[LLVMdev] Is LLVM appropriate for implementing a shell interpreter?

[Mu Qiao]

On 03/24/2011 11:05 PM, Johannes Schaub (litb) wrote:
> Mu Qiao wrote:
> 
>> Hi devs,
>>
>> We are implementing a library that interprets shell scripts so that
>> other programs could efficiently talk to bash. We'd like to hear your
>> advice on whether LLVM is appropriate for us. Here are our considerations:
>>
>> In most cases our library will interpret each script just once. Our
>> current approach is using a manual implementation based on ANTLR and
>> C++, so actually we are executing the scripts while interpreting. If we
>> turn to LLVM, we need to first compile it into LLVM IR, then into native
>> code. Our guess is this may be slower than our current approach. Is that
>> true?
>>
>> Anyway, we do have several scripts that need to be sourced and reused
>> while interpreting others. We guess this is where LLVM could help. LLVM
>> optimized code for those scripts should run faster than our manual
>> implementation. So the overall performance could be improved.
>>
>> Could you please point out if we are wrong? Thanks.
>>
> 
> I'm currently implementing such a thing (interactive shell / compiled 
> scripts (only the former of which is currently being implemented)). 
> 
> LLVM apparently has one problem regarding this: Its context caches all 
> constants ever created and doesn't free them, until the LLVMContext object 
> is free'ed itself. 
> 
> So if your shell for example is connected to a pipe, accepting generated 
> scripts or something in possibly fast succession, you will have problems 
> with inputs such as:
> 
>     print 0   # 0 is cached and never free'ed
>     print 1   # 1 is cached and never free'ed
>     ...
> 
> We haven't tried to tackle this problem yet. But we probably need to. 

Thank you for answering.
In our case we do not focus on interactive things so I think the problem
you mentioned is acceptable by us. But we're really not sure whether
LLVM could improve the overall performance compared to a manual
implementation as I said in the last mail.

-- 
Best wishes,
Mu Qiao
GnuPG fingerprint: 92B1 B0C4 8D14 F8C4 EFA5  3ACC 30B3 0DE4 17B1 57E9

-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 554 bytes
Desc: OpenPGP digital signature
URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20110325/be0ddb0c/attachment.sig>