Re: Statically linking a small piece of C into every GHC generated binary

2011/7/19 Johan Tibell :

On Tue, Jul 19, 2011 at 6:02 PM, Johan Tibell wrote:

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I've implemented the primop but run into some difficulty: to use the above fallback I need the code to be statically linked into every binary. I'm not quite sure how to achieve that.

If dynamic linking doesn't hurt performance (too much). Could I stick this piece of C code in ghc-prim? Are we guaranteed to always link against ghc-prim?

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GCC manages by having the above function definition in libc, which is always statically linked.

I just realized that this isn't true. I wonder if GCC's __builtin_popcount suffers a performance degradation when libc is dynamically linked.

I assume you meant libgcc and not libc. I think the linking is a bit of a red herring, ideally they want to inline it and that requires LTO and static linking and GHC can't do LTO anyway. There should be little overhead (one extra jump, a cycle or two) in calling a dynamically linked function compared to a non-inlined statically linked one. One small advantage of static linking is that the functions won't be included if they're not used.

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I think LLVM uses a small statically linked compiler run-time library for the same purpose.

However I believe this is the case still. I'll need to doublecheck.

Johan

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Cheers, Niklas