[PATCH] [SimplifyCFG] Swap to using TargetTransformInfo for cost analysis.

[James Molloy]

Hi hfinkel, t.p.northover,

We're already using TTI in SimplifyCFG, so remove the hard-baked "cheapness"
heuristic and use TTI directly. Generally NFC intended, but we're using a slightly
different heuristic now so there is a slight test churn.

Test changes:
  * combine-comparisons-by-cse.ll: Removed unneeded branch check.
  * 2014-08-04-muls-it.ll: Test now doesn't branch but emits muleq.
  * coalesce-subregs.ll: Superfluous block check.
  * 2008-01-02-hoist-fp-add.ll: fadd is safe to speculate. Change to udiv.
  * PhiBlockMerge.ll: Superfluous CFG checking code. Main checks still present.
  * select-gep.ll: A variable GEP is not expensive, just TCC_Basic, according to the TTI.

REPOSITORY
  rL LLVM

http://reviews.llvm.org/D7506

Files:
  lib/Transforms/Utils/SimplifyCFG.cpp
  test/CodeGen/AArch64/arm64-promote-const.ll
  test/CodeGen/AArch64/combine-comparisons-by-cse.ll
  test/CodeGen/ARM/2014-08-04-muls-it.ll
  test/CodeGen/ARM/coalesce-subregs.ll
  test/Transforms/SimplifyCFG/2008-01-02-hoist-fp-add.ll
  test/Transforms/SimplifyCFG/PhiBlockMerge.ll
  test/Transforms/SimplifyCFG/select-gep.ll

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