Rollup merge of #105420 - tmiasko:dest-prop-dead-code, r=JakobDegen

Remove dead code after destination propagation

Fixes #105428.

cc `@JakobDegen`

2 files changed, 104 insertions, 0 deletions

diff --git a/src/test/mir-opt/dest-prop/unreachable.f.DestinationPropagation.diff b/src/test/mir-opt/dest-prop/unreachable.f.DestinationPropagation.diff
new file mode 100644
index 00000000000..9ea756c2712
--- /dev/null
+++ b/src/test/mir-opt/dest-prop/unreachable.f.DestinationPropagation.diff
@@ -0,0 +1,86 @@
+- // MIR for `f` before DestinationPropagation
++ // MIR for `f` after DestinationPropagation
+  
+  fn f(_1: T) -> () {
+      debug a => _1;                       // in scope 0 at $DIR/unreachable.rs:+0:19: +0:20
+      let mut _0: ();                      // return place in scope 0 at $DIR/unreachable.rs:+0:25: +0:25
+      let _2: T;                           // in scope 0 at $DIR/unreachable.rs:+1:9: +1:10
+      let mut _3: bool;                    // in scope 0 at $DIR/unreachable.rs:+2:8: +2:13
+      let _4: ();                          // in scope 0 at $DIR/unreachable.rs:+3:9: +3:16
+      let mut _5: T;                       // in scope 0 at $DIR/unreachable.rs:+3:11: +3:12
+      let mut _6: T;                       // in scope 0 at $DIR/unreachable.rs:+3:14: +3:15
+      let _7: ();                          // in scope 0 at $DIR/unreachable.rs:+5:9: +5:16
+      let mut _8: T;                       // in scope 0 at $DIR/unreachable.rs:+5:11: +5:12
+      let mut _9: T;                       // in scope 0 at $DIR/unreachable.rs:+5:14: +5:15
+      scope 1 {
+-         debug b => _2;                   // in scope 1 at $DIR/unreachable.rs:+1:9: +1:10
++         debug b => _1;                   // in scope 1 at $DIR/unreachable.rs:+1:9: +1:10
+      }
+  
+      bb0: {
+-         StorageLive(_2);                 // scope 0 at $DIR/unreachable.rs:+1:9: +1:10
+-         _2 = _1;                         // scope 0 at $DIR/unreachable.rs:+1:13: +1:14
++         nop;                             // scope 0 at $DIR/unreachable.rs:+1:9: +1:10
++         nop;                             // scope 0 at $DIR/unreachable.rs:+1:13: +1:14
+          StorageLive(_3);                 // scope 1 at $DIR/unreachable.rs:+2:8: +2:13
+          _3 = const false;                // scope 1 at $DIR/unreachable.rs:+2:8: +2:13
+-         goto -> bb3;                     // scope 1 at $DIR/unreachable.rs:+2:8: +2:13
++         goto -> bb1;                     // scope 1 at $DIR/unreachable.rs:+2:8: +2:13
+      }
+  
+      bb1: {
+-         StorageLive(_4);                 // scope 1 at $DIR/unreachable.rs:+3:9: +3:16
+-         StorageLive(_5);                 // scope 1 at $DIR/unreachable.rs:+3:11: +3:12
+-         _5 = _1;                         // scope 1 at $DIR/unreachable.rs:+3:11: +3:12
+-         StorageLive(_6);                 // scope 1 at $DIR/unreachable.rs:+3:14: +3:15
+-         _6 = _2;                         // scope 1 at $DIR/unreachable.rs:+3:14: +3:15
+-         _4 = g::<T>(move _5, move _6) -> bb2; // scope 1 at $DIR/unreachable.rs:+3:9: +3:16
+-                                          // mir::Constant
+-                                          // + span: $DIR/unreachable.rs:11:9: 11:10
+-                                          // + literal: Const { ty: fn(T, T) {g::<T>}, val: Value(<ZST>) }
+-     }
+- 
+-     bb2: {
+-         StorageDead(_6);                 // scope 1 at $DIR/unreachable.rs:+3:15: +3:16
+-         StorageDead(_5);                 // scope 1 at $DIR/unreachable.rs:+3:15: +3:16
+-         StorageDead(_4);                 // scope 1 at $DIR/unreachable.rs:+3:16: +3:17
+-         _0 = const ();                   // scope 1 at $DIR/unreachable.rs:+2:14: +4:6
+-         goto -> bb5;                     // scope 1 at $DIR/unreachable.rs:+2:5: +6:6
+-     }
+- 
+-     bb3: {
+          StorageLive(_7);                 // scope 1 at $DIR/unreachable.rs:+5:9: +5:16
+-         StorageLive(_8);                 // scope 1 at $DIR/unreachable.rs:+5:11: +5:12
+-         _8 = _2;                         // scope 1 at $DIR/unreachable.rs:+5:11: +5:12
++         nop;                             // scope 1 at $DIR/unreachable.rs:+5:11: +5:12
++         nop;                             // scope 1 at $DIR/unreachable.rs:+5:11: +5:12
+          StorageLive(_9);                 // scope 1 at $DIR/unreachable.rs:+5:14: +5:15
+-         _9 = _2;                         // scope 1 at $DIR/unreachable.rs:+5:14: +5:15
+-         _7 = g::<T>(move _8, move _9) -> bb4; // scope 1 at $DIR/unreachable.rs:+5:9: +5:16
++         _9 = _1;                         // scope 1 at $DIR/unreachable.rs:+5:14: +5:15
++         _7 = g::<T>(move _1, move _9) -> bb2; // scope 1 at $DIR/unreachable.rs:+5:9: +5:16
+                                           // mir::Constant
+                                           // + span: $DIR/unreachable.rs:13:9: 13:10
+                                           // + literal: Const { ty: fn(T, T) {g::<T>}, val: Value(<ZST>) }
+      }
+  
+-     bb4: {
++     bb2: {
+          StorageDead(_9);                 // scope 1 at $DIR/unreachable.rs:+5:15: +5:16
+-         StorageDead(_8);                 // scope 1 at $DIR/unreachable.rs:+5:15: +5:16
++         nop;                             // scope 1 at $DIR/unreachable.rs:+5:15: +5:16
+          StorageDead(_7);                 // scope 1 at $DIR/unreachable.rs:+5:16: +5:17
+          _0 = const ();                   // scope 1 at $DIR/unreachable.rs:+4:12: +6:6
+-         goto -> bb5;                     // scope 1 at $DIR/unreachable.rs:+2:5: +6:6
++         goto -> bb3;                     // scope 1 at $DIR/unreachable.rs:+2:5: +6:6
+      }
+  
+-     bb5: {
++     bb3: {
+          StorageDead(_3);                 // scope 1 at $DIR/unreachable.rs:+6:5: +6:6
+-         StorageDead(_2);                 // scope 0 at $DIR/unreachable.rs:+7:1: +7:2
++         nop;                             // scope 0 at $DIR/unreachable.rs:+7:1: +7:2
+          return;                          // scope 0 at $DIR/unreachable.rs:+7:2: +7:2
+      }
+  }
+  
diff --git a/src/test/mir-opt/dest-prop/unreachable.rs b/src/test/mir-opt/dest-prop/unreachable.rs
new file mode 100644
index 00000000000..32b5def984a
--- /dev/null
+++ b/src/test/mir-opt/dest-prop/unreachable.rs
@@ -0,0 +1,18 @@
+// Check that unreachable code is removed after the destination propagation.
+// Regression test for issue #105428.
+//
+// compile-flags: --crate-type=lib -Zmir-opt-level=0
+// compile-flags: -Zmir-enable-passes=+ConstProp,+SimplifyConstCondition-after-const-prop,+DestinationPropagation
+
+// EMIT_MIR unreachable.f.DestinationPropagation.diff
+pub fn f<T: Copy>(a: T) {
+    let b = a;
+    if false {
+        g(a, b);
+    } else {
+        g(b, b);
+    }
+}
+
+#[inline(never)]
+pub fn g<T: Copy>(_: T, _: T) {}