[PATCH] D30466: AMDGPU: Add simple machine level computeKnownBits

[Matt Arsenault via Phabricator via llvm-commits]

arsenm created this revision.
Herald added subscribers: tpr, dstuttard, tony-tye, yaxunl, nhaehnle, wdng, kzhuravl.

The DAG makes it difficult/impossible to make the right
decisions when there are no direct equivalents between SALU
and VALU instructions.

     

For example, we can use the v_cvt_pk_u16_u32 instruction to
pack a v2i16 if the known high bits are 0. However there is no
scalar equivalent, so pattern matching this in the DAG
introduces divergences from what would be a simple bit pattern.
With known bits, we can pattern match this after it is known
to really be a vector op.

      

This also may be useful for the SDWA pass.


https://reviews.llvm.org/D30466

Files:
  lib/Target/AMDGPU/SIInstrInfo.cpp
  lib/Target/AMDGPU/SIInstrInfo.h

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