llvm dev - Jul 2010 - [LLVMdev] the generation of getelementptr instruction

Hi all,
I'm reading the language reference of LLVM here:
http://llvm.org/docs/LangRef.html#i_getelementptr

In the first example, it shows that the generated IR is supposed to be something
like:
%reg = getelementptr %ST* %s, i32 1, i32 2, i32 1, i32 5, i32 13
But when I copied the code and compile it myself (using v2.7), I got five
getelementptr instructions, which are just like the equivalent code given later
in the document. In the case above, why the resulting IRs are different? Thanks
a lot.Regards,--Wenbin
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2010/7/21 Wenbin Zhang <zhangwen at
cse.ohio-state.edu>:
> Hi all,
> I'm reading the language reference of LLVM here:
> http://llvm.org/docs/LangRef.html#i_getelementptr
>
> In the first example, it shows that the generated IR is supposed to be
> something like:
>
> %reg = getelementptr %ST* %s, i32 1, i32 2, i32 1, i32 5, i32 13
>
> But when I copied the code and compile it myself (using v2.7), I got five
> getelementptr instructions, which are just like the equivalent code given
> later in the document.
>
> In the case above, why the resulting IRs are different?
>
> Thanks a lot.
Just a quirk of frontend code generation; you'll get the shown result with
-O.

-Eli

Hi Wenbin,
> I'm reading the language reference of LLVM here:
> http://llvm.org/docs/LangRef.html#i_getelementptr
>
> In the first example, it shows that the generated IR is supposed to be
> something like:
> %reg = getelementptr %ST* %s, i32 1, i32 2, i32 1, i32 5, i32 13
> But when I copied the code and compile it myself (using v2.7), I got
> five getelementptr instructions, which are just like the equivalent
> code given later in the document. In the case above, why the
> resulting IRs are different?
if you enable optimizations in the frontend (-O1), the resulting LLVM
code will look just as shown in the example.

Regards,
Christoph