[clang] Revert "[Clang] Fix missed initializer instantiation bug for variable templates" (PR #140930)

[Paul Kirth via cfe-commits]

https://github.com/ilovepi created https://github.com/llvm/llvm-project/pull/140930

Reverts llvm/llvm-project#138122

The patch causes a regression and prevents compiling valid C++ code. 
The code was accepted by earlier versions of clang and GCC. 
See https://github.com/llvm/llvm-project/issues/140773 for details.

>From 1d92b5f9c270b86348d9d77e7946d4502f220163 Mon Sep 17 00:00:00 2001
From: Paul Kirth <paulkirth at google.com>
Date: Wed, 21 May 2025 09:53:54 -0700
Subject: [PATCH] =?UTF-8?q?Revert=20"[Clang]=20Fix=20missed=20initializer?=
 =?UTF-8?q?=20instantiation=20bug=20for=20variable=20templat=E2=80=A6"?=
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This reverts commit 0b553e055ad01ca6a2c88f7da92157df29e42fd0.
---
 clang/docs/ReleaseNotes.rst                        |  1 -
 clang/lib/Sema/SemaTemplateInstantiateDecl.cpp     |  6 +++---
 clang/test/CodeGenCXX/cxx1z-inline-variables.cpp   | 14 --------------
 clang/test/SemaTemplate/cxx17-inline-variables.cpp | 12 ------------
 4 files changed, 3 insertions(+), 30 deletions(-)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 648b32c659b4f..941b9ab45cf1c 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -743,7 +743,6 @@ Bug Fixes to C++ Support
   in a ``constexpr`` function. (#GH131432)
 - Fixed an incorrect TreeTransform for calls to ``consteval`` functions if a conversion template is present. (#GH137885)
 - Clang now emits a warning when class template argument deduction for alias templates is used in C++17. (#GH133806)
-- Fix missed initializer instantiation bug for variable templates. (#GH138122)
 - Fix a crash when checking the template template parameters of a dependent lambda appearing in an alias declaration.
   (#GH136432), (#GH137014), (#GH138018)
 - Fixed an assertion when trying to constant-fold various builtins when the argument
diff --git a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
index d1f313e9cb487..7fbda2a804d75 100644
--- a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
+++ b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
@@ -6032,11 +6032,11 @@ void Sema::BuildVariableInstantiation(
   Context.setStaticLocalNumber(NewVar, Context.getStaticLocalNumber(OldVar));
 
   // Figure out whether to eagerly instantiate the initializer.
-  if (NewVar->getType()->isUndeducedType()) {
+  if (InstantiatingVarTemplate || InstantiatingVarTemplatePartialSpec) {
+    // We're producing a template. Don't instantiate the initializer yet.
+  } else if (NewVar->getType()->isUndeducedType()) {
     // We need the type to complete the declaration of the variable.
     InstantiateVariableInitializer(NewVar, OldVar, TemplateArgs);
-  } else if (InstantiatingVarTemplate || InstantiatingVarTemplatePartialSpec) {
-    // We're producing a template. Don't instantiate the initializer yet.
   } else if (InstantiatingSpecFromTemplate ||
              (OldVar->isInline() && OldVar->isThisDeclarationADefinition() &&
               !NewVar->isThisDeclarationADefinition())) {
diff --git a/clang/test/CodeGenCXX/cxx1z-inline-variables.cpp b/clang/test/CodeGenCXX/cxx1z-inline-variables.cpp
index 1cb30b178e06f..812e438f30c9a 100644
--- a/clang/test/CodeGenCXX/cxx1z-inline-variables.cpp
+++ b/clang/test/CodeGenCXX/cxx1z-inline-variables.cpp
@@ -1,19 +1,5 @@
 // RUN: %clang_cc1 -std=c++1z %s -emit-llvm -o - -triple x86_64-linux-gnu | FileCheck %s
 
-template <typename T> struct InlineAuto {
-  template <typename G> inline static auto var = 5;
-};
-int inlineauto = InlineAuto<int>::var<int>;
-// CHECK: @_ZN10InlineAutoIiE3varIiEE = {{.*}}i32 5{{.*}}comdat
-//
-template <typename> struct PartialInlineAuto {
-  template <typename, typename> inline static auto var = 6;
-  template <typename T> inline static auto var<int, T> = 7;
-};
-
-int partialinlineauto = PartialInlineAuto<int>::var<int, int>;
-// CHECK: @_ZN17PartialInlineAutoIiE3varIiiEE = {{.*}}i32 7{{.*}}comdat
-
 struct Q {
   // CHECK: @_ZN1Q1kE = linkonce_odr constant i32 5, comdat
   static constexpr int k = 5;
diff --git a/clang/test/SemaTemplate/cxx17-inline-variables.cpp b/clang/test/SemaTemplate/cxx17-inline-variables.cpp
index 06f1ec17fb7a8..7fc0aa8eeeb0c 100644
--- a/clang/test/SemaTemplate/cxx17-inline-variables.cpp
+++ b/clang/test/SemaTemplate/cxx17-inline-variables.cpp
@@ -27,15 +27,3 @@ template <typename T> constexpr int A<T>::n = sizeof(A) + sizeof(T);
 template <typename T> inline constexpr int A<T>::m = sizeof(A) + sizeof(T);
 static_assert(A<int>().f() == 5);
 static_assert(A<int>().g() == 5);
-
-template <typename T> struct InlineAuto {
-  template <typename G> inline static auto var = 5;
-};
-
-template <typename> struct PartialInlineAuto {
-  template <typename, typename> inline static auto var = 6;
-  template <typename T> inline static auto var<int, T> = 7;
-};
-
-int inlineauto = InlineAuto<int>::var<int>;
-int partialinlineauto = PartialInlineAuto<int>::var<int, int>;