release/18.x: backport [C++20] [Moduls] Avoid computing odr hash for functions from comparing constraint expression

clang/include/clang/AST/DeclBase.h

@@ -673,6 +673,16 @@ class alignas(8) Decl {
   /// fragment. See [module.global.frag]p3,4 for details.
   bool isDiscardedInGlobalModuleFragment() const { return false; }
 
+  /// Check if we should skip checking ODRHash for declaration \param D.
+  ///
+  /// The existing ODRHash mechanism seems to be not stable enough and
+  /// the false positive ODR violation reports are annoying and we rarely see
+  /// true ODR violation reports. Also we learned that MSVC disabled ODR checks
+  /// for declarations in GMF. So we try to disable ODR checks in the GMF to
+  /// get better user experiences before we make the ODR violation checks stable
+  /// enough.
+  bool shouldSkipCheckingODR() const;
+
   /// Return true if this declaration has an attribute which acts as
   /// definition of the entity, such as 'alias' or 'ifunc'.
   bool hasDefiningAttr() const;

clang/include/clang/Serialization/ASTReader.h

@@ -2451,13 +2451,6 @@ class BitsUnpacker {
   uint32_t Value;
   uint32_t CurrentBitsIndex = ~0;
 };
-
-inline bool shouldSkipCheckingODR(const Decl *D) {
-  return D->getOwningModule() &&
-         D->getASTContext().getLangOpts().SkipODRCheckInGMF &&
-         D->getOwningModule()->isExplicitGlobalModule();
-}
-
 } // namespace clang
 
 #endif // LLVM_CLANG_SERIALIZATION_ASTREADER_H

clang/lib/AST/Decl.cpp

@@ -4476,7 +4476,7 @@ unsigned FunctionDecl::getODRHash() {
   }
 
   class ODRHash Hash;
-  Hash.AddFunctionDecl(this);
+  Hash.AddFunctionDecl(this, /*SkipBody=*/shouldSkipCheckingODR());
   setHasODRHash(true);
   ODRHash = Hash.CalculateHash();
   return ODRHash;

clang/lib/AST/DeclBase.cpp

@@ -1102,6 +1102,11 @@ bool Decl::isInAnotherModuleUnit() const {
   return M != getASTContext().getCurrentNamedModule();
 }
 
+bool Decl::shouldSkipCheckingODR() const {
+  return getASTContext().getLangOpts().SkipODRCheckInGMF && getOwningModule() &&
+         getOwningModule()->isExplicitGlobalModule();
+}
+
 static Decl::Kind getKind(const Decl *D) { return D->getKind(); }
 static Decl::Kind getKind(const DeclContext *DC) { return DC->getDeclKind(); }
 

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.
-            !shouldSkipCheckingODR(FD) &&
+            !FD->shouldSkipCheckingODR() &&
             FD->getODRHash() != NonConstDefn->getODRHash()) {
           if (!isa<CXXMethodDecl>(FD)) {
             PendingFunctionOdrMergeFailures[FD].push_back(NonConstDefn);

clang/lib/Serialization/ASTReaderDecl.cpp

@@ -832,7 +832,7 @@ 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 (!shouldSkipCheckingODR(ED) &&
+      if (!ED->shouldSkipCheckingODR() &&
           OldDef->getODRHash() != ED->getODRHash())
         Reader.PendingEnumOdrMergeFailures[OldDef].push_back(ED);
     } else {
@@ -874,7 +874,7 @@ 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(!shouldSkipCheckingODR(RD));
+  assert(!RD->shouldSkipCheckingODR());
   RD->setODRHash(Record.readInt());
 
   // Maintain the invariant of a redeclaration chain containing only
@@ -2152,7 +2152,7 @@ void ASTDeclReader::MergeDefinitionData(
   }
 
   // We don't want to check ODR for decls in the global module fragment.
-  if (shouldSkipCheckingODR(MergeDD.Definition))
+  if (MergeDD.Definition->shouldSkipCheckingODR())
     return;
 
   if (D->getODRHash() != MergeDD.ODRHash) {
@@ -3526,7 +3526,7 @@ ASTDeclReader::FindExistingResult ASTDeclReader::findExisting(NamedDecl *D) {
   // same template specialization into the same CXXRecordDecl.
   auto MergedDCIt = Reader.MergedDeclContexts.find(D->getLexicalDeclContext());
   if (MergedDCIt != Reader.MergedDeclContexts.end() &&
-      !shouldSkipCheckingODR(D) && MergedDCIt->second == D->getDeclContext())
+      !D->shouldSkipCheckingODR() && MergedDCIt->second == D->getDeclContext())
     Reader.PendingOdrMergeChecks.push_back(D);
 
   return FindExistingResult(Reader, D, /*Existing=*/nullptr,

clang/lib/Serialization/ASTWriter.cpp

@@ -6010,7 +6010,7 @@ void ASTRecordWriter::AddCXXDefinitionData(const CXXRecordDecl *D) {
 
   BitsPacker DefinitionBits;
 
-  bool ShouldSkipCheckingODR = shouldSkipCheckingODR(D);
+  bool ShouldSkipCheckingODR = D->shouldSkipCheckingODR();
   DefinitionBits.addBit(ShouldSkipCheckingODR);
 
 #define FIELD(Name, Width, Merge)                                              \

clang/lib/Serialization/ASTWriterDecl.cpp

@@ -488,7 +488,7 @@ void ASTDeclWriter::VisitEnumDecl(EnumDecl *D) {
   BitsPacker EnumDeclBits;
   EnumDeclBits.addBits(D->getNumPositiveBits(), /*BitWidth=*/8);
   EnumDeclBits.addBits(D->getNumNegativeBits(), /*BitWidth=*/8);
-  bool ShouldSkipCheckingODR = shouldSkipCheckingODR(D);
+  bool ShouldSkipCheckingODR = D->shouldSkipCheckingODR();
   EnumDeclBits.addBit(ShouldSkipCheckingODR);
   EnumDeclBits.addBit(D->isScoped());
   EnumDeclBits.addBit(D->isScopedUsingClassTag());
@@ -514,7 +514,7 @@ void ASTDeclWriter::VisitEnumDecl(EnumDecl *D) {
       !D->isTopLevelDeclInObjCContainer() &&
       !CXXRecordDecl::classofKind(D->getKind()) &&
       !D->getIntegerTypeSourceInfo() && !D->getMemberSpecializationInfo() &&
-      !needsAnonymousDeclarationNumber(D) && !shouldSkipCheckingODR(D) &&
+      !needsAnonymousDeclarationNumber(D) && !D->shouldSkipCheckingODR() &&
       D->getDeclName().getNameKind() == DeclarationName::Identifier)
     AbbrevToUse = Writer.getDeclEnumAbbrev();
 
@@ -680,7 +680,7 @@ void ASTDeclWriter::VisitFunctionDecl(FunctionDecl *D) {
   // FIXME: stable encoding
   FunctionDeclBits.addBits(llvm::to_underlying(D->getLinkageInternal()), 3);
   FunctionDeclBits.addBits((uint32_t)D->getStorageClass(), /*BitWidth=*/3);
-  bool ShouldSkipCheckingODR = shouldSkipCheckingODR(D);
+  bool ShouldSkipCheckingODR = D->shouldSkipCheckingODR();
   FunctionDeclBits.addBit(ShouldSkipCheckingODR);
   FunctionDeclBits.addBit(D->isInlineSpecified());
   FunctionDeclBits.addBit(D->isInlined());
@@ -1514,7 +1514,7 @@ void ASTDeclWriter::VisitCXXMethodDecl(CXXMethodDecl *D) {
       D->getFirstDecl() == D->getMostRecentDecl() && !D->isInvalidDecl() &&
       !D->hasAttrs() && !D->isTopLevelDeclInObjCContainer() &&
       D->getDeclName().getNameKind() == DeclarationName::Identifier &&
-      !shouldSkipCheckingODR(D) && !D->hasExtInfo() &&
+      !D->shouldSkipCheckingODR() && !D->hasExtInfo() &&
       !D->isExplicitlyDefaulted()) {
     if (D->getTemplatedKind() == FunctionDecl::TK_NonTemplate ||
         D->getTemplatedKind() == FunctionDecl::TK_FunctionTemplate ||

clang/test/Modules/hashing-decls-in-exprs-from-gmf.cppm

@@ -0,0 +1,67 @@
+// RUN: rm -rf %t
+// RUN: mkdir -p %t
+// RUN: split-file %s %t
+//
+// 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 %t/B.cppm -emit-module-interface -o %t/B.pcm
+// RUN: %clang_cc1 -std=c++20 -fskip-odr-check-in-gmf %t/test.cpp -fprebuilt-module-path=%t -fsyntax-only -verify
+
+//--- header.h
+#pragma once
+template <class _Tp>
+class Optional {};
+
+template <class _Tp>
+concept C = requires(const _Tp& __t) {
+    []<class _Up>(const Optional<_Up>&) {}(__t);
+};
+
+//--- func.h
+#include "header.h"
+template <C T>
+void func() {}
+
+//--- duplicated_func.h
+#include "header.h"
+template <C T>
+void duplicated_func() {}
+
+//--- test_func.h
+#include "func.h"
+
+void test_func() {
+    func<Optional<int>>();
+}
+
+//--- test_duplicated_func.h
+#include "duplicated_func.h"
+
+void test_duplicated_func() {
+    duplicated_func<Optional<int>>();
+}
+
+//--- A.cppm
+module;
+#include "header.h"
+#include "test_duplicated_func.h"
+export module A;
+export using ::test_duplicated_func;
+
+//--- B.cppm
+module;
+#include "header.h"
+#include "test_func.h"
+#include "test_duplicated_func.h"
+export module B;
+export using ::test_func;
+export using ::test_duplicated_func;
+
+//--- test.cpp
+// expected-no-diagnostics
+import A;
+import B;
+
+void test() {
+    test_func();
+    test_duplicated_func();
+}