Address Richard's feedback.

Author: cor3ntin

clang/include/clang/Sema/ExternalSemaSource.h

@@ -181,7 +181,7 @@ class ExternalSemaSource : public ExternalASTSource {
                  SmallVectorImpl<std::pair<ValueDecl *,
                                            SourceLocation> > &Pending) {}
 
-  virtual void ReadPendingOfInstantiationsForConstexprEntity(
+  virtual void ReadPendingInstantiationsOfConstexprEntity(
       const NamedDecl *D, llvm::SmallSetVector<NamedDecl *, 4> &Decls){};
 
   /// Read the set of late parsed template functions for this source.

clang/include/clang/Sema/MultiplexExternalSemaSource.h

@@ -319,7 +319,7 @@ class MultiplexExternalSemaSource : public ExternalSemaSource {
   void ReadPendingInstantiations(
      SmallVectorImpl<std::pair<ValueDecl*, SourceLocation> >& Pending) override;
 
-  virtual void ReadPendingOfInstantiationsForConstexprEntity(
+  virtual void ReadPendingInstantiationsOfConstexprEntity(
       const NamedDecl *D, llvm::SmallSetVector<NamedDecl *, 4> &Decls) override;
 
   /// Read the set of late parsed template functions for this source.

clang/include/clang/Sema/Sema.h

@@ -10413,8 +10413,7 @@ class Sema final {
                                      bool DefinitionRequired = false,
                                      bool AtEndOfTU = false);
 
-  void InstantiateFunctionTemplateSpecializations(
-      SourceLocation PointOfInstantiation, FunctionDecl *Template);
+  void PerformPendingInstantiationsOfConstexprFunctions(FunctionDecl *Template);
 
   VarTemplateSpecializationDecl *BuildVarTemplateInstantiation(
       VarTemplateDecl *VarTemplate, VarDecl *FromVar,

clang/include/clang/Serialization/ASTReader.h

@@ -2104,7 +2104,7 @@ class ASTReader
                   SmallVectorImpl<std::pair<ValueDecl *,
                                             SourceLocation>> &Pending) override;
 
-  virtual void ReadPendingOfInstantiationsForConstexprEntity(
+  virtual void ReadPendingInstantiationsOfConstexprEntity(
       const NamedDecl *D, llvm::SmallSetVector<NamedDecl *, 4> &Decls) override;
 
   void ReadLateParsedTemplates(

clang/lib/Sema/MultiplexExternalSemaSource.cpp

@@ -310,10 +310,10 @@ void MultiplexExternalSemaSource::ReadPendingInstantiations(
     Sources[i]->ReadPendingInstantiations(Pending);
 }
 
-void MultiplexExternalSemaSource::ReadPendingOfInstantiationsForConstexprEntity(
+void MultiplexExternalSemaSource::ReadPendingInstantiationsOfConstexprEntity(
     const NamedDecl *D, llvm::SmallSetVector<NamedDecl *, 4> &Decls) {
   for (size_t i = 0; i < Sources.size(); ++i)
-    Sources[i]->ReadPendingOfInstantiationsForConstexprEntity(D, Decls);
+    Sources[i]->ReadPendingInstantiationsOfConstexprEntity(D, Decls);
 };
 
 void MultiplexExternalSemaSource::ReadLateParsedTemplates(

clang/lib/Sema/SemaDecl.cpp

@@ -16276,7 +16276,7 @@ Decl *Sema::ActOnFinishFunctionBody(Decl *dcl, Stmt *Body,
     checkTypeSupport(FD->getType(), FD->getLocation(), FD);
 
   if (FD && FD->isConstexpr() && FD->isTemplated())
-    InstantiateFunctionTemplateSpecializations(FD->getEndLoc(), FD);
+    PerformPendingInstantiationsOfConstexprFunctions(FD);
 
   return dcl;
 }

clang/lib/Sema/SemaTemplateInstantiateDecl.cpp

@@ -6496,28 +6496,29 @@ void Sema::PerformPendingInstantiations(bool LocalOnly) {
 }
 
 // Instantiate all referenced specializations of the given function template
-// definition. This make sure that function template that are defined after the
-// point of instantiation of their used can be evaluated after they are defined.
-// see CWG2497.
-void Sema::InstantiateFunctionTemplateSpecializations(
-    SourceLocation PointOfInstantiation, FunctionDecl *Tpl) {
+// definition. This make sure that constexpr function templates that are defined
+// after the point of instantiation of their use can be evaluated after they
+// are defined. see CWG2497.
+void Sema::PerformPendingInstantiationsOfConstexprFunctions(FunctionDecl *Tpl) {
 
   auto InstantiateAll = [&](const auto &Range) {
-    for (NamedDecl *Fun : Range) {
-      InstantiateFunctionDefinition(PointOfInstantiation,
-                                    cast<FunctionDecl>(Fun));
+    for (NamedDecl *D : Range) {
+      FunctionDecl *Fun = cast<FunctionDecl>(D);
+      InstantiateFunctionDefinition(Fun->getPointOfInstantiation(), Fun);
     }
   };
 
   auto It =
       PendingInstantiationsOfConstexprEntities.find(Tpl->getCanonicalDecl());
   if (It != PendingInstantiationsOfConstexprEntities.end()) {
-    InstantiateAll(It->second);
+    auto Decls = std::move(It->second);
+    PendingInstantiationsOfConstexprEntities.erase(It);
+    InstantiateAll(Decls);
   }
 
   llvm::SmallSetVector<NamedDecl *, 4> Decls;
   if (ExternalSource) {
-    ExternalSource->ReadPendingOfInstantiationsForConstexprEntity(Tpl, Decls);
+    ExternalSource->ReadPendingInstantiationsOfConstexprEntity(Tpl, Decls);
     InstantiateAll(Decls);
   }
 }

clang/lib/Serialization/ASTReader.cpp

@@ -8731,9 +8731,11 @@ void ASTReader::ReadPendingInstantiations(
   PendingInstantiations.clear();
 }
 
-void ASTReader::ReadPendingOfInstantiationsForConstexprEntity(
+void ASTReader::ReadPendingInstantiationsOfConstexprEntity(
     const NamedDecl *D, llvm::SmallSetVector<NamedDecl *, 4> &Decls) {
   for (auto *Redecl : D->redecls()) {
+    if (!Redecl->isFromASTFile())
+      continue;
     DeclID Id = Redecl->getGlobalID();
     auto It = PendingInstantiationsOfConstexprEntities.find(Id);
     if (It == PendingInstantiationsOfConstexprEntities.end())

clang/lib/Serialization/ASTWriter.cpp

@@ -4837,7 +4837,7 @@ ASTFileSignature ASTWriter::WriteASTCore(Sema &SemaRef, StringRef isysroot,
   assert(SemaRef.PendingLocalImplicitInstantiations.empty() &&
          "There are local ones at end of translation unit!");
 
-  // Build a record containing all of pending instantiations of constexpr
+  // Build a record containing all pending instantiations of constexpr
   // entities.
   RecordData PendingInstantiationsOfConstexprEntities;
   for (const auto &I : SemaRef.PendingInstantiationsOfConstexprEntities) {

clang/test/SemaCXX/cxx2b-consteval-propagate.cpp

@@ -105,12 +105,13 @@ template <typename T>
 constexpr int f(T t);
 
 auto a = &f<char>;
-auto b = &f<int>; // expected-error {{immediate function 'f<int>' used before it is defined}}
+auto b = &f<int>; // expected-error {{immediate function 'f<int>' used before it is defined}} \
+                  // expected-note {{in instantiation of function template specialization}}
 
 template <typename T>
 constexpr int f(T t) { // expected-note {{'f<int>' defined here}}
     return id(t); // expected-note {{'f<int>' is an immediate function because its body contains a call to a consteval function 'id' and that call is not a constant expression}}
-} // expected-note {{in instantiation of function template specialization}}
+}