Re: More help for ams statements needed (Was: [Help] Need help for architecture specific code)
Hi Patrick,
On Fri, Sep 05, 2014 at 11:22:02AM -0500, Patrick Baggett wrote:
> > > ebwt.h:1909: asm ("popcntq %[x],%[count]\n": [count]
> > "=&r" (count): [x] "r" (x));
> > Unless someone investigates why GCC on i386 doesn't know this instruction,
> > I suggest compiling with POPCNT_CAPABILITY=0 on i386.
> >
> > popcntq, or more specificially, the 'q' suffix, is a 64-bit only
> instruction. It does population count on 64-bit general purpose register
> (GPR). Obviously if you're running in 32-bit mode, you only have 32-bit
> GPRs. Something like this is better written with intrinsics that can handle
> details of "How do I get the popcount of a 64-bit value on this machine?".
> For example, 2 x 32-bit popcounts summed provide exactly the same answer as
> a single 64-bit popcount. Compilers can handle this stuff automatically, so
> let them. Upstream should really use a more general popcount() function and
> let the build architecture decide what implementation to use. If they
> really, really want an SSE 4.2 codepath, they should detect it, then use
> intrinsics, which can produce proper SSE 4.2 code for both 32-bit and
> 64-bit builds.
I totally agree with you here. Can you provide a patch that implements
your suggestion?
Kind regards
Andreas.
--
http://fam-tille.de
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