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Re: CLOBBER MEM in stack ops on x86
- From: Jan Hubicka <jh at suse dot cz>
- To: Richard Kenner <kenner at vlsi1 dot ultra dot nyu dot edu>
- Cc: rth at redhat dot com, gcc at gcc dot gnu dot org
- Date: Thu, 22 Nov 2001 14:36:25 +0100
- Subject: Re: CLOBBER MEM in stack ops on x86
- References: <10111220218.AA17114@vlsi1.ultra.nyu.edu>
> > Won't that happen due to the dependency on SP itself?
>
> Not necessarily. Consider if a stack frame address has been
> saved in a register.
>
> If I understand the issue you are raising correctly, why is this problem
> unique to the epilogue?
>
> There are blocks that allocate stack space and then at the end of the block
> restore SP to the value at the start of the block: we do this as part of
> block cleanup. What prevents stores into the allocated area from being
> scheduled past that SP restore?
>
> If we're going to do this, I think we need to teach the scheduler about the
> dependence of any memory reference to an adjustment of SP, not kludge a
> few of the cases.
True, this has been discussed previously and I think the conclusion has been
same.
Honza