[llvm-commits] [llvm] r96598 - /llvm/trunk/docs/AdvancedGetElementPtr.html

[Török Edwin]

On 02/18/2010 08:40 PM, Dan Gohman wrote:
> Author: djg
> Date: Thu Feb 18 12:40:29 2010
> New Revision: 96598
> 
> URL: http://llvm.org/viewvc/llvm-project?rev=96598&view=rev
> Log:
> Clarify that ptrtoint+inttoptr are an alternative to GEP which are
> not restricted by the GEP rules.
> 
> Modified:
>     llvm/trunk/docs/AdvancedGetElementPtr.html
> 
> Modified: llvm/trunk/docs/AdvancedGetElementPtr.html
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/docs/AdvancedGetElementPtr.html?rev=96598&r1=96597&r2=96598&view=diff
> 
> ==============================================================================
> --- llvm/trunk/docs/AdvancedGetElementPtr.html (original)
> +++ llvm/trunk/docs/AdvancedGetElementPtr.html Thu Feb 18 12:40:29 2010
> @@ -200,9 +200,9 @@
>                       to null?</b></a>
>  </div>
>  <div class="doc_text">
> -  <p>You can compute an address that way, but you can't use that pointer to
> -     actually access the object if you do, unless the object is managed
> -     outside of LLVM.</p>
> +  <p>You can compute an address that way, but if you use GEP to do the add,
> +     you can't use that pointer to actually access the object, unless the
> +     object is managed outside of LLVM.</p>
>  
>    <p>The underlying integer computation is sufficiently defined; null has a
>       defined value -- zero -- and you can add whatever value you want to it.</p>
> @@ -211,6 +211,11 @@
>       object with such a pointer. This includes GlobalVariables, Allocas, and
>       objects pointed to by noalias pointers.</p>
>  
> +  <p>If you really need this functionality, you can do the arithmetic with
> +     explicit integer instructions, and use inttoptr to convert the result to
> +     an address. Most of GEP's special aliasing rules do not apply to pointers
> +     computed from ptrtoint, arithmetic, and inttoptr sequences.</p>

Won't optimizers convert that back to a GEP?

Best regards,
--Edwin