[PATCH] D12765: [LV] Allow vectorization of loops with induction post-inc expressions

[Michael Zolotukhin via llvm-commits]

mzolotukhin added a comment.

Hi Jakub,

The problem with the current approach is that it only fixes one case, that is caused by a different problem (as you showed - the actual problem is in IndVarSimplify/SCEVExpander). We fix consequences, not the rootcause itself. Maybe next week someone will come up with a patch, that would fix the same issue in LoopUnroller, and next week - in LoopInterchange or any other loop transformation.

It might be not-trivial to fix it in SCEV/IndVarSimplify, but I think it should be possible, and that's what we need to try first. For this case we just need to teach SCEV/IndVarSimplify to take into account loop invariants. E.g. the entire expression `(zext i32 (-3 + (-1 * (-4097 smax (-1 + (-1 * %y))))<nsw>) to i64)` is a loop invariant, so it shouldn't have high cost.

The fix in vectorizer might be simple, but I believe it's a (small) step in a wrong direction.

Michael


Repository:
  rL LLVM

http://reviews.llvm.org/D12765