https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88115
--- Comment #6 from James Y Knight <foom at fuhm dot net> --- > c++: Change the mangling of __alignof__ [PR88115] The new mangling chosen for __alignof__(type) seems problematic, and I think this commit ought to be reverted until a new mangling scheme has been chosen. At the very least, both __alignof__(expression) and __alignof__(type) can't both be encoded as "v111__alignof__", with no indication of whether the argument is a type or an expression, because that's ambiguous. Possibly it'd be okay to use v112__alignof__z and v112__alignof__t, similar to how "az" and "at" are used for standard alignof expression/type. That solves the ambiguity. But -- this violates the generic grammar, which doesn't allow for a vendor operator to take type arguments at all. <operator-name> ::= v <digit> <source-name> <expression> ::= <unary operator-name> <expression> Now...possibly it's okay to violate that and pass a type, regardless. But, then the demangler needs to know what every vendor extension operator's semantics are in order to demangle -- which seems against the intent of the standardized "vendor operator" syntax. So, that's not great. This seems like a problem which may be worth solving properly and generally in the itanium ABI -- maybe now's the time to actually do this? (Fixing this would allow __typeof__, __builtin_convertvector, and __builtin_offsetof to be mangleable too...) See also PR13740 and PR11078, for earlier (MUCH earlier!) discussion of possible mangling syntax extensions for this sort of thing. Unfortunately, it never went anywhere... ISTM that the most promising proposal in those earlier threads was to add a "Y" to both type and expression expansions. To support vendor-specific builtins which returns a type, and can take types or expressions as arguments (e.g. typeof), add: <type> ::= Y <sourcename> <template-arg>+ E To support vendor-specific builtins which return a value, and can take types or expressions as arguments (e.g. __builtin_offsetof, or __alignof__): <expression> ::= Y <sourcename> <template-arg>+ E
