https://github.com/cor3ntin updated
https://github.com/llvm/llvm-project/pull/73463
>From a1d36de81074ad17bc5d22a4c5906f5a0bfa65c4 Mon Sep 17 00:00:00 2001
From: Corentin Jabot <corentinja...@gmail.com>
Date: Sun, 26 Nov 2023 22:47:51 +0100
Subject: [PATCH 1/2] [Clang] Eagerly instantiate used constexpr function upon
definition.
Despite CWG2497 not being resolved, it is reasonable to expect the following
code to compile (and which is supported by other compilers)
```cpp
template<typename T> constexpr T f();
constexpr int g() { return f<int>(); } // #1
template<typename T> constexpr T f() { return 123; }
int k[g()];
// #2
```
To that end, we eagerly instantiate all referenced
specializations of constexpr functions when they are defined.
We maintain a map of (pattern, [instantiations]) independant of
`PendingInstantiations` to avoid having to iterate that list after
each function definition.
We should apply the same logic to constexpr variables,
but I wanted to keep the PR small.
Fixes #73232
---
clang/docs/ReleaseNotes.rst | 5 ++++
clang/include/clang/Sema/Sema.h | 11 +++++++
clang/lib/Sema/SemaDecl.cpp | 3 ++
clang/lib/Sema/SemaExpr.cpp | 9 ++++--
.../lib/Sema/SemaTemplateInstantiateDecl.cpp | 17 +++++++++++
.../SemaCXX/cxx2b-consteval-propagate.cpp | 8 +++--
.../instantiate-used-constexpr-function.cpp | 30 +++++++++++++++++++
7 files changed, 78 insertions(+), 5 deletions(-)
create mode 100644
clang/test/SemaTemplate/instantiate-used-constexpr-function.cpp
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 7c909ac3cab6419..f46891364e4764b 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -783,6 +783,11 @@ Bug Fixes to C++ Support
completes (except deduction guides). Fixes:
(`#59827 <https://github.com/llvm/llvm-project/issues/59827>`_)
+- Clang now immediately instantiates function template specializations
+ at the end of the definition of the corresponding function template
+ when the definition appears after the first point of instantiation.
+ (`#73232 <https://github.com/llvm/llvm-project/issues/73232>`_)
+
Bug Fixes to AST Handling
^^^^^^^^^^^^^^^^^^^^^^^^^
- Fixed an import failure of recursive friend class template.
diff --git a/clang/include/clang/Sema/Sema.h b/clang/include/clang/Sema/Sema.h
index f7c9d0e2e6412b7..091e1e3b4c1fd64 100644
--- a/clang/include/clang/Sema/Sema.h
+++ b/clang/include/clang/Sema/Sema.h
@@ -59,6 +59,7 @@
#include "clang/Sema/TypoCorrection.h"
#include "clang/Sema/Weak.h"
#include "llvm/ADT/ArrayRef.h"
+#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/SetVector.h"
#include "llvm/ADT/SmallBitVector.h"
#include "llvm/ADT/SmallPtrSet.h"
@@ -10078,6 +10079,12 @@ class Sema final {
/// but have not yet been performed.
std::deque<PendingImplicitInstantiation> PendingInstantiations;
+ /// Track constexpr functions referenced before they are (lexically) defined.
+ /// The key is the pattern, associated with a list of specialisations that
+ /// need to be instantiated when the pattern is defined.
+ llvm::DenseMap<NamedDecl *, SmallVector<NamedDecl *>>
+ PendingInstantiationsOfConstexprEntities;
+
/// Queue of implicit template instantiations that cannot be performed
/// eagerly.
SmallVector<PendingImplicitInstantiation, 1> LateParsedInstantiations;
@@ -10396,6 +10403,10 @@ class Sema final {
bool Recursive = false,
bool DefinitionRequired = false,
bool AtEndOfTU = false);
+
+ void InstantiateFunctionTemplateSpecializations(
+ SourceLocation PointOfInstantiation, FunctionDecl *Template);
+
VarTemplateSpecializationDecl *BuildVarTemplateInstantiation(
VarTemplateDecl *VarTemplate, VarDecl *FromVar,
const TemplateArgumentList &TemplateArgList,
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 23dd8ae15c16583..1030ba0d21b1906 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -16255,6 +16255,9 @@ Decl *Sema::ActOnFinishFunctionBody(Decl *dcl, Stmt
*Body,
if (FD && !FD->isDeleted())
checkTypeSupport(FD->getType(), FD->getLocation(), FD);
+ if (FD && FD->isConstexpr() && FD->isTemplated())
+ InstantiateFunctionTemplateSpecializations(FD->getEndLoc(), FD);
+
return dcl;
}
diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index fc39d6149c1cc65..37b0d0eed35845c 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -19047,12 +19047,17 @@ void Sema::MarkFunctionReferenced(SourceLocation Loc,
FunctionDecl *Func,
CodeSynthesisContexts.size())
PendingLocalImplicitInstantiations.push_back(
std::make_pair(Func, PointOfInstantiation));
- else if (Func->isConstexpr())
+ else if (Func->isConstexpr()) {
// Do not defer instantiations of constexpr functions, to avoid the
// expression evaluator needing to call back into Sema if it sees a
// call to such a function.
InstantiateFunctionDefinition(PointOfInstantiation, Func);
- else {
+ if (!Func->isDefined()) {
+ PendingInstantiationsOfConstexprEntities
+ [Func->getTemplateInstantiationPattern()->getCanonicalDecl()]
+ .push_back(Func);
+ }
+ } else {
Func->setInstantiationIsPending(true);
PendingInstantiations.push_back(
std::make_pair(Func, PointOfInstantiation));
diff --git a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
index 08f4ba00fc9f7de..9afbf139a1c2b88 100644
--- a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
+++ b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
@@ -6481,6 +6481,23 @@ void Sema::PerformPendingInstantiations(bool LocalOnly) {
PendingInstantiations.swap(delayedPCHInstantiations);
}
+// 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) {
+ auto It =
+ PendingInstantiationsOfConstexprEntities.find(Tpl->getCanonicalDecl());
+ if (It == PendingInstantiationsOfConstexprEntities.end())
+ return;
+ for (NamedDecl *Fun : It->second) {
+ InstantiateFunctionDefinition(PointOfInstantiation,
+ cast<FunctionDecl>(Fun));
+ }
+ PendingInstantiationsOfConstexprEntities.erase(It);
+}
+
void Sema::PerformDependentDiagnostics(const DeclContext *Pattern,
const MultiLevelTemplateArgumentList &TemplateArgs) {
for (auto *DD : Pattern->ddiags()) {
diff --git a/clang/test/SemaCXX/cxx2b-consteval-propagate.cpp
b/clang/test/SemaCXX/cxx2b-consteval-propagate.cpp
index 531a62622873357..a2b4039a31db778 100644
--- a/clang/test/SemaCXX/cxx2b-consteval-propagate.cpp
+++ b/clang/test/SemaCXX/cxx2b-consteval-propagate.cpp
@@ -105,13 +105,15 @@ 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}} \
- // expected-note {{in instantiation of function template
specialization}}
+auto b = &f<int>; // expected-error {{immediate function 'f<int>' used before
it is defined}}
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}}
+
+
+
}
namespace constructors {
diff --git a/clang/test/SemaTemplate/instantiate-used-constexpr-function.cpp
b/clang/test/SemaTemplate/instantiate-used-constexpr-function.cpp
new file mode 100644
index 000000000000000..61a7fb01376805f
--- /dev/null
+++ b/clang/test/SemaTemplate/instantiate-used-constexpr-function.cpp
@@ -0,0 +1,30 @@
+// RUN: %clang_cc1 -fsyntax-only -verify %s
+// expected-no-diagnostics
+
+namespace GH73232 {
+
+template <typename _CharT>
+struct basic_string {
+ constexpr void _M_construct();
+ constexpr basic_string() {
+ _M_construct();
+ }
+};
+
+basic_string<char> a;
+
+template <typename _CharT>
+constexpr void basic_string<_CharT>::_M_construct(){}
+constexpr basic_string<char> str{};
+
+template <typename T>
+constexpr void g(T);
+
+constexpr int f() { g(0); return 0; }
+
+template <typename T>
+constexpr void g(T) {}
+
+constexpr int z = f();
+
+}
>From b0724384cb9ccb3ac47cf5988a97acfc242ff1a6 Mon Sep 17 00:00:00 2001
From: Corentin Jabot <corentinja...@gmail.com>
Date: Tue, 28 Nov 2023 19:47:46 +0100
Subject: [PATCH 2/2] WIP: Serialize pending constexr instantiations
I wanted to avoid loading eagerly all function templates
and their instantiations -
even if ultimately `PendingInstantiations` - which contains the same information
is going to be loaded at the end of the TU.
So instead, when we find the definition of a constexpr
function template we load the associated instantiation from the
external modules at that point.
I'm not sure there is a better way to get to a DeclID from a Decl*
than to iterate over all redeclarations?
I still need to cleanup but I'd like feedback on direction first!
---
clang/include/clang/Sema/ExternalSemaSource.h | 3 +++
.../clang/Sema/MultiplexExternalSemaSource.h | 3 +++
.../include/clang/Serialization/ASTBitCodes.h | 4 +++
clang/include/clang/Serialization/ASTReader.h | 6 +++++
.../lib/Sema/MultiplexExternalSemaSource.cpp | 6 +++++
.../lib/Sema/SemaTemplateInstantiateDecl.cpp | 22 +++++++++++-----
clang/lib/Serialization/ASTReader.cpp | 25 +++++++++++++++++++
clang/lib/Serialization/ASTWriter.cpp | 16 ++++++++++++
.../instantiate-used-constexpr-function.cpp | 17 +++++++++++++
9 files changed, 96 insertions(+), 6 deletions(-)
create mode 100644 clang/test/PCH/instantiate-used-constexpr-function.cpp
diff --git a/clang/include/clang/Sema/ExternalSemaSource.h
b/clang/include/clang/Sema/ExternalSemaSource.h
index 22d1ee2df115a6e..67bac7f0a5a91f5 100644
--- a/clang/include/clang/Sema/ExternalSemaSource.h
+++ b/clang/include/clang/Sema/ExternalSemaSource.h
@@ -181,6 +181,9 @@ class ExternalSemaSource : public ExternalASTSource {
SmallVectorImpl<std::pair<ValueDecl *,
SourceLocation> > &Pending) {}
+ virtual void ReadPendingOfInstantiationsForConstexprEntity(
+ const NamedDecl *D, llvm::SmallSetVector<NamedDecl *, 4> &Decls){};
+
/// Read the set of late parsed template functions for this source.
///
/// The external source should insert its own late parsed template functions
diff --git a/clang/include/clang/Sema/MultiplexExternalSemaSource.h
b/clang/include/clang/Sema/MultiplexExternalSemaSource.h
index 2bf91cb5212c5eb..25c200a0bc33c0e 100644
--- a/clang/include/clang/Sema/MultiplexExternalSemaSource.h
+++ b/clang/include/clang/Sema/MultiplexExternalSemaSource.h
@@ -319,6 +319,9 @@ class MultiplexExternalSemaSource : public
ExternalSemaSource {
void ReadPendingInstantiations(
SmallVectorImpl<std::pair<ValueDecl*, SourceLocation> >& Pending)
override;
+ virtual void ReadPendingOfInstantiationsForConstexprEntity(
+ const NamedDecl *D, llvm::SmallSetVector<NamedDecl *, 4> &Decls)
override;
+
/// Read the set of late parsed template functions for this source.
///
/// The external source should insert its own late parsed template functions
diff --git a/clang/include/clang/Serialization/ASTBitCodes.h
b/clang/include/clang/Serialization/ASTBitCodes.h
index fdd64f2abbe9375..08642889b0cf3eb 100644
--- a/clang/include/clang/Serialization/ASTBitCodes.h
+++ b/clang/include/clang/Serialization/ASTBitCodes.h
@@ -695,6 +695,10 @@ enum ASTRecordTypes {
/// Record code for an unterminated \#pragma clang assume_nonnull begin
/// recorded in a preamble.
PP_ASSUME_NONNULL_LOC = 67,
+
+ /// Record code for constexpr templated entities that have been used but not
+ /// yet instantiated.
+ PENDING_INSTANTIATIONS_OF_CONSTEXPR_ENTITIES = 68,
};
/// Record types used within a source manager block.
diff --git a/clang/include/clang/Serialization/ASTReader.h
b/clang/include/clang/Serialization/ASTReader.h
index 7eefdca6815cdad..358b09ac3e4aa3e 100644
--- a/clang/include/clang/Serialization/ASTReader.h
+++ b/clang/include/clang/Serialization/ASTReader.h
@@ -814,6 +814,9 @@ class ASTReader
/// is the instantiation location.
SmallVector<serialization::DeclID, 64> PendingInstantiations;
+ llvm::DenseMap<serialization::DeclID, std::set<serialization::DeclID>>
+ PendingInstantiationsOfConstexprEntities;
+
//@}
/// \name DiagnosticsEngine-relevant special data
@@ -2101,6 +2104,9 @@ class ASTReader
SmallVectorImpl<std::pair<ValueDecl *,
SourceLocation>> &Pending)
override;
+ virtual void ReadPendingOfInstantiationsForConstexprEntity(
+ const NamedDecl *D, llvm::SmallSetVector<NamedDecl *, 4> &Decls)
override;
+
void ReadLateParsedTemplates(
llvm::MapVector<const FunctionDecl *,
std::unique_ptr<LateParsedTemplate>>
&LPTMap) override;
diff --git a/clang/lib/Sema/MultiplexExternalSemaSource.cpp
b/clang/lib/Sema/MultiplexExternalSemaSource.cpp
index 058e22cb2b814e6..e5b06184d9867cc 100644
--- a/clang/lib/Sema/MultiplexExternalSemaSource.cpp
+++ b/clang/lib/Sema/MultiplexExternalSemaSource.cpp
@@ -310,6 +310,12 @@ void
MultiplexExternalSemaSource::ReadPendingInstantiations(
Sources[i]->ReadPendingInstantiations(Pending);
}
+void
MultiplexExternalSemaSource::ReadPendingOfInstantiationsForConstexprEntity(
+ const NamedDecl *D, llvm::SmallSetVector<NamedDecl *, 4> &Decls) {
+ for (size_t i = 0; i < Sources.size(); ++i)
+ Sources[i]->ReadPendingOfInstantiationsForConstexprEntity(D, Decls);
+};
+
void MultiplexExternalSemaSource::ReadLateParsedTemplates(
llvm::MapVector<const FunctionDecl *, std::unique_ptr<LateParsedTemplate>>
&LPTMap) {
diff --git a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
index 9afbf139a1c2b88..afddb156ab34593 100644
--- a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
+++ b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
@@ -6487,15 +6487,25 @@ void Sema::PerformPendingInstantiations(bool LocalOnly)
{
// see CWG2497.
void Sema::InstantiateFunctionTemplateSpecializations(
SourceLocation PointOfInstantiation, FunctionDecl *Tpl) {
+
+ auto InstantiateAll = [&](const auto &Range) {
+ for (NamedDecl *Fun : Range) {
+ InstantiateFunctionDefinition(PointOfInstantiation,
+ cast<FunctionDecl>(Fun));
+ }
+ };
+
auto It =
PendingInstantiationsOfConstexprEntities.find(Tpl->getCanonicalDecl());
- if (It == PendingInstantiationsOfConstexprEntities.end())
- return;
- for (NamedDecl *Fun : It->second) {
- InstantiateFunctionDefinition(PointOfInstantiation,
- cast<FunctionDecl>(Fun));
+ if (It != PendingInstantiationsOfConstexprEntities.end()) {
+ InstantiateAll(It->second);
+ }
+
+ llvm::SmallSetVector<NamedDecl *, 4> Decls;
+ if (ExternalSource) {
+ ExternalSource->ReadPendingOfInstantiationsForConstexprEntity(Tpl, Decls);
+ InstantiateAll(Decls);
}
- PendingInstantiationsOfConstexprEntities.erase(It);
}
void Sema::PerformDependentDiagnostics(const DeclContext *Pattern,
diff --git a/clang/lib/Serialization/ASTReader.cpp
b/clang/lib/Serialization/ASTReader.cpp
index f22da838424b415..bf65ac2d607dce9 100644
--- a/clang/lib/Serialization/ASTReader.cpp
+++ b/clang/lib/Serialization/ASTReader.cpp
@@ -3709,6 +3709,19 @@ llvm::Error ASTReader::ReadASTBlock(ModuleFile &F,
}
break;
+ case PENDING_INSTANTIATIONS_OF_CONSTEXPR_ENTITIES:
+ if (Record.size() % 2 != 0)
+ return llvm::createStringError(
+ std::errc::illegal_byte_sequence,
+ "Invalid PENDING_INSTANTIATIONS_OF_CONSTEXPR_ENTITIES block");
+
+ for (unsigned I = 0, N = Record.size(); I != N; /* in loop */) {
+ DeclID Key = getGlobalDeclID(F, Record[I++]);
+ DeclID Value = getGlobalDeclID(F, Record[I++]);
+ PendingInstantiationsOfConstexprEntities[Key].insert(Value);
+ }
+ break;
+
case SEMA_DECL_REFS:
if (Record.size() != 3)
return llvm::createStringError(std::errc::illegal_byte_sequence,
@@ -8718,6 +8731,18 @@ void ASTReader::ReadPendingInstantiations(
PendingInstantiations.clear();
}
+void ASTReader::ReadPendingOfInstantiationsForConstexprEntity(
+ const NamedDecl *D, llvm::SmallSetVector<NamedDecl *, 4> &Decls) {
+ for (auto *Redecl : D->redecls()) {
+ DeclID Id = Redecl->getGlobalID();
+ auto It = PendingInstantiationsOfConstexprEntities.find(Id);
+ if (It == PendingInstantiationsOfConstexprEntities.end())
+ continue;
+ for (DeclID InstantiationId : It->second)
+ Decls.insert(cast<NamedDecl>(GetDecl(InstantiationId)));
+ }
+}
+
void ASTReader::ReadLateParsedTemplates(
llvm::MapVector<const FunctionDecl *, std::unique_ptr<LateParsedTemplate>>
&LPTMap) {
diff --git a/clang/lib/Serialization/ASTWriter.cpp
b/clang/lib/Serialization/ASTWriter.cpp
index 6df815234e235fb..c6ad3bd725af3a7 100644
--- a/clang/lib/Serialization/ASTWriter.cpp
+++ b/clang/lib/Serialization/ASTWriter.cpp
@@ -849,6 +849,7 @@ void ASTWriter::WriteBlockInfoBlock() {
RECORD(SEMA_DECL_REFS);
RECORD(WEAK_UNDECLARED_IDENTIFIERS);
RECORD(PENDING_IMPLICIT_INSTANTIATIONS);
+ RECORD(PENDING_INSTANTIATIONS_OF_CONSTEXPR_ENTITIES);
RECORD(UPDATE_VISIBLE);
RECORD(DECL_UPDATE_OFFSETS);
RECORD(DECL_UPDATES);
@@ -4836,6 +4837,16 @@ 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
+ // entities.
+ RecordData PendingInstantiationsOfConstexprEntities;
+ for (const auto &I : SemaRef.PendingInstantiationsOfConstexprEntities) {
+ for (const auto &Elem : I.second) {
+ AddDeclRef(I.first, PendingInstantiationsOfConstexprEntities);
+ AddDeclRef(Elem, PendingInstantiationsOfConstexprEntities);
+ }
+ }
+
// Build a record containing some declaration references.
RecordData SemaDeclRefs;
if (SemaRef.StdNamespace || SemaRef.StdBadAlloc || SemaRef.StdAlignValT) {
@@ -5153,6 +5164,11 @@ ASTFileSignature ASTWriter::WriteASTCore(Sema &SemaRef,
StringRef isysroot,
if (!PendingInstantiations.empty())
Stream.EmitRecord(PENDING_IMPLICIT_INSTANTIATIONS, PendingInstantiations);
+ // Write the record containing pending instantiations of constexpr entities.
+ if (!PendingInstantiationsOfConstexprEntities.empty())
+ Stream.EmitRecord(PENDING_INSTANTIATIONS_OF_CONSTEXPR_ENTITIES,
+ PendingInstantiationsOfConstexprEntities);
+
// Write the record containing declaration references of Sema.
if (!SemaDeclRefs.empty())
Stream.EmitRecord(SEMA_DECL_REFS, SemaDeclRefs);
diff --git a/clang/test/PCH/instantiate-used-constexpr-function.cpp
b/clang/test/PCH/instantiate-used-constexpr-function.cpp
new file mode 100644
index 000000000000000..3930d0467d866be
--- /dev/null
+++ b/clang/test/PCH/instantiate-used-constexpr-function.cpp
@@ -0,0 +1,17 @@
+// RUN: %clang_cc1 -std=c++2a -emit-pch %s -o %t
+// RUN: %clang_cc1 -std=c++2a -include-pch %t -verify %s
+
+// expected-no-diagnostics
+
+#ifndef HEADER
+#define HEADER
+
+template<typename T> constexpr T f();
+constexpr int g() { return f<int>(); } // #1
+
+#else /*included pch*/
+
+template<typename T> constexpr T f() { return 123; }
+int k[g()];
+
+#endif // HEADER
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