Yonghong Song 8fb3f84484 BPF: Workaround InstCombine trunc+icmp => mask+icmp Optimization ...

Patch [1] added further InstCombine trunc+icmp => mask+icmp
optimization and this caused a couple of bpf selftest failure.
Previous llvm BPF backend patch [2] introduced llvm.bpf.compare
builtin to handle such situations.

This patch further added support ">" and ">=" icmp opcodes.
Tested with bpf selftests and all tests are passed including two
previously failed ones.

Note Patch [1] also added optimization if the to-be-compared
constant is negative-power-of-2 (-C) or not-of-power-of-2 (~C).
This patch didn't implement these two cases as typical bpf
program compares a scalar to a positive length or boundary value,
and this scalar later is used as a index into an array buffer
or packet buffer.

  [1] https://reviews.llvm.org/D112634
  [2] https://reviews.llvm.org/D112938

Differential Revision: https://reviews.llvm.org/D114215

2021-11-18 20:25:28 -08:00

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