[all-commits] [llvm/llvm-project] f63405: BPF: Workaround an InstCombine ICmp transformation...

[yonghong-song via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: f63405f6e3d30f33e715ef5ad09136127535a3fb
      https://github.com/llvm/llvm-project/commit/f63405f6e3d30f33e715ef5ad09136127535a3fb
  Author: Yonghong Song <yhs at fb.com>
  Date:   2021-11-01 (Mon, 01 Nov 2021)

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

  Log Message:
  -----------
  BPF: Workaround an InstCombine ICmp transformation with llvm.bpf.compare builtin

Commit acabad9ff6bf ("[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.

Differential Revision: https://reviews.llvm.org/D112938