diff --git a/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp b/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
--- a/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
+++ b/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
@@ -1055,6 +1055,14 @@
   if (!MDepLen || !MLen || MDepLen->getZExtValue() < MLen->getZExtValue())
     return false;
 
+  // FIXME: Disable MemCpyOpt if 'a' is an argument of a coroutine function.
+  // We cannot optimize out the copy from argument to stack in coroutines
+  // because the argument may no longer be accessible after coroutine
+  // suspensions. This fix is temporary. We need a better way to handle this.
+  if (isa<Argument>(MDep->getSource()) &&
+      M->getFunction()->isPresplitCoroutine())
+    return false;
+
   // Verify that the copied-from memory doesn't change in between the two
   // transfers.  For example, in:
   //    memcpy(a <- b)
diff --git a/llvm/test/Transforms/MemCpyOpt/coroutine-params.ll b/llvm/test/Transforms/MemCpyOpt/coroutine-params.ll
new file mode 100644
--- /dev/null
+++ b/llvm/test/Transforms/MemCpyOpt/coroutine-params.ll
@@ -0,0 +1,137 @@
+; RUN: opt < %s -passes=memcpyopt -S | FileCheck %s
+
+%promise_type = type { i8 }
+%struct.A = type <{ i64, i64, i32, [4 x i8] }>
+
+; Function Attrs: noinline ssp uwtable mustprogress
+define %promise_type* @foo(%struct.A* nocapture readonly byval(%struct.A) align 8 %a1) #0 {
+entry:
+  %a1153 = alloca [24 x i8], align 8
+  %__promise = alloca %promise_type, align 1
+  %a2 = alloca %struct.A, align 8
+  %a1153.sub = getelementptr inbounds [24 x i8], [24 x i8]* %a1153, i64 0, i64 0
+  %0 = getelementptr inbounds %promise_type, %promise_type* %__promise, i64 0, i32 0
+  %1 = call token @llvm.coro.id(i32 16, i8* nonnull %0, i8* bitcast (%promise_type* (%struct.A*)* @foo to i8*), i8* null)
+  %2 = call i1 @llvm.coro.alloc(token %1)
+  br i1 %2, label %coro.alloc, label %coro.init
+
+coro.alloc:                                       ; preds = %entry
+  %3 = call i64 @llvm.coro.size.i64()
+  %call = call noalias nonnull i8* @_Znwm(i64 %3) #8
+  br label %coro.init
+
+coro.init:                                        ; preds = %coro.alloc, %entry
+  %4 = phi i8* [ null, %entry ], [ %call, %coro.alloc ]
+  %5 = call i8* @llvm.coro.begin(token %1, i8* %4) #9
+  %a1153.0.a1153.sub.sroa_idx = getelementptr inbounds [24 x i8], [24 x i8]* %a1153, i64 0, i64 0
+  call void @llvm.lifetime.start.p0i8(i64 24, i8* %a1153.0.a1153.sub.sroa_idx)
+  %6 = bitcast %struct.A* %a1 to i8*
+  call void @llvm.memcpy.p0i8.p0i8.i64(i8* noundef nonnull align 8 dereferenceable(24) %a1153.sub, i8* noundef nonnull align 8 dereferenceable(24) %6, i64 24, i1 false)
+  call void @llvm.lifetime.start.p0i8(i64 1, i8* nonnull %0) #2
+  %call2 = call %promise_type* @_ZN4task12promise_type17get_return_objectEv(%promise_type* nonnull dereferenceable(1) %__promise)
+  call void @initial_suspend(%promise_type* nonnull dereferenceable(1) %__promise)
+  %7 = call token @llvm.coro.save(i8* null)
+  call fastcc void @_ZNSt12experimental13coroutines_v116coroutine_handleIN4task12promise_typeEE12from_addressEPv(i8* %5) #2
+  %8 = call i8 @llvm.coro.suspend(token %7, i1 false)
+  switch i8 %8, label %coro.ret [
+    i8 0, label %init.ready
+    i8 1, label %cleanup33
+  ]
+
+init.ready:                                       ; preds = %coro.init
+  %9 = bitcast %struct.A* %a2 to i8*
+  call void @llvm.lifetime.start.p0i8(i64 24, i8* nonnull %9) #2
+  call void @llvm.memcpy.p0i8.p0i8.i64(i8* noundef nonnull align 8 dereferenceable(24) %9, i8* noundef nonnull align 8 dereferenceable(24) %a1153.sub, i64 24, i1 false)
+  call void @llvm.lifetime.end.p0i8(i64 24, i8* nonnull %9) #2
+  call void @_ZN4task12promise_type13final_suspendEv(%promise_type* nonnull dereferenceable(1) %__promise) #2
+  %10 = call token @llvm.coro.save(i8* null)
+  call fastcc void @_ZNSt12experimental13coroutines_v116coroutine_handleIN4task12promise_typeEE12from_addressEPv(i8* %5) #2
+  %11 = call i8 @llvm.coro.suspend(token %10, i1 true) #9
+  %switch = icmp ult i8 %11, 2
+  br i1 %switch, label %cleanup33, label %coro.ret
+
+cleanup33:                                        ; preds = %init.ready, %coro.init
+  call void @llvm.lifetime.end.p0i8(i64 1, i8* nonnull %0) #2
+  %a1153.0.a1153.sub.sroa_idx58 = getelementptr inbounds [24 x i8], [24 x i8]* %a1153, i64 0, i64 0
+  call void @llvm.lifetime.end.p0i8(i64 24, i8* %a1153.0.a1153.sub.sroa_idx58)
+  %12 = call i8* @llvm.coro.free(token %1, i8* %5)
+  %.not = icmp eq i8* %12, null
+  br i1 %.not, label %coro.ret, label %coro.free
+
+coro.free:                                        ; preds = %cleanup33
+  call void @_ZdlPv(i8* nonnull %12) #2
+  br label %coro.ret
+
+coro.ret:                                         ; preds = %coro.free, %cleanup33, %init.ready, %coro.init
+  %13 = call i1 @llvm.coro.end(i8* null, i1 false) #9
+  ret %promise_type* %call2
+}
+
+; CHECK-LABEL: define %promise_type* @foo(
+; CHECK:         %[[A1:.*]] = bitcast %struct.A* %a1 to i8*
+; CHECK:         call void @llvm.memcpy.p0i8.p0i8.i64(i8* noundef nonnull align 8 dereferenceable(24) %a1153.sub, i8* noundef nonnull align 8 dereferenceable(24) %[[A1]], i64 24, i1 false)
+; CHECK:         %[[A2:.*]] = bitcast %struct.A* %a2 to i8*
+; CHECK:         call void @llvm.memcpy.p0i8.p0i8.i64(i8* noundef nonnull align 8 dereferenceable(24) %[[A2]], i8* noundef nonnull align 8 dereferenceable(24) %a1153.sub, i64 24, i1 false)
+
+; Function Attrs: argmemonly nounwind readonly
+declare token @llvm.coro.id(i32, i8* readnone, i8* nocapture readonly, i8*) #1
+
+; Function Attrs: nounwind
+declare i1 @llvm.coro.alloc(token) #2
+
+; Function Attrs: nobuiltin nofree allocsize(0)
+declare nonnull i8* @_Znwm(i64) local_unnamed_addr #3
+
+; Function Attrs: nounwind readnone
+declare i64 @llvm.coro.size.i64() #4
+
+; Function Attrs: nounwind
+declare i8* @llvm.coro.begin(token, i8* writeonly) #2
+
+; Function Attrs: argmemonly nofree nosync nounwind willreturn
+declare void @llvm.lifetime.start.p0i8(i64 immarg, i8* nocapture) #5
+
+; Function Attrs: argmemonly nofree nosync nounwind willreturn
+declare void @llvm.memcpy.p0i8.p0i8.i64(i8* noalias nocapture writeonly, i8* noalias nocapture readonly, i64, i1 immarg) #5
+
+; Function Attrs: noinline nounwind ssp uwtable willreturn mustprogress
+declare %promise_type* @_ZN4task12promise_type17get_return_objectEv(%promise_type* nonnull dereferenceable(1)) local_unnamed_addr #6 align 2
+
+; Function Attrs: noinline nounwind ssp uwtable willreturn mustprogress
+declare void @initial_suspend(%promise_type* nonnull dereferenceable(1)) local_unnamed_addr #6 align 2
+
+; Function Attrs: nounwind
+declare token @llvm.coro.save(i8*) #2
+
+; Function Attrs: noinline nounwind ssp uwtable willreturn mustprogress
+declare hidden fastcc void @_ZNSt12experimental13coroutines_v116coroutine_handleIN4task12promise_typeEE12from_addressEPv(i8*) unnamed_addr #6 align 2
+
+; Function Attrs: argmemonly nofree nosync nounwind willreturn
+declare void @llvm.lifetime.end.p0i8(i64 immarg, i8* nocapture) #5
+
+; Function Attrs: nounwind
+declare i8 @llvm.coro.suspend(token, i1) #2
+
+; Function Attrs: noinline nounwind ssp uwtable willreturn mustprogress
+declare void @_ZN4task12promise_type13final_suspendEv(%promise_type* nonnull dereferenceable(1)) local_unnamed_addr #6 align 2
+
+; Function Attrs: nounwind
+declare i1 @llvm.coro.end(i8*, i1) #2
+
+; Function Attrs: nobuiltin nounwind
+declare void @_ZdlPv(i8*) local_unnamed_addr #7
+
+; Function Attrs: argmemonly nounwind readonly
+declare i8* @llvm.coro.free(token, i8* nocapture readonly) #1
+
+attributes #0 = { noinline ssp uwtable mustprogress "coroutine.presplit"="1" "frame-pointer"="all" "no-trapping-math"="true" "stack-protector-buffer-size"="8" "target-cpu"="penryn" "target-features"="+cx16,+cx8,+fxsr,+mmx,+sahf,+sse,+sse2,+sse3,+sse4.1,+ssse3,+x87" "tune-cpu"="generic" }
+attributes #1 = { argmemonly nounwind readonly }
+attributes #2 = { nounwind }
+attributes #3 = { nobuiltin nofree allocsize(0) "frame-pointer"="all" "no-trapping-math"="true" "stack-protector-buffer-size"="8" "target-cpu"="penryn" "target-features"="+cx16,+cx8,+fxsr,+mmx,+sahf,+sse,+sse2,+sse3,+sse4.1,+ssse3,+x87" "tune-cpu"="generic" }
+attributes #4 = { nounwind readnone }
+attributes #5 = { argmemonly nofree nosync nounwind willreturn }
+attributes #6 = { noinline nounwind ssp uwtable willreturn mustprogress "frame-pointer"="all" "no-trapping-math"="true" "stack-protector-buffer-size"="8" "target-cpu"="penryn" "target-features"="+cx16,+cx8,+fxsr,+mmx,+sahf,+sse,+sse2,+sse3,+sse4.1,+ssse3,+x87" "tune-cpu"="generic" }
+attributes #7 = { nobuiltin nounwind "frame-pointer"="all" "no-trapping-math"="true" "stack-protector-buffer-size"="8" "target-cpu"="penryn" "target-features"="+cx16,+cx8,+fxsr,+mmx,+sahf,+sse,+sse2,+sse3,+sse4.1,+ssse3,+x87" "tune-cpu"="generic" }
+attributes #8 = { allocsize(0) }
+attributes #9 = { noduplicate }
+