[LLVMdev] size of const_ptr for array index

[Alexander Poddey]

Hi,

I tried different things, but none did give me the correct size.
Any ideas?



Mehdi Amini wrote:

> Hi,
> 
> 
>> On Mar 16, 2015, at 12:44 PM, Alexander Poddey <alexander.poddey at gmx.net>
>> wrote:
>> 
>> Hi all,
>> 
>> when e.g. accessing a global variable residing in a structure, the c++API
>> code looks like:
>> 
>> std::vector<Constant*> const_ptr_183_indices;
>> const_ptr_183_indices.push_back(const_int32_172);
>> const_ptr_183_indices.push_back(const_int32_184);
>> const_ptr_183_indices.push_back(const_int64_175);
>> Constant* const_ptr_183 = ConstantExpr::getGetElementPtr(gvar_struct_foo,
>> const_ptr_183_indices);
>> 
>> 
>> the struct could be
>> 
>> struct stest {
>>    double age;
>>   double darray[3];
>> }
>> 
>> The indices for accessing 'age' would be
>> 0 (32bit)
>> 0 (32bit).
>> 
>> For an element of the darray, one however needs
>> 0 (32bit)
>> 1 (32bit)
>> 0-2 (64bit)
>> 
>> The same for indices of vectors.
>> 
>> The question:
>> Can I at runtime determine (how?) which size I have to use per case?
>> I made some tests but could not figure it out.
> 
> I believe you have to check the pointer size in the DataLayout.
> 
> Mehdi
> 
> 
> 
>> 
>> So for now (at my architecture) it seems hardcoding 32 bit as default,
>> and 64bit for indices (of arrays and vectors) works. But this is not
>> portable.
>> 
>> Thanks
>> Alexander
>> 
>> _______________________________________________
>> LLVM Developers mailing list
>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev