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Re: Question regarding constraint usage within inline asm


On Mon, 25 Feb 2019, Segher Boessenkool wrote:

> Yup.  All good points, I didn't think this through enough obviously.
> The _1+_1 isn't great if that single pseudo then ends up in mem (it will 
> need a reload again on most archs, probably causing another spill), btw.

But at least it'll get only a single reload, not two ...

> You get worse code that way.  Reload is much too late to make optimised
> code, and that isn't its task anyway: its task is to make something that
> works where the passes before it couldn't manage.

... but yes, if we're entering the optimization- (in difference to 
correctness-) territory, then sure, expand (or any other pass between it 
and reload) might want to handle some sitations in a special way to ensure 
good code with the least amount of work.

> Yes, reload should be able to fix up anything (well, within some 
> limits). That is not an excuse to generate code that we know will need 
> such fixups though.

(Within some limits :) ), I agree.


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