[PATCH] D112938: BPF: Workaround an InstCombine ICmp transformation with llvm.bpf.compare builtin

[Yonghong Song via Phabricator via llvm-commits]

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Commit acabad9ff6bf <https://reviews.llvm.org/rGacabad9ff6bf13e00305d9d8621ee8eafc1f8b08> ("[InstCombine] try to canonicalize icmp with
trunc op into mask and cmp") added a transformation to
convert "(conv)a < power_2_const" to "a & <const>" in certain
cases and bpf kernel verifier has to handle the resulted code
conservatively and this may reject otherwise legitimate program.

This commit tries to prevent such a transformation. A bpf backend
builtin llvm.bpf.compare is added. The ICMP insn, which is subject to
above InstCombine transformation, is converted to the builtin
function. The builtin function is later lowered to original ICMP insn,
certainly after InstCombine pass.

With this change, all affected bpf strobemeta* selftests are 
passed now.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D112938

Files:
  llvm/include/llvm/IR/IntrinsicsBPF.td
  llvm/lib/Target/BPF/BPFAdjustOpt.cpp
  llvm/lib/Target/BPF/BPFCheckAndAdjustIR.cpp
  llvm/test/CodeGen/BPF/adjust-opt-icmp3.ll

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