[LLVMdev] Is Loop Dependence Analysis Printing Correct Stats?

[Arnamoy Bhattacharyya]

Thanks for the pointer Charles.  Now I do:

Code:

#include <stdio.h>
void main()
{
int a[20]={0};
int i;
for(i = 0; i < 10; i ++)
{
a[i] = a[i+1]+1;
}
}

Output:

Printing analysis 'Loop Dependence Analysis':
Loop at depth 1, header block: %for.cond
  Load/store instructions: 7
0:   %1 = load i32* %i, align 4
1:   %5 = load i32* %i, align 4
2:   store i32 %inc, i32* %i, align 4
3:   %2 = load i32* %i, align 4
4:   %3 = load i32* %arrayidx, align 4
5:   %4 = load i32* %i, align 4
6:   store i32 %add1, i32* %arrayidx2, align 4
  Pairwise dependence results:
0,2: dependent
0,6: dependent
1,2: dependent
1,6: dependent
2,3: dependent
2,4: dependent
2,5: dependent
2,6: dependent
3,6: dependent
4,6: dependent
5,6: dependent
===-------------------------------------------------------------------------===
                          ... Statistics Collected ...
===-------------------------------------------------------------------------===

11 lda - Number of dependence queries answered
11 lda - Number of distinct dependence pairs analysed
11 lda - Number of pairs with unknown accesses




On Wed, Jun 20, 2012 at 3:48 PM, Caldarale, Charles R <
Chuck.Caldarale at unisys.com> wrote:

> > From: llvmdev-bounces at cs.uiuc.edu [mailto:llvmdev-bounces at cs.uiuc.edu]
> On Behalf Of Arnamoy Bhattacharyya
> > Subject: [LLVMdev] Is Loop Dependence Analysis Printing Correct Stats?
>
> >       for(i = 0; i < 4; i ++)
> >       {
> >               a[i] = a[i-1]+1;
> >       }
>
> > Am I doing anything wrong or the code seems buggy?
>
> Your code is buggy.  The first time through the loop, you're referencing
> a[-1], which is undefined.
>
>  - Chuck
>
>
> THIS COMMUNICATION MAY CONTAIN CONFIDENTIAL AND/OR OTHERWISE PROPRIETARY
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>


-- 
Arnamoy Bhattacharyya
Athabasca Hall 143
Department of Computing Science - University of Alberta
Edmonton, Alberta, Canada, T6G 2E8
587-710-7073
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