Re: Calls to built-in functions are not Binary Compatible

[Bryce McKinlay <mckinlay@redhat.com>]

Andrew Haley wrote:
> Bryce McKinlay writes:
>  > Doesn't this disable builtins mechanism entirely when 
>  > -findirect-dispatch is used?
>
> Yes.
>
>  > These builtins improve GCJ's performance significantly on some numeric 
>  > code (scimark, for example).
>
> So you don't use indirect dispatch, surely.
>   
To not use indirect dispatch would make the benchmark rather artificial 
- since most of the code we're running on libgcj these days uses the BC ABI.
>  > Wouldn't it be better to fix whatever problem is causing direct
>  > calls to be generated rather than disabling them completely?
>
> I don't understand your point -- this is the code that is causing
> direct calls to be made.  Built-in functions in gcc either generate
> direct calls or they get replaced by inline code.
>   

Surely it is a bug, rather than a feature of this code, that it is 
causing direct (non-BC) calls to Java functions to be made. Direct calls 
to gcc/libc internal functions or inlining code is another matter.

You could argue that it is not strictly "binary compatible" to inline, 
say, Math.min() - but realistically, the Math.* functions are well 
enough defined that they can always be safely inlined or converted to 
direct OS calls - since they are pure functions, that read only their 
arguments and do not depend on object layout and such.

Bryce