[swift-dev] deprecating -Ounchecked

[Johannes Weiß]

Definitely a +1 from me, a haven't recently seen much of a difference either.

Said that I do sometimes use it in a micro-benchmark just to convince myself we don't lose much performance on the checks. Usually it turns out fine, I'm happy and move on. But I guess there's some value in being able to elide a lot of checks just to see how much of a difference it does. And if there's a big difference then I'd try to optimise the program and elide unnecessary checks myself. Clearly -Ounchecked should never be used in any real code but I find having a baseline when optimising performance very helpful and -Ounchecked sometimes seemed like a cheap, automatic baseline for some code ;).

And lastly I always thought having it as an 'optimisation' is a misnomer, it's not an optimisation as it clearly changes the semantics of the program quite a bit. I thought '-unsafe-remove-checks' or something describes it better, a bit like '-assume-single-threaded'. But probably the 'no checks' mode adds too much complexity to just keep it around for a questionable way to do performance baselines.

> On 2 Nov 2017, at 9:52 am, Erik Eckstein via swift-dev <swift-dev at 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
> 
> Thanks,
> Erik
> 
> 
> 
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