[clang] 01d8e09 - [clang][CodeGen] Fix wrong memcpy size of no_unique_address in FieldMemcpyizer

[Fangrui Song via cfe-commits]

Author: Senran Zhang
Date: 2019-11-25T18:15:34-08:00
New Revision: 01d8e09fdba0c9d3fe316a86e5ce4481e6ed71d1

URL: https://github.com/llvm/llvm-project/commit/01d8e09fdba0c9d3fe316a86e5ce4481e6ed71d1
DIFF: https://github.com/llvm/llvm-project/commit/01d8e09fdba0c9d3fe316a86e5ce4481e6ed71d1.diff

LOG: [clang][CodeGen] Fix wrong memcpy size of no_unique_address in FieldMemcpyizer

When generating ctor, FieldMemcpyizer wrongly treated zero-sized class members
as what should be copied, and generated wrong memcpy size under some special
circumstances. This patch tries to fix it.

Reviewed By: MaskRay, rjmccall

Differential Revision: https://reviews.llvm.org/D70671

Added: 
    clang/test/CodeGenCXX/no-unique-address-2.cpp

Modified: 
    clang/lib/CodeGen/CGClass.cpp

Removed: 
    


################################################################################
diff  --git a/clang/lib/CodeGen/CGClass.cpp b/clang/lib/CodeGen/CGClass.cpp
index 04ef912b18bd..d07b1c665cc4 100644
--- a/clang/lib/CodeGen/CGClass.cpp
+++ b/clang/lib/CodeGen/CGClass.cpp
@@ -914,6 +914,8 @@ namespace {
     }
 
     void addMemcpyableField(FieldDecl *F) {
+      if (F->isZeroSize(CGF.getContext()))
+        return;
       if (!FirstField)
         addInitialField(F);
       else

diff  --git a/clang/test/CodeGenCXX/no-unique-address-2.cpp b/clang/test/CodeGenCXX/no-unique-address-2.cpp
new file mode 100644
index 000000000000..aa0c67758a19
--- /dev/null
+++ b/clang/test/CodeGenCXX/no-unique-address-2.cpp
@@ -0,0 +1,25 @@
+// RUN: %clang_cc1 -std=c++2a %s -emit-llvm -o - -triple x86_64-linux-gnu | FileCheck %s
+
+struct TriviallyCopyable {};
+
+struct NonTriviallyCopyable {
+  NonTriviallyCopyable() = default;
+  NonTriviallyCopyable(const NonTriviallyCopyable&) = default;
+  NonTriviallyCopyable(NonTriviallyCopyable &&) {}
+};
+
+struct Foo {
+  int i;
+  [[no_unique_address]] TriviallyCopyable m;
+  [[no_unique_address]] NonTriviallyCopyable n;
+};
+
+void call() {
+  Foo foo;
+  Foo foo2(static_cast<Foo&&>(foo));
+}
+
+// The memcpy call should copy exact 4 bytes for member 'int i'
+// CHECK: define {{.*}} void @_ZN3FooC2EOS_
+// CHECK:  call void @llvm.memcpy.p0i8.p0i8.i64(i8* {{.+}}, i8* {{.+}}, i64 4, i1 false)
+// CHECK:  call void @_ZN20NonTriviallyCopyableC2EOS_