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" mailto:conrad@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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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 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" mailto:conrad@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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