[LLVMdev] GetElementPtr

[Ryan Taylor]

Eli,

   Ok, thanks, this is a big help. So how can I use the TargetData (or get
the TargetData) without having a DAG?

On Thu, Dec 8, 2011 at 3:45 PM, Eli Friedman <eli.friedman at gmail.com> wrote:

> On Thu, Dec 8, 2011 at 3:29 PM, Ryan Taylor <ryta1203 at gmail.com> wrote:
> > Ok, thanks, this makes sense. But there is no way to get the
> SelectionDAG to
> > do it for me via something like visitGetElementrPtr?
>
> SelectionDAGBuilder::visitGetElementPtr uses the same algorithm you
> want to use, but it is specialized for building a SelectionDAG, which
> is lower level than LLVM IR.
>
> -Eli
>
> >
> >
> > On Thu, Dec 8, 2011 at 2:54 PM, Eli Friedman <eli.friedman at gmail.com>
> wrote:
> >>
> >> > On Thu, Dec 8, 2011 at 2:37 PM, Ryan Taylor <ryta1203 at gmail.com>
> wrote:
> >> >>
> >> >> Thanks.
> >> >>
> >> >> So basically then this operation is not target-independent like the
> >> >> docs
> >> >> suggest?
> >>
> >> It is target-independent in the sense that a frontend can generate
> >> code using GEP's without worrying about how a given target actually
> >> lays out structures.  It isn't target-independent in the sense that
> >> the actual computed offset in bytes isn't the same for every target.
> >> See also
> >>
> http://nondot.org/sabre/LLVMNotes/SizeOf-OffsetOf-VariableSizedStructs.txt
> >> .
> >>
> >> -Eli
> >
> >
>
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