fpc/compiler/aoptobj.pas

{
    Copyright (c) 1998-2004 by Jonas Maebe, member of the Free Pascal
    Development Team

    This unit contains the processor independent assembler optimizer
    object, base for the dataflow analyzer, peepholeoptimizer and
    common subexpression elimination objects.

    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 of the License, 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, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.

 ****************************************************************************
}
Unit AoptObj;

  {$i fpcdefs.inc}

  { general, processor independent objects for use by the assembler optimizer }

  Interface

    uses
      globtype,
      aasmbase,aasmcpu,aasmtai,
      cclasses,
      cgbase,cgutils,
      cpubase,
      aoptbase,aoptcpub,aoptda;

    { ************************************************************************* }
    { ********************************* Constants ***************************** }
    { ************************************************************************* }

    Const

    {Possible register content types}
      con_Unknown = 0;
      con_ref = 1;
      con_const = 2;

    {***************** Types ****************}

    Type

    { ************************************************************************* }
    { ************************* Some general type definitions ***************** }
    { ************************************************************************* }
      TRefCompare = Function(r1, r2: TReference): Boolean;
      //!!! FIXME
      TRegArray = Array[byte] of tsuperregister;
      TRegSet = Set of byte;
    { possible actions on an operand: read, write or modify (= read & write) }
      TOpAction = (OpAct_Read, OpAct_Write, OpAct_Modify, OpAct_Unknown);

    { ************************************************************************* }
    { * Object to hold information on which regiters are in use and which not * }
    { ************************************************************************* }
      TUsedRegs = class
        Constructor create;
        Constructor create_regset(Const _RegSet: TRegSet);

        Destructor Destroy;override;
        { update the info with the pairegalloc objects coming after }
        { p                                                         }
        Procedure Update(p: Tai);
        { is Reg currently in use }
        Function IsUsed(Reg: TRegister): Boolean;
        { get all the currently used registers }
        Function GetUsedRegs: TRegSet;

      Private

        UsedRegs: TRegSet;
      End;

    { ************************************************************************* }
    { ******************* Contents of the integer registers ******************* }
    { ************************************************************************* }

     { size of the integer that holds the state number of a register. Can be any }
     { integer type, so it can be changed to reduce the size of the TContent     }
     { structure or to improve alignment                                         }
      TStateInt = Byte;

      TContent = Record
        { start and end of block instructions that defines the }
        { content of this register. If Typ = con_const, then   }
        { Longint(StartMod) = value of the constant)           }
        StartMod: Tai;
        { starts at 0, gets increased everytime the register is }
        { written to                                            }
        WState: TStateInt;
        { starts at 0, gets increased everytime the register is read }
        { from                                                       }
        RState: TStateInt;
        { how many instructions starting with StarMod does the block }
        { consist of                                                 }
        NrOfMods: Byte;
        { the type of the content of the register: unknown, memory   }
        { (variable) or constant                                     }
        Typ: Byte;
      End;

      //!!! FIXME
      TRegContent = Array[byte] Of TContent;

    { ************************************************************************** }
    { information object with the contents of every register. Every Tai object   }
    { gets one of these assigned: a pointer to it is stored in the OptInfo field }
    { ************************************************************************** }

      TPaiProp = class(TAoptBaseCpu)
        Regs: TRegContent;
        { info about allocation of general purpose integer registers }
        UsedRegs: TUsedRegs;
        { can this instruction be removed? }
        CanBeRemoved: Boolean;

        Constructor create;

        { checks the whole sequence of which (so regs[which].StartMod and and  }
        { the next NrOfMods Tai objects) to see whether Reg is used somewhere, }
        { without it being loaded with something else first                    }
        Function RegInSequence(Reg, which: TRegister): Boolean;
        { destroy the contents of a register, as well as those whose contents }
        { are based on those of that register                                 }
        Procedure DestroyReg(Reg: TRegister; var InstrSinceLastMod:
          TInstrSinceLastMod);
        { if the contents of WhichReg (can be R_NO in case of a constant) are  }
        { written to memory at the location Ref, the contents of the registers }
        { that depend on Ref have to be  destroyed                             }
        Procedure DestroyRefs(Const Ref: TReference; WhichReg: TRegister; var
          InstrSinceLastMod: TInstrSinceLastMod);

        { an instruction reads from operand o }
        Procedure ReadOp(const o:toper);
        { an instruction reads from reference Ref }
        Procedure ReadRef(Ref: PReference);
        { an instruction reads from register Reg }
        Procedure ReadReg(Reg: TRegister);

        { an instruction writes/modifies operand o and this has special     }
        { side-effects or modifies the contents in such a way that we can't }
        { simply add this instruction to the sequence of instructions that  }
        { describe the contents of the operand, so destroy it               }
        Procedure DestroyOp(const o:Toper; var InstrSinceLastMod:
          TInstrSinceLastMod);
        { destroy the contents of all registers }
        Procedure DestroyAllRegs(var InstrSinceLastMod: TInstrSinceLastMod);
        { a register's contents are modified, but not destroyed (the new value }
        { depends on the old one)                                              }
        Procedure ModifyReg(reg: TRegister; var InstrSinceLastMod:
          TInstrSinceLastMod);
        { an operand's contents are modified, but not destroyed (the new value }
        { depends on the old one)                                              }
        Procedure ModifyOp(const oper: TOper; var InstrSinceLastMod:
          TInstrSinceLastMod);

        { increase the write state of a register (call every time a register is }
        { written to)                                                           }
        Procedure IncWState(Reg: TRegister);
        { increase the read state of a register (call every time a register is }
        { read from)                                                           }
        Procedure IncRState(Reg: TRegister);
        { get the write state of a register }
        Function GetWState(Reg: TRegister): TStateInt;
        { get the read state of a register }
        Function GetRState(Reg: TRegister): TStateInt;

        { get the type of contents of a register }
        Function GetRegContentType(Reg: TRegister): Byte;

        Destructor Done;

        Private

        Procedure IncState(var s: TStateInt);

        { returns whether the reference Ref is used somewhere in the loading }
        { sequence Content                                                   }
        Function RefInSequence(Const Ref: TReference; Content: TContent;
          RefsEq: TRefCompare): Boolean;

        { returns whether the instruction P reads from and/or writes }
        { to Reg                                                     }
        Function RefInInstruction(Const Ref: TReference; p: Tai;
          RefsEq: TRefCompare): Boolean;

        { returns whether two references with at least one pointing to an array }
        { may point to the same memory location                                 }

      End;


    { ************************************************************************* }
    { ************************ Label information ****************************** }
    { ************************************************************************* }
      TLabelTableItem = Record
        PaiObj: Tai;
      End;

    {$ifndef TP}
      TLabelTable = Array[0..2500000] Of TLabelTableItem;
    {$else TP}
      TLabelTable = Array[0..(65520 div sizeof(TLabelTableItem))] Of TLabelTableItem;
    {$endif TP}
      PLabelTable = ^TLabelTable;
      PLabelInfo = ^TLabelInfo;
      TLabelInfo = Record
        { the highest and lowest label number occurring in the current code }
        { fragment                                                          }
        LowLabel, HighLabel: AWord;
        LabelDif: AWord;
        { table that contains the addresses of the Pai_Label objects associated
          with each label number                                                }
        LabelTable: PLabelTable;
      End;

    { ************************************************************************* }
    { ********** General optimizer object, used to derive others from ********* }
    { ************************************************************************* }

      TAOptObj = class(TAoptBaseCpu)
        { the PAasmOutput list this optimizer instance works on }
        AsmL: TAasmOutput;

        { The labelinfo record contains the addresses of the Tai objects }
        { that are labels, how many labels there are and the min and max }
        { label numbers                                                  }
        LabelInfo: PLabelInfo;

        { Start and end of the block that is currently being optimized }
        BlockStart, BlockEnd: Tai;

        DFA: TAOptDFA;
        { _AsmL is the PAasmOutpout list that has to be optimized,     }
        { _BlockStart and _BlockEnd the start and the end of the block }
        { that has to be optimized and _LabelInfo a pointer to a       }
        { TLabelInfo record                                            }
        Constructor create(_AsmL: TAasmOutput; _BlockStart, _BlockEnd: Tai;
                           _LabelInfo: PLabelInfo); virtual;

        { processor independent methods }

        { returns true if the label L is found between hp and the next }
        { instruction                                                  }
        Function FindLabel(L: TasmLabel; Var hp: Tai): Boolean;

        { inserts new_one between prev and foll in AsmL }
        Procedure InsertLLItem(prev, foll, new_one: TLinkedListItem);


        { If P is a Tai object releveant to the optimizer, P is returned
          If it is not relevant tot he optimizer, the first object after P
          that is relevant is returned                                     }
        Function SkipHead(P: Tai): Tai;

        { returns true if the operands o1 and o2 are completely equal }
        Function OpsEqual(const o1,o2:toper): Boolean;

        { Returns true if a ait_alloc object for Reg is found in the block
          of Tai's starting with StartPai and ending with the next "real"
          instruction                                                      }
        Function FindRegAlloc(Reg: TRegister; StartPai: Tai): Boolean;

       { traces sucessive jumps to their final destination and sets it, e.g.
         je l1                je l3
         <code>               <code>
         l1:       becomes    l1:
         je l2                je l3
         <code>               <code>
         l2:                  l2:
         jmp l3               jmp l3

         the level parameter denotes how deeep we have already followed the jump,
         to avoid endless loops with constructs such as "l5: ; jmp l5"           }
        function GetFinalDestination(hp: taicpu; level: longint): boolean;

        function getlabelwithsym(sym: tasmlabel): tai;

        { peephole optimizer }
        procedure PrePeepHoleOpts;
        procedure PeepHoleOptPass1;
        procedure PeepHoleOptPass2;
        procedure PostPeepHoleOpts;

        { processor dependent methods }
        // if it returns true, perform a "continue"
        function PeepHoleOptPass1Cpu(var p: tai): boolean; virtual;
        function PostPeepHoleOptsCpu(var p: tai): boolean; virtual;
      End;

       Function ArrayRefsEq(const r1, r2: TReference): Boolean;

    { ***************************** Implementation **************************** }

  Implementation

    uses
      globals,
      verbose,
      procinfo;

      { ************************************************************************* }
      { ******************************** TUsedRegs ****************************** }
      { ************************************************************************* }

      Constructor TUsedRegs.create;
      Begin
        UsedRegs := [];
      End;

      Constructor TUsedRegs.create_regset(Const _RegSet: TRegSet);
      Begin
        UsedRegs := _RegSet;
      End;

      Procedure TUsedRegs.Update(p: Tai);
      {updates UsedRegs with the RegAlloc Information coming after P}
      Begin
        Repeat
          While Assigned(p) And
                ((p.typ in (SkipInstr - [ait_RegAlloc])) or
                 ((p.typ = ait_label) And
                  Not(Tai_Label(p).l.is_used))) Do
               p := Tai(p.next);
          While Assigned(p) And
                (p.typ=ait_RegAlloc) Do
            Begin
          {!!!!!!!! FIXME
              if tai_regalloc(p).ratype=ra_alloc then
                UsedRegs := UsedRegs + [tai_regalloc(p).Reg]
              else
                UsedRegs := UsedRegs - [tai_regalloc(p).Reg];
              p := Tai(p.next);
          }
            End;
        Until Not(Assigned(p)) Or
              (Not(p.typ in SkipInstr) And
               Not((p.typ = ait_label) And
                  Not(Tai_Label(p).l.is_used)));
      End;

      Function TUsedRegs.IsUsed(Reg: TRegister): Boolean;
      Begin
        //!!!!!!!!!!! IsUsed := Reg in UsedRegs
      End;

      Function TUsedRegs.GetUsedRegs: TRegSet;
      Begin
        GetUsedRegs := UsedRegs;
      End;

      Destructor TUsedRegs.Destroy;
        Begin
          inherited destroy;
        end;

      { ************************************************************************* }
      { **************************** TPaiProp *********************************** }
      { ************************************************************************* }

      Constructor TPaiProp.Create;
        Begin
        {!!!!!!
          UsedRegs.Init;
          CondRegs.init;
        }
        {  DirFlag: TFlagContents; I386 specific}
        End;

      Function TPaiProp.RegInSequence(Reg, which: TRegister): Boolean;
      Var p: Tai;
          RegsChecked: TRegSet;
          content: TContent;
          Counter: Byte;
          TmpResult: Boolean;
      Begin
      {!!!!!!!!!!1
        RegsChecked := [];
        content := regs[which];
        p := content.StartMod;
        TmpResult := False;
        Counter := 1;
        While Not(TmpResult) And
              (Counter <= Content.NrOfMods) Do
          Begin
            If IsLoadMemReg(p) Then
              With PInstr(p)^.oper[LoadSrc]^.ref^ Do
                If (Base = ProcInfo.FramePointer)
      {$ifdef RefsHaveIndexReg}
                   And (Index = R_NO)
      {$endif RefsHaveIndexReg} Then
                  Begin
                    RegsChecked := RegsChecked +
                      [RegMaxSize(PInstr(p)^.oper[LoadDst]^.reg)];
                    If Reg = RegMaxSize(PInstr(p)^.oper[LoadDst]^.reg) Then
                      Break;
                  End
                Else
                  Begin
                    If (Base = Reg) And
                       Not(Base In RegsChecked)
                      Then TmpResult := True;
      {$ifdef RefsHaveIndexReg}
                    If Not(TmpResult) And
                       (Index = Reg) And
                         Not(Index In RegsChecked)
                      Then TmpResult := True;
      {$Endif RefsHaveIndexReg}
                  End
            Else TmpResult := RegInInstruction(Reg, p);
            Inc(Counter);
            GetNextInstruction(p,p)
          End;
        RegInSequence := TmpResult
      }
      End;


      Procedure TPaiProp.DestroyReg(Reg: TRegister; var InstrSinceLastMod:
                  TInstrSinceLastMod);
      { Destroys the contents of the register Reg in the PPaiProp p1, as well as }
      { the contents of registers are loaded with a memory location based on Reg }
      Var TmpWState, TmpRState: Byte;
          Counter: TRegister;
      Begin
      {!!!!!!!
        Reg := RegMaxSize(Reg);
        If (Reg in [LoGPReg..HiGPReg]) Then
          For Counter := LoGPReg to HiGPReg Do
            With Regs[Counter] Do
              If (Counter = reg) Or
                 ((Typ = Con_Ref) And
                  RegInSequence(Reg, Counter)) Then
                Begin
                  InstrSinceLastMod[Counter] := 0;
                  IncWState(Counter);
                  TmpWState := GetWState(Counter);
                  TmpRState := GetRState(Counter);
                  FillChar(Regs[Counter], SizeOf(TContent), 0);
                  WState := TmpWState;
                  RState := TmpRState
                End
      }
      End;

      Function ArrayRefsEq(const r1, r2: TReference): Boolean;
      Begin
      {!!!!!!!!!!
        ArrayRefsEq := (R1.Offset+R1.OffsetFixup = R2.Offset+R2.OffsetFixup) And
      {$ifdef refsHaveSegmentReg}
                       (R1.Segment = R2.Segment) And
      {$endif}
                       (R1.Base = R2.Base) And
                       (R1.Symbol=R2.Symbol);
      }
      End;

      Procedure TPaiProp.DestroyRefs(Const Ref: TReference; WhichReg: TRegister;
                  var InstrSinceLastMod: TInstrSinceLastMod);
      { destroys all registers which possibly contain a reference to Ref, WhichReg }
      { is the register whose contents are being written to memory (if this proc   }
      { is called because of a "mov?? %reg, (mem)" instruction)                    }
      Var RefsEq: TRefCompare;
          Counter: TRegister;
      Begin
      {!!!!!!!!!!!
        WhichReg := RegMaxSize(WhichReg);
        If (Ref.base = procinfo.FramePointer) or
            Assigned(Ref.Symbol) Then
          Begin
            If
      {$ifdef refsHaveIndexReg}
               (Ref.Index = R_NO) And
      {$endif refsHaveIndexReg}
               (Not(Assigned(Ref.Symbol)) or
                (Ref.base = R_NO)) Then
        { local variable which is not an array }
              RefsEq := {$ifdef fpc}@{$endif}RefsEqual
            Else
        { local variable which is an array }
              RefsEq := {$ifdef fpc}@{$endif}ArrayRefsEq;
      {write something to a parameter, a local or global variable, so
         * with uncertain optimizations on:
            - destroy the contents of registers whose contents have somewhere a
              "mov?? (Ref), %reg". WhichReg (this is the register whose contents
              are being written to memory) is not destroyed if it's StartMod is
              of that form and NrOfMods = 1 (so if it holds ref, but is not a
              pointer or value based on Ref)
          * with uncertain optimizations off:
             - also destroy registers that contain any pointer}
            For Counter := LoGPReg to HiGPReg Do
              With Regs[Counter] Do
                Begin
                  If (typ = Con_Ref) And
                     ((Not(cs_UncertainOpts in aktglobalswitches) And
                       (NrOfMods <> 1)
                      ) Or
                      (RefInSequence(Ref,Regs[Counter], RefsEq) And
                       ((Counter <> WhichReg) Or
                        ((NrOfMods <> 1) And
       {StarMod is always of the type ait_instruction}
                         (PInstr(StartMod)^.oper[0].typ = top_ref) And
                         RefsEq(PInstr(StartMod)^.oper[0].ref^, Ref)
                        )
                       )
                      )
                     )
                    Then
                      DestroyReg(Counter, InstrSinceLastMod)
                End
          End
        Else
      {write something to a pointer location, so
         * with uncertain optimzations on:
            - do not destroy registers which contain a local/global variable or a
              parameter, except if DestroyRefs is called because of a "movsl"
         * with uncertain optimzations off:
            - destroy every register which contains a memory location
            }
            For Counter := LoGPReg to HiGPReg Do
              With Regs[Counter] Do
                If (typ = Con_Ref) And
                   (Not(cs_UncertainOpts in aktglobalswitches) Or
      {$ifdef x86}
              {for movsl}
                    (Ref.Base = R_EDI) Or
      {$endif}
              {don't destroy if reg contains a parameter, local or global variable}
                    Not((NrOfMods = 1) And
                        (PInstr(StartMod)^.oper[0].typ = top_ref) And
                        ((PInstr(StartMod)^.oper[0].ref^.base = ProcInfo.FramePointer) Or
                          Assigned(PInstr(StartMod)^.oper[0].ref^.Symbol)
                        )
                       )
                   )
                Then DestroyReg(Counter, InstrSinceLastMod)
      }
      End;

      Procedure TPaiProp.DestroyAllRegs(var InstrSinceLastMod: TInstrSinceLastMod);
      Var Counter: TRegister;
      Begin {initializes/desrtoys all registers}
      {!!!!!!!!!
        For Counter := LoGPReg To HiGPReg Do
          Begin
            ReadReg(Counter);
            DestroyReg(Counter, InstrSinceLastMod);
          End;
        CondRegs.Init;
      { FPURegs.Init; }
      }
      End;

      Procedure TPaiProp.DestroyOp(const o:Toper; var InstrSinceLastMod:
                  TInstrSinceLastMod);
      Begin
      {!!!!!!!
        Case o.typ Of
          top_reg: DestroyReg(o.reg, InstrSinceLastMod);
          top_ref:
            Begin
              ReadRef(o.ref);
              DestroyRefs(o.ref^, R_NO, InstrSinceLastMod);
            End;
          top_symbol:;
        End;
      }
      End;

      Procedure TPaiProp.ReadReg(Reg: TRegister);
      Begin
      {!!!!!!!
        Reg := RegMaxSize(Reg);
        If Reg in General_Registers Then
          IncRState(RegMaxSize(Reg))
      }
      End;

      Procedure TPaiProp.ReadRef(Ref: PReference);
      Begin
      {!!!!!!!
        If Ref^.Base <> R_NO Then
          ReadReg(Ref^.Base);
      {$ifdef refsHaveIndexReg}
        If Ref^.Index <> R_NO Then
          ReadReg(Ref^.Index);
      {$endif}
      }
      End;

      Procedure TPaiProp.ReadOp(const o:toper);
      Begin
        Case o.typ Of
          top_reg: ReadReg(o.reg);
          top_ref: ReadRef(o.ref);
        else
          internalerror(200410241);
        End;
      End;

      Procedure TPaiProp.ModifyReg(reg: TRegister; Var InstrSinceLastMod:
                                     TInstrSinceLastMod);
      Begin
      {!!!!!!!
        With Regs[reg] Do
          If (Typ = Con_Ref)
            Then
              Begin
                IncState(WState);
       {also store how many instructions are part of the sequence in the first
        instructions PPaiProp, so it can be easily accessed from within
        CheckSequence}
                Inc(NrOfMods, InstrSinceLastMod[Reg]);
                PPaiProp(StartMod.OptInfo)^.Regs[Reg].NrOfMods := NrOfMods;
                InstrSinceLastMod[Reg] := 0;
              End
            Else
              DestroyReg(Reg, InstrSinceLastMod);
      }
      End;

      Procedure TPaiProp.ModifyOp(const oper: TOper; var InstrSinceLastMod:
                  TInstrSinceLastMod);
      Begin
        If oper.typ = top_reg Then
          ModifyReg(RegMaxSize(oper.reg),InstrSinceLastMod)
        Else
          Begin
            ReadOp(oper);
            DestroyOp(oper, InstrSinceLastMod);
          End
      End;

      Procedure TPaiProp.IncWState(Reg: TRegister);{$ifdef inl} inline;{$endif inl}
      Begin
        //!!!! IncState(Regs[Reg].WState);
      End;

      Procedure TPaiProp.IncRState(Reg: TRegister);{$ifdef inl} inline;{$endif inl}
      Begin
        //!!!! IncState(Regs[Reg].RState);
      End;

      Function TPaiProp.GetWState(Reg: TRegister): TStateInt; {$ifdef inl} inline;{$endif inl}
      Begin
        //!!!! GetWState := Regs[Reg].WState
      End;

      Function TPaiProp.GetRState(Reg: TRegister): TStateInt; {$ifdef inl} inline;{$endif inl}
      Begin
        //!!!! GetRState := Regs[Reg].RState
      End;

      Function TPaiProp.GetRegContentType(Reg: TRegister): Byte; {$ifdef inl} inline;{$endif inl}
      Begin
        //!!!! GetRegContentType := Regs[Reg].typ
      End;

      Destructor TPaiProp.Done;
      Begin
        //!!!! UsedRegs.Done;
        //!!!! CondRegs.Done;
      {  DirFlag: TFlagContents; I386 specific}
      End;
      { ************************ private TPaiProp stuff ************************* }

      Procedure TPaiProp.IncState(Var s: TStateInt); {$ifdef inl} inline;{$endif inl}
      Begin
        If s <> High(TStateInt) Then Inc(s)
        Else s := 0
      End;

      Function TPaiProp.RefInInstruction(Const Ref: TReference; p: Tai;
        RefsEq: TRefCompare): Boolean;
      Var Count: AWord;
          TmpResult: Boolean;
      Begin
        TmpResult := False;
        If (p.typ = ait_instruction) Then
          Begin
            Count := 0;
            Repeat
              If (TInstr(p).oper[Count]^.typ = Top_Ref) Then
                TmpResult := RefsEq(Ref, PInstr(p)^.oper[Count]^.ref^);
              Inc(Count);
            Until (Count = MaxOps) or TmpResult;
          End;
        RefInInstruction := TmpResult;
      End;

      Function TPaiProp.RefInSequence(Const Ref: TReference; Content: TContent;
        RefsEq: TRefCompare): Boolean;
      Var p: Tai;
          Counter: Byte;
          TmpResult: Boolean;
      Begin
        p := Content.StartMod;
        TmpResult := False;
        Counter := 1;
        While Not(TmpResult) And
              (Counter <= Content.NrOfMods) Do
          Begin
            If (p.typ = ait_instruction) And
               RefInInstruction(Ref, p, {$ifdef fpc}@{$endif}references_equal)
              Then TmpResult := True;
            Inc(Counter);
            GetNextInstruction(p,p)
          End;
        RefInSequence := TmpResult
      End;

      { ************************************************************************* }
      { ***************************** TAoptObj ********************************** }
      { ************************************************************************* }

      Constructor TAoptObj.create(_AsmL: TAasmOutput; _BlockStart, _BlockEnd: Tai;
                                  _LabelInfo: PLabelInfo);
      Begin
        AsmL := _AsmL;
        BlockStart := _BlockStart;
        BlockEnd := _BlockEnd;
        LabelInfo := _LabelInfo
      End;

      Function TAOptObj.FindLabel(L: TasmLabel; Var hp: Tai): Boolean;
      Var TempP: Tai;
      Begin
        TempP := hp;
        While Assigned(TempP) and
             (TempP.typ In SkipInstr + [ait_label]) Do
          If (TempP.typ <> ait_Label) Or
             (Tai_label(TempP).l <> L)
            Then GetNextInstruction(TempP, TempP)
            Else
              Begin
                hp := TempP;
                FindLabel := True;
                exit
              End;
        FindLabel := False;
      End;

      Procedure TAOptObj.InsertLLItem(prev, foll, new_one : TLinkedListItem);
      Begin
        If Assigned(prev) Then
          If Assigned(foll) Then
            Begin
              If Assigned(new_one) Then
                Begin
                  new_one.previous := prev;
                  new_one.next := foll;
                  prev.next := new_one;
                  foll.previous := new_one;
                  { should we update line information? }
                  if (not (tai(new_one).typ in SkipLineInfo)) and
                     (not (tai(foll).typ in SkipLineInfo)) then
                    Tailineinfo(new_one).fileinfo := Tailineinfo(foll).fileinfo
                End
            End
          Else AsmL.Concat(new_one)
        Else If Assigned(Foll) Then AsmL.Insert(new_one)
      End;


      Function TAOptObj.SkipHead(P: Tai): Tai;
      Var OldP: Tai;
      Begin
        Repeat
          OldP := P;
          If (P.typ in SkipInstr) Or
             ((P.typ = ait_marker) And
              (Tai_Marker(P).Kind = AsmBlockEnd)) Then
            GetNextInstruction(P, P)
          Else If ((P.Typ = Ait_Marker) And
              (Tai_Marker(P).Kind = NoPropInfoStart)) Then
       { a marker of the type NoPropInfoStart can't be the first instruction of a }
       { paasmoutput list                                                         }
            GetNextInstruction(Tai(P.Previous),P);
          If (P.Typ = Ait_Marker) And
             (Tai_Marker(P).Kind = AsmBlockStart) Then
            Begin
              P := Tai(P.Next);
              While (P.typ <> Ait_Marker) Or
                    (Tai_Marker(P).Kind <> AsmBlockEnd) Do
                P := Tai(P.Next)
            End;
          Until P = OldP;
        SkipHead := P;
      End;

      Function TAOptObj.OpsEqual(const o1,o2:toper): Boolean;
      Begin
        if o1.typ=o2.typ then
          Case o1.typ Of
            Top_Reg :
              OpsEqual:=o1.reg=o2.reg;
            Top_Ref :
              OpsEqual := references_equal(o1.ref^, o2.ref^);
            Top_Const :
              OpsEqual:=o1.val=o2.val;
            Top_None :
              OpsEqual := True
            else OpsEqual := False
          End;
      End;

      Function TAOptObj.FindRegAlloc(Reg: TRegister; StartPai: Tai): Boolean;
      Begin
        FindRegAlloc:=False;
        Repeat
          While Assigned(StartPai) And
                ((StartPai.typ in (SkipInstr - [ait_regAlloc])) Or
                 ((StartPai.typ = ait_label) and
                  Not(Tai_Label(StartPai).l.Is_Used))) Do
            StartPai := Tai(StartPai.Next);
          If Assigned(StartPai) And
             (StartPai.typ = ait_regAlloc) and (tai_regalloc(StartPai).ratype=ra_alloc) Then
            Begin
              if tai_regalloc(StartPai).Reg = Reg then
               begin
                 FindRegAlloc:=true;
                 exit;
               end;
              StartPai := Tai(StartPai.Next);
            End
          else
            exit;
        Until false;
      End;


    function SkipLabels(hp: tai; var hp2: tai): boolean;
      {skips all labels and returns the next "real" instruction}
      begin
        while assigned(hp.next) and
              (tai(hp.next).typ in SkipInstr + [ait_label,ait_align]) Do
          hp := tai(hp.next);
        if assigned(hp.next) then
          begin
            SkipLabels := True;
            hp2 := tai(hp.next)
          end
        else
          begin
            hp2 := hp;
            SkipLabels := False
          end;
      end;


    function FindAnyLabel(hp: tai; var l: tasmlabel): Boolean;
      begin
        FindAnyLabel := false;
        while assigned(hp.next) and
              (tai(hp.next).typ in (SkipInstr+[ait_align])) Do
          hp := tai(hp.next);
        if assigned(hp.next) and
           (tai(hp.next).typ = ait_label) then
          begin
            FindAnyLabel := true;
            l := tai_label(hp.next).l;
          end
      end;


{$ifopt r+}
{$define rangewason}
{$r-}
{$endif}
    function tAOptObj.getlabelwithsym(sym: tasmlabel): tai;
      begin
        if (sym.labelnr >= labelinfo^.lowlabel) and
           (sym.labelnr <= labelinfo^.highlabel) then   { range check, a jump can go past an assembler block! }
          getlabelwithsym := labelinfo^.labeltable^[sym.labelnr-labelinfo^.lowlabel].paiobj
        else
          getlabelwithsym := nil;
      end;
{$ifdef rangewason}
{$r+}
{$undef rangewason}
{$endif}

    function TAOptObj.GetFinalDestination(hp: taicpu; level: longint): boolean;
      {traces sucessive jumps to their final destination and sets it, e.g.
       je l1                je l3
       <code>               <code>
       l1:       becomes    l1:
       je l2                je l3
       <code>               <code>
       l2:                  l2:
       jmp l3               jmp l3

       the level parameter denotes how deeep we have already followed the jump,
       to avoid endless loops with constructs such as "l5: ; jmp l5"           }

      var p1, p2: tai;
          l: tasmlabel;

      begin
        GetfinalDestination := false;
        if level > 20 then
          exit;
        p1 := getlabelwithsym(tasmlabel(hp.oper[0]^.ref^.symbol));
        if assigned(p1) then
          begin
            SkipLabels(p1,p1);
            if (tai(p1).typ = ait_instruction) and
               (taicpu(p1).is_jmp) then
              if { the next instruction after the label where the jump hp arrives}
                 { is unconditional or of the same type as hp, so continue       }
                 (((taicpu(p1).opcode = aopt_uncondjmp) and
                   (taicpu(p1).oper[0]^.typ = top_ref) and
                   (assigned(taicpu(p1).oper[0]^.ref^.symbol)) and
                   (taicpu(p1).oper[0]^.ref^.symbol is TAsmLabel)) or
                  conditions_equal(taicpu(p1).condition,hp.condition)) or
                 { the next instruction after the label where the jump hp arrives}
                 { is the opposite of hp (so this one is never taken), but after }
                 { that one there is a branch that will be taken, so perform a   }
                 { little hack: set p1 equal to this instruction (that's what the}
                 { last SkipLabels is for, only works with short bool evaluation)}
                 (conditions_equal(taicpu(p1).condition,inverse_cond(hp.condition)) and
                  SkipLabels(p1,p2) and
                  (p2.typ = ait_instruction) and
                  (taicpu(p2).is_jmp) and
                  (((taicpu(p2).opcode = aopt_uncondjmp) and
                    (taicpu(p2).oper[0]^.typ = top_ref) and
                    (assigned(taicpu(p2).oper[0]^.ref^.symbol)) and
                    (taicpu(p2).oper[0]^.ref^.symbol is TAsmLabel)) or
                   (conditions_equal(taicpu(p2).condition,hp.condition))) and
                  SkipLabels(p1,p1)) then
                begin
                  { quick check for loops of the form "l5: ; jmp l5 }
                  if (tasmlabel(taicpu(p1).oper[0]^.ref^.symbol).labelnr =
                       tasmlabel(hp.oper[0]^.ref^.symbol).labelnr) then
                    exit;
                  if not GetFinalDestination(taicpu(p1),succ(level)) then
                    exit;
                  tasmlabel(hp.oper[0]^.ref^.symbol).decrefs;
                  hp.oper[0]^.ref^.symbol:=taicpu(p1).oper[0]^.ref^.symbol;
                  tasmlabel(hp.oper[0]^.ref^.symbol).increfs;
                end
              else
                if conditions_equal(taicpu(p1).condition,inverse_cond(hp.condition)) then
                  if not FindAnyLabel(p1,l) then
                    begin
      {$ifdef finaldestdebug}
                      insertllitem(asml,p1,p1.next,tai_comment.Create(
                        strpnew('previous label inserted'))));
      {$endif finaldestdebug}
                      objectlibrary.getjumplabel(l);
                      insertllitem(p1,p1.next,tai_label.Create(l));
                      tasmlabel(taicpu(hp).oper[0]^.ref^.symbol).decrefs;
                      hp.oper[0]^.ref^.symbol := l;
                      l.increfs;
      {               this won't work, since the new label isn't in the labeltable }
      {               so it will fail the rangecheck. Labeltable should become a   }
      {               hashtable to support this:                                   }
      {               GetFinalDestination(asml, hp);                               }
                    end
                  else
                    begin
      {$ifdef finaldestdebug}
                      insertllitem(asml,p1,p1.next,tai_comment.Create(
                        strpnew('next label reused'))));
      {$endif finaldestdebug}
                      l.increfs;
                      hp.oper[0]^.ref^.symbol := l;
                      if not GetFinalDestination(hp,succ(level)) then
                        exit;
                    end;
          end;
        GetFinalDestination := true;
      end;


    procedure TAOptObj.PrePeepHoleOpts;
      begin
      end;


    procedure TAOptObj.PeepHoleOptPass1;
      var
        p,hp1,hp2 : tai;
      begin
        p := BlockStart;
        //!!!! UsedRegs := [];
        while (p <> BlockEnd) Do
          begin
            //!!!! UpDateUsedRegs(UsedRegs, tai(p.next));
            if PeepHoleOptPass1Cpu(p) then
              continue;
            case p.Typ Of
              ait_instruction:
                begin
                  { Handle Jmp Optimizations }
                  if taicpu(p).is_jmp then
                    begin
                      { the following if-block removes all code between a jmp and the next label,
                        because it can never be executed
                      }
                      if (taicpu(p).opcode = aopt_uncondjmp) and
                         (taicpu(p).oper[0]^.typ = top_ref) and
                         (assigned(taicpu(p).oper[0]^.ref^.symbol)) and
                         (taicpu(p).oper[0]^.ref^.symbol is TAsmLabel) then
                        begin
                          while GetNextInstruction(p, hp1) and
                                (hp1.typ <> ait_label) do
                            if not(hp1.typ in ([ait_label,ait_align]+skipinstr)) then
                              begin
                                asml.remove(hp1);
                                hp1.free;
                              end
                            else break;
                          end;
                      { remove jumps to a label coming right after them }
                      if GetNextInstruction(p, hp1) then
                        begin
                          if FindLabel(tasmlabel(taicpu(p).oper[0]^.ref^.symbol), hp1) and
        {$warning FIXME removing the first instruction fails}
                              (p<>blockstart) then
                            begin
                              hp2:=tai(hp1.next);
                              asml.remove(p);
                              p.free;
                              p:=hp2;
                              continue;
                            end
                          else
                            begin
                              if hp1.typ = ait_label then
                                SkipLabels(hp1,hp1);
                              if (tai(hp1).typ=ait_instruction) and
                                  (taicpu(hp1).opcode=aopt_uncondjmp) and
                                  (taicpu(hp1).oper[0]^.typ = top_ref) and
                                  (assigned(taicpu(hp1).oper[0]^.ref^.symbol)) and
                                  (taicpu(hp1).oper[0]^.ref^.symbol is TAsmLabel) and
                                  GetNextInstruction(hp1, hp2) and
                                  FindLabel(tasmlabel(taicpu(p).oper[0]^.ref^.symbol), hp2) then
                                begin
                                  if taicpu(p).opcode=aopt_condjmp then
                                    begin
                                      taicpu(p).condition:=inverse_cond(taicpu(p).condition);
                                      tai_label(hp2).l.decrefs;
                                      taicpu(p).oper[0]^.ref^.symbol:=taicpu(hp1).oper[0]^.ref^.symbol;
                                      { when freeing hp1, the reference count 
                                        isn't decreased, so don't increase
 
                                       taicpu(p).oper[0]^.ref^.symbol.increfs;
                                      }
{$ifdef SPARC}
                                      hp2:=tai(hp1.next);
                                      asml.remove(hp2);
                                      hp2.free;
{$endif SPARC}
                                      asml.remove(hp1);
                                      hp1.free;
                                      GetFinalDestination(taicpu(p),0);
                                    end
                                  else
                                    begin
                                      GetFinalDestination(taicpu(p),0);
                                      p:=tai(p.next);
                                      continue;
                                    end;
                                end
                              else
                                GetFinalDestination(taicpu(p),0);
                            end;
                        end;
                    end
                  else
                  { All other optimizes }
                    begin
                    end; { if is_jmp }
                end;
            end;
            //!!!!!!!! updateUsedRegs(UsedRegs,p);
            p:=tai(p.next);
          end;
      end;


    procedure TAOptObj.PeepHoleOptPass2;
      begin
      end;


    procedure TAOptObj.PostPeepHoleOpts;
      var
        p: tai;
      begin
        p := BlockStart;
        //!!!! UsedRegs := [];
        while (p <> BlockEnd) Do
          begin
            //!!!! UpDateUsedRegs(UsedRegs, tai(p.next));
            if PostPeepHoleOptsCpu(p) then
              continue;
            //!!!!!!!! updateUsedRegs(UsedRegs,p);
            p:=tai(p.next);
          end;
      end;


    function TAOptObj.PeepHoleOptPass1Cpu(var p: tai): boolean;
      begin
        result := false;
      end;


    function TAOptObj.PostPeepHoleOptsCpu(var p: tai): boolean;
      begin
        result := false;
      end;

End.