[PATCH] D12196: [ARM] Extract shifts out of multiply-by-constant

[John Brawn via llvm-commits]

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Turning (op x (mul y k)) into (op x (lsl (mul y k>>n) n)) is beneficial when we can do the lsl as a shifted operand and the resulting multiply constant is simpler to generate.

Do this by doing the transformation when trying to select a shifted operand, as that ensures that it actually turns out better (the alternative would be to do it in PreprocessISelDAG, but we don't know for sure there if extracting the shift would allow a shifted operand to be used).


Repository:
  rL LLVM

http://reviews.llvm.org/D12196

Files:
  lib/Target/ARM/ARMISelDAGToDAG.cpp
  test/CodeGen/ARM/shifter_operand.ll

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