[rtlopt] runtime iterations unrolling fix

[Zdenek Dvorak]

Hello,

> the test to disable exit conditional in peeled copy of loop body is
> reversed compared to the comment.  I guess the comment is what you've
> intended so I've changed it.  Still I am not able to come with
> testcase when we need exit test in all copies.  Can you enlighten me?

thinking about it, I come to belief the comment is the thing that is wrong --
suppose that we have a preincr loop, that means we are
trying to arrange things so that the exit from loop body is in the last
block of the loop; it is, we must arrange that after entering the body,
there will be -1 (mod # of unrollings) iterations left. I must have
tests for exit in every copy (in preconditioning), as we may exit
in some of these copies (in case the loops rolls less than # of
unrollings times).

So I will revert the change and fix the comment.

Did the code as it was cause some problem?

Zdenek