[PATCH] D27714: [DAGCombiner] Use SelectionDAG::isKnownToBeAPowerOfTwo instead of just APInt::isPowerOf2

[Simon Pilgrim via Phabricator via llvm-commits]

RKSimon created this revision.
RKSimon added reviewers: majnemer, eli.friedman, spatel, andreadb.
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RKSimon set the repository for this revision to rL LLVM.

Generalize sdiv/udiv/srem/urem combines using APInt::isPowerOf2, which only works for const/splat-const values to call SelectionDAG::isKnownToBeAPowerOfTwo instead which recognises many more cases.

Added a DAGCombiner::BuildLogBase2 helper since PowerOf2 combines often involve taking the log2 of such a value.


Repository:
  rL LLVM

https://reviews.llvm.org/D27714

Files:
  lib/CodeGen/SelectionDAG/DAGCombiner.cpp
  lib/CodeGen/SelectionDAG/SelectionDAG.cpp
  test/CodeGen/X86/combine-sdiv.ll
  test/CodeGen/X86/combine-srem.ll
  test/CodeGen/X86/combine-udiv.ll
  test/CodeGen/X86/combine-urem.ll
  test/CodeGen/X86/urem-power-of-two.ll

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