[LLVMdev] GC infrastructure checked in

[Gordon Henriksen]

On Jan 7, 2008, at 10:54, Carl Friedrich Bolz wrote:

> Gordon Henriksen wrote:
>
>> That said, the PyPy group has llvmgcroot support on a branch; you  
>> could ask Armin Rigo <arigo at tunes dot org> for details about  
>> accessing it.
>>
>> On his benchmarks, Armin saw an 8% speedup vs. a shadow stack.   
>> Their gcc backend still outperforms the LLVM backend, though—and  
>> llvm-gcc outperforms that further still.
>
> The second part of this is not correct. I don't think we ever even  
> tried llvm-gcc on the output of our C backend. What we see on x86  
> machines is that LLVM's own code generators produce slower code than  
> using LLVM's C backend and then running GCC on this. This however is  
> then faster than our own C backend using GCC.

Thanks for the clarification, Carl.

> Hm, summary:
>
>    pypy-llvm-backend with llvm's codegen
>  < pypy-c-backend with GCC
>  < pypy-llvm-backend using llvm's C backend and then GCC

I wonder what the impact of using llvm-gcc instead of GCC is in this  
final pipeline. If that actually works, you could indeed eliminate the  
shadow stack here as well, since llvm-gcc has extensions to emit  
gcroot intrinsic calls. It's currently hardwired to the shadow-stack  
codegen, but that's very fixable.

— Gordon

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