[LLVMdev] Re: Dependence Analysis

[Naftali Schwartz]

OK, I've tried this, and it does convert the p_b's to B[] references.  How 
would I get this to work for the p_a and p_c references?

Naftali

On Thu, 21 Jul 2005, Chris Lattner wrote:

> On Thu, 21 Jul 2005, Naftali Schwartz wrote:
>>> If you're interested in dependence analysis, the next important step is 
>> to
>>> start analyzing distance and direction vectors.
>> 
>> Well, specifically, I was thinking of a mechanism to turn this:
>
> The indvars pass is *intentionally* restricted to only promoting affine 
> expressions to array subscripts, not arbitrary expressions.  To enable this, 
> remove the two if's at IndVarSimplify.cpp:647 (unconditionally pushing the 
> discovered indvar on the IndVars list).
>
> See the comments in that code for a justification.
>
> -Chris
>
>> int A[100], B[100], C[100], X, Y, Z;
>> 
>>        int *p_a = &A[0];
>>        int *p_b = &B[0];
>>        int *p_c = &C[0];
>> 
>>        int i, j, k, f;
>>        for ( k = 0; k < Z; k++ )
>>        {
>>                p_a = &A[0];
>>                for ( i = 0; i < X; i++ )
>>                {
>>                        p_b = &B[k*Y];
>>                        *p_c = *p_a++ * *p_b++;
>>                        for ( f = 0; f < Y-2; f++ )
>>                                *p_c += *p_a++ * *p_b++;
>>                        *p_c++ += *p_a++ * *p_b++;
>>                }
>>        }
>> 
>> ...into:
>> 
>> int A[100], B[100], C[100], X, Y, Z;
>> 
>>        int i, j, k, f;
>>        for ( k = 0; k < Z; k++ )
>>                for ( i = 0; i < X; i++ )
>>                {
>>                        C[X*k+i] = A[Y*i] * B[Y*k];
>>                        for (f = 0; f < Y-2; f++ )
>>                                C[X*k+i] += A[Y*i+f+1] * B[Y*k+f+1];
>>                        C[X*k+i] += A[Y*i+Y-1] * B[Y*k+Y-1];
>>                }
>> 
>> a la Frank and O'Boyle, which -indvars seems not to be able to handle 
>> (unless I'm doing something wrong...)
>> 
>> Naftali
>> 
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>
> -Chris
>
> -- 
> http://nondot.org/sabre/
> http://llvm.org/
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