Index: lib/Transforms/Utils/SimplifyLibCalls.cpp
===================================================================
--- lib/Transforms/Utils/SimplifyLibCalls.cpp
+++ lib/Transforms/Utils/SimplifyLibCalls.cpp
@@ -840,12 +840,8 @@
   if (!FillValue || FillValue->getZExtValue() != 0)
     return nullptr;
 
-  // TODO: We should handle the case where the malloc has more than one use.
-  // This is necessary to optimize common patterns such as when the result of
-  // the malloc is checked against null or when a memset intrinsic is used in
-  // place of a memset library call.
   auto *Malloc = dyn_cast<CallInst>(Memset->getArgOperand(0));
-  if (!Malloc || !Malloc->hasOneUse())
+  if (!Malloc)
     return nullptr;
 
   // Is the inner call really malloc()?
@@ -2219,7 +2215,8 @@
       return optimizeLog(CI, Builder);
     case Intrinsic::sqrt:
       return optimizeSqrt(CI, Builder);
-    // TODO: Use foldMallocMemset() with memset intrinsic.
+    case Intrinsic::memset:
+      return foldMallocMemset(CI, Builder, *TLI);
     default:
       return nullptr;
     }
@@ -2393,7 +2390,8 @@
 
 Value *FortifiedLibCallSimplifier::optimizeMemSetChk(CallInst *CI,
                                                      IRBuilder<> &B) {
-  // TODO: Try foldMallocMemset() here.
+  if (auto *Calloc = foldMallocMemset(CI, B, *TLI))
+    return Calloc;
 
   if (isFortifiedCallFoldable(CI, 3, 2, false)) {
     Value *Val = B.CreateIntCast(CI->getArgOperand(1), B.getInt8Ty(), false);
Index: test/Transforms/InstCombine/memset-1.ll
===================================================================
--- test/Transforms/InstCombine/memset-1.ll
+++ test/Transforms/InstCombine/memset-1.ll
@@ -26,6 +26,28 @@
 ; CHECK-NEXT:  ret i8* %calloc
 }
 
+
+define i8* @pr45344(i32 %n) #0 {
+  %n.addr = alloca i32, align 4
+  %b = alloca i8*, align 8
+  store i32 %n, i32* %n.addr, align 4
+  %0 = load i32, i32* %n.addr, align 4
+  %conv = sext i32 %0 to i64
+  %call = call i8* @malloc(i64 %conv)
+  store i8* %call, i8** %b, align 8
+  %1 = load i8*, i8** %b, align 8
+  %2 = load i32, i32* %n.addr, align 4
+  %conv1 = sext i32 %2 to i64
+  call void @llvm.memset.p0i8.i64(i8* %1, i8 0, i64 %conv1, i32 1, i1 false)
+  %3 = load i8*, i8** %b, align 8
+  ret i8* %3
+
+; CHECK-LABEL: @pr45344(
+; CHECK-NEXT:  %conv = sext i32 %n to i64
+; CHECK-NEXT:  %calloc = tail call i8* @calloc(i64 1, i64 %conv) #1
+; CHECK-NEXT:  ret i8* %calloc
+}
+
 ; This should not create a calloc and not crash the compiler.
 ; CHECK-LABEL: @notmalloc_memset
 ; CHECK-NOT: @calloc
@@ -67,6 +89,7 @@
 
 declare noalias i8* @malloc(i32) #1
 declare i64 @llvm.objectsize.i64.p0i8(i8*, i1) #2
+declare void @llvm.memset.p0i8.i64(i8* nocapture writeonly, i8, i64, i32, i1) #3
 
 attributes #0 = { nounwind ssp uwtable }
 attributes #1 = { nounwind }