From: Joseph Myers <josmyers@redhat.com>
Date: Wed, 24 Sep 2025 19:53:01 +0000 (+0000)
Subject: c: Fix handling of register atomic compound literals
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=dfbce1feae0a88dd94bdba1adc5040e4a86c6219;p=thirdparty%2Fgcc.git

c: Fix handling of register atomic compound literals

The logic for loads and stores of _Atomic objects in the C front end
involves taking the address of such objects, with really_atomic_lvalue
detecting cases where this cannot be done (and also no special
handling is needed for atomicity), in particular register _Atomic
objects.  This logic failed to deal with the case of register _Atomic
compound literals, so resulting in spurious errors "error: address of
register compound literal requested" followed by "error: argument 1 of
'__atomic_load' must be a non-void pointer type".  (This is a C23 bug
that I found while changing really_atomic_lvalue as part of previous
C2y changes.)  Add a use of COMPOUND_LITERAL_EXPR_DECL in that case.

Bootstrapped with no regressions for x86_64-pc-linux-gnu.

gcc/c/
	* c-typeck.cc (really_atomic_lvalue): For a COMPOUND_LITERAL_EXPR,
	check C_DECL_REGISTER on the COMPOUND_LITERAL_EXPR_DECL.

gcc/testsuite/
	* gcc.dg/c23-complit-9.c: New test.
---

diff --git a/gcc/c/c-typeck.cc b/gcc/c/c-typeck.cc
index 624e7a3fa35..6c807a2a792 100644
--- a/gcc/c/c-typeck.cc
+++ b/gcc/c/c-typeck.cc
@@ -2531,6 +2531,8 @@ really_atomic_lvalue (tree expr)
 	return false;
       expr = TREE_OPERAND (expr, 0);
     }
+  if (TREE_CODE (expr) == COMPOUND_LITERAL_EXPR)
+    expr = COMPOUND_LITERAL_EXPR_DECL (expr);
   if (DECL_P (expr) && C_DECL_REGISTER (expr))
     return false;
   return true;
diff --git a/gcc/testsuite/gcc.dg/c23-complit-9.c b/gcc/testsuite/gcc.dg/c23-complit-9.c
new file mode 100644
index 00000000000..738f1a6213f
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/c23-complit-9.c
@@ -0,0 +1,9 @@
+/* Test register _Atomic compound literals.  */
+/* { dg-do compile } */
+/* { dg-options "-std=c23 -pedantic-errors" } */
+
+void
+f ()
+{
+  (register _Atomic int) { 1 };
+}