[cxx-abi-dev] Mangling late-specified return types/decltype

[Jason Merrill]

More generally, within decltype/sizeof/alignof we aren't interested in 
the value of a type, only the type itself, so there's a lot of 
information in the expression which is irrelevant.  Within decltype, 
*(T*)0 and t are equivalent: both are T lvalues. T(42) and T() and 
T(a,b,0932) are also equivalent: all are T rvalues.

In all these cases, it seems like we could replace these expressions 
with "lvalue placeholder" (sT) or "rvalue placeholder", and simplify 
decltype (T lvalue placeholder) to T so we don't have to mangle as much 
random expression gunk.

Otherwise we still need to establish a mangling for T(more,than,one,arg).

Jason