[PATCH] fold: sqrt(x * x * y) -> fabs(x) * sqrt(y)

[Sanjay Patel]

Code and regression tests updated to use a function-level attribute to enable the optimization.

Note that the existing optimization to do (X*Y) * X => (X*X) * Y in InstCombineMulDivRem also needs to detect the function-level attribute, otherwise it won't reassociate the factors to the square root into the canonical form.

http://reviews.llvm.org/D5787

Files:
  include/llvm/Transforms/Utils/SimplifyLibCalls.h
  lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
  lib/Transforms/Utils/SimplifyLibCalls.cpp
  test/Transforms/InstCombine/fast-math.ll
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