[PATCH] Improve performance of vector code on A15

[James Molloy]

Hi Quentin,


> > Maybe a stupid remark, looking at your patch, unless I miss
> > something, if I choose to disable your pass, I don't get the
> > previous behavior for CortexA15 as the
> > createExecutionDependencyFixPass will be skipped.
> > Is that intended/desirable?

You're entirely right, and that wasn't intended. Thanks for spotting
this, I attach a version with this modified.


Joey,

> Minor thing: You should be using a triple slash /// for documentation
> (especially for A15SDOptimizer::runOnMachineInstruction), and
> I think they have to go above the function.

It's intended to be a comment describing the inner workings of the
algorithm, not documentation (how to use a module/algorithm). It's not
even externally accessible as it's in an anonymous namespace.

But if you want me to, I can convert it to a doxygen comment.

Cheers,

James

On Thu, 2013-02-21 at 18:33 +0000, Quentin Colombet wrote:
> Hi James,
>
>
> Maybe a stupid remark, looking at your patch, unless I miss something,
> if I choose to disable your pass, I don't get the previous behavior
> for CortexA15 as the createExecutionDependencyFixPass will be skipped.
> Is that intended/desirable?
>
> -Quentin
>
> On Feb 21, 2013, at 10:13 AM, James Molloy <James.Molloy at arm.com>
> wrote:
>
> > Hi,
> >
> > Attached is a patch which improves performance of vector code on
> > Cortex-A15.
> >
> > Certain code sequences, where an S register is written but read as a
> > D
> > register, can execute slowly. This patch defines a pass which
> > detects
> > when SPRs are written but read as DPRs and inserts code sequences
> > which,
> > although nonobvious, make code run much quicker.
> >
> > The second patch, implicit-ops.diff, fixes an unrelated bug with
> > implicit defs/uses that happens to impact the A15 pass's efficiency.
> >
> > Please review!
> >
> > Cheers,
> >
> > James
> >
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>


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