[llvm-commits] [llvm] r92411 - in /llvm/trunk: lib/Transforms/Scalar/InstructionCombining.cpp test/Transforms/InstCombine/load-cmp.ll

[Chris Lattner]

On Jan 4, 2010, at 10:17 AM, Duncan Sands wrote:

> Hi Bill,
>
>>> nice transform.  However if this is not an inbounds GEP and the  
>>> index "i" is
>>>> 64 bits on a 32 bit machine, then there are other possible values  
>>>> for "i",
>>>> such as i == 6 + 232.
>>>>
>> At least in C, accessing outside of an array is undefined. Isn't  
>> this a case of "they get what they deserve"?  :-)
>
> front-ends should turn C array accesses into inbounds GEPs, so my  
> comment
> wouldn't apply to code coming from C.  In fact it probably doesn't  
> apply
> to code from any language - it's a theoretical correctness issue  
> rather
> than a practical one :)  I guess it can be fixed by truncating i to  
> the
> pointer size for the target before doing the compare.

Duncan's right about this, I'll fix it.  Unfortunately, this will make  
the xform require TD information, but hey, correctness is king.

-Chris