Merging r293635:

Merging r293635:
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r293635 | nha | 2017-01-31 06:35:37 -0800 (Tue, 31 Jan 2017) | 16 lines

[DAGCombine] require UnsafeFPMath for re-association of addition

Summary:
The affected transforms all implicitly use associativity of addition,
for which we usually require unsafe math to be enabled.

The "Aggressive" flag is only meant to convey information about the
performance of the fused ops relative to a fmul+fadd sequence.

Fixes Bug 31626.

Reviewers: spatel, hfinkel, mehdi_amini, arsenm, tstellarAMD

Subscribers: jholewinski, nemanjai, wdng, llvm-commits

Differential Revision: https://reviews.llvm.org/D28675
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git-svn-id: https://llvm.org/svn/llvm-project/llvm/branches/release_40@293940 91177308-0d34-0410-b5e6-96231b3b80d8