http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29776
Steven Bosscher <steven at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Last reconfirmed|2011-12-24 00:00:00 |2012-07-29 0:00
CC| |uros at gcc dot gnu.org
--- Comment #3 from Steven Bosscher <steven at gcc dot gnu.org> 2012-07-29
13:23:30 UTC ---
Tested with trunk r189929 on x86-64 (generic).
#define MODE signed // or unsigned
unsigned mask[8];
unsigned foo(unsigned y, unsigned char x)
{
MODE int c = (MODE) __builtin_ctz(x);
unsigned int m = mask[c];
return y & m;
}
With MODE==signed:
movzbl %sil, %esi
movl %edi, %eax
rep; bsfl %esi, %esi
movslq %esi, %rsi
andl mask(,%rsi,4), %eax
ret
With MODE==unsigned:
movzbl %sil, %esi
movl %edi, %eax
rep; bsfl %esi, %esi
movl %esi, %esi
andl mask(,%rsi,4), %eax
ret
The "movl %esi, %esi" is a zeroextendsidi:
#(insn:TI 9 2 10 2 (parallel [
# (set (reg:SI 4 si [orig:60 D.1716 ] [60])
# (ctz:SI (reg:SI 4 si [orig:68 D.1715 ] [68])))
# (clobber (reg:CC 17 flags))
# ]) t.c:6 666 {ctzsi2}
# (expr_list:REG_UNUSED (reg:CC 17 flags)
# (nil)))
rep; bsfl %esi, %esi # 9 ctzsi2 [length = 4]
#(insn:TI 10 9 12 2 (set (reg:DI 4 si [orig:70 D.1716 ] [70])
# (zero_extend:DI (reg:SI 4 si [orig:60 D.1716 ] [60]))) t.c:7 113
{*zero_extendsidi2_rex64}
# (nil))
movl %esi, %esi # 10 *zero_extendsidi2_rex64/1 [length
= 2]
Perhaps REE can be taught about ctz giving a non-negative result.
