[Bug rtl-optimization/61984] use mr. to remove extra cmp instruction on ppc

[segher at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61984

Segher Boessenkool <segher at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2014-08-10
                 CC|                            |segher at gcc dot gnu.org
          Component|target                      |rtl-optimization
     Ever confirmed|0                           |1

--- Comment #2 from Segher Boessenkool <segher at gcc dot gnu.org> ---
GCC already does this transformation: the pattern
used for the compare is mov<mode>_internal2.

With -m32, the wanted "mr. 3,4" comes out.

With -m64, IRA makes a non-optimal decision: it
gets {r125:CC=(r4<=>0); r124=r4} as a first insn,
and as a secon insn it gets (in a different BB)
r3=r124, and then it decides assigning r4 to the
pseudo r124 is the best idea.