[PATCH] D13297: [CGP] transform select instructions into branches and sink expensive operands

[Sanjay Patel via llvm-commits]

spatel created this revision.
spatel added reviewers: reames, hfinkel, joker.eph, bkramer.
spatel added a subscriber: llvm-commits.

This is a follow-up to the discussion in D12882. 

Ideally, we would like SimplifyCFG to be able to form select instructions even when the operands are expensive (as defined by the TTI cost model) because that may expose further optimizations. However, we would then like a later pass like CodeGenPrepare to undo that transformation if the target would likely benefit from not speculatively executing an expensive op (this patch). 

Once we have this safety mechanism in place, we can adjust SimplifyCFG to restore its select-formation behavior that changed with r248439.

http://reviews.llvm.org/D13297

Files:
  lib/CodeGen/CodeGenPrepare.cpp
  test/Transforms/CodeGenPrepare/select.ll

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