[LLVMdev] the pred_begin and pred_end of BasicBlock

[Chris Lattner]

On Thu, 13 Jan 2005, Zhou Feng wrote:

> Sorry, still a bit confused. Say we have two basic blocks: A and B. B has a 
> label. There is no branch/control flow instructions explicit uses B. like 
> this:
> A: code sequence does not contain br/other control flow instruction
> B:
> lable_of_b:
>   code sequence
> Is A still a predecessor of B?

There is no such thing as a fall through block in LLVM.  All blocks end in 
a "terminator" instruction.  If the block is logically a fall-through, it 
will end with an unconditional branch to the block after it.

What are you trying to do?

-Chris

> Chris Lattner wrote:
>
>> On Thu, 13 Jan 2005, Zhou Feng wrote:
>> 
>>> hi,
>>> I'm a bit confused by the pred_begin/end of BasicBlock in CFG.h. I cann't 
>>> understand what is a **use** of a BasicBlock. Also, I have no idea of when 
>>> CFG would be constructed in LLVM.
>> 
>> 
>> The CFG is always implicit in LLVM.  The two things that "use" BasicBlocks 
>> are branch/control flow instructions and PHI nodes.
>> 
>> -Chris
>> 
>
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-Chris

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