Tracking issue for opt-level={s,z}

[alexcrichton]

Added in #32386 these options are still unstable, this issue will track their progress to becoming stable!

[alexcrichton]

Also note that rust-lang/cargo#3007 is adding Cargo support, currently through opt-level = "z" and "s", but as pointed out we may want more human readable names.

[whitequark]

I don't even think there is a single word that describes what -Oz does. As far as I know it was first introduced in clang and selected for its closeness to -Os and connotations of compression, but this doesn't help at all when you need an immediately understandable token in Cargo.toml.

[matklad]

size/size-1 for s and size-2 for z?

[Timmmm]

@matklad is right, "s" and "z" are not clear at all. I had no idea what "z" even did until I looked it up. Apparently it is the same as "s" but without loop vectorisation. According to the BSD man page it is intended to reduce size even further.

I like the "size-1"/"size-2" idea.

[bholley]

We are potentially interested in this for Gecko's integration of Rust code, see [1]. We'd need to do more measurements to determine if the performance impact is acceptable though.

[1] https://bugzilla.mozilla.org/show_bug.cgi?id=1328497

[alexcrichton]

@bholley thanks for the info! We haven't seen a lot of movement here in awhile and we've got support in Cargo/build scripts now, so I'd like to propose we stabilize this:

@rfcbot fcp merge

[rfcbot]

Team member @alexcrichton has proposed to merge this. The next step is review by the rest of the tagged teams:

• @Aatch
• @alexcrichton
• @arielb1
• @bkoropoff
• @brson
• @dotdash
• @eddyb
• @japaric
• @michaelwoerister
• @nikomatsakis
• @nrc
• @pnkfelix
• @vadimcn
• @wycats

No concerns currently listed.

Once these reviewers reach consensus, this will enter its final comment period. If you spot a major issue that hasn't been raised at any point in this process, please speak up!

See this document for info about what commands tagged team members can give me.

[nrc]

IS this properly documented? That can come after we've approved for stability, right?

[alexcrichton]

@nrc good point! I think we should definitely make sure it's documented at least in --help or the various man pages.