[PATCH] D142746: AMDGPU: Fold fneg into bitcast of build_vector

[Matt Arsenault via Phabricator via llvm-commits]

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The math libraries have a lot of code that performs
manual sign bit operations by bitcasting doubles to int2
and doing bithacking on them. This is a bad canonical form
we should rewrite to use high level sign operations directly
on double. To avoid codegen regressions, we need to do a better
job moving fnegs to operate only on the high 32-bits.

      

This is only halfway to fixing the real case.


https://reviews.llvm.org/D142746

Files:
  llvm/lib/Target/AMDGPU/AMDGPUISelLowering.cpp
  llvm/test/CodeGen/AMDGPU/fneg-modifier-casting.ll

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