recompilation on --main-is

[Conrad Parker]

Hi Simon,

I've tested with current master (commit 6f4a073) and the link time is
back down. In fact the compile time seems fast in general, and an
unrelated ld error which I hadn't yet tracked down has disappeared
too.

Thanks for the quick patch!

Conrad.

On 16 February 2012 19:45, Simon Marlow <marlowsd at gmail.com> wrote:
> Will be fixed in 7.4.2:
>
> http://hackage.haskell.org/trac/ghc/ticket/5878
>
> Cheers,
>        Simon
>
>
> On 16/02/2012 05:10, Evan Laforge wrote:
>>
>> Thanks for bringing this up. I've been having the same problem and was
>> thinking there was something wrong with my system. I have 3 main files
>> and one util that they all import. Every build recompiles every file,
>> even if there were no changes.
>>
>> On Feb 15, 2012 8:39 PM, "Conrad Parker" <conrad at metadecks.org
>> <mailto:conrad at metadecks.org>> wrote:
>>
>>    Hi,
>>
>>    We have a project with around 200 Haskell source files, and around 20
>>    executables which import these (as well as importing third-party
>>    libraries). We first build all the non-main files using a makefile
>>    generated with ghc -M. We then build the executables using a separate
>>    invocation of "ghc --make --main-is foo.hs", for each foo.hs. This
>>    worked fine with ghc-7.2.1; each final "ghc --make" would simply link
>>    the pre-built object files -- but with ghc-7.4.1 all these files are
>>    recompiled for each target executable. As a result our full build
>>    takes around 10-20x longer with ghc-7.4.1 than ghc-7.2.1.
>>
>>    Looking at compiler/iface/FlagChecker.hs, it seems that the --main-is
>>    flag is used as an input to the recompilation checker. It would make
>>    sense that --main-is should force recompilation of the particular file
>>    that exports 'main', but it also forces recompilation of its
>>    dependencies. Is this a bug or is there a good reason to recompile
>>    everything?
>>
>>    Conrad.
>>
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