c++: Fix up attribute handling in methods in templates [PR100872]

The following testcase FAILs because a dependent (late) attribute is never
tsubsted.  While the testcase is OpenMP, I think it is a generic C++ FE problem
that could affect any other dependent attribute.

apply_late_template_attributes documents that it relies on
  /* save_template_attributes puts the dependent attributes at the beginning of
     the list; find the non-dependent ones.  */
The "operator binding" attributes that are sometimes added are added to the
head of DECL_ATTRIBUTES list though and because it doesn't have
ATTR_IS_DEPENDENT set it violates this requirement.

The following patch fixes it by adding that attribute after all
ATTR_IS_DEPENDENT attributes.  I'm not 100% sure if DECL_ATTRIBUTES can't be
shared by multiple functions (e.g. the cdtor clones), but the code uses
later remove_attribute which could break that too.

Other option would be to copy_list the ATTR_IS_DEPENDENT portion of the
DECL_ATTRIBUTES list if we need to do this, that would be the same as this
patch but replace that *ap = op_attr; at the end with
      *ap = NULL_TREE;
      DECL_ATTRIBUTES (cfn) = chainon (copy_list (DECL_ATTRIBUTES (cfn)),
                                       op_attr);
Or perhaps set ATTR_IS_DEPENDENT on the "operator bindings" attribute,
though it would need to be studied what would it try to do with the
attribute during tsubst.

2021-06-04  Jakub Jelinek  <jakub@redhat.com>

	PR c++/100872
	* name-lookup.c (maybe_save_operator_binding): Add op_attr after all
	ATTR_IS_DEPENDENT attributes in the DECL_ATTRIBUTES list rather than
	to the start.

	* g++.dg/gomp/declare-simd-8.C: New test.

2 files changed, 20 insertions, 2 deletions

diff --git a/gcc/cp/name-lookup.c b/gcc/cp/name-lookup.c
index a6c9e68..241ad2b 100644
--- a/gcc/cp/name-lookup.c
+++ b/gcc/cp/name-lookup.c
@@ -9136,9 +9136,12 @@ maybe_save_operator_binding (tree e)
   tree op_attr = lookup_attribute (op_bind_attrname, attributes);
   if (!op_attr)
     {
+      tree *ap = &DECL_ATTRIBUTES (cfn);
+      while (*ap && ATTR_IS_DEPENDENT (*ap))
+	ap = &TREE_CHAIN (*ap);
       op_attr = tree_cons (get_identifier (op_bind_attrname),
-			   NULL_TREE, attributes);
-      DECL_ATTRIBUTES (cfn) = op_attr;
+			   NULL_TREE, *ap);
+      *ap = op_attr;
     }
 
   tree op_bind = purpose_member (fnname, TREE_VALUE (op_attr));
diff --git a/gcc/testsuite/g++.dg/gomp/declare-simd-8.C b/gcc/testsuite/g++.dg/gomp/declare-simd-8.C
new file mode 100644
index 0000000..01c91e8
--- /dev/null
+++ b/gcc/testsuite/g++.dg/gomp/declare-simd-8.C
@@ -0,0 +1,15 @@
+// PR c++/100872
+
+template <int N, typename T>
+struct S {
+  #pragma omp declare simd aligned(a : N * 2) aligned(b) linear(ref(b): N)
+  float foo (float *a, T *&b) { return *a + *b; }
+};
+
+S<16, float> s;
+
+float
+bar (float *a, float *p)
+{
+  return s.foo (a, p);
+}