Stack: enable-split-objs

[tinkyholloway]

Feature request

(Apparently) there is a cabal configure option --enable-split-objs that passes --split-objs to ghc for project sources and dependencies. This creates one object file per function and therefore can reduce the size of resulting binaries as the linker only includes necessary objects files (functions).

The cabal configure --enable-split-objs is cited as a solution to the "large binary" problem (http://stackoverflow.com/questions/9198112/haskell-unnecessary-binary-growth-with-module-imports/9198223#9198223, http://stackoverflow.com/questions/6115459/small-haskell-program-compiled-with-ghc-into-huge-binary/6115703#6115703, http://stackoverflow.com/questions/12019072/compilation-dependencies-and-executable-size-with-ghc-in-linux/12019307#12019307) and there are deployments where a reduced size, statically linked binary is preferred.

[borsboom]

I agree, this would be a good enhancement. A pull request would be welcome.

[mgsloan]

Should split-objs be on by default? AFAIK the tradeoff is between compilation time and output size. I wonder how large the impact to compiletime is.

[mgsloan]

Initial support done, with the following caveats:

Building with --split-objs is enabled. Note that this feature is EXPERIMENTAL, and its behavior may be changed and improved. You will need to clean your workdirs befure use. If you want to compile all dependencies with split-objs, you will need to delete the snapshot (and all snapshots that could reference that snapshot.

This will hopefully be improved by the resolution of the cluster of issues around https://github.com/commercialhaskell/stack/issues/1265 .

I actually got a segmentation fault out of stack built with --split-objs (but not its deps), so I'm not sure if this stuff is fully reliable (another reason for the EXPERIMENTAL marking). Doing another --split-objs build did not reproduce the issue.

[mgsloan]

Till #1265 is addressed, if you want to use split-objs all the time and don't want to worry about clearing out snapshots so that they can be rebuilt, then a good approach is to add the following to your config.yaml:

build:
  split-objs: true