[llvm-commits] Possible bug in cost model?

[Renato Golin]

Hi Nadav,

This part of the code seems odd:

  // Check for NOOP conversions.
  if (SrcLT.first == DstLT.first &&
      SrcLT.second.getSizeInBits() == DstLT.second.getSizeInBits()) {

      // Bitcast between types that are legalized to the same type are free.
      if (Opcode == Instruction::BitCast || Opcode == Instruction::Trunc)
        return 0;
  }

It looks as though it's stating that if the legalization of both types is
the same, the cost is zero. I'd assume the cost would be the legalization
cost.

It may not matter much on most cases because it's an invariant when all
paths have the legalization phase, but if one of the paths can avoid the
legalization (by completely removing it), than the benefit won't be
accounted for.

Does it make sense?

The attached patch "fixes" this (assuming it's wrong) ;)

cheers,
--renato
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