[swift-users] Long compilation times

Diego Sánchez diego.sanchezr at gmail.com
Tue Aug 23 08:34:28 CDT 2016

I haven't been able to synthesise a project where this reproduces that
badly *yet*. Anyways I've filled https://bugs.swift.org/browse/SR-2461 with
some more info in case it helps.


2016-08-22 21:47 GMT+01:00 Michael Gottesman <mgottesman at apple.com>:

> On Aug 19, 2016, at 9:23 PM, Diego Sánchez via swift-users <
> swift-users at swift.org> wrote:
> Hi all,
> We're suffering from very long Swift compilation times in our project.
> Each file takes ~1 second to compile (-Onone), (measured with xctool -jobs
> 1), which is hitting our development experience as we keep adding swift
> code (~350 .swift files) :(
> I've gone through all the googling already and the
> debug-time-function-bodies thing, but I didn't find any particular function
> taking too long. However, I did notice:
>  a) Each file takes more or less the same amount of time to compile (~1
> second), even for very simple files.
>  b) Each "swift -frontend -c" command with the debug-time-function-bodies
> dumps basically the same info for each file, which is around 1500 lines.
> Most of the times are 0.0ms, and the total sum for a random choice gave me
> 167.3 ms, far away from 1 second
> From a) and b) looks like the same heavy operation is being performed for
> each file (type checking?) and that this heavy operation grows with the
> size of the project. Would it be possible to do this upfront and not pay
> for it in every file? Basically, if I have 3 classes in one file it will
> take 1 second to compile them but if I do 1 file per class then it will be
> 3 seconds :(
> I'd like some input to whether my assumption is correct and suggestions on
> how to improve the compilation time, apart from splitting the code into
> smaller frameworks. Can I expect improvements with Swift 3 or future
> releases? (I tried migrating a small framework to Swift 3 and didn't see a
> big difference)
> Do you have a small example of this? Can you file a bug on bugs.swift.org?
> Then we can look at your specific example.
> Cheers,
> Diego
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