[Bug target/28791] New: sh64-elf -mdiv= options bitrot

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

The -mdiv=inv:minlat option no longer rearranges the computations;
It appears the combiner pattern falls foul of the combine_validate_cost
check.  The assumed cost of the three constituent instructions is 4 each,
while the cost of the combined instruction is assumed to be 16.
sh_rtx_costs needs to be adjusted to make sure that the combination
happens; preferrably give the constituent insns a realistic cost.

-mdiv=inv:call performs the transformation, but the transformed instruction
is not recognized, causing an ICE. 

testcase (add -O2 to options):
int
f (int a, int b)
{
  return a/b;
}


-- 
           Summary: sh64-elf -mdiv= options bitrot
           Product: gcc
           Version: 4.2.0
            Status: UNCONFIRMED
          Keywords: ice-on-valid-code, missed-optimization
          Severity: normal
          Priority: P3
         Component: target
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: amylaar at gcc dot gnu dot org
GCC target triplet: sh64-elf


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28791