[PATCH] D113496: BPF: change btf_type_tag BTF output format

[Yonghong Song via Phabricator via llvm-commits]

yonghong-song created this revision.
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For the declaration like below:

  int __tag1 * __tag1 __tag2 *g

Commit 41860e602aaa <https://reviews.llvm.org/rG41860e602aaa94556ba996fae7b8baa268e25096> ("BPF: Support btf_type_tag attribute")
implemented the following encoding:

  VAR(g) -> __tag1 --> __tag2 -> pointer -> __tag1 -> pointer -> int 

Some further experiments with linux btf_type_tag support, esp.
with generating attributes in vmlinux.h, and also some internal
discussion showed the following format is more desirable:

  VAR(g) -> pointer -> __tag2 -> __tag1 -> pointer -> __tag1 -> int 

The format makes it similar to other modifier like 'const', e.g.,

  const int *g

which has encoding VAR(g) -> PTR -> CONST -> int


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D113496

Files:
  llvm/lib/Target/BPF/BTFDebug.cpp
  llvm/lib/Target/BPF/BTFDebug.h
  llvm/test/CodeGen/BPF/BTF/type-tag-var.ll

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