Death To __stginit_

[Wolfgang Thaller]

The __stginit_ module initialisation functions are currently used for 
two purposes:

a) initialise foreign exports
b) initialise cost centers in profiled builds

So in non-profiled builds, they are only really needed in a few 
modules. This is inefficient because:

1) useless code (init functions that are empty except for the call to 
sub-modules) is generated
2) code from every module is swapped in at program startup
3) during static linking, a lot of modules are included in the program 
just because they are imported, even if nothing from them is used.

Number 2 is not a big problem, because most of the code gets swapped in 
anyway when the first garbage collection accesses the info tables.

Number 3 however can have a very big impact with libraries that are 
built without split-objs and/or re-export a lot of modules from one big 
parent module.

Instead of having a tree of functions which are explicitly invoked from 
the RTS at startup, we could use GCC's __attribute__((constructor)) to 
have foreign imports registered before main() is run.

Attached is a patch which makes GHC emit such 
__attribute__((constructor)) functions to .stub.c files, thus making 
__stginit_ functions unnecessary for non-profiled builds.

This greatly improves link times and executable sizes for the 
Haskell/Objective-C binding HOC (hoc.sourceforge.net) :-).

Comments?

Cheers,
	Wolfgang

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