Index: llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
===================================================================
--- llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
+++ llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
@@ -945,6 +945,14 @@
             C->getArgOperand(ArgI)->getType()->getPointerAddressSpace())
       return false;
 
+  // If merging alias scopes results in a non-null, bail
+  // TODO: merging should be legal if no new domains get introduced
+  auto callScope = C->getMetadata(LLVMContext::MD_alias_scope);
+  auto cpyScope = C->getMetadata(LLVMContext::MD_alias_scope);
+  if (MDNode::getMostGenericAliasScope(callScope, cpyScope) != nullptr) {
+    return false;
+  }
+
   // All the checks have passed, so do the transformation.
   bool changedArgument = false;
   for (unsigned ArgI = 0; ArgI < C->arg_size(); ++ArgI)
Index: llvm/test/Transforms/MemCpyOpt/callslot_badaa.ll
===================================================================
--- /dev/null
+++ llvm/test/Transforms/MemCpyOpt/callslot_badaa.ll
@@ -0,0 +1,39 @@
+; RUN: opt < %s -S -memcpyopt | FileCheck %s
+
+; Make sure callslot optimization does not allow merging here because of alias.scope.
+; Merging here generates:
+;  call void @llvm.memcpy.p0i8.p0i8.i64(i8* align 8 %dst, i8* align 8 %src, i64 1, i1 false), !alias.scope !3
+;  call void @llvm.lifetime.end.p0i8(i64 8, i8* nonnull %src), !noalias !0
+;   ...
+;  !0 = !{!1}
+;  !1 = distinct !{!1, !2, !"hello2: %a"}
+;  !2 = distinct !{!2, !"hello2"}
+;  !3 = !{!1, !4, !5, !"hello: %a"}
+;  !4 = distinct !{!4, !5, !"hello: %a"}
+;  !5 = distinct !{!5, !"hello"}
+; Which is incorrect because the lifetime.end of %src will now "noalias" the above memcpy.
+define i8 @test(i8 %input) {
+  %tmp = alloca i8
+  %dst = alloca i8
+  %src = alloca i8
+; CHECK:   call void @llvm.memcpy.p0i8.p0i8.i64(i8* align 8 %tmp, i8* align 8 %src, i64 1, i1 false)
+; CHECK:   call void @llvm.memcpy.p0i8.p0i8.i64(i8* align 8 %dst, i8* align 8 %tmp, i64 1, i1 false)
+  call void @llvm.lifetime.start.p0i8(i64 8, i8* nonnull %src), !noalias !3
+  store i8 %input, i8* %src
+  call void @llvm.memcpy.p0i8.p0i8.i64(i8* align 8 %tmp, i8* align 8 %src, i64 1, i1 false), !alias.scope !0
+  call void @llvm.lifetime.end.p0i8(i64 8, i8* nonnull %src), !noalias !3
+  call void @llvm.memcpy.p0i8.p0i8.i64(i8* align 8 %dst, i8* align 8 %tmp, i64 1, i1 false), !alias.scope !3
+  %ret_value = load i8, i8* %dst
+  ret i8 %ret_value
+}
+
+declare void @llvm.lifetime.start.p0i8(i64, i8* nocapture)
+declare void @llvm.lifetime.end.p0i8(i64, i8* nocapture)
+declare void @llvm.memcpy.p0i8.p0i8.i64(i8*, i8*, i64, i1)
+
+!0 = !{!1}
+!1 = distinct !{!1, !2, !"hello: %a"}
+!2 = distinct !{!2, !"hello"}
+!3 = !{!4}
+!4 = distinct !{!4, !5, !"hello2: %a"}
+!5 = distinct !{!5, !"hello2"}