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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.