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bug#42147: 28.0.50; pure vs side-effect-free, missing optimizations?
From: |
Paul Eggert |
Subject: |
bug#42147: 28.0.50; pure vs side-effect-free, missing optimizations? |
Date: |
Fri, 3 Jul 2020 11:31:19 -0700 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.8.0 |
On 7/3/20 1:32 AM, Mattias Engdegård wrote:
> In practice, the extra precision of x87 code is so unreliable and fickle
> (unless the 80-bit long double is used throughout) that it's almost never
> worth it.
Depends on whether you want reproducibility or accuracy. We prefer the former,
it seems.
> Fortunately modern compilers generate SSE code by default
No, GCC generates x87 code by default. You need to specify -mfpmath=sse to
convince it to not generate x87 code. (Or, when you build GCC, you need to pass
--with-mfpmath=sse to 'configure'; but I think this is uncommon, at least in the
GNU/Linux world.)
Having Emacs use --with-mfpmath=sse should improve performance a bit on x86. But
more important, it should make floating point more reproducible. If I get the
time I'll look into having 'configure' add it automatically.
- bug#42147: 28.0.50; pure vs side-effect-free, missing optimizations?, (continued)
- bug#42147: 28.0.50; pure vs side-effect-free, missing optimizations?, Andrea Corallo, 2020/07/08
- bug#42147: 28.0.50; pure vs side-effect-free, missing optimizations?, Mattias Engdegård, 2020/07/08
- bug#42147: 28.0.50; pure vs side-effect-free, missing optimizations?, Andrea Corallo, 2020/07/08
- bug#42147: 28.0.50; pure vs side-effect-free, missing optimizations?, Mattias Engdegård, 2020/07/09
- bug#42147: 28.0.50; pure vs side-effect-free, missing optimizations?, Stefan Monnier, 2020/07/09
- bug#42147: 28.0.50; pure vs side-effect-free, missing optimizations?, Andrea Corallo, 2020/07/09
- bug#42147: 28.0.50; pure vs side-effect-free, missing optimizations?, Stefan Monnier, 2020/07/09
- bug#42147: 28.0.50; pure vs side-effect-free, missing optimizations?, Paul Eggert, 2020/07/09
- bug#42147: 28.0.50; pure vs side-effect-free, missing optimizations?, Andrea Corallo, 2020/07/09
- bug#42147: 28.0.50; pure vs side-effect-free, missing optimizations?, Mattias Engdegård, 2020/07/05
- bug#42147: 28.0.50; pure vs side-effect-free, missing optimizations?,
Paul Eggert <=
- bug#42147: 28.0.50; pure vs side-effect-free, missing optimizations?, Mattias Engdegård, 2020/07/03
- bug#42147: 28.0.50; pure vs side-effect-free, missing optimizations?, Paul Eggert, 2020/07/04
- bug#42147: 28.0.50; pure vs side-effect-free, missing optimizations?, Eli Zaretskii, 2020/07/04
- bug#42147: 28.0.50; pure vs side-effect-free, missing optimizations?, Paul Eggert, 2020/07/04
- bug#42147: 28.0.50; pure vs side-effect-free, missing optimizations?, Stefan Monnier, 2020/07/04
- bug#42147: 28.0.50; pure vs side-effect-free, missing optimizations?, Mattias Engdegård, 2020/07/04
- bug#42147: 28.0.50; pure vs side-effect-free, missing optimizations?, Paul Eggert, 2020/07/04
- bug#42147: 28.0.50; pure vs side-effect-free, missing optimizations?, Pip Cet, 2020/07/04
- bug#42147: 28.0.50; pure vs side-effect-free, missing optimizations?, Stefan Monnier, 2020/07/04
- bug#42147: 28.0.50; pure vs side-effect-free, missing optimizations?, Pip Cet, 2020/07/04