Added statics

[fw/sdcc] / src / z80 / ralloc.c

/** @name Z80 Register allocation functions.
    @author Michael Hope

    Note: much of this is ripped straight from Sandeep's mcs51 code.

    This code maps the virtual symbols and code onto the real
    hardware.  It allocates based on usage and how long the varible
    lives into registers or temporary memory on the stack.

    On the Z80 hl, ix, iy, and a are reserved for the code generator,
    leaving bc and de for allocation.  The extra register pressure
    from reserving hl is made up for by how much easier the sub
    operations become.  You could swap hl for iy if the undocumented
    iyl/iyh instructions are available.

    The stack frame is the common ix-bp style.  Basically:

    ix+4+n:     param 1 
    ix+4:       param 0 
    ix+2:       return address 
    ix+0:       calling functions ix 
    ix-n:       local varibles 
    ...  
    sp:         end of local varibles

    There is currently no support for bit spaces or banked functions.
    
    This program is free software; you can redistribute it and/or
    modify it under the terms of the GNU General Public License as
    published by the Free Software Foundation; either version 2, or (at
    your option) any later version.  This program is distributed in the
    hope that it will be useful, but WITHOUT ANY WARRANTY; without even
    the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
    PURPOSE.  See the GNU General Public License for more details.
    
    You should have received a copy of the GNU General Public License
    along with this program; if not, write to the Free Software
    Foundation, 59 Temple Place - Suite 330, Boston, MA 02111-1307,
    USA.  In other words, you are welcome to use, share and improve
    this program.  You are forbidden to forbid anyone else to use,
    share and improve what you give them.  Help stamp out
    software-hoarding!  
*/

#include <stdio.h>
#include <stdlib.h>
#include "SDCCglobl.h"
#include "SDCCast.h"
#include "SDCCmem.h"
#include "SDCCy.h" 
#include "SDCChasht.h"
#include "SDCCbitv.h"
#include "SDCCset.h"
#include "SDCCicode.h"
#include "SDCClabel.h"
#include "SDCCBBlock.h"
#include "SDCCloop.h"
#include "SDCCcse.h"
#include "SDCCcflow.h"
#include "SDCCdflow.h"
#include "SDCClrange.h"
#include "ralloc.h"

/*-----------------------------------------------------------------*/
/* At this point we start getting processor specific although      */
/* some routines are non-processor specific & can be reused when   */
/* targetting other processors. The decision for this will have    */
/* to be made on a routine by routine basis                        */
/* routines used to pack registers are most definitely not reusable*/
/* since the pack the registers depending strictly on the MCU      */
/*-----------------------------------------------------------------*/

bitVect *spiltSet = NULL ; 
set *stackSpil = NULL;
bitVect *regAssigned = NULL;
short blockSpil = 0;
int slocNum = 0 ;
extern void genZ80Code(iCode *);
int ptrRegReq = 0; /* one byte pointer register required */
bitVect *funcrUsed = NULL; /* registers used in a function */
int stackExtend = 0;
int dataExtend  = 0;

/** Set to help debug register pressure related problems */
#define DEBUG_FAKE_EXTRA_REGS   0

static regs regsZ80[] = 
{
    { REG_GPR, C_IDX , "c", 1 },
    { REG_GPR, B_IDX , "b", 1 },
    { REG_GPR, E_IDX , "e", 1 },
    { REG_GPR, D_IDX , "d", 1 },
    /*    { REG_GPR, L_IDX , "l", 1 },
    { REG_GPR, H_IDX , "h", 1 },*/
#if DEBUG_FAKE_EXTRA_REGS
    { REG_GPR, M_IDX , "m", 1 },
    { REG_GPR, N_IDX , "n", 1 },
    { REG_GPR, O_IDX , "o", 1 },
    { REG_GPR, P_IDX , "p", 1 },
    { REG_GPR, Q_IDX , "q", 1 },
    { REG_GPR, R_IDX , "r", 1 },
    { REG_GPR, S_IDX , "s", 1 },
    { REG_GPR, T_IDX , "t", 1 },
#endif
    { REG_CND, CND_IDX, "c", 1}
};

/** Number of usable registers (all but C) */
#define MAX_REGS ((sizeof(regsZ80)/sizeof(regs))-1)

static void spillThis (symbol *);

/** Allocates register of given type.
    'type' is not used on the z80 version.  It was used to select
    between pointer and general purpose registers on the mcs51 version.

    @return             Pointer to the newly allocated register.
 */
static regs *allocReg (short type)
{
    int i;

    for ( i = 0 ; i < MAX_REGS ; i++ ) {
        /* For now we allocate from any free */
        if (regsZ80[i].isFree ) {
            regsZ80[i].isFree = 0;
            if (currFunc)
                currFunc->regsUsed = 
                    bitVectSetBit(currFunc->regsUsed,i);
            return &regsZ80[i];
        }
    }
    return NULL;
}

/** Returns pointer to register wit index number
 */
regs *regWithIdx (int idx)
{
    int i;
    
    for (i=0;i < MAX_REGS;i++)
        if (regsZ80[i].rIdx == idx)
            return &regsZ80[i];

    werror(E_INTERNAL_ERROR,__FILE__,__LINE__,
           "regWithIdx not found");
    exit(1);
}

/** Frees a register.
 */
static void freeReg (regs *reg)
{
    assert(!reg->isFree);
    reg->isFree = 1;
}


/** Returns number of free registers.
 */
static int nFreeRegs (int type)
{
    int i;
    int nfr=0;
    
    for (i = 0 ; i < MAX_REGS; i++ ) {
        /* For now only one reg type */
        if (regsZ80[i].isFree)
            nfr++;
    }
    return nfr;
}

/** Free registers with type.
 */
static int nfreeRegsType (int type)
{
    int nfr ;
    if (type == REG_PTR) {
        if ((nfr = nFreeRegs(type)) == 0)
            return nFreeRegs(REG_GPR);
    } 
    
    return nFreeRegs(type);
}


#if 0
/*-----------------------------------------------------------------*/
/* allDefsOutOfRange - all definitions are out of a range          */
/*-----------------------------------------------------------------*/
static bool allDefsOutOfRange (bitVect *defs,int fseq, int toseq) 
{
    int i ;

    if (!defs)
        return TRUE ;

    for ( i = 0 ;i < defs->size ; i++ ) {
        iCode *ic;

        if (bitVectBitValue(defs,i)             &&
            (ic = hTabItemWithKey(iCodehTab,i)) &&
            ( ic->seq >= fseq  && ic->seq <= toseq))
            
            return FALSE;
        
    }
    
    return TRUE;
}
#endif
  
/*-----------------------------------------------------------------*/
/* computeSpillable - given a point find the spillable live ranges */
/*-----------------------------------------------------------------*/
static bitVect *computeSpillable (iCode *ic)
{
    bitVect *spillable ;

    /* spillable live ranges are those that are live at this 
       point . the following categories need to be subtracted
       from this set. 
       a) - those that are already spilt
       b) - if being used by this one
       c) - defined by this one */
    
    spillable = bitVectCopy(ic->rlive);
    spillable = 
        bitVectCplAnd(spillable,spiltSet); /* those already spilt */
    spillable = 
        bitVectCplAnd(spillable,ic->uses); /* used in this one */    
    bitVectUnSetBit(spillable,ic->defKey);
    spillable = bitVectIntersect(spillable,regAssigned);
    return spillable;
    
}

/*-----------------------------------------------------------------*/
/* noSpilLoc - return true if a variable has no spil location      */
/*-----------------------------------------------------------------*/
static int noSpilLoc (symbol *sym, eBBlock *ebp,iCode *ic)
{
    return (sym->usl.spillLoc ? 0 : 1);
}

/*-----------------------------------------------------------------*/
/* hasSpilLoc - will return 1 if the symbol has spil location      */
/*-----------------------------------------------------------------*/
static int hasSpilLoc (symbol *sym, eBBlock *ebp, iCode *ic)
{
    return (sym->usl.spillLoc ? 1 : 0);
}

/** Will return 1 if the remat flag is set.
    A symbol is rematerialisable if it doesnt need to be allocated
    into registers at creation as it can be re-created at any time -
    i.e. it's constant in some way.
*/
static int rematable (symbol *sym, eBBlock *ebp, iCode *ic)
{
    return sym->remat;
}

/*-----------------------------------------------------------------*/
/* allLRs - return true for all                                    */
/*-----------------------------------------------------------------*/
static int allLRs (symbol *sym, eBBlock *ebp, iCode *ic)
{
    return 1;
}

/*-----------------------------------------------------------------*/
/* liveRangesWith - applies function to a given set of live range  */
/*-----------------------------------------------------------------*/
set *liveRangesWith (bitVect *lrs, int (func)(symbol *,eBBlock *, iCode *),
                     eBBlock *ebp, iCode *ic)
{
    set *rset = NULL;
    int i;

    if (!lrs || !lrs->size)
        return NULL;

    for ( i = 1 ; i < lrs->size ; i++ ) {
        symbol *sym;
        if (!bitVectBitValue(lrs,i))
            continue ;

        /* if we don't find it in the live range 
           hash table we are in serious trouble */
        if (!(sym = hTabItemWithKey(liveRanges,i))) {
            werror(E_INTERNAL_ERROR,__FILE__,__LINE__,
                   "liveRangesWith could not find liveRange");
            exit(1);
        }
        
        if (func(sym,ebp,ic) && bitVectBitValue(regAssigned,sym->key))
            addSetHead(&rset,sym);
    }

    return rset;
}


/*-----------------------------------------------------------------*/
/* leastUsedLR - given a set determines which is the least used    */
/*-----------------------------------------------------------------*/
symbol *leastUsedLR (set *sset)
{
    symbol *sym = NULL, *lsym = NULL ;
    
    sym = lsym = setFirstItem(sset);

    if (!lsym)
        return NULL;

    for (; lsym; lsym = setNextItem(sset)) {
        
        /* if usage is the same then prefer
           the spill the smaller of the two */
        if ( lsym->used == sym->used )
            if (getSize(lsym->type) < getSize(sym->type))
                sym = lsym;

        /* if less usage */
        if (lsym->used < sym->used )
            sym = lsym;
        
   }

    setToNull((void **)&sset);
    sym->blockSpil = 0;
    return sym;
}

/*-----------------------------------------------------------------*/
/* noOverLap - will iterate through the list looking for over lap  */
/*-----------------------------------------------------------------*/
static int noOverLap (set *itmpStack, symbol *fsym)
{
    symbol *sym;
   

    for (sym = setFirstItem(itmpStack); sym;
         sym = setNextItem(itmpStack)) {
        if (sym->liveTo > fsym->liveFrom )
            return 0;
            
    }

    return 1;
}

/*-----------------------------------------------------------------*/
/* isFree - will return 1 if the a free spil location is found     */
/*-----------------------------------------------------------------*/
DEFSETFUNC(isFree)
{
    symbol *sym = item;
    V_ARG(symbol **,sloc);
    V_ARG(symbol *,fsym);

    /* if already found */
    if (*sloc)
        return 0;

    /* if it is free && and the itmp assigned to
       this does not have any overlapping live ranges
       with the one currently being assigned and
       the size can be accomodated  */
    if (sym->isFree                        && 
        noOverLap(sym->usl.itmpStack,fsym) &&
        getSize(sym->type) >= getSize(fsym->type)) {
        *sloc = sym;
        return 1;
    }

    return 0;
}

/*-----------------------------------------------------------------*/
/* spillLRWithPtrReg :- will spil those live ranges which use PTR  */
/*-----------------------------------------------------------------*/
static void spillLRWithPtrReg (symbol *forSym)
{
    /* Always just return */
}

/*-----------------------------------------------------------------*/
/* createStackSpil - create a location on the stack to spil        */
/*-----------------------------------------------------------------*/
symbol *createStackSpil (symbol *sym)
{
    symbol *sloc= NULL;

    /* first go try and find a free one that is already 
       existing on the stack */
    if (applyToSet(stackSpil,isFree,&sloc, sym)) {
        /* found a free one : just update & return */
        sym->usl.spillLoc = sloc;
        sym->stackSpil= 1;
        sloc->isFree = 0;
        addSetHead(&sloc->usl.itmpStack,sym);
        return sym;
    }

    /* could not then have to create one , this is the hard part
       we need to allocate this on the stack : this is really a
       hack!! but cannot think of anything better at this time */
        
    sprintf(buffer,"sloc%d",slocNum++);
    sloc = newiTemp(buffer);

    /* set the type to the spilling symbol */
    sloc->type = copyLinkChain(sym->type);
    sloc->etype = getSpec(sloc->type);
    SPEC_SCLS(sloc->etype) = S_AUTO ;    

    /* we don't allow it to be allocated`
       onto the external stack since : so we
       temporarily turn it off ; we also
       turn off memory model to prevent
       the spil from going to the external storage
       and turn off overlaying 
    */
    allocLocal(sloc);

    sloc->isref = 1; /* to prevent compiler warning */
    
    /* if it is on the stack then update the stack */
    if (IN_STACK(sloc->etype)) {
        currFunc->stack += getSize(sloc->type);
        stackExtend += getSize(sloc->type);
    } else
        dataExtend += getSize(sloc->type);

    /* add it to the stackSpil set */
    addSetHead(&stackSpil,sloc);
    sym->usl.spillLoc = sloc;
    sym->stackSpil = 1;
    
    /* add it to the set of itempStack set 
       of the spill location */
    addSetHead(&sloc->usl.itmpStack,sym);
    return sym;
}

/*-----------------------------------------------------------------*/
/* isSpiltOnStack - returns true if the spil location is on stack  */
/*-----------------------------------------------------------------*/
bool isSpiltOnStack (symbol *sym)
{
    link *etype;

    if (!sym)
        return FALSE ;
    
    if (!sym->isspilt)
        return FALSE ;

/*     if (sym->stackSpil) */
/*      return TRUE; */
    
    if (!sym->usl.spillLoc)
        return FALSE;

    etype = getSpec(sym->usl.spillLoc->type);
    if (IN_STACK(etype))
        return TRUE;

    return FALSE ;
}

/*-----------------------------------------------------------------*/
/* spillThis - spils a specific operand                            */
/*-----------------------------------------------------------------*/
static void spillThis (symbol *sym)
{
    int i;
    /* if this is rematerializable or has a spillLocation
       we are okay, else we need to create a spillLocation
       for it */
    if (!(sym->remat || sym->usl.spillLoc)) 
        createStackSpil (sym);
    

    /* mark it has spilt & put it in the spilt set */
    sym->isspilt = 1;
    spiltSet = bitVectSetBit(spiltSet,sym->key);
       
    bitVectUnSetBit(regAssigned,sym->key);

    for (i = 0 ; i < sym->nRegs ; i++)

        if (sym->regs[i]) {
            freeReg(sym->regs[i]);
            sym->regs[i] = NULL;
        }
    
    /* if spilt on stack then free up r0 & r1 
       if they could have been assigned to some
       LIVE ranges */
    if (!ptrRegReq && isSpiltOnStack(sym)) {
        ptrRegReq++ ;
        spillLRWithPtrReg(sym);
    }

    if (sym->usl.spillLoc && !sym->remat)
        sym->usl.spillLoc->allocreq = 1;
    return;
}

/** Select a iTemp to spil : rather a simple procedure.
 */
symbol *selectSpil (iCode *ic, eBBlock *ebp, symbol *forSym)
{
    bitVect *lrcs= NULL ; 
    set *selectS ;
    symbol *sym;

    /* get the spillable live ranges */
    lrcs = computeSpillable (ic);

    /* get all live ranges that are rematerizable */
    if ((selectS = liveRangesWith(lrcs,rematable,ebp,ic))) {

        /* return the least used of these */
        return leastUsedLR(selectS);
    }

#if 0
    /* get live ranges with spillLocations in direct space */
    if ((selectS = liveRangesWith(lrcs,directSpilLoc,ebp,ic))) {
        sym = leastUsedLR(selectS);
        strcpy(sym->rname,(sym->usl.spillLoc->rname[0] ? 
                           sym->usl.spillLoc->rname : 
                           sym->usl.spillLoc->name)); 
        sym->spildir = 1;
        /* mark it as allocation required */
        sym->usl.spillLoc->allocreq = 1;
        return sym;
    }

    /* if the symbol is local to the block then */        
    if (forSym->liveTo < ebp->lSeq ) {       

        /* check if there are any live ranges allocated
           to registers that are not used in this block */
        if (!blockSpil && (selectS = liveRangesWith(lrcs,notUsedInBlock,ebp,ic))) {
            sym = leastUsedLR(selectS);
            /* if this is not rematerializable */
            if (!sym->remat) {
                blockSpil++;
                sym->blockSpil = 1;
            }
            return sym;
        } 

        /* check if there are any live ranges that not
           used in the remainder of the block */
        if (!blockSpil && (selectS = liveRangesWith(lrcs,notUsedInRemaining,ebp,ic))) {
            sym = leastUsedLR (selectS);
            if (!sym->remat) {
                sym->remainSpil = 1;
                blockSpil++;
            }
            return sym;
        }
    }
    /* find live ranges with spillocation && not used as pointers */
    if ((selectS = liveRangesWith(lrcs,hasSpilLocnoUptr,ebp,ic))) {
       
        sym =  leastUsedLR(selectS);
        /* mark this as allocation required */
        sym->usl.spillLoc->allocreq = 1;
        return sym;
    }
#endif   

    /* find live ranges with spillocation */
    if ((selectS = liveRangesWith(lrcs,hasSpilLoc,ebp,ic))) {
        
        sym = leastUsedLR(selectS);
        sym->usl.spillLoc->allocreq = 1;
        return sym;
    }

    /* couldn't find then we need to create a spil
       location on the stack , for which one? the least
       used ofcourse */
    if ((selectS = liveRangesWith(lrcs,noSpilLoc,ebp,ic))) {
        /* return a created spil location */
        sym = createStackSpil(leastUsedLR(selectS));
        sym->usl.spillLoc->allocreq = 1;
        return sym;
    }
    
    /* this is an extreme situation we will spill
       this one : happens very rarely but it does happen */
    spillThis ( forSym );
    return forSym;
   
}

/** Spil some variable & mark registers as free.
    A spill occurs when an iTemp wont fit into the available registers.
 */
bool spilSomething (iCode *ic, eBBlock *ebp, symbol *forSym)
{
    symbol *ssym;
    int i ;

    /* get something we can spil */
    ssym = selectSpil(ic,ebp,forSym);
    
    /* mark it as spilt */
    ssym->isspilt = 1;
    spiltSet = bitVectSetBit(spiltSet,ssym->key);
    
    /* mark it as not register assigned &
       take it away from the set */   
    bitVectUnSetBit(regAssigned,ssym->key);
 
    /* mark the registers as free */    
    for (i = 0 ; i < ssym->nRegs ;i++ )
        if (ssym->regs[i])
            freeReg(ssym->regs[i]);
     
#if 0
    /* if spilt on stack then free up r0 & r1 
       if they could have been assigned to as gprs */
    if (!ptrRegReq && isSpiltOnStack(ssym) ) {
        ptrRegReq++ ;
        spillLRWithPtrReg(ssym);
    }

    /* if this was a block level spil then insert push & pop 
       at the start & end of block respectively */
    if (ssym->blockSpil) {
        iCode *nic = newiCode(IPUSH,operandFromSymbol(ssym),NULL);
        /* add push to the start of the block */
        addiCodeToeBBlock(ebp,nic,( ebp->sch->op == LABEL ? 
                                    ebp->sch->next : ebp->sch));
        nic = newiCode(IPOP,operandFromSymbol(ssym),NULL);
        /* add pop to the end of the block */
        addiCodeToeBBlock(ebp,nic,NULL);
    }       

    /* if spilt because not used in the remainder of the
       block then add a push before this instruction and
       a pop at the end of the block */
    if (ssym->remainSpil) {

        iCode *nic = newiCode(IPUSH,operandFromSymbol(ssym),NULL);
        /* add push just before this instruction */
        addiCodeToeBBlock(ebp,nic,ic);
                                    
        nic = newiCode(IPOP,operandFromSymbol(ssym),NULL);
        /* add pop to the end of the block */
        addiCodeToeBBlock(ebp,nic,NULL);    
    }
#endif

    if (ssym == forSym )
        return FALSE ;
    else
        return TRUE ;
}

/** Will try for GPR if not spil.
 */
regs *getRegGpr (iCode *ic, eBBlock *ebp,symbol *sym)
{
    regs *reg;

 tryAgain:
    /* try for gpr type */
    if ((reg = allocReg(REG_GPR)))        
        return reg;    

    if (!ptrRegReq)
        if ((reg = allocReg(REG_PTR)))
            return reg ;

    /* we have to spil */
    if (!spilSomething (ic,ebp,sym))
        return NULL ;

    /* this looks like an infinite loop but 
       in really selectSpil will abort  */
    goto tryAgain ;    
}

/** Symbol has a given register.
 */
static bool symHasReg(symbol *sym,regs *reg)
{
    int i;

    for ( i = 0 ; i < sym->nRegs ; i++)
        if (sym->regs[i] == reg)
            return TRUE;
            
    return FALSE;
}

/** Check the live to and if they have registers & are not spilt then
    free up the registers 
*/
static void deassignLRs (iCode *ic, eBBlock *ebp)
{
    symbol *sym;
    int k;
    symbol *result;

    for (sym = hTabFirstItem(liveRanges,&k); sym;
         sym = hTabNextItem(liveRanges,&k)) {
        
        symbol *psym= NULL;
        /* if it does not end here */
        if (sym->liveTo > ic->seq )
            continue ;

        /* if it was spilt on stack then we can 
           mark the stack spil location as free */
        if (sym->isspilt ) {
            if (sym->stackSpil) {
                sym->usl.spillLoc->isFree = 1;
                sym->stackSpil = 0;
            }
            continue ;
        }
        
        if (!bitVectBitValue(regAssigned,sym->key))
            continue;
        
        /* special case check if this is an IFX &
           the privious one was a pop and the 
           previous one was not spilt then keep track
           of the symbol */     
        if (ic->op == IFX && ic->prev &&
            ic->prev->op == IPOP && 
            !ic->prev->parmPush  &&
            !OP_SYMBOL(IC_LEFT(ic->prev))->isspilt) 
            psym = OP_SYMBOL(IC_LEFT(ic->prev));

        if (sym->nRegs) {
            int i = 0;
            
            bitVectUnSetBit(regAssigned,sym->key);

            /* if the result of this one needs registers
               and does not have it then assign it right
               away */
            if (IC_RESULT(ic) &&
                !  (SKIP_IC2(ic) ||               /* not a special icode */
                    ic->op == JUMPTABLE ||
                    ic->op == IFX ||
                    ic->op == IPUSH ||
                    ic->op == IPOP ||
                    ic->op == RETURN)   &&
                (result = OP_SYMBOL(IC_RESULT(ic))) && /* has a result */
                result->liveTo > ic->seq &&            /* and will live beyond this */
                result->liveTo <= ebp->lSeq &&         /* does not go beyond this block */
                result->regType == sym->regType &&     /* same register types */
                result->nRegs            &&            /* which needs registers */
                ! result->isspilt        &&            /* and does not already have them */
                ! result->remat          &&
                ! bitVectBitValue(regAssigned,result->key) &&
                /* the number of free regs + number of regs in this LR
                   can accomodate the what result Needs */
                ((nfreeRegsType(result->regType) +
                  sym->nRegs) >= result->nRegs)
                ) {
                
                for (i = 0 ; i < max(sym->nRegs,result->nRegs) ; i++)
                    if (i < sym->nRegs )
                        result->regs[i] = sym->regs[i] ;
                    else
                        result->regs[i] = getRegGpr (ic,ebp,result);

                regAssigned = bitVectSetBit(regAssigned,result->key);
            }                   
            
            /* free the remaining */
            for (; i < sym->nRegs ; i++) {
                if (psym) {
                    if (!symHasReg(psym,sym->regs[i]))
                        freeReg(sym->regs[i]);
                } else
                    freeReg(sym->regs[i]);
            }
        }
    }
}


/** Reassign this to registers.
 */
static void reassignLR (operand *op)
{
    symbol *sym = OP_SYMBOL(op);
    int i;

    /* not spilt any more */     
    sym->isspilt = sym->blockSpil  = sym->remainSpil = 0;
    bitVectUnSetBit(spiltSet,sym->key);
      
    regAssigned = bitVectSetBit(regAssigned,sym->key);

    blockSpil--;

    for (i=0;i<sym->nRegs;i++)
        sym->regs[i]->isFree = 0;
}

/** Determines if allocating will cause a spill.
 */
static int willCauseSpill ( int nr, int rt)
{
    /* first check if there are any avlb registers
       of te type required */
    if (nFreeRegs(0) >= nr)
        return 0;

    /* it will cause a spil */
    return 1;
}

/** The allocator can allocate same registers to result and operand,
    if this happens make sure they are in the same position as the operand
    otherwise chaos results.
*/
static void positionRegs (symbol *result, symbol *opsym, int lineno)
{
        int count = min(result->nRegs,opsym->nRegs);
        int i , j = 0, shared = 0;

        /* if the result has been spilt then cannot share */
        if (opsym->isspilt)
                return ;
 again:
        shared = 0;
        /* first make sure that they actually share */
        for ( i = 0 ; i < count; i++ ) {
                for (j = 0 ; j < count ; j++ ) {
                        if (result->regs[i] == opsym->regs[j] && i !=j) {
                                shared = 1;
                                goto xchgPositions;
                        }
                }
        }
 xchgPositions:
        if (shared) {
                regs *tmp = result->regs[i];
                result->regs[i] = result->regs[j];
                result->regs[j] = tmp;          
                goto again;
        }
}

/** Try to allocate a pair of registers to the symbol.
 */
bool tryAllocatingRegPair(symbol *sym)
{
    int i;
    assert(sym->nRegs == 2);
    for ( i = 0 ; i < MAX_REGS ; i+=2 ) {
        if ((regsZ80[i].isFree)&&(regsZ80[i+1].isFree)) {
            regsZ80[i].isFree = 0;
            sym->regs[0] = &regsZ80[i];
            regsZ80[i+1].isFree = 0;
            sym->regs[1] = &regsZ80[i+1];
            if (currFunc) {
                currFunc->regsUsed = 
                    bitVectSetBit(currFunc->regsUsed,i);
                currFunc->regsUsed = 
                    bitVectSetBit(currFunc->regsUsed,i+1);
            }
            return TRUE;
        }
    }
    return FALSE;
}

/** Serially allocate registers to the variables.
    This is the main register allocation function.  It is called after
    packing.
 */
static void serialRegAssign (eBBlock **ebbs, int count)
{
    int i;

    /* for all blocks */
    for (i = 0; i < count ; i++ ) {
        
        iCode *ic;
        
        if (ebbs[i]->noPath &&
            (ebbs[i]->entryLabel != entryLabel &&
             ebbs[i]->entryLabel != returnLabel ))
            continue ;

        /* of all instructions do */
        for (ic = ebbs[i]->sch ; ic ; ic = ic->next) {
         
            /* if this is an ipop that means some live
               range will have to be assigned again */
            if (ic->op == IPOP)
                reassignLR (IC_LEFT(ic));

            /* if result is present && is a true symbol */
            if (IC_RESULT(ic) && ic->op != IFX &&
                IS_TRUE_SYMOP(IC_RESULT(ic)))
                OP_SYMBOL(IC_RESULT(ic))->allocreq = 1;

            /* take away registers from live
               ranges that end at this instruction */      
            deassignLRs (ic, ebbs[i]) ;         
                    
            /* some don't need registers */
            /* MLH: removed RESULT and POINTER_SET condition */
            if (SKIP_IC2(ic) ||
                ic->op == JUMPTABLE ||
                ic->op == IFX ||
                ic->op == IPUSH ||
                ic->op == IPOP)
                continue;   
            
            /* now we need to allocate registers only for the result */
            if (IC_RESULT(ic)) {
                symbol *sym = OP_SYMBOL(IC_RESULT(ic));
                bitVect *spillable;
                int willCS ;
                int j;

                /* if it does not need or is spilt 
                   or is already assigned to registers
                   or will not live beyond this instructions */
                if (!sym->nRegs      || 
                    sym->isspilt     || 
                    bitVectBitValue(regAssigned,sym->key) ||
                    sym->liveTo <= ic->seq)
                    continue ;

                /* if some liverange has been spilt at the block level
                   and this one live beyond this block then spil this
                   to be safe */
                if (blockSpil && sym->liveTo > ebbs[i]->lSeq) {
                    spillThis (sym);
                    continue ;
                }
                /* if trying to allocate this will cause
                   a spill and there is nothing to spill 
                   or this one is rematerializable then
                   spill this one */
                willCS = willCauseSpill(sym->nRegs,sym->regType);
                spillable = computeSpillable(ic);
                if ( sym->remat ||                  
                    (willCS  && bitVectIsZero(spillable) ) ) {

                    spillThis (sym) ;
                    continue ;

                }

                /* if it has a spillocation & is used less than
                   all other live ranges then spill this */
                if ( willCS && sym->usl.spillLoc ) {

                    symbol *leastUsed = 
                        leastUsedLR(liveRangesWith (spillable ,
                                                    allLRs,
                                                    ebbs[i],
                                                    ic));
                    if (leastUsed && 
                        leastUsed->used > sym->used) {
                        spillThis (sym);
                        continue;
                    }
                }               

                /* else we assign registers to it */            
                regAssigned = bitVectSetBit(regAssigned,sym->key);

                /* Special case:  Try to fit into a reg pair if
                   available */
                if ((sym->nRegs == 2)&&tryAllocatingRegPair(sym)) {
                }
                else {
                    for (j = 0 ; j < sym->nRegs ;j++ ) {
                        sym->regs[j] = getRegGpr(ic,ebbs[i],sym);
                        
                        /* if the allocation falied which means
                           this was spilt then break */
                        if (!sym->regs[j]) {
                            break;
                        }
                    }
                }
                /* if it shares registers with operands make sure
                   that they are in the same position */
                if (IC_LEFT(ic) && IS_SYMOP(IC_LEFT(ic)) &&
                    OP_SYMBOL(IC_LEFT(ic))->nRegs  && ic->op != '=')
                        positionRegs(OP_SYMBOL(IC_RESULT(ic)),
                                     OP_SYMBOL(IC_LEFT(ic)),ic->lineno);
                /* do the same for the right operand */
                if (IC_RIGHT(ic) && IS_SYMOP(IC_RIGHT(ic)) &&
                    OP_SYMBOL(IC_RIGHT(ic))->nRegs && ic->op != '=')
                        positionRegs(OP_SYMBOL(IC_RESULT(ic)),
                                     OP_SYMBOL(IC_RIGHT(ic)),ic->lineno);
                
            }       
        }
    }
}

/*-----------------------------------------------------------------*/
/* rUmaskForOp :- returns register mask for an operand             */
/*-----------------------------------------------------------------*/
bitVect *rUmaskForOp (operand *op)
{
    bitVect *rumask;
    symbol *sym;
    int j;
    
    /* only temporaries are assigned registers */
    if (!IS_ITEMP(op)) 
        return NULL;

    sym = OP_SYMBOL(op);
    
    /* if spilt or no registers assigned to it
       then nothing */
    if (sym->isspilt || !sym->nRegs)
        return NULL;

    rumask = newBitVect(MAX_REGS);

    for (j = 0; j < sym->nRegs; j++) {
        rumask = bitVectSetBit(rumask,
                               sym->regs[j]->rIdx);
    }

    return rumask;
}

/** Returns bit vector of registers used in iCode.
 */
bitVect *regsUsedIniCode (iCode *ic)
{
    bitVect *rmask = newBitVect(MAX_REGS);

    /* do the special cases first */
    if (ic->op == IFX ) {
        rmask = bitVectUnion(rmask,
                             rUmaskForOp(IC_COND(ic)));
        goto ret;
    }

    /* for the jumptable */
    if (ic->op == JUMPTABLE) {
        rmask = bitVectUnion(rmask,
                             rUmaskForOp(IC_JTCOND(ic)));

        goto ret;
    }

    /* of all other cases */
    if (IC_LEFT(ic)) 
        rmask = bitVectUnion(rmask,
                             rUmaskForOp(IC_LEFT(ic)));
        
    
    if (IC_RIGHT(ic))
        rmask = bitVectUnion(rmask,
                             rUmaskForOp(IC_RIGHT(ic)));

    if (IC_RESULT(ic))
        rmask = bitVectUnion(rmask,
                             rUmaskForOp(IC_RESULT(ic)));

 ret:
    return rmask;
}

/** For each instruction will determine the regsUsed.
 */
static void createRegMask (eBBlock **ebbs, int count)
{
    int i;

    /* for all blocks */
    for (i = 0; i < count ; i++ ) {
        iCode *ic ;

        if ( ebbs[i]->noPath &&
             ( ebbs[i]->entryLabel != entryLabel &&
               ebbs[i]->entryLabel != returnLabel ))
            continue ;

        /* for all instructions */
        for ( ic = ebbs[i]->sch ; ic ; ic = ic->next ) {
            
            int j;

            if (SKIP_IC2(ic) || !ic->rlive)
                continue ;
            
            /* first mark the registers used in this
               instruction */
            ic->rUsed = regsUsedIniCode(ic);
            funcrUsed = bitVectUnion(funcrUsed,ic->rUsed);

            /* now create the register mask for those 
               registers that are in use : this is a
               super set of ic->rUsed */
            ic->rMask = newBitVect(MAX_REGS+1);

            /* for all live Ranges alive at this point */
            for (j = 1; j < ic->rlive->size; j++ ) {
                symbol *sym;
                int k;

                /* if not alive then continue */
                if (!bitVectBitValue(ic->rlive,j))
                    continue ;

                /* find the live range we are interested in */
                if (!(sym = hTabItemWithKey(liveRanges,j))) {
                    werror (E_INTERNAL_ERROR,__FILE__,__LINE__,
                            "createRegMask cannot find live range");
                    exit(0);
                }

                /* if no register assigned to it */
                if (!sym->nRegs || sym->isspilt)
                    continue ;

                /* for all the registers allocated to it */
                for (k = 0 ; k < sym->nRegs ;k++)
                    if (sym->regs[k])
                        ic->rMask =
                            bitVectSetBit(ic->rMask,sym->regs[k]->rIdx);
            }
        }
    }
}

/** Returns the rematerialized string for a remat var.
 */
char *rematStr (symbol *sym)
{
    char *s = buffer;   
    iCode *ic = sym->rematiCode;    

    while (1) {

        /* if plus or minus print the right hand side */
        if (ic->op == '+' || ic->op == '-') {
            sprintf(s,"0x%04x %c ",(int) operandLitValue(IC_RIGHT(ic)),
                    ic->op );
            s += strlen(s);
            ic = OP_SYMBOL(IC_LEFT(ic))->rematiCode;
            continue ;
        }
        /* we reached the end */
        sprintf(s,"%s",OP_SYMBOL(IC_LEFT(ic))->rname);
        break;
    }

    return buffer ;
}

/*-----------------------------------------------------------------*/
/* regTypeNum - computes the type & number of registers required   */
/*-----------------------------------------------------------------*/
static void regTypeNum ()
{
    symbol *sym;
    int k;

    /* for each live range do */
    for ( sym = hTabFirstItem(liveRanges,&k); sym ;
          sym = hTabNextItem(liveRanges,&k)) {

        /* if used zero times then no registers needed */
        if ((sym->liveTo - sym->liveFrom) == 0)
            continue ;

        /* if the live range is a temporary */
        if (sym->isitmp) {

            /* if the type is marked as a conditional */
            if (sym->regType == REG_CND)
                continue ;

            /* if used in return only then we don't 
               need registers */
            if (sym->ruonly || sym->accuse) {
                if (IS_AGGREGATE(sym->type) || sym->isptr)
                    sym->type = aggrToPtr(sym->type,FALSE);
                continue ;
            }

            /* if not then we require registers */
            sym->nRegs = ((IS_AGGREGATE(sym->type) || sym->isptr ) ?
                          getSize(sym->type = aggrToPtr(sym->type,FALSE)) :
                          getSize(sym->type));

            if (sym->nRegs > 4) {
                fprintf(stderr,"allocated more than 4 or 0 registers for type ");
                printTypeChain(sym->type,stderr);fprintf(stderr,"\n");
            }
            
            /* determine the type of register required */
            /* Always general purpose */
            sym->regType = REG_GPR ;
            
        } else 
            /* for the first run we don't provide */
            /* registers for true symbols we will */
            /* see how things go                  */
            sym->nRegs = 0 ;    
    }
    
}

/** Mark all registers as free.
 */
static void freeAllRegs()
{
    int i;

    for (i=0;i< MAX_REGS;i++ )
        regsZ80[i].isFree = 1;
}

/*-----------------------------------------------------------------*/
/* deallocStackSpil - this will set the stack pointer back         */
/*-----------------------------------------------------------------*/
DEFSETFUNC(deallocStackSpil)
{
    symbol *sym = item;

    deallocLocal(sym);
    return 0;
}

/** Register reduction for assignment.
 */
static int packRegsForAssign (iCode *ic,eBBlock *ebp)
{
    iCode *dic, *sic;
    
    if (
        !IS_TRUE_SYMOP(IC_RESULT(ic)) ||
        !IS_ITEMP(IC_RIGHT(ic))       ||        
        OP_LIVETO(IC_RIGHT(ic)) > ic->seq ||
        OP_SYMBOL(IC_RIGHT(ic))->isind)
        return 0;

#if 0        
    /* if the true symbol is defined in far space or on stack
       then we should not since this will increase register pressure */
    if (isOperandInFarSpace(IC_RESULT(ic))) {
        if ((dic = farSpacePackable(ic)))
            goto pack;
        else
            return 0;
    }
#endif

    /* find the definition of iTempNN scanning backwards if we find a 
       a use of the true symbol in before we find the definition then 
       we cannot */     
    for ( dic = ic->prev ; dic ; dic = dic->prev) {

        /* if there is a function call and this is
           a parameter & not my parameter then don't pack it */
        if ( (dic->op == CALL || dic->op == PCALL) &&
             (OP_SYMBOL(IC_RESULT(ic))->_isparm &&
              !OP_SYMBOL(IC_RESULT(ic))->ismyparm)) {
            dic = NULL;
            break;
        }

        if (SKIP_IC2(dic))
            continue;

#if 0   
        if (IS_SYMOP(IC_RESULT(dic)) &&
            IC_RESULT(dic)->key == IC_RIGHT(ic)->key) {
            if (POINTER_SET(dic))
                dic = NULL;
            break;          
        }

        if (IS_SYMOP(IC_RIGHT(dic)) && 
            (IC_RIGHT(dic)->key == IC_RESULT(ic)->key ||
             IC_RIGHT(dic)->key == IC_RIGHT(ic)->key)) {
            dic = NULL;
            break;
        }
        
        if (IS_SYMOP(IC_LEFT(dic)) && 
            (IC_LEFT(dic)->key == IC_RESULT(ic)->key ||
             IC_LEFT(dic)->key == IC_RIGHT(ic)->key)) {
            dic = NULL;
            break;
        }
        if (POINTER_SET(dic) && 
            IC_RESULT(dic)->key == IC_RESULT(ic)->key ) {
            dic = NULL ;
            break;
        }
#endif
    }
    
    if (!dic)
        return 0 ; /* did not find */
            
    /* if the result is on stack or iaccess then it must be
       the same atleast one of the operands */
    if (OP_SYMBOL(IC_RESULT(ic))->onStack  || 
        OP_SYMBOL(IC_RESULT(ic))->iaccess ) {
        
        /* the operation has only one symbol
           operator then we can pack */
        if ((IC_LEFT(dic) && !IS_SYMOP(IC_LEFT(dic))) ||
            (IC_RIGHT(dic) && !IS_SYMOP(IC_RIGHT(dic))))
            goto pack;

        if (!((IC_LEFT(dic) &&
             IC_RESULT(ic)->key == IC_LEFT(dic)->key) ||
              (IC_RIGHT(dic) &&
               IC_RESULT(ic)->key == IC_RIGHT(dic)->key)))
            return 0;                
    }
pack:
    /* found the definition */
    /* replace the result with the result of */
    /* this assignment and remove this assignment */
    IC_RESULT(dic) = IC_RESULT(ic) ;

    if (IS_ITEMP(IC_RESULT(dic)) && OP_SYMBOL(IC_RESULT(dic))->liveFrom > dic->seq) {
            OP_SYMBOL(IC_RESULT(dic))->liveFrom = dic->seq;
    }
    /* delete from liverange table also 
       delete from all the points inbetween and the new
       one */
    for ( sic = dic; sic != ic ; sic = sic->next ) {    
        bitVectUnSetBit(sic->rlive,IC_RESULT(ic)->key);
        if (IS_ITEMP(IC_RESULT(dic)))
            bitVectSetBit(sic->rlive,IC_RESULT(dic)->key);
    }
        
    remiCodeFromeBBlock(ebp,ic);
    return 1;
    
}

/** Scanning backwards looks for first assig found.
 */
iCode *findAssignToSym (operand *op,iCode *ic)
{
    iCode *dic;

    for (dic = ic->prev ; dic ; dic = dic->prev) {
        
        /* if definition by assignment */
        if (dic->op == '='                 && 
            !POINTER_SET(dic)              &&
            IC_RESULT(dic)->key == op->key)
            /*      &&  IS_TRUE_SYMOP(IC_RIGHT(dic))*/
            {      

            /* we are interested only if defined in far space */
            /* or in stack space in case of + & - */

            /* if assigned to a non-symbol then return
               true */
            if (!IS_SYMOP(IC_RIGHT(dic)))
                break ;

            /* if the symbol is in far space then
               we should not */
            if (isOperandInFarSpace(IC_RIGHT(dic)))
                return NULL ;

            /* for + & - operations make sure that
               if it is on the stack it is the same
               as one of the three operands */
            if ((ic->op == '+' || ic->op == '-') &&
                OP_SYMBOL(IC_RIGHT(dic))->onStack) {

                if ( IC_RESULT(ic)->key != IC_RIGHT(dic)->key &&
                     IC_LEFT(ic)->key   != IC_RIGHT(dic)->key &&
                     IC_RIGHT(ic)->key  != IC_RIGHT(dic)->key)
                    return NULL;
            }           

            break ;
                
        }

        /* if we find an usage then we cannot delete it */
        if (IC_LEFT(dic) && IC_LEFT(dic)->key == op->key)
            return NULL;
            
        if (IC_RIGHT(dic) && IC_RIGHT(dic)->key == op->key)
            return NULL;

        if (POINTER_SET(dic) && IC_RESULT(dic)->key == op->key)
            return NULL;
    }

    /* now make sure that the right side of dic
       is not defined between ic & dic */       
    if (dic) {
        iCode *sic = dic->next ;

        for (; sic != ic ; sic = sic->next)
            if (IC_RESULT(sic) &&
                IC_RESULT(sic)->key == IC_RIGHT(dic)->key)
                return NULL;
    }

    return dic;
        
        
}

#if 0
/*-----------------------------------------------------------------*/
/* packRegsForSupport :- reduce some registers for support calls   */
/*-----------------------------------------------------------------*/
static int packRegsForSupport (iCode *ic, eBBlock *ebp)
{
    int change = 0 ;
    /* for the left & right operand :- look to see if the
       left was assigned a true symbol in far space in that
       case replace them */
    if (IS_ITEMP(IC_LEFT(ic)) && 
        OP_SYMBOL(IC_LEFT(ic))->liveTo <= ic->seq) {
        iCode *dic = findAssignToSym(IC_LEFT(ic),ic);
        iCode *sic;

        if (!dic)
            goto right ;

        /* found it we need to remove it from the
           block */
        for ( sic = dic; sic != ic ; sic = sic->next )
            bitVectUnSetBit(sic->rlive,IC_LEFT(ic)->key);

        IC_LEFT(ic)->operand.symOperand =
            IC_RIGHT(dic)->operand.symOperand;
        IC_LEFT(ic)->key = IC_RIGHT(dic)->operand.symOperand->key;
        remiCodeFromeBBlock(ebp,dic);   
        change++;      
    }
    
    /* do the same for the right operand */
 right:    
    if (!change && 
        IS_ITEMP(IC_RIGHT(ic)) &&
        OP_SYMBOL(IC_RIGHT(ic))->liveTo <= ic->seq) {
        iCode *dic = findAssignToSym(IC_RIGHT(ic),ic);
        iCode *sic;
        
        if (!dic)
            return change ;

        /* found it we need to remove it from the block */
        for ( sic = dic; sic != ic ; sic = sic->next )
            bitVectUnSetBit(sic->rlive,IC_RIGHT(ic)->key);
        
        IC_RIGHT(ic)->operand.symOperand =
            IC_RIGHT(dic)->operand.symOperand;
        IC_RIGHT(ic)->key = IC_RIGHT(dic)->operand.symOperand->key;
        
        remiCodeFromeBBlock(ebp,dic);
        change ++;
    }
   
    return change ;
}
#endif

#define IS_OP_RUONLY(x) (x && IS_SYMOP(x) && OP_SYMBOL(x)->ruonly)

/** Will reduce some registers for single use.
 */
static iCode *packRegsForOneuse (iCode *ic, operand *op , eBBlock *ebp)
{
    bitVect *uses ;
    iCode *dic, *sic;

    /* if returning a literal then do nothing */
    if (!IS_SYMOP(op))
        return NULL;
    
    /* only upto 2 bytes since we cannot predict
       the usage of b, & acc */
    if (getSize(operandType(op)) > 2 && 
        ic->op != RETURN             &&
        ic->op != SEND)
        return NULL;

    /* this routine will mark the a symbol as used in one 
       instruction use only && if the defintion is local 
       (ie. within the basic block) && has only one definition &&
       that definiion is either a return value from a 
       function or does not contain any variables in
       far space */
    uses = bitVectCopy(OP_USES(op));
    bitVectUnSetBit(uses,ic->key); /* take away this iCode */
    if (!bitVectIsZero(uses)) /* has other uses */
        return NULL ;
    
    /* if it has only one defintion */
    if (bitVectnBitsOn(OP_DEFS(op)) > 1)
        return NULL ; /* has more than one definition */

    /* get the that definition */
    if (!(dic = 
          hTabItemWithKey(iCodehTab,
                          bitVectFirstBit(OP_DEFS(op)))))
        return NULL ;

    /* found the definition now check if it is local */
    if (dic->seq < ebp->fSeq ||
        dic->seq > ebp->lSeq)
        return NULL ; /* non-local */

    /* now check if it is the return from a function call */
    if (dic->op == CALL || dic->op == PCALL ) {
        if (ic->op != SEND && ic->op != RETURN) {
            OP_SYMBOL(op)->ruonly = 1;
            return dic;
        }
        dic = dic->next ;
    }
        
    /* otherwise check that the definition does
       not contain any symbols in far space */
    if (isOperandInFarSpace(IC_LEFT(dic))  ||
        isOperandInFarSpace(IC_RIGHT(dic)) ||
        IS_OP_RUONLY(IC_LEFT(ic))          ||
        IS_OP_RUONLY(IC_RIGHT(ic)) )        {
        return NULL;
    }
    
    /* if pointer set then make sure the pointer is one byte */
    if (POINTER_SET(dic))
      return NULL;

    if (POINTER_GET(dic))
      return NULL;
    
    sic = dic;

    /* also make sure the intervenening instructions
       don't have any thing in far space */
    for (dic = dic->next ; dic && dic != ic ; dic = dic->next) {
        /* if there is an intervening function call then no */
        if (dic->op == CALL || dic->op == PCALL)
                return NULL;
        /* if pointer set then make sure the pointer
           is one byte */
        if (POINTER_SET(dic))
            return NULL ;
        
        if (POINTER_GET(dic))
            return NULL ;

        /* if address of & the result is remat the okay */
        if (dic->op == ADDRESS_OF &&
            OP_SYMBOL(IC_RESULT(dic))->remat)
            continue ;
           
        /* if left or right or result is in far space */
        if (isOperandInFarSpace(IC_LEFT(dic))   ||
            isOperandInFarSpace(IC_RIGHT(dic))  ||
            isOperandInFarSpace(IC_RESULT(dic)) ||
            IS_OP_RUONLY(IC_LEFT(dic))          ||
            IS_OP_RUONLY(IC_RIGHT(dic))         ||
            IS_OP_RUONLY(IC_RESULT(dic))            ) {
            return NULL;
        }
    }
                
    OP_SYMBOL(op)->ruonly = 1;
    return sic;
}

/*-----------------------------------------------------------------*/
/* isBitwiseOptimizable - requirements of JEAN LOUIS VERN          */
/*-----------------------------------------------------------------*/
static bool isBitwiseOptimizable (iCode *ic)
{
    link *rtype = getSpec(operandType(IC_RIGHT(ic)));

    /* bitwise operations are considered optimizable
       under the following conditions (Jean-Louis VERN) 
       
       x & lit
       bit & bit
       bit & x
       bit ^ bit
       bit ^ x
       x   ^ lit
       x   | lit
       bit | bit
       bit | x
    */    
    if (IS_LITERAL(rtype))
        return TRUE;
    return FALSE; 
}

/** Optimisations:
    Certian assignments involving pointers can be temporarly stored
    in HL.  Esp.
genAssign
    ld  iy,#_Blah
    ld  bc,(iy)
genAssign (ptr)
    ld  hl,bc
    ld  iy,#_Blah2
    ld  (iy),(hl)
*/

/** Pack registers for acc use.
    When the result of this operation is small and short lived it may
    be able to be stored in the accumelator.
 */
static void packRegsForAccUse (iCode *ic)
{
    iCode *uic;
    
    /* if + or - then it has to be one byte result */
    if ((ic->op == '+' || ic->op == '-')
        && getSize(operandType(IC_RESULT(ic))) > 1)
        return ;
    
    /* if shift operation make sure right side is not a literal */
    if (ic->op == RIGHT_OP  &&
        (isOperandLiteral(IC_RIGHT(ic)) ||
          getSize(operandType(IC_RESULT(ic))) > 1))
        return ;
        
    if (ic->op == LEFT_OP &&        
        ( isOperandLiteral(IC_RIGHT(ic)) ||
          getSize(operandType(IC_RESULT(ic))) > 1))
        return ;
        
    /* has only one definition */
    if (bitVectnBitsOn(OP_DEFS(IC_RESULT(ic))) > 1)
        return ;

    /* has only one use */
    if (bitVectnBitsOn(OP_USES(IC_RESULT(ic))) > 1)
        return ;

    /* and the usage immediately follows this iCode */
    if (!(uic = hTabItemWithKey(iCodehTab,
                                bitVectFirstBit(OP_USES(IC_RESULT(ic))))))
        return ;

    if (ic->next != uic)
        return ;
    
    /* if it is a conditional branch then we definitely can */
    if (uic->op == IFX  ) 
        goto accuse;

    if ( uic->op == JUMPTABLE )
        return ;

#if 0
    /* if the usage is not is an assignment or an 
       arithmetic / bitwise / shift operation then not */
    if (POINTER_SET(uic) && 
        getSize(aggrToPtr(operandType(IC_RESULT(uic)),FALSE)) > 1)
        return;
#endif

    if (uic->op != '=' && 
        !IS_ARITHMETIC_OP(uic) &&
        !IS_BITWISE_OP(uic)    &&
        uic->op != LEFT_OP &&
        uic->op != RIGHT_OP )
        return;

    /* if used in ^ operation then make sure right is not a 
       literl */
    if (uic->op == '^' && isOperandLiteral(IC_RIGHT(uic)))
        return ;

    /* if shift operation make sure right side is not a literal */
    if (uic->op == RIGHT_OP  &&
        ( isOperandLiteral(IC_RIGHT(uic)) ||
          getSize(operandType(IC_RESULT(uic))) > 1))
        return ;

    if (uic->op == LEFT_OP &&        
        ( isOperandLiteral(IC_RIGHT(uic)) ||
          getSize(operandType(IC_RESULT(uic))) > 1))
        return ;
            
#if 0
    /* make sure that the result of this icode is not on the
       stack, since acc is used to compute stack offset */
    if (IS_TRUE_SYMOP(IC_RESULT(uic)) &&
        OP_SYMBOL(IC_RESULT(uic))->onStack)
        return ;
#endif

#if 0
    /* if either one of them in far space then we cannot */
    if ((IS_TRUE_SYMOP(IC_LEFT(uic)) &&
         isOperandInFarSpace(IC_LEFT(uic))) ||
        (IS_TRUE_SYMOP(IC_RIGHT(uic)) &&
         isOperandInFarSpace(IC_RIGHT(uic))))
        return ;
#endif

    /* if the usage has only one operand then we can */
    if (IC_LEFT(uic) == NULL ||
        IC_RIGHT(uic) == NULL) 
        goto accuse;

    /* make sure this is on the left side if not
       a '+' since '+' is commutative */
    if (ic->op != '+' &&
        IC_LEFT(uic)->key != IC_RESULT(ic)->key)
        return;

    /* if one of them is a literal then we can */
    if ((IC_LEFT(uic) && IS_OP_LITERAL(IC_LEFT(uic))) ||
        (IC_RIGHT(uic) && IS_OP_LITERAL(IC_RIGHT(uic)))) {
        OP_SYMBOL(IC_RESULT(ic))->accuse = 1;
        return ;
    }

    /** This is confusing :)  Guess for now */
    if (IC_LEFT(uic)->key == IC_RESULT(ic)->key &&
        (IS_ITEMP(IC_RIGHT(uic)) ||
         (IS_TRUE_SYMOP(IC_RIGHT(uic)))))
        goto accuse;
    
    if (IC_RIGHT(uic)->key == IC_RESULT(ic)->key &&
        (IS_ITEMP(IC_LEFT(uic)) ||
         (IS_TRUE_SYMOP(IC_LEFT(uic)))))
        goto accuse ;
    return ;
 accuse:
    OP_SYMBOL(IC_RESULT(ic))->accuse = 1;
}

/** Does some transformations to reduce register pressure.
 */
static void packRegisters (eBBlock *ebp)
{
    iCode *ic ;
    int change = 0 ;
    
    while (1) {
        change = 0;
        /* look for assignments of the form */
        /* iTempNN = TRueSym (someoperation) SomeOperand */
        /*       ....                       */
        /* TrueSym := iTempNN:1             */
        for ( ic = ebp->sch ; ic ; ic = ic->next ) {
            /* find assignment of the form TrueSym := iTempNN:1 */
            if (ic->op == '=' && !POINTER_SET(ic))
                change += packRegsForAssign(ic,ebp);
        }
        if (!change)
            break;
    }

    for ( ic = ebp->sch ; ic ; ic = ic->next ) {
        /* Safe: address of a true sym is always constant. */
        /* if this is an itemp & result of a address of a true sym 
           then mark this as rematerialisable   */
        if (ic->op == ADDRESS_OF && 
            IS_ITEMP(IC_RESULT(ic)) &&
            IS_TRUE_SYMOP(IC_LEFT(ic)) &&
            bitVectnBitsOn(OP_DEFS(IC_RESULT(ic))) == 1 &&
            !OP_SYMBOL(IC_LEFT(ic))->onStack ) {

            OP_SYMBOL(IC_RESULT(ic))->remat = 1;
            OP_SYMBOL(IC_RESULT(ic))->rematiCode = ic;
            OP_SYMBOL(IC_RESULT(ic))->usl.spillLoc = NULL;
        }

        /* Safe: just propagates the remat flag */
        /* if straight assignment then carry remat flag if this is the
           only definition */
        if (ic->op == '='    && 
            !POINTER_SET(ic) &&
            IS_SYMOP(IC_RIGHT(ic)) && 
            OP_SYMBOL(IC_RIGHT(ic))->remat &&
            bitVectnBitsOn(OP_SYMBOL(IC_RESULT(ic))->defs) <= 1) {

            OP_SYMBOL(IC_RESULT(ic))->remat = 
                OP_SYMBOL(IC_RIGHT(ic))->remat;
            OP_SYMBOL(IC_RESULT(ic))->rematiCode = 
                OP_SYMBOL(IC_RIGHT(ic))->rematiCode ;
        }

        /* if the condition of an if instruction is defined in the
           previous instruction then mark the itemp as a conditional */
        if ((IS_CONDITIONAL(ic) ||
             ( ( ic->op == BITWISEAND      ||
                 ic->op == '|'             ||
                 ic->op == '^' ) &&
               isBitwiseOptimizable(ic))) &&        
            ic->next && ic->next->op == IFX &&
            isOperandEqual(IC_RESULT(ic),IC_COND(ic->next)) &&
            OP_SYMBOL(IC_RESULT(ic))->liveTo <= ic->next->seq) {
            
            OP_SYMBOL(IC_RESULT(ic))->regType = REG_CND;            
            continue ;
        }

#if 0
        /* reduce for support function calls */
        if (ic->supportRtn || ic->op == '+' || ic->op == '-' )
            packRegsForSupport(ic,ebp); 
#endif

#if 0
        /* some cases the redundant moves can
           can be eliminated for return statements */
        if ((ic->op == RETURN || ic->op == SEND) &&
            !isOperandInFarSpace(IC_LEFT(ic))    &&
            !options.model)
            packRegsForOneuse (ic,IC_LEFT(ic),ebp);     
#endif

        /* if pointer set & left has a size more than
           one and right is not in far space */
        if (POINTER_SET(ic)                    &&
            /* MLH: no such thing.
               !isOperandInFarSpace(IC_RIGHT(ic)) && */
            !OP_SYMBOL(IC_RESULT(ic))->remat   &&
            !IS_OP_RUONLY(IC_RIGHT(ic))        &&
            getSize(aggrToPtr(operandType(IC_RESULT(ic)),FALSE)) > 1 )

            packRegsForOneuse (ic,IC_RESULT(ic),ebp);

        /* if pointer get */
        if (POINTER_GET(ic)                    &&
            /* MLH: dont have far space
               !isOperandInFarSpace(IC_RESULT(ic))&& */
            !OP_SYMBOL(IC_LEFT(ic))->remat     &&
            !IS_OP_RUONLY(IC_RESULT(ic))         &&
            getSize(aggrToPtr(operandType(IC_LEFT(ic)),FALSE)) > 1 )
            packRegsForOneuse (ic,IC_LEFT(ic),ebp);

        /* pack registers for accumulator use, when the result of an
           arithmetic or bit wise operation has only one use, that use is
           immediately following the defintion and the using iCode has
           only one operand or has two operands but one is literal & the
           result of that operation is not on stack then we can leave the
           result of this operation in acc:b combination */
        if ((IS_ARITHMETIC_OP(ic) 
             || IS_BITWISE_OP(ic)
             || ic->op == LEFT_OP || ic->op == RIGHT_OP
             ) &&
            IS_ITEMP(IC_RESULT(ic)) &&
            getSize(operandType(IC_RESULT(ic))) <= 2)
            packRegsForAccUse (ic);
    }
}
  
/*-----------------------------------------------------------------*/
/* assignRegisters - assigns registers to each live range as need  */
/*-----------------------------------------------------------------*/
void z80_assignRegisters (eBBlock **ebbs, int count)
{
    iCode *ic;
    int i ;

    setToNull((void *)&funcrUsed);
    ptrRegReq = stackExtend = dataExtend = 0;

    /* change assignments this will remove some
       live ranges reducing some register pressure */
    for (i = 0 ; i < count ;i++ )
        packRegisters (ebbs[i]);

    if (options.dump_pack)
        dumpEbbsToFileExt(".dumppack",ebbs,count);

    /* first determine for each live range the number of 
       registers & the type of registers required for each */
    regTypeNum ();
    
    /* and serially allocate registers */ 
    serialRegAssign(ebbs,count);

    /* if stack was extended then tell the user */
    if (stackExtend) {
/*      werror(W_TOOMANY_SPILS,"stack", */
/*             stackExtend,currFunc->name,""); */
        stackExtend = 0 ;
    }

    if (dataExtend) {
/*      werror(W_TOOMANY_SPILS,"data space", */
/*             dataExtend,currFunc->name,""); */
        dataExtend = 0 ;
    }

    if (options.dump_rassgn)
        dumpEbbsToFileExt(".dumprassgn",ebbs,count);

    /* after that create the register mask
       for each of the instruction */
    createRegMask (ebbs,count);

    /* now get back the chain */
    ic = iCodeLabelOptimize(iCodeFromeBBlock (ebbs,count));

    /* redo that offsets for stacked automatic variables */
    redoStackOffsets ();

    genZ80Code(ic);

    /* free up any stackSpil locations allocated */   
    applyToSet(stackSpil,deallocStackSpil);
    slocNum = 0;
    setToNull((void **)&stackSpil);
    setToNull((void **)&spiltSet);
    /* mark all registers as free */
    freeAllRegs();

    return ;
}