[PATCH] D118459: [ISEL] Canonicalize STEP_VECTOR to LHS if RHS is a splat.

[Sander de Smalen via Phabricator via llvm-commits]

sdesmalen added inline comments.


================
Comment at: llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp:5644
+             N2.getOpcode() == ISD::STEP_VECTOR)
+      std::swap(N1, N2);
   }
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RKSimon wrote:
> I expect we're going to need this for a lot of the DAG combines as well - is it worth adding a helper wrapper for isConstantIntBuildVectorOrConstantInt/isConstantFPBuildVectorOrConstantFP with SPLAT_VECTOR  and STEP_VECTOR as well?
I'd rather avoid creating another `isConstant....` method, because we already have so many of them and despite the name, `isConstantIntBuildVectorOrConstantInt` already supports SPLAT_VECTOR  (it would actually be good to clean that up a bit at some point).

For this patch, it may be worth moving this commutativity code as a whole to a separate function (e.g. `swapCommutativeOperands`), would that help?


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D118459/new/

https://reviews.llvm.org/D118459