[LLVMdev] Possible instruction combine bug with pointer icmp?

[Richard Osborne]

On 28/06/13 15:56, Eli Friedman wrote:
> On Fri, Jun 28, 2013 at 6:13 AM, Richard Osborne <richard at xmos.com 
> <mailto:richard at xmos.com>> wrote:
>
>     If I give instcombine the following IR:
>
>     define i1 @f([1 x i8]* %a, [1 x i8]* %b) {
>       %c = getelementptr [1 x i8]* %a, i32 0, i32 0
>       %d = getelementptr [1 x i8]* %b, i32 0, i32 0
>       %cmp = icmp ult i8* %c, %d
>       ret i1 %cmp
>     }
>
>     It optimizes it into:
>
>     define i1 @f([1 x i8]* %a, [1 x i8]* %b) {
>       %cmp = icmp slt [1 x i8]* %a, %b
>       ret i1 %cmp
>     }
>
>     Is this a bug, or are there some semantics of icmp or
>     getelementptr I'm missing that mean it's OK to change this from an
>     unsigned comparison to a signed comparison?
>
>
> Looks like a bug to me.
>
> -Eli
Thanks for confirming this, I've filed it as PR16483:

http://llvm.org/PR16483

-- 
Richard Osborne | XMOS
http://www.xmos.com

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