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The term pretty printer used by :print shouldn't output 
the contents of TypeRep values, e.g. inside Dynamic values

- Fixes a bug introduced with the patch named 
  'check for unreachable code only with -DDEBUG'
- Breakage occured only without -DDEBUG (which is 'valdiate's default!)

Interface MkZipCfgCmm should now be sufficient for all construction
needs, though some identifiers are re-exported from (and explained in)
MkZipCfg.  ZipCfgCmmRep should be used only by modules involved in
analysis, optimization, or translation of Cmm programs.

(Previously, ppr had tried to make the zipper representation look as
much like the ListGraph representation as possible.  This decision was
unhelpful for debugging, so although the old code has been retained,
the new default is to tell it like it is.  It may be possible to
retire PprCmmZ one day, although it may be desirable to retain it as
the internal form becomes less readable.

Iterative coalescing interleaves conservative coalesing with the regular
simplify/scan passes. This increases the chance that nodes will be coalesced
as they will have a lower degree than at the beginning of simplify. The end
result is that more register to register moves will be eliminated in the
output code, though the iterative nature of the algorithm makes it slower
compared to non-iterative coloring.

Use -fregs-iterative  for graph coloring allocation with iterative coalescing
    -fregs-graph      for non-iterative coalescing.

The plan is for iterative coalescing to be enabled with -O2 and have a 
quicker, non-iterative algorithm otherwise. The time/benefit tradeoff
between iterative and not is still being tuned - optimal graph coloring
is NP-hard, afterall..

The term pretty printer used by :print shouldn't output 
the contents of TypeRep values, e.g. inside Dynamic values

An AP_STACK now ensures that there is at least AP_STACK_SPLIM words of
stack headroom available after unpacking the payload.  Continuations
that require more than AP_STACK_SPLIM words of stack must do their own
stack checks instead of aggregating their stack usage into the parent
frame.  I have made this change for the interpreter, but not for
compiled code yet - we should do this in the glorious rewrite of the
code generator.

    
    This flag works like -fbreak-on-exception, but only stops
    on uncaught exceptions.

A left over from the 1st GHCi debugger prototype

Somehow the "html" subdirs are gone, this change was not completely
intentional, but it is nice, anyway. Those subdirs never served any
real purpose...

MERGE TO STABLE

If it is set, we don't try to use clock_gettime

Improved the underlining of blocks.
With this patch it does:

Stopped at break020.hs:(6,20)-(7,29)
_result :: t1 () = _
5  
                     vv
6  in_another_decl _ = do line1 0
7                         line2 0
                                 ^^
8  

Instead of

Stopped at break020.hs:(6,20)-(7,29)
_result :: t1 () = _
5  
6  in_another_decl _ = do line1 0
                       ^^
7                         line2 0
                                 ^^
8  

We weren't taking into account the offset added by the line numbers:

Stopped at break020.hs:10:2-8
_result :: IO () = _
9  main = do
10    line1 0
     ^^^^^^^
11    line2 0


This patch adjusts that 

We also avoid using -fno-warn-orphans with older GHCs that don't understand
the flag.

We use this in the testsuite to find out which libraries we should run
the tests from.

This fixes the long-standing bug that prevents some code with
mutally-recursive modules from being compiled with --make and -O,
including GHC itself.  See the comments for details.

There are some additional cleanups that were forced/enabled by this
patch: I removed importedSrcLoc/importedSrcSpan: it wasn't adding any
useful information, since a Name already contains its defining Module.
In fact when re-typechecking an interface file we were wrongly
replacing the interesting SrcSpans in the Names with boring
importedSrcSpans, which meant that location information could degrade
after reloading modules.  Also, recreating all these Names was a waste
of space/time.

MERGE TO STABLE

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