This bug showed up when I touched Data.Generics.Schemes, and then said
	make build.library.base
This compiles the base library with --make, and I got an assertion failure
in TcIface.  The explanation is in Note [Tying the knot] in TcIface.

As well as fixing the bug, I also impoved the assertion message.

This might fix or improve other knot-tying problems with --make

Figuring out which type variables to generalise when inferring the type
of a let-bound function is always trickier than I think!  This patch
fixes a bug (related, inevitably, to functional depenencies) found by
iampure, Trac #1564.  I'll add a test shortly.

$(UseStage1) modifies $(HC) rather than $(GHC)

Instead of attaching the information whether a Label is going to be
accessed dynamically or not (distinction between IdLabel/DynLabel and
additional flags in ModuleInitLabel and PlainModuleInitLabel), we hand
dflags through the CmmOpt monad and the NatM monad. Before calling
labelDynamic in PositionIndependentCode, we extract thisPackage from
dflags and supply the current package to labelDynamic, so it can take
this information into account instead of extracting it from the labels
itself. This simplifies a lot of code in codeGen that just hands
through this_pkg.

The cmm parser classified all unknown variables as imported. This
behaviour is not changed with this patch. Explicitly imported
variables get a different internal label type, namely ForeignLabel
instead of RtsLabel. In PIC compilation, the NCG creates dynamic
access for ForeignLabel, while RtsLabel are not treated as PIC when
-package rts. Hence, putting explicit imports into cmm files enables
the NCG to distinguish between RTS-external and RTS-internal symbols,
and create the appropriate code.

Fix the knot-tying in loopDecls to actually do what its comment tells: provide access to global declarations

Compacting GC interacts badly with the new pointer-tagging feature, as
it also uses the low bits of a pointer to encode some information
during a collection.  My original workaround didn't work, this more
elaborate fix should be better.

ifBuildable now returns an exit code, with 1 indicating an unbuildable
non-core package, and 0 otherwise.  Hence we can now invoke the
recursive make from the shell, sidestepping the problems in #1559 and
#1560.

* ghc-asm: Finally did away with $* in a way that works with Perl 5.6~5.10+, by appending /m to all regexes.

  
This patch implements pointer tagging as per our ICFP'07 paper "Faster
laziness using dynamic pointer tagging".  It improves performance by
10-15% for most workloads, including GHC itself.

The original patches were by Alexey Rodriguez Yakushev
<mrchebas@gmail.com>, with additions and improvements by me.  I've
re-recorded the development as a single patch.

The basic idea is this: we use the low 2 bits of a pointer to a heap
object (3 bits on a 64-bit architecture) to encode some information
about the object pointed to.  For a constructor, we encode the "tag"
of the constructor (e.g. True vs. False), for a function closure its
arity.  This enables some decisions to be made without dereferencing
the pointer, which speeds up some common operations.  In particular it
enables us to avoid costly indirect jumps in many cases.

More information in the commentary:

http://hackage.haskell.org/trac/ghc/wiki/Commentary/Rts/HaskellExecution/PointerTagging

We now have a section that describes what hs_exit() does (including
the "wait for foreign calls to return" behaviour), and more
documentation on creating libraries of Haskell code.  I also imported
the section "Beware of DllMain()!" from the haskell.org wiki, with
some minor editing.