[LLVMdev] Why the fault?

[Mark Schimmel]

  for (BasicBlock::reverse_iterator I = BB.rbegin(), E = BB.rend(); I != E; ) {

    Instruction& inst = *I;

    ++I; <-- iterator should be advanced to the previous instruction

    // Happens to be an Instruction::SExt.
    // Works fine if I iterate forwards
    if (isInstructionTriviallyDead(&inst, TLI))
      inst.eraseFromParent();
  }

Sorry for the inexperienced question, but I'm confused why this works when using a forward iterator, but fails in reverse. The iterator is moved off the current instruction so why would erasing the current instruction cause an error?

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