[LLVMdev] Problem with LoopDependenceAnalysis

[shanmuk rao]

Hi Preston,

On Wed, Mar 21, 2012 at 2:40 AM, Preston Briggs <preston.briggs at gmail.com>wrote:

> Shanmuhka wrote:
> > I looked at the sanjoys patch for SIV Test. And i figured out that this
> is exactly what i need.
> > as the comments said, check if subscript A can possibly have the same
> value as B in analyseSIV(A,B)
> > but i didn't get How to use this information ?
> >
> > lets just say in the above program
> > When i use depends function it shows the dependency from load of x to
> store in x. similarily for array a.
> > but how can i be sure that there is no dependence from store of x to
> load of x in the next iteration ?
>
> LoopDependenceAnalysis isn't really ready for use yet.
> When it is ready, you would be able to ask explicitly:
>
>    Is there a dependence from the store of x to (one of) the loads of x?
>
> For your example, it would tell you that no such dependence exists.
>

Its not showing no such dependence exist.
I am new to llvm.
So i dont know how to use it properly.
could you please tell me how do i use it?


> Preston
>
>
> > On Thu, Mar 15, 2012 at 11:28 AM, shanmuk rao <shanmuk.rao008 at gmail.com>
> wrote:
> >>
> >> Hi,
> >> I am using LLVM for implementing LoopFission pass.
> >> I am using LoopPass.
> >> I know that for checking circular dependency in loop I have to use
> LoopDependenceAnalysis
> >>
> >> This is what i want to do.
> >>         for(int i = 0; i< n ; i++){
> >>
> >> s1 :                 a[i] = a[i] + x[i];
> >> s2 :                 x[i] = x[i+1] + i*2 ;
> >>         }
> >>
> >> /**there is no dependence from s2 to s1/
> >> so after distribution(it should be) :
> >>
> >>         for(int i = 0; i< n ; i++)
> >> s1:                a[i] = a[i] + x[i];
> >>
> >>         for(int i = 0; i< n ; i++)
> >> s2:                x[i] = x[i+1] + i*2 ;
> >>
> >>
> >> but in llvm i couldn't able to find there is no dependency from s2 to
> s1.
> >>
> >> LoopDependenceAnalyis always gives there is a dependency from every
> load instructions to every store instructions.
> >>
> >>
> >> is there any other alternative to LoopDependencyAnalysis ?
>
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-- 


......
Regards,
Shanmukha Rao
Compilers lab,
Indian Institute of Science, Bangalore.
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