[Bug tree-optimization/56935] New: Basic block is not SLP-vectorizeed after r197635.

[ysrumyan at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56935

             Bug #: 56935
           Summary: Basic block is not SLP-vectorizeed after r197635.
    Classification: Unclassified
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: ysrumyan@gmail.com


It looks that after cost model changing some performance opportunities were
lost.
It can be seen for the attached test-case:

before this change
t.c:29: note: Cost model analysis: 
  Vector inside of basic block cost: 5
  Vector prologue cost: 0
  Vector epilogue cost: 0
  Scalar cost of basic block: 6
t.c:29: note: Basic block will be vectorized using SLP
 after this change
t.c:29: note: Cost model analysis: 
  Vector inside of basic block cost: 5
  Vector prologue cost: 1
  Vector epilogue cost: 0
  Scalar cost of basic block: 6
t.c:29: note: not vectorized: vectorization is not profitable.

Note that this test was extracted from 253.perlbench (spec2000) for which we
got -4.5% performance degradation on corei7 (with avx).