[PATCH] Add iterator for PHINode value/BB pair

[Pete Cooper]

Hi David, Duncan

This is another iterator which i’d like to use to enable more foreach loops in LLVM.

This time its for returning both the value and basic block from a phi node.  Its very common to need both of these together, but currently involves a manual loop to do so.

The code here is similar to generic_gep_type_iterator where i’m wrapping an iterator (in this case 2) and on updates to the iterators I update the ‘Pair’ field.  operator* then returns the Pair when requested.

An alternative would be to only update Pair in operator*, but that would require making the field mutable.

I’ve added a single use of this in BasicAliasAnalysis.  A grep of the code finds 47 total loops over PN[.,->]getNumIncomingValues(), of which around 40 look eligible to use this.

Comments welcome.  

Cheers,
Pete

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