Re: [sdcc-devel] Optimizing conditional assignments

[Steve S. <ste...@gm...>]

But shouldn't that code generate something like

JB bitvar, set;
mov return, 250;
ret;
set:
mov return, 123;
ret;

Still has branching but minimal.

I guess i did not really get what you meant...

-- 
Steve SCHNEPP


On Tue, Sep 5, 2023, 07:32 Oleg Endo <ole...@t-...> wrote:

> Hi all,
>
> For a conditional assignments, like
>
>    return bitvar ? 123 : 250;
>
> SDCC/mcs51 currently generates conditional jumps around the assignments of
> the results:
>
>         genIfx
>         genIfxJump
>         ...
> label:
>         genAssign
>         ...
> label:
>         genAssign
>         ...
> label:
>
>
> While the resulting code is probably the smallest code for mcs51, if
> branches are expensive it can be better to compute the result with
> straight-
> line code instead.
>
> I would like to try to toy with some of those ideas.  What would be the
> easiest way to capture the conditional assignment at a higher level?  E.g.
> is it possible to somehow tap into mcs51's genIfx by looking around the
> related iCodes?  Or is better to do it at the ast level?
>
> Any pointers appreciated!
>
> Cheers,
> Oleg
>
>
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