PATCH: PR target/40838: gcc shouldn't assume that the stack is aligned

[H.J. Lu]

On Mon, Oct 19, 2009 at 10:47 AM, Ian Lance Taylor <iant@google.com> wrote:
> "H.J. Lu" <hjl.tools@gmail.com> writes:
>
>>> If somebody asked you "where does gcc set the required stack
>>> alignment?" would you expect the answer to be "in the vectorizer
>>> code?"
>>
>> Yes, vectorizer may put requirement on stack alignment. But it is up
>> to backend to decide and it isn't the only place gcc may require
>> certain stack alignment.
>
> It's the only place your patch changes.

I also changed ix86_minimum_alignment to handle
automatic stack variables.

>
>>> Is there any way we can fix incoming stack alignment so that it can be
>>> controlled by automatic stack variables?  I don't understand why this
>>
>> The incoming stack alignment can be controlled by automatic stack
>> variables. But it can't be controlled by pseudo registers.
>>
>>> is not done by the prologue and epilogue code.
>>>
>>
>> Because the prologue and epilogue code is generated after
>> RTL expansion starts?
>
> That just restates my question without answering it.
>

We don't "fix" the incoming stack alignment. We just need to
know what value it will be. Normally the incoming stack alignment
is a constant specified by psABI. I don't think we should
change the way we do RTL expansion just to work around a
quirk in gcc implementation of i386 psABI.


-- 
H.J.