--- /dev/null
+%
+% (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
+%
+% $Id: CgStackery.lhs,v 1.27 2004/09/30 10:35:49 simonpj Exp $
+%
+\section[CgStackery]{Stack management functions}
+
+Stack-twiddling operations, which are pretty low-down and grimy.
+(This is the module that knows all about stack layouts, etc.)
+
+\begin{code}
+module CgStackery (
+ spRel, getVirtSp, getRealSp, setRealSp,
+ setRealAndVirtualSp, getSpRelOffset,
+
+ allocPrimStack, allocStackTop, deAllocStackTop,
+ adjustStackHW, getFinalStackHW,
+ setStackFrame, getStackFrame,
+ mkVirtStkOffsets, mkStkAmodes,
+ freeStackSlots,
+ pushUpdateFrame, emitPushUpdateFrame,
+ ) where
+
+#include "HsVersions.h"
+
+import CgMonad
+import CgUtils ( cmmOffsetB, cmmRegOffW )
+import CgProf ( initUpdFrameProf )
+import SMRep
+import Cmm
+import CmmUtils ( CmmStmts, mkLblExpr )
+import CLabel ( mkUpdInfoLabel )
+import Constants
+import Util ( sortLe )
+import FastString ( LitString )
+import OrdList ( toOL )
+import Outputable
+\end{code}
+
+%************************************************************************
+%* *
+\subsection[CgUsages-stackery]{Monad things for fiddling with stack usage}
+%* *
+%************************************************************************
+
+spRel is a little function that abstracts the stack direction. Note that most
+of the code generator is dependent on the stack direction anyway, so
+changing this on its own spells certain doom. ToDo: remove?
+
+ THIS IS DIRECTION SENSITIVE!
+
+Stack grows down, positive virtual offsets correspond to negative
+additions to the stack pointer.
+
+\begin{code}
+spRel :: VirtualSpOffset -- virtual offset of Sp
+ -> VirtualSpOffset -- virtual offset of The Thing
+ -> WordOff -- integer offset
+spRel sp off = sp - off
+\end{code}
+
+@setRealAndVirtualSp@ sets into the environment the offsets of the
+current position of the real and virtual stack pointers in the current
+stack frame. The high-water mark is set too. It generates no code.
+It is used to initialise things at the beginning of a closure body.
+
+\begin{code}
+setRealAndVirtualSp :: VirtualSpOffset -- New real Sp
+ -> Code
+
+setRealAndVirtualSp new_sp
+ = do { stk_usg <- getStkUsage
+ ; setStkUsage (stk_usg {virtSp = new_sp,
+ realSp = new_sp,
+ hwSp = new_sp}) }
+
+getVirtSp :: FCode VirtualSpOffset
+getVirtSp
+ = do { stk_usg <- getStkUsage
+ ; return (virtSp stk_usg) }
+
+getRealSp :: FCode VirtualSpOffset
+getRealSp
+ = do { stk_usg <- getStkUsage
+ ; return (realSp stk_usg) }
+
+setRealSp :: VirtualSpOffset -> Code
+setRealSp new_real_sp
+ = do { stk_usg <- getStkUsage
+ ; setStkUsage (stk_usg {realSp = new_real_sp}) }
+
+getSpRelOffset :: VirtualSpOffset -> FCode CmmExpr
+getSpRelOffset virtual_offset
+ = do { real_sp <- getRealSp
+ ; return (cmmRegOffW spReg (spRel real_sp virtual_offset)) }
+\end{code}
+
+
+%************************************************************************
+%* *
+\subsection[CgStackery-layout]{Laying out a stack frame}
+%* *
+%************************************************************************
+
+'mkVirtStkOffsets' is given a list of arguments. The first argument
+gets the /largest/ virtual stack offset (remember, virtual offsets
+increase towards the top of stack).
+
+\begin{code}
+mkVirtStkOffsets
+ :: VirtualSpOffset -- Offset of the last allocated thing
+ -> [(CgRep,a)] -- things to make offsets for
+ -> (VirtualSpOffset, -- OUTPUTS: Topmost allocated word
+ [(a, VirtualSpOffset)]) -- things with offsets (voids filtered out)
+
+mkVirtStkOffsets init_Sp_offset things
+ = loop init_Sp_offset [] (reverse things)
+ where
+ loop offset offs [] = (offset,offs)
+ loop offset offs ((VoidArg,t):things) = loop offset offs things
+ -- ignore Void arguments
+ loop offset offs ((rep,t):things)
+ = loop thing_slot ((t,thing_slot):offs) things
+ where
+ thing_slot = offset + cgRepSizeW rep
+ -- offset of thing is offset+size, because we're
+ -- growing the stack *downwards* as the offsets increase.
+
+-- | 'mkStkAmodes' is a higher-level version of
+-- 'mkVirtStkOffsets'. It starts from the tail-call locations.
+-- It returns a single list of addressing modes for the stack
+-- locations, and therefore is in the monad. It /doesn't/ adjust the
+-- high water mark.
+
+mkStkAmodes
+ :: VirtualSpOffset -- Tail call positions
+ -> [(CgRep,CmmExpr)] -- things to make offsets for
+ -> FCode (VirtualSpOffset, -- OUTPUTS: Topmost allocated word
+ CmmStmts) -- Assignments to appropriate stk slots
+
+mkStkAmodes tail_Sp things
+ = do { rSp <- getRealSp
+ ; let (last_Sp_offset, offsets) = mkVirtStkOffsets tail_Sp things
+ abs_cs = [ CmmStore (cmmRegOffW spReg (spRel rSp offset)) amode
+ | (amode, offset) <- offsets
+ ]
+ ; returnFC (last_Sp_offset, toOL abs_cs) }
+\end{code}
+
+%************************************************************************
+%* *
+\subsection[CgStackery-monadery]{Inside-monad functions for stack manipulation}
+%* *
+%************************************************************************
+
+Allocate a virtual offset for something.
+
+\begin{code}
+allocPrimStack :: CgRep -> FCode VirtualSpOffset
+allocPrimStack rep
+ = do { stk_usg <- getStkUsage
+ ; let free_stk = freeStk stk_usg
+ ; case find_block free_stk of
+ Nothing -> do
+ { let push_virt_sp = virtSp stk_usg + size
+ ; setStkUsage (stk_usg { virtSp = push_virt_sp,
+ hwSp = hwSp stk_usg `max` push_virt_sp })
+ -- Adjust high water mark
+ ; return push_virt_sp }
+ Just slot -> do
+ { setStkUsage (stk_usg { freeStk = delete_block free_stk slot })
+ ; return slot }
+ }
+ where
+ size :: WordOff
+ size = cgRepSizeW rep
+
+ -- Find_block looks for a contiguous chunk of free slots
+ -- returning the offset of its topmost word
+ find_block :: [VirtualSpOffset] -> Maybe VirtualSpOffset
+ find_block [] = Nothing
+ find_block (slot:slots)
+ | take size (slot:slots) == [slot..top_slot]
+ = Just top_slot
+ | otherwise
+ = find_block slots
+ where -- The stack grows downwards, with increasing virtual offsets.
+ -- Therefore, the address of a multi-word object is the *highest*
+ -- virtual offset it occupies (top_slot below).
+ top_slot = slot+size-1
+
+ delete_block free_stk slot = [ s | s <- free_stk,
+ (s<=slot-size) || (s>slot) ]
+ -- Retain slots which are not in the range
+ -- slot-size+1..slot
+\end{code}
+
+Allocate a chunk ON TOP OF the stack.
+
+\begin{code}
+allocStackTop :: WordOff -> FCode VirtualSpOffset
+allocStackTop size
+ = do { stk_usg <- getStkUsage
+ ; let push_virt_sp = virtSp stk_usg + size
+ ; setStkUsage (stk_usg { virtSp = push_virt_sp,
+ hwSp = hwSp stk_usg `max` push_virt_sp })
+ ; return push_virt_sp }
+\end{code}
+
+Pop some words from the current top of stack. This is used for
+de-allocating the return address in a case alternative.
+
+\begin{code}
+deAllocStackTop :: WordOff -> FCode VirtualSpOffset
+deAllocStackTop size
+ = do { stk_usg <- getStkUsage
+ ; let pop_virt_sp = virtSp stk_usg - size
+ ; setStkUsage (stk_usg { virtSp = pop_virt_sp })
+ ; return pop_virt_sp }
+\end{code}
+
+\begin{code}
+adjustStackHW :: VirtualSpOffset -> Code
+adjustStackHW offset
+ = do { stk_usg <- getStkUsage
+ ; setStkUsage (stk_usg { hwSp = hwSp stk_usg `max` offset }) }
+\end{code}
+
+A knot-tying beast.
+
+\begin{code}
+getFinalStackHW :: (VirtualSpOffset -> Code) -> Code
+getFinalStackHW fcode
+ = do { fixC (\hw_sp -> do
+ { fcode hw_sp
+ ; stk_usg <- getStkUsage
+ ; return (hwSp stk_usg) })
+ ; return () }
+\end{code}
+
+\begin{code}
+setStackFrame :: VirtualSpOffset -> Code
+setStackFrame offset
+ = do { stk_usg <- getStkUsage
+ ; setStkUsage (stk_usg { frameSp = offset }) }
+
+getStackFrame :: FCode VirtualSpOffset
+getStackFrame
+ = do { stk_usg <- getStkUsage
+ ; return (frameSp stk_usg) }
+\end{code}
+
+
+%********************************************************
+%* *
+%* Setting up update frames *
+%* *
+%********************************************************
+
+@pushUpdateFrame@ $updatee$ pushes a general update frame which
+points to $updatee$ as the thing to be updated. It is only used
+when a thunk has just been entered, so the (real) stack pointers
+are guaranteed to be nicely aligned with the top of stack.
+@pushUpdateFrame@ adjusts the virtual and tail stack pointers
+to reflect the frame pushed.
+
+\begin{code}
+pushUpdateFrame :: CmmExpr -> Code -> Code
+
+pushUpdateFrame updatee code
+ = do {
+#ifdef DEBUG
+ EndOfBlockInfo _ sequel <- getEndOfBlockInfo ;
+ ASSERT(case sequel of { OnStack -> True; _ -> False})
+#endif
+
+ allocStackTop (fixedHdrSize +
+ sIZEOF_StgUpdateFrame_NoHdr `quot` wORD_SIZE)
+ ; vsp <- getVirtSp
+ ; setStackFrame vsp
+ ; frame_addr <- getSpRelOffset vsp
+ -- The location of the lowest-address
+ -- word of the update frame itself
+
+ ; setEndOfBlockInfo (EndOfBlockInfo vsp UpdateCode) $
+ do { emitPushUpdateFrame frame_addr updatee
+ ; code }
+ }
+
+emitPushUpdateFrame :: CmmExpr -> CmmExpr -> Code
+emitPushUpdateFrame frame_addr updatee = do
+ stmtsC [ -- Set the info word
+ CmmStore frame_addr (mkLblExpr mkUpdInfoLabel)
+ , -- And the updatee
+ CmmStore (cmmOffsetB frame_addr off_updatee) updatee ]
+ initUpdFrameProf frame_addr
+
+off_updatee :: ByteOff
+off_updatee = fixedHdrSize*wORD_SIZE + oFFSET_StgUpdateFrame_updatee
+\end{code}
+
+
+%************************************************************************
+%* *
+\subsection[CgStackery-free]{Free stack slots}
+%* *
+%************************************************************************
+
+Explicitly free some stack space.
+
+\begin{code}
+freeStackSlots :: [VirtualSpOffset] -> Code
+freeStackSlots extra_free
+ = do { stk_usg <- getStkUsage
+ ; let all_free = addFreeSlots (freeStk stk_usg) (sortLe (<=) extra_free)
+ ; let (new_vsp, new_free) = trim (virtSp stk_usg) all_free
+ ; setStkUsage (stk_usg { virtSp = new_vsp, freeStk = new_free }) }
+
+addFreeSlots :: [VirtualSpOffset] -> [VirtualSpOffset] -> [VirtualSpOffset]
+-- Merge the two, assuming both are in increasing order
+addFreeSlots cs [] = cs
+addFreeSlots [] ns = ns
+addFreeSlots (c:cs) (n:ns)
+ | c < n = c : addFreeSlots cs (n:ns)
+ | otherwise = n : addFreeSlots (c:cs) ns
+
+trim :: VirtualSpOffset -> [VirtualSpOffset] -> (VirtualSpOffset, [VirtualSpOffset])
+-- Try to trim back the virtual stack pointer, where there is a
+-- continuous bunch of free slots at the end of the free list
+trim vsp [] = (vsp, [])
+trim vsp (slot:slots)
+ = case trim vsp slots of
+ (vsp', [])
+ | vsp' < slot -> pprTrace "trim: strange" (ppr vsp <+> ppr (slot:slots))
+ (vsp', [])
+ | vsp' == slot -> (vsp'-1, [])
+ | otherwise -> (vsp', [slot])
+ (vsp', slots') -> (vsp', slot:slots')
+\end{code}
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