This is the mail archive of the gcc@gcc.gnu.org mailing list for the GCC project.


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]

Re: Performance of Integer Multiplication on PIII


> I am confused myself as to which architecture is meant by -march=i686,
> but I didn't think it was P-III.  I thought -march=pentiumpro was the one
> for P-II/P-III.  However, wouldn't many people wonder whether you mean P4
> when you talk about "faster Pentiums?" Some of us would not go out of our
> way to slow down the P4 by asking for imul on code meant to run on a
> variety of CPU's, although some would like to have -Os favor the use of
> imul.  It might be interesting to have a separate table of the penalties
> used in each version of gcc for each architecture selection, rather than
> having to peruse source.
Gcc do have set of costs for each supported x86 variant and for size
optimization separately.  The model is an estimate (it does not handle leas and
2 address machines perfectly), as the algorithm to construct sequences is not
trying all possibilities, so it is possible that the produced sequences are
suboptimal, but in case it makes truly big differences, we probably should
investigate it.

Honza


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]