On 10/08/11 12:40, Richard Guenther wrote:
On x86 we expand the code to ((xl& al) ^ al) | ((xh& ah) ^ ah) == 0
which is then if-converted. Modified testcase:
long long x;
_Bool __attribute__((regparm(2))) mask (long long a)
{
return (x& a) == a;
}
on i?86 gets you
mask:
.LFB0:
.cfi_startproc
pushl %ebx
.cfi_def_cfa_offset 8
.cfi_offset 3, -8
movl %eax, %ebx
andl x, %ebx
movl %edx, %ecx
andl x+4, %ecx
xorl %ebx, %eax
xorl %ecx, %edx
orl %edx, %eax
sete %al
popl %ebx
.cfi_restore 3
.cfi_def_cfa_offset 4
ret
so I wonder if you should investigate why the xor variant doesn't trigger
for you?
I can reproduce this result in GCC 4.6.1 for x86.
I can't understand what you mean by this though. From inspecting the
logs it seems that the if-conversion is done manually at expand time.
The final pass before expand shows the original (x & a) == a, however,
after expand the rtl already contains xor, ior, etc. So I guess I would
need to do something similar in my backend. I can't however, find in the
i386(.md|.c) where this is actually happening.
On i?86 if-conversion probably solves your specific issue,
but I guess the initial expansion is where you could improve placement
of the 1 (after all, the 0 is after the jumps).
This is happening on my own backend so I guess anything that is
implemented to do if-conversion on i386 needs to be implemented also on
my backend. Can you point me to the code on i386 so I can take a look at it?
Cheers,
--
PMatos
