| Commit message (Collapse) | Author | Age | Files | Lines |
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We now carry around with CmmJump statements a list of
the STG registers that are live at that jump site.
This is used by the LLVM backend so it can avoid
unnesecarily passing around dead registers, improving
perfromance. This gives us the framework to finally
fix trac #4308.
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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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And some knock-on changes
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some info<->entry conversions
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This is safe because GHC never generates a fast call to a data constructor
worker: if the call is seen statically it will be eta-expanded and the
allocation of the data will be inlined. We still need to export the _closure
in case the constructor is used in an unapplied fashion.
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Signed-off-by: Edward Z. Yang <ezyang@mit.edu>
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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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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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Fixes building with -Werror (i.e. validate) and GHC < 6.6
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I've renamed a number of type and data constructors within Cmm so that
the names used in the compiler may more closely reflect the C--
specification 2.1. I've done a bit of other renaming as well.
Highlights:
CmmFormal and CmmActual now bear a CmmKind (which for now is a
MachHint as before)
CmmFormals = [CmmFormal] and CmmActuals = [CmmActual]
suitable changes have been made to both code and nonterminals in the
Cmm parser (which is as yet untested)
For reasons I don't understand, parts of the code generator use a
sequence of 'formal parameters' with no C-- kinds. For these we now
have the types
type CmmFormalWithoutKind = LocalReg
type CmmFormalsWithoutKinds = [CmmFormalWithoutKind]
A great many appearances of (Tau, MachHint) have been simplified to
the appropriate CmmFormal or CmmActual, though I'm sure there are
more opportunities.
Kind and its data constructors are now renamed to
data GCKind = GCKindPtr | GCKindNonPtr
to avoid confusion with the Kind used in the type checker and with CmmKind.
Finally, in a somewhat unrelated bit (and in honor of Simon PJ, who
thought of the name), the Whalley/Davidson 'transaction limit' is now
called 'OptimizationFuel' with the net effect that there are no longer
two unrelated uses of the abbreviation 'tx'.
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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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Consistently make the type and description in the info table an offset
or a pointer, depending on whether tables are next to code or not.
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This patch implements pointer tagging as per our ICFP'07 paper "Faster
laziness using dynamic pointer tagging". It improves performance by
10-15% for most workloads, including GHC itself.
The original patches were by Alexey Rodriguez Yakushev
<mrchebas@gmail.com>, with additions and improvements by me. I've
re-recorded the development as a single patch.
The basic idea is this: we use the low 2 bits of a pointer to a heap
object (3 bits on a 64-bit architecture) to encode some information
about the object pointed to. For a constructor, we encode the "tag"
of the constructor (e.g. True vs. False), for a function closure its
arity. This enables some decisions to be made without dereferencing
the pointer, which speeds up some common operations. In particular it
enables us to avoid costly indirect jumps in many cases.
More information in the commentary:
http://hackage.haskell.org/trac/ghc/wiki/Commentary/Rts/HaskellExecution/PointerTagging
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* Fix code output order when printing C so things are defined before
they are used.
* Generate _ret rather than _entry functions for INFO_TABLE_RET.
* Use "ASSIGN_BaseReg" rather than "BaseReg =".
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(This required a bit of refactoring of CmmInfo.)
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This is a fairly complete implementation, however
two 'panic's have been placed in the critical path
where the implementation is still a bit lacking so
do not expect it to run quite yet.
One call to panic is because we still need to create
a GC block for procedures that don't have them yet.
(cmm/CmmCPS.hs:continuationToProc)
The other is due to the need to convert from a
ContinuationInfo to a CmmInfo.
(codeGen/CgInfoTbls.hs:emitClosureCodeAndInfoTable)
(codeGen/CgInfoTbls.hs:emitReturnTarget)
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Since a CmmCall returns CmmFormals which may include
global registers (and indeed one place in the code
returns the results of a CmmCall into BaseReg) and
since CPS conversion will change those return slots
into formal arguments for the continuation of the call,
CmmProc has to have CmmFormals for the formal arguments.
Oddly, the old code never made use of procedure arguments
so this change only effects the types and not any of the code.
(Because [] is both of type [LocalReg] and CmmFormals.)
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When the con_desc field of an info table was made into a relative
reference, this had the side effect of making the profiling fields
(closure_desc and closure_type) also relative, but only when compiling
via C, and the heap profiler was still treating them as absolute,
leading to crashes when profiling with -hd or -hy.
This patch fixes up the story to be consistent: these fields really
should be relative (otherwise we couldn't make shared versions of the
profiling libraries), so I've made them relative and fixed up the RTS
to know about this.
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Info tables, like everything else in the text section, MUST NOT contain
pointers. A pointer is, by definition, position dependent and is therefore
fundamentally incompatible with generating position independent code.
Therefore, we have to store an offset from the info label to the string
instead of the pointer, just as we already did for other things referred
to by the info table (SRTs, large bitmaps, etc.)
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We recently discovered that they aren't a win any more, and just cost
code size.
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This patch adds data constructor names into their info tables.
This is useful in the ghci debugger. It replaces the old scheme which
was based on tracking data con names in the linker.
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In the generated code for case-of-variable, test the tag of the
scrutinee closure and only enter if it is unevaluated. Also turn
*off* vectored returns.
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In the generated code for case-of-variable, test the tag of the
scrutinee closure and only enter if it is unevaluated. Also turn
*off* vectored returns.
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A GHC binary can generally build either registerised or unregisterised
code, unless it is unregisterised only.
The previous changes broke this, but I think I've now restored it.
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We were constructing info tables designed for TABLES_NEXT_TO_CODE,
but were building without TABLES_NEXT_TO_CODE.
This patch also fixes a bug when we are unregisterised on amd64 and
have code with an address above 2^32.
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This patch is a start on removing import lists and generally tidying
up the top of each module. In addition to removing import lists:
- Change DATA.IOREF -> Data.IORef etc.
- Change List -> Data.List etc.
- Remove $Id$
- Update copyrights
- Re-order imports to put non-GHC imports last
- Remove some unused and duplicate imports
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static relative offsets (eg .long l1-l2) are restricted to 32 bits on
x86-64 due to lack of support in the linker. The codegen, NCG and
runtime work around this, using 32-bit offsets instead of 64.
However, we were missing a workaround for vector tables, and it
happened to work by accident because the offsets were always positive
and resolved by the assembler. The bug was exposed by using the NCG
to compile the RTS, where the offsets became negative, again by
accident.
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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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