GitLab

o Fixed bug that emitted the copy-in code for closure entry
  in the wrong place -- at the initialization of the closure.
o Refactored some of the closure entry code.
o Added code to check that no LocalRegs are live-in to a procedure
   -- trip up some buggy programs earlier
o Fixed environment bindings for thunks
   -- we weren't (re)binding the free variables in a thunk
o Fixed a bug in proc-point splitting that dropped some updates
  to the entry block in a procedure.
o Fixed improper calls to code that generates CmmLit's for strings
o New invariant on cg_loc in CgIdInfo: the expression is always tagged
o Code to load free vars on entry to a thunk was (wrongly) placed before
  the heap check.
o Some of the StgCmm code was redundantly passing around Id's
  along with CgIdInfo's; no more.
o Initialize the LocalReg's that point to a closure before allocating and
  initializing the closure itself -- otherwise, we have problems with
  recursive closure bindings
o BlockEnv and BlockSet types are now abstract.
o Update frames:
  - push arguments in Old call area
  - keep track of the return sp in the FCode monad
  - keep the return sp in every call, tail call, and return
      (because it might be different at different call sites,
       e.g. tail calls to the gc after a heap check are performed
            before pushing the update frame)
  - set the sp appropriately on returns and tail calls
o Reduce call, tail call, and return to a single LastCall node
o Added slow entry code, using different calling conventions on entry and tail call
o More fixes to the calling convention code.
  The tricky stuff is all about the closure environment: it must be passed in R1,
  but in non-closures, there is no such argument, so we can't treat all arguments
  the same way: the closure environment is special. Maybe the right step forward
  would be to define a different calling convention for closure arguments.
o Let-no-escapes need to be emitted out-of-line -- otherwise, we drop code.
o Respect RTS requirement of word alignment for pointers
  My stack allocation can pack sub-word values into a single word on the stack,
  but it wasn't requiring word-alignment for pointers. It does now,
  by word-aligning both pointer registers and call areas.
o CmmLint was over-aggresively ruling out non-word-aligned memory references,
  which may be kosher now that we can spill small values into a single word.
o Wrong label order on a conditional branch when compiling switches.
o void args weren't dropped in many cases.
  To help prevent this kind of mistake, I defined a NonVoid wrapper,
  which I'm applying only to Id's for now, although there are probably
  other good candidates.
o A little code refactoring: separate modules for procpoint analysis splitting, 
  stack layout, and building infotables.
o Stack limit check: insert along with the heap limit check, using a symbolic
  constant (a special CmmLit), then replace it when the stack layout is known.
o Removed last node: MidAddToContext 
o Adding block id as a literal: means that the lowering of the calling conventions
  no longer has to produce labels early, which was inhibiting common-block elimination.
  Will also make it easier for the non-procpoint-splitting path.
o Info tables: don't try to describe the update frame!
o Over aggressive use of NonVoid!!!!
  Don't drop the non-void args before setting the type of the closure!!!
o Sanity checking:
  Added a pass to stub dead dead slots on the stack
  (only ~10 lines with the dataflow framework)
o More sanity checking:
  Check that incoming pointer arguments are non-stubbed.
  Note: these checks are still subject to dead-code removal, but they should
  still be quite helpful.
o Better sanity checking: why stop at function arguments?
  Instead, in mkAssign, check that _any_ assignment to a pointer type is non-null
  -- the sooner the crash, the easier it is to debug.
  Still need to add the debugging flag to turn these checks on explicitly.
o Fixed yet another calling convention bug.
  This time, the calls to the GC were wrong. I've added a new convention
  for GC calls and invoked it where appropriate.
  We should really straighten out the calling convention stuff:
    some of the code (and documentation) is spread across the compiler,
    and there's some magical use of the node register that should really
    be handled (not avoided) by calling conventions.
o Switch bug: the arms in mkCmmLitSwitch weren't returning to a single join point.
o Environment shadowing problem in Stg->Cmm:
  When a closure f is bound at the top-level, we should not bind f to the
  node register on entry to the closure.
  Why? Because if the body of f contains a let-bound closure g that refers
  to f, we want to make sure that it refers to the static closure for f.
  Normally, this would all be fine, because when we compile a closure,
  we rebind free variables in the environment. But f doesn't look like
  a free variable because it's a static value. So, the binding for f
  remains in the environment when we compile g, inconveniently referring
  to the wrong thing.
  Now, I bind the variable in the local environment only if the closure is not
  bound at the top level. It's still okay to make assumptions about the
  node holding the closure environment; we just won't find the binding
  in the environment, so code that names the closure will now directly
  get the label of the static closure, not the node register holding a
  pointer to the static closure.
o Don't generate bogus Cmm code containing SRTs during the STG -> Cmm pass!
  The tables made reference to some labels that don't exist when we compute and
  generate the tables in the back end.
o Safe foreign calls need some special treatment (at least until we have the integrated
  codegen). In particular:
  o they need info tables
  o they are not procpoints -- the successor had better be in the same procedure
  o we cannot (yet) implement the calling conventions early, which means we have
    to carry the calling-conv info all the way to the end
o We weren't following the old convention when registering a module.
  Now, we use update frames to push any new modules that have to be registered
  and enter the youngest one on the stack.
  We also use the update frame machinery to specify that the return should pop
  the return address off the stack.
o At each safe foreign call, an infotable must be at the bottom of the stack,
  and the TSO->sp must point to it.
o More problems with void args in a direct call to a function:
  We were checking the args (minus voids) to check whether the call was saturated,
  which caused problems when the function really wasn't saturated because it
  took an extra void argument.
o Forgot to distinguish integer != from floating != during Stg->Cmm
o Updating slotEnv and areaMap to include safe foreign calls
  The dataflow analyses that produce the slotEnv and areaMap give
  results for each basic block, but we also need the results for
  a safe foreign call, which is a middle node.
  After running the dataflow analysis, we have another pass that
  updates the results to includ any safe foreign calls.
o Added a static flag for the debugging technique that inserts
  instructions to stub dead slots on the stack and crashes when
  a stubbed value is loaded into a pointer-typed LocalReg.
o C back end expects to see return continuations before their call sites.
  Sorted the flowgraphs appropriately after splitting.
o PrimOp calling conventions are special -- unlimited registers, no stack
  Yet another calling convention...
o More void value problems: if the RHS of a case arm is a void-typed variable,
  don't try to return it.
o When calling some primOp, they may allocate memory; if so, we need to
  do a heap check when we return from the call.

This merge does not turn on the new codegen (which only compiles
a select few programs at this point),
but it does introduce some changes to the old code generator.

The high bits:
1. The Rep Swamp patch is finally here.
   The highlight is that the representation of types at the
   machine level has changed.
   Consequently, this patch contains updates across several back ends.
2. The new Stg -> Cmm path is here, although it appears to have a
   fair number of bugs lurking.
3. Many improvements along the CmmCPSZ path, including:
   o stack layout
   o some code for infotables, half of which is right and half wrong
   o proc-point splitting

This patch entails a major restructuring of HscMain and a small bugfix
to MkIface (which required the restructuring in HscMain).

In MkIface:

  - mkIface* no longer outputs orphan warnings directly and also no
    longer quits GHC when -Werror is set.  Instead, errors are
    reported using the common IO (Messages, Maybe result) scheme.

In HscMain:

  - Get rid of the 'Comp' monad.  This monad was mostly GhcMonad + two
    reader arguments, a ModSummary for the currently compiled module
    and a possible old interface.  The latter actually lead to a small
    space-leak since only its hash was needed (to check whether the
    newly-generated interface file was the same as the original one).

    Functions originally of type 'Comp' now only take the arguments
    that they actually need.  This leads to slighly longer argument
    lists in some places, however, it is now much easier to see what
    is actually going on.

  - Get rid of 'myParseModule'.  Rename 'parseFile' to 'hscParse'.

  - Join 'deSugarModule' and 'hscDesugar' (keeping the latter).

  - Rename 'typecheck{Rename}Module{'}' to 'hscTypecheck{Rename}'.
    One variant keeps the renamed syntax, the other doesn't.

  - Parameterise 'HscStatus', so that 'InteractiveStatus' is just a
    different parameterisation of 'HscStatus'.

  - 'hscCompile{OneShot,Batch,Nothing,Interactive}' are now
    implemented using a (local) typeclass called 'HsCompiler'.  The
    idea is to make the common structure more obvious.  Using this
    typeclass we now have two functions 'genericHscCompile' (original
    'hscCompiler') and 'genericHscRecompile' (original 'genComp')
    describing the default pipeline.  The methods of the typeclass
    describe a sort of "hook" interface (in OO-terms this would be
    called the "template method" pattern).

    One problem with this approach is that we parameterise over the
    /result/ type which, in fact, is not actually different for
    "nothing" and "batch" mode.  To avoid functional dependencies or
    associated types, we use type tags to make them artificially
    different and parameterise the type class over the result type.
    A perhaps better approach might be to use records instead.
    
  - Drop some redundant 'HscEnv' arguments.  These were likely
    different from what 'getSession' would return because during
    compilation we temporarily set the module's DynFlags as well as a
    few other fields.  We now use the 'withTempSession' combinator to
    temporarily change the 'HscEnv' and automatically restore the
    original session after the enclosed action has returned (even in
    case of exceptions).

  - Rename 'hscCompile' to 'hscGenHardCode' (since that is what it
    does).

Calls in 'GHC' and 'DriverPipeline' accordingly needed small
adaptions.

A missing case (for equality predicates) in isOverloadedTy make
bindInstsOfLocalFuns/Pats do the wrong thing.  Core Lint nailed it.

Merge to 6.10 branch.

Particularly boolean expresions: the conditional of an 'if', and
guards, were missing their free variables.

Currently it only affects the -t flag output

It now uses the standard warning log and error reporting mechanism.

Previously, the GC had its own pool of threads to use as workers when
doing parallel GC.  There was a "leader", which was the mutator thread
that initiated the GC, and the other threads were taken from the pool.

This was simple and worked fine for sequential programs, where we did
most of the benchmarking for the parallel GC, but falls down for
parallel programs.  When we have N mutator threads and N cores, at GC
time we would have to stop N-1 mutator threads and start up N-1 GC
threads, and hope that the OS schedules them all onto separate cores.
It practice it doesn't, as you might expect.

Now we use the mutator threads to do GC.  This works quite nicely,
particularly for parallel programs, where each mutator thread scans
its own spark pool, which is probably in its cache anyway.

There are some flag changes:

  -g<n> is removed (-g1 is still accepted for backwards compat).
  There's no way to have a different number of GC threads than mutator
  threads now.

  -q1       Use one OS thread for GC (turns off parallel GC)
  -qg<n>    Use parallel GC for generations >= <n> (default: 1)

Using parallel GC only for generations >=1 works well for sequential
programs.  Compiling an ordinary sequential program with -threaded and
running it with -N2 or more should help if you do a lot of GC.  I've
found that adding -qg0 (do parallel GC for generation 0 too) speeds up
some parallel programs, but slows down some sequential programs.
Being conservative, I left the threshold at 1.

ToDo: document the new options.

Parse errors during dependency analysis or options parsing really
shouldn't kill GHC; this is particularly annoying for GHC API clients.

After a deadlock it was possible for the timer signal to remain off,
which meant that the next deadlock would not be detected, and the
system would hang.  Spotted by conc047(threaded2).

Also avoid padding if possible using __attribute__((packed))
Fixes the Windows build

I discovered a new invariant while experimenting (blackholing is not
optional when using parallel GC), so documented it.

Fixes crashes when using reclaimSpark() (not used currently, but may
be in the future).

If we're using the system's installed GMP, we don't want to be picking
up the local gmp.h header file.

Fixes 2469(ghci) for me, because it turns out the system's GMP is more
up-to-date than GHC's version and has a fix for more recent versions
of gcc.  We also need to pull in a more recent GMP, but that's a
separte issue.

There were races between workerTaskStop() and freeTaskManager(): we
need to be sure that all Tasks have exited properly before we start
tearing things down.  This isn't completely straighforward, see
comments for details.

Eager blackholing can improve parallel performance by reducing the
chances that two threads perform the same computation.  However, it
has a cost: one extra memory write per thunk entry.  

To get the best results, any code which may be executed in parallel
should be compiled with eager blackholing turned on.  But since
there's a cost for sequential code, we make it optional and turn it on
for the parallel package only.  It might be a good idea to compile
applications (or modules) with parallel code in with
-feager-blackholing.

ToDo: document -feager-blackholing.

At some point we regressed on detecting simple black-hole loops.  This
happened due to the introduction of duplicate-work detection for
parallelism: a black-hole loop looks very much like duplicate work,
except it's duplicate work being performed by the very same thread.
So we have to detect and handle this case.

On x86_64, the RTS needs to allocate memory in the low 2Gb of the
address space.  On Linux we can do this with MAP_32BIT, but sometimes
this doesn't work (#2512) and other OSs don't support it at all
(#2063).  So to work around this:

  - Try MAP_32BIT first, if available.

  - Otherwise, try allocating memory from a fixed address (by default
    1Gb)

  - We now provide an option to configure the address to allocate
    from.  This allows a workaround on machines where the default
    breaks, and also provides a way for people to test workarounds
    that we can incorporate in future releases.

If we encounter a runnable thread during shutdown, just kill it.  All
the threads are supposed to be dead at this stage, but this catches
threads that might have just returned from a foreign call, or were
finalizers created by the GC.

Fixes memo002(threaded1)

Based on a patch from juhpetersen.