Re: Minimum target alignment for a datatype

[Chris Lattner <CLATTNER at apple dot com>]

On Jul 22, 2005, at 12:42 PM, Andrew Pinski wrote:
> > struct X {  int A; double B; };
> >
> > This is modified by things like ADJUST_FIELD_ALIGN and
> > ROUND_TYPE_ALIGN.  As such, I don't think there is a way to get this
> > alignment in a target-independent way.  Does that sound right?
>
> You want the alignment of B in that struct in source code and not  
> in GCC?
> If so you want to do:
> struct X {  int A; double B; };
> int f(void){struct X b; return __alignof__(b.B);}

Nope, I'm trying to use this in target-independent GCC code, not  
source code.  The reason I can't do something like the above (which  
amounts to looking at TYPE_ALIGN or DECL_ALIGN) is that I don't  
*know* all the ways that double can be used, and how the target will  
change its alignment.  IOW, I'm looking for  
give_me_the_minimum_alignment(double), which, on darwin, because of  
the above, is 4 bytes.

As RTH pointed out, it appears that there is no interesting minimum  
that I can get.

Thanks all,

-Chris