llvm-project

6da23b64 - [BoundsSafety] Add `-fexperimental-bounds-safety` CC1 and language option and use it to tweak `counted_by`'s semantics (#92623)

[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