[PATCH] Teach IRCE to look at branch weights when recognizing range checks

[Sanjoy Das]

Hi reames, hfinkel,

Splitting a loop to make range checks redundant is profitable only if the range check "never" fails.  Make this fact a part of recognizing a range check -- a branch is a range check only if it is expected to pass (via branch_weights metadata).

http://reviews.llvm.org/D7192

Files:
  lib/Transforms/Scalar/InductiveRangeCheckElimination.cpp
  test/Transforms/IRCE/multiple-access-no-preloop.ll
  test/Transforms/IRCE/no-branch-weight.ll
  test/Transforms/IRCE/single-access-no-preloop.ll
  test/Transforms/IRCE/single-access-with-preloop.ll
  test/Transforms/IRCE/with-parent-loops.ll

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