[PATCH] D23313: X86: FMA intrinsic + FNEG - sequence optimization

[Elena Demikhovsky via llvm-commits]

delena created this revision.
delena added reviewers: igorb, RKSimon, andreadb.
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Optimized FMA intrinsic + FNEG , like
   -(a*b+c)
and  FNEG + FMA, like
   a*b-c or (-a)*b+c

Legalization of ISD::FNEG is delayed to give a chance to combine it with X86ISD::FMADD/MSUB/NMADD/NMSUB.

7 out of 8 test cases are optimized. The last test case requires additional investigation and, probably, changes in the clang header.

Fixed https://llvm.org/bugs/show_bug.cgi?id=28892.

Repository:
  rL LLVM

https://reviews.llvm.org/D23313

Files:
  ../lib/Target/X86/X86ISelLowering.cpp
  ../test/CodeGen/X86/fma-fneg-combine.ll

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