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Re: Post-register-allocation opportunitistic optimizer?


Hi Toshi,

> For example, GCC generates this code for a right shift by 8 on the
> H8/300H:
> 
>         mov.w   e0,r2
>         mov.b   r0h,r0l
>         mov.b   r2l,r0h
>         mov.b   r2h,r2l
>         exts.w  r2
>         mov.w   r2,e0

I was thinking about the same thing.  Shifts that require loops are in
the same situation.  Also, if you want to use stw.l for argument push
on H8/S, you need to know what registers are available, but this might
require MACHINE_DEPENDENT_REORG.

> 3. New optimizer pass which runs after global alloc which 
>    opportunistically replaces slow sequences with fast sequences if hard
>    registers are available.

This sounds very reasonable to me.

Kazu Hirata


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