[LLVMdev] question about the LLVM JIT

[Eric van Riet Paap]

>> <snip>.
>> void    add_global_mapping(const char* name, void* address) {
>>    GlobalVariable  var(Type::IntTy, false,  
>> GlobalVariable::ExternalLinkage, 0, name, gp_module);
>>    gp_execution_engine->addGlobalMapping(&var, address);
>> }
>
> This is creating a new global variable on the stack, instead of  
> finding the existing global variable in the module.  Try something  
> like this:
>
>   gp_execution_engine->addGlobalMapping(YourModule->getNamedGlobal 
> (name),
>              address);
>

Hi Chris,

Thanks, that was simpler than I thought!
I actually thought I had to create a new global so it would be  
available for the JIT when it gets to process the "%var = external  
global int" line.

> <snip>
>
>> I do not see how I can tell the jit when this .ll code contains a  
>> function that should overwrite a previous version of it.
>> For instance, when there is a function "int %func() { ret int 5 }"  
>> and later I want this replaced by "int %func() { ret int 10 }".
>> If I remember correctly this gives a 'function already defined'  
>> error message. I tried to use a seperate module for each call to  
>> ParseAssemblyString + addModuleProvider.
>> In that way there was a problem with functions calling into other  
>> modules. (which perhaps I could try to solve if would understand  
>> addGlobalMapping better)
>
> This is somewhat tricky.  To replace a function in-place like this,  
> you should actually modify the function in the original module,  
> then call EE->recompileAndRelinkFunction(fn).  This will require  
> some C++ code to delete the original function body, then splice the  
> body of the new function into the old function.

For my purpose it would be ideal if I could give ParseAssemblyString  
an additional option (or maybe set a global flag somehow) to indicate  
what should happen when an already defined function is parsed. Would  
something like this be possible and fit into llvm's design?

 >>> Eric