[Bug target/47831] avoid if-convertion if the conditional instructions and following conditional branch has the same condition

[ibolton at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47831

Ian Bolton <ibolton at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |missed-optimization
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2011.02.22 14:50:03
                 CC|                            |ibolton at gcc dot gnu.org
     Ever Confirmed|0                           |1
      Known to fail|                            |4.6.0

--- Comment #1 from Ian Bolton <ibolton at gcc dot gnu.org> 2011-02-22 14:50:03 UTC ---
Confirmed on r170278 of trunk.

The better sequence that Carrot mentions comes from having if-conversion
disabled (-fno-if-conversion2).

I expect Basic Block Reordering might be able to help out in the case where
if-conversion is enabled, but I think it is still disabled for -Os, as it can
sometimes lead to larger code.

That is a separate issue though.  To tackle this properly, the if-conversion
heuristic would need to be enhanced to detect cases where the codesize will
likely increase and pessimise against those cases when using -Os.