[Bug rtl-optimization/32283] Missed induction variable optimization

[amonakov at gmail dot com]

------- Comment #15 from amonakov at gmail dot com  2007-12-05 16:26 -------
Zdenek,

please kindly share your thoughts on concerns expressed in previous comments. 
The failures of number-of-iterations analysis prohibit applying modulo
scheduling to many simple loops that are otherwise eligible; in fact, I now
test SMS with either your patch reverted, or with -funsafe-loop-optimizations,
but I believe this is not a healthy state.

Please correct me if I am wrong, but I think that optimizing out the variable
that holds number of iterations is not desirable on targets that have doloop
machine idiom, because doloop rtl pass will re-introduce it in a specially
designated register.  However, ia64 does not allow arithmetic operations with
loop counter, so it would be nice if iv-opts transformed the loop to the form
where decrement-and-branch-on-zero are the only uses of this variable, when
possible. 


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32283