On Wednesday 27 February 2008 03:06, J.C. Pizarro wrote:
> Compiling and executing the code of Nick Piggin at
> http://gcc.gnu.org/ml/gcc/2008-02/msg00601.html
>
> in my old Athlon64 Venice 3200+ 2.0 GHz,
> 3 GiB DDR400, 32-bit kernel, gcc 3.4.6, i got
>
> $ gcc -O3 -falign-functions=64 -falign-loo
> > At least on x86 it should also be a good idea to know which way
> > the branch is going to go, because it doesn't have explicit branch
> > hints, you really want to be able to optimize the cold branch
> > predictor case if converting from cmov to conditional branches.
>
> x86 as of Pentium 4 d
> At least on x86 it should also be a good idea to know which way
> the branch is going to go, because it doesn't have explicit branch
> hints, you really want to be able to optimize the cold branch
> predictor case if converting from cmov to conditional branches.
x86 as of Pentium 4 does have bra
On Tuesday 26 February 2008 21:14, Jan Hubicka wrote:
> Only cases we do so quite reliably IMO are:
> 1) loop branches that are not interesting for cmov conversion
> 2) branches leading to noreturn calls, also not interesting
> 3) builtin_expect mentioned.
> 4) when profile feedback is arou
It's a final summary for good performance of the tested machines:
+ unpredictable: * don't use conditional jmp (the worst).
/ * use cmov or C version.
/
\ + no deps: * use cmov or C version.
\ /
+ predictable: \
+ has deps: * do
On 2008/2/26, J.C. Pizarro <[EMAIL PROTECTED]>, i wrote:
> 4. C > cmov >> jmp when it's unpredictable and has not data dependencies.
I'm sorry of my error typo, the correct is (without the "not")
4. C > cmov >> jmp when it's unpredictable and has data dependencies.
and my forgotten 3rd annotatio
Compiling and executing the code of Nick Piggin at
http://gcc.gnu.org/ml/gcc/2008-02/msg00601.html
in my old Athlon64 Venice 3200+ 2.0 GHz,
3 GiB DDR400, 32-bit kernel, gcc 3.4.6, i got
$ gcc -O3 -falign-functions=64 -falign-loops=64 -falign-jumps=64
-falign-labels=64 -march=i686 foo.c -o foo
$ .
On Tuesday 26 February 2008 21:14, Jan Hubicka wrote:
> Hi,
>
> > Core2 follows a similar pattern, although it's not seeing any
> > slowdown in the "no deps, predictable, jmp" case like K8 does.
> >
> > Any comments? (please cc me) Should gcc be using conditional jumps
> > more often eg. in the cas
> Hi,
> > Core2 follows a similar pattern, although it's not seeing any
> > slowdown in the "no deps, predictable, jmp" case like K8 does.
> >
> > Any comments? (please cc me) Should gcc be using conditional jumps
> > more often eg. in the case of __builtin_expect())?
>
> The problem is that in g
Hi,
> Core2 follows a similar pattern, although it's not seeing any
> slowdown in the "no deps, predictable, jmp" case like K8 does.
>
> Any comments? (please cc me) Should gcc be using conditional jumps
> more often eg. in the case of __builtin_expect())?
The problem is that in general GCC's bra
10 matches
Mail list logo
