This patch addresses 66270, another case where may_alias disrupted the canonical
type system. We ICE as TYPE_CANONICALs differ, but comptypes think they are the
same.
There seems to be a bit of confusion as to whether pointers that differ only in
TYPE_REF_CAN_ALIAS_ALL are the same canonical type or not.
Firstly, in tree.c build_pointer_type_for_mode, when the pointed-to type is not
its own canonical type, that means the newly constructed pointer type is
(possibly) not canonical either. So we explicitly build a canonical type with:
else if (TYPE_CANONICAL (to_type) != to_type)
TYPE_CANONICAL (t)
= build_reference_type_for_mode (TYPE_CANONICAL (to_type),
mode, false);
But we're passing 'false' in as 'can_alias_all', rather than pass the value
passed into us. That'll make a difference if the caller passed in true and
to_type doesn't have may_alias set. This is inconsistent at least, because we
could sometimes end up with canonical types with T_R_C_A_A set (to-type is
canonical) and sometimes with it not set. It seems the right solution is to
consider T_R_C_A_A as a distinguisher, thus we should pass can_alias_all to the
canonical type builder. Note that it is ok to pass the possibly modified
can_alias_all in, and not the incoming value, because we only ever modify it to
make it true -- and in that case the same behavior would happen in the canonical
type builder because to_type and TYPE_CANONICAL (to_type) should have the same
may_alias attribute.
Anyway, that's a bit of collateral confusion I fell over investigating. With
that out of the way, we have to teach comptypes that T_R_C_A_A affects pointer
type equality. Hence add such a check to POINTER_TYPE case there.
bootstrapped on x86-linux & tested, ok?
nathan
2015-05-25 Nathan Sidwell <nat...@acm.org>
PR c++/66270
* tree.c (build_pointer_type_for_mode): Pass can_alias_all to
canonical type builder.
(build_reference_type_for_mode): Likewise.
cp/
* typeck.c (structural_comptypes) [POINTER_TYPE]: Compare
TYPE_REF_CAN_ALIAS_ALL.
testsuite/
* g++.dg/ext/alias-canon3.C: New.
Index: cp/typeck.c
===================================================================
--- cp/typeck.c (revision 223636)
+++ cp/typeck.c (working copy)
@@ -1307,6 +1307,8 @@ structural_comptypes (tree t1, tree t2,
if (TYPE_MODE (t1) != TYPE_MODE (t2)
|| !same_type_p (TREE_TYPE (t1), TREE_TYPE (t2)))
return false;
+ if (TYPE_REF_CAN_ALIAS_ALL (t1) != TYPE_REF_CAN_ALIAS_ALL (t2))
+ return false;
break;
case METHOD_TYPE:
Index: tree.c
===================================================================
--- tree.c (revision 223636)
+++ tree.c (working copy)
@@ -7759,7 +7759,7 @@ build_pointer_type_for_mode (tree to_typ
else if (TYPE_CANONICAL (to_type) != to_type)
TYPE_CANONICAL (t)
= build_pointer_type_for_mode (TYPE_CANONICAL (to_type),
- mode, false);
+ mode, can_alias_all);
/* Lay out the type. This function has many callers that are concerned
with expression-construction, and this simplifies them all. */
@@ -7826,7 +7826,7 @@ build_reference_type_for_mode (tree to_t
else if (TYPE_CANONICAL (to_type) != to_type)
TYPE_CANONICAL (t)
= build_reference_type_for_mode (TYPE_CANONICAL (to_type),
- mode, false);
+ mode, can_alias_all);
layout_type (t);
Index: testsuite/g++.dg/ext/alias-canon3.C
===================================================================
--- testsuite/g++.dg/ext/alias-canon3.C (revision 0)
+++ testsuite/g++.dg/ext/alias-canon3.C (working copy)
@@ -0,0 +1,12 @@
+// { dg-do compile }
+// PR c++/66270
+
+typedef float __m256 __attribute__ (( __vector_size__(32), __may_alias__ ));
+struct A {
+ __m256 ymm;
+ const float &f() const;
+};
+
+const float &A::f() const {
+ return ymm[1];
+}
