[PATCH] D124089: [RISCV] Add a test showing incorrect VSETVLI insertion

[Roger Ferrer Ibanez via Phabricator via llvm-commits]

rogfer01 added a comment.

One interesting thing is that `computeIncomingVLVTYPE` doesn't seem to be fully aligned with what `emitVSETVLIs` will do. If the latter chooses to skip a `vsetvl` then the `Exit` of that basic block might potentially be different to the one that we determined in `computeIncomingVLVTYPE`.

Maybe aligning `computeIncomingVLVTYPE` with the expectations of `emitVSETVLIs` is possible. Looks like once we have computed `InInfo` in `computeIncomingVLVTYPE` we may have to run again `computeVLVTYPEChanges` for that block (and there make sure we use the same skip criteria as in `emitVSETVLIs`). The latter would now receive the `InInfo` (in contrast to Phase 1 where it'd be unknown) and it would compute a potentially different `Exit` value. This also suggests that Phase 1 might be embedded as part of Phase 2 once we have computed the `InInfo`. This might make the algorithm a bit slower.

D119518 <https://reviews.llvm.org/D119518> mitigates the lack of alignment by reconciling both but it means that in your case (when we make `CurInfo = BlockInfo[MBB.getNumber()].Pred;`) we get an unnecessary change at the end of `bb1` which we'd want to have in `bb2` instead.


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  https://reviews.llvm.org/D124089/new/

https://reviews.llvm.org/D124089