[PATCH] D29605: [lanai] Add computeKnownBitsForTargetNode for Lanai.

[Jacques Pienaar via Phabricator via llvm-commits]

jpienaar added a comment.

In https://reviews.llvm.org/D29605#668363, @majnemer wrote:

> In https://reviews.llvm.org/D29605#668334, @majnemer wrote:
>
> > Hmm, this is the sort of thing I'd expect SelectionDAG to "just do"... Do other backends achieve the same end by similar means?
>


Yes, PPC does it in PPCTargetLowering::DAGCombineTruncBoolExt (https://github.com/llvm-mirror/llvm/blob/fb21e4d6fc9ff15b231354be4068c3f732deee02/lib/Target/PowerPC/PPCISelLowering.cpp#L9979) but in retrospect they were doing it as they have 2 different ways of setting conditional flags. For Lanai this was not needed.

> I'd expect this logic to zap away such an AND: https://github.com/llvm-mirror/llvm/blob/fb21e4d6fc9ff15b231354be4068c3f732deee02/lib/CodeGen/SelectionDAG/TargetLowering.cpp#L560

This was good suggestion: it let me to seeing that computeKnownBitsForTargetNode was not defined for Lanai and so this combination would not happen. So the resulting change is much simpler and covers more cases.


https://reviews.llvm.org/D29605