Re: PATCH: Don't use callgraph to increase preferred_stack_boundary

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

On Fri, May 9, 2008 at 12:31 PM, Jan Hubicka <hubicka@ucw.cz> wrote:
> Hi,
>> Without automatic stack alignment, we can't increase preferred stack boundary.
>> With automatic stack alignment, it is unnecessary to increase
>> preferred stack boundary
>> since unless we can guarantee that all callers will align the outgoing
>> stack properly,
>> callee has to align its stack anyway.
>>
>> Tested on Linux/ia32 and Linux/Intel64. OK for trunk?
>
> On the trunk preferred stack boundary in cgraph should be always at most
> PREFERRED_STACK_BOUNDARY the variable is initialized to earlier.
> With automatic stack alignment this should be non-issue.
> Do you have case where the cgraph's info ends up beaing greater?

For case like

void
foo ()
{
  int aligned __attribute__((aligned(64)));
...
}

void
bar ()
{
  foo ();
}

cgraph knows foo needs 64byte alignment and we will
align outgoing stack of bar to 64byte. But since we don't
know for sure all callers of foo will align their outgoing stack
to 64byte, we have to align stack to 64byte in foo. That
means the stack alignment in bar is unnecessary.

> Turning the variables to unsigned is definitly OK.
>
> Honza
>

H.J.