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Re: question about scheduling optimization in machine description
- From: Richard Henderson <rth at redhat dot com>
- To: Spundun Bhatt <spundun at ISI dot EDU>
- Cc: gcc at gcc dot gnu dot org
- Date: Thu, 9 Sep 2004 23:15:54 -0700
- Subject: Re: question about scheduling optimization in machine description
- References: <4140F779.1020102@isi.edu>
On Thu, Sep 09, 2004 at 05:38:17PM -0700, Spundun Bhatt wrote:
> On my architecture, floating point instructions run faster when put
> backto back with no integer or load/store instructions in the middle.
> So I want to ask the compiler to group as many such instructions
> togather as possible. The reason is that FP unit is pipelined and it
> stalls all instructions except other floating point instructions until
> the float pipeline is clear. (to save on WB hazard detection).
>
> I have thought about this a lot but ccant find a solution that will be
> helpful... any ideas?
You may be able to do clever things with the scheduling DFA.
We do instruction bundling for pentiumpro this way, for instance.
Also examine the TARGET_SCHED_REORDER target hook. That'll
let you choose from the ready instructions to fill just
about any packing scheme you need. You'll have to track
the instruction state yourself in that case; there are other
hooks to enable that.
r~