[Bug tree-optimization/52631] New: VN does not use simplified expression for lookup

[pinskia at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52631

             Bug #: 52631
           Summary: VN does not use simplified expression for lookup
    Classification: Unclassified
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: pinskia@gcc.gnu.org


Take:
unsigned f(unsigned a)
{
  unsigned b = a >> 31;
  return b&1;
}

--- CUT ---
Even though we have a simplified expression of a>>31 for b, VN does not use it.
SCC consists of: a_1(D)
Setting value number of a_1(D) to a_1(D)
SCC consists of: b_2
Value numbering b_2 stmt = b_2 = a_1(D) >> 31;
Setting value number of b_2 to b_2 (changed)
SCC consists of: D.1708_3
Value numbering D.1708_3 stmt = D.1708_3 = b_2 & 1;
RHS b_2 & 1 simplified to a_1(D) >> 31 has constants 1
Setting value number of D.1708_3 to D.1708_3 (changed)

This is a regression from 4.3.