llvm dev - Nov 2019 - Get the address of ConstantDataArray

Hi all,
I have a global array declared as: table = internal constant [8 x [256 x
i32]] ...

At the moment I'm able to get the reference to table using Constant* g_var
= cast<GlobalVariable>(I.getOperand(0))->getInitializer(); ( please
consider I to be a GetElementPtrInst object ).

Now I would like to understand how to get the address of table[2][3], for
instance, considering that I have the g_var variable.

In addition, I was able to access to the value table[2][3] so for me would
be also OK to have the address of that specific value once I already have
access to the value.

Thanks
Alberto
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Pointer arithmetic in LLVM is done using the getelementptr (GEP) instruction.

There’s a document which explains them [1], but I found this tutorial [2] from
EuroLLVM 2019 was the first resource to explain it in a way I understood.

I hope this helps!

Sam

[1]: https://llvm.org/docs/GetElementPtr.html
[2]: https://www.youtube.com/watch?v=m8G_S5LwlTo
> On 20 Nov 2019, at 12:24 pm, Alberto Barbaro via llvm-dev <llvm-dev at
lists.llvm.org> wrote:
> 
> Hi all,
> I have a global array declared as: table = internal constant [8 x [256 x
i32]] ...
> 
> At the moment I'm able to get the reference to table using Constant*
g_var = cast<GlobalVariable>(I.getOperand(0))->getInitializer(); (
please consider I to be a GetElementPtrInst object ).
> 
> Now I would like to understand how to get the address of table[2][3], for
instance, considering that I have the g_var variable.
> 
> In addition, I was able to access to the value table[2][3] so for me would
be also OK to have the address of that specific value once I already have access
to the value.
> 
> Thanks
> Alberto
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
--
Sam Elliott
Software Developer - LLVM
lowRISC CIC
--

Thanks a lot Sam,
I'll try to follow your suggestion and see if it works :)

Thanks again

On Thu, Nov 21, 2019, 13:36 Sam Elliott <selliott at lowrisc.org> wrote:
> Pointer arithmetic in LLVM is done using the getelementptr (GEP)
> instruction.
>
> There’s a document which explains them [1], but I found this tutorial [2]
> from EuroLLVM 2019 was the first resource to explain it in a way I
> understood.
>
> I hope this helps!
>
> Sam
>
> [1]: https://llvm.org/docs/GetElementPtr.html
> [2]: https://www.youtube.com/watch?v=m8G_S5LwlTo
>
> > On 20 Nov 2019, at 12:24 pm, Alberto Barbaro via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
> >
> > Hi all,
> > I have a global array declared as: table = internal constant [8 x [256
x
> i32]] ...
> >
> > At the moment I'm able to get the reference to table using
Constant*
> g_var = cast<GlobalVariable>(I.getOperand(0))->getInitializer(); (
please
> consider I to be a GetElementPtrInst object ).
> >
> > Now I would like to understand how to get the address of table[2][3],
> for instance, considering that I have the g_var variable.
> >
> > In addition, I was able to access to the value table[2][3] so for me
> would be also OK to have the address of that specific value once I already
> have access to the value.
> >
> > Thanks
> > Alberto
> > _______________________________________________
> > LLVM Developers mailing list
> > llvm-dev at lists.llvm.org
> > https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
> --
> Sam Elliott
> Software Developer - LLVM
> lowRISC CIC
> --
>
>
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