[LLVMdev] Address calculation

Eli Friedman eli.friedman at gmail.com
Mon Oct 6 16:41:15 PDT 2008

On Mon, Oct 6, 2008 at 9:03 AM, Villmow, Micah <Micah.Villmow at amd.com> wrote:
> I am attempting to get indexing code generation working with my backend.
> However, it seems that the addresses being calculated is being multiplied by
> the width of the data type.

That's how most normal architectures/address spaces work.  Is there
something unusual about address space 11 in your architecture?

> The value 23 in the getelementptr is being multiplied by 4 bytes and the
> generated code is the value 96. However, I don't want this multiplication to
> occur and I cannot figure out how to divide the immediate by 4 when lowering
> the Add instruction that is linked to a  load/store operation.

CodeGen doesn't have a gep instruction, so it has to convert the
implied arithmetic into explicit arithmetic.  Is your address space 11
byte addressable?  If it isn't, you have a  very unusual case; you'll
have to hack SelectionDAGBuild.cpp to get the lowering right, and I
think some IL-level transformations assume byte addressing.  If it is,
you really want to just fold the addition into the load; it's not
trivial to match, but it shouldn't be too hard.


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