DATA_ALIGNMENT vs. DECL_USER_ALIGNMENT

[Richard Henderson]

On Thu, Apr 10, 2003 at 05:49:40PM -0400, Richard Kenner wrote:
> Why?  It seems like what it means is "the alignment of this type was set the
> way it is for a reason.  Please don't change it."  And that applies here.

I'll concede that there's still too much language-specific
widgetry in layout_type, which causes you to want to set
such a flag, but that's as far as I'm willing to go.

Perhaps the short-term solution is as you suggest -- a new
lang hook such that Ada can avoid setting DECL_USER_ALIGN
when the languages allows a larger alignment to be used for
particular objects.

I definitely think the bug is *not* in varasm.c.  If I write
"double x __attribute__((aligned(1)))", I expect to see 

        .comm   x,8,1
not
	.comm	x,8,8

in the assembly file.

I do like Ulrich's change to the s390x backend to cope with
variables explicitly declared with 1 byte alignment.

I definitely think there's a bug in that the Ada front end
sets DECL_USER_ALIGN for these objects and the C front end
(in response to the auto-generated files) does not.  That
mis-match should be addressed in some way -- either by not
setting DECL_USER_ALIGN in Ada or by tagging the variables
with attribute aligned in C.  I think it's clear that the
former solution would be preferred, since it would result
in better code for this platform.  But this is up to yall.


r~