[Bug rtl-optimization/91865] Combine misses opportunity to remove (sign_extend (zero_extend)) before searching for insn patterns

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91865

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |missed-optimization
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2019-09-24
                 CC|                            |segher at gcc dot gnu.org
     Ever confirmed|0                           |1

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
Confirmed.  I guess either simplify-rtx or the combine variant could be
amended.
There may be guards against partial int modes preventing existing
simplifications to apply (for hysterical reasons).