[Mono-dev] [PATCH]Optimization of the generated IMT code

[Rodrigo Kumpera]

Hi,

The attached patch optimize the imt thunk code. The optimization is to
exploit the fact that IP don't need to be preserved under a particular
situation.

The magic trampoline needs to retrieve the vtable pointer used by the call
site to patch it and this address might be stored in a scratch register,
that's why the IMT code cannot change then. But if the code store the vtable
address within the scratch registers, the magic trampoline code won't
notice. This change allow us to branch without the POP hack.

The optimization loads the vtable pointer into IP and uses r0 and r1 to
compare values. To call the virtual method, we use "ldr pc, [ip + #]". These
changes reduce the code by 3 words for each entry.


Cheers,
Rodrigo
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