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I also removed the default values from the "Discounts and thresholds"
note: most of them were no longer up-to-date.
Along the way I added FloatSuffix to the argument parser, analogous to
IntSuffix.
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We only use it for "compiler" sources, i.e. not for libraries.
Many modules have a -fno-warn-tabs kludge for now.
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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In Core, the Note constructor has been replaced by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)
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and comment its invariants in Note [CoreProgram] in CoreSyn
I'm not totally convinced that CoreProgram is the right name
(perhaps CoreTopBinds might better), but it is useful to have
a clue that you are looking at the top-level bindings.
This is only a matter of a type synonym change; no deep
refactoring here.
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See the paper "Practical aspects of evidence based compilation in System FC"
* Coercion becomes a data type, distinct from Type
* Coercions become value-level things, rather than type-level things,
(although the value is zero bits wide, like the State token)
A consequence is that a coerion abstraction increases the arity by 1
(just like a dictionary abstraction)
* There is a new constructor in CoreExpr, namely Coercion, to inject
coercions into terms
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Max Bolingbroke suggested these two small improvements to LiberateCase
(most of the size increase is comments :-)):
a) Do LiberateCase on small functions even if they are mutually recursive
See Note [Small enough]
b) Don't do LiberateCase on functions for which it'd be fruitless,
namely when a free varible is scrutinised *outside* the function
See Note [Avoiding fruitless liberate-case]
There is virtually no effect on nofib, but Max tripped over cases
where it mattered slightly.
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This patch, written by Max Bolingbroke, does two things
1. It adds a new CoreM monad (defined in simplCore/CoreMonad),
which is used as the top-level monad for all the Core-to-Core
transformations (starting at SimplCore). It supports
* I/O (for debug printing)
* Unique supply
* Statistics gathering
* Access to the HscEnv, RuleBase, Annotations, Module
The patch therefore refactors the top "skin" of every Core-to-Core
pass, but does not change their functionality.
2. It adds a completely new facility to GHC: Core "annotations".
The idea is that you can say
{#- ANN foo (Just "Hello") #-}
which adds the annotation (Just "Hello") to the top level function
foo. These annotations can be looked up in any Core-to-Core pass,
and are persisted into interface files. (Hence a Core-to-Core pass
can also query the annotations of imported things.) Furthermore,
a Core-to-Core pass can add new annotations (eg strictness info)
of its own, which can be queried by importing modules.
The design of the annotation system is somewhat in flux. It's
designed to work with the (upcoming) dynamic plug-ins mechanism,
but is meanwhile independently useful.
Do not merge to 6.10!
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This patch does a lot of tidying up of the way that dead variables are
handled in Core. Just the sort of thing to do on an aeroplane.
* The tricky "binder-swap" optimisation is moved from the Simplifier
to the Occurrence Analyser. See Note [Binder swap] in OccurAnal.
This is really a nice change. It should reduce the number of
simplifier iteratoins (slightly perhaps). And it means that
we can be much less pessimistic about zapping occurrence info
on binders in a case expression.
* For example:
case x of y { (a,b) -> e }
Previously, each time around, even if y,a,b were all dead, the
Simplifier would pessimistically zap their OccInfo, so that we
can't see they are dead any more. As a result virtually no
case expression ended up with dead binders. This wasn't Bad
in itself, but it always felt wrong.
* I added a check to CoreLint to check that a dead binder really
isn't used. That showed up a couple of bugs in CSE. (Only in
this sense -- they didn't really matter.)
* I've changed the PprCore printer to print "_" for a dead variable.
(Use -dppr-debug to see it again.) This reduces clutter quite a
bit, and of course it's much more useful with the above change.
* Another benefit of the binder-swap change is that I could get rid of
the Simplifier hack (working, but hacky) in which the InScopeSet was
used to map a variable to a *different* variable. That allowed me
to remove VarEnv.modifyInScopeSet, and to simplify lookupInScopeSet
so that it doesn't look for a fixpoint. This fixes no bugs, but
is a useful cleanup.
* Roman pointed out that Id.mkWildId is jolly dangerous, because
of its fixed unique. So I've
- localied it to MkCore, where it is private (not exported)
- renamed it to 'mkWildBinder' to stress that you should only
use it at binding sites, unless you really know what you are
doing
- provided a function MkCore.mkWildCase that emodies the most
common use of mkWildId, and use that elsewhere
So things are much better
* A knock-on change is that I found a common pattern of localising
a potentially global Id, and made a function for it: Id.localiseId
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This patch replaces -fspec-threshold by -fspec-constr-threshold and
-fliberate-case-threshold. The thresholds can be disabled by
-fno-spec-constr-threshold and -fno-liberate-case-threshold.
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Merge to STABLE please
Liberate case was being far too gung-ho about what to specialise. This
bug only showed up when a recursive function 'f' has a nested recursive
function 'g', where 'g' calls 'f' (as well as recursively calling 'g').
This exact situation happens in GHC/IO.writeLines.
This patch puts things right; see Note [When to specialise]. Result:
much less code bloat.
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Older GHCs can't parse OPTIONS_GHC.
This also changes the URL referenced for the -w options from
WorkingConventions#Warnings to CodingStyle#Warnings for the compiler
modules.
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Andy Gill writes: consider the following code
f = g (case v of
V a b -> a : t f)
where g is expensive. Liberate case will turn this into
f = g (case v of
V a b -> a : t (letrec f = g (case v of
V a b -> a : f t)
in f)
)
Yikes! We evaluate g twice. This leads to a O(2^n) explosion
if g calls back to the same code recursively.
This may be the same as Trac #1366.
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Roman produced programs involving associated types that did not optimise well.
His programs were something like this:
data family T a
data instance T Int = MkT Bool Char
bar :: T Int -> Int
bar t = t `seq` loop 0
where
loop = ...
You'd think that the `seq` should unbox 't' outside the loop, since
a (T Int) is just a MkT pair.
The most robust way to make this happen is for the simplifier to understand
a bit about type-family instances. See
Note [Improving seq]
in Simplify.lhs. We use FamInstEnv.topNormaliseType to do the interesting
work.
To make this happen I did a bit of refactoring to the simplifier
monad.
I'd previously done a very similar transformation in LiberateCase, but it
was happening too late. So this patch takes it out of LiberateCase as
well as adding it to Simplify.
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- This changes the signature of FamInstEnv.lookupFamInstEnv and
FamInstEnv.lookupFamInstEnvUnify in a manner similar to SPJ's
previous patch for InstEnv.llokupInstEnv
- tcLookupFamInst now permits the lookup of instances that are more
general than the type instance requested.
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Somehow in the patch
* Record-ise the liberate-case envt, in preparation for new stuff
I managed to make lookupLevelEnv do entirely the wrong thing.
I think it was just a typo. The result was that LiberateCase essentially
never did anything any more.
Easily fixed though!
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This patch improves the SpecConstr pass, by
a) making it work with join points
b) making it generate specialisations transitively
As part of it, SpecConstr now carries a substitution with it, which
runs over the whole program as it goes. This turned out to be
a big win; simplified the implementation quite a bit.
I have *disabled* the specialisation on lambdas; it's pretty fragile,
and sometimes generates more and more specialisations. Something to
come back to, perhaps.
I rejigged the flag-handling a bit. Now the specification of passes
in DynFlags is a bit nicer; see
- optLevelFlags top-level data structure
- runWhen function
- CoreDoPasses constructor
There are now command-line flags
-fspec-constr
-fliberate-case
-fspec-threshold=N
which do the obvious thing. -O2 switches on both spec-constr and liberate-case.
You can use -fno-liberate-case, -fno-spec-constr after -O2 to switch them off again.
The spec-threshold applies to both these transformations; default value 200 for now.
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Consider this FC program:
data family AT a :: *
data instance AT Int = T1 Int Int
f :: AT Int -> Int
f t = case t of DEFAULT -> <body>
We'd like to replace the DEFAULT by a use of T1, so that if
we scrutinise t inside <body> we share the evaluation:
f t = case (t `cast` co) of T1 x y -> <body>
I decided to do this as part of the liberate-case transformation,
which is already trying to avoid redundant evals.
The new transformation requires knowledge of the family instance
environment, so I had to extend ModGuts to carry the fam_inst_env,
and put that envt into the liberate-case environment.
Otherwise it's all pretty straightforward.
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Note [Scrutinee with cast]
~~~~~~~~~~~~~~~~~~~~~~~~~~
Consider this:
f = \ t -> case (v `cast` co) of
V a b -> a : f t
Exactly the same optimistaion (unrolling one call to f) will work here,
despite the cast. See mk_alt_env in the Case branch of libCase.
This patch does the job. For a change, it was really easy.
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Most of the other users of the fptools build system have migrated to
Cabal, and with the move to darcs we can now flatten the source tree
without losing history, so here goes.
The main change is that the ghc/ subdir is gone, and most of what it
contained is now at the top level. The build system now makes no
pretense at being multi-project, it is just the GHC build system.
No doubt this will break many things, and there will be a period of
instability while we fix the dependencies. A straightforward build
should work, but I haven't yet fixed binary/source distributions.
Changes to the Building Guide will follow, too.
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