[LLVMdev] copy value of a global's data field to another global

[David Blaikie]

On Sun, May 17, 2015 at 9:39 PM, Alexander Poddey <alexander.poddey at gmx.net>
wrote:

>
>
> 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...
>

You want a global with the same value - or a global that points into the
subobject in the original global? If you want a separate global, I guess
you'd need to walk the constant yourself rather than using GEP.

- David


>
> 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
> >>
> >>
> >> _______________________________________________
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> >> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> >> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
> >>
>
>
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