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Re: __builtin_prefetch() question
On Tue 28 May 2002 21:58, Janis Johnson wrote:
> On Sun, May 26, 2002 at 11:41:11AM +0200, Guillermo Ballester Valor wrote:
> > Hi,
> > On Dom 26 May 2002 11:30, Bryce McKinlay wrote:
> > > Guillermo Ballester Valor wrote:
> > > >My question is: does __builtin_prefetch() in GCC 3.1 actually insert
> > > > any prefetch hint for pentium3 target? or it does nothing with it?
> > > >
> > > >I listed assembler outputs with -march=pentium3 (and some prefetch
> > > > calls) and I can't see any prefetch code, and diffs show me no
> > > > differences with __builtin_prefetch() calls and without it.
> > >
> > > Try -mcpu=pentium3
> > I've tried all combinations of '-mcpu=pentium3' and '-march=pentium3'
> > without success. I also read in gcc info that -march=CPU-TYPE implies
> > -mcpu=CPU-TYPE.
> > Guillermo
> -mcpu=pentium3 works for me with GCC 3.1, and it doesn't require the use
> of -O2.
> See the comments in gcc/testsuite/gcc.misc-tests/i386-prefetch.exp about
> which prefetch instructions are expected to be generated for various x86
> variants. Try compiling the test i386-pf-sse-1.c from that directory;
> it should generate a variety of prefetch instructions.
Confirmed, you're right. After checking that the test from gcc-testsuite
generates the right code, I've revised my scripts and it was a fault of mine,
sorry. Now my listings show the prefetch hints I like to see :)
Janis, thanks a lot.
Guillermo Ballester Valor