This is a follow up to https://reviews.llvm.org/D126864, addressing some remaining
comments.
It also considers union with a single zero-length array field as FAM for each
value of -fstrict-flex-arrays.
Differential Revision: https://reviews.llvm.org/D132944
Some code [0] consider that trailing arrays are flexible, whatever their size.
Support for these legacy code has been introduced in
f8f6324983 but it prevents evaluation of
__builtin_object_size and __builtin_dynamic_object_size in some legit cases.
Introduce -fstrict-flex-arrays=<n> to have stricter conformance when it is
desirable.
n = 0: current behavior, any trailing array member is a flexible array. The default.
n = 1: any trailing array member of undefined, 0 or 1 size is a flexible array member
n = 2: any trailing array member of undefined or 0 size is a flexible array member
This takes into account two specificities of clang: array bounds as macro id
disqualify FAM, as well as non standard layout.
Similar patch for gcc discuss here: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101836
[0] https://docs.freebsd.org/en/books/developers-handbook/sockets/#sockets-essential-functions
Some code [0] consider that trailing arrays are flexible, whatever their size.
Support for these legacy code has been introduced in
f8f6324983 but it prevents evaluation of
__builtin_object_size and __builtin_dynamic_object_size in some legit cases.
Introduce -fstrict-flex-arrays=<n> to have stricter conformance when it is
desirable.
n = 0: current behavior, any trailing array member is a flexible array. The default.
n = 1: any trailing array member of undefined, 0 or 1 size is a flexible array member
n = 2: any trailing array member of undefined or 0 size is a flexible array member
n = 3: any trailing array member of undefined size is a flexible array member (strict c99 conformance)
Similar patch for gcc discuss here: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101836
[0] https://docs.freebsd.org/en/books/developers-handbook/sockets/#sockets-essential-functions
serge-sans-paille