[LLVMdev] Useless check in TailDuplication

[Devang Patel]

On May 14, 2008, at 7:26 AM, Matthijs Kooijman wrote:

> Hi,
>
> while reading the TailDuplication pass, I found a check that looks  
> rather
> pointless.
>
> TailDuplication looks at an unconditional branch instruction, BI. It  
> performs
> a number of checks on the successor of this branch instruction,  
> Dest. One of
> this checks is counting the number of predecessor. If this count is  
> zero, Dest
> is regarded as dead and no tail duplication happens.
>
> However, as far as I can see, there is no way that Dest can have zero
> predecessors. By definition, it has at least one: The block  
> containing BI. Is
> there a point I am missing here, or is this really a useless check?
>
> In particular, I'm talking about the following piece of code from
> lib/Transforms/Scalar/TailDuplication.cpp:
>
> 	pred_iterator PI = pred_begin(Dest), PE = pred_end(Dest);
> 		if (PI == PE && Dest != Dest->getParent()->begin())
> 			return false;   // It's just a dead block, ignore it...
>
> The attached patch removes this check. I can't find any problems  
> with it, it
> causes no tests to fail.

Looks good.
Committed revision 51154.


>
>
> Gr.
>
> Matthijs
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-
Devang