diff --git a/clang/lib/CodeGen/CGBuiltin.cpp b/clang/lib/CodeGen/CGBuiltin.cpp
index 497a0b3952af8..2032451525667 100644
--- a/clang/lib/CodeGen/CGBuiltin.cpp
+++ b/clang/lib/CodeGen/CGBuiltin.cpp
@@ -4531,6 +4531,13 @@ RValue CodeGenFunction::EmitBuiltinExpr(const GlobalDecl GD, unsigned BuiltinID,
     Value *SizeVal = EmitScalarExpr(E->getArg(2));
     EmitArgCheck(TCK_Store, Dest, E->getArg(0), 0);
     EmitArgCheck(TCK_Load, Src, E->getArg(1), 1);
+    if (BuiltinID == Builtin::BImemcpy || BuiltinID == Builtin::BImempcpy) {
+      Value *NullSize = Builder.CreateIsNull(SizeVal);
+      Builder.CreateAssumption(Builder.CreateOr(
+          NullSize, Builder.CreateIsNotNull(Dest.emitRawPointer(*this))));
+      Builder.CreateAssumption(Builder.CreateOr(
+          NullSize, Builder.CreateIsNotNull(Src.emitRawPointer(*this))));
+    }
     Builder.CreateMemCpy(Dest, Src, SizeVal, false);
     if (BuiltinID == Builtin::BImempcpy ||
         BuiltinID == Builtin::BI__builtin_mempcpy)
diff --git a/clang/test/CodeGen/catch-undef-behavior.c b/clang/test/CodeGen/catch-undef-behavior.c
index 7580290b0b033..22161141acf4a 100644
--- a/clang/test/CodeGen/catch-undef-behavior.c
+++ b/clang/test/CodeGen/catch-undef-behavior.c
@@ -366,11 +366,17 @@ void call_memcpy_nonnull(void *p, void *q, int sz) {
   // CHECK-TRAP: call void @llvm.ubsantrap(i8 16)
   // CHECK-COMMON-NOT: call
 
-  // CHECK-COMMON: icmp ne ptr {{.*}}, null
+  // CHECK-COMMON: icmp ne ptr %[[#]], null
   // CHECK-UBSAN: call void @__ubsan_handle_nonnull_arg
   // CHECK-TRAP: call void @llvm.ubsantrap(i8 16)
-  // CHECK-COMMON-NOT: call
-
+  //
+  // CHECK-COMMON: icmp eq i64 %conv, 0
+  // CHECK-COMMON: icmp ne ptr %0, null
+  // CHECK-COMMON: or i1 %[[#]], %[[#]]
+  // CHECK-COMMON: call void @llvm.assume(i1 %[[#]])
+  // CHECK-COMMON: icmp ne ptr %1, null
+  // CHECK-COMMON: or i1 %[[#]], %[[#]]
+  // CHECK-COMMON: call void @llvm.assume(i1 %[[#]])
   // CHECK-COMMON: call void @llvm.memcpy.p0.p0.i64(ptr align 1 %0, ptr align 1 %1, i64 %conv, i1 false)
   memcpy(p, q, sz);
 }