<div dir="ltr"><div class="gmail_extra"><div class="gmail_quote">On Wed, Feb 4, 2015 at 11:08 PM, John McCall <span dir="ltr"><<a href="mailto:rjmccall@apple.com" target="_blank">rjmccall@apple.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div style="word-wrap:break-word"><div><blockquote type="cite"><span class=""><div>On Feb 4, 2015, at 9:36 PM, Richard Smith <<a href="mailto:richard@metafoo.co.uk" target="_blank">richard@metafoo.co.uk</a>> wrote:</div></span><div><div dir="ltr"><div class="gmail_extra"><div class="gmail_quote"><span class="">On Wed, Feb 4, 2015 at 6:38 PM, John McCall <span dir="ltr"><<a href="mailto:rjmccall@apple.com" target="_blank">rjmccall@apple.com</a>></span> wrote:<br></span><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex"><span><span class="">On Jun 5, 2014, at 4:17 PM, Richard Smith <<a href="mailto:richard@metafoo.co.uk" target="_blank">richard@metafoo.co.uk</a>> wrote:<br></span><div><div class="h5">> John: any chance we could get the ABI document updated with these? (<a href="http://sourcerytools.com/pipermail/cxx-abi-dev/2012-January/000024.html" target="_blank">http://sourcerytools.com/pipermail/cxx-abi-dev/2012-January/000024.html</a>)<br>
<br>
</div></div></span><div><div class="h5">After much delay, added. We don’t seem to get this right, though, at least not when the destination type isn’t dependent:<br>
<br>
template <class T, class U> T fst(T, U);<br>
struct A {<br>
int x[3];<br>
};<br>
template <class T> decltype(fst(A{1,2},T())) foo(T t) {}<br>
<br>
int main() {<br>
foo(1);<br>
}<br>
<br>
We produce:<br>
_Z3fooIiEDTcl3fstcv1AililLi1ELi2EEEcvT__EEES1_<br>
It should be:<br>
_Z3fooIiEDTcl3fsttl1ALi1ELi2EcvT__EEES1_<br></div></div></blockquote><div><div class="h5"><div><br></div><div>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.</div><div><br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex">
If you parenthesize the argument to A:<br>
template <class T> decltype(fst(A({1,2}),T())) foo(T t) {}<br>
We produce:<br>
_Z3fooIiEDTcl3fstcv1AcvS0_ililLi1ELi2EEEcvT__EEES1_<br>
It should be:<br>
_Z3fooIiEDTcl3fstcv1AliLi1ELi2EcvT__EEES1_<br></blockquote><div><br></div><div>Somewhat related, we also get this wrong:</div><div><br></div><div>struct X { X(int); };</div><div>int f(X);</div><div>template<typename T> void f(decltype(f(0), T())) { f(0); }</div><div>void g() { f<int>(0); }</div><div><br></div><div>... because we explicitly mangle the implicit conversion from int to X. I see</div><div><br></div><div>_Z1fIiEvDTcmcl1fLi0EEcvT__EE from EDG<br></div><div>_Z1fIiEvDTcmclL_Z1f1XELi0EEcvT__EE from GCC<br></div><div>_Z1fIiEvDTcmclL_Z1f1XEcvS0_cvS0_Li0EEcvT__EE from Clang</div></div></div></div></div></div></div></blockquote><div><br></div>Ugh, that’s awful.</div><span class=""><div><br><blockquote type="cite"><div><div dir="ltr"><div class="gmail_extra"><div class="gmail_quote"><div>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?</div></div></div></div>
</div></blockquote></div><div><br></div></span><span class=""><div><div><blockquote type="cite"><div dir="ltr"><div class="gmail_extra">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?</div></div></blockquote></div><br></div></span><div>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.</div><div><br></div><div><span class=""><blockquote type="cite"><div dir="ltr"><div class="gmail_extra">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.</div></div></blockquote><div><br></div></span>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?</div></div></blockquote><div><br></div><div>Right. The oddball cases are CXXConstructExpr-used-for-list-initialization:</div><div><br></div><div> f({1}, {2})</div><div><br></div><div>(which clearly isn't a CXXFunctionalCastExpr but probably shouldn't be just a CXXConstructExpr either) and CXXConstructExpr-used-for-direct-intiialization:</div><div><br></div><div> T var(1, 2); // #1</div><div> T var{1, 2}; // #2</div><div><br></div><div>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</div><div><br></div><div> int var(1);</div><div><br></div><div>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*<br></div></div></div></div>