Reorganisation of the source tree

Most of the other users of the fptools build system have migrated to
Cabal, and with the move to darcs we can now flatten the source tree
without losing history, so here goes.

The main change is that the ghc/ subdir is gone, and most of what it
contained is now at the top level.  The build system now makes no
pretense at being multi-project, it is just the GHC build system.

No doubt this will break many things, and there will be a period of
instability while we fix the dependencies.  A straightforward build
should work, but I haven't yet fixed binary/source distributions.
Changes to the Building Guide will follow, too.

1 files changed, 208 insertions, 0 deletions

diff --git a/HACKING b/HACKING
new file mode 100644
index 0000000000..cbff47d6db
--- /dev/null
+++ b/HACKING
@@ -0,0 +1,208 @@
+Getting started with hacking on GHC
+-----------------------------------
+
+So you've decided to hack on GHC, congratulations!  We hope you have a
+rewarding experience.  This file contains a few nuggets of information
+that will help get you started right away, and point you in the
+direction of more comprehensive documentation for later.
+
+
+Setting up your build
+---------------------
+
+The GHC build tree is set up so that, by default, it builds a compiler
+ready for installing and using.  That means full optimisation, and the
+build can take a *long* time.  If you unpack your source tree and
+right away say "./configure; make", expect to have to wait a while.
+
+For hacking, you want the build to be quick - quick to build in the
+first place, and quick to rebuild after making changes.  Tuning your
+build setup can make the difference between several hours to build
+GHC, and less than an hour.  Here's how to do it.
+
+mk/build.mk is a GNU makefile that contains all your build settings.
+By default, this file doesn't exist, and all the parameters are set to
+their defaults in mk/config.mk (mk/config.mk is the place to look for
+*all* the things you might want to tune).
+
+A good mk/build.mk to start hacking on GHC is:
+
+------
+SRC_HC_OPTS     = -H32m -O -fasm -Rghc-timing
+GhcStage1HcOpts = -O0 -DDEBUG
+GhcLibHcOpts    = -O -fgenerics
+GhcLibWays      =
+SplitObjs       = NO
+------
+
+What do these options do?
+
+SRC_HC_OPTS = -H32m -O -fasm -Rghc-timing
+
+  These options are added to the command line for all Haskell
+  compilations.  We turn on -fasm, because that halves compilation
+  time at the expense of a few percent performance.  -Rghc-timing
+  prints out a line of timing info about each compilation.  It's handy
+  to keep an eye on.
+
+GhcStage1HcOpts = -O0 -DDEBUG
+
+  The options for building the stage1 compiler (these come after
+  SRC_HC_OPTS, so you can override settings from there).  We turn off
+  optimisation here, assuming you'll be modifying and testing stage1.
+  With optimisation off, rebuilding GHC after modifying it will be
+  *much* quicker, not only because the individual compilations will be
+  quicker, but also there will be fewer dependencies between modules,
+  so less stuff needs to be rebuilt after each modification.
+
+  Also we turn on -DDEBUG, because that enables assertions and
+  debugging code in the compiler itself.  Turning on DEBUG makes
+  the compiler about 30% slower.
+
+GhcLibHcOpts = -O -fgenerics
+
+  You almost certainly want optimisation *on* when building
+  libraries, otherwise the code you build with this compiler
+  goes really slowly.  -fgenerics add generics support to the
+  libraries - you can turn this off if you like (it'll make the
+  libraries a bit smaller), but you won't be able to use Generics in
+  the code you build against these libraries.
+
+GhcLibWays =
+
+  Normally the profiled libs are built.  Setting GhcLibWays to
+  empty disables this, so you only build the normal libs.
+
+SplitObjs = NO
+
+  Object splitting causes each module to be split into smaller
+  pieces in the final library, to reduce executable sizes when
+  linking against the library.  It can be quite time and
+  memory-consuming, so turn it off when you're hacking.
+
+
+Actually building the bits
+--------------------------
+
+To just build everything, from the top level:
+
+  $ autoreconf
+  $ ./configure
+  $ make
+  $ make install
+
+
+Building individual parts of the tree
+-------------------------------------
+
+The first thing to understand is that the source tree is built in two
+passes.  First 'make boot' builds dependencies and any other tools
+required as part of the build itself.  For example,
+ghc/utils/genprimopcode is built as part of 'make boot', because it is
+required to preprocess ghc/compiler/prelude/primops.txt.pp.
+
+After 'make boot', 'make' will build everything.
+
+If you say 'make' from the very top-level, the build system will
+arrange to do the appropriate 'make boot' steps for you.  If you just
+want to build in a subdirectory (eg. ghc), you have to do 'make boot'
+yourself.  You don't need to 'make boot' after every single change,
+but you might want to do it to update dependencies, for example.
+
+
+Refining the setup
+------------------
+
+If you will be hacking mostly on libraries, then you probably want to
+build stage1 with optimisation, because you're only building it once
+but using it many times.
+
+  GhcStage1HcOpts = -O
+
+If you are working on GHCi or Template Haskell, then you will be
+building and modifying the stage 2 compiler.  Hence, you want to build
+stage 1 with, and stage 2 without, optimisation.
+
+  GhcStage1HcOpts = -O
+  GhcStage2HcOpts = -O0 -DDEBUG
+
+Take a look through mk/config.mk for more settings you might want to
+override in build.mk.  Remember: don't modify config.mk directly (it
+gets overwritten when you run ./configure).
+
+
+Full optimisation
+-----------------
+
+To turn up everything to the max, for running performance tests for
+example, try theses:
+
+  SRC_HC_OPTS  = -H64m -O2 
+  GhcLibHcOpts = -O2
+  SplitObjs    = YES
+
+You can even add some more aggresive options, such as
+-fliberate-case-threshold50, -funfolding-use-threshold50.
+
+
+Roadmap
+-------
+
+A rough roadmap to the source tree:
+
+ distrib        materials for building distributions
+
+ docs           build system documentation
+
+ ghc            The GHC Compiler
+   rts          the runtime system and storage manager
+   lib          libraries used in GHC and its tools
+   utils	tools that come with GHC, and tools used in the build
+   compiler     the compiler itself
+   driver       various scripts, and package databases
+   docs         compiler documentation
+   includes     header files shipped with GHC
+
+ glafp-utils    tools for the build system
+
+ libraries	The hierarchical libraries
+
+ nofib          A benchmark suite
+
+ testsuite      The regression test suite
+
+
+Resources
+---------
+
+The GHC Developer's Wiki
+
+   The home for GHC Developers, with information on accessing the latest sources,
+   the bug tracker, and further documentation on the code.
+   http://hackage.haskell.org/trac/ghc
+
+
+The Building Guide
+
+   Full documentation on the build system.
+   http://www.haskell.org/ghc/docs/latest/html/building/index.html
+
+
+The GHC Commentary
+
+   Notes on the internals and architecture of GHC.  Much of this isn't
+   up to date, but there is still lots of useful stuff in there.  Read
+   in conjunction with the source code.
+   http://www.cse.unsw.edu.au/~chak/haskell/ghc/comm/
+
+
+Mailing lists
+
+   Ask on glasgow-haskell-users@haskell.org if you have difficulties.
+   If you're working with the current CVS sources of GHC, then
+   cvs-ghc@haskell.org might be a more appropriate (developers hang
+   out here).  See http://www.haskell.org/mailman/listinfo for
+   subscription.
+
+
+Happy Hacking!  --The GHC Team