[Bug rtl-optimization/32475] [4.3 Regression] function with asm() does not setup stack frame

[zadeck at naturalbridge dot com]

------- Comment #18 from zadeck at naturalbridge dot com  2007-07-02 02:45 -------
Subject: Re:  [4.3 Regression] function with asm()
 does not setup stack frame

ian at airs dot com wrote:
> ------- Comment #17 from ian at airs dot com  2007-07-02 01:45 -------
> Before I tackle the specific questions, let me try to explain the issue that I
> see.  The issue is that during a function the value of the stack pointer
> register must always be at or below the local variables.  An interrupt can
> occur at any time.  On a processor which does not use a separate interrupt
> stack, the interrupt will push values on the stack and pass control to the
> kernel.  The stack pointer must be set such that when an interrupt pushes
> values on the stack the local variables are not corrupted.  Does that make
> sense?  My hope is that understanding how this has to work will make clear what
> must be done.
>
>   
>> 1) Do i do this for both the frame_pointer and hard_frame_pointer?
>>     
>
> I think this kind of dependency will only be relevant after the prologue has
> set up the stack.  Therefore, it is only necessary to consider the hard frame
> pointer.
>
>   
>> 2) There is currently code in the scanning for adding the stack pointer
>> for call insns.
>>     
>
> Sure, makes sense.
>
>   
>> This code marks that ref so that it is not considered when building log
>> links for combine.
>>     
>
> That makes sense too.  It doesn't make sense to build log links for the stack
> pointer for a call instruction; there isn't going to be anything combine.
>
>   
>> a) Should I mark the stack pointer ref added for asm's this way?
>>     
>
> It's not obvious to me that asm's should have an implicit stack pointer ref. 
> But maybe they should, I don't know.
>
> If asm's should have an explicit stack pointer ref, then regarding log links
> you should do whatever is simplest.  asm's can not be combined anyhow.
>
>   
>> b) Should I mark the stack pointer refs put in for the mems in this way?
>>     
>
> Yes, I would think so.
>
>
>   
there is an inconsistency in your answers.  Because if i am only marking
the hard frame pointer and this is not set up until after reload, then
the questions about the log_links and combine are moot since combine
runs long before reload.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32475