[cfe-dev] Fwd: external function codegen bug

[Chris Lattner]

On May 23, 2008, at 4:15 AM, Eli Friedman wrote:

> On Fri, May 23, 2008 at 2:37 AM, Csaba Hruska  
> <csaba.hruska at gmail.com> wrote:
>> buggy code:
>>
>> extern double g ();
>> void f()
>> {
>> double t, g();
>> t = g();
>> }
>
> I'm pretty sure it's an issue with merging function decls.  The issue
> is that t essentially disappears from the AST (try running this code
> through -ast-dump to see what I mean), so CodeGen ends up seeing a
> reference to an undeclared variable.  Declaration merging and whatnot
> is tricky code that I never really studied closely, though, so it's
> not obvious why this is happening.

One approach would be to have two predicates: one for "real i-c-e" and  
one for "gcc i-c-e".  If it is a GCC ICE but not a standards one,  
accept but emit a diagnostic?  In this case, it is pretty easy, in  
other cases (such as when dealing with ?: promotion rules) it is much  
harder.

I don't know if it is worth it though.  The set of stuff accepted by  
GCC is, uh, "poorly defined".

-Chris