[gcc r16-6472] c: Fix construction of composite type for atomic pointers [PR121081]

[Martin Uecker]

https://gcc.gnu.org/g:41177976c5e4448365f1966f6594458232db05fc

commit r16-6472-g41177976c5e4448365f1966f6594458232db05fc
Author: Martin Uecker <uecker@tugraz.at>
Date:   Thu Dec 25 18:27:33 2025 +0100

    c: Fix construction of composite type for atomic pointers [PR121081]
    
    When constructing the composite type of two atomic pointer types,
    we used "qualify_type" which did not copy the "atomic" qualifier.
    Use c_build_type_attribute_qual_variant instead.
    
            PR c/121081
    
    gcc/c/ChangeLog:
            * c-typeck.cc (composite_type_internal): Properly copy
            atomic qualifier.
    
    gcc/testsuite/ChangeLog:
            * gcc.dg/pr121081.c: New test.

Diff:
---
 gcc/c/c-typeck.cc               | 12 +++++-------
 gcc/testsuite/gcc.dg/pr121081.c |  9 +++++++++
 2 files changed, 14 insertions(+), 7 deletions(-)

diff --git a/gcc/c/c-typeck.cc b/gcc/c/c-typeck.cc
index dd2a948872b2..26805e5cfd6b 100644
--- a/gcc/c/c-typeck.cc
+++ b/gcc/c/c-typeck.cc
@@ -689,13 +689,11 @@ composite_type_internal (tree t1, tree t2, tree cond,
     case POINTER_TYPE:
       /* For two pointers, do this recursively on the target type.  */
       {
-	tree pointed_to_1 = TREE_TYPE (t1);
-	tree pointed_to_2 = TREE_TYPE (t2);
-	tree target = composite_type_internal (pointed_to_1, pointed_to_2,
+	tree target = composite_type_internal (TREE_TYPE (t1), TREE_TYPE (t2),
 					       cond, cache);
-	t1 = c_build_pointer_type_for_mode (target, TYPE_MODE (t1), false);
-	t1 = c_build_type_attribute_variant (t1, attributes);
-	return qualify_type (t1, t2);
+	tree n = c_build_pointer_type_for_mode (target, TYPE_MODE (t1), false);
+	return c_build_type_attribute_qual_variant (n, attributes,
+						    TYPE_QUALS (t2));
       }
 
     case ARRAY_TYPE:
@@ -1720,7 +1718,7 @@ comptypes_internal (const_tree type1, const_tree type2,
 
   /* 1 if no need for warning yet, 2 if warning cause has been seen.  */
   if (!(attrval = comp_type_attributes (t1, t2)))
-     return false;
+    return false;
 
   if (2 == attrval)
     data->warning_needed = true;
diff --git a/gcc/testsuite/gcc.dg/pr121081.c b/gcc/testsuite/gcc.dg/pr121081.c
new file mode 100644
index 000000000000..244d0e2e6e38
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr121081.c
@@ -0,0 +1,9 @@
+/* { dg-do compile } */ 
+/* { dg-options "-std=c11" } */
+
+int * _Atomic __attribute__((visibility(""))) a;	/* { dg-warning "attribute ignored" } */
+int * _Atomic a;
+
+int * _Atomic __attribute__((visibility("hidden"))) b;	/* { dg-warning "attribute ignored" } */
+int * _Atomic b;
+