Don't zap back to back volatile load/stores

llvm-svn: 41759

2 files changed, 15 insertions, 1 deletions

diff --git a/llvm/lib/Transforms/Scalar/InstructionCombining.cpp b/llvm/lib/Transforms/Scalar/InstructionCombining.cpp
index 26df55531a8..f9abafa34c0 100644
--- a/llvm/lib/Transforms/Scalar/InstructionCombining.cpp
+++ b/llvm/lib/Transforms/Scalar/InstructionCombining.cpp
@@ -9066,7 +9066,7 @@ Instruction *InstCombiner::visitStoreInst(StoreInst &SI) {
     // the pointer we're loading and is producing the pointer we're storing,
     // then *this* store is dead (X = load P; store X -> P).
     if (LoadInst *LI = dyn_cast<LoadInst>(BBI)) {
-      if (LI == Val && LI->getOperand(0) == Ptr) {
+      if (LI == Val && LI->getOperand(0) == Ptr && !SI.isVolatile()) {
         EraseInstFromFunction(SI);
         ++NumCombined;
         return 0;
diff --git a/llvm/test/Transforms/InstCombine/volatile_store.ll b/llvm/test/Transforms/InstCombine/volatile_store.ll
new file mode 100644
index 00000000000..09651ba302d
--- /dev/null
+++ b/llvm/test/Transforms/InstCombine/volatile_store.ll
@@ -0,0 +1,14 @@
+; RUN: llvm-as < %s | opt -instcombine | llvm-dis | grep {volatile store}
+; RUN: llvm-as < %s | opt -instcombine | llvm-dis | grep {volatile load}
+
+@x = weak global i32 0		; <i32*> [#uses=2]
+
+define void @self_assign_1() {
+entry:
+	%tmp = volatile load i32* @x		; <i32> [#uses=1]
+	volatile store i32 %tmp, i32* @x
+	br label %return
+
+return:		; preds = %entry
+	ret void
+}