Index: lib/Transforms/Instrumentation/MemorySanitizer.cpp
===================================================================
--- lib/Transforms/Instrumentation/MemorySanitizer.cpp
+++ lib/Transforms/Instrumentation/MemorySanitizer.cpp
@@ -557,6 +557,9 @@
 
   /// MSan runtime replacements for memmove, memcpy and memset.
   Value *MemmoveFn, *MemcpyFn, *MemsetFn;
+  /// _nosanitize variants of memmove, memcpy and memset for use in
+  /// non-sanitized functions.
+  Value *MemmoveNosanFn, *MemcpyNosanFn, *MemsetNosanFn;
 
   /// KMSAN callback for task-local function argument shadow.
   Value *MsanGetContextStateFn;
@@ -773,6 +776,17 @@
   MemsetFn = M.getOrInsertFunction(
     "__msan_memset", IRB.getInt8PtrTy(), IRB.getInt8PtrTy(), IRB.getInt32Ty(),
     IntptrTy);
+
+  MemmoveNosanFn =
+      M.getOrInsertFunction("__msan_memmove_nosanitize", IRB.getInt8PtrTy(),
+                            IRB.getInt8PtrTy(), IRB.getInt8PtrTy(), IntptrTy);
+  MemcpyNosanFn =
+      M.getOrInsertFunction("__msan_memcpy_nosanitize", IRB.getInt8PtrTy(),
+                            IRB.getInt8PtrTy(), IRB.getInt8PtrTy(), IntptrTy);
+  MemsetNosanFn =
+      M.getOrInsertFunction("__msan_memset_nosanitize", IRB.getInt8PtrTy(),
+                            IRB.getInt8PtrTy(), IRB.getInt32Ty(), IntptrTy);
+
   // We insert an empty inline asm after __msan_report* to avoid callback merge.
   EmptyAsm = InlineAsm::get(FunctionType::get(IRB.getVoidTy(), false),
                             StringRef(""), StringRef(""),
@@ -970,6 +984,7 @@
   // blacklist contents and command-line options.
   bool InsertChecks;
   bool PropagateShadow;
+  bool InstrumentMemIntrinsics;
   bool PoisonStack;
   bool PoisonUndef;
   bool CheckReturnValue;
@@ -990,6 +1005,7 @@
     bool SanitizeFunction = F.hasFnAttribute(Attribute::SanitizeMemory);
     InsertChecks = SanitizeFunction;
     PropagateShadow = SanitizeFunction;
+    InstrumentMemIntrinsics = SanitizeFunction;
     PoisonStack = SanitizeFunction && ClPoisonStack;
     PoisonUndef = SanitizeFunction && ClPoisonUndef;
     // FIXME: Consider using SpecialCaseList to specify a list of functions that
@@ -2324,7 +2340,7 @@
   void visitMemMoveInst(MemMoveInst &I) {
     IRBuilder<> IRB(&I);
     IRB.CreateCall(
-        MS.MemmoveFn,
+        InstrumentMemIntrinsics ? MS.MemmoveFn : MS.MemmoveNosanFn,
         {IRB.CreatePointerCast(I.getArgOperand(0), IRB.getInt8PtrTy()),
          IRB.CreatePointerCast(I.getArgOperand(1), IRB.getInt8PtrTy()),
          IRB.CreateIntCast(I.getArgOperand(2), MS.IntptrTy, false)});
@@ -2338,7 +2354,7 @@
   void visitMemCpyInst(MemCpyInst &I) {
     IRBuilder<> IRB(&I);
     IRB.CreateCall(
-        MS.MemcpyFn,
+        InstrumentMemIntrinsics ? MS.MemcpyFn : MS.MemcpyNosanFn,
         {IRB.CreatePointerCast(I.getArgOperand(0), IRB.getInt8PtrTy()),
          IRB.CreatePointerCast(I.getArgOperand(1), IRB.getInt8PtrTy()),
          IRB.CreateIntCast(I.getArgOperand(2), MS.IntptrTy, false)});
@@ -2349,7 +2365,7 @@
   void visitMemSetInst(MemSetInst &I) {
     IRBuilder<> IRB(&I);
     IRB.CreateCall(
-        MS.MemsetFn,
+        InstrumentMemIntrinsics ? MS.MemsetFn : MS.MemsetNosanFn,
         {IRB.CreatePointerCast(I.getArgOperand(0), IRB.getInt8PtrTy()),
          IRB.CreateIntCast(I.getArgOperand(1), IRB.getInt32Ty(), false),
          IRB.CreateIntCast(I.getArgOperand(2), MS.IntptrTy, false)});
Index: test/Instrumentation/MemorySanitizer/msan_basic.ll
===================================================================
--- test/Instrumentation/MemorySanitizer/msan_basic.ll
+++ test/Instrumentation/MemorySanitizer/msan_basic.ll
@@ -210,6 +210,16 @@
 ; CHECK: call i8* @__msan_memset
 ; CHECK: ret void
 
+; _nosanitize version of memset
+define void @MemSetNosanitize(i8* nocapture %x) nounwind uwtable {
+entry:
+  call void @llvm.memset.p0i8.i64(i8* %x, i8 42, i64 10, i1 false)
+  ret void
+}
+
+; CHECK-LABEL: @MemSetNosanitize
+; CHECK: call i8* @__msan_memset_nosanitize
+; CHECK: ret void
 
 ; memcpy
 define void @MemCpy(i8* nocapture %x, i8* nocapture %y) nounwind uwtable sanitize_memory {
@@ -224,6 +234,16 @@
 ; CHECK: call i8* @__msan_memcpy
 ; CHECK: ret void
 
+; _nosanitize version of memcpy
+define void @MemCpyNosanitize(i8* nocapture %x, i8* nocapture %y) nounwind uwtable {
+entry:
+  call void @llvm.memcpy.p0i8.p0i8.i64(i8* %x, i8* %y, i64 10, i1 false)
+  ret void
+}
+
+; CHECK-LABEL: @MemCpyNosanitize
+; CHECK: call i8* @__msan_memcpy_nosanitize
+; CHECK: ret void
 
 ; memmove is lowered to a call
 define void @MemMove(i8* nocapture %x, i8* nocapture %y) nounwind uwtable sanitize_memory {
@@ -238,6 +258,16 @@
 ; CHECK: call i8* @__msan_memmove
 ; CHECK: ret void
 
+define void @MemMoveNosanitize(i8* nocapture %x, i8* nocapture %y) nounwind uwtable {
+entry:
+  call void @llvm.memmove.p0i8.p0i8.i64(i8* %x, i8* %y, i64 10, i1 false)
+  ret void
+}
+
+; CHECK-LABEL: @MemMoveNosanitize
+; CHECK: call i8* @__msan_memmove_nosanitize
+; CHECK: ret void
+
 ;; ------------
 ;; Placeholder tests that will fail once element atomic @llvm.mem[cpy|move|set] instrinsics have
 ;; been added to the MemIntrinsic class hierarchy. These will act as a reminder to