Postpone expanding va_arg until pass_stdarg

[Tom de Vries]

On 13-02-15 09:57, Richard Biener wrote:
>> [ We're still expanding ifn_va_arg before the va_list_gpr/fpr_size
>> >optimization. ]
> Yeah, and the point of the exercise was of course to change that;)

Well, there are two parts.

The first is postpone expansion of va_arg to before the va_list_gpr/fpr_size 
optimization. This eliminates disturbance between the expansion and the 
optimization, and  makes pass_stdarg more robust. This allows us to insert 
optimizations before pass_stdarg without breaking pass_starg.

The second is to simplify pass_starg by handling va_arg rather than the 
expansion of va_arg.

I think the first part by itself (which is done now) is already worthwhile on 
its own.

Thanks,
- Tom