[Bug lto/41578] New: 7% slower runtime with -flto than without

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

AMD Athlon64 4800+ (dual core, 1MB L2 cache each, SSE, SSE2, SSE3), 4GB DDR400
with
[LTO]   gfortran -march=native -ffast-math -funroll-loops -flto -O3
[noLTO] gfortran -march=opteron -ffast-math -funroll-loops -ftree-loop-linear
-ftree-vectorize -msse3

When running the Polyhedron Benchmark suite, the LTO version beats the non-LTO
version in the geometric mean value: 23.91s [100%] vs 23.83s [99%]
 (http://www.polyhedron.co.uk/MFL6VW74649).

However, the capacita benchmark is significantly slower, others are also a bit
slower:
            [noLTO]       [LTO]
  capacita  81.54 [100]   87.41 [107]
  mdbx      19.49 [100]   20.07 [102]
  rnflow    34.91 [100]   36.04 [103]
  test_fpu  21.66 [100]   22.40 [103]

(Largest performance gain: aermod (35.14 [100], 31.46 [89]) followed by induct 
(36.51 [100], 35.18 [96]); the others are 2% to 0% faster with LTO.)


-- 
           Summary: 7% slower runtime with -flto than without
           Product: gcc
           Version: 4.5.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: normal
          Priority: P3
         Component: lto
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: burnus at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41578