[PATCH] D62223: [DAGCombiner][X86][AArch64][AMDGPU] (x + C) - y -> (x - y) + C fold

[Roman Lebedev via Phabricator via llvm-commits]

lebedev.ri added inline comments.


================
Comment at: lib/CodeGen/SelectionDAG/DAGCombiner.cpp:2926
+  // Hoist one-use addition by constant:  (x + C) - y  ->  (x - y) + C
+  if (N0.hasOneUse() && N0.getOpcode() == ISD::ADD &&
+      isConstantOrConstantVector(N0.getOperand(1))) {
----------------
bjope wrote:
> Not sure if it is super important, or common, in reality. But maybe this should be trigger for an add-like-or as well? 
> 
> An ADD with no common bits set in the operands is canonicalized into OR by DAGCombiner, so there could be lots of OR:s out there that really are ADD:s.
Yes, correct observation. I did think about it when writing,
but i did not see any easy way to do that here.
Any suggestions?


Repository:
  rL LLVM

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  https://reviews.llvm.org/D62223/new/

https://reviews.llvm.org/D62223