Index: llvm/trunk/lib/Transforms/Scalar/MemCpyOptimizer.cpp
===================================================================
--- llvm/trunk/lib/Transforms/Scalar/MemCpyOptimizer.cpp
+++ llvm/trunk/lib/Transforms/Scalar/MemCpyOptimizer.cpp
@@ -488,6 +488,16 @@
 
 bool MemCpyOpt::processStore(StoreInst *SI, BasicBlock::iterator &BBI) {
   if (!SI->isSimple()) return false;
+
+  // Avoid merging nontemporal stores since the resulting
+  // memcpy/memset would not be able to preserve the nontemporal hint.
+  // In theory we could teach how to propagate the !nontemporal metadata to
+  // memset calls. However, that change would force the backend to
+  // conservatively expand !nontemporal memset calls back to sequences of
+  // store instructions (effectively undoing the merging).
+  if (SI->getMetadata(LLVMContext::MD_nontemporal))
+    return false;
+
   const DataLayout &DL = SI->getModule()->getDataLayout();
 
   // Detect cases where we're performing call slot forwarding, but
Index: llvm/trunk/test/Transforms/MemCpyOpt/nontemporal.ll
===================================================================
--- llvm/trunk/test/Transforms/MemCpyOpt/nontemporal.ll
+++ llvm/trunk/test/Transforms/MemCpyOpt/nontemporal.ll
@@ -0,0 +1,49 @@
+; RUN: opt < %s -memcpyopt -S | FileCheck %s
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+
+; Verify that we don't combine nontemporal stores into memset calls.
+
+define void @nontemporal_stores_1(<4 x float>* nocapture %dst) {
+; CHECK-LABEL: @nontemporal_stores_1
+; CHECK: store <4 x float> zeroinitializer, <4 x float>* %dst, align 16, !nontemporal !0
+; CHECK: store <4 x float> zeroinitializer, <4 x float>* %ptr1, align 16, !nontemporal !0
+; CHECK: store <4 x float> zeroinitializer, <4 x float>* %ptr2, align 16, !nontemporal !0
+; CHECK: store <4 x float> zeroinitializer, <4 x float>* %ptr3, align 16, !nontemporal !0
+; CHECK: store <4 x float> zeroinitializer, <4 x float>* %ptr4, align 16, !nontemporal !0
+; CHECK: store <4 x float> zeroinitializer, <4 x float>* %ptr5, align 16, !nontemporal !0
+; CHECK: store <4 x float> zeroinitializer, <4 x float>* %ptr6, align 16, !nontemporal !0
+; CHECK: store <4 x float> zeroinitializer, <4 x float>* %ptr7, align 16, !nontemporal !0
+; CHECK-NEXT: ret void
+entry:
+  store <4 x float> zeroinitializer, <4 x float>* %dst, align 16, !nontemporal !0
+  %ptr1 = getelementptr inbounds <4 x float>, <4 x float>* %dst, i64 1
+  store <4 x float> zeroinitializer, <4 x float>* %ptr1, align 16, !nontemporal !0
+  %ptr2 = getelementptr inbounds <4 x float>, <4 x float>* %dst, i64 2
+  store <4 x float> zeroinitializer, <4 x float>* %ptr2, align 16, !nontemporal !0
+  %ptr3 = getelementptr inbounds <4 x float>, <4 x float>* %dst, i64 3
+  store <4 x float> zeroinitializer, <4 x float>* %ptr3, align 16, !nontemporal !0
+  %ptr4 = getelementptr inbounds <4 x float>, <4 x float>* %dst, i64 4
+  store <4 x float> zeroinitializer, <4 x float>* %ptr4, align 16, !nontemporal !0
+  %ptr5 = getelementptr inbounds <4 x float>, <4 x float>* %dst, i64 5
+  store <4 x float> zeroinitializer, <4 x float>* %ptr5, align 16, !nontemporal !0
+  %ptr6 = getelementptr inbounds <4 x float>, <4 x float>* %dst, i64 6
+  store <4 x float> zeroinitializer, <4 x float>* %ptr6, align 16, !nontemporal !0
+  %ptr7 = getelementptr inbounds <4 x float>, <4 x float>* %dst, i64 7
+  store <4 x float> zeroinitializer, <4 x float>* %ptr7, align 16, !nontemporal !0
+  ret void
+}
+
+define void @nontemporal_stores_2(<4 x float>* nocapture %dst) {
+; CHECK-LABEL: @nontemporal_stores_2
+; CHECK: store <4 x float> zeroinitializer, <4 x float>* %dst, align 16, !nontemporal !0
+; CHECK: store <4 x float> zeroinitializer, <4 x float>* %ptr1, align 16, !nontemporal !0
+; CHECK-NEXT: ret void
+entry:
+  store <4 x float> zeroinitializer, <4 x float>* %dst, align 16, !nontemporal !0
+  %ptr1 = getelementptr inbounds <4 x float>, <4 x float>* %dst, i64 1
+  store <4 x float> zeroinitializer, <4 x float>* %ptr1, align 16, !nontemporal !0
+  ret void
+}
+
+!0 = !{i32 1}