[LLVMdev] Scheme + LLVM JIT

[Chris Lattner]

On Thu, 12 May 2005, Alexander Friedman wrote:
>> llvm_function_new/llvm_value_set_name/llvm_executionengine_run_function,
>> etc.
>>
>> If kept simple, standardized, and generic, I think it would be very useful
>> to people (even if incomplete).  This would allow others to build on it,
>> and we could 'ship' it as a standard llvm library.
>
> It looks like my interface will look vaguely like this. Functions like
> "llvm_make_module" will take in text representations of the
> module. This seems to be the fastest way of getting our scheme
> implementation to talk to the jit.

ok

> This requires being able to parse strings. The LLVM 'Parser.h' interface 
> (and implementation) has the built in assumptions that it will always be 
> parsing from the file system. Would you guys accept a patch that makes 
> it more general (ie, parse from file or string)?

Yes, that's a generally useful thing to have, I'd like to see it happen if 
it doesn't impact the efficiency of the lexer.

> If so, what's an easy way to do it? Is it possible to have a "FILE" 
> struct backed by a string?

Hrm, I really don't know.  :(

> FYI, here is a sketch of what the fib example would look like:
>
> #include "llvm_c.h"
>
> /*
>  Everything takes and recieves void * pointers. This to avoid redefining C++
>  types.

Makes sense.

>  This is the C 'version' of the Fib example, at least in spirit.
> */
>
> char* fib_function =
> "int %fib (int %AnArg) {"
>
> " EntryBlock: "
> " %cond = setle int AnArg, 2"
> " branch bool %cond, label return, label recur"
>
> " return:"
> " ret int 1"
>
> " recur:"
> " %sub1 = sub int %AnArg, 1"
> " %fibx1 = call tail int %fib (int %sub1) "
> " %sub2 = sub int %AnArg, 2"
> " %fibx2 = call tail int %fib (int %sub2) "
> " %result = add int %fibx1, %fibx2"
> " ret int %result"
> "}";

Some typeos (branch -> br, 'call tail' -> 'tail call', etc) but general 
idea makes sense.

> void * M = llvm_make_module_from_text (program, "test") ;

One of these should be fib_function right?  What is the 'test' string?

> // now we want to run some optimizations on this thing.
> // make a pass manager
> void * PM = llvm_make_pass_manager();
>
> // add 'target data' to module
> llvm_addPass(PM, make_target_data("jit-lib",M));
>
> llvm_addPass (PM, llvm_createVerifierPass());

I'd suggest using C style llvm_create_verifier_pass consistently, but your 
call :)

> // add optimization passes here
> // addPass (PM, ... )
>
> llvm_run_passes(PM,M);
>
> // merge modules - not relevant here
>
> // make an execution engine from the module
> void * JE = llvm_make_jit_engine (M);
>
> // get a function pointer by name. If you have several functions with the same
> // name, you are out of luck
> int (*fib) (int) = (int (*)(int)) llvm_get_function_pointer(JE,M,"fib");
>
> // the above cast is probably wrong.
>
> int result =fib (24);

Looks good!

-Chris

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