On Jul 22, 2005, at 12:33 PM, Mike Stump wrote:
On Friday, July 22, 2005, at 11:07 AM, Chris Lattner wrote:
I'm trying to determine (in target-independent code) what the
*minimum* target alignment of a type is. For example, on darwin,
double's are normally 4-byte aligned, but are 8-byte aligned in
some cases (e.g. when they are the first element of a struct).
TYPE_ALIGN on a double returns 8 bytes, is there any way to find
out that they may end up being aligned to a 4-byte boundary?
I'm having a hard time with the simplicity of your question:
I don't know if there is a good answer, unfortunately.
/* The alignment necessary for objects of this type.
The value is an int, measured in bits. */
#define TYPE_ALIGN(NODE) (TYPE_CHECK (NODE)->type.align)
On darwin, for a 'double' this will return 64.
/* 1 if the alignment for this type was requested by "aligned"
attribute,
0 if it is the default for this type. */
#define TYPE_USER_ALIGN(NODE) (TYPE_CHECK (NODE)->type.user_align)
I'm not interested in user alignment.
/* The alignment for NODE, in bytes. */
#define TYPE_ALIGN_UNIT(NODE) (TYPE_ALIGN (NODE) / BITS_PER_UNIT)
This is just 64/8.
? Certainly, I don't expect that to answer your question, but I
don't understand why.
The problem I am running into is that the double in this struct is
only 4-byte aligned on darwin:
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?
Thanks!
-Chris
