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Fixes some gratuitous warnings when compiling via C with -fhpc

I misread the code, now added a comment to explain why it isn't necessary

For some reason the C-- version of recordMutable wasn't verifying that
the object was in an old generation before attempting to add it to the
mutable list, and this broke maessen_hashtab.  This version of
recordMutable is only used in unsafeThaw#.

These changes were apparently lost during "massive changes to add a
'zipper' representation of C-"

MERGE TO STABLE

* A bug reported by Andrew Appleyard revealed that subFunTys did take
  neither type families nor equalities into account.  In a fairly obscure
  case there was also a coercion ignored.

Also common-up some duplicate bits in the platform-specific code

The massive 'Uni' program produced a situation in which a function that
had a worker/wrapper split was chosen as a loop breaker.  If the worker
is exposed in the interface file, then an importing module may go into
an inlining loop: see comments on TidyPgm.tidyWorker.

This patch fixes the inlining bug.  The code that gives rise to this
bizarre case is still not good (it's a bunch of implication constraints
and we are choosing a bad loop breaker) but the first thing is to fix the
bug.

It's rather hard to produce a test case!

Please merge to the 6.8 branch.

See Note [Arrows and patterns] in TcPat.  

This fixes Trac 1662.   Test is arrows/should_compile/arrowpat.hs

Please merge

This patch implements three new features:
* view patterns (syntax: expression -> pat in a pattern)
* working versions of record wildcards and record puns
See the manual for detailed descriptions.

Other minor observable changes:
* There is a check prohibiting local fixity declarations
  when the variable being fixed is not defined in the same let
* The warn-unused-binds option now reports warnings for do and mdo stmts

Implementation notes: 

* The pattern renamer is now in its own module, RnPat, and the
implementation is now in a CPS style so that the correct context is
delivered to pattern expressions.

* These features required a fairly major upheaval to the renamer.
Whereas the old version used to collect up all the bindings from a let
(or top-level, or recursive do statement, ...) and put them into scope
before renaming anything, the new version does the collection as it
renames.  This allows us to do the right thing with record wildcard
patterns (which need to be expanded to see what names should be
collected), and it allows us to implement the desired semantics for view
patterns in lets.  This change had a bunch of domino effects brought on
by fiddling with the top-level renaming.

* Prior to this patch, there was a tricky bug in mkRecordSelId in HEAD,
which did not maintain the invariant necessary for loadDecl.  See note
[Tricky iface loop] for details.

Now allocate() is a synonym for allocateInGen().  

I also made various cleanups: there is now less special-case code for
supporting -G1 (two-space collection), and -G1 now works with
-threaded.

we now have
Processing Coverage files:
  sum         Sum multiple .tix files in a single .tix file
  combine     Combine two .tix files in a single .tix file
  map         Map a function over a single .tix file

Where sum joins many .tix files, combine joins two files (with
extra functionality possible), and map just applied a function
to single .tix file.

These changes were improvements driven by hpc use cases.

END OF DESCRIPTION***

Place the long patch description above the ***END OF DESCRIPTION*** marker.
The first line of this file will be the patch name.


This patch contains the following changes:

M ./utils/hpc/Hpc.hs -1 +3
M ./utils/hpc/HpcCombine.hs -33 +84
M ./utils/hpc/HpcFlags.hs -11 +59

For some reason TcSimplify.extractResults is quite difficult to get right.
This is another attempt; finally I think I have it.

Strangely enough, it's only Sergey's DoCon program that shows up the
bug, which manifested as a failure in the Simplifier

        lookupRecBndr $dGCDRing{v a1Lz} [lid]

But it was due to extractResults producing multiple bindings for
the same dictionary.

Please merge this to the stable branch (after previous patches to
TcSimplify though).

Previously MVars were always on the mutable list of the old
generation, which meant every MVar was visited during every minor GC.
With lots of MVars hanging around, this gets expensive.  We addressed
this problem for MUT_VARs (aka IORefs) a while ago, the solution is to
use a traditional GC write-barrier when the object is modified.  This
patch does the same thing for MVars.

TVars are still done the old way, they could probably benefit from the
same treatment too.

This fixes the unreg build, and in general building the RTS code
via-C. I'm not sure at what stage this was broken, but I think it
was working accidentally before.

GHC spots that an 'otherwise' guard is true, and uses that knowledge to 
avoid reporting spurious missing-pattern or overlaps with -Wall.

The HPC ticks were disguising the 'otherwise', which led to this failure.
Now we check.  The key change is defining DsGRHSs.isTrueLHsExpr.

Test is ds062

There are a number of situations in which you aren't allowed to use
a quoted Name in a TH program, such as
	\x -> 'x
But we weren't checking for that!  Now we are.

Merge to stable branch.

Test is TH_qname.