[PATCH] D64394: [MachineCSE][MachinePRE] Do not hoist common computations into loop bodies

[Kai Luo via Phabricator via llvm-commits]

lkail added a comment.

@hfinkel , thanks for review.

> do you have performance results from the test suite, or something else, showing otherwise?

Yes.

> However, if CMBB is in a loop body, we might get performance degradation.

This conclusion comes from my observation of the test suite code, I'm to paste a reduced case to tests soon, similar to current test, except for its branches are `switch`s.

> But we might also get a performance improvement, because the performance of the inner loop is more significant than that of the outer loop.

I do miss this point you have mentioned. @nemanjai has already suggested me to take a look at `MachineBlockFrequency`.

> Is the problem hoisting out of a cold inner region into a hot loop?

I agree with it. This patch should consider more about hotness of loops.


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https://reviews.llvm.org/D64394