------- Additional Comments From danglin at gcc dot gnu dot org 2005-06-14
00:14 -------
Here's what we have at the test to see if function pointer canonicalization
should be done in dojump.c:
Breakpoint 1, do_compare_and_jump (exp=0x400ec708, signed_code=NE,
unsigned_code=NE, if_false_label=0x400ecd70, if_true_label=0x0)
at ../../gcc/gcc/dojump.c:928
928 if (HAVE_canonicalize_funcptr_for_compare
(gdb) p debug_tree (exp)
<ne_expr 0x400ec708
type <boolean_type 0x4000c620 _Bool public unsigned QI
size <integer_cst 0x400030f0 constant invariant 8>
unit size <integer_cst 0x40003108 constant invariant 1>
align 8 symtab 0 alias set -1 precision 1 min <integer_cst 0x400034e0
0>
max <integer_cst 0x40003510 1>>
arg 0 <var_decl 0x400ef850 p
type <pointer_type 0x400174d0 type <void_type 0x40017460 void>
sizes-gimplified public unsigned SI
size <integer_cst 0x400032e8 constant invariant 32>
unit size <integer_cst 0x40003078 constant invariant 4>
align 32 symtab 0 alias set -1
pointer_to_this <pointer_type 0x4007fbd0>>
used unsigned SI file cffc-bug.c line 8 size <integer_cst 0x400032e8
32>
unit size <integer_cst 0x40003078 4>
align 32 context <function_decl 0x400ef700 main>
(reg/v/f:SI 94 [ p ])
chain <var_decl 0x400ef8c0 result type <integer_type 0x4000c380 int>
SI file cffc-bug.c line 9 size <integer_cst 0x400032e8 32> unit
size
<integer_cst 0x40003078 4>
align 32 context <function_decl 0x400ef700 main>>>
arg 1 <addr_expr 0x400eb820
type <pointer_type 0x400f3070 type <function_type 0x400ef690>
unsigned SI size <integer_cst 0x400032e8 32> unit size <integer_cst
0x40003078 4>
align 32 symtab 0 alias set -1>
constant invariant
arg 0 <function_decl 0x400ef700 main type <function_type 0x400ef690>
addressable used public static decl_5 SI file cffc-bug.c line 7
arguments <parm_decl 0x400ef540 argc> result <result_decl 0x400ef770 D.2328>
initial <block 0x400f0b98>
(mem:SI (symbol_ref/v:SI ("@main") <function_decl 0x400ef700 main>)
[0 S4 A32])
saved-insns 0x400de800>>>
$3 = void
The "(int (*)(int, char **))" cast appears to have been dropped from the
comparison.
I also believe that casts to int types are also being dropped when applied
to function pointer causing the opposite problem (unnecessary canonicalization).
In cffc-bug.c.t19.dce1, we have:
<L1>:;
p___23_4 = (int (*<T4ef>) (int, char * *)) p_3;
if (p___23_4 != main) goto <L2>; else goto <L3>;
In cffc-bug.c.t20.dom1, we have:
<L1>:;
p___23_4 = (int (*<T4ef>) (int, char * *)) p_2;
if (p_2 != main) goto <L2>; else goto <L3>;
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22051
