How to link with the GNU gold linker instead of ld in Haskell

Question

My Haskell project spends lots of time in Linking dist/build/myapp/myapp ... and also in loading shared libraries when executing TemplateHaskell code.

I suspect this is because ld is slow.

How can I improve link times by switching to the gold linker?

Answer 1

Link 3x faster with gold

Since GHC 7.8, you can tell GHC and cabal (at run time without having to recompile GHC) to link with GNU gold.

You need in your .cabal file:

library:
  ghc-options: -optl-fuse-ld=gold
  ld-options:  -fuse-ld=gold

executable myExecutable
  ghc-options: -optl-fuse-ld=gold
  ld-options:  -fuse-ld=gold

(Note you might want to pass these flags to stack/cabal/Setup.hs on the command line instead of hardcoding them in the .cabal file in order to not reduce the portability of the package.)

For me it's 3.5x faster, bringing down the total link time of a project from 150 seconds to 40 seconds.

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Update: Link 10x faster with lld

See https://github.com/nh2/link-with-lld-example for a full example; key parts:

library
  ghc-options: "-pgmP clang" "-pgmc clang" "-pgma clang" "-pgml clang" "-optl-fuse-ld=lld"
  ld-options:  -fuse-ld=lld

executable myExecutable
  ghc-options: "-pgmP clang" "-pgmc clang" "-pgma clang" "-pgml clang"
  ld-options:  -fuse-ld=lld

Comparison of link time for the final executable link times my project:

ld   124 seconds
gold  36 seconds
lld   11 seconds