r210295 - Remove old proposal notices

[Richard Smith]

On Wed, Feb 4, 2015 at 11:08 PM, John McCall <rjmccall at apple.com> wrote:

> On Feb 4, 2015, at 9:36 PM, Richard Smith <richard at metafoo.co.uk> wrote:
> On Wed, Feb 4, 2015 at 6:38 PM, John McCall <rjmccall at apple.com> wrote:
>
>> On Jun 5, 2014, at 4:17 PM, Richard Smith <richard at metafoo.co.uk> wrote:
>> > John: any chance we could get the ABI document updated with these? (
>> http://sourcerytools.com/pipermail/cxx-abi-dev/2012-January/000024.html)
>>
>> After much delay, added.  We don’t seem to get this right, though, at
>> least not when the destination type isn’t dependent:
>>
>> template <class T, class U> T fst(T, U);
>> struct A {
>>   int x[3];
>> };
>> template <class T> decltype(fst(A{1,2},T())) foo(T t) {}
>>
>> int main() {
>>   foo(1);
>> }
>>
>> We produce:
>>   _Z3fooIiEDTcl3fstcv1AililLi1ELi2EEEcvT__EEES1_
>> It should be:
>>   _Z3fooIiEDTcl3fsttl1ALi1ELi2EcvT__EEES1_
>>
>
> There are quite a few bugs conspiring to give that result :( Our AST is
> also poorly-suited to this mangling, because the braces are not considered
> to be part of the functional cast itself; they're part of its subexpression.
>
> If you parenthesize the argument to A:
>>   template <class T> decltype(fst(A({1,2}),T())) foo(T t) {}
>> We produce:
>>   _Z3fooIiEDTcl3fstcv1AcvS0_ililLi1ELi2EEEcvT__EEES1_
>> It should be:
>>   _Z3fooIiEDTcl3fstcv1AliLi1ELi2EcvT__EEES1_
>>
>
> Somewhat related, we also get this wrong:
>
> struct X { X(int); };
> int f(X);
> template<typename T> void f(decltype(f(0), T())) { f(0); }
> void g() { f<int>(0); }
>
> ... because we explicitly mangle the implicit conversion from int to X. I
> see
>
> _Z1fIiEvDTcmcl1fLi0EEcvT__EE from EDG
> _Z1fIiEvDTcmclL_Z1f1XELi0EEcvT__EE from GCC
> _Z1fIiEvDTcmclL_Z1f1XEcvS0_cvS0_Li0EEcvT__EE from Clang
>
>
> Ugh, that’s awful.
>
> I think GCC and Clang are right to use the resolved name L_Z1f1XE rather
> than the unresolved name 1f here, and GCC's mangling is right overall. Do
> you agree?
>
>
> As an aside: if we have a fully-resolved call in an
> instantiation-dependent expression, should we really be putting any used
> default arguments into the mangling?
>
>
> I feel like both of these points need to be asked on the cxx-abi-dev.  I
> definitely don’t think we should be mangling default arguments, but I’m not
> sure that resolving ‘f’ here is really consistent with the general dictate
> to follow the syntactic tree.
>
> All of the above fixed in r228274. I'm not really very happy with our AST
> representation here; we've overloaded CXXConstructExpr to mean too many
> different syntactic things that it's hard to reconstruct the right mangling.
>
>
> The rule used to be that a “bare" CXXConstructExpr — neither a specific
> subclass nor the implementation of a cast — was always implicit, and that
> there were subclasses which provided additional syntactic information.  I
> think it would make sense to have a dedicated subclass for the truly
> implicit case as well.  The implicit case is always a constructor
> conversion or copy-construction, right?
>

Right. The oddball cases are CXXConstructExpr-used-for-list-initialization:

  f({1}, {2})

(which clearly isn't a CXXFunctionalCastExpr but probably shouldn't be just
a CXXConstructExpr either) and
CXXConstructExpr-used-for-direct-intiialization:

  T var(1, 2); // #1
  T var{1, 2}; // #2

According to the rules we use in -ast-print, the parens belong to the
initialization of the variable, not to the CXXConstructExpr, so that we can
support

  int var(1);

with no additional AST nodes beyond the IntegerLiteral expression, but the
braces in #2 usually belong to the CXXConstructExpr. Except when T has a
constructor that takes std::initializer_list<int>, when they don't, because
the braces belong to the construction of the underlying array of int. *sigh*
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