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

[Quentin Colombet]

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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