import StgSyn
-import MkZipCfgCmm
+import MkGraph
import BlockId
-import Cmm()
import CmmExpr
import CoreSyn
import DataCon
import ForeignCall
import Id
import PrimOp
+import SMRep
import TyCon
+import Type
import CostCentre ( CostCentreStack, currentCCS )
+import Control.Monad (when)
import Maybes
import Util
import FastString
import Outputable
+import UniqSupply
------------------------------------------------------------------------
-- cgExpr: the main function
cgExpr (StgLit lit) = do cmm_lit <- cgLit lit
emitReturn [CmmLit cmm_lit]
-cgExpr (StgLet binds expr) = do { cgBind binds; cgExpr expr }
-cgExpr (StgLetNoEscape _ _ binds expr) = do { cgLneBinds binds; cgExpr expr }
+cgExpr (StgLet binds expr) = do { cgBind binds; cgExpr expr }
+cgExpr (StgLetNoEscape _ _ binds expr) =
+ do { us <- newUniqSupply
+ ; let join_id = mkBlockId (uniqFromSupply us)
+ ; cgLneBinds join_id binds
+ ; cgExpr expr
+ ; emit $ mkLabel join_id}
cgExpr (StgCase expr _live_vars _save_vars bndr srt alt_type alts) =
cgCase expr bndr srt alt_type alts
execute *next*, just like the scrutinee of a case. -}
-------------------------
-cgLneBinds :: StgBinding -> FCode ()
-cgLneBinds (StgNonRec bndr rhs)
- = do { local_cc <- saveCurrentCostCentre
- -- See Note [Saving the current cost centre]
- ; info <- cgLetNoEscapeRhs local_cc bndr rhs
- ; addBindC (cg_id info) info }
-
-cgLneBinds (StgRec pairs)
- = do { local_cc <- saveCurrentCostCentre
- ; new_bindings <- fixC (\ new_bindings -> do
- { addBindsC new_bindings
- ; listFCs [ cgLetNoEscapeRhs local_cc b e
- | (b,e) <- pairs ] })
-
- ; addBindsC new_bindings }
+cgLneBinds :: BlockId -> StgBinding -> FCode ()
+cgLneBinds join_id (StgNonRec bndr rhs)
+ = do { local_cc <- saveCurrentCostCentre
+ -- See Note [Saving the current cost centre]
+ ; info <- cgLetNoEscapeRhs join_id local_cc bndr rhs
+ ; addBindC (cg_id info) info }
+
+cgLneBinds join_id (StgRec pairs)
+ = do { local_cc <- saveCurrentCostCentre
+ ; new_bindings <- fixC (\ new_bindings -> do
+ { addBindsC new_bindings
+ ; listFCs [ cgLetNoEscapeRhs join_id local_cc b e
+ | (b,e) <- pairs ] })
+ ; addBindsC new_bindings }
-------------------------
-cgLetNoEscapeRhs, cgLetNoEscapeRhsBody
- :: Maybe LocalReg -- Saved cost centre
+cgLetNoEscapeRhs
+ :: BlockId -- join point for successor of let-no-escape
+ -> Maybe LocalReg -- Saved cost centre
-> Id
-> StgRhs
-> FCode CgIdInfo
-cgLetNoEscapeRhs local_cc bndr rhs =
+cgLetNoEscapeRhs join_id local_cc bndr rhs =
do { (info, rhs_body) <- getCodeR $ cgLetNoEscapeRhsBody local_cc bndr rhs
; let (bid, _) = expectJust "cgLetNoEscapeRhs" $ maybeLetNoEscape info
- ; emit (outOfLine $ mkLabel bid emptyStackInfo <*> rhs_body)
+ ; emit (outOfLine $ mkLabel bid <*> rhs_body <*> mkBranch join_id)
; return info
}
-cgLetNoEscapeRhsBody local_cc bndr (StgRhsClosure cc _bi _ _upd srt args body)
- = cgLetNoEscapeClosure bndr local_cc cc srt (nonVoidIds args) body
+cgLetNoEscapeRhsBody
+ :: Maybe LocalReg -- Saved cost centre
+ -> Id
+ -> StgRhs
+ -> FCode CgIdInfo
+cgLetNoEscapeRhsBody local_cc bndr (StgRhsClosure cc _bi _ _upd _ args body)
+ = cgLetNoEscapeClosure bndr local_cc cc (nonVoidIds args) body
cgLetNoEscapeRhsBody local_cc bndr (StgRhsCon cc con args)
- = cgLetNoEscapeClosure bndr local_cc cc NoSRT [] (StgConApp con args)
+ = cgLetNoEscapeClosure bndr local_cc cc [] (StgConApp con args)
-- For a constructor RHS we want to generate a single chunk of
-- code which can be jumped to from many places, which will
-- return the constructor. It's easy; just behave as if it
:: Id -- binder
-> Maybe LocalReg -- Slot for saved current cost centre
-> CostCentreStack -- XXX: *** NOT USED *** why not?
- -> SRT
-> [NonVoid Id] -- Args (as in \ args -> body)
-> StgExpr -- Body (as in above)
-> FCode CgIdInfo
-cgLetNoEscapeClosure bndr cc_slot _unused_cc srt args body
+cgLetNoEscapeClosure bndr cc_slot _unused_cc args body
= do { arg_regs <- forkProc $ do
{ restoreCurrentCostCentre cc_slot
; arg_regs <- bindArgsToRegs args
- ; c_srt <- getSRTInfo srt
- ; altHeapCheck arg_regs c_srt (cgExpr body)
+ ; altHeapCheck arg_regs (cgExpr body)
-- Using altHeapCheck just reduces
-- instructions to save on stack
; return arg_regs }
-- of the case alternative(s) into the upstream check
-------------------------------------
+-- See Note [case on Bool]
cgCase :: StgExpr -> Id -> SRT -> AltType -> [StgAlt] -> FCode ()
--- cgCase (OpApp ) bndr srt AlgAlt [(DataAlt flase, a2]
- -- | isBoolTy (idType bndr)
- -- , isDeadBndr bndr
- -- =
+{-
+cgCase (OpApp ) bndr srt AlgAlt [(DataAlt flase, a2]
+ | isBoolTy (idType bndr)
+ , isDeadBndr bndr
+ =
+-}
+
+ -- Note [ticket #3132]: we might be looking at a case of a lifted Id
+ -- that was cast to an unlifted type. The Id will always be bottom,
+ -- but we don't want the code generator to fall over here. If we
+ -- just emit an assignment here, the assignment will be
+ -- type-incorrect Cmm. Hence, we emit the usual enter/return code,
+ -- (and because bottom must be untagged, it will be entered and the
+ -- program will crash).
+ -- The Sequel is a type-correct assignment, albeit bogus.
+ -- The (dead) continuation loops; it would be better to invoke some kind
+ -- of panic function here.
+ --
+ -- However, we also want to allow an assignment to be generated
+ -- in the case when the types are compatible, because this allows
+ -- some slightly-dodgy but occasionally-useful casts to be used,
+ -- such as in RtClosureInspect where we cast an HValue to a MutVar#
+ -- so we can print out the contents of the MutVar#. If we generate
+ -- code that enters the HValue, then we'll get a runtime panic, because
+ -- the HValue really is a MutVar#. The types are compatible though,
+ -- so we can just generate an assignment.
+cgCase (StgApp v []) bndr _ alt_type@(PrimAlt _) alts
+ | isUnLiftedType (idType v)
+ || reps_compatible
+ = -- assignment suffices for unlifted types
+ do { when (not reps_compatible) $
+ panic "cgCase: reps do not match, perhaps a dodgy unsafeCoerce?"
+ ; v_info <- getCgIdInfo v
+ ; emit (mkAssign (CmmLocal (idToReg (NonVoid bndr))) (idInfoToAmode v_info))
+ ; _ <- bindArgsToRegs [NonVoid bndr]
+ ; cgAlts NoGcInAlts (NonVoid bndr) alt_type alts }
+ where
+ reps_compatible = idCgRep v == idCgRep bndr
+
+cgCase scrut@(StgApp v []) _ _ (PrimAlt _) _
+ = -- fail at run-time, not compile-time
+ do { mb_cc <- maybeSaveCostCentre True
+ ; withSequel (AssignTo [idToReg (NonVoid v)] False) (cgExpr scrut)
+ ; restoreCurrentCostCentre mb_cc
+ ; emit $ mkComment $ mkFastString "should be unreachable code"
+ ; emit $ withFreshLabel "l" (\l -> mkLabel l <*> mkBranch l)}
cgCase scrut bndr srt alt_type alts
- = do { up_hp_usg <- getVirtHp -- Upstream heap usage
- ; let ret_bndrs = chooseReturnBndrs bndr alt_type alts
- alt_regs = map idToReg ret_bndrs
- simple_scrut = isSimpleScrut scrut alt_type
- gcInAlts | not simple_scrut = True
- | isSingleton alts = False
- | up_hp_usg > 0 = False
- | otherwise = True
- gc_plan = if gcInAlts then GcInAlts alt_regs srt else NoGcInAlts
-
- ; mb_cc <- maybeSaveCostCentre simple_scrut
- ; c_srt <- getSRTInfo srt
- ; withSequel (AssignTo alt_regs gcInAlts) (cgExpr scrut)
- ; restoreCurrentCostCentre mb_cc
-
- ; bindArgsToRegs ret_bndrs
- ; cgAlts gc_plan (NonVoid bndr) alt_type alts }
+ = -- the general case
+ do { up_hp_usg <- getVirtHp -- Upstream heap usage
+ ; let ret_bndrs = chooseReturnBndrs bndr alt_type alts
+ alt_regs = map idToReg ret_bndrs
+ simple_scrut = isSimpleScrut scrut alt_type
+ gcInAlts | not simple_scrut = True
+ | isSingleton alts = False
+ | up_hp_usg > 0 = False
+ | otherwise = True
+ gc_plan = if gcInAlts then GcInAlts alt_regs srt else NoGcInAlts
+
+ ; mb_cc <- maybeSaveCostCentre simple_scrut
+ ; withSequel (AssignTo alt_regs gcInAlts) (cgExpr scrut)
+ ; restoreCurrentCostCentre mb_cc
+
+ -- JD: We need Note: [Better Alt Heap Checks]
+ ; _ <- bindArgsToRegs ret_bndrs
+ ; cgAlts gc_plan (NonVoid bndr) alt_type alts }
-----------------
maybeSaveCostCentre :: Bool -> FCode (Maybe LocalReg)
isSimpleOp :: StgOp -> Bool
-- True iff the op cannot block or allocate
isSimpleOp (StgFCallOp (CCall (CCallSpec _ _ safe)) _) = not (playSafe safe)
-isSimpleOp (StgFCallOp (DNCall _) _) = False -- Safe!
isSimpleOp (StgPrimOp op) = not (primOpOutOfLine op)
+isSimpleOp (StgPrimCallOp _) = False
-----------------
chooseReturnBndrs :: Id -> AltType -> [StgAlt] -> [NonVoid Id]
cg_alt (con, bndrs, _uses, rhs)
= getCodeR $
maybeAltHeapCheck gc_plan $
- do { pprTrace "binding args for" (ppr bndr <+> ppr con) $ bindConArgs con base_reg bndrs
+ do { _ <- bindConArgs con base_reg bndrs
; cgExpr rhs
; return con }
maybeAltHeapCheck :: GcPlan -> FCode a -> FCode a
-maybeAltHeapCheck NoGcInAlts code
- = code
-maybeAltHeapCheck (GcInAlts regs srt) code
- = do { c_srt <- getSRTInfo srt
- ; altHeapCheck regs c_srt code }
+maybeAltHeapCheck NoGcInAlts code = code
+maybeAltHeapCheck (GcInAlts regs _) code = altHeapCheck regs code
-----------------------------------------------------------------------------
-- Tail calls
<*> mkBranch blk_id) }
cgTailCall :: Id -> CgIdInfo -> [StgArg] -> FCode ()
-cgTailCall fun_id fun_info args
- = case (getCallMethod fun_name (idCafInfo fun_id) lf_info (length args)) of
+cgTailCall fun_id fun_info args = do
+ dflags <- getDynFlags
+ case (getCallMethod dflags fun_name (idCafInfo fun_id) lf_info (length args)) of
-- A value in WHNF, so we can just return it.
ReturnIt -> emitReturn [fun] -- ToDo: does ReturnIt guarantee tagged?
do { let fun' = CmmLoad fun (cmmExprType fun)
; [ret,call] <- forkAlts [
getCode $ emitReturn [fun], -- Is tagged; no need to untag
- getCode $ do emit (mkAssign nodeReg fun)
- emitCall Native (entryCode fun') []] -- Not tagged
+ getCode $ do -- emit (mkAssign nodeReg fun)
+ emitCall (NativeNodeCall, NativeReturn)
+ (entryCode fun') [fun]] -- Not tagged
; emit (mkCmmIfThenElse (cmmIsTagged fun) ret call) }
SlowCall -> do -- A slow function call via the RTS apply routines
do emit $ mkComment $ mkFastString "directEntry"
emit (mkAssign nodeReg fun)
directCall lbl arity args
- -- directCall lbl (arity+1) (StgVarArg fun_id : args))
- -- >>= (emit . (mkComment (mkFastString "DirectEntry") <*>))
else do emit $ mkComment $ mkFastString "directEntry else"
directCall lbl arity args }
node_points = nodeMustPointToIt lf_info
+{- Note [case on Bool]
+ ~~~~~~~~~~~~~~~~~~~
+A case on a Boolean value does two things:
+ 1. It looks up the Boolean in a closure table and assigns the
+ result to the binder.
+ 2. It branches to the True or False case through analysis
+ of the closure assigned to the binder.
+But the indirection through the closure table is unnecessary
+if the assignment to the binder will be dead code (use isDeadBndr).
+
+The following example illustrates how badly the code turns out:
+ STG:
+ case <=## [ww_s7Hx y_s7HD] of wild2_sbH8 {
+ GHC.Types.False -> <true code> // sbH8 dead
+ GHC.Types.True -> <false code> // sbH8 dead
+ };
+ Cmm:
+ _s7HD::F64 = F64[_sbH7::I64 + 7]; // MidAssign
+ _ccsW::I64 = %MO_F_Le_W64(_s7Hx::F64, _s7HD::F64); // MidAssign
+ // emitReturn // MidComment
+ _sbH8::I64 = I64[ghczmprim_GHCziBool_Bool_closure_tbl + (_ccsW::I64 << 3)]; // MidAssign
+ _ccsX::I64 = _sbH8::I64 & 7; // MidAssign
+ if (_ccsX::I64 >= 2) goto ccsH; else goto ccsI; // LastCondBranch
+
+The assignments to _sbH8 and _ccsX are completely unnecessary.
+Instead, we should branch based on the value of _ccsW.
+-}
+
+{- Note [Better Alt Heap Checks]
+If two function calls can share a return point, then they will also
+get the same info table. Therefore, it's worth our effort to make
+those opportunities appear as frequently as possible.
+
+Here are a few examples of how it should work:
+
+ STG:
+ case f x of
+ True -> <True code -- including allocation>
+ False -> <False code>
+ Cmm:
+ r = call f(x) returns to L;
+ L:
+ if r & 7 >= 2 goto L1 else goto L2;
+ L1:
+ if Hp > HpLim then
+ r = gc(r);
+ goto L;
+ <True code -- including allocation>
+ L2:
+ <False code>
+Note that the code following both the call to f(x) and the code to gc(r)
+should be the same, which will allow the common blockifier to discover
+that they are the same. Therefore, both function calls will return to the same
+block, and they will use the same info table.
+
+Here's an example of the Cmm code we want from a primOp.
+The primOp doesn't produce an info table for us to reuse, but that's okay:
+we should still generate the same code:
+ STG:
+ case f x of
+ 0 -> <0-case code -- including allocation>
+ _ -> <default-case code>
+ Cmm:
+ r = a +# b;
+ L:
+ if r == 0 then goto L1 else goto L2;
+ L1:
+ if Hp > HpLim then
+ r = gc(r);
+ goto L;
+ <0-case code -- including allocation>
+ L2:
+ <default-case code>
+-}
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