Added test for dead-live edge case

Author: ohadravid

compiler/rustc_mir_transform/src/gvn.rs

@@ -164,7 +164,7 @@ impl<'tcx> crate::MirPass<'tcx> for GVN {
             // Conservatively remove all storage statements for reused locals.
             state.reused_locals.clone()
         };
-        
+
         debug!(?storage_to_remove);
 
         StorageRemover { tcx, reused_locals: state.reused_locals, storage_to_remove }

tests/mir-opt/gvn_storage_twice.repeat_local.GVN.diff

@@ -0,0 +1,17 @@
+- // MIR for `repeat_local` before GVN
++ // MIR for `repeat_local` after GVN
+  
+  fn repeat_local(_1: usize, _2: usize, _3: i32) -> i32 {
+      let mut _0: i32;
+      let mut _4: [i32; 5];
+      let mut _5: &i32;
+  
+      bb0: {
+          _4 = [copy _3; 5];
+          _5 = &_4[_1];
+-         _0 = copy (*_5);
++         _0 = copy _3;
+          return;
+      }
+  }
+  

tests/mir-opt/gvn_storage_twice.repeat_local_dead.GVN.diff

@@ -0,0 +1,19 @@
+- // MIR for `repeat_local_dead` before GVN
++ // MIR for `repeat_local_dead` after GVN
+  
+  fn repeat_local_dead(_1: usize, _2: usize, _3: i32) -> i32 {
+      let mut _0: i32;
+      let mut _4: [i32; 5];
+      let mut _5: &i32;
+  
+      bb0: {
+          _4 = [copy _3; 5];
+          _5 = &_4[_1];
+-         StorageDead(_3);
+-         _0 = copy (*_5);
++         nop;
++         _0 = copy _3;
+          return;
+      }
+  }
+  

tests/mir-opt/gvn_storage_twice.repeat_local_dead_live.GVN.diff

@@ -0,0 +1,19 @@
+- // MIR for `repeat_local_dead_live` before GVN
++ // MIR for `repeat_local_dead_live` after GVN
+  
+  fn repeat_local_dead_live(_1: usize, _2: usize, _3: i32) -> i32 {
+      let mut _0: i32;
+      let mut _4: [i32; 5];
+      let mut _5: &i32;
+  
+      bb0: {
+          _4 = [copy _3; 5];
+          _5 = &_4[_1];
+          StorageDead(_3);
+          StorageLive(_3);
+-         _0 = copy (*_5);
++         _0 = copy _3;
+          return;
+      }
+  }
+  

tests/mir-opt/gvn_storage_twice.rs

@@ -0,0 +1,65 @@
+// skip-filecheck
+//@ test-mir-pass: GVN
+//@ compile-flags: -Zlint-mir=false
+
+#![feature(custom_mir, core_intrinsics)]
+
+use std::intrinsics::mir::*;
+
+// EMIT_MIR gvn_storage_twice.repeat_local.GVN.diff
+// EMIT_MIR gvn_storage_twice.repeat_local_dead.GVN.diff
+// EMIT_MIR gvn_storage_twice.repeat_local_dead_live.GVN.diff
+
+// Check that we remove the storage statements if the local
+// doesn't have valid storage when it is used.
+//
+// Based on `gvn_repeat.rs::repeat_local`, were GVN should replace
+// `let RET = *_5;` with `let RET = _3;`.
+
+#[custom_mir(dialect = "runtime")]
+pub fn repeat_local(_1: usize, _2: usize, _3: i32) -> i32 {
+    mir! {
+        {
+            let _4 = [_3; 5];
+            let _5 = &_4[_1];
+            RET = *_5;
+            Return()
+        }
+    }
+}
+
+// Since _3 is dead when we access _5, GVN should remove the storage statements.
+
+#[custom_mir(dialect = "runtime")]
+pub fn repeat_local_dead(_1: usize, _2: usize, _3: i32) -> i32 {
+    mir! {
+        {
+            let _4 = [_3; 5];
+            let _5 = &_4[_1];
+            StorageDead(_3);
+            RET = *_5;
+            Return()
+        }
+    }
+}
+
+// Since _3 is uninitizaled when we access _5, GVN should _not_ optimze the code.
+
+#[custom_mir(dialect = "runtime")]
+pub fn repeat_local_dead_live(_1: usize, _2: usize, _3: i32) -> i32 {
+    mir! {
+        {
+            let _4 = [_3; 5];
+            let _5 = &_4[_1];
+            StorageDead(_3);
+            StorageLive(_3);
+            RET = *_5;
+            Return()
+        }
+    }
+}
+
+#[inline(never)]
+fn opaque<T>(a: T) -> T {
+    a
+}