| ``incremental`` |
| Compiles each Swift source in the module separately, resulting in better |
| parallelism in the build. The compiler emits additional information into |
| the build directory improving rebuild performance when small changes are made |
| to the source between rebuilds. This is the best option to use while |
| iterating on changes in a project. |
| |
| ``wholemodule`` |
| Whole-module optimizations are slowest to compile, but results in the most |
| optimized library. The entire context is loaded into once instance of the |
| compiler, so there is no parallelism across source files in the module. |
| |
| ``singlefile`` |
| Compiles each source in a Swift modules separately, resulting in better |
| parallelism. Unlike the ``incremental`` build mode, no additional information |
| is emitted by the compiler during the build, so rebuilding after making small |
| changes to the source file will not run faster. This option should be used |
| sparingly, preferring ``incremental`` builds, unless working around a compiler |
| bug. |
