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:6:1: 6:2
+      debug x => _1;                       // in scope 0 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:3:8: 3:9
+      let mut _0: std::option::Option<std::boxed::Box<()>>; // return place in scope 0 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:3:31: 3:46
+-     let mut _2: isize;                   // in scope 0 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:5:9: 5:13
+-     let _3: std::boxed::Box<()>;         // in scope 0 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:6:14: 6:15
+-     let mut _4: std::boxed::Box<()>;     // in scope 0 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:6:25: 6:26
+-     let mut _5: bool;                    // in scope 0 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:8:1: 8:2
+-     let mut _6: isize;                   // in scope 0 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:8:1: 8:2
+-     let mut _7: isize;                   // in scope 0 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:8:1: 8:2
       scope 1 {
-          debug x => ((_0 as Some).0: std::boxed::Box<()>); // in scope 1 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:4:14: 4:15
+          debug x => ((_0 as Some).0: std::boxed::Box<()>); // in scope 1 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:6:14: 6:15
       }
 
       bb0: {
--         _5 = const false;                // scope 0 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:3:9: 3:13
--         _5 = const true;                 // scope 0 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:3:9: 3:13
--         _2 = discriminant(_1);           // scope 0 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:3:9: 3:13
-          _0 = move _1;                    // scope 1 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:4:20: 4:27
--         _6 = discriminant(_1);           // scope 0 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:6:1: 6:2
-          return;                          // scope 0 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:6:2: 6:2
+-         _5 = const false;                // scope 0 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:5:9: 5:13
+-         _5 = const true;                 // scope 0 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:5:9: 5:13
+-         _2 = discriminant(_1);           // scope 0 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:5:9: 5:13
+          _0 = move _1;                    // scope 1 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:6:20: 6:27
+-         _6 = discriminant(_1);           // scope 0 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:8:1: 8:2
+          return;                          // scope 0 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:8:2: 8:2
       }
   }
 

src/test/mir-opt/simplify_locals_removes_unused_discriminant_reads.map.SimplifyLocals.64bit.diff

@@ -2,25 +2,25 @@
 + // MIR for `map` after SimplifyLocals
 
   fn map(_1: Option<Box<()>>) -> Option<Box<()>> {
-      debug x => _1;                       // in scope 0 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:1:8: 1:9
-      let mut _0: std::option::Option<std::boxed::Box<()>>; // return place in scope 0 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:1:31: 1:46
--     let mut _2: isize;                   // in scope 0 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:3:9: 3:13
--     let _3: std::boxed::Box<()>;         // in scope 0 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:4:14: 4:15
--     let mut _4: std::boxed::Box<()>;     // in scope 0 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:4:25: 4:26
--     let mut _5: bool;                    // in scope 0 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:6:1: 6:2
--     let mut _6: isize;                   // in scope 0 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:6:1: 6:2
--     let mut _7: isize;                   // in scope 0 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:6:1: 6:2
+      debug x => _1;                       // in scope 0 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:3:8: 3:9
+      let mut _0: std::option::Option<std::boxed::Box<()>>; // return place in scope 0 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:3:31: 3:46
+-     let mut _2: isize;                   // in scope 0 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:5:9: 5:13
+-     let _3: std::boxed::Box<()>;         // in scope 0 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:6:14: 6:15
+-     let mut _4: std::boxed::Box<()>;     // in scope 0 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:6:25: 6:26
+-     let mut _5: bool;                    // in scope 0 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:8:1: 8:2
+-     let mut _6: isize;                   // in scope 0 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:8:1: 8:2
+-     let mut _7: isize;                   // in scope 0 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:8:1: 8:2
       scope 1 {
-          debug x => ((_0 as Some).0: std::boxed::Box<()>); // in scope 1 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:4:14: 4:15
+          debug x => ((_0 as Some).0: std::boxed::Box<()>); // in scope 1 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:6:14: 6:15
       }
 
       bb0: {
--         _5 = const false;                // scope 0 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:3:9: 3:13
--         _5 = const true;                 // scope 0 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:3:9: 3:13
--         _2 = discriminant(_1);           // scope 0 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:3:9: 3:13
-          _0 = move _1;                    // scope 1 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:4:20: 4:27
--         _6 = discriminant(_1);           // scope 0 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:6:1: 6:2
-          return;                          // scope 0 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:6:2: 6:2
+-         _5 = const false;                // scope 0 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:5:9: 5:13
+-         _5 = const true;                 // scope 0 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:5:9: 5:13
+-         _2 = discriminant(_1);           // scope 0 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:5:9: 5:13
+          _0 = move _1;                    // scope 1 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:6:20: 6:27
+-         _6 = discriminant(_1);           // scope 0 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:8:1: 8:2
+          return;                          // scope 0 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:8:2: 8:2
       }
   }
 

src/test/mir-opt/simplify_try.rs

@@ -1,3 +1,4 @@
+// compile-flags: -Zunsound-mir-opts
 // EMIT_MIR simplify_try.try_identity.SimplifyArmIdentity.diff
 // EMIT_MIR simplify_try.try_identity.SimplifyBranchSame.after.mir
 // EMIT_MIR simplify_try.try_identity.SimplifyLocals.after.mir

src/test/mir-opt/simplify_try.try_identity.DestinationPropagation.diff

@@ -2,35 +2,35 @@
 + // MIR for `try_identity` after DestinationPropagation
 
   fn try_identity(_1: std::result::Result<u32, i32>) -> std::result::Result<u32, i32> {
-      debug x => _1;                       // in scope 0 at $DIR/simplify_try.rs:6:17: 6:18
-      let mut _0: std::result::Result<u32, i32>; // return place in scope 0 at $DIR/simplify_try.rs:6:41: 6:57
-      let _2: u32;                         // in scope 0 at $DIR/simplify_try.rs:7:9: 7:10
-      let mut _3: std::result::Result<u32, i32>; // in scope 0 at $DIR/simplify_try.rs:7:13: 7:15
-      let mut _4: std::result::Result<u32, i32>; // in scope 0 at $DIR/simplify_try.rs:7:13: 7:14
-      let mut _5: isize;                   // in scope 0 at $DIR/simplify_try.rs:7:14: 7:15
-      let _6: i32;                         // in scope 0 at $DIR/simplify_try.rs:7:14: 7:15
-      let mut _7: !;                       // in scope 0 at $DIR/simplify_try.rs:7:14: 7:15
-      let mut _8: i32;                     // in scope 0 at $DIR/simplify_try.rs:7:14: 7:15
-      let mut _9: i32;                     // in scope 0 at $DIR/simplify_try.rs:7:14: 7:15
-      let _10: u32;                        // in scope 0 at $DIR/simplify_try.rs:7:13: 7:15
-      let mut _11: u32;                    // in scope 0 at $DIR/simplify_try.rs:8:8: 8:9
+      debug x => _1;                       // in scope 0 at $DIR/simplify_try.rs:7:17: 7:18
+      let mut _0: std::result::Result<u32, i32>; // return place in scope 0 at $DIR/simplify_try.rs:7:41: 7:57
+      let _2: u32;                         // in scope 0 at $DIR/simplify_try.rs:8:9: 8:10
+      let mut _3: std::result::Result<u32, i32>; // in scope 0 at $DIR/simplify_try.rs:8:13: 8:15
+      let mut _4: std::result::Result<u32, i32>; // in scope 0 at $DIR/simplify_try.rs:8:13: 8:14
+      let mut _5: isize;                   // in scope 0 at $DIR/simplify_try.rs:8:14: 8:15
+      let _6: i32;                         // in scope 0 at $DIR/simplify_try.rs:8:14: 8:15
+      let mut _7: !;                       // in scope 0 at $DIR/simplify_try.rs:8:14: 8:15
+      let mut _8: i32;                     // in scope 0 at $DIR/simplify_try.rs:8:14: 8:15
+      let mut _9: i32;                     // in scope 0 at $DIR/simplify_try.rs:8:14: 8:15
+      let _10: u32;                        // in scope 0 at $DIR/simplify_try.rs:8:13: 8:15
+      let mut _11: u32;                    // in scope 0 at $DIR/simplify_try.rs:9:8: 9:9
       scope 1 {
-          debug y => ((_0 as Ok).0: u32);  // in scope 1 at $DIR/simplify_try.rs:7:9: 7:10
+          debug y => ((_0 as Ok).0: u32);  // in scope 1 at $DIR/simplify_try.rs:8:9: 8:10
       }
       scope 2 {
-          debug err => ((_0 as Err).0: i32); // in scope 2 at $DIR/simplify_try.rs:7:14: 7:15
+          debug err => ((_0 as Err).0: i32); // in scope 2 at $DIR/simplify_try.rs:8:14: 8:15
           scope 3 {
               scope 7 {
                   debug t => ((_0 as Err).0: i32); // in scope 7 at $SRC_DIR/core/src/convert/mod.rs:LL:COL
               }
               scope 8 {
                   debug v => ((_0 as Err).0: i32); // in scope 8 at $SRC_DIR/core/src/result.rs:LL:COL
-                  let mut _12: i32;        // in scope 8 at $DIR/simplify_try.rs:7:14: 7:15
+                  let mut _12: i32;        // in scope 8 at $DIR/simplify_try.rs:8:14: 8:15
               }
           }
       }
       scope 4 {
-          debug val => ((_0 as Ok).0: u32); // in scope 4 at $DIR/simplify_try.rs:7:13: 7:15
+          debug val => ((_0 as Ok).0: u32); // in scope 4 at $DIR/simplify_try.rs:8:13: 8:15
           scope 5 {
           }
       }
@@ -40,29 +40,29 @@
       }
 
       bb0: {
-          StorageLive(_2);                 // scope 0 at $DIR/simplify_try.rs:7:9: 7:10
--         StorageLive(_3);                 // scope 0 at $DIR/simplify_try.rs:7:13: 7:15
--         StorageLive(_4);                 // scope 0 at $DIR/simplify_try.rs:7:13: 7:14
--         _4 = _1;                         // scope 0 at $DIR/simplify_try.rs:7:13: 7:14
+          StorageLive(_2);                 // scope 0 at $DIR/simplify_try.rs:8:9: 8:10
+-         StorageLive(_3);                 // scope 0 at $DIR/simplify_try.rs:8:13: 8:15
+-         StorageLive(_4);                 // scope 0 at $DIR/simplify_try.rs:8:13: 8:14
+-         _4 = _1;                         // scope 0 at $DIR/simplify_try.rs:8:13: 8:14
 -         _3 = move _4;                    // scope 6 at $SRC_DIR/core/src/result.rs:LL:COL
--         StorageDead(_4);                 // scope 0 at $DIR/simplify_try.rs:7:14: 7:15
--         _5 = discriminant(_3);           // scope 0 at $DIR/simplify_try.rs:7:14: 7:15
-+         nop;                             // scope 0 at $DIR/simplify_try.rs:7:13: 7:15
-+         nop;                             // scope 0 at $DIR/simplify_try.rs:7:13: 7:14
-+         _0 = _1;                         // scope 0 at $DIR/simplify_try.rs:7:13: 7:14
+-         StorageDead(_4);                 // scope 0 at $DIR/simplify_try.rs:8:14: 8:15
+-         _5 = discriminant(_3);           // scope 0 at $DIR/simplify_try.rs:8:14: 8:15
++         nop;                             // scope 0 at $DIR/simplify_try.rs:8:13: 8:15
++         nop;                             // scope 0 at $DIR/simplify_try.rs:8:13: 8:14
++         _0 = _1;                         // scope 0 at $DIR/simplify_try.rs:8:13: 8:14
 +         nop;                             // scope 6 at $SRC_DIR/core/src/result.rs:LL:COL
-+         nop;                             // scope 0 at $DIR/simplify_try.rs:7:14: 7:15
-+         _5 = discriminant(_0);           // scope 0 at $DIR/simplify_try.rs:7:14: 7:15
-          goto -> bb1;                     // scope 0 at $DIR/simplify_try.rs:7:14: 7:15
++         nop;                             // scope 0 at $DIR/simplify_try.rs:8:14: 8:15
++         _5 = discriminant(_0);           // scope 0 at $DIR/simplify_try.rs:8:14: 8:15
+          goto -> bb1;                     // scope 0 at $DIR/simplify_try.rs:8:14: 8:15
       }
 
       bb1: {
--         _0 = move _3;                    // scope 1 at $DIR/simplify_try.rs:8:5: 8:10
--         StorageDead(_3);                 // scope 0 at $DIR/simplify_try.rs:7:15: 7:16
-+         nop;                             // scope 1 at $DIR/simplify_try.rs:8:5: 8:10
-+         nop;                             // scope 0 at $DIR/simplify_try.rs:7:15: 7:16
-          StorageDead(_2);                 // scope 0 at $DIR/simplify_try.rs:9:1: 9:2
-          return;                          // scope 0 at $DIR/simplify_try.rs:9:2: 9:2
+-         _0 = move _3;                    // scope 1 at $DIR/simplify_try.rs:9:5: 9:10
+-         StorageDead(_3);                 // scope 0 at $DIR/simplify_try.rs:8:15: 8:16
++         nop;                             // scope 1 at $DIR/simplify_try.rs:9:5: 9:10
++         nop;                             // scope 0 at $DIR/simplify_try.rs:8:15: 8:16
+          StorageDead(_2);                 // scope 0 at $DIR/simplify_try.rs:10:1: 10:2
+          return;                          // scope 0 at $DIR/simplify_try.rs:10:2: 10:2
       }
   }