[LLVMdev] Fwd: GetElementPtr

[Ryan Taylor]

---------- Forwarded message ----------
From: Ryan Taylor <ryta1203 at gmail.com>
Date: Mon, Dec 12, 2011 at 4:58 PM
Subject: Re: [LLVMdev] GetElementPtr
To: Eli Friedman <eli.friedman at gmail.com>


Sorry,

  So what I'm trying to ask is are the widths given (32, 64) for the index
and the offset the widths of the index and offset values or the width of
the type they are offsetting and indexing or both?

  I apologize if you already answered this and I didn't get it.


On Mon, Dec 12, 2011 at 4:50 PM, Eli Friedman <eli.friedman at gmail.com>wrote:

> On Mon, Dec 12, 2011 at 4:46 PM, Ryan Taylor <ryta1203 at gmail.com> wrote:
> > So in the second example I gave, why is the pointer type 32 but the index
> > type is 64?
>
> Because that's what the frontend chose the generate?  I'm not sure
> what you're trying to ask.
>
> -Eli
>
> > On Mon, Dec 12, 2011 at 4:43 PM, Eli Friedman <eli.friedman at gmail.com>
> > wrote:
> >>
> >> On Mon, Dec 12, 2011 at 4:38 PM, Ryan Taylor <ryta1203 at gmail.com>
> wrote:
> >> > By LLVM do you mean the backend? I'm not using the backend, so is that
> >> > i32
> >> > on the 0 index the type of the index value or the type of the value to
> >> > which
> >> > exists at that index?
> >> >
> >> > it seems the pointer itself has no width, it's arbitrary and is
> handled
> >> > in
> >> > the lowering and is target dependent on the bus width.
> >> >
> >> > Basically, when I am computing offset I need to know the sizes for
> add.
> >> > The
> >> > size of the pointer (dedicated by bus width) and the size of the
> index.
> >>
> >> The size of the index is simply its type.  You would normally
> >> sign-extend or truncate to the width of a pointer to do arithmetic,
> >> though.
> >>
> >> You can grab the pointer size from TargetData::getPointerSizeInBits().
> >>
> >> -Eli
> >
> >
>
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