[Mono-list] mcs compiles on linux. Now what?

[Paolo Molaro]

On 03/08/02 Martin Baulig wrote:
> if we're talking about optimizations, won't it make more sense to
> do the optimization based on profiling data from mcs run with mono,
> not with mint ?

This is a good point, but we work with the data we have :-)
It would be excellent if someone contributed a profiler for the 
code generatd by the jit. I already posted some time ago profile data
for the JIT itself.

> If we start optimizing based on profiling data from mint, we may end
> up trying to "optimize away" small functions which are inlined by
> the runtime, but which need a function call in mint.
[...]
> If I understand this correctly, this'll result in one million function
> calls when run with mint, but will look more like
> 
> ====
>         public static void TestIt ()
>         {
>                 long result = 0;
> 
>                 for (long count = 0; count < 1000000; count++)
>                         result++;
>         }
> ====
> 
> when run with mono, so it won't make much sense to optimize this.

There is hope this can result in the following code with an optimizing
JIT:

         public static void TestIt ()
         {
         }

;-)
Note that the interpreter could start inlining some methods as well,
so I don't think there will be a huge difference in the profile data.

> Same in the Array.Copy implementation, the code currently does
> something like
> 
>         for (int i = 0; i < count; i++)
>         {
>                 object value = array.GetValue (i);
>                 array.SetValue (value, i);
>         }
> 
> which are 2*count function calls in mint, but the same than implementing
> this function in C when run in mono.

This is a perfect reason for avoiding internalcalls that do the checks:
if you have the check in C# code, the jit will use the generic code to
optimize them away, but if you hide the checks in the internalcall
the jit will either have to hand-craft the checks or suffer them even if
they are not needed.

> Btw. does mcs already run with mono, or what needs to be done to make
> it run with it ?

From my tests mono works with mcs just as well as mint, but it doesn't
work with garbage collection enabled and that prevents it's use in
compiling large programs.

lupus

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