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Re: GCSE store motion


On Wed, 15 May 2002, Roger Sayle wrote:

> 
> I'm more than happy to attempt to fix GCSE store motion, but my current
> understanding is that its working perfectly!
And doing nothing.
> 
> PR opt/5200 was filed by Andreas Jaeger on the supporting evidence of
> PR opt/5172 and postings by Dan Berlin to gcc-patches last year.
> 
> In the review of my patch to that attempted to fix PR/5172
> http://gcc.gnu.org/ml/gcc-patches/2002-01/msg01142.html, it
> became clear that it was glibc at fault and not the store motion
> pass at all.
> 
> Hence the only remaining claims that store motion is broken are
> the comments by Dan Berlin, but as far as I am aware there are
> no known examples of failing test cases.

I'm not going through this again.
We've been over this before.


>  Dan also claimed that
> store motion wasn't currently doing anything, but clearly PR/5172
> showed that duplicate stores are being eliminated in real code.

I "claimed" it wasn't doing anything because SPEC95/2000 runs show it 
making no improvement whatsoever.

In addition, never, in any RTL dumps of any code, ever, have I seen it 
remove a single store. 

Nobody has claimed that it is generally useful in it's current state. In 
fact, the person who submitted it has claimed otherwise.
It was written to address a specific case, which i've no doubt it does.
This case rarely, if ever, occurs.
If you want to claim it is a functional optimization that has useful 
application, please provide benchmarks that show store motion making any
difference.
If you want to improve store motion such that is generally useful, again, 
feel free.  I'd be happy to guide you in doing this.
However, nobody needs to provide a failing test case for you to do this.

Please stop trying to chalk up my statement that store motion is not 
useful in it's current state to bullshit or whatnot.

No benchmarks, test, or otherwise have shown it helping code in it's 
current state.  The only person to claim otherwise is you.

--Dan


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