[PATCH] D128119: [clang] enforce instantiation of constexpr template functions

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Fix #55560


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D128119

Files:
  clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
  clang/test/SemaCXX/constexpr-late-instantiation.cpp


Index: clang/test/SemaCXX/constexpr-late-instantiation.cpp
===================================================================
--- /dev/null
+++ clang/test/SemaCXX/constexpr-late-instantiation.cpp
@@ -0,0 +1,17 @@
+// Make sure foo is sinstantiated and we don't get a link error
+// RUN: %clang_cc1 -S -emit-llvm %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-LABEL: define {{.*}} @_Z3fooIiET_S0_
+template <typename T>
+constexpr T foo(T a) {
+  return a;
+}
Index: clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
===================================================================
--- clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
+++ clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
@@ -4853,6 +4853,10 @@
         if (getLangOpts().CPlusPlus11)
           Diag(PointOfInstantiation, diag::note_inst_declaration_hint)
             << Function;
+      } else if (!Recursive) {
+        Function->setInstantiationIsPending(true);
+        PendingInstantiations.push_back(
+            std::make_pair(Function, PointOfInstantiation));
       }
     }
 


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