clang14/trunk/enforce-instantiation-of-constexpr-template-functions.patch

   1 From 2ba4e83e61617daee70f98fcdd76cb8bc3d6ac38 Mon Sep 17 00:00:00 2001
   2 From: serge-sans-paille <sguelton@redhat.com>
   3 Date: Sat, 18 Jun 2022 13:48:41 +0200
   4 Subject: [PATCH] [clang] Enforce instantiation of constexpr template functions
   5  during non-constexpr evaluation
   6
   7 Otherwise these functions are not instantiated and we end up with an undefined
   8 symbol.
   9
  10 Fix #55560
  11
  12 Differential Revision: https://reviews.llvm.org/D128119
  13
  14 (cherry picked from commit da6a14b91ad999327b41a9040577273591e4ad1d)
  15 ---
  16  clang/lib/Sema/SemaTemplateInstantiateDecl.cpp  |  5 +++--
  17  .../CodeGenCXX/constexpr-late-instantiation.cpp | 17 +++++++++++++++++
  18  .../SemaCXX/constexpr-late-instantiation.cpp    | 15 +++++++++++++++
  19  3 files changed, 35 insertions(+), 2 deletions(-)
  20  create mode 100644 clang/test/CodeGenCXX/constexpr-late-instantiation.cpp
  21  create mode 100644 clang/test/SemaCXX/constexpr-late-instantiation.cpp
  22
  23 diff --git a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
  24 index 467372c71496..293782822e83 100644
  25 --- a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
  26 +++ b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
  27 @@ -4826,7 +4826,8 @@ void Sema::InstantiateFunctionDefinition(SourceLocation PointOfInstantiation,
  28                                       /*Complain*/DefinitionRequired)) {
  29      if (DefinitionRequired)
  30        Function->setInvalidDecl();
  31 -    else if (TSK == TSK_ExplicitInstantiationDefinition) {
  32 +    else if (TSK == TSK_ExplicitInstantiationDefinition ||
  33 +             (Function->isConstexpr() && !Recursive)) {
  34        // Try again at the end of the translation unit (at which point a
  35        // definition will be required).
  36        assert(!Recursive);
  37 @@ -4841,7 +4842,7 @@ void Sema::InstantiateFunctionDefinition(SourceLocation PointOfInstantiation,
  38          Diag(PatternDecl->getLocation(), diag::note_forward_template_decl);
  39          if (getLangOpts().CPlusPlus11)
  40            Diag(PointOfInstantiation, diag::note_inst_declaration_hint)
  41 -            << Function;
  42 +              << Function;
  43        }
  44      }
  45
  46 diff --git a/clang/test/CodeGenCXX/constexpr-late-instantiation.cpp b/clang/test/CodeGenCXX/constexpr-late-instantiation.cpp
  47 new file mode 100644
  48 index 000000000000..1c8eef73f2dd
  49 --- /dev/null
  50 +++ b/clang/test/CodeGenCXX/constexpr-late-instantiation.cpp
  51 @@ -0,0 +1,17 @@
  52 +// Make sure foo is instantiated and we don't get a link error
  53 +// RUN: %clang_cc1 -S -emit-llvm -triple %itanium_abi_triple %s -o- | FileCheck %s
  54 +
  55 +template <typename T>
  56 +constexpr T foo(T a);
  57 +
  58 +// CHECK-LABEL: define {{.*}} @main
  59 +int main() {
  60 +  // CHECK: call {{.*}} @_Z3fooIiET_S0_
  61 +  int k = foo<int>(5);
  62 +}
  63 +// CHECK: }
  64 +
  65 +template <typename T>
  66 +constexpr T foo(T a) {
  67 +  return a;
  68 +}
  69 diff --git a/clang/test/SemaCXX/constexpr-late-instantiation.cpp b/clang/test/SemaCXX/constexpr-late-instantiation.cpp
  70 new file mode 100644
  71 index 000000000000..ec8e071217c1
  72 --- /dev/null
  73 +++ b/clang/test/SemaCXX/constexpr-late-instantiation.cpp
  74 @@ -0,0 +1,15 @@
  75 +// RUN: %clang_cc1 %s -fsyntax-only -verify
  76 +
  77 +template <typename T>
  78 +constexpr T foo(T a);   // expected-note {{declared here}}
  79 +
  80 +int main() {
  81 +  int k = foo<int>(5);  // Ok
  82 +  constexpr int j =     // expected-error {{constexpr variable 'j' must be initialized by a constant expression}}
  83 +          foo<int>(5);  // expected-note {{undefined function 'foo<int>' cannot be used in a constant expression}}
  84 +}
  85 +
  86 +template <typename T>
  87 +constexpr T foo(T a) {
  88 +  return a;
  89 +}