tryMergingIntoMemset can only handle constant length memsets.

llvm-svn: 123090

1 files changed, 6 insertions, 5 deletions

diff --git a/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp b/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
index 4210f0d9b79..76fab1cd281 100644
--- a/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
+++ b/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
@@ -515,11 +515,12 @@ bool MemCpyOpt::processStore(StoreInst *SI, BasicBlock::iterator &BBI) {
 bool MemCpyOpt::processMemSet(MemSetInst *MSI, BasicBlock::iterator &BBI) {
   // See if there is another memset or store neighboring this memset which
   // allows us to widen out the memset to do a single larger store.
-  if (Instruction *I = tryMergingIntoMemset(MSI, MSI->getDest(),
-                                            MSI->getValue())) {
-    BBI = I;  // Don't invalidate iterator.
-    return true;
-  }
+  if (isa<ConstantInt>(MSI->getLength()) && !MSI->isVolatile())
+    if (Instruction *I = tryMergingIntoMemset(MSI, MSI->getDest(),
+                                              MSI->getValue())) {
+      BBI = I;  // Don't invalidate iterator.
+      return true;
+    }
   return false;
 }