[PATCH] D74101: [BPF] implement isTruncateFree and isZExtFree in BPFTargetLowering

[Yonghong Song via Phabricator via llvm-commits]

yonghong-song added a comment.

Note that I cannot do

  In isTruncateFree() do
  return NumBits1 > NumBits2;

This will permit a type truncate operation e.g., from 64bit to 8bit. This will cause a llvm internal assertion later since llvm expects
it produces a backend supported legal subregister type , which is 32bit in this case. PowerPC has similar implementation

  bool PPCTargetLowering::isTruncateFree(Type *Ty1, Type *Ty2) const {
    if (!Ty1->isIntegerTy() || !Ty2->isIntegerTy())
      return false;
    unsigned NumBits1 = Ty1->getPrimitiveSizeInBits();
    unsigned NumBits2 = Ty2->getPrimitiveSizeInBits();
    return NumBits1 == 64 && NumBits2 == 32;
  }


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D74101/new/

https://reviews.llvm.org/D74101