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We were using the SRT information generated by the computeSRTs pass to
decide whether to add a static link field to a constructor or not, and
this broke when I disabled computeSRTs for the new code generator. So
I've hacked it for now to only rely on the SRT information generated
by CoreToStg.
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Also:
- improvements to code generation: push slow-call continuations
on the stack instead of generating explicit continuations
- remove unused CmmInfo wrapper type (replace with CmmInfoTable)
- squash Area and AreaId together, remove now-unused RegSlot
- comment out old unused stack-allocation code that no longer
compiles after removal of RegSlot
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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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See Note [atomic CAFs] in rts/sm/Storage.c
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And some knock-on changes
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1c2f89535394958f75cfb15c8c5e0433a20953ed (symptom was broken
biographical profiling, see #5451).
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* Move CgRep (private to old codgen) from SMRep to ClosureInfo
* Avoid using CgRep in new codegen
* Move SMRep and Bitmap from codeGen/ to cmm/
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When allocating new objects on the heap, we previously returned
a CmmExpr containing the heap pointer as well as the tag expression,
which would be added to the code graph upon first usage. Unfortunately,
this meant that untagged heap pointers living in registers might
be spilled to the stack, where they interacted poorly with garbage
collection (we saw this bug specifically with the compacting garbage
collector.)
This fix immediately tags the register containing the heap pointer,
so that unless we have extremely unfriendly spill code, the new pointer
will never be spilled to the stack untagged.
An alternate solution might have been to modify allocDynClosure to
tag the pointer upon the initial register allocation, but not all
invocations of allocDynClosure tag the resulting pointer, and
threading the consequent CgIdInfo for the cases that did would have
been annoying.
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This changes the new code generator to make use of the Hoopl package
for dataflow analysis. Hoopl is a new boot package, and is maintained
in a separate upstream git repository (as usual, GHC has its own
lagging darcs mirror in http://darcs.haskell.org/packages/hoopl).
During this merge I squashed recent history into one patch. I tried
to rebase, but the history had some internal conflicts of its own
which made rebase extremely confusing, so I gave up. The history I
squashed was:
- Update new codegen to work with latest Hoopl
- Add some notes on new code gen to cmm-notes
- Enable Hoopl lag package.
- Add SPJ note to cmm-notes
- Improve GC calls on new code generator.
Work in this branch was done by:
- Milan Straka <fox@ucw.cz>
- John Dias <dias@cs.tufts.edu>
- David Terei <davidterei@gmail.com>
Edward Z. Yang <ezyang@mit.edu> merged in further changes from GHC HEAD
and fixed a few bugs.
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The type of the CmmLabel ctor is now
CmmLabel :: PackageId -> FastString -> CmmLabelInfo -> CLabel
- When you construct a CmmLabel you have to explicitly say what
package it is in. Many of these will just use rtsPackageId, but
I've left it this way to remind people not to pretend labels are
in the RTS package when they're not.
- When parsing a Cmm file, labels that are not defined in the
current file are assumed to be in the RTS package.
Labels imported like
import label
are assumed to be in a generic "foreign" package, which is different
from the current one.
Labels imported like
import "package-name" label
are marked as coming from the named package.
This last one is needed for the integer-gmp library as we want to
refer to labels that are not in the same compilation unit, but
are in the same non-rts package.
This should help remove the nasty #ifdef __PIC__ stuff from
integer-gmp/cbits/gmp-wrappers.cmm
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node argument is managed
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We used to use StaticFlags
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The interesting examples talk about our story with heap checks in
case alternatives and our story with the case scrutinee as a Boolean.
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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.
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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
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