[LLVMdev] function pointer from name?

[Alexander Popolitov]

Ok, I've managed to get pointer to a function via ptr attribute of 
Function object.

now
(defun foo (x) x)
(defun bar (x) (funcall 'foo x))

generates the following LLVM IR:

define i8* @foo(i8* %x) {
entry:
   ret i8* %x
}

define i8* @bar(i8* %x) {
entry:
   %0 = alloca [4 x i8], align 1
   store [4 x i8] c"foo\00", [4 x i8]* %0, align 1
   %calltmp = call i8* @intern([4 x i8]* %0)
   %ptrfind = call i8* @find_llvm_function(i8* %calltmp)
   %cast = bitcast i8* %ptrfind to i8* (i8*)*
   %calltmp1 = call i8* %cast(i8* %x)
   ret i8* %calltmp1
}

except last two lines (with %calltmp1 and ret) do not actually get 
generated, because generation of call instruction fails with
error 'argument is neither a function nor a function pointer'

I thought, that bitcast instruction before should do the trick of 
transforming return value of @find_llvm_function
(which is a wrapper around Python code, which searches in the Module 
object) to a function pointer.
Also, there is some possibility, that I got the guts of 
@find_llvm_function wrong, however, in that case I'd expect,
that code would still be generated, and problems would manifestate only 
at runtime.

Any ideas what am I doing wrong?

On 05/04/2014 05:24 PM, Alexander Potapenko wrote:
>
> Don't you have the same problem with other atoms, e.g. variable names?
> This sounds like something that should be implemented in the 
> language's runtime library.
>
> On May 4, 2014 7:15 PM, "Alexander Popolitov" <popolit at gmail.com 
> <mailto:popolit at gmail.com>> wrote:
>
>     Hi everyone!
>
>     I'm trying to implement lisp's funcall function, which roughly
>     calls a function, name of which
>     is known only at runtime.
>     I know that LLVM IR 'call' directive can accept function pointers,
>     so the question is,
>     is there a simple way to get a function pointer from a function
>     name (represented as e.g. i8*)?
>
>     BTW, I'm using llvmpy to generate LLVM IR, so if there is a way to
>     do this using llvmpy tools, it would also do.
>
>     Yours sincerely,
>     Alexandr Popolitov
>     _______________________________________________
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>     LLVMdev at cs.uiuc.edu <mailto:LLVMdev at cs.uiuc.edu>
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>

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