[LLVMdev] Program order in inst_iterator?

[Nick Lewycky]

Anirudh Sivaraman wrote:
> On Mon, Jun 15, 2015 at 10:50 AM, mats petersson<mats at planetcatfish.com>  wrote:
>> It will iterate over the instructions in the order that they are stored in
>> the module/function/basicblock that they belong to. And that SHOULD,
>> assuming llvm-dis does what it is expected to do, be the same order.
>>
>
> Thanks for the reply. What about instruction ordering across basic
> blocks? Let's say instructions IA and IB belong to basic blocks BBa
> and BBb, where BBa is before BBb in program order. Then, will IA be
> printed before IB?

Yes, llvm-dis does print in the same order that inst_iterator visits. 
The llvm::Function has a linked list of llvm::BasicBlock objects. Both 
llvm-dis and the inst_iterator will iterate over that list, and then for 
each basic block iterate over the linked list of llvm::Instruction 
objects. Both of these lists are ordered, and their order is preserved 
through .ll and .bc files.

However, I wouldn't call that program order, though I couldn't find a 
definition of the term easily. The only guarantee on the order is that 
the first block visited/printed is the entry block. It's entirely 
possible to have a three block program where A branches to C branches to 
B, but will be visited/printed in order A B C.

>
> Anirudh
>
>> --
>> Mats
>>
>> On 15 June 2015 at 18:10, Anirudh Sivaraman<sk.anirudh at gmail.com>  wrote:
>>>
>>> Does inst_iterator
>>>
>>> (http://llvm.org/docs/ProgrammersManual.html#iterating-over-the-instruction-in-a-function)
>>> guarantee that the iterated instructions are in program order: the
>>> order of instructions printed by llvm-dis?
>>>
>>> Thanks in advance,
>>> Anirudh
>>> _______________________________________________
>>> LLVM Developers mailing list
>>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
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>>
>>
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