[llvm-commits] [llvm] r43120 - in /llvm/trunk: lib/CodeGen/SelectionDAG/LegalizeDAG.cpp test/CodeGen/PowerPC/2007-10-18-PtrArithmetic.ll

[Chris Lattner]

On Oct 18, 2007, at 10:58 AM, Bill Wendling wrote:

> On 10/18/07, Chris Lattner <clattner at apple.com> wrote:
>>
>> On Oct 18, 2007, at 1:32 AM, Bill Wendling wrote:
>>
>>> Author: void
>>> Date: Thu Oct 18 03:32:37 2007
>>> New Revision: 43120
>>>
>>> URL: http://llvm.org/viewvc/llvm-project?rev=43120&view=rev
>>> Log:
>>> Pointer arithmetic should be done with the index the same size as
>>> the pointer.
>>
>> Nice catch Bill.  Should this use sign extend or zero extend if the
>> value is too small?  It seems like zext would be more appropriate,
>>
> There was a similar case before with CFA_OFFSET that I tackled before.
> I went back and forth with Anton a few times and he came up with
> essentially the patch you saw there:
>
> http://lists.cs.uiuc.edu/pipermail/llvmdev/2007-August/010424.html
>
> I was thinking about sign-extend vs. zero-extend afterwards and I
> think the reason behind the sign-extend is to allow for negative
> indexes. Does that sound reasonable?

Negative indices aren't allowed in EXTRAACT_VECTOR_ELT.

-Chris