[Bug rtl-optimization/14483] More aggressive compare insn elimination

[Bug rtl-optimization/14483] More aggressive compare insn elimination

[steven at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14483

Steven Bosscher <steven at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to fail|                            |4.8.0

--- Comment #4 from Steven Bosscher <steven at gcc dot gnu.org> 2012-10-25 23:36:13 UTC ---
(In reply to comment #2)
> The problem with extending cse_condition_code_reg() in cse.c is that
> we have to determine the result of "testl", (reg 17) dies at the conditional
> jump insn, but cse_condition_code_reg() is run before the flow analysis.
> So we don't have liveness information.  If this is to be implemented,
> we may have to do this after the combine or something.

This is not a problem anymore since the DF merge. Liveness is now
available (and used) in all CSE passes.

[Bug tree-optimization/14483] More aggressive compare insn elimination

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=14483

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
          Component|rtl-optimization            |tree-optimization
                 CC|                            |pinskia at gcc dot gnu.org

--- Comment #5 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
What we could do in isel pass:
find a == 0 (in gimple_cond or in gimple_assign).
for gimple_cond see if either branch only has a == 1 in it. and change `a == 0`
to `(unsigned)a < 1`

This can be a generic part of isel even.
And then the RTL passes should be able to remove the comparison.