[swift-users] Long compilation times

Diego Sánchez diego.sanchezr at gmail.com
Fri Aug 19 20:23:00 CDT 2016

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)

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