Re: [PATCH] Improved trailing bit counting operation

[Daniel Gutson <dgutson at codesourcery dot com>]

Sorry guys, I'm not sure I understand your point.

ctz is not an ARM instruction, that's why __builtin_ctz is implemented 
using other existing instructions (rbit, clz).

Is that what you are referring to?

  Daniel.

Adam Nemet wrote:
> Basile STARYNKEVITCH writes:
> > Daniel Gutson wrote:
> > > Adam,
> > >   could you please elaborate?
> > Well the test file name contain ctz, so I would expect that the 
> > generated assembler contain that string also.
>
> Right, this is what I meant.  E.g.:
>
> anemet@ropi:~/src/gcc/mipsisa64r2-elf/gcc$ touch foo.c
> anemet@ropi:~/src/gcc/mipsisa64r2-elf/gcc$ ./cc1 foo.c -quiet -o - |grep foo 
>         .file   1 "foo.c"
>
> > But I am not an ARM expert!
>
> and neither am I :).
>
> > > Adam Nemet wrote:
> > > > Daniel Gutson <dgutson@codesourcery.com> writes:
> > > > > Index: src/gcc-mainline/gcc/testsuite/gcc.target/arm/ctz.c
> > > > > ===================================================================
> > > > > --- src/gcc-mainline/gcc/testsuite/gcc.target/arm/ctz.c    (revision 0)
> > > > > +++ src/gcc-mainline/gcc/testsuite/gcc.target/arm/ctz.c    (revision 0)
> > > > > @@ -0,0 +1,12 @@
> > > > > +/* { dg-do compile } */
> > > > > +/* { dg-require-effective-target arm32 } */
> > > > > +/* { dg-options "-O2 -march=armv6t2" } */
> > > > > +
> > > > > +unsigned int functest(unsigned int x)
> > > > > +{
> > > > > +    return __builtin_ctz(x);
> > > > > +}
> > > > > +
> > > > > +/* { dg-final { scan-assembler "rbit" } } */
> > > > > +/* { dg-final { scan-assembler "ctz" } } */
> > > > Watch out, this will match the .file directive.
> > > >
> > > > Adam
> >
> > --
> > Basile STARYNKEVITCH         http://starynkevitch.net/Basile/
> > email: basile<at>starynkevitch<dot>net mobile: +33 6 8501 2359
> > 8, rue de la Faiencerie, 92340 Bourg La Reine, France
> > *** opinions {are only mines, sont seulement les miennes} ***

--
Daniel Gutson
CodeSourcery
www.codesourcery.com