[PATCH] D122070: [SDAG] enable binop identity constant folds for shifts

Sat Mar 19 08:59:12 PDT 2022

RKSimon added inline comments.

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Comment at: llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp:2167
+      case ISD::SRA: // X s>> 0 --> X
+      case ISD::SRL: // X u>> 0 --> X
         return C->isZero();
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pengfei wrote:
> Can it apply to ROTL/ROTR ?
Yes, we'd have to account for the implicit modulo though.

There's plenty of other ops we could attempt with this as well, including some non-binops (funnel shifts and fma for instance) - I'm also wondering what target binops will need to be supported.

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D122070/new/

https://reviews.llvm.org/D122070