[PATCH] D27004: Set unroll remainder to epilog if profitable

[Evgeny Stupachenko via Phabricator via llvm-commits]

evstupac added inline comments.


================
Comment at: test/Transforms/LoopUnroll/epilog_const_phi.ll:4
+; Epilog unroll allows to keep PHI constant value.
+; For the test this means that inscombine can completle eliminate XOR.
+
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mzolotukhin wrote:
> s/inscombine/instcombine/
> s/completle/completely/
> 
> I'd rather not rely on other passes (instcombine) to check loop-unroll. Can we check the CFG instead? That'll make the test smaller (since it'll be enough to have a minimal loop) and more robust to unrelated changes (say, instcombine for some reason stopped to simplify XOR through phis). It would be also nice to have a test, in which we don't use epilog (i.e. arguments of phis are not constant), to check that we're not doing it everywhere.
>I'd rather not rely on other passes (instcombine) to check loop-unroll. Can we check the CFG instead? That'll make the test smaller (since it'll be enough to have a minimal loop) and more robust to unrelated changes (say, instcombine for some reason stopped to simplify XOR through phis). 
I agree, that right now it is more than unroll test. We can switch to CFG, but I'd like to leave XOR or smth else that shows clear profitability (when other optimizations are applied) instead of minimizing the loop.

>It would be also nice to have a test, in which we don't use epilog (i.e. arguments of phis are not constant), to check that we're not doing it everywhere.
Good point. I'll add such.



Repository:
  rL LLVM

https://reviews.llvm.org/D27004