Bug#1095863: release.debian.org: Raising the i386 baseline for Trixie to include SSE2/MMX

[Samuel Thibault <sthibault@debian.org>]

Matthias Klose, le jeu. 13 févr. 2025 12:35:51 +0100, a ecrit:
> Mixing fp87 and SSE instructions leads to a performance penalty

When they are mixed within a function, sure.

But between functions (and actually it's even about between libraries
here, so even less often), I don't see why.

So again, I don't see why bumping in rust (which will really fix things
there) should imply bumping in the rest of the toolchain. Raising the
*allowed* i386 baseline does not suddenly force the whole toolchain to
actively try more to use more than it currently does.

> (I don't have references to that, so people might want to
> investigate).

The references I can find only talk about within a function.

> fp87 instructions also show some excess precision, so test cases and test
> suites of packages might be affected by this change as well.

Indeed. In the case of the rust toolchain, it's actually in the good
direction: upstream tests do assume not using fp87.

> Is this really worth doing that change,

To avoid the fp87 unsoundness in rust that does produce bugs, yes.

Samuel