[PATCH] D153947: [RISCV] Teach targetShrinkDemandedConstant to preserve (and X, neg)

[Liao Chunyu via Phabricator via llvm-commits]

liaolucy added a comment.

This patch relies on the D153934 <https://reviews.llvm.org/D153934>. 
Otherwise, I tried another method:

  diff --git a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
  index ef9e96b6cca4..9a46455017c6 100644
  --- a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
  +++ b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
  @@ -13020,7 +13020,7 @@ bool RISCVTargetLowering::targetShrinkDemandedConstant(
  
     // For the remaining optimizations, we need to be able to make a negative
     // number through a combination of mask and undemanded bits.
  -  if (!ExpandedMask.isNegative())
  +  if (!ExpandedMask.isNegative() && Opcode != ISD::AND)
       return false;
  
     // What is the fewest number of bits we need to represent the negative number.
  @@ -13034,8 +13034,13 @@ bool RISCVTargetLowering::targetShrinkDemandedConstant(
       NewMask.setBitsFrom(11);
     else if (!C->isOpaque() && MinSignedBits <= 32 && !ShrunkMask.isSignedIntN(32))
       NewMask.setBitsFrom(31);
  -  else
  -    return false;
  +  else {
  +    NewMask.setBitsFrom(31);
  +    if (Opcode == ISD::AND && !C->isOpaque() && MinSignedBits <= 32 && !ShrunkMask.isSignedIntN(32) && NewMask.isSignedIntN(12))
  +     return UseMask(NewMask);
  +    else
  +     return false;
  +  }
  
     // Check that our new mask is a subset of the demanded mask.
     assert(IsLegalMask(NewMask));


Repository:
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  https://reviews.llvm.org/D153947/new/

https://reviews.llvm.org/D153947