[PATCH] D39262: [CodeGen] Peel off the dominant case in switch statement in lowering

[Rong Xu via Phabricator via llvm-commits]

xur created this revision.

This patch peels off the top case in switch statement into a branch if the probability exceeds a threshold.
This will help the branch prediction and avoids the extra compares when lowering into chain of branches.
A previous patch of the same idea was on CFG simplification pass:
https://reviews.llvm.org/D37940
This patch is implemented in SelectionDAG.


https://reviews.llvm.org/D39262

Files:
  lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
  test/CodeGen/Generic/MachineBranchProb.ll
  test/CodeGen/Generic/switch-lower-peel-top-case.ll
  test/CodeGen/X86/switch.ll

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