llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-clang
Author: cor3ntin (cor3ntin)
<details>
<summary>Changes</summary>
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
---
Full diff: https://github.com/llvm/llvm-project/pull/73463.diff
7 Files Affected:
- (modified) clang/docs/ReleaseNotes.rst (+5)
- (modified) clang/include/clang/Sema/Sema.h (+11)
- (modified) clang/lib/Sema/SemaDecl.cpp (+3)
- (modified) clang/lib/Sema/SemaExpr.cpp (+7-2)
- (modified) clang/lib/Sema/SemaTemplateInstantiateDecl.cpp (+17)
- (modified) clang/test/SemaCXX/cxx2b-consteval-propagate.cpp (+5-3)
- (added) clang/test/SemaTemplate/instantiate-used-constexpr-function.cpp (+30)
``````````diff
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 29a06d0f713f588..b34b66ec7dcabc2 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -762,6 +762,11 @@ 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..57353d681ac7708
--- /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> z{};
+
+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();
+
+}
``````````
</details>
https://github.com/llvm/llvm-project/pull/73463
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