[Bug tree-optimization/53342] New: [4.8 Regression] rnflow.f90 is ~5% slower after revision 187340

[dominiq at lps dot ens.fr]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53342

             Bug #: 53342
           Summary: [4.8 Regression] rnflow.f90 is ~5% slower after
                    revision 187340
    Classification: Unclassified
           Product: gcc
           Version: 4.8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: dominiq@lps.ens.fr
                CC: matz@gcc.gnu.org, rguenth@gcc.gnu.org,
                    ubizjak@gmail.com


Created attachment 27401
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=27401
source evlrnf.f90 extracted from rnflow.f90

On x86_64-apple-darwin10, rnflow.f90 is ~5% slower after revision 187340

[macbook] test/dbg_rnflow% /opt/gcc/gcc4.8p-187339/bin/gfortran -O3 -ffast-math
-funroll-loops rnflow.f90
[macbook] test/dbg_rnflow% time a.out > /dev/null
27.542u 0.348s 0:27.93 99.8%    0+0k 0+0io 0pf+0w
[macbook] test/dbg_rnflow% /opt/gcc/gcc4.8p-187340/bin/gfortran -O3 -ffast-math
-funroll-loops rnflow.f90
[macbook] test/dbg_rnflow% time a.out > /dev/null
29.196u 0.348s 0:29.59 99.7%    0+0k 0+0io 0pf+0w

The slowdown comes from the optimization of evlrnf (compiled on top of the last
last set in pr53340#c1)

[macbook] test/dbg_rnflow% /opt/gcc/gcc4.8p-187339/bin/gfortran -c -O3
-ffast-math -funroll-loops evlrnf.f90
[macbook] test/dbg_rnflow% makeo ; time a.out > /dev/null
21.168u 0.348s 0:21.52 99.9%    0+0k 0+0io 0pf+0w
[macbook] test/dbg_rnflow% /opt/gcc/gcc4.8p-187340/bin/gfortran -c -O3
-ffast-math -funroll-loops evlrnf.f90
[macbook] test/dbg_rnflow% makeo ; time a.out > /dev/null
22.758u 0.347s 0:23.11 99.9%    0+0k 0+0io 0pf+0w