[cxx-abi-dev] Mangling string constants

[John McCall]

> On Feb 19, 2015, at 11:44 PM, Dennis Handly <dhandly at cup.hp.com> wrote:
>> From: David Majnemer <david.majnemer at gmail.com>
>> It seems that the ABI has no means to mangle the contents of string constants.
> 
> Why is that needed?
> The current scheme is to just number the constants in order.
> And that handles both strings and wide strings.
> And by the ODR rule the inlines must be the same.

I think this is what David means by numbering like a reference temporary.

To the extent that this is needed, I agree with you that that’s the right solution: string literals should be mangled in the same sequence as reference temporaries.  (Which already applies to more than just reference temporaries anyway, since the same concept of lifetime extension applies to std::initializer_list temporaries.)

I have some of the same concerns here as I do with guaranteeing the uniqueness of string literals within inline functions: I want to make sure the language isn’t accidentally promising something that grotesquely affects performance far out of proportion to its utility to the programmer.  It would be very unfortunate if we, say, introduced thousands of new global weak symbols just to unique the strings used by assertions.  We can take things like this back to the committee if necessary.

But if we can restrict this guarantee to string literals that appear in reference-temporary-like positions in constexpr initializers, I think it’s reasonable enough.

John.