Index: llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
===================================================================
--- llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
+++ llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
@@ -373,22 +373,14 @@
   if (!Later.Size.isPrecise() || !Earlier.Size.isPrecise()) {
     // In case no constant size is known, try to an IR values for the number
     // of bytes written and check if they match.
-    auto GetSizeFromInstr = [](const Instruction *I) -> Value * {
-      if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
-        switch (II->getIntrinsicID()) {
-        default:
-          return nullptr;
-        case Intrinsic::memcpy:
-        case Intrinsic::memset:
-          return II->getArgOperand(2);
-        }
-      }
-      return nullptr;
-    };
-    Value *LaterV = GetSizeFromInstr(LaterI);
-    Value *EarlierV = GetSizeFromInstr(EarlierI);
-    if (LaterV && LaterV == EarlierV && AA.isMustAlias(Earlier, Later))
-      return OW_Complete;
+    const auto *LaterMemI = dyn_cast<MemIntrinsic>(LaterI);
+    const auto *EarlierMemI = dyn_cast<MemIntrinsic>(EarlierI);
+    if (LaterMemI && EarlierMemI) {
+      const Value *LaterV = LaterMemI->getLength();
+      const Value *EarlierV = EarlierMemI->getLength();
+      if (LaterV == EarlierV && AA.isMustAlias(Earlier, Later))
+        return OW_Complete;
+    }
 
     // Masked stores have imprecise locations, but we can reason about them
     // to some extent.
Index: llvm/test/Transforms/DeadStoreElimination/memory-intrinsics-sizes.ll
===================================================================
--- llvm/test/Transforms/DeadStoreElimination/memory-intrinsics-sizes.ll
+++ llvm/test/Transforms/DeadStoreElimination/memory-intrinsics-sizes.ll
@@ -199,5 +199,135 @@
   ret void
 }
 
+define void @memmove_equal_size_values(i8* noalias %src, i8* noalias %dst, i64 %len) {
+; CHECK-LABEL: @memmove_equal_size_values(
+; CHECK-NEXT:    call void @llvm.memmove.p0i8.p0i8.i64(i8* [[DST:%.*]], i8* [[SRC:%.*]], i64 [[LEN:%.*]], i1 false)
+; CHECK-NEXT:    ret void
+;
+  call void @llvm.memmove.p0i8.p0i8.i64(i8* %dst, i8* %src, i64 %len, i1 false)
+  call void @llvm.memmove.p0i8.p0i8.i64(i8* %dst, i8* %src, i64 %len, i1 false)
+  ret void
+}
+
+define void @memmove_different_size_values_1(i8* noalias %src, i8* noalias %dst, i64 %len.1, i64 %len.2) {
+; CHECK-LABEL: @memmove_different_size_values_1(
+; CHECK-NEXT:    call void @llvm.memmove.p0i8.p0i8.i64(i8* [[DST:%.*]], i8* [[SRC:%.*]], i64 [[LEN_1:%.*]], i1 false)
+; CHECK-NEXT:    call void @llvm.memmove.p0i8.p0i8.i64(i8* [[DST]], i8* [[SRC]], i64 [[LEN_2:%.*]], i1 false)
+; CHECK-NEXT:    ret void
+;
+  call void @llvm.memmove.p0i8.p0i8.i64(i8* %dst, i8* %src, i64 %len.1, i1 false)
+  call void @llvm.memmove.p0i8.p0i8.i64(i8* %dst, i8* %src, i64 %len.2, i1 false)
+  ret void
+}
+
+define void @memmove_different_size_values_2(i8* noalias %src, i8* noalias %dst, i64 %len) {
+; CHECK-LABEL: @memmove_different_size_values_2(
+; CHECK-NEXT:    call void @llvm.memmove.p0i8.p0i8.i64(i8* [[DST:%.*]], i8* [[SRC:%.*]], i64 [[LEN:%.*]], i1 false)
+; CHECK-NEXT:    call void @llvm.memmove.p0i8.p0i8.i64(i8* [[DST]], i8* [[SRC]], i64 100, i1 false)
+; CHECK-NEXT:    ret void
+;
+  call void @llvm.memmove.p0i8.p0i8.i64(i8* %dst, i8* %src, i64 %len, i1 false)
+  call void @llvm.memmove.p0i8.p0i8.i64(i8* %dst, i8* %src, i64 100, i1 false)
+  ret void
+}
+
+define void @memmove_different_size_values_3(i8* noalias %src, i8* noalias %dst, i64 %len) {
+; CHECK-LABEL: @memmove_different_size_values_3(
+; CHECK-NEXT:    call void @llvm.memmove.p0i8.p0i8.i64(i8* [[DST:%.*]], i8* [[SRC:%.*]], i64 100, i1 false)
+; CHECK-NEXT:    call void @llvm.memmove.p0i8.p0i8.i64(i8* [[DST]], i8* [[SRC]], i64 [[LEN:%.*]], i1 false)
+; CHECK-NEXT:    ret void
+;
+  call void @llvm.memmove.p0i8.p0i8.i64(i8* %dst, i8* %src, i64 100, i1 false)
+  call void @llvm.memmove.p0i8.p0i8.i64(i8* %dst, i8* %src, i64 %len, i1 false)
+  ret void
+}
+
+define void @memset_and_memmove_equal_size_values(i8* noalias %src, i8* noalias %dst, i64 %len) {
+; CHECK-LABEL: @memset_and_memmove_equal_size_values(
+; CHECK-NEXT:    call void @llvm.memmove.p0i8.p0i8.i64(i8* [[DST:%.*]], i8* [[SRC:%.*]], i64 [[LEN:%.*]], i1 false)
+; CHECK-NEXT:    ret void
+;
+  call void @llvm.memset.p0i8.i64(i8* align 1 %dst, i8 0, i64 %len, i1 false)
+  call void @llvm.memmove.p0i8.p0i8.i64(i8* %dst, i8* %src, i64 %len, i1 false)
+  ret void
+}
+
+define void @memset_and_memmove_different_size_values_1(i8* noalias %src, i8* noalias %dst, i64 %len.1, i64 %len.2) {
+; CHECK-LABEL: @memset_and_memmove_different_size_values_1(
+; CHECK-NEXT:    call void @llvm.memset.p0i8.i64(i8* align 1 [[DST:%.*]], i8 0, i64 [[LEN_1:%.*]], i1 false)
+; CHECK-NEXT:    call void @llvm.memmove.p0i8.p0i8.i64(i8* [[DST]], i8* [[SRC:%.*]], i64 [[LEN_2:%.*]], i1 false)
+; CHECK-NEXT:    ret void
+;
+  call void @llvm.memset.p0i8.i64(i8* align 1 %dst, i8 0, i64 %len.1, i1 false)
+  call void @llvm.memmove.p0i8.p0i8.i64(i8* %dst, i8* %src, i64 %len.2, i1 false)
+  ret void
+}
+
+define void @memset_and_memmove_different_size_values_2(i8* noalias %src, i8* noalias %dst, i64 %len.1) {
+; CHECK-LABEL: @memset_and_memmove_different_size_values_2(
+; CHECK-NEXT:    call void @llvm.memset.p0i8.i64(i8* align 1 [[DST:%.*]], i8 0, i64 [[LEN_1:%.*]], i1 false)
+; CHECK-NEXT:    call void @llvm.memmove.p0i8.p0i8.i64(i8* [[DST]], i8* [[SRC:%.*]], i64 100, i1 false)
+; CHECK-NEXT:    ret void
+;
+  call void @llvm.memset.p0i8.i64(i8* align 1 %dst, i8 0, i64 %len.1, i1 false)
+  call void @llvm.memmove.p0i8.p0i8.i64(i8* %dst, i8* %src, i64 100, i1 false)
+  ret void
+}
+
+define void @memset_and_memmove_different_size_values_3(i8* noalias %src, i8* noalias %dst, i64 %len.1) {
+; CHECK-LABEL: @memset_and_memmove_different_size_values_3(
+; CHECK-NEXT:    call void @llvm.memset.p0i8.i64(i8* align 1 [[DST:%.*]], i8 0, i64 100, i1 false)
+; CHECK-NEXT:    call void @llvm.memmove.p0i8.p0i8.i64(i8* [[DST]], i8* [[SRC:%.*]], i64 [[LEN_1:%.*]], i1 false)
+; CHECK-NEXT:    ret void
+;
+  call void @llvm.memset.p0i8.i64(i8* align 1 %dst, i8 0, i64 100, i1 false)
+  call void @llvm.memmove.p0i8.p0i8.i64(i8* %dst, i8* %src, i64 %len.1, i1 false)
+  ret void
+}
+
+define void @memmove_and_memset_equal_size_values(i8* noalias %src, i8* noalias %dst, i64 %len) {
+; CHECK-LABEL: @memmove_and_memset_equal_size_values(
+; CHECK-NEXT:    call void @llvm.memset.p0i8.i64(i8* align 1 [[DST:%.*]], i8 0, i64 [[LEN:%.*]], i1 false)
+; CHECK-NEXT:    ret void
+;
+  call void @llvm.memmove.p0i8.p0i8.i64(i8* %dst, i8* %src, i64 %len, i1 false)
+  call void @llvm.memset.p0i8.i64(i8* align 1 %dst, i8 0, i64 %len, i1 false)
+  ret void
+}
+
+define void @memmove_and_memset_different_size_values_1(i8* noalias %src, i8* noalias %dst, i64 %len.1, i64 %len.2) {
+; CHECK-LABEL: @memmove_and_memset_different_size_values_1(
+; CHECK-NEXT:    call void @llvm.memmove.p0i8.p0i8.i64(i8* [[DST:%.*]], i8* [[SRC:%.*]], i64 [[LEN_1:%.*]], i1 false)
+; CHECK-NEXT:    call void @llvm.memset.p0i8.i64(i8* align 1 [[DST]], i8 0, i64 [[LEN_2:%.*]], i1 false)
+; CHECK-NEXT:    ret void
+;
+  call void @llvm.memmove.p0i8.p0i8.i64(i8* %dst, i8* %src, i64 %len.1, i1 false)
+  call void @llvm.memset.p0i8.i64(i8* align 1 %dst, i8 0, i64 %len.2, i1 false)
+  ret void
+}
+
+define void @memmove_and_memset_different_size_values_2(i8* noalias %src, i8* noalias %dst, i64 %len.1) {
+; CHECK-LABEL: @memmove_and_memset_different_size_values_2(
+; CHECK-NEXT:    call void @llvm.memmove.p0i8.p0i8.i64(i8* [[DST:%.*]], i8* [[SRC:%.*]], i64 [[LEN_1:%.*]], i1 false)
+; CHECK-NEXT:    call void @llvm.memset.p0i8.i64(i8* align 1 [[DST]], i8 0, i64 100, i1 false)
+; CHECK-NEXT:    ret void
+;
+  call void @llvm.memmove.p0i8.p0i8.i64(i8* %dst, i8* %src, i64 %len.1, i1 false)
+  call void @llvm.memset.p0i8.i64(i8* align 1 %dst, i8 0, i64 100, i1 false)
+  ret void
+}
+
+define void @memmove_and_memset_different_size_values_3(i8* noalias %src, i8* noalias %dst, i64 %len.1) {
+; CHECK-LABEL: @memmove_and_memset_different_size_values_3(
+; CHECK-NEXT:    call void @llvm.memmove.p0i8.p0i8.i64(i8* [[DST:%.*]], i8* [[SRC:%.*]], i64 100, i1 false)
+; CHECK-NEXT:    call void @llvm.memset.p0i8.i64(i8* align 1 [[DST]], i8 0, i64 [[LEN_1:%.*]], i1 false)
+; CHECK-NEXT:    ret void
+;
+  call void @llvm.memmove.p0i8.p0i8.i64(i8* %dst, i8* %src, i64 100, i1 false)
+  call void @llvm.memset.p0i8.i64(i8* align 1 %dst, i8 0, i64 %len.1, i1 false)
+  ret void
+}
+
 declare void @llvm.memset.p0i8.i64(i8* nocapture writeonly, i8, i64, i1 immarg)
 declare void @llvm.memcpy.p0i8.p0i8.i64(i8* nocapture, i8* nocapture, i64, i1)
+declare void @llvm.memmove.p0i8.p0i8.i64(i8* nocapture, i8* nocapture, i64, i1)