From 62dc98295c89c2553910c228dd55a47ba8b403b5 Mon Sep 17 00:00:00 2001
From: Arnold Schwaighofer <aschwaighofer@apple.com>
Date: Mon, 6 May 2024 09:37:48 -0700
Subject: [PATCH] IRGen: memcpy instead of the outlined copy with take

The outlined copy with take would instantiate metadata to call the value
witness table's copy function.

rdar://126751753
---
 lib/IRGen/GenEnum.cpp             |  5 ++++-
 test/IRGen/copy_addr_lowering.sil | 24 ++++++++++++++++++++++++
 2 files changed, 28 insertions(+), 1 deletion(-)
 create mode 100644 test/IRGen/copy_addr_lowering.sil

diff --git a/lib/IRGen/GenEnum.cpp b/lib/IRGen/GenEnum.cpp
index f8e1c1de0a425..87e1eec265635 100644
--- a/lib/IRGen/GenEnum.cpp
+++ b/lib/IRGen/GenEnum.cpp
@@ -3283,7 +3283,10 @@ namespace {
                             bool zeroizeIfSensitive) const override {
       if (!ElementsAreABIAccessible) {
         emitInitializeWithTakeCall(IGF, T, dest, src);
-      } else if (isOutlined || T.hasParameterizedExistential()) {
+      } else if (isOutlined || T.hasParameterizedExistential() ||
+                 (getPayloadTypeInfo().isFixedSize() && // can use memcpy
+                  getPayloadTypeInfo().
+                  isBitwiseTakable(ResilienceExpansion::Maximal))) {
         emitIndirectInitialize(IGF, dest, src, T, IsTake, isOutlined);
       } else {
         callOutlinedCopy(IGF, dest, src, T, IsInitialization, IsTake);
diff --git a/test/IRGen/copy_addr_lowering.sil b/test/IRGen/copy_addr_lowering.sil
new file mode 100644
index 0000000000000..63d3a4771df66
--- /dev/null
+++ b/test/IRGen/copy_addr_lowering.sil
@@ -0,0 +1,24 @@
+// RUN: %target-swift-frontend -module-name A -Xllvm -sil-disable-pass=LowerAggregateInstr -emit-ir %s | %FileCheck %s
+sil_stage lowered
+
+import Builtin
+import Swift
+import SwiftShims
+
+struct S {
+    var s: ArraySlice<UInt8>
+    var i: ArraySlice<UInt8>.Index
+}
+
+
+// CHECK: define{{.*}} swiftcc void @copy_test(
+// CHECK-NOT:  call ptr @"$s1A1SVSgWOb"(
+// CHECK: memcpy
+// CHECK:  ret void
+
+sil @copy_test : $@convention(thin) (@in Optional<S>) -> @out Optional<S> {
+bb0(%0 : $*Optional<S>, %1 : $*Optional<S>):
+  copy_addr [take] %1 to [init] %0 : $*Optional<S>
+  %5 = tuple ()
+  return %5 : $()
+}