https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107671
--- Comment #5 from Iain Buclaw <ibuclaw at gdcproject dot org> ---
(In reply to Uroš Bizjak from comment #4)
> from:
> movl %esi, %ecx
> movl $1, %eax
> sall %cl, %eax
> testl %edi, %eax
> setne %al
> movzbl %al, %eax
>
> to:
> xorl %eax, %eax
> btl %esi, %edi
> setc %al
>
> The patch adapts *jcc_bt patterns to similar *scc_bt patterns.
Thanks, have been tinkering with the pointer index version, and found that I
can coax scc_bt_mask to match if I cast the lhs to a signed type. It's not
obvious to me why there would be a difference.
return ((__INT32_TYPE__)p[bitnum >> 5] & (1 << (bitnum & 31))) != 0;
movl %esi, %eax
shrl $5, %eax
movl (%rdi,%rax,4), %eax
btl %esi, %eax
setc %al
Things get even stranger once I expand to "bit test and op" variants though
(better to put in another PR though)
__INT32_TYPE__ btc32(__UINT32_TYPE__ *p, __UINT32_TYPE__ bitnum)
{
__INT32_TYPE__ result = ((__INT32_TYPE__)p[bitnum >> 5]
& (1 << (bitnum & 31))) != 0;
p[bitnum >> 5] ^= 1 << (bitnum & 31);
return result;
}
Patch changes code-gen in the following way.
from:
movl %esi, %eax
movl %esi, %ecx
shrl $5, %eax
leaq (%rdi,%rax,4), %rdx
movl (%rdx), %eax
movl %eax, %esi
sarl %cl, %eax
btcl %ecx, %esi
andl $1, %eax
movl %esi, (%rdx)
to:
movl %esi, %eax
shrl $5, %eax
leaq (%rdi,%rax,4), %rdx
movl (%rdx), %eax
movl %eax, %ecx
btcl %esi, %ecx
btl %esi, %eax
setc %al
movl %ecx, (%rdx)
movzbl %al, %eax
