option -mprfchw

[NightStrike]

Ping?

On Mon, Apr 18, 2016 at 12:38 AM, NightStrike <nightstrike@gmail.com> wrote:
> Also, FWIW:
>
> 1) The march=native version that uses prefetcht0 is very repeatedly
> faster by about 15% in the particular test case I'm looking at.
>
> 2) The compilers in both instances are not just the same version, they
> are the same compiler installed on an NFS mount and shared to both
> computers.
>
>
> On Mon, Apr 18, 2016 at 12:26 AM, NightStrike <nightstrike@gmail.com> wrote:
>> Not sure if this applies:
>> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=54210
>>
>> If I compile on a k8 Opteron 248 with -march=native, I do not see
>> -mprfchw listed in the options in -fverbose-asm.  In the assembly, I
>> see this:
>>
>> prefetcht0      (%rax)  # ivtmp.1160
>> prefetcht0      304(%rcx)       #
>> prefetcht0      (%rax)  # ivtmp.1160
>>
>> If I compile on a bdver2 Opteron 6386 SE with -march=k8 (thus trying
>> to target the older system), I do see it listed in the options in
>> -fverbose-asm.  In the assembly, I see this:
>>
>> prefetcht0      (%rax)  # ivtmp.1160
>> prefetcht0      304(%rcx)       #
>> prefetchw       (%rax)  # ivtmp.1160
>>
>> (The third line is the only difference)
>>
>> In both cases, I'm using gcc 4.9.3.  Which is correct for a k8 Opteron 248?