http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50413
Uros Bizjak <ubizjak at gmail dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |RESOLVED
Resolution| |INVALID
--- Comment #3 from Uros Bizjak <ubizjak at gmail dot com> 2011-09-15 13:29:23
UTC ---
(In reply to comment #0)
> After compilation an attached code with -O2 and -ftree-vectorize flags, it
> doesn't work properly.
>
> Assembler code shows that G++ tries to replace the following code
>
> V.uint128.uint64_lower = (V.uint128.uint64_lower >> 1);
> V.bitmap.b63 = V.bitmap.b64;
> V.uint128.uint64_upper = (V.uint128.uint64_upper >> 1);
>
> with SSE instructions:
>
> 400a10: movdqa 0x103d8(%rip),%xmm0 # 410df0 <V>
> 400a17: and $0x1,%edi
> 400a1b: psrlq $0x1,%xmm0
> 400a20: movdqa %xmm0,0x103c8(%rip) # 410df0 <V>
>
>
> But psrlq shifts 64 bit value, it's necessary to use psrldq here
You are wrong. The code above describes shift of two 64bit elements, each by
one, so psrlq [1] is correct.
[1] http://www.rz.uni-karlsruhe.de/rz/docs/VTune/reference/vc259.htm
