[LLVMdev] An enhancement for MCJIT::getFunctionAddress

[Jim Grosbach]

I don’t follow. Why are we looking at the module at all? That query should work even (especially) after the Module is deleted. We should be able to have a local symbol table that’s a DenseMap or something similar to resolve from names to target addresses. That map would be updated as part of the compilation when the object’s symbol table gets read.

-Jim

On Oct 21, 2013, at 4:55 PM, Kaylor, Andrew <andrew.kaylor at intel.com> wrote:

> There’s probably a lot that we could do, but I can’t think of anything easy.
>  
> Basically every time we need to look up a symbol by name we’re going to each module and saying “Do you have this symbol?”  It would likely be much better if we grabbed the function names from the module and did the search ourselves so that we could keep some information about the things that didn’t match and optimize the next search.
>  
> -Andy
>  
> From: Jim Grosbach [mailto:grosbach at apple.com] 
> Sent: Monday, October 21, 2013 4:39 PM
> To: Kaylor, Andrew; Yaron Keren
> Cc: <llvmdev at cs.uiuc.edu>
> Subject: Re: [LLVMdev] An enhancement for MCJIT::getFunctionAddress
>  
> The search is linear? If that’s really true, we should fix that.
>  
> On Oct 21, 2013, at 10:14 AM, Kaylor, Andrew <andrew.kaylor at intel.com> wrote:
> 
> 
> I should have read this before sending my previous reply. :-)
>  
> I’m not a big fan of default parameters, but some form of what you are suggesting may be useful.  See my other comments on this topic in the other reply.
>  
> -Andy
>  
>  
> From: Yaron Keren [mailto:yaron.keren at gmail.com] 
> Sent: Saturday, October 19, 2013 3:17 PM
> To: Kaylor, Andrew; <llvmdev at cs.uiuc.edu>
> Subject: An enhancement for MCJIT::getFunctionAddress
>  
> In MCJIT, the old JIT functions are deprecated in favor of getFunctionAddress. 
> Code like:
>  
>   llvm::Function *F = M->getFunction(FuncName);
>   void *FN = EE->getPointerToFunction(F);
>  
> should be rewritten as
>  
>   uint64_t FN = EE->getFunctionAddress(FuncName);
>  
> While functionally identical, in case the correct module is known the new version will be much slower, linear with the number of added (but not loaded) modules, since it has to (possibly) search for the correct module while old code directly searches the correct module.
>  
> To solve the issue, getFunctionAddress could get an optional Module "hint" (=NULL by default) which - if provided - will make getSymbolAddress skip calling findModuleForSymbol (a very slow operation) and instead directly use the Module provided.
>  
> Yaron
>  
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