[PATCH] D144014: [LSR] Improve filtered uses in NarrowSearchSpaceByPickingWinnerRegs

[Dave Green via Phabricator via llvm-commits]

dmgreen created this revision.
dmgreen added reviewers: chill, fhahn, samtebbs, aemerson.
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NarrowSearchSpaceByPickingWinnerRegs has an aggressive filtering method to reduce the complexity of the search space down by picking a best formula with the highest number of reuses and assuming it will yield profitable reuse. In certain cases we can find a "best" formula like `{X+30,+,1}` and later check a formula like `{X,+,1}` with the same number of Uses. On certain architectures it can be better to pick `{X,+,1}`, especially if an offset of 30 can be used as a legal addressing mode, but -30 cannot. That happens under Thumb1 code, which has fairly limited addressing modes. This patch adds a check to see if it can pick the simpler formula, if it looks more profitable.


https://reviews.llvm.org/D144014

Files:
  llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
  llvm/test/CodeGen/Thumb/arm_q15_to_q31.ll

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