[LLVMdev] Drop the machine code while executing

[Filip Pizlo]

This isn't currently supported directly. It depends on what you're doing, which JIT you're using, how you use modules, and to what extent you're relying on LLVM to do linking for you. 

You can't safely drop a function's code if you have other functions in that module. 

You can't safely drop a module if there are other modules that have calls that you've already resolved to functions in the module you're dropping unless you have your own mechanism for unlinking those calls. 

The MCJIT currently does support dropping the memory for a module, but it involves destroying the MCJIT execution engine object. This works best if you use your own JIT memory manager and you steal the executable memory from the MCJIT, and delete the MCJIT after code is generated. Then your own memory manager can manage the memory however you like. This depends on not having LLVM call instructions resolve to any of the functions you would be dropping. WebKit is an example of a system that does this. Each function gets it's own module and all LLVM data structures are dropped once the code is compiled. Call instructions are only used for intrinsics and for runtime calls; source level calls are implemented as patchpoints and WebKit does all of the linking (and unlinking). 

Long story short, there is no shrink-wrapped solution but it's doable if you're willing to get dirty. 

-Fil

> On Apr 25, 2014, at 3:44 PM, Sri <emdcdeveloper at gmail.com> wrote:
> 
> Hi
>         Currently , I have doing some experimental work by using llvm, Is it possible to drop the machine code once it has been generated for particular function while program executing. For example some void test(int) function has been executed on native machine , I want to drop the code before I start  execute some other function in my long running program.
> 
> Thanks.
> 
> With regards 
> Sri. 
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