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[Bug middle-end/88085] User alignments on var decls not respected if smaller than type alignment
- From: "rguenth at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: Mon, 19 Nov 2018 12:29:42 +0000
- Subject: [Bug middle-end/88085] User alignments on var decls not respected if smaller than type alignment
- Auto-submitted: auto-generated
- References: <bug-88085-4@http.gcc.gnu.org/bugzilla/>
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88085
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |rguenth at gcc dot gnu.org
--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
ISTR you have to use packed to decrease alignment. OTOH
/* We can set the alignment from the type if we are making an object or if
this is an INDIRECT_REF. */
if (objectp || TREE_CODE (t) == INDIRECT_REF)
attrs.align = MAX (attrs.align, TYPE_ALIGN (type));
is fishy but so is the preceeding
/* Otherwise, default values from the mode of the MEM reference. */
else
{
...
/* Respect mode alignment for STRICT_ALIGNMENT targets if T is a type;
if T is an object, always compute the object alignment below. */
if (TYPE_P (t))
attrs.align = defattrs->align;
else
attrs.align = BITS_PER_UNIT;
IMHO alignment setting should be left to the callers and it should be
conservative here (the objectp == true case can probably be preserved).
Note we already set the alignment later in a correct way if ! TYPE_P
but likewise using
attrs.align = MAX (attrs.align, obj_align);
which is bogus again unless the caller already had pre-existing attrs
on the MEM. I guess using
attrs.align = refattrs ? MAX (refattrs.align, obj_align) : obj_align;
fixes your issue? Or are you objectp == true? I think an INDIRECT_REF never
happens today.