[LLVMdev] PHINode in entry block

[John Criswell]

On 7/15/14, 9:55 AM, William Moses wrote:
> All,
>
> Consider the case where the entry block to a function acts like a loop 
> (e.g. it ends with a conditional break to itself and somewhere else). 
> How would one create a PHINode (representing an index perhaps) which 
> has a constant index (say 0) when entering the function, and 
> (oldval+1) when looping.
>
> I understand how to do this if the loop were not in the entry block 
> (by simply using node->addIncoming(ConstantInt(...), entry), 
> node->addIncoming(builder.CreateAdd(node,...),loopBlock) ).
>
> My question is how would one do this using the C++ API when there is 
> no predecessor since it is the entry block.

An entry block cannot have any phi-nodes.  If you have a function that 
starts with a loop, then your entry block will be a single unconditional 
branch to a basic block which is the first basic block of the loop.

Regards,

John Criswell

>
> Thanks,
> Billy Moses
>
>
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