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From 2ba4e83e61617daee70f98fcdd76cb8bc3d6ac38 Mon Sep 17 00:00:00 2001
From: serge-sans-paille <sguelton@redhat.com>
Date: Sat, 18 Jun 2022 13:48:41 +0200
Subject: [PATCH] [clang] Enforce instantiation of constexpr template functions
during non-constexpr evaluation
Otherwise these functions are not instantiated and we end up with an undefined
symbol.
Fix #55560
Differential Revision: https://reviews.llvm.org/D128119
(cherry picked from commit da6a14b91ad999327b41a9040577273591e4ad1d)
---
clang/lib/Sema/SemaTemplateInstantiateDecl.cpp | 5 +++--
.../CodeGenCXX/constexpr-late-instantiation.cpp | 17 +++++++++++++++++
.../SemaCXX/constexpr-late-instantiation.cpp | 15 +++++++++++++++
3 files changed, 35 insertions(+), 2 deletions(-)
create mode 100644 clang/test/CodeGenCXX/constexpr-late-instantiation.cpp
create mode 100644 clang/test/SemaCXX/constexpr-late-instantiation.cpp
diff --git a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
index 467372c71496..293782822e83 100644
--- a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
+++ b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
@@ -4826,7 +4826,8 @@ void Sema::InstantiateFunctionDefinition(SourceLocation PointOfInstantiation,
/*Complain*/DefinitionRequired)) {
if (DefinitionRequired)
Function->setInvalidDecl();
- else if (TSK == TSK_ExplicitInstantiationDefinition) {
+ else if (TSK == TSK_ExplicitInstantiationDefinition ||
+ (Function->isConstexpr() && !Recursive)) {
// Try again at the end of the translation unit (at which point a
// definition will be required).
assert(!Recursive);
@@ -4841,7 +4842,7 @@ void Sema::InstantiateFunctionDefinition(SourceLocation PointOfInstantiation,
Diag(PatternDecl->getLocation(), diag::note_forward_template_decl);
if (getLangOpts().CPlusPlus11)
Diag(PointOfInstantiation, diag::note_inst_declaration_hint)
- << Function;
+ << Function;
}
}
diff --git a/clang/test/CodeGenCXX/constexpr-late-instantiation.cpp b/clang/test/CodeGenCXX/constexpr-late-instantiation.cpp
new file mode 100644
index 000000000000..1c8eef73f2dd
--- /dev/null
+++ b/clang/test/CodeGenCXX/constexpr-late-instantiation.cpp
@@ -0,0 +1,17 @@
+// Make sure foo is instantiated and we don't get a link error
+// RUN: %clang_cc1 -S -emit-llvm -triple %itanium_abi_triple %s -o- | FileCheck %s
+
+template <typename T>
+constexpr T foo(T a);
+
+// CHECK-LABEL: define {{.*}} @main
+int main() {
+ // CHECK: call {{.*}} @_Z3fooIiET_S0_
+ int k = foo<int>(5);
+}
+// CHECK: }
+
+template <typename T>
+constexpr T foo(T a) {
+ return a;
+}
diff --git a/clang/test/SemaCXX/constexpr-late-instantiation.cpp b/clang/test/SemaCXX/constexpr-late-instantiation.cpp
new file mode 100644
index 000000000000..ec8e071217c1
--- /dev/null
+++ b/clang/test/SemaCXX/constexpr-late-instantiation.cpp
@@ -0,0 +1,15 @@
+// RUN: %clang_cc1 %s -fsyntax-only -verify
+
+template <typename T>
+constexpr T foo(T a); // expected-note {{declared here}}
+
+int main() {
+ int k = foo<int>(5); // Ok
+ constexpr int j = // expected-error {{constexpr variable 'j' must be initialized by a constant expression}}
+ foo<int>(5); // expected-note {{undefined function 'foo<int>' cannot be used in a constant expression}}
+}
+
+template <typename T>
+constexpr T foo(T a) {
+ return a;
+}
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