GitLab

Commit 3fcf5bdf made the output of
-ddump-rule-firings and -ddump-rule-rewrites excessively verbose.

Fixed by removing the extra blank lines and separator when the header
of dump is empty.

Make -ddump-rules, -ddump-rule-firings and -ddump-rule-rewrites
behave like the other -ddump flags, by using the dumpSDoc function
instance of pprDefiniteTrace.

Simon Peyton Jones authored May 27, 2012 and chak@cse.unsw.edu.au. committed Jun 27, 2012

Silent superclass parameters solve the problem that
the superclasses of a dicionary construction can easily
turn out to be (wrongly) bottom.  The problem and solution
are described in
   Note [Silent superclass arguments] in TcInstDcls

I first implemented this fix (with Dimitrios) in Dec 2010, but removed
it again in Jun 2011 becuase we thought it wasn't necessary any
more. (The reason we thought it wasn't necessary is that we'd stopped
generating derived superclass constraints for *wanteds*.  But we were
wrong; that didn't solve the superclass-loop problem.)

So we have to re-implement it.  It's not hard.  Main features:

  * The IdDetails for a DFunId says how many silent arguments it has

  * A DFunUnfolding describes which dictionary args are
    just parameters (DFunLamArg) and which are a function to apply
    to the parameters (DFunPolyArg).  This adds the DFunArg type
    to CoreSyn

  * Consequential changes to IfaceSyn.  (Binary hi file format changes
    slightly.)

  * TcInstDcls changes to generate the right dfuns

  * CoreSubst.exprIsConApp_maybe handles the new DFunUnfolding

The thing taht is *not* done yet is to alter the vectoriser to
pass the relevant extra argument when building a PA dictionary.

To help with this, we now also pass DynFlags around inside the SpecM
monad.

By using Haskell's debugIsOn rather than CPP's "#ifdef DEBUG", we
don't need to kludge things to keep the warning checker happy etc.

* Put the result type in the Stop continuation
* No need for the alts type in Select

The result is a modest but useful simplification

This patch allows, for the first time, case expressions with an empty
list of alternatives. Max suggested the idea, and Trac #6067 showed
that it is really quite important.

So I've implemented the idea, fixing #6067. Main changes

 * See Note [Empty case alternatives] in CoreSyn

 * Various foldr1's become foldrs

 * IfaceCase does not record the type of the alternatives.
   I added IfaceECase for empty-alternative cases.

 * Core Lint does not complain about empty cases

 * MkCore.castBottomExpr constructs an empty-alternative case
   expression   (case e of ty {})

 * CoreToStg converts '(case e of {})' to just 'e'

This reverts commit 745ec959.

Sigh. Seg fault

This reverts commit e3f8557c.

Sigh. Seg fault.

In the previous commit about "aggressive primops" I wanted a new
function CoreUtils.exprCertainlyTerminates.  In doing this I ended up
with a significant refactoring in CoreUtils.  The new structure has
quite a lot of nice sharing:

         exprIsCheap             = exprIsCheap' isHNFApp
         exprIsExpandable        = exprIsCheap' isConLikeApp

         exprIsHNF               = exprIsHNFlike isHNFApp
         exprIsConLike           = exprIsHNFlike isConLikeApp
         exprCertainlyTerminates = exprIsHNFlike isTerminatingApp

This patch also does some renaming

    CheapAppFun      -->   FunAppAnalyser
    isCheapApp       -->   isHNFApp
    isExpandableApp  -->   isConLikeApp

I'm experimenting with making GHC a bit more aggressive about

  a) dropping case expressions if the result is unused
        Simplify.rebuildCase, CaseElim equation

  b) floating case expressions inwards
        FloatIn.fiExpr, AnnCase

In both cases the new behaviour is gotten with a static (debug)
flag -faggressive-primops.  The extra "aggression" is to allow
discarding and floating in for side-effecting operations.  See
the new, extensive Note [PrimOp can_fail and has_side_effects]
and Note [Aggressive PrimOps] in PrimoOp.

When discarding a case with unused binders, in the lifted-type
case it's definitely ok if the scrutinee terminates; previously
we were checking exprOkForSpeculation, which is significantly
worse.

There's a related change to CoreUtils/CoreArity, but I'll put that
in the next commit.

Makes the following changes:
 1. Generalises the type signatures of some functions relating to alternatives
    so that the type of "variables" and "expression" is not specified
 2. Puts the bulk of the alternative-filtering code into a new function filterAlts
    (in CoreUtils) that can be used outside of the SimplM monad
 3. Allows prepareAlts to return a null alternatives list if none are applicable -
    it turns out that this case was already handled by the caller (in the simplifier).
    This should result in a modest optimisation improvement in some cases.

Conflicts:

	compiler/coreSyn/CoreUtils.lhs
	compiler/simplCore/SimplUtils.lhs

(Roman wanted this.)

This reverts commit 601c983d.

I'm experimenting with making GHC a bit more aggressive about
  a) dropping case expressions if the result is unused
        Simplify.rebuildCase, CaseElim equation

  b) floating case expressions inwards
        FloatIn.fiExpr, AnnCase

In both cases the new behaviour is gotten with a static (debug)
flag -faggressive-primops.  The extra "aggression" is to allow
discarding and floating in for side-effecting operations.  See
the new, extensive Note [PrimOp can_fail and has_side_effects]
in PrimoOp.

When discarding a case with unused binders, in the lifted-type
case it's definitely ok if the scrutinee terminates; previously
we were checking exprOkForSpeculation, which is significantly
worse.

So I wanted a new function CoreUtils.exprCertainlyTerminates.
In doing this I ended up with a significant refactoring in
CoreUtils.  The new structure has quite a lot of nice sharing:

    exprIsCheap             = exprIsCheap' isHNFApp
    exprIsExpandable        = exprIsCheap' isConLikeApp

    exprIsHNF               = exprIsHNFlike isHNFApp
    exprIsConLike           = exprIsHNFlike isConLikeApp
    exprCertainlyTerminates = exprIsHNFlike isTerminatingApp

Two changes here

* The main change here is to enhance the FloatIn pass so that it can
  float case-bindings inwards.  In particular the case bindings for
  array indexing.

* Also change the code in Simplify, to allow a case on array
  indexing (ie can_fail is true) to be discarded altogether if its
  results are unused.

Lots of new comments in PrimOp about can_fail and has_side_effects

Some refactoring to share the FloatBind data structure between
FloatIn and FloatOut

Otherwise the RHS is utterly bogus.  I also added some asserts.
Thanks to Max for pointing this out.

We had some special cases to handle things like

  case (scc c (case E of alts)) of alts'

but it only worked when there was a single scc in the way.  This
generalises the optimisation to handle multiple sccs and ticks, so
that we can catch most case-of-case optimisations that would normally
apply in the absence of profiling.

This fixes the example in #5363, and nofib results (with -prof
-fprof-auto) show that allocation universally goes down or stays the
same.

See comments for details

This big patch implements a kind-polymorphic core for GHC. The current
implementation focuses on making sure that all kind-monomorphic programs still
work in the new core; it is not yet guaranteed that kind-polymorphic programs
(using the new -XPolyKinds flag) will work.

For more information, see http://haskell.org/haskellwiki/GHC/Kinds

Fixes some core-lint errors when compiling with profiling

...and make sure it is, esp in the call to findAlt in
the mighty Simplifier.  Failing to check this led to
searching a bunch of DataAlts for a LitAlt Integer.
Naughty.  See Trac #5603 for a case in point.

We want to prevent the SCC from getting in the way when we have
case-of-scc-of-case, and the case-of-case would transform, so we push
the scc inside the inner case to allow the case-of-case to take
place.  See comments for details.

We only use it for "compiler" sources, i.e. not for libraries.
Many modules have a -fno-warn-tabs kludge for now.

User visible changes
====================

Profilng
--------

Flags renamed (the old ones are still accepted for now):

  OLD            NEW
  ---------      ------------
  -auto-all      -fprof-auto
  -auto          -fprof-exported
  -caf-all       -fprof-cafs

New flags:

  -fprof-auto              Annotates all bindings (not just top-level
                           ones) with SCCs

  -fprof-top               Annotates just top-level bindings with SCCs

  -fprof-exported          Annotates just exported bindings with SCCs

  -fprof-no-count-entries  Do not maintain entry counts when profiling
                           (can make profiled code go faster; useful with
                           heap profiling where entry counts are not used)

Cost-centre stacks have a new semantics, which should in most cases
result in more useful and intuitive profiles.  If you find this not to
be the case, please let me know.  This is the area where I have been
experimenting most, and the current solution is probably not the
final version, however it does address all the outstanding bugs and
seems to be better than GHC 7.2.

Stack traces
------------

+RTS -xc now gives more information.  If the exception originates from
a CAF (as is common, because GHC tends to lift exceptions out to the
top-level), then the RTS walks up the stack and reports the stack in
the enclosing update frame(s).

Result: +RTS -xc is much more useful now - but you still have to
compile for profiling to get it.  I've played around a little with
adding 'head []' to GHC itself, and +RTS -xc does pinpoint the problem
quite accurately.

I plan to add more facilities for stack tracing (e.g. in GHCi) in the
future.

Coverage (HPC)
--------------

 * derived instances are now coloured yellow if they weren't used
 * likewise record field names
 * entry counts are more accurate (hpc --fun-entry-count)
 * tab width is now correct (markup was previously off in source with
   tabs)

Internal changes
================

In Core, the Note constructor has been replaced by

        Tick (Tickish b) (Expr b)

which is used to represent all the kinds of source annotation we
support: profiling SCCs, HPC ticks, and GHCi breakpoints.

Depending on the properties of the Tickish, different transformations
apply to Tick.  See CoreUtils.mkTick for details.

Tickets
=======

This commit closes the following tickets, test cases to follow:

  - Close #2552: not a bug, but the behaviour is now more intuitive
    (test is T2552)

  - Close #680 (test is T680)

  - Close #1531 (test is result001)

  - Close #949 (test is T949)

  - Close #2466: test case has bitrotted (doesn't compile against current
    version of vector-space package)

This addresses the rare cases where the simplifier diverges
(see the above ticket).  We were already counting how many simplifier
steps were taking place, but with no limit.  This patch adds a limit;
at which point we halt compilation, and print out useful stats. The
stats show what is begin inlined, and how often, which points you
directly to the problem.  The limit is set based on the size of the
program.

Instead of halting compilation, we could instead just inhibit
inlining, which would let compilation of the module complete. This is
a bit harder to implement, and it's likely to mean that you unrolled
the function 1143 times and then ran out of ticks; you probably don't
want to complete parsing on this highly-unrolled program.

Flags: -dsimpl-tick-factor=N.  Default is 100 (percent).
       A bigger number increases the allowed maximum tick count.

I realised that my recently-added cunning stuff about
RULES for imported Ids was simply wrong, so this patch
removes it.   See Note [Rules for imported functions],
which explains it all.

This patch also does quite a bit of refactoring in
the treatment of loop breakers.