Re: memcpy() inlining and alignment

["Martin v. Loewis" <martin at loewis dot home dot cs dot tu-berlin dot de>]

> 	   struct s *src, dst;
> 
> 	   src = (struct s *)(cp + 1);
> 
> 	   memcpy(&dst, src, sizeof(struct s));
[...]
> I believe the compiler is correctly assuming that the structure is
> aligned to whatever alignment is required by the members of the
> structure type for a particular processor's ABI.  In this case, most
> likely the required alignment is 4 bytes on 32-bit systems.

I don't think so. In 7.12.2 of standard C, the description of memcpy
is

# The memcpy function copies n characters from the object pointed to
# by s2 into the object pointed to by s1. If copying takes place
# between objects that overlap, the behavior is undefined.

There is no mentioning of alignment constraints, and it says that it
is copying characters. So I think the compiler is wrong in assuming
that it can inline the memcpy using word-size instructions.

Regards,
Martin