[InstCombine] Handle atomic memset in the same way as regular memset

Summary:
This change adds handling of the atomic memset intrinsic to the
code path that simplifies the regular memset. In practice this means
that we will now also expand a small constant-length atomic memset
into a single unordered atomic store.

Reviewers: apilipenko, skatkov, mkazantsev, anna, reames

Reviewed By: reames

Subscribers: reames, llvm-commits

Differential Revision: https://reviews.llvm.org/D46660

llvm-svn: 332132

1 files changed, 5 insertions, 3 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
index e11d49251ad..82a26f348cd 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -199,7 +199,7 @@ Instruction *InstCombiner::SimplifyAnyMemTransfer(AnyMemTransferInst *MI) {
   return MI;
 }
 
-Instruction *InstCombiner::SimplifyMemSet(MemSetInst *MI) {
+Instruction *InstCombiner::SimplifyAnyMemSet(AnyMemSetInst *MI) {
   unsigned Alignment = getKnownAlignment(MI->getDest(), DL, MI, &AC, &DT);
   if (MI->getDestAlignment() < Alignment) {
     MI->setDestAlignment(Alignment);
@@ -232,6 +232,8 @@ Instruction *InstCombiner::SimplifyMemSet(MemSetInst *MI) {
     StoreInst *S = Builder.CreateStore(ConstantInt::get(ITy, Fill), Dest,
                                        MI->isVolatile());
     S->setAlignment(Alignment);
+    if (isa<AtomicMemSetInst>(MI))
+      S->setOrdering(AtomicOrdering::Unordered);
 
     // Set the size of the copy to 0, it will be deleted on the next iteration.
     MI->setLength(Constant::getNullValue(LenC->getType()));
@@ -1758,8 +1760,8 @@ Instruction *InstCombiner::visitCallInst(CallInst &CI) {
     if (auto *MTI = dyn_cast<AnyMemTransferInst>(MI)) {
       if (Instruction *I = SimplifyAnyMemTransfer(MTI))
         return I;
-    } else if (MemSetInst *MSI = dyn_cast<MemSetInst>(MI)) {
-      if (Instruction *I = SimplifyMemSet(MSI))
+    } else if (auto *MSI = dyn_cast<AnyMemSetInst>(MI)) {
+      if (Instruction *I = SimplifyAnyMemSet(MSI))
         return I;
     }