c++: Fix up instantiation of pointer/reference/array types with attributes [PR119138]

My r15-7822 PR118787 change unfortunately broke build on x86_64-w64-mingw32.
The reduced testcase below shows what is going on.
va_list on this target is char * with extra (non-dependent) attributes
on it.
Before my r15-7822 change, instantiation of such type used the fast path and
just returned t, but as it has non-NULL TYPE_ATTRIBUTES, it now falls
through, builds a pointer type and then calls
apply_late_template_attributes.  And in there triggers a bug, that function
has been written for types with RECORD_TYPE/UNION_TYPE (or ENUMERAL_TYPE?)
in mind, where we call apply_late_template_attributes with
ATTR_FLAG_TYPE_IN_PLACE and can just apply the non-dependent attributes
directly to TYPE_ATTRIBUTES.  That is wrong for shared types like
{POINTER,REFERENCE,ARRAY}_TYPE etc., we should just force
cp_build_type_attribute_variant to build a variant type for the
non-dependent attributes and then process dependent attributes (which
given attr_flag will DTRT already).

The second change in the patch is an optimization, we can actually return
back to returning t even when TYPE_ATTRIBUTES is non-NULL, as long as it
is non-dependent (dependent attributes are stored first, so it is enough
to check the first attribute).

2025-03-06  Jakub Jelinek  <jakub@redhat.com>

	PR c++/119138
	* pt.cc (apply_late_template_attributes): Set p to NULL if
	ATTR_FLAG_TYPE_IN_PLACE is not set in attr_flags.
	(tsubst) <case POINTER_TYPE, case REFERENCE_TYPE, case ARRAY_TYPE>:
	Reuse original type even if TYPE_ATTRIBUTES is non-NULL, but all
	the attributes are non-dependent.

	* g++.dg/template/pr119138.C: New test.

diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index c09a934580f2c26891510bf933a5cb8979c366c6..2775af7701b8a29f0f8ca97a132da208706903fb 100644 (file)
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -12393,7 +12393,8 @@ apply_late_template_attributes (tree *decl_p, tree attributes, int attr_flags,
          to our attributes parameter.  */
       gcc_assert (*p == attributes);
     }
-  else if (FUNC_OR_METHOD_TYPE_P (*decl_p))
+  else if (FUNC_OR_METHOD_TYPE_P (*decl_p)
+          || (attr_flags & ATTR_FLAG_TYPE_IN_PLACE) == 0)
     p = NULL;
   else
     {
@@ -16867,7 +16868,8 @@ tsubst (tree t, tree args, tsubst_flags_t complain, tree in_decl)
       {
        if (type == TREE_TYPE (t)
            && TREE_CODE (type) != METHOD_TYPE
-           && TYPE_ATTRIBUTES (t) == NULL_TREE)
+           && (TYPE_ATTRIBUTES (t) == NULL_TREE
+               || !ATTR_IS_DEPENDENT (TYPE_ATTRIBUTES (t))))
          return t;
 
        /* [temp.deduct]
@@ -17029,7 +17031,8 @@ tsubst (tree t, tree args, tsubst_flags_t complain, tree in_decl)
           it will obviously be the same as T.  */
        if (type == TREE_TYPE (t)
            && domain == TYPE_DOMAIN (t)
-           && TYPE_ATTRIBUTES (t) == NULL_TREE)
+           && (TYPE_ATTRIBUTES (t) == NULL_TREE
+               || !ATTR_IS_DEPENDENT (TYPE_ATTRIBUTES (t))))
          return t;
 
        /* These checks should match the ones in create_array_type_for_decl.

diff --git a/gcc/testsuite/g++.dg/template/pr119138.C b/gcc/testsuite/g++.dg/template/pr119138.C
new file mode 100644 (file)
index 0000000..b089387
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/pr119138.C
@@ -0,0 +1,16 @@
+// PR c++/119138
+// { dg-do compile }
+
+#include <stdarg.h>
+
+template <typename>
+void
+foo (va_list)
+{
+}
+
+void
+bar (va_list ap)
+{
+  foo <char> (ap);
+}