insert ICmpInst/BranchIns in Pass?

In a pass I would like to insert a ICmpInst/BranchInst pair to check
if 2 GlobalVariables are equal or not. If they are not I would like to
call a function. I've tried splitting the current block and then
inserting before the existing instructions, but for some reason this
seems to ruin the iterator(i). What is the correct way todo something
like this?

void checkShadowPtr(Module &M, Function &F, inst_iterator i,
GlobalVariable *shadow, Value *val) {
    /* Split old Block */
    BasicBlock *bb = i->getParent();
    BasicBlock *bb_after = i->getParent()->splitBasicBlock(&*i);
    /* Test */
    ICmpInst *test = new ICmpInst(*bb, CmpInst::ICMP_NE, shadow, val,
"Shadow check");
    /* Fail */
    BasicBlock *trueBlock = BasicBlock::Create(M.getContext(), "Shadow
Check FAIL", &F);
    CallInst::Create(qv_segFault, "", trueBlock);
    BranchInst::Create(bb_after, trueBlock);
    /* Profit */
    BranchInst::Create(trueBlock, bb_after, test, bb);

inst_iterator is hiding iterators which aren't going to stay
consistent across this kind of change. I'd suggest explicitly using
Function::iterator and BasicBlock::iterator to keep track of where you
are in the function; that should make it obvious what is going wrong.


All I really see from this change is that I somehow created a infinite
loop. Arn't these implemented as linked lists? Shouldn't they be
stable? I am very confused. I also can't seem to find a example where
much is being add.

Thank you