[PATCH] Fix information loss in branch probability computation.

[Diego Novillo]

This modifies the  scaling to do it based on the sum of all branch weights. If
the sum of weights exceeds 32 bits, compute an integer scale to bring all the
weights within the range.

Additionally, remove the use of scaled integers. Use 64 bit integers for
all the calculations.

Adjust tests and an assertion in switch lowering. The assertion was
using the previous branch weight limits.


http://reviews.llvm.org/D9442

Files:
  lib/Analysis/BranchProbabilityInfo.cpp
  lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
  test/Analysis/BranchProbabilityInfo/pr22718.ll
  test/CodeGen/X86/MachineBranchProb.ll

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