[PATCH] D70586: [BPF] Fix a recursion bug in BPF Peephole ZEXT optimization

[Yonghong Song via Phabricator via llvm-commits]

yonghong-song created this revision.
yonghong-song added reviewers: ast, anakryiko.
Herald added subscribers: llvm-commits, hiraditya.
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Commit a0841dfe8594 <https://reviews.llvm.org/rGa0841dfe8594f189d79f3612fec019eda4824474> ("[BPF] Fix a bug in peephole optimization")
fixed a bug in peephole optimization. Recursion is introduced
to handle COPY and PHI instructions.

Unfortunately, multiple PHI instructions may form a cycle
and this will cause infinite recursion, eventual segfault.
For Commit a0841dfe8594 <https://reviews.llvm.org/rGa0841dfe8594f189d79f3612fec019eda4824474>, I indeed tried a few loops to ensure
that I won't see the recursion, but I did not try with
complex control flows, which, as demonstrated with the test case
in this patch, may introduce PHI cycles.

This patch fixed the issue by introducing a set to remember
visited PHI instructions. This way, cycles can be properly
detected and handled.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D70586

Files:
  llvm/lib/Target/BPF/BPFMIPeephole.cpp
  llvm/test/CodeGen/BPF/32-bit-subreg-peephole-phi-3.ll

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