llvm dev - May 2009 - [LLVMdev] jump to function

Hello,

Is it possible to jump from one function to the beginning of another function?

For instance, assume wrapper_FOO is a wrapper for FOO. I replace the code
..............................
bar() {
 FOO(...)
}
..............................
with
..............................
bar() {
 
wrapper_FOO(...)

}

..............................

Now, for efficiency, I'd like to have
wrapper_FOO() {
  <do some work>
  jump FOO;
}

Thank you,
Dan

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On May 20, 2009, at 2:22 PMPDT, dan mihai wrote:
> Hello,
>
> Is it possible to jump from one function to the beginning of another  
> function?
This can't be represented in llvm IR (or in standard C/C++).  An  
optimization called (in LLVM) "tail call" will generate this at the  
assembly level, but not all back ends have this implemented.
> For instance, assume wrapper_FOO is a wrapper for FOO. I replace the  
> code
> ..............................
> bar() {
>  FOO(...)
> }
> ..............................
> with
> ..............................
> bar() {
>   wrapper_FOO(...)
> }
> ..............................
>
> Now, for efficiency, I'd like to have
> wrapper_FOO() {
>   <do some work>
>   jump FOO;
> }
>
> Thank you,
> Dan
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dan mihai wrote:
> Hello,
>
> Is it possible to jump from one function to the beginning of another 
> function?
>
> For instance, assume wrapper_FOO is a wrapper for FOO. I replace the code
> ..............................
> bar() {
>  FOO(...)
> }
> ..............................
> with
> ..............................
> bar() {
>   wrapper_FOO(...)
> }
> ..............................
>
> Now, for efficiency, I'd like to have
> wrapper_FOO() {
>   <do some work>
>   jump FOO;
> }
Tail call optimization can optimize calls into jumps. See 
http://llvm.org/docs/CodeGenerator.html#tailcallopt for details.

-- 
Richard Osborne | XMOS
http://www.xmos.com