[PATCH] D108049: [InstCombine] Canonicalize saturate with shift and xor to min/max clamp

[Dave Green via Phabricator via llvm-commits]

dmgreen created this revision.
dmgreen added reviewers: spatel, efriedma, lebedev.ri, RKSimon, nikic.
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This takes sequences of shift/xor/truncates that together perform a saturate, but a difficult to analyze, and canonicalizes them to min(max(..)) patterns in instcombine.
https://alive2.llvm.org/ce/z/rXLTv8

This is now less instructions (whether you count them as min/max , and with an extra addition can potentially be folded into a sadd.sat. The matched sequence is fairly big but I've not managed to simplify it in smaller steps, so this does it all at once. The code to match it is fairly concise, but it can be moved to aggressive instcombine if that is preferable.


https://reviews.llvm.org/D108049

Files:
  llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
  llvm/test/Transforms/InstCombine/truncating-saturate.ll

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