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Compiler performance
f#compiler.net

Hi,

For my project I am generating f# code. I would like to be able to compile this code then dynamically load it at run-time. Is this possible with f#? Or is it a .net issue - something to do with reflection maybe? The function prototype is fairly simple:

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unit -> (signal_t list)

Before getting there though I have hit a bit of a problem with the f# compiler. The functions I generate can be fairly long. One example may be, say, 1000 lines. When compiling this it takes about 90 seconds. The rest of the project is much larger than this and only takes a few seconds to compile. Below is a short example of the code.

Cheers,

Andy

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let bitonic_test () = 
 let i0 = input "i0" 8 in

 let i1 = input "i1" 8 in
...

 let hdfs_2 = (constb "1") in

 let hdfs_1 = (constb "0") in
...

 let hdfs_651 = (i31 <: i30) in

 let hdfs_646 = (i29 <: i28) in
...

 let hdfs_141 = (hdfs_1 ==: hdfs_140) in

 let hdfs_136 = (hdfs_2 ==: hdfs_135) in
...

 let hdfs_654 = (mux hdfs_652 [ i31; i30 ]) in

 let hdfs_649 = (mux hdfs_647 [ i29; i28 ]) in
...

 [
...

  output "o30" hdfs_1221;
  output "o31" hdfs_1222;
 ]
.

One way is to generate a DLL to disk, then load it at runtime and find your entry-point through reflection. You can find the MethodInfo on your type for your function and call it via an Invoke.

With the compile times for your generated code, i would first try building the result list via

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let res = []
let res = x1 :: res
let res = x2 :: res
res

That may help. If not, can you send a sample to fsbugs@m...

Thanks.

By on 9/29/2006 5:59 AM ()

Hi,

First thanks for the tips on reflection which I have now got working.

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  exception Dynload_method of MethodInfo
  let outputs = 
    let assembly = Assembly.LoadFrom ("simple.dll") in
    let typ = assembly.GetType("Simple", true) in
    let methods = typ.GetMethods() in
    let func = 
      try
        Idioms.foreach methods (fun (m : MethodInfo) ->
          if m.Name = "simple"
          then raise (Dynload_method m)
        );
        failwith "Couldnt find correct method"
      with
      | Dynload_method m -> m
      | e -> raise e
    in
    unbox (func.Invoke(null,null))
  in

(please excuse the "worse than gotos" use of exception handling for flow control here, but I couldnt think of another way to do it).

I've sent some example code the fsbugs@.. which exposes the performance (both memory and time) problems I have seen.

Cheers,

Andy

By on 9/29/2006 8:27 AM ()

Exceptions are not cheap on .NET, so you will want to avoid them in cases which are not "exceptional". There are functions in MLLib.Array for finding an item in an Array, given a predicate or selector function.

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Array.find : ('a -> bool) -> 'a array -> 'a
Array.first : ('a -> 'b option) -> 'a array -> 'b option

See:

[link:research.microsoft.com]

For consistency with List, there *should* also be:

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Array.tryfind : ('a -> bool) -> 'a array -> 'a option
By on 9/29/2006 10:24 AM ()

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