[Bug rtl-optimization/60757] New: combine uses exponential time in nonzero_bits1 recursion

[amylaar at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60757

            Bug ID: 60757
           Summary: combine uses exponential time in nonzero_bits1
                    recursion
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: rtl-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: amylaar at gcc dot gnu.org

Created attachment 32540
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=32540&action=edit
pruned down testcase

With a small fix to the rtx_costs for epiphany, gcc.c-torture/compile/pr43415.c
times out compiling at -O3.
Even when the loop iteration counts are pruned, it's still too much,
as nonzero_bits recurses for both operands of a binary operator...
going through 40 operations means 2^40 paths being followed...