llvm dev - Apr 2011 - [LLVMdev] LoopInfo are not able to identify some natural loops?

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
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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
> 
> 
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
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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.

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
> <http://www.cs.wm.edu/~bwu>www.cs.wm.edu/~bwu
>
>
>  _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu          <http://llvm.cs.uiuc.edu>
> http://llvm.cs.uiuc.edu
> http://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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