binary compatibility ABI (was: Re: [boehm-gc] Import 6.3 alpha 1)

[Jeff Sturm]

On Thu, 14 Aug 2003, Andrew Haley wrote:
> Jeff Sturm writes:
>  >
>  > One of my sore points is the performance gap between static and
>  > position-independent code with the current gcj compiler.  For example:
>  > reading a static field requires one memory load without -fPIC, but two
>  > loads with -fPIC (to obtain the memory address from the GOT offset).
>
> Short of overwriting the instruction that does the fetch, how would you
> do that?

That wasn't really such a good example.

Consider:

static int a, b;
...
return a + b;

Does this require 2, 3 or 4 memory loads?

(I believe 2 is the answer for non-PIC, 4 for PIC.  If we take advantage
of the fact that static fields are at a fixed offset from the class
record, it can be done in three, while preserving position independence.)

Jeff