GVN unnit analysis shouldn't check unreachable blocks

Author: ohadravid

compiler/rustc_mir_transform/src/gvn.rs

@@ -154,7 +154,9 @@ impl<'tcx> crate::MirPass<'tcx> for GVN {
                 maybe_uninit,
             };
 
-            storage_checker.visit_body(body);
+            for (bb, data) in traversal::reachable(body) {
+                storage_checker.visit_basic_block_data(bb, data);
+            }
 
             storage_checker.storage_to_remove
         } else {

tests/mir-opt/gvn_storage_unreachable.f.GVN.diff

@@ -0,0 +1,28 @@
+- // MIR for `f` before GVN
++ // MIR for `f` after GVN
+  
+  fn f(_1: u32) -> () {
+      let mut _0: ();
+      let mut _2: S;
+      let mut _3: S;
+      let mut _4: S;
+  
+      bb0: {
+          StorageLive(_2);
+          _2 = S(copy _1, const 2_u32);
+          StorageLive(_3);
+-         _3 = S(copy _1, const 2_u32);
++         _3 = copy _2;
+          StorageDead(_3);
+          StorageDead(_2);
+          return;
+      }
+  
+      bb1: {
+          StorageLive(_2);
+          _4 = copy _2;
+          StorageDead(_2);
+          return;
+      }
+  }
+  

tests/mir-opt/gvn_storage_unreachable.rs

@@ -0,0 +1,41 @@
+//! Check that we do not remove the storage statements if a reused local
+//! is uninitialized in an unreachable block.
+//@ test-mir-pass: GVN
+// EMIT_MIR gvn_storage_unreachable.f.GVN.diff
+
+#![feature(custom_mir, core_intrinsics)]
+
+use std::intrinsics::mir::*;
+
+struct S(u32, u32);
+
+#[custom_mir(dialect = "runtime", phase = "post-cleanup")]
+pub fn f(_1: u32) {
+    // CHECK-LABEL: fn f(
+    mir! {
+        let _2: S;
+        let _3: S;
+        let _4: S;
+        {
+            // CHECK: StorageLive(_2);
+            // CHECK: StorageLive(_3);
+            // CHECK: _3 = copy _2;
+            // CHECK: StorageDead(_3);
+            // CHECK: StorageDead(_2);
+            StorageLive(_2);
+            _2 = S(_1, 2);
+            StorageLive(_3);
+            _3 = S(_1, 2);
+            StorageDead(_3);
+            StorageDead(_2);
+            Return()
+        }
+        bb1 = {
+            StorageLive(_2);
+            // CHECK: _4 = copy _2;
+            _4 = _2;
+            StorageDead(_2);
+            Return()
+        }
+    }
+}