[PATCH] Optimize unrolled reductions in LoopStrengthReduce

[Quentin Colombet]

Hi Olivier,

AFAIK, most, if not all, heuristics in LSR are careful not to increase register pressure. You can see that, in particular, when we rate the formulae.
On the other hand, your optimization increases the register pressure for the whole loop. This may not be a good idea in general.

Ultimately, I would like we have some kind of register pressure estimation to decide whether or not we should perform the transformation for a given loop.
Short term, it should, in my opinion, be at least parameterized on the target, i.e., we should have a target hook to decide whether or not we want to perform this optimization.

Side question, how does this patch impact the performances on the llvm test-suite?

Thanks,
-Quentin


http://reviews.llvm.org/D7128

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