https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78103
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Target| |x86_64-*-*, i?86-*-*
Status|UNCONFIRMED |NEW
Version|unknown |6.2.1
Keywords| |missed-optimization
Last reconfirmed| |2016-10-25
Component|tree-optimization |target
CC| |rguenth at gcc dot gnu.org
Ever confirmed|0 |1
--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
There isn't a find-last-set builtin thus this is a target (or RTL optimization)
issue. I believe find-last-set is also computed by ffs (x & -x) so that might
be a more canonical way to express this on GIMPLE?
constexpr
unsigned long findLastSet3(unsigned long x) {
return __builtin_ffsl (x & -x);
}
_Z12findLastSet3m:
.LFB2:
.cfi_startproc
movq %rdi, %rax
movq $-1, %rdx
negq %rax
andq %rax, %rdi
bsfq %rdi, %rax
cmove %rdx, %rax
addq $1, %rax
cltq
ret
not really optimal either though.
