[Bug target/32392] New: Support using -mrecip w/o additional Newton-Raphson run

["burnus at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>]

Paolo Bonzini wrote:
>> That said, there is a whole bunch of applications that would kill for -mrecip, 
> even for 11bit ones. Games are one of them, for sure ;)
> What about -mrecip=0/1/2 for the number of NR steps? Or would two steps be 
> slower than divss?
>
> I was thinking of adding this as a follow-up patch ;) Just look how the 
> operations are grouped together.

As Richard pointed out: Having two NR does not make sense. For some cases doing
with out Newton-Raphson is enough. (Example: Games -- or SPEC CPU 2006:
http://www.hpcwire.com/hpc/1556972.html)

Other compilers have this option, e.g. Pathscale's -OPT:rsqrt=2 [yes, this is
used for SPEC runs ;-)]


-- 
           Summary: Support using -mrecip w/o additional Newton-Raphson run
           Product: gcc
           Version: 4.3.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: enhancement
          Priority: P3
         Component: target
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: burnus at gcc dot gnu dot org
GCC target triplet: x86_64-*-* i686-*-*


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32392