[llvm-branch-commits] [clang] release/22.x: [clang][c23] Avoid assertion on an invalid static constexpr variable (#175927) (PR #175960)

[via llvm-branch-commits]

https://github.com/llvmbot created https://github.com/llvm/llvm-project/pull/175960

Backport 5b0270cb72f707f55e2ff5e97fc938afb3b81053

Requested by: @Fznamznon

>From 37a2056adf2f39227c482d5a5ef856bd1501d4d0 Mon Sep 17 00:00:00 2001
From: Mariya Podchishchaeva <mariya.podchishchaeva at intel.com>
Date: Wed, 14 Jan 2026 15:37:53 +0100
Subject: [PATCH] [clang][c23] Avoid assertion on an invalid static constexpr
 variable (#175927)

In C static variables should have constant expressions in initializers
so we were checking this twice for constexpr variables and failing with
an assertion that was makes sure we don't do it.
This patch postpones the check just like it is done for file
scope constexpr variables in C already.

Fixes https://github.com/llvm/llvm-project/issues/173605

(cherry picked from commit 5b0270cb72f707f55e2ff5e97fc938afb3b81053)
---
 clang/lib/Sema/SemaDecl.cpp | 5 ++++-
 clang/test/Sema/constexpr.c | 8 ++++++++
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index f9580b34aaec6..d67220a2f170d 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -14156,7 +14156,10 @@ void Sema::AddInitializerToDecl(Decl *RealDecl, Expr *Init, bool DirectInit) {
     // C99 6.7.8p4: All the expressions in an initializer for an object that has
     // static storage duration shall be constant expressions or string literals.
     } else if (VDecl->getStorageClass() == SC_Static) {
-      CheckForConstantInitializer(Init);
+      // Avoid evaluating the initializer twice for constexpr variables. It will
+      // be evaluated later.
+      if (!VDecl->isConstexpr())
+        CheckForConstantInitializer(Init);
 
       // C89 is stricter than C99 for aggregate initializers.
       // C89 6.5.7p3: All the expressions [...] in an initializer list
diff --git a/clang/test/Sema/constexpr.c b/clang/test/Sema/constexpr.c
index b5b62863cfdad..ae01c71e09b06 100644
--- a/clang/test/Sema/constexpr.c
+++ b/clang/test/Sema/constexpr.c
@@ -1,4 +1,5 @@
 // RUN: %clang_cc1 -std=c23 -verify -triple x86_64 -pedantic -Wno-conversion -Wno-constant-conversion -Wno-div-by-zero %s
+// RUN: %clang_cc1 -std=c23 -verify -triple x86_64 -pedantic -Wno-conversion -Wno-constant-conversion -Wno-div-by-zero -fexperimental-new-constant-interpreter %s
 
 // Check that constexpr only applies to variables.
 constexpr void f0() {} // expected-error {{'constexpr' can only be used in variable declarations}}
@@ -416,3 +417,10 @@ void gh173847_test() {
   constexpr double d_const = gh173847_double(2.0);             // expected-error {{constexpr variable 'd_const' must be initialized by a constant expression}}
   constexpr long double ld_const = gh173847_long_double(2.0L); // expected-error {{constexpr variable 'ld_const' must be initialized by a constant expression}}
 }
+
+int gh173605(int x) {
+  static constexpr int c = c; // expected-error {{constexpr variable 'c' must be initialized by a constant expression}}\
+                              // expected-note {{read of object outside its lifetime is not allowed in a constant expression}}
+  static int justincase = justincase; // expected-error {{initializer element is not a compile-time constant}}
+  return x;
+}