[LLVMdev] LoopInfo are not able to identify some natural loops?

[Bo Wu]

Thanks for the reply. The LoopInfo pass can actually identify the loop I
mentioned. My former question is due to a bug in my pass. What I worried is
that LoopInfo can not identify all the natural loops for the benchmarks I
use, but now I haven't found any such cases.

Bo

On Sun, May 1, 2011 at 4:24 PM, John Criswell <criswell at illinois.edu> wrote:

>  On 4/30/11 8:52 AM, Bo Wu wrote:
>
> In C code, if a loop is not a natural loop, that means its loop body should
> at least have one label, right? In that case, some BB out of the loop can
> jump to the loop body, so the loop has more than on entry.
>
>
> Off the top of my head, I would think you are right: a C label would have
> to exist within the loop in order to have a jump from outside the loop to
> the inside of the loop.
>
> That said, have you looked at the LLVM IR generated for the function and
> determined that the loop meets all the criteria of a natural loop?  Just my
> two cents, but I think looking at the IR directly is much more accurate than
> ensuring that your conclusion about C code and natural loops is correct.
>
> -- John T.
>
>
>
>  Does LoopInfo guarantee to identify all natural loops? This property is
> very important for my pass.
>
>  regards,
> Bo
>
> On Fri, Apr 29, 2011 at 11:50 PM, Cameron Zwarich <zwarich at apple.com>wrote:
>
>>  A natural loop is one whose header dominates all of the nodes in the
>> loop. There is probably some block outside of the loop jumping to a block in
>> the loop body.
>>
>> Cameron
>>
>> On Apr 29, 2011, at 7:43 PM, Bo Wu <bwu at cs.wm.edu> wrote:
>>
>>  Hi,
>>
>>  I found that some loops can not be identified by LoopInfo pass. For
>> example, the loop at line 3094 of rdopt.c of benchmark 464.h264ref from spec
>> cpu2006 is not a loop or a child (pr grandchild) of any loop in the loop
>> list generated by LoopInfo pass. The documentation of LoopInfo says that it
>> identifies natural loops, who have exactly one entry point. But the IR of
>> this loops shows that it's header only has one BB in preds. Does that mean
>> LoopInfo can not identify some natural loops?
>>
>>  Thanks,
>> Bo
>>
>> --
>> Bo Wu
>>
>> Ph.D. student
>> CAPS group
>> Computer Science Department
>> The College of William & Mary
>> www.cs.wm.edu/~bwu <http://www.cs.wm.edu/%7Ebwu>
>>
>>
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>>
>>
>
>
> --
> Bo Wu
>
> Ph.D. student
> CAPS group
> Computer Science Department
> The College of William & Mary
> www.cs.wm.edu/~bwu <http://www.cs.wm.edu/%7Ebwu>
>
>
>
> _______________________________________________
> LLVM Developers mailing listLLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.eduhttp://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>
>
>


-- 
Bo Wu

Ph.D. student
CAPS group
Computer Science Department
The College of William & Mary
www.cs.wm.edu/~bwu
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