------- Comment #3 from rguenth at gcc dot gnu dot org 2007-07-05 19:06 -------
We compare two pointer-to-method types that "look" the same:
Breakpoint 3, useless_type_conversion_p (outer_type=0xb7d869b4,
inner_type=0xb7d866c0) at /home/richard/src/trunk2/gcc/tree-ssa.c:917
917 inner_type = TYPE_MAIN_VARIANT (inner_type);
QWidget:: *
QWidget:: *
(gdb) call debug_tree (outer_type)
<pointer_type 0xb7d869b4
type <method_type 0xb7d86360
type <void_type 0xb7cc15e8 void VOID
align 8 symtab 0 alias set -1 canonical type 0xb7cc15e8
pointer_to_this <pointer_type 0xb7cc1654>>
QI
size <integer_cst 0xb7ca84b4 constant invariant 8>
unit size <integer_cst 0xb7ca84d0 constant invariant 1>
align 8 symtab 0 alias set -1 canonical type 0xb7d86438 method basetype
<record_type 0xb7d860d8 QWidget>
arg-types <tree_list 0xb7d32dac value <pointer_type 0xb7d863cc>
chain <tree_list 0xb7d32d74
purpose <integer_cst 0xb7ca8c08 constant invariant 1> value
<boolean_type 0xb7cba57c bool>
chain <tree_list 0xb7ca8e70 value <void_type 0xb7cc15e8
void>>>>
pointer_to_this <pointer_type 0xb7d869b4>>
unsigned SI
size <integer_cst 0xb7ca863c type <integer_type 0xb7cba06c bit_size_type>
constant invariant 32>
unit size <integer_cst 0xb7ca8428 type <integer_type 0xb7cba000 unsigned
int> constant invariant 4>
align 32 symtab 0 alias set -1 canonical type 0xb7d866c0>
(gdb) call debug_tree (inner_type)
<pointer_type 0xb7d866c0
type <method_type 0xb7d86438
type <void_type 0xb7cc15e8 void VOID
align 8 symtab 0 alias set -1 canonical type 0xb7cc15e8
pointer_to_this <pointer_type 0xb7cc1654>>
QI
size <integer_cst 0xb7ca84b4 constant invariant 8>
unit size <integer_cst 0xb7ca84d0 constant invariant 1>
align 8 symtab 0 alias set -1 canonical type 0xb7d86438 method basetype
<record_type 0xb7d860d8 QWidget>
arg-types <tree_list 0xb7d32de4 value <pointer_type 0xb7d863cc>
chain <tree_list 0xb7d32dc8 value <boolean_type 0xb7cba57c bool>
chain <tree_list 0xb7ca8e70 value <void_type 0xb7cc15e8
void>>>>
pointer_to_this <pointer_type 0xb7d866c0>>
sizes-gimplified unsigned SI
size <integer_cst 0xb7ca863c type <integer_type 0xb7cba06c bit_size_type>
constant invariant 32>
unit size <integer_cst 0xb7ca8428 type <integer_type 0xb7cba000 unsigned
int> constant invariant 4>
align 32 symtab 0 alias set -1 canonical type 0xb7d866c0>
(note they have the same canonical types, for both the pointer and the
pointed-to type. note they both have their alias set not computed.)
Now at the point we verify if those pointer types are compatible we check
/* Do not lose casts between pointers with different
TYPE_REF_CAN_ALIAS_ALL setting or alias sets. */
if ((TYPE_REF_CAN_ALIAS_ALL (inner_type)
!= TYPE_REF_CAN_ALIAS_ALL (outer_type))
|| (get_alias_set (TREE_TYPE (inner_type))
!= get_alias_set (TREE_TYPE (outer_type))))
return false;
which calls get_alias_set on both pointed-to types which (surprisingly?)
returns 2 for one and 3 for the other one. Because, while we specialize
FUNCTION_TYPE
/* There are no objects of FUNCTION_TYPE, so there's no point in
using up an alias set for them. (There are, of course, pointers
and references to functions, but that's different.) */
else if (TREE_CODE (t) == FUNCTION_TYPE)
set = 0;
we do not so for METHOD_TYPE, which looks like an omission. Also it looks
like in useless_type_conversion_p we can move the canonical types check
to the top and use it for all types.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32639
