> On Nov 2, 2017, at 8:50 PM, Chris Lattner <clatt...@nondot.org> wrote: > > >> On Nov 2, 2017, at 9:52 AM, Erik Eckstein via swift-dev >> <swift-dev@swift.org> wrote: >> >> Hi, >> >> I’d like to propose to deprecate the -Ounchecked swift optimization mode. >> >> The -Ounchecked mode actually contradicts one of the main goals of swift: to >> be a safe language. >> In the past we didn’t see lot of significant performance differences >> compared to -O (there were some improvements but also some regressions). >> Also, we want to reduce the effort of maintaining too many different >> optimization modes, especially because we recently added -Osize. >> >> Deprecating would mean that we map -Ounchecked to -O. >> >> If you have any comments or concerns, please let me know > > What’s the motivation for this? What problem does it solve?
There are several issues: First, Ounchecked does not come for free. To really support this mode we would have to constantly track performance metrics for this, investigate performance/codesize regressions, etc. This is a lot of effort. So if we replace Ounchecked with an option -unsafe-remove-checks (similar to -assume-single-threaded), as Johannes suggested, this is more like a “at your own risk” thing (regarding performance). For example, it might happen that users see perf regressions from one release to another, using this option. The second thing is, IMO, that -Ounchecked suggests that it’s just another choice like -O. But I think we should encourage people to not use Ounchecked. I think it’s fine if experienced developers, who know what they are doing, use -unsafe-remove-checks, but we should not promote this mode in a prominent place like in the -O namespace. This is just my personal opinion and I’m sure some people have other opinions on this. The third issue is that we now have -Osize. The -unsafe-remove-checks would be orthogonal to -O and -Osize. BTW, we should rename -O to -Ospeed for consistency (keeping -O as an alias for -Ospeed). > > Swift isn’t a "strict safety at all costs” language. It is a pragmatic > language which aims to give people tools to solve problems. One of the nice > things about -Ounchecked is that it provides an easy way to get a data point > about the cost of runtime checks. > > -Chris >
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