Segfault when derefing iterator - c++

Question

I'm following the example here. My complete code is
#include "llvm/IR/Function.h"
#include "llvm/Pass.h"
#include "llvm/IR/InstIterator.h"
using namespace llvm;
namespace {
struct Hello2 : public FunctionPass {
static char ID; // Pass identification, replacement for typeid
Hello2() : FunctionPass(ID) {}
bool runOnFunction(Function &F) override {
inst_iterator iter = inst_begin(F); // causes a segfault
return false;
}
};
}
char Hello2::ID = 0;
static RegisterPass<Hello2> Y("hello2", "Hello World Pass");
following the "HelloWorld" pass example explained here. When I followed the example exactly, it worked fine, but with the modified pass code above, I get the segfault when I run opt.
(I'm using the same "hello.c" file for input as in the "HelloWorld" pass example, compiling it with clang, running make and calling my library with opt just as in the example.)
What's causing my segfault, and is there any way to test for it/avoid it?
EDIT
I traced the segfault to line 61 of InstIterator.h: BI = BB->begin();. When my code reaches that point, BBs is non-NULL, but BB=BBs->begin() is NULL. Thus the dereference of BB results in a segfault. The question of why BB is NULL (and why the constructor doesn't check for that) remains.

Answer 1

This problem was resolved when my system did an automatic update and got a new version of several llvm-3.5 packages (today). Previously, opt --version returned
LLVM version 3.5
Optimized build.
Built Mar 23 2014 (21:41:30).
Default target: x86_64-pc-linux-gnu
Host CPU: corei7
now it returns
LLVM version 3.5.0
Optimized build.
Built Jan 27 2015 (00:14:48).
Default target: x86_64-pc-linux-gnu
Host CPU: corei7