[all-commits] [llvm/llvm-project] 6da23b: [BoundsSafety] Add `-fexperimental-bounds-safety` ...

[Dan Liew via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 6da23b647ea0c7961a31742e3daac80f4c08e99c
      https://github.com/llvm/llvm-project/commit/6da23b647ea0c7961a31742e3daac80f4c08e99c
  Author: Dan Liew <dan at su-root.co.uk>
  Date:   2024-07-19 (Fri, 19 Jul 2024)

  Changed paths:
    M clang/include/clang/Basic/LangOptions.def
    M clang/include/clang/Driver/Options.td
    M clang/lib/Sema/SemaDeclAttr.cpp
    A clang/test/Sema/attr-counted-by-bounds-safety-vlas.c

  Log Message:
  -----------
  [BoundsSafety] Add `-fexperimental-bounds-safety` CC1 and language option and use it to tweak `counted_by`'s semantics (#92623)

This adds the `-fexperimental-bounds-safety` cc1 and corresponding
language option. This language option enables "-fbounds-safety" which is
a bounds-safety extension for C that is being incrementally upstreamed.

This cc1 flag is not exposed as a driver flag yet because most of the
implementation isn't upstream yet.

The language option is used to make a small semantic change to how the
`counted_by` attribute is treated. Without
`-fexperimental-bounds-safety` the attribute is allowed (but emits a
warning) on a flexible array member where the element type is a struct
with a flexible array member. With the flag this situation is an error.

E.g.

```
struct has_unannotated_FAM {
  int count;
  char buffer[];
};

struct buffer_of_structs_with_unnannotated_FAM {
  int count;
  // Forbidden with `-fexperimental-bounds-safety`
  struct has_unannotated_FAM Arr[] __counted_by(count);
};
```

rdar://125400392



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