[LLVMdev] llvm::ConvertibleToGEP

[Chris Lattner]

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

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