[LLVMdev] sunkaddr var names

[Eli Friedman]

On Tue, Sep 6, 2011 at 10:42 AM, Garrison Venn <gvenn.cfe.dev at gmail.com> wrote:
> When viewing generated IR code in a module I generated, I'm seeing %sunkaddr??
> IR variables, being created that I did not generate. What is the point of these var names,
> and implementations of their use  such as:
>
>  %sunkaddr16 = sext i32 %25 to i64
>
>  %sunkaddr15 = ptrtoint i8* %addr to i64
>  %sunkaddr17 = mul i64 %sunkaddr16, 4
>  %sunkaddr18 = add i64 %sunkaddr15, %sunkaddr17
>  %sunkaddr19 = add i64 %sunkaddr18, 28
>  %sunkaddr20 = inttoptr i64 %sunkaddr19 to i32*
>  store i32 %27, i32* %sunkaddr20
>
> I can guess sunkaddr means sunk address, and that the implementation is
> combining two pointers into a 64bit value but in a strange way; two bit shift
> of one pointer added to another along with added offset of 28. Except for the
> value of the last constant offset addition, this pattern is repeated in my IR. The
> constants do however always have the 2 least significant bits clear. Is this final
> sunkaddr20 address special to the target platform, which is OS X 10.7.x?
>
> Thanks for any clarification

CodeGenPrepare does some rather messy transformations to work around
the fact that isel can't see anything cross-block.  This is one of
those transformations; it's basically expanding out the equivalent of
a getelementptr instruction.

-Eli