[cxx-abi-dev] Mangling "transaction-safe function"

[Jason Merrill]

On 09/29/2015 08:34 PM, Richard Smith wrote:
> On 29 September 2015 at 11:09, Jason Merrill <jason at redhat.com> wrote:
>
>> The Transactional Memory TS introduces "transaction-safe function" types,
>> which are distinct from non-transaction-safe function types, though the
>> former converts to the latter.  So we need to represent this in mangling.
>>
>> I think no change to mangling of actual functions is necessary, since
>> functions that differ only in their tx-qualifier cannot be overloaded.
>
> I thought the intent was that we'd emit two function bodies for a
> transaction-safe function definition (one for the case where we are inside
> an atomic block, another for the case where we are not). Do we also need a
> new function mangling for the former case?

Yes, I thought I had mentioned that in a follow-up, but evidently not. 
GCC currently mangles the transaction entry point as

<special_name> ::= GTt <encoding>

>> So we only need to worry about function types.
>>
>> One possibility for handling it would be to add a qualifier 'T' after the
>> <ref-qualifier> at the end of <function-type>, but that complicates the
>> ambiguity between these qualifiers and parameter types.
>>
>> I think my preference is to make it a normal type qualifier, perhaps using
>> "Dx", so void (*)() transaction_safe becomes "PDxFvvE".
>>
>> We also need to add a __transaction_safe_mask to
>> __pbase_type_info::__masks so that exception handlers can perform the
>> transaction safety conversion.
>
> Would you also use the same __function_type_info for the pointee type in
> typeid(void (*)() transaction_safe) and typeid(void(*)())? That seems like
> an odd fit for the language semantics ("transaction_safe" is part of the
> function type, not a layer on top of it like cv-qualifiers are), but
> necessary if we want the exception handler to be able to efficiently check
> for a match.

Right.  This seemed simpler to me than adding a new 
__tx_safe_function_type_info class.

Jason