[PATCH, PR 32824] Add an additional LIM pass to assist dead code elimination

[Fang, Changpeng]

Attached is the updated patch (with testcase). And below is the changelog entry.



2010-03-16  Changpeng Fang  <changpeng.fang@amd.com>

	PR middle-end/32824
	* passes.c (init_optimization_passes): move pass_lim before
	  pass_copy_prop,pass_dce_loop in the loop optimizer.

	* gcc.dg/vect/pr32824: New.

Thanks,

Changpeng










________________________________________
From: Richard Guenther [richard.guenther@gmail.com]
Sent: Wednesday, March 17, 2010 12:39 PM
To: Fang, Changpeng
Cc: gcc-patches@gcc.gnu.org; rakdver@gcc.gnu.org; spop@gcc.gnu.org
Subject: Re: [PATCH, PR 32824] Add an additional LIM pass to assist dead code   elimination

On Wed, Mar 17, 2010 at 6:03 PM, Fang, Changpeng <Changpeng.Fang@amd.com> wrote:
> Hi,
>  I have updated the patch to move the existing LIM pass before copyprop/dce in the loop optimizer.
> This patch helps eliminate dead code and make the reduction statement vectorizable when the reduction
> variable is global. The patch fixes PR 32824.
>
> Note that the problem reported in PR32824 is very popular in fortran code. I am working on Levine benchmark
> and found that there are at least 9 such cases.
>
> This patch passed bootstrapping and regression tests. I also tested on spec cpu2006 and found there is no
> performance impact.
>
> Is it OK for the trunk?

It is ok once stage1 opens.

Thanks,
Richard.

> Thanks,
>
> Changpeng
>
>
> ________________________________________
> From: Richard Guenther [richard.guenther@gmail.com]
> Sent: Tuesday, March 16, 2010 5:24 AM
> To: Fang, Changpeng
> Cc: gcc-patches@gcc.gnu.org; rakdver@gcc.gnu.org; spop@gcc.gnu.org
> Subject: Re: [PATCH, PR 32824] Add an additional LIM pass to assist dead code   elimination
>
> On Mon, Mar 15, 2010 at 10:14 PM, Fang, Changpeng
> <Changpeng.Fang@amd.com> wrote:
>> This patch fixes bug 32824: Missed reduction vectorizer after store to global is LIM'd
>>
>> Patch Description:
>> After store to global is LIM'ed, we need a copy propagation and dead code elimination to eliminate
>> the dead store in the loop, and thus make the reduction vectorizable. In this patch, I added an additional LIM
>> pass at the very beginning of the loop optimizer, then the dead code can be eliminated by pass_dce_loop
>> before the vectorizer.
>>
>> With this patch, the related fortran code (refer to bug 32824 report) can also be vectorized.
>>
>> I have bootstrapped gcc with the patch and compiled and spec cpu2006 and found no apparent regression
>> in both compilation time and spec scores.
>
> I'm not too keen on adding another expensive pass like LIM.  Did you
> try simply moving the existing LIM pass before copyprop/dce?
>
> Thanks,
> Richard.
>
>> Thanks,
>>
>> Changpeng
>>
>>
>
>

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