[Bug middle-end/46837] New: induct compiled with -ffast-math -fschedule-insns -fsched-pressure -O3 ~30% slower

["howarth at nitro dot med.uc.edu" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46837

           Summary: induct compiled with -ffast-math -fschedule-insns
                    -fsched-pressure -O3 ~30% slower
           Product: gcc
           Version: 4.6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: howarth@nitro.med.uc.edu


The Polyhedron 2005 benchmark induct is 28% slower when compiled with
-ffast-math -fschedule-insns -fsched-pressure -O3 compared to -ffast-math -O3
(15.86 sec vs 12.43 sec) on x86_64-apple-darwin10 using -mtune=core2. This same
performance regression doesn't occur at -ffast-math -fschedule-insns
-fsched-pressure -O2 vs -ffast-math -O2.

The same effect is seen with both -mtune=generic (24%) as -mtune=core2 (28%) as
well as at
-m32 (33% with -mtune=core2 and 5% with -mtune=generic).

gfortran -ffast-math -O3 induct.f90 -o induct

tuning                       -mtune=core2                                      
                                mtune=generic
                      ------------------------------------    
---------------------------------------
                      stock          -fschedule-insns -fsched-pressure    
stock   -fschedule-insns -fsched-pressure
-m64           12.43s                      15.86s                              
             12.44s             15.57s
-m32           13.91s                      18.63s                              
             13.93s             14.69s

Using built-in specs.
COLLECT_GCC=gfortran
COLLECT_LTO_WRAPPER=/sw/lib/gcc4.6/libexec/gcc/x86_64-apple-darwin10.5.0/4.6.0/lto-wrapper
Target: x86_64-apple-darwin10.5.0
Configured with: ../gcc-4.6-20101206/configure --prefix=/sw
--prefix=/sw/lib/gcc4.6 --mandir=/sw/share/man --infodir=/sw/lib/gcc4.6/info
--enable-languages=c,c++,fortran,objc,obj-c++,java --with-gmp=/sw
--with-libiconv-prefix=/sw --with-ppl=/sw --with-cloog=/sw --with-mpc=/sw
--with-system-zlib --x-includes=/usr/X11R6/include --x-libraries=/usr/X11R6/lib
--program-suffix=-fsf-4.6 --enable-checking=yes --enable-cloog-backend=isl
Thread model: posix
gcc version 4.6.0 20101207 (experimental) (GCC) 
r167525 with