Re: PATCH: PR middle-end/48608: Alignment adjust of local variables is lost

["H.J. Lu" <hjl.tools@gmail.com>]

On Thu, Apr 14, 2011 at 8:26 AM, Michael Matz <matz@suse.de> wrote:
> Hi,
>
> On Thu, 14 Apr 2011, Richard Guenther wrote:
>
>> > +  if (align > DECL_ALIGN (decl))
>> > +    DECL_ALIGN (decl) = align;
>>
>> Shouldn't this unconditionally set DECL_ALIGN in case
>> LOCAL_DECL_ALINGMENT returns something smaller?
>
> Decreasing alignment of DECLs points to a problem elsewhere, so perhaps an
> assert that this doesn't happen is better.  Decreasing is a problem
> because it's not conservative: there might have been code generated
> already assuming the once larger alignment that then possibly breaks if it
> turns out the alignment is actually smaller.

ia32 may decrease local variable alignment:

  /* Don't do dynamic stack realignment for long long objects with
     -mpreferred-stack-boundary=2.  */
  if (!TARGET_64BIT
      && align == 64
      && ix86_preferred_stack_boundary < 64
      && (mode == DImode || (type && TYPE_MODE (type) == DImode))
      && (!type || !TYPE_USER_ALIGN (type))
      && (!decl || !DECL_USER_ALIGN (decl)))
    align = 32;

I am running bootstrap/test on Linux/x86-64 and Linux/ia32.

-- 
H.J.