[PATCH] Add straight-line strength reduction to LLVM

[Andrew Trick]

Mainly, I would like to reiterate both of Hal's very good points above.

Out of curiosity, can you explain what sort of real-world source code results in this IR pattern?

You should keep in mind, that this level of optimization is currently the job of LSR. If you're doing this within a loop the IVChain part of LSR will try to do something similar.

I only reviewed it quickly, but your implementation looks good. Thank you for putting a bound on the number of candidate checks. I hate finding those quadratic behaviors later when compile time blows up.

LGTM given that it's not enabled in the standard pipeline yet.


http://reviews.llvm.org/D7310

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