[Bug rtl-optimization/19210] [4.0 Regression] not using do-loop for some loops

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

------- Additional Comments From rakdver at gcc dot gnu dot org  2004-12-30 22:28 -------
Doloop optimizer believes that the loop may be infinite.  There are two ways 
how to prove that this is not the case:

1) k is signed, and thus cannot overflow with -fno-wrapv
2) k cannot run out of the bounds of the array

On rtl level 1) is no longer available.  Using 2) would probably be possible, 
but relatively difficult.

The simplest solution seems to be using information about number of iterations 
computed at tree level.  This is however also a nontrivial project requiring 
changes in many parts of gcc (and at least a few weeks of work), and as such 
this solution cannot be used in 4.0.

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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19210