Re: nano printf + powerpc gcc

[Craig Howland <howland at LGSInnovations dot com>]

On 01/24/2018 11:46 AM, Andre Vieira (lists) wrote:
> Hi,
>
> I looked a bit further into this and I can't reproduce this behavior for
> the i386 backend. So I had a look through GCC's parser implementation
> for _Generic and it seems GCC evaluates the expressions in each matching
> case, that is to say it will also parse the default case. In arm, the
> type of va_list is a struct, since it is invalid to cast structs to
> pointers, the c-parser will error out when it parses this cast in the
> default case. For an i386 gcc, and I'm guessing your case is the same,
> the type of va_list can be cast to a pointer type, so it parses it
> without errors.
>
> I don't know if parsing the expression of default if another case has
> matched is intended behavior. I will investigate this further and if I
> can convince myself this is wrong behavior I'll chase it with upstream gcc.
The final draft of the C11 standard, which I assume was not changed in the final 
release, does say that only the chosen expression is evaluated.  (Which is as it 
must be.  If it is choosing function names, for example, it can hardly evaluate 
a non-chosen option, as that means calling the function.  The example they give 
is actually choosing a function.)  A cast is an expression, so it appears that 
you do need to chase it with upstream GCC.  It obviously has to parse each 
selection, but it must only evaluate one.
Craig