[PATCH] D128123: [SDAG] try to replace subtract-from-constant with xor

[Sergei Barannikov via Phabricator via llvm-commits]

barannikov88 added inline comments.


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Comment at: llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp:3766
+  // If there's no chance any bit will need to borrow from an adjacent bit:
+  // sub C, X --> xor X, C
+  if (ConstantSDNode *C0 = isConstOrConstSplat(N0)) {
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It might be more profitable to do this transformation in SimplifyDemandedBits. Some bits of the result might not be used downstream, in which case the check can be relaxed.



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  https://reviews.llvm.org/D128123/new/

https://reviews.llvm.org/D128123