[LLVMdev] llvm::ConvertibleToGEP

[Naftali Schwartz]

Well, I guess I was hoping soemthing like this would help in the 
pointer-to-array transformation for the following code:

> > 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++;
> >                }
> >        }

which, as you had pointed out, removal of the if statement in 
IndVarSimplify:647 takes care of, but only partially, as it leaves the 
p_a and p_c references exactly as before.  On the other hand, maybe I'm 
just a little confused...

Naftali

On Tue, 26 Jul 2005, Chris Lattner wrote:

> On Tue, 26 Jul 2005, Naftali Schwartz wrote:
>> I'm sorry, it had seemed to me that the documented functionality:
>> 
>> // ConvertibleToGEP - This function returns true if the specified value V 
>> is
>> // a valid index into a pointer of type Ty.  If it is valid, Idx is filled 
>> in
>> // with the values that would be appropriate to make this a getelementptr
>> // instruction.  The type returned is the root type that the GEP would 
>> point to
>> 
>> would be quite useful (and in particular for dependence analysis).
>> Are you going to remove it because it's functionality is already present 
>> elsewhere or is simply not needed anymore?
>
> I'm not sure I follow how it is useful for dep analysis.  The -instcombine 
> pass already does this transformation in a more general way.  In particular, 
> this code was used to change code like this:
>
> int* %foo({int, float}* %P) {
>  %Y = cast {int, float}* %P to int*
>  ret int* %Y
> }
>
> into:
>
> int* %foo({int, float}* %P) {
>  %Y = getelementptr {int, float}* %P, int 0, uint 0
>  ret int* %Y
> }
>
> In your depedence analyzer, you shouldn't worry about cases like this: 
> instead, just assume that the optimizer has already cleaned them up for you.
>
> -Chris
>
>
>> On Tue, 26 Jul 2005, Chris Lattner wrote:
>> 
>>> On Tue, 26 Jul 2005, Naftali Schwartz wrote:
>>>> But it's completely empty, no?
>>>> 
>>>> const Type *llvm::ConvertibleToGEP(const Type *Ty, Value *OffsetVal,
>>>>                                   std::vector<Value*> &Indices,
>>>>                                   const TargetData &TD,
>>>>                                   BasicBlock::iterator *BI) {
>>>>  return 0;
>>>> }
>>>> 
>>>> in lib/Transforms/TransformInternals.cpp, how can this be?
>>> 
>>> Huh, interesting.  I'll remove it, thanks for pointing it out!
>>> 
>>> -Chris
>>> 
>>>> On Tue, 26 Jul 2005, Chris Lattner wrote:
>>>> 
>>>>> On Tue, 26 Jul 2005, Naftali Schwartz wrote:
>>>>>> It seems like general dependence analysis in LLVM should require that 
>>>>>> this function be, well, functional.  Is it simply a placeholder waiting 
>>>>>> for someone to come and fill in the details?  It also appears that some 
>>>>>> other things besides dependence analysis depend on it as well...anyone 
>>>>>> working on this?
>>>>> 
>>>>> I don't understand what you mean.  This function is just a little 
>>>>> utility function used by the "-raise" pass.
>>>>> 
>>>>> -Chris
>>>>> 
>>>>> -- 
>>>>> http://nondot.org/sabre/
>>>>> http://llvm.org/
>>>>> 
>>>>> _______________________________________________
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>>>>> 
>>>>> 
>>>> 
>>>> _______________________________________________
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>>> 
>>> -Chris
>>> 
>>> -- 
>>> http://nondot.org/sabre/
>>> http://llvm.org/
>>> 
>>> _______________________________________________
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>>> 
>> 
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>
> -Chris
>
> -- 
> http://nondot.org/sabre/
> http://llvm.org/
>
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