[swift-dev] -whole-module-optimization with -Onone

Ben Asher benasher44 at gmail.com
Thu Dec 1 13:51:05 CST 2016

Hello! Someone recently tipped me off to using -whole-module-optimization
flag with -Onone for use during debug builds to speed up compile times. In
our project, the speedup feels quite dramatic, but when it gets to the
linking step (after compiling both Swift and Obj-C in the project) it fails
because ld can't find the individual object files that normally get emitted
during the debug-type build presumably because -whole-module-optimization
only emits one (and this isn't a normal "-Owholemodule"-type build which
works fine).

I can't seem to reproduce this outside of Xcode, but I was curious if
anyone has tried this and knows of a workaround to get
-whole-module-optimization to work with -Onone in Xcode?

I'm currently using Xcode 8.1 (App Store build) and Swift 3 on macOS Sierra.


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