GNU bug report logs - #42147
28.0.50; pure vs side-effect-free, missing optimizations?

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From: Stefan Monnier <monnier <at> iro.umontreal.ca>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: mattiase <at> acm.org, Paul Eggert <eggert <at> cs.ucla.edu>, andrea_corallo <at> yahoo.it, pipcet <at> gmail.com, 42147 <at> debbugs.gnu.org
Subject: bug#42147: 28.0.50; pure vs side-effect-free, missing optimizations?
Date: Sun, 05 Jul 2020 11:30:47 -0400

> That's not what I meant: I meant "non-standard" in the sense that the
> compiler doesn't generate these instructions by default when dealing
> with FP calculations.

It depends on the architecture you generate for.
It's clear that when that architecture is too old to include SSE2
instructions, GCC won't use SSE2 instructions (tho it still could at the cost
of runtime tests for the presence of the feature).

I don't know what GCC does if the target architecture is recent enough
to include SSE2, but I'd expect it to then use SSE2 for most/all
floating point operations since it generally leads to more efficient
code (and it's easier for GCC to generate efficient code with it).

>> I suspect they think x86 is on its way out and not worth worrying about.
> Then why won't we do the same, and simply ignore the issue?

Sounds good to me,


        Stefan

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