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Re: Question on insn scheduling and SP
- From: Richard Henderson <rth at redhat dot com>
- To: Richard Kenner <kenner at vlsi1 dot ultra dot nyu dot edu>
- Cc: dalej at apple dot com, gcc at gcc dot gnu dot org
- Date: Tue, 22 Oct 2002 11:11:26 -0700
- Subject: Re: Question on insn scheduling and SP
- References: <10210221724.AA24996@vlsi1.ultra.nyu.edu>
On Tue, Oct 22, 2002 at 01:24:33PM -0400, Richard Kenner wrote:
> *Two* clobbers are necessary.
>
> (clobber (mem:BLK (scratch)))
> (clobber (mem:BLK stack_pointer_rtx))
>
> The first has the magic form that conflicts with all memory,
> the second contains a reference to the stack pointer. Thus
> the stack pointer adjustment depends on the second clobber,
> the second clobber depends on the first clobber, and the
> first clobber depends on all memory references.
>
> Well if that's what's going on, why not keep it simpler and have the
> first clobber and then
> (use (stack_pointer_rtx))
Because the USE won't conflict with the first clobber.
And if you put them in a PARALLEL, then we're not using
the canonical "bare clobber" that is recognized in a
target-independent manner.
r~