[LLVMdev] subtle problem with inst_iterator

[Vladimir Prus]

Hello, I think there's a rather subtle problem with the inst_iterator. It 
declares its iterator category as std::bidirectional_iterator_tag but C++ 
standard requirements for forward iterator (which are included in 
requirements for bidirection iterator), say that the type of expression 

   *r;

should be T&, where 'r' is the iterator and T is its value type. The 
inst_iterator, though, returns pointer to Instruction, not a reference to a 
pointer to instruction.

The above might sound like I've gone crazy reading C++ standard, but my real 
reason is that with the current code the following:

    for_each(inst_begin(f), inst_end(f), boost::bind(
        apply_phi_semantics, result, _1, instruction2vertex));

does not compile, where 'apply_phi_semantics' is my function and boost::bind 
is a tool for binding function arguments described in 

     http://www.boost.org/libs/bind/bind.html

The reason it does not compile is somewhat contrived. for_each passes the 
result of *it to functional object returned by boost::bind. The operator() of 
that object has the following signature:

   template<class Arg1>
   .... operator()(Arg& a1)

and since result of *it is considered to be rvalue it can't be accepted by 
this operator. The complete discussion is in 

    http://std.dkuug.dk/jtc1/sc22/wg21/docs/papers/2002/n1385.htm

I'd suggest to apply the following patch which makes operator* return 
reference to pointer. It makes my code compile and the rest of LLVM compiles 
too. Comments?

- Volodya







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