[llvm-branch-commits] [clang] [llvm] [backport] [C++20] [Modules] Backport the ability to skip ODR checks in GMF (PR #80249)
Chuanqi Xu via llvm-branch-commits
llvm-branch-commits at lists.llvm.org
Wed Jan 31 22:56:14 PST 2024
https://github.com/ChuanqiXu9 updated https://github.com/llvm/llvm-project/pull/80249
>From 85dc0ff79515cc439cc3e0d8c991709ad789a50b Mon Sep 17 00:00:00 2001
From: Chuanqi Xu <yedeng.yd at linux.alibaba.com>
Date: Mon, 29 Jan 2024 11:42:08 +0800
Subject: [PATCH 1/3] [C++20] [Modules] Don't perform ODR checks in GMF
Close https://github.com/llvm/llvm-project/issues/79240.
See the linked issue for details. Given the frequency of issue reporting
about false positive ODR checks (I received private issue reports too),
I'd like to backport this to 18.x too.
---
clang/docs/ReleaseNotes.rst | 5 ++
clang/include/clang/Serialization/ASTReader.h | 4 ++
clang/lib/Serialization/ASTReader.cpp | 3 ++
clang/lib/Serialization/ASTReaderDecl.cpp | 37 +++++++++----
clang/lib/Serialization/ASTWriter.cpp | 8 ++-
clang/lib/Serialization/ASTWriterDecl.cpp | 13 +++--
clang/test/Modules/concept.cppm | 14 ++---
clang/test/Modules/no-eager-load.cppm | 53 -------------------
clang/test/Modules/polluted-operator.cppm | 8 ++-
clang/test/Modules/pr76638.cppm | 6 +--
10 files changed, 68 insertions(+), 83 deletions(-)
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 060bc7669b72a..e8dfdfa63717c 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -188,6 +188,11 @@ C++20 Feature Support
This feature is still experimental. Accordingly, ``__cpp_nontype_template_args`` was not updated.
However, its support can be tested with ``__has_extension(cxx_generalized_nttp)``.
+- Clang won't perform ODR checks for decls in the global module fragment any
+ more to ease the implementation and improve the user's using experience.
+ This follows the MSVC's behavior.
+ (`#79240 <https://github.com/llvm/llvm-project/issues/79240>`_).
+
C++23 Feature Support
^^^^^^^^^^^^^^^^^^^^^
- Implemented `P0847R7: Deducing this <https://wg21.link/P0847R7>`_. Some related core issues were also
diff --git a/clang/include/clang/Serialization/ASTReader.h b/clang/include/clang/Serialization/ASTReader.h
index dd1451bbf2d2c..ba06ab0cd4509 100644
--- a/clang/include/clang/Serialization/ASTReader.h
+++ b/clang/include/clang/Serialization/ASTReader.h
@@ -2452,6 +2452,10 @@ class BitsUnpacker {
uint32_t CurrentBitsIndex = ~0;
};
+inline bool isFromExplicitGMF(const Decl *D) {
+ return D->getOwningModule() && D->getOwningModule()->isExplicitGlobalModule();
+}
+
} // namespace clang
#endif // LLVM_CLANG_SERIALIZATION_ASTREADER_H
diff --git a/clang/lib/Serialization/ASTReader.cpp b/clang/lib/Serialization/ASTReader.cpp
index fecd94e875f67..e91c5fe08a043 100644
--- a/clang/lib/Serialization/ASTReader.cpp
+++ b/clang/lib/Serialization/ASTReader.cpp
@@ -9743,6 +9743,9 @@ void ASTReader::finishPendingActions() {
if (!FD->isLateTemplateParsed() &&
!NonConstDefn->isLateTemplateParsed() &&
+ // We only perform ODR checks for decls not in the explicit
+ // global module fragment.
+ !isFromExplicitGMF(FD) &&
FD->getODRHash() != NonConstDefn->getODRHash()) {
if (!isa<CXXMethodDecl>(FD)) {
PendingFunctionOdrMergeFailures[FD].push_back(NonConstDefn);
diff --git a/clang/lib/Serialization/ASTReaderDecl.cpp b/clang/lib/Serialization/ASTReaderDecl.cpp
index a149d82153037..7697f29b9054b 100644
--- a/clang/lib/Serialization/ASTReaderDecl.cpp
+++ b/clang/lib/Serialization/ASTReaderDecl.cpp
@@ -804,8 +804,10 @@ void ASTDeclReader::VisitEnumDecl(EnumDecl *ED) {
ED->setScopedUsingClassTag(EnumDeclBits.getNextBit());
ED->setFixed(EnumDeclBits.getNextBit());
- ED->setHasODRHash(true);
- ED->ODRHash = Record.readInt();
+ if (!isFromExplicitGMF(ED)) {
+ ED->setHasODRHash(true);
+ ED->ODRHash = Record.readInt();
+ }
// If this is a definition subject to the ODR, and we already have a
// definition, merge this one into it.
@@ -827,7 +829,9 @@ void ASTDeclReader::VisitEnumDecl(EnumDecl *ED) {
Reader.MergedDeclContexts.insert(std::make_pair(ED, OldDef));
ED->demoteThisDefinitionToDeclaration();
Reader.mergeDefinitionVisibility(OldDef, ED);
- if (OldDef->getODRHash() != ED->getODRHash())
+ // We don't want to check the ODR hash value for declarations from global
+ // module fragment.
+ if (!isFromExplicitGMF(ED) && OldDef->getODRHash() != ED->getODRHash())
Reader.PendingEnumOdrMergeFailures[OldDef].push_back(ED);
} else {
OldDef = ED;
@@ -866,6 +870,9 @@ ASTDeclReader::VisitRecordDeclImpl(RecordDecl *RD) {
void ASTDeclReader::VisitRecordDecl(RecordDecl *RD) {
VisitRecordDeclImpl(RD);
+ // We should only reach here if we're in C/Objective-C. There is no
+ // global module fragment.
+ assert(!isFromExplicitGMF(RD));
RD->setODRHash(Record.readInt());
// Maintain the invariant of a redeclaration chain containing only
@@ -1094,8 +1101,10 @@ void ASTDeclReader::VisitFunctionDecl(FunctionDecl *FD) {
if (FD->isExplicitlyDefaulted())
FD->setDefaultLoc(readSourceLocation());
- FD->ODRHash = Record.readInt();
- FD->setHasODRHash(true);
+ if (!isFromExplicitGMF(FD)) {
+ FD->ODRHash = Record.readInt();
+ FD->setHasODRHash(true);
+ }
if (FD->isDefaulted()) {
if (unsigned NumLookups = Record.readInt()) {
@@ -1971,9 +1980,12 @@ void ASTDeclReader::ReadCXXDefinitionData(
#include "clang/AST/CXXRecordDeclDefinitionBits.def"
#undef FIELD
- // Note: the caller has deserialized the IsLambda bit already.
- Data.ODRHash = Record.readInt();
- Data.HasODRHash = true;
+ // We only perform ODR checks for decls not in GMF.
+ if (!isFromExplicitGMF(D)) {
+ // Note: the caller has deserialized the IsLambda bit already.
+ Data.ODRHash = Record.readInt();
+ Data.HasODRHash = true;
+ }
if (Record.readInt()) {
Reader.DefinitionSource[D] =
@@ -2134,6 +2146,10 @@ void ASTDeclReader::MergeDefinitionData(
}
}
+ // We don't want to check ODR for decls in the global module fragment.
+ if (isFromExplicitGMF(MergeDD.Definition))
+ return;
+
if (D->getODRHash() != MergeDD.ODRHash) {
DetectedOdrViolation = true;
}
@@ -3498,10 +3514,13 @@ ASTDeclReader::FindExistingResult ASTDeclReader::findExisting(NamedDecl *D) {
// If this declaration is from a merged context, make a note that we need to
// check that the canonical definition of that context contains the decl.
//
+ // Note that we don't perform ODR checks for decls from the global module
+ // fragment.
+ //
// FIXME: We should do something similar if we merge two definitions of the
// same template specialization into the same CXXRecordDecl.
auto MergedDCIt = Reader.MergedDeclContexts.find(D->getLexicalDeclContext());
- if (MergedDCIt != Reader.MergedDeclContexts.end() &&
+ if (MergedDCIt != Reader.MergedDeclContexts.end() && !isFromExplicitGMF(D) &&
MergedDCIt->second == D->getDeclContext())
Reader.PendingOdrMergeChecks.push_back(D);
diff --git a/clang/lib/Serialization/ASTWriter.cpp b/clang/lib/Serialization/ASTWriter.cpp
index 03bddfe0f5047..b64a6abb90f82 100644
--- a/clang/lib/Serialization/ASTWriter.cpp
+++ b/clang/lib/Serialization/ASTWriter.cpp
@@ -6022,8 +6022,12 @@ void ASTRecordWriter::AddCXXDefinitionData(const CXXRecordDecl *D) {
Record->push_back(DefinitionBits);
- // getODRHash will compute the ODRHash if it has not been previously computed.
- Record->push_back(D->getODRHash());
+ // We only perform ODR checks for decls not in GMF.
+ if (!isFromExplicitGMF(D)) {
+ // getODRHash will compute the ODRHash if it has not been previously
+ // computed.
+ Record->push_back(D->getODRHash());
+ }
bool ModulesDebugInfo =
Writer->Context->getLangOpts().ModulesDebugInfo && !D->isDependentType();
diff --git a/clang/lib/Serialization/ASTWriterDecl.cpp b/clang/lib/Serialization/ASTWriterDecl.cpp
index bb1f51786d281..86d40436a9bac 100644
--- a/clang/lib/Serialization/ASTWriterDecl.cpp
+++ b/clang/lib/Serialization/ASTWriterDecl.cpp
@@ -493,7 +493,9 @@ void ASTDeclWriter::VisitEnumDecl(EnumDecl *D) {
EnumDeclBits.addBit(D->isFixed());
Record.push_back(EnumDeclBits);
- Record.push_back(D->getODRHash());
+ // We only perform ODR checks for decls not in GMF.
+ if (!isFromExplicitGMF(D))
+ Record.push_back(D->getODRHash());
if (MemberSpecializationInfo *MemberInfo = D->getMemberSpecializationInfo()) {
Record.AddDeclRef(MemberInfo->getInstantiatedFrom());
@@ -510,7 +512,7 @@ void ASTDeclWriter::VisitEnumDecl(EnumDecl *D) {
!D->isTopLevelDeclInObjCContainer() &&
!CXXRecordDecl::classofKind(D->getKind()) &&
!D->getIntegerTypeSourceInfo() && !D->getMemberSpecializationInfo() &&
- !needsAnonymousDeclarationNumber(D) &&
+ !needsAnonymousDeclarationNumber(D) && !isFromExplicitGMF(D) &&
D->getDeclName().getNameKind() == DeclarationName::Identifier)
AbbrevToUse = Writer.getDeclEnumAbbrev();
@@ -701,7 +703,9 @@ void ASTDeclWriter::VisitFunctionDecl(FunctionDecl *D) {
if (D->isExplicitlyDefaulted())
Record.AddSourceLocation(D->getDefaultLoc());
- Record.push_back(D->getODRHash());
+ // We only perform ODR checks for decls not in GMF.
+ if (!isFromExplicitGMF(D))
+ Record.push_back(D->getODRHash());
if (D->isDefaulted()) {
if (auto *FDI = D->getDefaultedFunctionInfo()) {
@@ -1506,7 +1510,8 @@ void ASTDeclWriter::VisitCXXMethodDecl(CXXMethodDecl *D) {
D->getFirstDecl() == D->getMostRecentDecl() && !D->isInvalidDecl() &&
!D->hasAttrs() && !D->isTopLevelDeclInObjCContainer() &&
D->getDeclName().getNameKind() == DeclarationName::Identifier &&
- !D->hasExtInfo() && !D->isExplicitlyDefaulted()) {
+ !isFromExplicitGMF(D) && !D->hasExtInfo() &&
+ !D->isExplicitlyDefaulted()) {
if (D->getTemplatedKind() == FunctionDecl::TK_NonTemplate ||
D->getTemplatedKind() == FunctionDecl::TK_FunctionTemplate ||
D->getTemplatedKind() == FunctionDecl::TK_MemberSpecialization ||
diff --git a/clang/test/Modules/concept.cppm b/clang/test/Modules/concept.cppm
index 0e85a46411a54..a343c9cd76a11 100644
--- a/clang/test/Modules/concept.cppm
+++ b/clang/test/Modules/concept.cppm
@@ -70,13 +70,6 @@ module;
export module B;
import A;
-#ifdef DIFFERENT
-// expected-error at foo.h:41 {{'__fn::operator()' from module 'A.<global>' is not present in definition of '__fn' provided earlier}}
-// expected-note@* 1+{{declaration of 'operator()' does not match}}
-#else
-// expected-no-diagnostics
-#endif
-
template <class T>
struct U {
auto operator+(U) { return 0; }
@@ -94,3 +87,10 @@ void foo() {
__fn{}(U<int>(), U<int>());
}
+
+#ifdef DIFFERENT
+// expected-error at B.cppm:* {{call to object of type '__fn' is ambiguous}}
+// expected-note@* 1+{{candidate function}}
+#else
+// expected-no-diagnostics
+#endif
diff --git a/clang/test/Modules/no-eager-load.cppm b/clang/test/Modules/no-eager-load.cppm
index 6632cc60c8eb8..8a2c7656bca2b 100644
--- a/clang/test/Modules/no-eager-load.cppm
+++ b/clang/test/Modules/no-eager-load.cppm
@@ -9,19 +9,10 @@
// RUN: %clang_cc1 -std=c++20 -fsyntax-only -verify %t/d.cpp \
// RUN: -fprebuilt-module-path=%t
//
-// RUN: %clang_cc1 -std=c++20 -emit-module-interface %t/e.cppm -o %t/e.pcm
-// RUN: %clang_cc1 -std=c++20 -emit-module-interface %t/f.cppm -o %t/f.pcm
-// RUN: %clang_cc1 -std=c++20 -fsyntax-only -verify %t/g.cpp \
-// RUN: -fprebuilt-module-path=%t
-//
// RUN: %clang_cc1 -std=c++20 -emit-module-interface %t/h.cppm \
// RUN: -fprebuilt-module-path=%t -o %t/h.pcm
-// RUN: %clang_cc1 -std=c++20 -emit-module-interface %t/i.cppm \
-// RUN: -fprebuilt-module-path=%t -o %t/i.pcm
// RUN: %clang_cc1 -std=c++20 -fsyntax-only -verify %t/j.cpp \
// RUN: -fprebuilt-module-path=%t
-// RUN: %clang_cc1 -std=c++20 -fsyntax-only -verify %t/k.cpp \
-// RUN: -fprebuilt-module-path=%t
//--- a.cppm
export module a;
@@ -53,58 +44,14 @@ void use() {
// expected-note@* {{but in 'a' found a different body}}
}
-//--- foo.h
-void foo() {
-
-}
-
-//--- bar.h
-void bar();
-void foo() {
- bar();
-}
-
-//--- e.cppm
-module;
-#include "foo.h"
-export module e;
-export using ::foo;
-
-//--- f.cppm
-module;
-#include "bar.h"
-export module f;
-export using ::foo;
-
-//--- g.cpp
-import e;
-import f;
-void use() {
- foo(); // expected-error@* {{'foo' has different definitions in different modules;}}
- // expected-note@* {{but in 'e.<global>' found a different body}}
-}
-
//--- h.cppm
export module h;
export import a;
export import b;
-//--- i.cppm
-export module i;
-export import e;
-export import f;
-
//--- j.cpp
import h;
void use() {
foo(); // expected-error@* {{'foo' has different definitions in different modules;}}
// expected-note@* {{but in 'a' found a different body}}
}
-
-//--- k.cpp
-import i;
-void use() {
- foo(); // expected-error@* {{'foo' has different definitions in different modules;}}
- // expected-note@* {{but in 'e.<global>' found a different body}}
-}
-
diff --git a/clang/test/Modules/polluted-operator.cppm b/clang/test/Modules/polluted-operator.cppm
index b24464aa6ad21..d4b0041b5d346 100644
--- a/clang/test/Modules/polluted-operator.cppm
+++ b/clang/test/Modules/polluted-operator.cppm
@@ -46,12 +46,10 @@ module;
export module a;
//--- b.cppm
+// This is actually an ODR violation. But given https://github.com/llvm/llvm-project/issues/79240,
+// we don't count it as an ODR violation any more.
+// expected-no-diagnostics
module;
#include "bar.h"
export module b;
import a;
-
-// expected-error@* {{has different definitions in different modules; first difference is defined here found data member '_S_copy_ctor' with an initializer}}
-// expected-note@* {{but in 'a.<global>' found data member '_S_copy_ctor' with a different initializer}}
-// expected-error@* {{from module 'a.<global>' is not present in definition of 'variant<_Types...>' provided earlier}}
-// expected-note@* {{declaration of 'swap' does not match}}
diff --git a/clang/test/Modules/pr76638.cppm b/clang/test/Modules/pr76638.cppm
index 8cc807961421b..28d03384634ab 100644
--- a/clang/test/Modules/pr76638.cppm
+++ b/clang/test/Modules/pr76638.cppm
@@ -57,6 +57,9 @@ export module mod3;
export using std::align_val_t;
//--- mod4.cppm
+// This is actually an ODR violation. But given https://github.com/llvm/llvm-project/issues/79240,
+// we don't count it as an ODR violation now.
+// expected-no-diagnostics
module;
#include "signed_size_t.h"
#include "csize_t"
@@ -64,6 +67,3 @@ module;
export module mod4;
import mod3;
export using std::align_val_t;
-
-// expected-error at align.h:* {{'std::align_val_t' has different definitions in different modules; defined here first difference is enum with specified type 'size_t' (aka 'int')}}
-// expected-note at align.h:* {{but in 'mod3.<global>' found enum with specified type 'size_t' (aka 'unsigned int')}}
>From 1b447d33452de02427172bc56da417acf834e04f Mon Sep 17 00:00:00 2001
From: Chuanqi Xu <yedeng.yd at linux.alibaba.com>
Date: Mon, 29 Jan 2024 14:32:29 +0800
Subject: [PATCH 2/3] [C++20] [Modules] Remove previous workaround for odr
hashing enums
Previosly we land
https://github.com/llvm/llvm-project/commit/085eae6b863881fb9fda323e5b672b04a00ed19e
to workaround the false positive ODR violations in
https://github.com/llvm/llvm-project/issues/76638.
However, we decided to not perform ODR checks for decls from GMF in
https://github.com/llvm/llvm-project/issues/79240 and we land the
corresponding change. So we should be able to remove the workaround now.
The original tests get remained.
---
clang/docs/ReleaseNotes.rst | 3 --
clang/lib/AST/ODRHash.cpp | 49 +-----------------
.../test/Modules/cxx20-modules-enum-odr.cppm | 51 +++++++++++++++++++
3 files changed, 52 insertions(+), 51 deletions(-)
create mode 100644 clang/test/Modules/cxx20-modules-enum-odr.cppm
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index e8dfdfa63717c..97f05c9368539 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -1046,9 +1046,6 @@ Bug Fixes to C++ Support
in different visibility.
Fixes (`#67893 <https://github.com/llvm/llvm-project/issues/67893>`_)
-- Fix a false-positive ODR violation for different definitions for `std::align_val_t`.
- Fixes (`#76638 <https://github.com/llvm/llvm-project/issues/76638>`_)
-
- Remove recorded `#pragma once` state for headers included in named modules.
Fixes (`#77995 <https://github.com/llvm/llvm-project/issues/77995>`_)
diff --git a/clang/lib/AST/ODRHash.cpp b/clang/lib/AST/ODRHash.cpp
index 5b98646a1e8dc..2dbc259138a89 100644
--- a/clang/lib/AST/ODRHash.cpp
+++ b/clang/lib/AST/ODRHash.cpp
@@ -745,55 +745,8 @@ void ODRHash::AddEnumDecl(const EnumDecl *Enum) {
if (Enum->isScoped())
AddBoolean(Enum->isScopedUsingClassTag());
- if (Enum->getIntegerTypeSourceInfo()) {
- // FIMXE: This allows two enums with different spellings to have the same
- // hash.
- //
- // // mod1.cppm
- // module;
- // extern "C" {
- // typedef unsigned __int64 size_t;
- // }
- // namespace std {
- // using :: size_t;
- // }
- //
- // extern "C++" {
- // namespace std {
- // enum class align_val_t : std::size_t {};
- // }
- // }
- //
- // export module mod1;
- // export using std::align_val_t;
- //
- // // mod2.cppm
- // module;
- // extern "C" {
- // typedef unsigned __int64 size_t;
- // }
- //
- // extern "C++" {
- // namespace std {
- // enum class align_val_t : size_t {};
- // }
- // }
- //
- // export module mod2;
- // import mod1;
- // export using std::align_val_t;
- //
- // The above example should be disallowed since it violates
- // [basic.def.odr]p14:
- //
- // Each such definition shall consist of the same sequence of tokens
- //
- // The definitions of `std::align_val_t` in two module units have different
- // spellings but we failed to give an error here.
- //
- // See https://github.com/llvm/llvm-project/issues/76638 for details.
+ if (Enum->getIntegerTypeSourceInfo())
AddQualType(Enum->getIntegerType().getCanonicalType());
- }
// Filter out sub-Decls which will not be processed in order to get an
// accurate count of Decl's.
diff --git a/clang/test/Modules/cxx20-modules-enum-odr.cppm b/clang/test/Modules/cxx20-modules-enum-odr.cppm
new file mode 100644
index 0000000000000..831c01143a27b
--- /dev/null
+++ b/clang/test/Modules/cxx20-modules-enum-odr.cppm
@@ -0,0 +1,51 @@
+// RUN: rm -rf %t
+// RUN: mkdir -p %t
+// RUN: split-file %s %t
+//
+// RUN: %clang_cc1 -std=c++20 %t/mod1.cppm -emit-module-interface -o %t/mod1.pcm
+// RUN: %clang_cc1 -std=c++20 %t/mod2.cppm -emit-module-interface -o %t/mod2.pcm
+// RUN: %clang_cc1 -std=c++20 %t/test.cpp -fprebuilt-module-path=%t -verify -fsyntax-only
+
+//--- size_t.h
+
+extern "C" {
+ typedef unsigned int size_t;
+}
+
+//--- csize_t
+namespace std {
+ using :: size_t;
+}
+
+//--- align.h
+namespace std {
+ enum class align_val_t : size_t {};
+}
+
+//--- mod1.cppm
+module;
+#include "size_t.h"
+#include "align.h"
+export module mod1;
+namespace std {
+export using std::align_val_t;
+}
+
+//--- mod2.cppm
+module;
+#include "size_t.h"
+#include "csize_t"
+#include "align.h"
+export module mod2;
+namespace std {
+export using std::align_val_t;
+}
+
+//--- test.cpp
+// expected-no-diagnostics
+import mod1;
+import mod2;
+void test() {
+ std::align_val_t v;
+}
+
>From 494ef4ae5e4d6ca0029de7d2b73e2a56d797dc79 Mon Sep 17 00:00:00 2001
From: Chuanqi Xu <yedeng.yd at linux.alibaba.com>
Date: Thu, 1 Feb 2024 13:44:32 +0800
Subject: [PATCH 3/3] [C++20] [Modules] Introduce -fskip-odr-check-in-gmf
(#79959)
Close https://github.com/llvm/llvm-project/issues/79240
Cite the comment from @mizvekov in
//github.com/llvm/llvm-project/issues/79240:
> There are two kinds of bugs / issues relevant here:
>
> Clang bugs that this change hides
> Here we can add a Frontend flag that disables the GMF ODR check, just
> so
> we can keep tracking, testing and fixing these issues.
> The Driver would just always pass that flag.
> We could add that flag in this current issue.
> Bugs in user code:
> I don't think it's worth adding a corresponding Driver flag for
> controlling the above Frontend flag, since we intend it's behavior to
> become default as we fix the problems, and users interested in testing
> the more strict behavior can just use the Frontend flag directly.
This patch follows the suggestion:
- Introduce the CC1 flag `-fskip-odr-check-in-gmf` which is by default
off, so that the every existing test will still be tested with checking
ODR violations.
- Passing `-fskip-odr-check-in-gmf` in the driver to keep the behavior
we intended.
- Edit the document to tell the users who are still interested in more
strict checks can use `-Xclang -fno-skip-odr-check-in-gmf` to get the
existing behavior.
---
clang/docs/ReleaseNotes.rst | 3 +-
clang/docs/StandardCPlusPlusModules.rst | 23 ++++++++
clang/include/clang/Basic/LangOptions.def | 1 +
clang/include/clang/Driver/Options.td | 8 +++
clang/include/clang/Serialization/ASTReader.h | 6 +-
clang/lib/Driver/ToolChains/Clang.cpp | 4 ++
clang/lib/Serialization/ASTReader.cpp | 2 +-
clang/lib/Serialization/ASTReaderDecl.cpp | 17 +++---
clang/lib/Serialization/ASTWriter.cpp | 2 +-
clang/lib/Serialization/ASTWriterDecl.cpp | 8 +--
.../Driver/modules-skip-odr-check-in-gmf.cpp | 10 ++++
clang/test/Modules/concept.cppm | 23 +++++---
clang/test/Modules/polluted-operator.cppm | 18 +++++-
clang/test/Modules/pr76638.cppm | 16 +++++-
clang/test/Modules/skip-odr-check-in-gmf.cppm | 56 +++++++++++++++++++
15 files changed, 167 insertions(+), 30 deletions(-)
create mode 100644 clang/test/Driver/modules-skip-odr-check-in-gmf.cpp
create mode 100644 clang/test/Modules/skip-odr-check-in-gmf.cppm
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 97f05c9368539..ca6f4439971f1 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -190,7 +190,8 @@ C++20 Feature Support
- Clang won't perform ODR checks for decls in the global module fragment any
more to ease the implementation and improve the user's using experience.
- This follows the MSVC's behavior.
+ This follows the MSVC's behavior. Users interested in testing the more strict
+ behavior can use the flag '-Xclang -fno-skip-odr-check-in-gmf'.
(`#79240 <https://github.com/llvm/llvm-project/issues/79240>`_).
C++23 Feature Support
diff --git a/clang/docs/StandardCPlusPlusModules.rst b/clang/docs/StandardCPlusPlusModules.rst
index 81043ff25be02..0f85065f464a8 100644
--- a/clang/docs/StandardCPlusPlusModules.rst
+++ b/clang/docs/StandardCPlusPlusModules.rst
@@ -457,6 +457,29 @@ Note that **currently** the compiler doesn't consider inconsistent macro definit
Currently Clang would accept the above example. But it may produce surprising results if the
debugging code depends on consistent use of ``NDEBUG`` also in other translation units.
+Definitions consistency
+^^^^^^^^^^^^^^^^^^^^^^^
+
+The C++ language defines that same declarations in different translation units should have
+the same definition, as known as ODR (One Definition Rule). Prior to modules, the translation
+units don't dependent on each other and the compiler itself can't perform a strong
+ODR violation check. With the introduction of modules, now the compiler have
+the chance to perform ODR violations with language semantics across translation units.
+
+However, in the practice, we found the existing ODR checking mechanism is not stable
+enough. Many people suffers from the false positive ODR violation diagnostics, AKA,
+the compiler are complaining two identical declarations have different definitions
+incorrectly. Also the true positive ODR violations are rarely reported.
+Also we learned that MSVC don't perform ODR check for declarations in the global module
+fragment.
+
+So in order to get better user experience, save the time checking ODR and keep consistent
+behavior with MSVC, we disabled the ODR check for the declarations in the global module
+fragment by default. Users who want more strict check can still use the
+``-Xclang -fno-skip-odr-check-in-gmf`` flag to get the ODR check enabled. It is also
+encouraged to report issues if users find false positive ODR violations or false negative ODR
+violations with the flag enabled.
+
ABI Impacts
-----------
diff --git a/clang/include/clang/Basic/LangOptions.def b/clang/include/clang/Basic/LangOptions.def
index 8fc75e1cca039..4942dcaa086ea 100644
--- a/clang/include/clang/Basic/LangOptions.def
+++ b/clang/include/clang/Basic/LangOptions.def
@@ -174,6 +174,7 @@ LANGOPT(MathErrno , 1, 1, "errno in math functions")
BENIGN_LANGOPT(HeinousExtensions , 1, 0, "extensions that we really don't like and may be ripped out at any time")
LANGOPT(Modules , 1, 0, "modules semantics")
COMPATIBLE_LANGOPT(CPlusPlusModules, 1, 0, "C++ modules syntax")
+LANGOPT(SkipODRCheckInGMF, 1, 0, "Skip ODR checks for decls in the global module fragment")
LANGOPT(BuiltinHeadersInSystemModules, 1, 0, "builtin headers belong to system modules, and _Builtin_ modules are ignored for cstdlib headers")
BENIGN_ENUM_LANGOPT(CompilingModule, CompilingModuleKind, 3, CMK_None,
"compiling a module interface")
diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td
index 773bc1dcda01d..e8d03fc269023 100644
--- a/clang/include/clang/Driver/Options.td
+++ b/clang/include/clang/Driver/Options.td
@@ -2985,6 +2985,14 @@ def fmodule_output : Flag<["-"], "fmodule-output">, Flags<[NoXarchOption]>,
Visibility<[ClangOption, CC1Option]>,
HelpText<"Save intermediate module file results when compiling a standard C++ module unit.">;
+defm skip_odr_check_in_gmf : BoolOption<"f", "skip-odr-check-in-gmf",
+ LangOpts<"SkipODRCheckInGMF">, DefaultFalse,
+ PosFlag<SetTrue, [], [CC1Option],
+ "Skip ODR checks for decls in the global module fragment.">,
+ NegFlag<SetFalse, [], [CC1Option],
+ "Perform ODR checks for decls in the global module fragment.">>,
+ Group<f_Group>;
+
def fmodules_prune_interval : Joined<["-"], "fmodules-prune-interval=">, Group<i_Group>,
Visibility<[ClangOption, CC1Option]>, MetaVarName<"<seconds>">,
HelpText<"Specify the interval (in seconds) between attempts to prune the module cache">,
diff --git a/clang/include/clang/Serialization/ASTReader.h b/clang/include/clang/Serialization/ASTReader.h
index ba06ab0cd4509..cd28226c295b3 100644
--- a/clang/include/clang/Serialization/ASTReader.h
+++ b/clang/include/clang/Serialization/ASTReader.h
@@ -2452,8 +2452,10 @@ class BitsUnpacker {
uint32_t CurrentBitsIndex = ~0;
};
-inline bool isFromExplicitGMF(const Decl *D) {
- return D->getOwningModule() && D->getOwningModule()->isExplicitGlobalModule();
+inline bool shouldSkipCheckingODR(const Decl *D) {
+ return D->getOwningModule() &&
+ D->getASTContext().getLangOpts().SkipODRCheckInGMF &&
+ D->getOwningModule()->isExplicitGlobalModule();
}
} // namespace clang
diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
index 8092fc050b0ee..98272a27574d4 100644
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -3942,6 +3942,10 @@ static bool RenderModulesOptions(Compilation &C, const Driver &D,
Args.ClaimAllArgs(options::OPT_fmodules_disable_diagnostic_validation);
}
+ // FIXME: We provisionally don't check ODR violations for decls in the global
+ // module fragment.
+ CmdArgs.push_back("-fskip-odr-check-in-gmf");
+
// Claim `-fmodule-output` and `-fmodule-output=` to avoid unused warnings.
Args.ClaimAllArgs(options::OPT_fmodule_output);
Args.ClaimAllArgs(options::OPT_fmodule_output_EQ);
diff --git a/clang/lib/Serialization/ASTReader.cpp b/clang/lib/Serialization/ASTReader.cpp
index e91c5fe08a043..028610deb3001 100644
--- a/clang/lib/Serialization/ASTReader.cpp
+++ b/clang/lib/Serialization/ASTReader.cpp
@@ -9745,7 +9745,7 @@ void ASTReader::finishPendingActions() {
!NonConstDefn->isLateTemplateParsed() &&
// We only perform ODR checks for decls not in the explicit
// global module fragment.
- !isFromExplicitGMF(FD) &&
+ !shouldSkipCheckingODR(FD) &&
FD->getODRHash() != NonConstDefn->getODRHash()) {
if (!isa<CXXMethodDecl>(FD)) {
PendingFunctionOdrMergeFailures[FD].push_back(NonConstDefn);
diff --git a/clang/lib/Serialization/ASTReaderDecl.cpp b/clang/lib/Serialization/ASTReaderDecl.cpp
index 7697f29b9054b..1fadd8039462d 100644
--- a/clang/lib/Serialization/ASTReaderDecl.cpp
+++ b/clang/lib/Serialization/ASTReaderDecl.cpp
@@ -804,7 +804,7 @@ void ASTDeclReader::VisitEnumDecl(EnumDecl *ED) {
ED->setScopedUsingClassTag(EnumDeclBits.getNextBit());
ED->setFixed(EnumDeclBits.getNextBit());
- if (!isFromExplicitGMF(ED)) {
+ if (!shouldSkipCheckingODR(ED)) {
ED->setHasODRHash(true);
ED->ODRHash = Record.readInt();
}
@@ -831,7 +831,8 @@ void ASTDeclReader::VisitEnumDecl(EnumDecl *ED) {
Reader.mergeDefinitionVisibility(OldDef, ED);
// We don't want to check the ODR hash value for declarations from global
// module fragment.
- if (!isFromExplicitGMF(ED) && OldDef->getODRHash() != ED->getODRHash())
+ if (!shouldSkipCheckingODR(ED) &&
+ OldDef->getODRHash() != ED->getODRHash())
Reader.PendingEnumOdrMergeFailures[OldDef].push_back(ED);
} else {
OldDef = ED;
@@ -872,7 +873,7 @@ void ASTDeclReader::VisitRecordDecl(RecordDecl *RD) {
VisitRecordDeclImpl(RD);
// We should only reach here if we're in C/Objective-C. There is no
// global module fragment.
- assert(!isFromExplicitGMF(RD));
+ assert(!shouldSkipCheckingODR(RD));
RD->setODRHash(Record.readInt());
// Maintain the invariant of a redeclaration chain containing only
@@ -1101,7 +1102,7 @@ void ASTDeclReader::VisitFunctionDecl(FunctionDecl *FD) {
if (FD->isExplicitlyDefaulted())
FD->setDefaultLoc(readSourceLocation());
- if (!isFromExplicitGMF(FD)) {
+ if (!shouldSkipCheckingODR(FD)) {
FD->ODRHash = Record.readInt();
FD->setHasODRHash(true);
}
@@ -1981,7 +1982,7 @@ void ASTDeclReader::ReadCXXDefinitionData(
#undef FIELD
// We only perform ODR checks for decls not in GMF.
- if (!isFromExplicitGMF(D)) {
+ if (!shouldSkipCheckingODR(D)) {
// Note: the caller has deserialized the IsLambda bit already.
Data.ODRHash = Record.readInt();
Data.HasODRHash = true;
@@ -2147,7 +2148,7 @@ void ASTDeclReader::MergeDefinitionData(
}
// We don't want to check ODR for decls in the global module fragment.
- if (isFromExplicitGMF(MergeDD.Definition))
+ if (shouldSkipCheckingODR(MergeDD.Definition))
return;
if (D->getODRHash() != MergeDD.ODRHash) {
@@ -3520,8 +3521,8 @@ ASTDeclReader::FindExistingResult ASTDeclReader::findExisting(NamedDecl *D) {
// FIXME: We should do something similar if we merge two definitions of the
// same template specialization into the same CXXRecordDecl.
auto MergedDCIt = Reader.MergedDeclContexts.find(D->getLexicalDeclContext());
- if (MergedDCIt != Reader.MergedDeclContexts.end() && !isFromExplicitGMF(D) &&
- MergedDCIt->second == D->getDeclContext())
+ if (MergedDCIt != Reader.MergedDeclContexts.end() &&
+ !shouldSkipCheckingODR(D) && MergedDCIt->second == D->getDeclContext())
Reader.PendingOdrMergeChecks.push_back(D);
return FindExistingResult(Reader, D, /*Existing=*/nullptr,
diff --git a/clang/lib/Serialization/ASTWriter.cpp b/clang/lib/Serialization/ASTWriter.cpp
index b64a6abb90f82..3b79a9238d1af 100644
--- a/clang/lib/Serialization/ASTWriter.cpp
+++ b/clang/lib/Serialization/ASTWriter.cpp
@@ -6023,7 +6023,7 @@ void ASTRecordWriter::AddCXXDefinitionData(const CXXRecordDecl *D) {
Record->push_back(DefinitionBits);
// We only perform ODR checks for decls not in GMF.
- if (!isFromExplicitGMF(D)) {
+ if (!shouldSkipCheckingODR(D)) {
// getODRHash will compute the ODRHash if it has not been previously
// computed.
Record->push_back(D->getODRHash());
diff --git a/clang/lib/Serialization/ASTWriterDecl.cpp b/clang/lib/Serialization/ASTWriterDecl.cpp
index 86d40436a9bac..f224075643e99 100644
--- a/clang/lib/Serialization/ASTWriterDecl.cpp
+++ b/clang/lib/Serialization/ASTWriterDecl.cpp
@@ -494,7 +494,7 @@ void ASTDeclWriter::VisitEnumDecl(EnumDecl *D) {
Record.push_back(EnumDeclBits);
// We only perform ODR checks for decls not in GMF.
- if (!isFromExplicitGMF(D))
+ if (!shouldSkipCheckingODR(D))
Record.push_back(D->getODRHash());
if (MemberSpecializationInfo *MemberInfo = D->getMemberSpecializationInfo()) {
@@ -512,7 +512,7 @@ void ASTDeclWriter::VisitEnumDecl(EnumDecl *D) {
!D->isTopLevelDeclInObjCContainer() &&
!CXXRecordDecl::classofKind(D->getKind()) &&
!D->getIntegerTypeSourceInfo() && !D->getMemberSpecializationInfo() &&
- !needsAnonymousDeclarationNumber(D) && !isFromExplicitGMF(D) &&
+ !needsAnonymousDeclarationNumber(D) && !shouldSkipCheckingODR(D) &&
D->getDeclName().getNameKind() == DeclarationName::Identifier)
AbbrevToUse = Writer.getDeclEnumAbbrev();
@@ -704,7 +704,7 @@ void ASTDeclWriter::VisitFunctionDecl(FunctionDecl *D) {
Record.AddSourceLocation(D->getDefaultLoc());
// We only perform ODR checks for decls not in GMF.
- if (!isFromExplicitGMF(D))
+ if (!shouldSkipCheckingODR(D))
Record.push_back(D->getODRHash());
if (D->isDefaulted()) {
@@ -1510,7 +1510,7 @@ void ASTDeclWriter::VisitCXXMethodDecl(CXXMethodDecl *D) {
D->getFirstDecl() == D->getMostRecentDecl() && !D->isInvalidDecl() &&
!D->hasAttrs() && !D->isTopLevelDeclInObjCContainer() &&
D->getDeclName().getNameKind() == DeclarationName::Identifier &&
- !isFromExplicitGMF(D) && !D->hasExtInfo() &&
+ !shouldSkipCheckingODR(D) && !D->hasExtInfo() &&
!D->isExplicitlyDefaulted()) {
if (D->getTemplatedKind() == FunctionDecl::TK_NonTemplate ||
D->getTemplatedKind() == FunctionDecl::TK_FunctionTemplate ||
diff --git a/clang/test/Driver/modules-skip-odr-check-in-gmf.cpp b/clang/test/Driver/modules-skip-odr-check-in-gmf.cpp
new file mode 100644
index 0000000000000..b00b6d330ba45
--- /dev/null
+++ b/clang/test/Driver/modules-skip-odr-check-in-gmf.cpp
@@ -0,0 +1,10 @@
+// RUN: %clang -std=c++20 -### -c %s 2>&1 | FileCheck %s
+// RUN: %clang -std=c++20 -fno-skip-odr-check-in-gmf -### -c %s 2>&1 \
+// RUN: | FileCheck %s --check-prefix=UNUSED
+// RUN: %clang -std=c++20 -Xclang -fno-skip-odr-check-in-gmf -### -c %s 2>&1 \
+// RUN: | FileCheck %s --check-prefix=NO-SKIP
+
+// CHECK: -fskip-odr-check-in-gmf
+// UNUSED: warning: argument unused during compilation: '-fno-skip-odr-check-in-gmf'
+// UNUSED-NOT: -fno-skip-odr-check-in-gmf
+// NO-SKIP: -fskip-odr-check-in-gmf{{.*}}-fno-skip-odr-check-in-gmf
diff --git a/clang/test/Modules/concept.cppm b/clang/test/Modules/concept.cppm
index a343c9cd76a11..0fdb5ea896808 100644
--- a/clang/test/Modules/concept.cppm
+++ b/clang/test/Modules/concept.cppm
@@ -5,6 +5,12 @@
// RUN: %clang_cc1 -std=c++20 %t/A.cppm -emit-module-interface -o %t/A.pcm
// RUN: %clang_cc1 -std=c++20 -fprebuilt-module-path=%t -I%t -DDIFFERENT %t/B.cppm -verify
// RUN: %clang_cc1 -std=c++20 -fprebuilt-module-path=%t -I%t %t/B.cppm -verify
+//
+// Testing the behavior of `-fskip-odr-check-in-gmf`
+// RUN: %clang_cc1 -std=c++20 -fskip-odr-check-in-gmf %t/A.cppm -emit-module-interface -o %t/A.pcm
+// RUN: %clang_cc1 -std=c++20 -fskip-odr-check-in-gmf -fprebuilt-module-path=%t -I%t \
+// RUN: -DDIFFERENT -DSKIP_ODR_CHECK_IN_GMF %t/B.cppm -verify
+
//--- foo.h
#ifndef FOO_H
@@ -70,6 +76,16 @@ module;
export module B;
import A;
+#ifdef SKIP_ODR_CHECK_IN_GMF
+// expected-error at B.cppm:* {{call to object of type '__fn' is ambiguous}}
+// expected-note@* 1+{{candidate function}}
+#elif defined(DIFFERENT)
+// expected-error at foo.h:41 {{'__fn::operator()' from module 'A.<global>' is not present in definition of '__fn' provided earlier}}
+// expected-note@* 1+{{declaration of 'operator()' does not match}}
+#else
+// expected-no-diagnostics
+#endif
+
template <class T>
struct U {
auto operator+(U) { return 0; }
@@ -87,10 +103,3 @@ void foo() {
__fn{}(U<int>(), U<int>());
}
-
-#ifdef DIFFERENT
-// expected-error at B.cppm:* {{call to object of type '__fn' is ambiguous}}
-// expected-note@* 1+{{candidate function}}
-#else
-// expected-no-diagnostics
-#endif
diff --git a/clang/test/Modules/polluted-operator.cppm b/clang/test/Modules/polluted-operator.cppm
index d4b0041b5d346..721ca061c939f 100644
--- a/clang/test/Modules/polluted-operator.cppm
+++ b/clang/test/Modules/polluted-operator.cppm
@@ -4,6 +4,12 @@
//
// RUN: %clang_cc1 -std=c++20 -emit-module-interface %t/a.cppm -o %t/a.pcm
// RUN: %clang_cc1 -std=c++20 %t/b.cppm -fprebuilt-module-path=%t -emit-module-interface -o %t/b.pcm -verify
+//
+// Testing the behavior of `-fskip-odr-check-in-gmf`
+// RUN: %clang_cc1 -std=c++20 -fskip-odr-check-in-gmf -emit-module-interface %t/a.cppm -o \
+// RUN: %t/a.pcm
+// RUN: %clang_cc1 -std=c++20 -fskip-odr-check-in-gmf %t/b.cppm -fprebuilt-module-path=%t \
+// RUN: -emit-module-interface -DSKIP_ODR_CHECK_IN_GMF -o %t/b.pcm -verify
//--- foo.h
@@ -46,10 +52,16 @@ module;
export module a;
//--- b.cppm
-// This is actually an ODR violation. But given https://github.com/llvm/llvm-project/issues/79240,
-// we don't count it as an ODR violation any more.
-// expected-no-diagnostics
module;
#include "bar.h"
export module b;
import a;
+
+#ifdef SKIP_ODR_CHECK_IN_GMF
+// expected-no-diagnostics
+#else
+// expected-error@* {{has different definitions in different modules; first difference is defined here found data member '_S_copy_ctor' with an initializer}}
+// expected-note@* {{but in 'a.<global>' found data member '_S_copy_ctor' with a different initializer}}
+// expected-error@* {{from module 'a.<global>' is not present in definition of 'variant<_Types...>' provided earlier}}
+// expected-note@* {{declaration of 'swap' does not match}}
+#endif
diff --git a/clang/test/Modules/pr76638.cppm b/clang/test/Modules/pr76638.cppm
index 28d03384634ab..e4820ba3d79d9 100644
--- a/clang/test/Modules/pr76638.cppm
+++ b/clang/test/Modules/pr76638.cppm
@@ -10,6 +10,12 @@
// RUN: %clang_cc1 -std=c++20 %t/mod4.cppm -fmodule-file=mod3=%t/mod3.pcm \
// RUN: -fsyntax-only -verify
+// Testing the behavior of `-fskip-odr-check-in-gmf`
+// RUN: %clang_cc1 -std=c++20 %t/mod3.cppm -fskip-odr-check-in-gmf \
+// RUN: -emit-module-interface -o %t/mod3.pcm
+// RUN: %clang_cc1 -std=c++20 %t/mod4.cppm -fmodule-file=mod3=%t/mod3.pcm \
+// RUN: -fskip-odr-check-in-gmf -DSKIP_ODR_CHECK_IN_GMF -fsyntax-only -verify
+
//--- size_t.h
extern "C" {
@@ -57,9 +63,6 @@ export module mod3;
export using std::align_val_t;
//--- mod4.cppm
-// This is actually an ODR violation. But given https://github.com/llvm/llvm-project/issues/79240,
-// we don't count it as an ODR violation now.
-// expected-no-diagnostics
module;
#include "signed_size_t.h"
#include "csize_t"
@@ -67,3 +70,10 @@ module;
export module mod4;
import mod3;
export using std::align_val_t;
+
+#ifdef SKIP_ODR_CHECK_IN_GMF
+// expected-no-diagnostics
+#else
+// expected-error at align.h:* {{'std::align_val_t' has different definitions in different modules; defined here first difference is enum with specified type 'size_t' (aka 'int')}}
+// expected-note at align.h:* {{but in 'mod3.<global>' found enum with specified type 'size_t' (aka 'unsigned int')}}
+#endif
diff --git a/clang/test/Modules/skip-odr-check-in-gmf.cppm b/clang/test/Modules/skip-odr-check-in-gmf.cppm
new file mode 100644
index 0000000000000..3ee7d09224bfa
--- /dev/null
+++ b/clang/test/Modules/skip-odr-check-in-gmf.cppm
@@ -0,0 +1,56 @@
+// RUN: rm -rf %t
+// RUN: mkdir -p %t
+// RUN: split-file %s %t
+//
+// Baseline testing to make sure we can detect the ODR violation from the CC1 invocation.
+// RUNX: %clang_cc1 -std=c++20 %t/a.cppm -emit-module-interface -o %t/a.pcm
+// RUNX: %clang_cc1 -std=c++20 %t/b.cppm -emit-module-interface -o %t/b.pcm
+// RUNX: %clang_cc1 -std=c++20 %t/test.cc -fprebuilt-module-path=%t -fsyntax-only -verify
+//
+// Testing that we can ignore the ODR violation from the driver invocation.
+// RUN: %clang -std=c++20 %t/a.cppm --precompile -o %t/a.pcm
+// RUN: %clang -std=c++20 %t/b.cppm --precompile -o %t/b.pcm
+// RUN: %clang -std=c++20 %t/test.cc -fprebuilt-module-path=%t -fsyntax-only -Xclang -verify \
+// RUN: -DIGNORE_ODR_VIOLATION
+//
+// Testing that the driver can require to check the ODR violation.
+// RUN: %clang -std=c++20 -Xclang -fno-skip-odr-check-in-gmf %t/a.cppm --precompile -o %t/a.pcm
+// RUN: %clang -std=c++20 -Xclang -fno-skip-odr-check-in-gmf %t/b.cppm --precompile -o %t/b.pcm
+// RUN: %clang -std=c++20 -Xclang -fno-skip-odr-check-in-gmf %t/test.cc -fprebuilt-module-path=%t \
+// RUN: -fsyntax-only -Xclang -verify
+
+//--- func1.h
+bool func(int x, int y) {
+ return true;
+}
+
+//--- func2.h
+bool func(int x, int y) {
+ return false;
+}
+
+//--- a.cppm
+module;
+#include "func1.h"
+export module a;
+export using ::func;
+
+//--- b.cppm
+module;
+#include "func2.h"
+export module b;
+export using ::func;
+
+//--- test.cc
+import a;
+import b;
+bool test() {
+ return func(1, 2);
+}
+
+#ifdef IGNORE_ODR_VIOLATION
+// expected-no-diagnostics
+#else
+// expected-error at func2.h:1 {{'func' has different definitions in different modules;}}
+// expected-note at func1.h:1 {{but in 'a.<global>' found a different body}}
+#endif
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