llvm dev - May 2015 - [LLVMdev] copy value of a global's data field to another global

Hi all,

I can get access to the data stored in globals as follows:

GlobalVariable* pGvarAct=_set_a_valid_global_;
const_ptr_indicesVec=_the_indexes_

llvm::Constant* pConst;
pConst=ConstantExpr::getGetElementPtr(pGvarAct, const_ptr_indicesVec);

and e.g. use this to repalece an argumrnt of an instruction like:

I->setOperand(someArgumentIndex,pConst); 

However, getGetElementPtr returns a pointerType, which holds the actual type 
as sub_type.
This is a problem when I want to use the data from one global for the 
initializer of another

    pGvar->setInitializer(__NeedsAFloatTy_here__); //not pointerTy

So what I'm trying to do is copy some data-fields of one global to another. 
I know the 'index-trace' used in getGetElementPtr, but I need the actual
type, not 'covered' by a pointerType. 


Thank You!
Alexander

On Sat, May 16, 2015 at 10:28 PM, Alexander Poddey <alexander.poddey at
gmx.net
> wrote:
> Hi all,
>
> I can get access to the data stored in globals as follows:
>
> GlobalVariable* pGvarAct=_set_a_valid_global_;
> const_ptr_indicesVec=_the_indexes_
>
> llvm::Constant* pConst;
> pConst=ConstantExpr::getGetElementPtr(pGvarAct, const_ptr_indicesVec);
>
> and e.g. use this to repalece an argumrnt of an instruction like:
>
> I->setOperand(someArgumentIndex,pConst);
>
> However, getGetElementPtr returns a pointerType, which holds the actual
> type
> as sub_type.
> This is a problem when I want to use the data from one global for the
> initializer of another
>
>     pGvar->setInitializer(__NeedsAFloatTy_here__); //not pointerTy
>
> So what I'm trying to do is copy some data-fields of one global to
another.
> I know the 'index-trace' used in getGetElementPtr, but I need the
actual
> type, not 'covered' by a pointerType.
>
Perhaps you want getInitializer on the other GlobalVariable?

>
>
> Thank You!
> Alexander
>
>
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>
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getInitializer returns the complete initializer of the global.
My globals are complex nested structs, from which I want to extract e.g. one 
double datafield.

Example:
>From a struct Stuct having double,array(3xint),float fields, I could extract
the second int value using the index sequence 0,1,1 with getGetElementPtr.
This gives me a constantPointer, but I would need to get a constInt...

Alex


David Blaikie wrote:
> On Sat, May 16, 2015 at 10:28 PM, Alexander Poddey
> <alexander.poddey at gmx.net
>> wrote:
> 
>> Hi all,
>>
>> I can get access to the data stored in globals as follows:
>>
>> GlobalVariable* pGvarAct=_set_a_valid_global_;
>> const_ptr_indicesVec=_the_indexes_
>>
>> llvm::Constant* pConst;
>> pConst=ConstantExpr::getGetElementPtr(pGvarAct, const_ptr_indicesVec);
>>
>> and e.g. use this to repalece an argumrnt of an instruction like:
>>
>> I->setOperand(someArgumentIndex,pConst);
>>
>> However, getGetElementPtr returns a pointerType, which holds the actual
>> type
>> as sub_type.
>> This is a problem when I want to use the data from one global for the
>> initializer of another
>>
>>     pGvar->setInitializer(__NeedsAFloatTy_here__); //not pointerTy
>>
>> So what I'm trying to do is copy some data-fields of one global to
>> another. I know the 'index-trace' used in getGetElementPtr, but
I need
>> the actual type, not 'covered' by a pointerType.
>>
> 
> Perhaps you want getInitializer on the other GlobalVariable?
> 
> 
>>
>>
>> Thank You!
>> Alexander
>>
>>
>> _______________________________________________
>> LLVM Developers mailing list
>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>>