https://github.com/dmpolukhin updated
https://github.com/llvm/llvm-project/pull/143168
>From cc00e6ad5192bbd6059542196fac286e7182d153 Mon Sep 17 00:00:00 2001
From: Dmitry Polukhin <dmitry.poluk...@gmail.com>
Date: Fri, 23 May 2025 14:22:21 -0700
Subject: [PATCH 1/2] [C++20][Modules] Fix false compilation error with
constexpr
Use cannonical field decl when evaluating constexpr to avoid resetting
computed union value due to using different instances of merged decls.
---
clang/lib/AST/ExprConstant.cpp | 2 +-
.../constexpr-initialization-failure.cpp | 44 +++++++++++++++++++
2 files changed, 45 insertions(+), 1 deletion(-)
create mode 100644 clang/test/Modules/constexpr-initialization-failure.cpp
diff --git a/clang/lib/AST/ExprConstant.cpp b/clang/lib/AST/ExprConstant.cpp
index fa4e10e84de05..6843a37337861 100644
--- a/clang/lib/AST/ExprConstant.cpp
+++ b/clang/lib/AST/ExprConstant.cpp
@@ -6836,7 +6836,7 @@ static bool HandleConstructorCall(const Expr *E, const
LValue &This,
// and make sure we've initialized every step along it.
auto IndirectFieldChain = IFD->chain();
for (auto *C : IndirectFieldChain) {
- FD = cast<FieldDecl>(C);
+ FD = cast<FieldDecl>(C)->getCanonicalDecl();
CXXRecordDecl *CD = cast<CXXRecordDecl>(FD->getParent());
// Switch the union field if it differs. This happens if we had
// preceding zero-initialization, and we're now initializing a union
diff --git a/clang/test/Modules/constexpr-initialization-failure.cpp
b/clang/test/Modules/constexpr-initialization-failure.cpp
new file mode 100644
index 0000000000000..8ff20f2fc8ac6
--- /dev/null
+++ b/clang/test/Modules/constexpr-initialization-failure.cpp
@@ -0,0 +1,44 @@
+// RUN: rm -fR %t
+// RUN: split-file %s %t
+// RUN: cd %t
+// RUN: %clang_cc1 -verify -w -std=c++20 -fmodule-name=h1.h -emit-header-unit
-xc++-user-header h1.h -o h1.pcm
+// RUN: %clang_cc1 -verify -w -std=c++20 -fmodule-map-file=module.modulemap
-fmodule-file=h1.h=h1.pcm main.cpp -o main.o
+
+//--- module.modulemap
+module "h1.h" {
+ header "h1.h"
+ export *
+}
+
+//--- h0.h
+// expected-no-diagnostics
+#pragma once
+
+template <typename T> struct A {
+ union {
+ struct {
+ T x, y, z;
+ };
+ };
+ constexpr A(T, T, T) : x(), y(), z() {}
+};
+typedef A<float> packed_vec3;
+
+//--- h1.h
+// expected-no-diagnostics
+#pragma once
+
+#include "h0.h"
+
+constexpr packed_vec3 kMessThingsUp = packed_vec3(5.0f, 5.0f, 5.0f);
+
+//--- main.cpp
+// expected-no-diagnostics
+#include "h0.h"
+
+static_assert(sizeof(packed_vec3) == sizeof(float) * 3);
+static_assert(alignof(packed_vec3) == sizeof(float));
+
+import "h1.h";
+
+constexpr packed_vec3 kDefaultHalfExtents = packed_vec3(5.0f, 5.0f, 5.0f);
>From 15aaef040f615a0f2f5d90d61ee41b13a775012a Mon Sep 17 00:00:00 2001
From: Dmitry Polukhin <dmitry.poluk...@gmail.com>
Date: Mon, 9 Jun 2025 02:53:14 -0700
Subject: [PATCH 2/2] Use declaresSameEntity, added release notes.
---
clang/docs/ReleaseNotes.rst | 1 +
clang/lib/AST/ExprConstant.cpp | 5 +++--
2 files changed, 4 insertions(+), 2 deletions(-)
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 322686fce0b04..d62ecb438ae68 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -689,6 +689,7 @@ Bug Fixes in This Version
- Fixed type mismatch error when 'builtin-elementwise-math' arguments have
different qualifiers, this should be well-formed. (#GH141397)
- Constant evaluation now correctly runs the destructor of a variable declared
in
the second clause of a C-style ``for`` loop. (#GH139818)
+- Fixed a bug with constexpr evaluation for structs containing unions in case
of C++ modules. (#GH143168)
Bug Fixes to Compiler Builtins
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
diff --git a/clang/lib/AST/ExprConstant.cpp b/clang/lib/AST/ExprConstant.cpp
index 6843a37337861..27ea55e981446 100644
--- a/clang/lib/AST/ExprConstant.cpp
+++ b/clang/lib/AST/ExprConstant.cpp
@@ -6836,7 +6836,7 @@ static bool HandleConstructorCall(const Expr *E, const
LValue &This,
// and make sure we've initialized every step along it.
auto IndirectFieldChain = IFD->chain();
for (auto *C : IndirectFieldChain) {
- FD = cast<FieldDecl>(C)->getCanonicalDecl();
+ FD = cast<FieldDecl>(C);
CXXRecordDecl *CD = cast<CXXRecordDecl>(FD->getParent());
// Switch the union field if it differs. This happens if we had
// preceding zero-initialization, and we're now initializing a union
@@ -6844,7 +6844,8 @@ static bool HandleConstructorCall(const Expr *E, const
LValue &This,
// FIXME: In this case, the values of the other subobjects are
// specified, since zero-initialization sets all padding bits to zero.
if (!Value->hasValue() ||
- (Value->isUnion() && Value->getUnionField() != FD)) {
+ (Value->isUnion() &&
+ !declaresSameEntity(Value->getUnionField(), FD))) {
if (CD->isUnion())
*Value = APValue(FD);
else
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