[C++20] [Moduls] Avoid computing odr hash for functions from comparing constraint expression

Previously we disabled to compute ODR hash for declarations from the
global module fragment. However, we missed the case that the functions
lives in the concept requiments (see the attached the test files for
example). And the mismatch causes the potential crashment.

Due to we will set the function body as lazy after we deserialize it and
we will only take its body when needed. However, we don't allow to take
the body during deserializing. So it is actually potentially problematic
if we set the body as lazy first and computing the hash value of the
function, which requires to deserialize its body. So we will meet a
crash here.

This patch tries to solve the issue by not taking the body of the
function from GMF. Note that we can't skip comparing the constraint
expression from the GMF directly since it is an key part of the
function selecting and it may be the reason why we can't return 0
directly for `FunctionDecl::getODRHash()` from the GMF.

Author: ChuanqiXu9

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();
+}