[LLVMdev] Debug Info and MergeFunctions Transform

Stepan Dyatkovskiy stpworld at narod.ru
Tue Oct 7 12:20:29 PDT 2014

Hi David,
Thanks for attention to MergeFunctions! I have read your mail briefly, 
tomorrow I'll provide you with detailed information. By now you could 
use tests from  $LLVM/test/Transforms/MergeFunc/ as examples.


David Blaikie wrote:
> Hi Stepan,
> After discovering several bugs in ArgumentPromotion and
> DeadArgumentElimination where llvm::Functions were replaced with similar
> functions (with the same name) to transform their type in some way, I
> started looking at all calls to llvm::Function::takeName to see if there
> were any other debug info quality bugs in similar callers.
> One such caller is MergeFunctions, and I don't see any debug info tests
> for this so I'm wondering what /should/ happen here.
> In the case where the functions are internal I'm not sure there's
> anything we can do, we simply remove one function and keep the other -
> the debug info can only be ascribed to one of the two and this probably
> comes out naturally (whichever name we choose to keep). I don't think we
> can have the debug info for one function reference a global alias, while
> the debug info for another function references the thing that alias
> refers to. So be it.
> But in the case of MergeFunctions::writeThunk we can probably do better
> - by updating the debug info for the thunk'd function so we at least
> describe this trivial function in the debug info.
> Does that sound about right?
> Could you provide any C/C++ source examples where MergeFunctions fires
> fairly reliably so I could play around with the debug info behavior (&
> fixes) here?
> Thanks,
> - David

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