[llvm-branch-commits] [clang] [clang] Reject if constexpr in C (#112685) (PR #112697)

[Tobias Hieta via llvm-branch-commits]

https://github.com/tru updated https://github.com/llvm/llvm-project/pull/112697

>From 062adaf7d2f101ed9e83c09d192dd228dcbd9ffd Mon Sep 17 00:00:00 2001
From: Mariya Podchishchaeva <mariya.podchishchaeva at intel.com>
Date: Thu, 17 Oct 2024 13:42:35 +0200
Subject: [PATCH] [clang] Reject if constexpr in C (#112685)

Fixes https://github.com/llvm/llvm-project/issues/112587
---
 clang/lib/Parse/ParseStmt.cpp | 11 +++++++----
 clang/test/Sema/constexpr.c   |  7 +++++++
 2 files changed, 14 insertions(+), 4 deletions(-)

diff --git a/clang/lib/Parse/ParseStmt.cpp b/clang/lib/Parse/ParseStmt.cpp
index 22d38adc28ebe9..3ac1f0fa27f83f 100644
--- a/clang/lib/Parse/ParseStmt.cpp
+++ b/clang/lib/Parse/ParseStmt.cpp
@@ -1508,10 +1508,13 @@ StmtResult Parser::ParseIfStatement(SourceLocation *TrailingElseLoc) {
   SourceLocation ConstevalLoc;
 
   if (Tok.is(tok::kw_constexpr)) {
-    Diag(Tok, getLangOpts().CPlusPlus17 ? diag::warn_cxx14_compat_constexpr_if
-                                        : diag::ext_constexpr_if);
-    IsConstexpr = true;
-    ConsumeToken();
+    // C23 supports constexpr keyword, but only for object definitions.
+    if (getLangOpts().CPlusPlus) {
+      Diag(Tok, getLangOpts().CPlusPlus17 ? diag::warn_cxx14_compat_constexpr_if
+                                          : diag::ext_constexpr_if);
+      IsConstexpr = true;
+      ConsumeToken();
+    }
   } else {
     if (Tok.is(tok::exclaim)) {
       NotLocation = ConsumeToken();
diff --git a/clang/test/Sema/constexpr.c b/clang/test/Sema/constexpr.c
index 8286cd2107d2f2..a874fd64808404 100644
--- a/clang/test/Sema/constexpr.c
+++ b/clang/test/Sema/constexpr.c
@@ -357,3 +357,10 @@ void infsNaNs() {
   constexpr double db5 = LD_SNAN; // expected-error {{constexpr initializer evaluates to nan which is not exactly representable in type 'const double'}}
   constexpr double db6 = INF;
 }
+
+void constexprif() {
+  if constexpr (300) {} //expected-error {{expected '(' after 'if'}}
+}
+void constevalif() {
+  if consteval (300) {} //expected-error {{expected '(' after 'if'}}
+}