[PATCH] D10979: Update the branch weight metadata in JumpThreading pass.

[Cong Hou]

congh added reviewers: chandlerc, davidxl.
congh added a subscriber: llvm-commits.

Currently in JumpThreading pass, the branch weight metadata is not updated after CFG modification. Consider the jump threading on PredBB, BB, and SuccBB. After jump threading, the weight on BB->SuccBB should be adjusted as some of it is contributed by the edge PredBB->BB, which doesn't exist anymore. This patch tries to update the edge weight in metadata on BB->SuccBB by scaling it by 1 - Freq(PredBB->BB) / Freq(BB->SuccBB). Two more analyses (BlockFrequencyInfo and BranchProbabilityInfo) are needed then.

http://reviews.llvm.org/D10979

Files:
  lib/Transforms/Scalar/JumpThreading.cpp

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