llvm dev - May 2011 - [LLVMdev] ReplaceInstWithInst appears to invalidate BB iterator?

On May 7, 2011, at 1:00 PM, llvmdev-request at cs.uiuc.edu wrote:
> 
> Hi Justin,
> 
>> I have a call to ReplaceInstWithInst(Instruction *From, Instruction
*To) inside of a for loop iterating through a BasicBlock::iterator.  On the very
next pass after I replace the instruction, the iterator appears to be
invalidated.  Is this supposed to happen or am I doing something silly?  Is
there a more appropriate way to do this?  Thanks,
> 
> since ReplaceInstWithInst deletes (i.e. frees) the instruction
"From", any
> iterators referring to From will be invalidated.
> 
> Ciao, Duncan.
> 
Thanks Duncan.  I was able to correct my code to work around that nuance.  I was
under the impression that BasicBlock::iterators mapped onto something similar to
an STL list which supports erasing arbitrary elements.  Thanks for the help!

-Justin

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Hi Justin,
> Thanks Duncan. I was able to correct my code to work around that nuance. I
was
> under the impression that BasicBlock::iterators mapped onto something
similar to
> an STL list which supports erasing arbitrary elements. Thanks for the help!
instructions contain pointers to the next and previous instructions; an
iterator is just a pointer to an instruction that advances by looking at
the value of the instructions "next" pointer.  IIRC.

Ciao, Duncan.