[PATCH] D104066: [SCEV] Use knowledge of stride to prove loops finite for LT exit count computation

[Eli Friedman via Phabricator via llvm-commits]

efriedma added a comment.

If the stride is zero, and RHS is invariant, the comparison feeding the backedge is invariant.  If we don't exit via any other exit, that implies the backedge-taken count is either zero or infinity.

So if we know the loop is finite, the RHS is invariant, we don't exit via any other exit, and the IV doesn't overflow, we can divide strides into three cases:

1. Stride is zero.  The backedge-taken count is zero, as noted above.
2. Stride is negative.  I think we can also prove the backedge-taken count is zero here?
3. Stride is positive.  We can use the standard formula.


Repository:
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