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More type functions
~~~~~~~~~~~~~~~~~~~
* Allow {tv = TYPE ty) as a non-rec binding in Core
* Use this to make equality constraints more uniform
* Can a Dict can contain an EqPred?
How does that differ from an EqInst?
* Make DictBinds into Core
* In zonking, do we need to zonk the kinds of coercion variables?
Type functions
~~~~~~~~~~~~~~
* A Given inst should be a CoVar, not a coercion
* finaliseEqInst should not need to call zonk
* Why do we need fromGivenEqDict? How could we construct
a Dict that had an EqPred?
newDictBndr should make an EqInst directly
* tc_co should be accessed only inside Inst
* Inst.mkImplicTy needs a commment about filtering out EqInsts
How *do* we deal with wanted equalities?
* Inst.instType behaves inconsistently for EqInsts: it should
return an EqPred, like the instType' hack in pprDictsTheta
Consequences: adjust the uses of instType in TcSimplify
* tcDeref* functions are unused, except in tcGenericNormalizeFamInst, when
we can equally well use TcMType.lookupTcTyVar
* Coercion.mkEqPredCoI looks very peculiar.
-------------------------
*** unexpected failure for jtod_circint(opt)
New back end thoughts
-----------------------------------------------------------------------------
Codegen notes
* jumps to ImpossibleBranch should be removed.
* Profiling:
- when updating a closure with an indirection to a function,
we should make a permanent indirection.
- check that we're bumping the scc count appropriately
* check perf & binary sizes against the HEAD
-----------------------------------------------------------------------------
C backend notes
* use STGCALL macros for foreign calls (doesn't look like volatile regs
are handled properly at the mo).
-----------------------------------------------------------------------------
Cmm parser notes
* switches
* need to cater for unexported procedures/info tables?
* We should be able to get rid of entry labels, use info labels only.
- we need a %ENTRY_LBL(info_lbl) macro, so that instead of
JMP_(foo_entry) we can write jump %ENTRY_LBL(foo_info).
-----------------------------------------------------------------------------
* Move arg-descr from LFInfo to ClosureInfo?
But: only needed for functions
* Move all of CgClosure.link_caf into NewCaf, and newDynCaf
* If the case binder is dead, and the constr is nullary,
do we need to assign to Node?
-------------------------------
NB: all floats are let-binds, but some non-rec lets
may be unlifted (with RHS ok-for-speculation)
simplArg: [use strictness]
[used for non-top-lvl non-rec RHS or function arg]
if strict-type || demanded
simplStrictExpr
else
simplExpr ---> (floats,expr)
float all the floats if exposes constr app, return expr
simpl (applied lambda) ==> simplNonRecBind
simpl (Let (NonRec ...) ..) ==> simplNonRecBind
simpl (Let (Rec ...) ..) ==> simplRecBind
simplRecBind:
simplify binders (but not its IdInfo)
simplify the pairs one at a time
using simplRecPair
simplNonRecBind: [was simplBeta]
[used for non-top-lvl non-rec bindings]
- check for PreInlineUnconditionally
- simplify binder, including its IdInfo
- simplArg
- if strict-type
addCaseBind [which makes a let if ok-for-spec]
else
completeLazyBind
simplLazyBind: [binder already simplified, but not its IdInfo]
[used for both rec and top-lvl non-rec]
[must not be strict/unboxed; case not allowed]
- check for PreInlineUnconditionally
- substituteIdInfo and add result to in-scope
[so that rules are available in rec rhs]
- simplExpr --> (floats,expr)
- float: lifted floats only
if exposes constructor or pap (even if non-triv args)
or if top level
- completeLazyBind
completeLazyBind: [given a simplified RHS]
[used for both rec and non-rec bindings, top level and not]
- try discarding dead
- try PostInlineUnconditionally
- let-bind coerce arg and repeat
- try rhs tylam (float)
- try eta expand (float) [not if any float is unlifted && (non-spec || top_lvl || rec)]
- let-bind constructor args [not if any float is ..as above..]
- add unfolding [this is the only place we add an unfolding]
add arity
Eta expansion
~~~~~~~~~~~~~~
For eta expansion, we want to catch things like
case e of (a,b) -> \x -> case a of (p,q) -> \y -> r
If the \x was on the RHS of a let, we'd eta expand to bring the two
lambdas together. And in general that's a good thing to do. Perhaps
we should eta expand wherever we find a (value) lambda? Then the eta
expansion at a let RHS can concentrate solely on the PAP case.
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