freepascal.compiler/compiler/i386/aoptcpu.pas

{
    Copyright (c) 1998-2002 by Florian Klaempfl and Jonas Maebe

    This unit contains the peephole optimizer for i386

    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 aoptcpu;

{$i fpcdefs.inc}

{ $define DEBUG_AOPTCPU}

  Interface

    uses
      cgbase,
      cpubase, aopt, aoptx86,
      Aasmbase,aasmtai,aasmdata;

    Type
      TCpuAsmOptimizer = class(TX86AsmOptimizer)
        procedure Optimize; override;
        procedure PrePeepHoleOpts; override;
        procedure PeepHoleOptPass1; override;
        procedure PeepHoleOptPass2; override;
        procedure PostPeepHoleOpts; override;
      end;

    Var
      AsmOptimizer : TCpuAsmOptimizer;

  Implementation

    uses
      verbose,globtype,globals,
      cpuinfo,
      aasmcpu,
      aoptutils,
      procinfo,
      cgutils,
      { units we should get rid off: }
      symsym,symconst;


  { Checks if the register is a 32 bit general purpose register }
  function isgp32reg(reg: TRegister): boolean;
    begin
      {$push}{$warnings off}
      isgp32reg:=(getregtype(reg)=R_INTREGISTER) and (getsupreg(reg)>=RS_EAX) and (getsupreg(reg)<=RS_EBX);
      {$pop}
    end;


{ returns true if p contains a memory operand with a segment set }
function InsContainsSegRef(p: taicpu): boolean;
var
  i: longint;
begin
  result:=true;
  for i:=0 to p.opercnt-1 do
    if (p.oper[i]^.typ=top_ref) and
       (p.oper[i]^.ref^.segment<>NR_NO) then
      exit;
  result:=false;
end;


procedure TCPUAsmOptimizer.PrePeepHoleOpts;
var
  p: tai;
begin
  p := BlockStart;
  while (p <> BlockEnd) Do
    begin
      case p.Typ Of
        Ait_Instruction:
          begin
            if InsContainsSegRef(taicpu(p)) then
              begin
                p := tai(p.next);
                continue;
              end;
            case taicpu(p).opcode Of
              A_IMUL:
                if PrePeepholeOptIMUL(p) then
                  Continue;
              A_SAR,A_SHR:
                if PrePeepholeOptSxx(p) then
                  continue;
              A_XOR:
                begin
                  if (taicpu(p).oper[0]^.typ = top_reg) and
                     (taicpu(p).oper[1]^.typ = top_reg) and
                     (taicpu(p).oper[0]^.reg = taicpu(p).oper[1]^.reg) then
                   { temporarily change this to 'mov reg,0' to make it easier }
                   { for the CSE. Will be changed back in pass 2              }
                    begin
                      taicpu(p).opcode := A_MOV;
                      taicpu(p).loadConst(0,0);
                    end;
                end;
              else
                ;
            end;
          end;
        else
          ;
      end;
      p := tai(p.next)
    end;
end;


{ First pass of peephole optimizations }
procedure TCPUAsmOPtimizer.PeepHoleOptPass1;

function WriteOk : Boolean;
  begin
    writeln('Ok');
    Result:=True;
  end;

var
  p,hp1,hp2 : tai;
  hp3,hp4: tai;
  v:aint;

  function GetFinalDestination(asml: TAsmList; 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;

    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).labsym;
        end
    end;

  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).condition in [C_None,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)}
             ((taicpu(p1).condition = inverse_cond(hp.condition)) and
              SkipLabels(p1,p2) and
              (p2.typ = ait_instruction) and
              (taicpu(p2).is_jmp) and
              (taicpu(p2).condition in [C_None,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(asml, 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 (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}
                  current_asmdata.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(asml, hp,succ(level)) then
                    exit;
                end;
      end;
    GetFinalDestination := true;
  end;

begin
  p := BlockStart;
  ClearUsedRegs;
  while (p <> BlockEnd) Do
    begin
      UpDateUsedRegs(UsedRegs, tai(p.next));
      case p.Typ Of
        ait_instruction:
          begin
            current_filepos:=taicpu(p).fileinfo;
            if InsContainsSegRef(taicpu(p)) then
              begin
                p := tai(p.next);
                continue;
              end;
            { 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 = A_JMP) then
                  begin
                    hp2:=p;
                    while GetNextInstruction(hp2, hp1) and
                          (hp1.typ <> ait_label) do
                      if not(hp1.typ in ([ait_label]+skipinstr)) then
                        begin
                          { don't kill start/end of assembler block,
                            no-line-info-start/end etc }
                          if not(hp1.typ in [ait_align,ait_marker]) then
                            begin
                              asml.remove(hp1);
                              hp1.free;
                            end
                          else
                            hp2:=hp1;
                        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
  { TODO: 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=A_JMP) and
                            GetNextInstruction(hp1, hp2) and
                            FindLabel(tasmlabel(taicpu(p).oper[0]^.ref^.symbol), hp2) then
                          begin
                            if taicpu(p).opcode=A_Jcc then
                              begin
                                taicpu(p).condition:=inverse_cond(taicpu(p).condition);
                                tai_label(hp2).labsym.decrefs;
                                taicpu(p).oper[0]^.ref^.symbol:=taicpu(hp1).oper[0]^.ref^.symbol;
                                { when free'ing hp1, the ref. isn't decresed, so we don't
                                  increase it (FK)

                                  taicpu(p).oper[0]^.ref^.symbol.increfs;
                                }
                                asml.remove(hp1);
                                hp1.free;
                                GetFinalDestination(asml, taicpu(p),0);
                              end
                            else
                              begin
                                GetFinalDestination(asml, taicpu(p),0);
                                p:=tai(p.next);
                                continue;
                              end;
                          end
                        else
                          GetFinalDestination(asml, taicpu(p),0);
                      end;
                  end;
              end
            else
            { All other optimizes }
              begin
                case taicpu(p).opcode Of
                  A_AND:
                    if OptPass1And(p) then
                      continue;
                  A_CMP:
                    begin
                      { cmp register,$8000                neg register
                        je target                 -->     jo target

                        .... only if register is deallocated before jump.}
                      case Taicpu(p).opsize of
                        S_B: v:=$80;
                        S_W: v:=$8000;
                        S_L: v:=aint($80000000);
                        else
                          internalerror(2013112905);
                      end;
                      if (taicpu(p).oper[0]^.typ=Top_const) and
                         (taicpu(p).oper[0]^.val=v) and
                         (Taicpu(p).oper[1]^.typ=top_reg) and
                         GetNextInstruction(p, hp1) and
                         (hp1.typ=ait_instruction) and
                         (taicpu(hp1).opcode=A_Jcc) and
                         (Taicpu(hp1).condition in [C_E,C_NE]) and
                         not(RegInUsedRegs(Taicpu(p).oper[1]^.reg, UsedRegs)) then
                        begin
                          Taicpu(p).opcode:=A_NEG;
                          Taicpu(p).loadoper(0,Taicpu(p).oper[1]^);
                          Taicpu(p).clearop(1);
                          Taicpu(p).ops:=1;
                          if Taicpu(hp1).condition=C_E then
                            Taicpu(hp1).condition:=C_O
                          else
                            Taicpu(hp1).condition:=C_NO;
                          continue;
                        end;
                      {
                      @@2:                              @@2:
                        ....                              ....
                        cmp operand1,0
                        jle/jbe @@1
                        dec operand1             -->      sub operand1,1
                        jmp @@2                           jge/jae @@2
                      @@1:                              @@1:
                        ...                               ....}
                      if (taicpu(p).oper[0]^.typ = top_const) and
                         (taicpu(p).oper[1]^.typ in [top_reg,top_ref]) and
                         (taicpu(p).oper[0]^.val = 0) and
                         GetNextInstruction(p, hp1) and
                         (hp1.typ = ait_instruction) and
                         (taicpu(hp1).is_jmp) and
                         (taicpu(hp1).opcode=A_Jcc) and
                         (taicpu(hp1).condition in [C_LE,C_BE]) and
                         GetNextInstruction(hp1,hp2) and
                         (hp2.typ = ait_instruction) and
                         (taicpu(hp2).opcode = A_DEC) and
                         OpsEqual(taicpu(hp2).oper[0]^,taicpu(p).oper[1]^) and
                         GetNextInstruction(hp2, hp3) and
                         (hp3.typ = ait_instruction) and
                         (taicpu(hp3).is_jmp) and
                         (taicpu(hp3).opcode = A_JMP) and
                         GetNextInstruction(hp3, hp4) and
                         FindLabel(tasmlabel(taicpu(hp1).oper[0]^.ref^.symbol),hp4) then
                        begin
                          taicpu(hp2).Opcode := A_SUB;
                          taicpu(hp2).loadoper(1,taicpu(hp2).oper[0]^);
                          taicpu(hp2).loadConst(0,1);
                          taicpu(hp2).ops:=2;
                          taicpu(hp3).Opcode := A_Jcc;
                          case taicpu(hp1).condition of
                            C_LE: taicpu(hp3).condition := C_GE;
                            C_BE: taicpu(hp3).condition := C_AE;
                            else
                              internalerror(2019050903);
                          end;
                          asml.remove(p);
                          asml.remove(hp1);
                          p.free;
                          hp1.free;
                          p := hp2;
                          continue;
                        end
                    end;
                  A_FLD:
                    if OptPass1FLD(p) then
                      continue;
                  A_FSTP,A_FISTP:
                    if OptPass1FSTP(p) then
                      continue;
                  A_LEA:
                    begin
                      if OptPass1LEA(p) then
                        continue;
                    end;

                  A_MOV:
                    begin
                      If OptPass1MOV(p) then
                        Continue;
                    end;

                  A_MOVSX,
                  A_MOVZX :
                    begin
                      If OptPass1Movx(p) then
                        Continue
                    end;

(* should not be generated anymore by the current code generator
                  A_POP:
                    begin
                      if target_info.system=system_i386_go32v2 then
                      begin
                        { Transform a series of pop/pop/pop/push/push/push to }
                        { 'movl x(%esp),%reg' for go32v2 (not for the rest,   }
                        { because I'm not sure whether they can cope with     }
                        { 'movl x(%esp),%reg' with x > 0, I believe we had    }
                        { such a problem when using esp as frame pointer (JM) }
                        if (taicpu(p).oper[0]^.typ = top_reg) then
                          begin
                            hp1 := p;
                            hp2 := p;
                            l := 0;
                            while getNextInstruction(hp1,hp1) and
                                  (hp1.typ = ait_instruction) and
                                  (taicpu(hp1).opcode = A_POP) and
                                  (taicpu(hp1).oper[0]^.typ = top_reg) do
                              begin
                                hp2 := hp1;
                                inc(l,4);
                              end;
                            getLastInstruction(p,hp3);
                            l1 := 0;
                            while (hp2 <> hp3) and
                                  assigned(hp1) and
                                  (hp1.typ = ait_instruction) and
                                  (taicpu(hp1).opcode = A_PUSH) and
                                  (taicpu(hp1).oper[0]^.typ = top_reg) and
                                  (taicpu(hp1).oper[0]^.reg.enum = taicpu(hp2).oper[0]^.reg.enum) do
                              begin
                                { change it to a two op operation }
                                taicpu(hp2).oper[1]^.typ:=top_none;
                                taicpu(hp2).ops:=2;
                                taicpu(hp2).opcode := A_MOV;
                                taicpu(hp2).loadoper(1,taicpu(hp1).oper[0]^);
                                reference_reset(tmpref);
                                tmpRef.base.enum:=R_INTREGISTER;
                                tmpRef.base.number:=NR_STACK_POINTER_REG;
                                convert_register_to_enum(tmpref.base);
                                tmpRef.offset := l;
                                taicpu(hp2).loadRef(0,tmpRef);
                                hp4 := hp1;
                                getNextInstruction(hp1,hp1);
                                asml.remove(hp4);
                                hp4.free;
                                getLastInstruction(hp2,hp2);
                                dec(l,4);
                                inc(l1);
                              end;
                            if l <> -4 then
                              begin
                                inc(l,4);
                                for l1 := l1 downto 1 do
                                  begin
                                    getNextInstruction(hp2,hp2);
                                    dec(taicpu(hp2).oper[0]^.ref^.offset,l);
                                  end
                              end
                          end
                        end
                      else
                        begin
                          if (taicpu(p).oper[0]^.typ = top_reg) and
                            GetNextInstruction(p, hp1) and
                            (tai(hp1).typ=ait_instruction) and
                            (taicpu(hp1).opcode=A_PUSH) and
                            (taicpu(hp1).oper[0]^.typ = top_reg) and
                            (taicpu(hp1).oper[0]^.reg.enum=taicpu(p).oper[0]^.reg.enum) then
                            begin
                              { change it to a two op operation }
                              taicpu(p).oper[1]^.typ:=top_none;
                              taicpu(p).ops:=2;
                              taicpu(p).opcode := A_MOV;
                              taicpu(p).loadoper(1,taicpu(p).oper[0]^);
                              reference_reset(tmpref);
                              TmpRef.base.enum := R_ESP;
                              taicpu(p).loadRef(0,TmpRef);
                              asml.remove(hp1);
                              hp1.free;
                            end;
                        end;
                    end;
*)
                  A_PUSH:
                    begin
                      if (taicpu(p).opsize = S_W) and
                         (taicpu(p).oper[0]^.typ = Top_Const) and
                         GetNextInstruction(p, hp1) and
                         (tai(hp1).typ = ait_instruction) and
                         (taicpu(hp1).opcode = A_PUSH) and
                         (taicpu(hp1).oper[0]^.typ = Top_Const) and
                         (taicpu(hp1).opsize = S_W) then
                        begin
                          taicpu(p).changeopsize(S_L);
                          taicpu(p).loadConst(0,taicpu(p).oper[0]^.val shl 16 + word(taicpu(hp1).oper[0]^.val));
                          asml.remove(hp1);
                          hp1.free;
                        end;
                    end;
                  A_SHL, A_SAL:
                    if OptPass1SHLSAL(p) then
                      Continue;
                  A_SUB:
                    if OptPass1Sub(p) then
                      continue;
                  A_VMOVAPS,
                  A_VMOVAPD:
                    if OptPass1VMOVAP(p) then
                      continue;
                  A_VDIVSD,
                  A_VDIVSS,
                  A_VSUBSD,
                  A_VSUBSS,
                  A_VMULSD,
                  A_VMULSS,
                  A_VADDSD,
                  A_VADDSS,
                  A_VANDPD,
                  A_VANDPS,
                  A_VORPD,
                  A_VORPS,
                  A_VXORPD,
                  A_VXORPS:
                    if OptPass1VOP(p) then
                      continue;
                  A_MULSD,
                  A_MULSS,
                  A_ADDSD,
                  A_ADDSS:
                    if OptPass1OP(p) then
                      continue;
                  A_MOVAPD,
                  A_MOVAPS:
                    if OptPass1MOVAP(p) then
                      continue;
                  A_VMOVSD,
                  A_VMOVSS,
                  A_MOVSD,
                  A_MOVSS:
                    if OptPass1MOVXX(p) then
                      continue;
                  A_SETcc:
                    begin
                      if OptPass1SETcc(p) then
                        continue;
                    end
                  else
                    ;
                end;
            end; { if is_jmp }
          end;
        else
          ;
      end;
      updateUsedRegs(UsedRegs,p);
      p:=tai(p.next);
    end;
end;


procedure TCPUAsmOptimizer.PeepHoleOptPass2;
var
  p : tai;
begin
  p := BlockStart;
  ClearUsedRegs;
  while (p <> BlockEnd) Do
    begin
      UpdateUsedRegs(UsedRegs, tai(p.next));
      case p.Typ Of
        Ait_Instruction:
          begin
            if InsContainsSegRef(taicpu(p)) then
              begin
                p := tai(p.next);
                continue;
              end;
            case taicpu(p).opcode Of
              A_Jcc:
                if OptPass2Jcc(p) then
                  continue;
              A_FSTP,A_FISTP:
                if OptPass1FSTP(p) then
                  continue;
              A_IMUL:
                if OptPass2Imul(p) then
                  continue;
              A_JMP:
                if OptPass2Jmp(p) then
                  continue;
              A_MOV:
                begin
                  if OptPass2MOV(p) then
                    continue;
                end
              else
                ;
            end;
          end;
        else
          ;
      end;
      p := tai(p.next)
    end;
end;


procedure TCPUAsmOptimizer.PostPeepHoleOpts;
var
  p,hp1: tai;
begin
  p := BlockStart;
  ClearUsedRegs;
  while (p <> BlockEnd) Do
    begin
      UpdateUsedRegs(UsedRegs, tai(p.next));
      case p.Typ Of
        Ait_Instruction:
          begin
            if InsContainsSegRef(taicpu(p)) then
              begin
                p := tai(p.next);
                continue;
              end;
            case taicpu(p).opcode Of
              A_CALL:
                if PostPeepHoleOptCall(p) then
                  Continue;
              A_LEA:
                if PostPeepholeOptLea(p) then
                  Continue;
              A_CMP:
                if PostPeepholeOptCmp(p) then
                  Continue;
              A_MOV:
                if PostPeepholeOptMov(p) then
                  Continue;
              A_MOVZX:
                { if register vars are on, it's possible there is code like }
                {   "cmpl $3,%eax; movzbl 8(%ebp),%ebx; je .Lxxx"           }
                { so we can't safely replace the movzx then with xor/mov,   }
                { since that would change the flags (JM)                    }
                if not(cs_opt_regvar in current_settings.optimizerswitches) then
                 begin
                  if (taicpu(p).oper[1]^.typ = top_reg) then
                    if (taicpu(p).oper[0]^.typ = top_reg)
                      then
                        case taicpu(p).opsize of
                          S_BL:
                            begin
                              if IsGP32Reg(taicpu(p).oper[1]^.reg) and
                                 not(cs_opt_size in current_settings.optimizerswitches) and
                                 (current_settings.optimizecputype = cpu_Pentium) then
                                  {Change "movzbl %reg1, %reg2" to
                                   "xorl %reg2, %reg2; movb %reg1, %reg2" for Pentium and
                                   PentiumMMX}
                                begin
                                  hp1 := taicpu.op_reg_reg(A_XOR, S_L,
                                              taicpu(p).oper[1]^.reg, taicpu(p).oper[1]^.reg);
                                  InsertLLItem(p.previous, p, hp1);
                                  taicpu(p).opcode := A_MOV;
                                  taicpu(p).changeopsize(S_B);
                                  setsubreg(taicpu(p).oper[1]^.reg,R_SUBL);
                                end;
                            end;
                          else
                            ;
                        end
                      else if (taicpu(p).oper[0]^.typ = top_ref) and
                          (taicpu(p).oper[0]^.ref^.base <> taicpu(p).oper[1]^.reg) and
                          (taicpu(p).oper[0]^.ref^.index <> taicpu(p).oper[1]^.reg) and
                          not(cs_opt_size in current_settings.optimizerswitches) and
                          IsGP32Reg(taicpu(p).oper[1]^.reg) and
                          (current_settings.optimizecputype = cpu_Pentium) and
                          (taicpu(p).opsize = S_BL) then
                        {changes "movzbl mem, %reg" to "xorl %reg, %reg; movb mem, %reg8" for
                          Pentium and PentiumMMX}
                        begin
                          hp1 := taicpu.Op_reg_reg(A_XOR, S_L, taicpu(p).oper[1]^.reg,
                                      taicpu(p).oper[1]^.reg);
                          taicpu(p).opcode := A_MOV;
                          taicpu(p).changeopsize(S_B);
                          setsubreg(taicpu(p).oper[1]^.reg,R_SUBL);
                          InsertLLItem(p.previous, p, hp1);
                        end;
                 end;
              A_TEST, A_OR:
                begin
                  if PostPeepholeOptTestOr(p) then
                    Continue;
                end;
              else
                ;
            end;
          end;
        else
          ;
      end;
      p := tai(p.next)
    end;
  OptReferences;
end;


Procedure TCpuAsmOptimizer.Optimize;
Var
  HP: Tai;
  pass: longint;
  slowopt, changed, lastLoop: boolean;
Begin
  slowopt := (cs_opt_level3 in current_settings.optimizerswitches);
  pass := 0;
  changed := false;
  repeat
     lastLoop :=
       not(slowopt) or
       (not changed and (pass > 2)) or
      { prevent endless loops }
       (pass = 4);
     changed := false;
   { Setup labeltable, always necessary }
     blockstart := tai(asml.first);
     pass_1;
   { Blockend now either contains an ait_marker with Kind = mark_AsmBlockStart, }
   { or nil                                                                }
     While Assigned(BlockStart) Do
       Begin
         if (cs_opt_peephole in current_settings.optimizerswitches) then
           begin
            if (pass = 0) then
              PrePeepHoleOpts;
              { Peephole optimizations }
               PeepHoleOptPass1;
              { Only perform them twice in the first pass }
               if pass = 0 then
                 PeepHoleOptPass1;
           end;
        { More peephole optimizations }
         if (cs_opt_peephole in current_settings.optimizerswitches) then
           begin
             PeepHoleOptPass2;
             if lastLoop then
               PostPeepHoleOpts;
           end;

        { Continue where we left off, BlockEnd is either the start of an }
        { assembler block or nil                                         }
         BlockStart := BlockEnd;
         While Assigned(BlockStart) And
               (BlockStart.typ = ait_Marker) And
               (Tai_Marker(BlockStart).Kind = mark_AsmBlockStart) Do
           Begin
           { We stopped at an assembler block, so skip it }
            Repeat
              BlockStart := Tai(BlockStart.Next);
            Until (BlockStart.Typ = Ait_Marker) And
                  (Tai_Marker(Blockstart).Kind = mark_AsmBlockEnd);
           { Blockstart now contains a Tai_marker(mark_AsmBlockEnd) }
             If GetNextInstruction(BlockStart, HP) And
                ((HP.typ <> ait_Marker) Or
                 (Tai_Marker(HP).Kind <> mark_AsmBlockStart)) Then
             { There is no assembler block anymore after the current one, so }
             { optimize the next block of "normal" instructions              }
               pass_1
             { Otherwise, skip the next assembler block }
             else
               blockStart := hp;
           End;
       End;
     inc(pass);
  until lastLoop;
  dfa.free;

End;


begin
  casmoptimizer:=TCpuAsmOptimizer;
end.