[LLVMdev] Any known-reliable numbering scheme for basic blocks?

[Christian Convey]

Hi Quentin, thanks for the tip.  I'll have a look.  Much appreciated.

- C

On Wed, Jul 1, 2015 at 2:39 PM, Quentin Colombet <qcolombet at apple.com>
wrote:

> Hi Christian,
>
> I’m guessing you would want a mechanism similar to what we use for PGO
> (which I do not know how it works :)).
>
> + Justin who works on PGO.
>
> Cheers,
> -Quentin
>
> On Jun 24, 2015, at 6:05 PM, Christian Convey <christian.convey at gmail.com>
> wrote:
>
> Hi all,
>
> Does anyone know of a good solution to the following?  I'm trying to find
> a good way to stably associate distinct ID numbers with different BB in a
> module.  As long as the module's IR hasn't changed in any way whatsoever,
> I'd like to be guaranteed to always generate the same ID <--> BB mapping.
> Or if the mapping is ambiguous, because two or more mappings between BB's
> and ID's are indistinguishable (isomorphic?), I'd like to be sure I at
> least can reliably re-obtain some mapping in that equivalence class.
>
> This seems related to a debate / bug-report
> <https://urldefense.proofpoint.com/v2/url?u=https-3A__llvm.org_bugs_show-5Fbug.cgi-3Fid-3D16043&d=AwMFaQ&c=8hUWFZcy2Z-Za5rBPlktOQ&r=Mfk2qtn1LTDThVkh6-oGglNfMADXfJdty4_bhmuhMHA&m=VyhVlhie270AiA60rcYOf3Vw5xKKZFKAgr5GK6hPXu0&s=Kv0Xo7jx0HJ8mumCx_vW368qV5lXoVdMAygrhChMMFU&e=>
> regarding the arbitrary nature of (pseudo?) labels in LLVM assembly.  E.g.,*";
> label:3"*.
>
> It also looks like *llvm-diff* does something similar to what I want in
> its *FunctionDifferenceEngine* class.  But I think *llvm-diff* allows for
> the two IR's to differ, and uses approximate matching.  I don't need any
> graceful degradation when the IR has changed, but I need exact matching
> when the IR hasn't changed.
>
> In the worst-case scenario, I could make a sweep through all of the
> module's BB's and just tag each BB with a distinct serial number in its
> metadata.  But I'd like to avoid this if possible, partly because I'd like
> there to be a chance of the BB <--> ID mapping remaining valid if I run
> Clang.
>
> Thanks, Christian
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