https://github.com/llvmbot created
https://github.com/llvm/llvm-project/pull/152149
Backport 30a5d56
Requested by: @AaronBallman
>From 7fa2cd5f8dc6b619895289e7e53dff0974c19fd5 Mon Sep 17 00:00:00 2001
From: Aaron Ballman <aa...@aaronballman.com>
Date: Tue, 29 Jul 2025 14:09:02 -0400
Subject: [PATCH] [C23] AST equivalence of attributes (#151196)
Implicitly declared types (like __NSConstantString_tag, etc) will be
declared with visibility attributes. This causes problems when merging
ASTs because we currently reject declaration merging for declarations
with attributes.
This relaxes that restriction somewhat; implicit declarations can now
have attributes when merging; we assume that if the compiler generated
it, it's fine.
(cherry picked from commit 30a5d569b2102bba1cfb5d253bd73ec2ebce7ee0)
---
clang/lib/AST/ASTStructuralEquivalence.cpp | 6 ++++--
clang/test/ASTMerge/enum/test2.c | 6 ++----
2 files changed, 6 insertions(+), 6 deletions(-)
diff --git a/clang/lib/AST/ASTStructuralEquivalence.cpp
b/clang/lib/AST/ASTStructuralEquivalence.cpp
index d46f60facc8d6..25d19a3dcd486 100644
--- a/clang/lib/AST/ASTStructuralEquivalence.cpp
+++ b/clang/lib/AST/ASTStructuralEquivalence.cpp
@@ -456,7 +456,9 @@
CheckStructurallyEquivalentAttributes(StructuralEquivalenceContext &Context,
const Decl *D1, const Decl *D2,
const Decl *PrimaryDecl = nullptr) {
// If either declaration has an attribute on it, we treat the declarations
- // as not being structurally equivalent.
+ // as not being structurally equivalent unless both declarations are implicit
+ // (ones generated by the compiler like __NSConstantString_tag).
+ //
// FIXME: this should be handled on a case-by-case basis via tablegen in
// Attr.td. There are multiple cases to consider: one declaration with the
// attribute, another without it; different attribute syntax|spellings for
@@ -468,7 +470,7 @@
CheckStructurallyEquivalentAttributes(StructuralEquivalenceContext &Context,
D1Attr = *D1->getAttrs().begin();
if (D2->hasAttrs())
D2Attr = *D2->getAttrs().begin();
- if (D1Attr || D2Attr) {
+ if ((D1Attr || D2Attr) && !D1->isImplicit() && !D2->isImplicit()) {
const auto *DiagnoseDecl = cast<TypeDecl>(PrimaryDecl ? PrimaryDecl : D2);
Context.Diag2(DiagnoseDecl->getLocation(),
diag::warn_odr_tag_type_with_attributes)
diff --git a/clang/test/ASTMerge/enum/test2.c b/clang/test/ASTMerge/enum/test2.c
index 2955d8fe50b2e..bdd8b13ee4c21 100644
--- a/clang/test/ASTMerge/enum/test2.c
+++ b/clang/test/ASTMerge/enum/test2.c
@@ -1,9 +1,7 @@
// RUN: %clang_cc1 -std=c23 -emit-pch -o %t.1.ast %S/Inputs/enum3.c
// RUN: %clang_cc1 -std=c23 -emit-pch -o %t.2.ast %S/Inputs/enum4.c
-// RUN: not %clang_cc1 -std=c23 -ast-merge %t.1.ast -ast-merge %t.2.ast
-fsyntax-only %s 2>&1 | FileCheck %s
+// RUN: %clang_cc1 -std=c23 -ast-merge %t.1.ast -ast-merge %t.2.ast
-fsyntax-only %s 2>&1 | FileCheck %s
-// FIXME: this error should not happen!
-// CHECK: error: type 'struct __NSConstantString_tag' has an attribute which
currently causes the types to be treated as though they are incompatible
// CHECK: enum3.c:2:6: warning: type 'enum E1' has incompatible definitions in
different translation units
// CHECK: enum4.c:2:6: note: enumeration 'E1' missing fixed underlying type
here
// CHECK: enum3.c:2:6: note: enumeration 'E1' has fixed underlying type here
@@ -12,5 +10,5 @@
// CHECK: enum3.c:6:6: note: enumeration 'E2' missing fixed underlying type
here
// CHECK: enum3.c:11:6: warning: type 'enum E3' has incompatible definitions
in different translation units
// CHECK: enum3.c:11:6: note: enumeration 'E3' declared with incompatible
fixed underlying types ('long' vs. 'short')
-// CHECK: 3 warnings and 1 error generated
+// CHECK: 3 warnings generated
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