M2compiler-V3/compiler/src/Lower.mod

IMPLEMENTATION MODULE Lower;
(* Scalar/boolean/control-flow walk (L0-L2): see Lower.def and
   docs/plan-lower.md.  No FORWARD declarations: sequence iteration and
   statement dispatch are merged into CanStmt / LowerStmt. *)

IMPORT AST, SymTab, QbeGen;

(* ---------------- self-contained symbol tables (zero SymTab surface) ----
   Flat arrays only, no ARRAY OF RECORD: a record's array field loses its
   length word in static array data, and V3 miscompiles that when the
   field is passed as an open array (docs/wip/nested-array-field-bug.mod).
   Names live in flat CHAR arrays indexed manually at slot * 64. *)

CONST
  MaxSym  = 512;
  MaxName = 63;
  MaxProc = 64;
  MaxPar  = 32;

VAR
  symName  : ARRAY [0 .. MaxSym * 64 - 1] OF CHAR;
  symKind  : ARRAY [0 .. MaxSym - 1] OF INTEGER;
  symTy    : ARRAY [0 .. MaxSym - 1] OF SymTab.TypeIndex;
  nSyms    : CARDINAL;
  procName : ARRAY [0 .. MaxProc * 64 - 1] OF CHAR;
  procUid  : ARRAY [0 .. MaxProc - 1] OF CARDINAL;
  procRes  : ARRAY [0 .. MaxProc - 1] OF SymTab.TypeIndex;
  procDep  : ARRAY [0 .. MaxProc - 1] OF CARDINAL;
  procExt  : ARRAY [0 .. MaxProc - 1] OF BOOLEAN;
  procNpar : ARRAY [0 .. MaxProc - 1] OF CARDINAL;
  parTy    : ARRAY [0 .. MaxProc * MaxPar - 1] OF SymTab.TypeIndex;
  parVar   : ARRAY [0 .. MaxProc * MaxPar - 1] OF BOOLEAN;
  parName  : ARRAY [0 .. MaxProc * MaxPar * 64 - 1] OF CHAR;
  nProcs   : CARDINAL;
  withRec  : ARRAY [0 .. 15] OF SymTab.TypeIndex;
  withTop  : CARDINAL;

PROCEDURE CopyN (src: ARRAY OF CHAR; VAR dst: ARRAY OF CHAR);
  VAR i: CARDINAL;
  BEGIN
    i := 0;
    WHILE (i < MaxName) AND (src[i] # CHR(0)) DO dst[i] := src[i]; INC(i) END;
    dst[i] := CHR(0)
  END CopyN;

PROCEDURE CopySpan (src: ARRAY OF CHAR; VAR dst: ARRAY OF CHAR;
                    srcOff, dstOff: CARDINAL);
  VAR i: CARDINAL;
  BEGIN
    i := 0;
    WHILE (i < MaxName) AND (src[srcOff + i] # CHR(0)) DO
      dst[dstOff + i] := src[srcOff + i]; INC(i)
    END;
    dst[dstOff + i] := CHR(0)
  END CopySpan;

PROCEDURE Reset;
  BEGIN
    nSyms := 0; nProcs := 0
  END Reset;

PROCEDURE NoteVar (name: ARRAY OF CHAR; kind: INTEGER; t: SymTab.TypeIndex);
  BEGIN
    IF nSyms >= MaxSym THEN RETURN END;
    CopySpan(name, symName, 0, nSyms * 64);
    symKind[nSyms] := kind; symTy[nSyms] := t; INC(nSyms)
  END NoteVar;

PROCEDURE ScopeEnter;
  BEGIN
  END ScopeEnter;

PROCEDURE ScopeLeave;
  BEGIN
  END ScopeLeave;

PROCEDURE NoteProc (name: ARRAY OF CHAR; uid: CARDINAL;
                    res: SymTab.TypeIndex; depth: CARDINAL; ext: BOOLEAN);
  BEGIN
    IF nProcs >= MaxProc THEN RETURN END;
    CopySpan(name, procName, 0, nProcs * 64);
    procUid[nProcs] := uid; procRes[nProcs] := res;
    procDep[nProcs] := depth; procExt[nProcs] := ext;
    procNpar[nProcs] := 0;
    INC(nProcs)
  END NoteProc;

PROCEDURE SetProcRes (t: SymTab.TypeIndex);
  BEGIN
    IF nProcs > 0 THEN procRes[nProcs - 1] := t END
  END SetProcRes;

PROCEDURE NoteParam (name: ARRAY OF CHAR; t: SymTab.TypeIndex; isVar: BOOLEAN);
  VAR j: CARDINAL;
  BEGIN
    IF nProcs = 0 THEN RETURN END;
    j := procNpar[nProcs - 1];
    IF j >= MaxPar THEN RETURN END;
    CopySpan(name, parName, 0, (nProcs - 1) * MaxPar * 64 + j * 64);
    parTy[(nProcs - 1) * MaxPar + j] := t;
    parVar[(nProcs - 1) * MaxPar + j] := isVar;
    procNpar[nProcs - 1] := j + 1
  END NoteParam;

PROCEDURE FindSym (name: ARRAY OF CHAR; VAR kind: INTEGER;
                   VAR t: SymTab.TypeIndex): BOOLEAN;
  VAR i: CARDINAL; j: CARDINAL; ok: BOOLEAN;
  BEGIN
    i := nSyms;
    WHILE i > 0 DO
      DEC(i);
      ok := TRUE; j := 0;
      WHILE ok AND (j < 64) AND (symName[i * 64 + j] # CHR(0)) DO
        IF symName[i * 64 + j] # name[j] THEN ok := FALSE END;
        INC(j)
      END;
      IF ok AND (symName[i * 64 + j] = name[j]) THEN
        kind := symKind[i]; t := symTy[i]; RETURN TRUE
      END
    END;
    RETURN FALSE
  END FindSym;

PROCEDURE FindProc (name: ARRAY OF CHAR): INTEGER;
  VAR i: CARDINAL; j: CARDINAL; ok: BOOLEAN;
  BEGIN
    i := nProcs;
    WHILE i > 0 DO
      DEC(i);
      ok := TRUE; j := 0;
      WHILE ok AND (j < 64) AND (procName[i * 64 + j] # CHR(0)) DO
        IF procName[i * 64 + j] # name[j] THEN ok := FALSE END;
        INC(j)
      END;
      IF ok AND (procName[i * 64 + j] = name[j]) THEN RETURN VAL(INTEGER, i) END
    END;
    RETURN -1
  END FindProc;

PROCEDURE Resolve (nm: ARRAY OF CHAR; VAR k: INTEGER;
                   VAR t: SymTab.TypeIndex): BOOLEAN;
  VAR kind: INTEGER; ti: SymTab.TypeIndex;
  BEGIN
    IF FindSym(nm, kind, ti) THEN k := kind; t := ti; RETURN TRUE END;
    IF SymTab.Lookup(nm) THEN k := SymTab.SymKind(nm); t := SymTab.SymType(nm);
      RETURN TRUE
    END;
    RETURN FALSE
  END Resolve;

PROCEDURE ProcInfo (nm: ARRAY OF CHAR; VAR uid: CARDINAL;
                    VAR res: SymTab.TypeIndex; VAR depth: CARDINAL;
                    VAR ext: BOOLEAN; VAR npar: CARDINAL): BOOLEAN;
  VAR i: INTEGER;
  BEGIN
    i := FindProc(nm);
    IF i < 0 THEN RETURN FALSE END;
    uid := procUid[i]; res := procRes[i]; depth := procDep[i];
    ext := procExt[i]; npar := procNpar[i];
    RETURN TRUE
  END ProcInfo;

PROCEDURE ParamInfo (nm: ARRAY OF CHAR; i: CARDINAL;
                     VAR t: SymTab.TypeIndex; VAR isVar: BOOLEAN;
                     VAR pn: ARRAY OF CHAR): BOOLEAN;
  VAR k: INTEGER;
  BEGIN
    k := FindProc(nm);
    IF (k < 0) OR (i >= procNpar[k]) THEN RETURN FALSE END;
    t := parTy[VAL(CARDINAL, k) * MaxPar + i];
    isVar := parVar[VAL(CARDINAL, k) * MaxPar + i];
    CopySpan(parName, pn, VAL(CARDINAL, k) * MaxPar * 64 + i * 64, 0);
    RETURN TRUE
  END ParamInfo;

PROCEDURE WithField (nm: ARRAY OF CHAR; VAR k: INTEGER;
                     VAR t: SymTab.TypeIndex; VAR q: QbeGen.QVal): BOOLEAN;
(* Resolves a bare ident as a field of an open WITH record (innermost
   first), leaving the field address in q and k=KindField. *)
  VAR wt: CARDINAL; fo: INTEGER; qb: QbeGen.QVal;
  BEGIN
    wt := withTop;
    WHILE wt > 0 DO
      DEC(wt);
      IF SymTab.FieldExists(withRec[wt], nm) THEN
        t := SymTab.FieldType(withRec[wt], nm);
        fo := SymTab.FieldOffset(withRec[wt], nm);
        k := SymTab.KindField;
        IF QbeGen.TopWith(qb) THEN QbeGen.FieldAddr(qb, fo, q)
        ELSE QbeGen.CopyOp("0", q)
        END;
        RETURN TRUE
      END
    END;
    RETURN FALSE
  END WithField;

PROCEDURE Name (n: AST.Node; VAR s: ARRAY OF CHAR);
  BEGIN
    IF n = AST.NoNode THEN s[0] := CHR(0)
    ELSE AST.Txt(AST.Child(n, 0), s)
    END
  END Name;

PROCEDURE ParamName (proc: ARRAY OF CHAR; i: CARDINAL;
                     VAR s: ARRAY OF CHAR);
  VAR t: SymTab.TypeIndex; isV: BOOLEAN;
  BEGIN
    IF NOT ParamInfo(proc, i, t, isV, s) THEN s[0] := CHR(0) END
  END ParamName;

PROCEDURE IsArith (op: INTEGER): BOOLEAN;
  BEGIN
    RETURN (op = AST.OpAdd) OR (op = AST.OpSub) OR (op = AST.OpMul)
        OR (op = AST.OpDiv) OR (op = AST.OpMod)
  END IsArith;

PROCEDURE IsRel (op: INTEGER): BOOLEAN;
  BEGIN
    RETURN ((op >= AST.OpEq) AND (op <= AST.OpGe)) OR (op = AST.OpIn)
  END IsRel;

PROCEDURE RelSym (a: INTEGER; VAR s: INTEGER): BOOLEAN;
  BEGIN
    IF a = AST.OpEq THEN s := SymTab.OpEq
    ELSIF a = AST.OpNe THEN s := SymTab.OpNeq1
    ELSIF a = AST.OpLt THEN s := SymTab.OpLt
    ELSIF a = AST.OpLe THEN s := SymTab.OpLe
    ELSIF a = AST.OpGt THEN s := SymTab.OpGt
    ELSIF a = AST.OpGe THEN s := SymTab.OpGe
    ELSE RETURN FALSE
    END;
    RETURN TRUE
  END RelSym;

PROCEDURE IsScalarClass (cls: INTEGER): BOOLEAN;
  BEGIN
    RETURN (cls = SymTab.ClInt) OR (cls = SymTab.ClBool)
        OR (cls = SymTab.ClChar) OR (cls = SymTab.ClUChar)
        OR (cls = SymTab.ClEnum)
  END IsScalarClass;

PROCEDURE IsSimpleScalar (n: AST.Node): BOOLEAN;
  VAR nm: SymTab.Name; k: INTEGER; t: SymTab.TypeIndex;
  BEGIN
    IF (AST.Kind(n) # AST.NkDesignator) OR (AST.NChild(n) # 1) THEN
      RETURN FALSE END;
    IF AST.Kind(AST.Child(n, 0)) # AST.NkIdent THEN RETURN FALSE END;
    Name(AST.Child(n, 0), nm);
    IF NOT Resolve(nm, k, t) THEN RETURN FALSE END;
    IF (k # SymTab.KindVar) AND (k # SymTab.KindParam)
       AND (k # SymTab.KindConst) THEN
      RETURN FALSE END;
    IF SymTab.Equal(nm, "TRUE") OR SymTab.Equal(nm, "FALSE") THEN
      RETURN TRUE END;
    RETURN IsScalarClass(SymTab.ClassOf(t))
  END IsSimpleScalar;

PROCEDURE CalleeName (call: AST.Node; VAR nm: SymTab.Name);
(* The callee of NkCall: child 0 is a designator (or bare ident). *)
  VAR d: AST.Node;
  BEGIN
    nm[0] := CHR(0);
    d := AST.Child(call, 0);
    IF d = AST.NoNode THEN RETURN END;
    IF AST.Kind(d) = AST.NkDesignator THEN d := AST.Child(d, 0) END;
    IF (d # AST.NoNode) AND (AST.Kind(d) = AST.NkIdent) THEN Name(d, nm) END
  END CalleeName;

PROCEDURE IsCall (n: AST.Node): BOOLEAN;
  VAR nm: SymTab.Name;
  BEGIN
    IF (AST.Kind(n) # AST.NkCall) OR (AST.NChild(n) < 1) THEN RETURN FALSE END;
    CalleeName(n, nm);
    RETURN FindProc(nm) >= 0
  END IsCall;

PROCEDURE CanCallArgs (n: AST.Node): BOOLEAN;
  VAR nm: SymTab.Name; i: CARDINAL;
      uid, depth, np: CARDINAL; res: SymTab.TypeIndex; ext: BOOLEAN;
  BEGIN
    CalleeName(n, nm);
    IF NOT ProcInfo(nm, uid, res, depth, ext, np) THEN RETURN FALSE END;
    IF np # (AST.NChild(n) - 1) THEN RETURN FALSE END;
    i := 1;
    WHILE i < AST.NChild(n) DO
      IF NOT CanExpr(AST.Child(n, i)) THEN RETURN FALSE END;
      INC(i)
    END;
    RETURN TRUE
  END CanCallArgs;

PROCEDURE CanType (t: SymTab.TypeIndex): BOOLEAN;
  VAR cls: INTEGER;
  BEGIN
    IF t = SymTab.InvalidType THEN RETURN FALSE END;
    cls := SymTab.ClassOf(t);
    RETURN (cls = SymTab.ClInt) OR (cls = SymTab.ClBool)
        OR (cls = SymTab.ClChar) OR (cls = SymTab.ClUChar)
        OR (cls = SymTab.ClEnum) OR (cls = SymTab.ClReal)
        OR (cls = SymTab.ClLong) OR (cls = SymTab.ClArray)
        OR (cls = SymTab.ClSet) OR (cls = SymTab.ClRecord)
        OR (cls = SymTab.ClPtr)
  END CanType;

PROCEDURE CanWithField (nm: ARRAY OF CHAR; VAR t: SymTab.TypeIndex): BOOLEAN;
  VAR wt: CARDINAL;
  BEGIN
    wt := withTop;
    WHILE wt > 0 DO
      DEC(wt);
      IF SymTab.FieldExists(withRec[wt], nm) THEN
        t := SymTab.FieldType(withRec[wt], nm); RETURN TRUE
      END
    END;
    RETURN FALSE
  END CanWithField;

PROCEDURE DesignTypeOf (n: AST.Node): SymTab.TypeIndex;
(* Static type of a designator (no emit); used to push WITH scopes. *)
  VAR nm, fn: SymTab.Name; k: INTEGER; t: SymTab.TypeIndex;
      i: CARDINAL; sel: AST.Node;
  BEGIN
    IF (n = AST.NoNode) OR (AST.Kind(n) # AST.NkDesignator) THEN
      RETURN SymTab.InvalidType
    END;
    Name(AST.Child(n, 0), nm);
    IF NOT Resolve(nm, k, t) THEN
      IF NOT CanWithField(nm, t) THEN RETURN SymTab.InvalidType END
    END;
    i := 1;
    WHILE i < AST.NChild(n) DO
      sel := AST.Child(n, i);
      IF AST.Op(sel) = AST.SelField THEN
        Name(AST.Child(sel, 0), fn); t := SymTab.FieldType(t, fn)
      ELSIF AST.Op(sel) = AST.SelIndex THEN
        t := SymTab.ArrayElem(t)
      ELSIF AST.Op(sel) = AST.SelDeref THEN
        t := SymTab.PtrBase(t)
      END;
      INC(i)
    END;
    RETURN t
  END DesignTypeOf;

PROCEDURE CanDesign (n: AST.Node): BOOLEAN;
  VAR nm, fn: SymTab.Name; k: INTEGER; t: SymTab.TypeIndex;
      i: CARDINAL; sel: AST.Node;
  BEGIN
    IF AST.Kind(n) # AST.NkDesignator THEN RETURN FALSE END;
    IF AST.Kind(AST.Child(n, 0)) # AST.NkIdent THEN RETURN FALSE END;
    Name(AST.Child(n, 0), nm);
    IF NOT Resolve(nm, k, t) THEN
      IF NOT CanWithField(nm, t) THEN RETURN FALSE END;
      k := SymTab.KindField
    END;
    IF (k # SymTab.KindVar) AND (k # SymTab.KindParam)
       AND (k # SymTab.KindConst) AND (k # SymTab.KindField) THEN
      RETURN FALSE
    END;
    IF NOT CanType(t) THEN RETURN FALSE END;
    i := 1;
    WHILE i < AST.NChild(n) DO
      sel := AST.Child(n, i);
      IF AST.Op(sel) = AST.SelField THEN
        IF (t = SymTab.InvalidType)
           OR ((SymTab.ClassOf(t) # SymTab.ClRecord)
               AND (SymTab.ClassOf(t) # SymTab.ClClass)) THEN
          RETURN FALSE
        END;
        Name(AST.Child(sel, 0), fn);
        IF NOT SymTab.FieldExists(t, fn) THEN RETURN FALSE END;
        t := SymTab.FieldType(t, fn)
      ELSIF AST.Op(sel) = AST.SelIndex THEN
        IF (t = SymTab.InvalidType)
           OR (SymTab.ClassOf(t) # SymTab.ClArray) THEN RETURN FALSE END;
        IF NOT CanExpr(AST.Child(sel, 0)) THEN RETURN FALSE END;
        t := SymTab.ArrayElem(t)
      ELSIF AST.Op(sel) = AST.SelDeref THEN
        IF (t = SymTab.InvalidType)
           OR (SymTab.ClassOf(t) # SymTab.ClPtr) THEN RETURN FALSE END;
        t := SymTab.PtrBase(t)
      ELSE RETURN FALSE
      END;
      IF NOT CanType(t) THEN RETURN FALSE END;
      INC(i)
    END;
    RETURN TRUE
  END CanDesign;

PROCEDURE CanBuiltin (n: AST.Node): BOOLEAN;
  VAR i: CARDINAL;
  BEGIN
    i := 1;
    WHILE i < AST.NChild(n) DO
      IF NOT CanExpr(AST.Child(n, i)) THEN RETURN FALSE END;
      INC(i)
    END;
    RETURN TRUE
  END CanBuiltin;

PROCEDURE CanCaseLabel (lab: AST.Node): BOOLEAN;
  BEGIN
    IF AST.Kind(lab) = AST.NkSubrange THEN
      RETURN CanExpr(AST.Child(lab, 0)) AND CanExpr(AST.Child(lab, 1))
    END;
    RETURN CanExpr(lab)
  END CanCaseLabel;

PROCEDURE CanExpr (n: AST.Node): BOOLEAN;
  VAR op: INTEGER; nm: SymTab.Name; i: CARDINAL;
  BEGIN
    IF n = AST.NoNode THEN RETURN FALSE END;
    IF AST.Kind(n) = AST.NkIntLit THEN RETURN TRUE END;
    IF AST.Kind(n) = AST.NkCharLit THEN RETURN TRUE END;
    IF AST.Kind(n) = AST.NkRealLit THEN RETURN TRUE END;
    IF AST.Kind(n) = AST.NkStrLit THEN RETURN TRUE END;
    IF AST.Kind(n) = AST.NkSetLit THEN
      i := 0;
      WHILE i < AST.NChild(n) DO
        IF AST.Kind(AST.Child(n, i)) = AST.NkSubrange THEN
          IF NOT CanExpr(AST.Child(AST.Child(n, i), 0)) THEN RETURN FALSE END;
          IF NOT CanExpr(AST.Child(AST.Child(n, i), 1)) THEN RETURN FALSE END
        ELSIF NOT CanExpr(AST.Child(n, i)) THEN RETURN FALSE
        END;
        INC(i)
      END;
      RETURN TRUE
    END;
    IF AST.Kind(n) = AST.NkDesignator THEN RETURN CanDesign(n) END;
    IF AST.Kind(n) = AST.NkCall THEN
      CalleeName(n, nm);
      IF IsBuiltin(nm) THEN RETURN CanBuiltin(n) END;
      RETURN IsCall(n) AND CanCallArgs(n)
    END;
    IF AST.Kind(n) = AST.NkUnary THEN
      op := AST.Op(n);
      IF (op # AST.OpSub) AND (op # AST.OpNot) THEN RETURN FALSE END;
      RETURN CanExpr(AST.Child(n, 0))
    END;
    IF AST.Kind(n) = AST.NkBinExpr THEN
      op := AST.Op(n);
      IF NOT (IsArith(op) OR IsRel(op)
              OR (op = AST.OpAnd) OR (op = AST.OpOr)) THEN
        RETURN FALSE END;
      RETURN CanExpr(AST.Child(n, 0)) AND CanExpr(AST.Child(n, 1))
    END;
    RETURN FALSE
  END CanExpr;

PROCEDURE CanStmt (n: AST.Node): BOOLEAN;
  VAR i: CARDINAL; k: INTEGER; by: AST.Node; nm: SymTab.Name;
      arm: AST.Node; j: CARDINAL; withSave: CARDINAL; ok: BOOLEAN;
  BEGIN
    IF n = AST.NoNode THEN RETURN TRUE END;
    k := AST.Kind(n);
    IF k = AST.NkBlock THEN
      i := 0;
      WHILE i < AST.NChild(n) DO
        IF NOT CanStmt(AST.Child(n, i)) THEN RETURN FALSE END;
        INC(i)
      END;
      RETURN TRUE
    END;
    IF k = AST.NkAssign THEN
      RETURN CanDesign(AST.Child(n, 0)) AND CanExpr(AST.Child(n, 1))
    END;
    IF k = AST.NkIf THEN
      RETURN CanExpr(AST.Child(n, 0)) AND CanStmt(AST.Child(n, 1))
             AND CanStmt(AST.Child(n, 2))
    END;
    IF k = AST.NkWhile THEN
      RETURN CanExpr(AST.Child(n, 0)) AND CanStmt(AST.Child(n, 1))
    END;
    IF k = AST.NkRepeat THEN
      RETURN CanStmt(AST.Child(n, 0)) AND CanExpr(AST.Child(n, 1))
    END;
    IF k = AST.NkLoop THEN RETURN CanStmt(AST.Child(n, 0)) END;
    IF k = AST.NkExit THEN RETURN TRUE END;
    IF k = AST.NkFor THEN
      by := AST.Child(n, 3);
      IF (by # AST.NoNode) AND (AST.Kind(by) # AST.NkIntLit) THEN
        RETURN FALSE END;
      RETURN (AST.Kind(AST.Child(n, 0)) = AST.NkIdent)
             AND CanExpr(AST.Child(n, 1)) AND CanExpr(AST.Child(n, 2))
             AND CanStmt(AST.Child(n, 4))
    END;
    IF k = AST.NkWith THEN
      withSave := withTop;
      j := 0;
      WHILE j + 1 < AST.NChild(n) DO
        IF NOT CanDesign(AST.Child(n, j)) THEN
          withTop := withSave; RETURN FALSE
        END;
        IF withTop <= HIGH(withRec) THEN
          withRec[withTop] := DesignTypeOf(AST.Child(n, j)); INC(withTop)
        END;
        INC(j)
      END;
      ok := CanStmt(AST.Child(n, AST.NChild(n) - 1));
      withTop := withSave;
      RETURN ok
    END;
    IF k = AST.NkCase THEN
      IF NOT CanExpr(AST.Child(n, 0)) THEN RETURN FALSE END;
      i := 1;
      WHILE i < AST.NChild(n) DO
        arm := AST.Child(n, i);
        IF AST.Op(arm) = 1 THEN
          IF NOT CanStmt(AST.Child(arm, 0)) THEN RETURN FALSE END
        ELSE
          j := 0;
          WHILE j + 1 < AST.NChild(arm) DO
            IF NOT CanCaseLabel(AST.Child(arm, j)) THEN RETURN FALSE END;
            INC(j)
          END;
          IF NOT CanStmt(AST.Child(arm, AST.NChild(arm) - 1)) THEN
            RETURN FALSE
          END
        END;
        INC(i)
      END;
      RETURN TRUE
    END;
    IF k = AST.NkHalt THEN
      IF AST.Child(n, 0) = AST.NoNode THEN RETURN TRUE END;
      RETURN CanExpr(AST.Child(n, 0))
    END;
    IF k = AST.NkReturn THEN
      IF AST.Child(n, 0) = AST.NoNode THEN RETURN TRUE END;
      RETURN CanExpr(AST.Child(n, 0))
    END;
    IF k = AST.NkCall THEN
      CalleeName(n, nm);
      IF IsBuiltin(nm) THEN RETURN CanBuiltin(n) END;
      RETURN IsCall(n) AND CanCallArgs(n)
    END;
    RETURN FALSE
  END CanStmt;

PROCEDURE CanDecl (c: AST.Node): BOOLEAN;
  VAR i: CARDINAL;
  BEGIN
    IF AST.Kind(c) = AST.NkTypeDecl THEN RETURN TRUE END;
    IF AST.Kind(c) = AST.NkVarDecl THEN
      IF NOT CanType(AST.Ty(c)) THEN RETURN FALSE END;
      IF AST.NChild(c) < 1 THEN RETURN FALSE END;
      i := 0;
      WHILE i < AST.NChild(c) DO
        IF AST.Kind(AST.Child(c, i)) # AST.NkIdent THEN RETURN FALSE END;
        INC(i)
      END;
      RETURN TRUE
    END;
    IF AST.Kind(c) = AST.NkConstDecl THEN
      RETURN IsScalarClass(SymTab.ClassOf(AST.Ty(c)))
             AND (AST.Kind(AST.Child(c, 1)) = AST.NkIntLit)
    END;
    IF AST.Kind(c) = AST.NkProcDecl THEN RETURN CanProc(c) END;
    RETURN FALSE
  END CanDecl;

PROCEDURE CanDecls (seq: AST.Node): BOOLEAN;
  VAR i: CARDINAL; c: AST.Node;
  BEGIN
    IF seq = AST.NoNode THEN RETURN TRUE END;
    i := 0;
    WHILE i < AST.NChild(seq) DO
      c := AST.Child(seq, i);
      IF i = AST.MaxChild - 1 THEN
        IF NOT CanDecls(c) THEN RETURN FALSE END
      ELSIF AST.Kind(c) = AST.NkDeclSeq THEN
        IF NOT CanDecls(c) THEN RETURN FALSE END
      ELSIF NOT CanDecl(c) THEN RETURN FALSE
      END;
      INC(i)
    END;
    RETURN TRUE
  END CanDecls;

PROCEDURE CanLower (unit: AST.Node): BOOLEAN;
  BEGIN
    withTop := 0;
    IF AST.Kind(unit) # AST.NkUnit THEN RETURN FALSE END;
    IF AST.Kind(AST.Child(unit, 0)) # AST.NkIdent THEN RETURN FALSE END;
    IF AST.Child(unit, 3) # AST.NoNode THEN RETURN FALSE END;
    RETURN CanDecls(AST.Child(unit, 1)) AND CanStmt(AST.Child(unit, 2))
  END CanLower;

PROCEDURE CanProc (proc: AST.Node): BOOLEAN;
  VAR nm: SymTab.Name; i: CARDINAL;
      uid, depth, np: CARDINAL; res: SymTab.TypeIndex; ext: BOOLEAN;
      t: SymTab.TypeIndex; isV: BOOLEAN; pn: SymTab.Name;
  BEGIN
    IF AST.Op(proc) # 0 THEN RETURN FALSE END;
    Name(AST.Child(proc, 0), nm);
    IF NOT ProcInfo(nm, uid, res, depth, ext, np) THEN RETURN FALSE END;
    IF (res # SymTab.InvalidType) AND NOT IsScalarClass(SymTab.ClassOf(res)) THEN
      RETURN FALSE END;
    i := 0;
    WHILE i < np DO
      IF NOT ParamInfo(nm, i, t, isV, pn) THEN RETURN FALSE END;
      IF NOT IsScalarClass(SymTab.ClassOf(t)) THEN RETURN FALSE END;
      INC(i)
    END;
    RETURN CanDecls(AST.Child(proc, 2)) AND CanStmt(AST.Child(proc, 1))
  END CanProc;
PROCEDURE FinalLoad (t: SymTab.TypeIndex; sfx: BOOLEAN; VAR q: QbeGen.QVal);
(* Fact's final load after a designator/result suffix: scalars/pointers
   are loaded from their address; aggregates keep the address. *)
  VAR cls: INTEGER; q2: QbeGen.QVal;
  BEGIN
    IF NOT sfx THEN RETURN END;
    IF t = SymTab.InvalidType THEN QbeGen.CopyOp("0", q); RETURN END;
    cls := SymTab.ClassOf(t);
    IF (cls # SymTab.ClRecord) AND (cls # SymTab.ClSet)
       AND (cls # SymTab.ClArray) AND (cls # SymTab.ClClass) THEN
      QbeGen.ElemLoad(q, t, q2); QbeGen.CopyOp(q2, q)
    END
  END FinalLoad;

PROCEDURE LowerDesign (n: AST.Node; VAR t: SymTab.TypeIndex; VAR k: INTEGER;
                       VAR q: QbeGen.QVal; VAR qn: SymTab.Name;
                       VAR sfx: BOOLEAN);
(* Base ident then selectors (mirrors the grammar's Design).  Leaves the
   address in q with sfx=TRUE for selectors; base vars/consts load. *)
  VAR nm, fn: SymTab.Name; cv: QbeGen.QVal; cls, op: INTEGER;
      i: CARDINAL; sel: AST.Node; eT, it: SymTab.TypeIndex;
      iq, ql, qlo, qhi, qe: QbeGen.QVal;
      lo, hi, fo: INTEGER; isOpen: BOOLEAN;
  BEGIN
    Name(AST.Child(n, 0), nm);
    QbeGen.CopyOp(nm, qn);
    sfx := FALSE;
    IF NOT Resolve(nm, k, t) THEN
      IF NOT WithField(nm, k, t, q) THEN
        t := SymTab.InvalidType; k := -1; QbeGen.CopyOp("0", q); RETURN
      END;
      sfx := TRUE
    END;
    IF k = SymTab.KindConst THEN
      IF SymTab.Equal(nm, "TRUE") THEN
        t := SymTab.BoolType(); QbeGen.CopyOp("1", q)
      ELSIF SymTab.Equal(nm, "FALSE") THEN
        t := SymTab.BoolType(); QbeGen.CopyOp("0", q)
      ELSIF SymTab.Equal(nm, "NIL") THEN
        QbeGen.CopyOp("0", q)
      ELSIF SymTab.GetSymVal(nm, cv) AND QbeGen.IsImm(cv) THEN
        QbeGen.CopyOp(cv, q)
      ELSE QbeGen.CopyOp("0", q)
      END
    ELSIF (k = SymTab.KindVar) OR (k = SymTab.KindParam) THEN
      cls := SymTab.ClassOf(t);
      IF (cls = SymTab.ClInt) OR (cls = SymTab.ClBool)
         OR (cls = SymTab.ClChar) OR (cls = SymTab.ClUChar)
         OR (cls = SymTab.ClEnum) OR (cls = SymTab.ClReal) THEN
        QbeGen.LoadVar(nm, cls = SymTab.ClReal, q)
      ELSIF (cls = SymTab.ClPtr) OR (cls = SymTab.ClProc) THEN
        QbeGen.LoadPtr(nm, q)
      ELSIF cls = SymTab.ClLong THEN
        QbeGen.LoadLong(nm, q)
      ELSE QbeGen.AddrOf(nm, q)
      END
    ELSIF k = SymTab.KindField THEN
      (* q already holds the field address (WithField) *)
    ELSE QbeGen.CopyOp("0", q)
    END;
    i := 1;
    WHILE i < AST.NChild(n) DO
      sel := AST.Child(n, i);
      op := AST.Op(sel);
      IF op = AST.SelField THEN
        Name(AST.Child(sel, 0), fn);
        IF t = SymTab.InvalidType THEN
        ELSIF NOT SymTab.FieldExists(t, fn) THEN t := SymTab.InvalidType
        ELSE
          fo := SymTab.FieldOffset(t, fn);
          t := SymTab.FieldType(t, fn);
          QbeGen.FieldAddr(q, fo, qe);
          QbeGen.CopyOp(qe, q);
          sfx := TRUE
        END
      ELSIF op = AST.SelIndex THEN
        LowerExpr(AST.Child(sel, 0), it, iq);
        IF t = SymTab.InvalidType THEN
        ELSE
          QbeGen.WidenIndex(iq, ql);
          isOpen := SymTab.IsOpenArray(t);
          IF isOpen THEN
            QbeGen.CopyOp("0", qlo);
            IF SymTab.IsCharArray(t) OR SymTab.IsUCharArray(t) THEN
              QbeGen.OpenHiChar(q, qhi)
            ELSE QbeGen.OpenHi(q, qhi)
            END
          ELSE
            lo := SymTab.ArrayLo(t); hi := SymTab.ArrayHi(t);
            IF SymTab.IsCharArray(t) OR SymTab.IsUCharArray(t) THEN
              hi := hi + 1
            END;
            QbeGen.IntStr(lo, qlo); QbeGen.IntStr(hi, qhi)
          END;
          QbeGen.CheckRange(ql, qlo, qhi);
          eT := SymTab.ArrayElem(t);
          QbeGen.ElemAddr(q, ql, qlo, t, qe);
          IF SymTab.ClassOf(eT) = SymTab.ClArray THEN
            QbeGen.ElemLoad(qe, eT, q)
          ELSE QbeGen.CopyOp(qe, q)
          END;
          t := eT; sfx := TRUE
        END
      ELSIF op = AST.SelDeref THEN
        IF t = SymTab.InvalidType THEN
        ELSIF SymTab.ClassOf(t) # SymTab.ClPtr THEN t := SymTab.InvalidType
        ELSE
          IF sfx THEN QbeGen.ElemLoad(q, t, qe); QbeGen.CopyOp(qe, q) END;
          t := SymTab.PtrBase(t); sfx := TRUE
        END
      END;
      INC(i)
    END
  END LowerDesign;

PROCEDURE LowerCall (n: AST.Node; VAR t: SymTab.TypeIndex;
                     VAR q: QbeGen.QVal; want: BOOLEAN);
  VAR nm: SymTab.Name; i: CARDINAL; at, ft, res: SymTab.TypeIndex;
      qa, qt, qe: QbeGen.QVal; mg: QbeGen.QVal; cls: CHAR; conv, isV: BOOLEAN;
      uid, depth, np: CARDINAL; ext: BOOLEAN; pn: SymTab.Name;
  BEGIN
    CalleeName(n, nm);
    IF NOT ProcInfo(nm, uid, res, depth, ext, np) THEN END;
    QbeGen.Mangled(nm, uid, mg);
    QbeGen.CallBegin(mg, res, depth, ext);
    i := 1;
    WHILE i < AST.NChild(n) DO
      LowerExpr(AST.Child(n, i), at, qe);
      IF NOT ParamInfo(nm, i - 1, ft, isV, pn) THEN END;
      IF isV THEN
        IF QbeGen.AddrOfVal(qe, qa) THEN
          IF NOT QbeGen.CallArg(qa, "l") THEN END
        END
      ELSE
        conv := (SymTab.ClassOf(ft) = SymTab.ClReal)
                AND SymTab.IsIntFamily(at);
        IF conv THEN
          QbeGen.ConvIR(qe, qt);
          IF NOT QbeGen.CallArg(qt, "d") THEN END
        ELSE
          IF NOT QbeGen.CallArg(qe, QbeGen.ArgClass(ft)) THEN END
        END
      END;
      INC(i)
    END;
    IF want THEN
      t := res; QbeGen.CallEnd(TRUE, q)
    ELSE
      t := SymTab.InvalidType; QbeGen.CopyOp("0", q); QbeGen.CallEnd(FALSE, q)
    END
  END LowerCall;

PROCEDURE IsBuiltin (nm: ARRAY OF CHAR): BOOLEAN;
  BEGIN
    RETURN SymTab.Equal(nm, "ABS") OR SymTab.Equal(nm, "CAP")
        OR SymTab.Equal(nm, "CHR") OR SymTab.Equal(nm, "ORD")
        OR SymTab.Equal(nm, "SIZE") OR SymTab.Equal(nm, "TSIZE")
        OR SymTab.Equal(nm, "MIN") OR SymTab.Equal(nm, "MAX")
        OR SymTab.Equal(nm, "SHIFT") OR SymTab.Equal(nm, "ROTATE")
        OR SymTab.Equal(nm, "ADR")
        OR SymTab.Equal(nm, "INC") OR SymTab.Equal(nm, "DEC")
        OR SymTab.Equal(nm, "INCL") OR SymTab.Equal(nm, "EXCL")
        OR SymTab.Equal(nm, "NEW") OR SymTab.Equal(nm, "DISPOSE")
  END IsBuiltin;

PROCEDURE LowerBuiltinExpr (n: AST.Node; nm: SymTab.Name;
                            VAR t: SymTab.TypeIndex; VAR q: QbeGen.QVal);
(* Value builtins (Fact). *)
  VAR et, et2, dt: SymTab.TypeIndex; qa, qt, q2, qd: QbeGen.QVal;
      k, lo, hi: INTEGER; qn: SymTab.Name; sfx: BOOLEAN; isMax: BOOLEAN;
  BEGIN
    IF SymTab.Equal(nm, "ABS") THEN
      LowerExpr(AST.Child(n, 1), et, q);
      QbeGen.AbsQ(q, qa, SymTab.ClassOf(et) = SymTab.ClReal);
      QbeGen.CopyOp(qa, q); t := et
    ELSIF SymTab.Equal(nm, "CAP") THEN
      LowerExpr(AST.Child(n, 1), et, q);
      QbeGen.CapQ(q, qa); QbeGen.CopyOp(qa, q); t := SymTab.CharType()
    ELSIF SymTab.Equal(nm, "CHR") THEN
      LowerExpr(AST.Child(n, 1), et, q); t := SymTab.CharType()
    ELSIF SymTab.Equal(nm, "ORD") THEN
      LowerExpr(AST.Child(n, 1), et, q); t := SymTab.IntType()
    ELSIF SymTab.Equal(nm, "SIZE") THEN
      LowerDesign(AST.Child(n, 1), dt, k, qd, qn, sfx);
      QbeGen.IntStr(VAL(INTEGER, SymTab.ObjectSize(dt)), q);
      t := SymTab.IntType()
    ELSIF SymTab.Equal(nm, "MIN") OR SymTab.Equal(nm, "MAX") THEN
      isMax := SymTab.Equal(nm, "MAX");
      LowerDesign(AST.Child(n, 1), dt, k, qd, qn, sfx);
      IF SymTab.ClassOf(dt) = SymTab.ClReal THEN
        IF isMax THEN QbeGen.NormReal("3.402823e38", q)
        ELSE QbeGen.NormReal("-3.402823e38", q) END;
        t := SymTab.RealType()
      ELSIF SymTab.ClassOf(dt) = SymTab.ClLong THEN
        IF isMax THEN QbeGen.CopyOp("9223372036854775807", q)
        ELSE QbeGen.CopyOp("-9223372036854775808", q) END;
        t := SymTab.LongType()
      ELSIF SymTab.TypeBounds(dt, lo, hi) THEN
        IF isMax THEN QbeGen.IntStr(hi, q) ELSE QbeGen.IntStr(lo, q) END;
        t := SymTab.IntType()
      ELSE t := SymTab.InvalidType; QbeGen.CopyOp("0", q)
      END
    ELSIF SymTab.Equal(nm, "SHIFT") OR SymTab.Equal(nm, "ROTATE") THEN
      LowerExpr(AST.Child(n, 1), et, q);
      LowerExpr(AST.Child(n, 2), et2, q2);
      QbeGen.SetShift(q, q2, SymTab.SetWords(et), SymTab.SetCount(et),
                      SymTab.Equal(nm, "ROTATE"), qt);
      t := et; QbeGen.CopyOp(qt, q)
    ELSIF SymTab.Equal(nm, "ADR") THEN
      LowerDesign(AST.Child(n, 1), dt, k, qd, qn, sfx);
      IF sfx THEN QbeGen.CopyOp(qd, q)
      ELSIF (k = SymTab.KindVar) OR (k = SymTab.KindParam) THEN
        QbeGen.AddrOf(qn, q)
      ELSE QbeGen.CopyOp("0", q)
      END;
      t := SymTab.AddrType()
    ELSE t := SymTab.InvalidType; QbeGen.CopyOp("0", q)
    END
  END LowerBuiltinExpr;

PROCEDURE LowerBuiltinStmt (n: AST.Node; nm: SymTab.Name);
(* Statement builtins (AssOrCall): INC/DEC, INCL/EXCL, NEW/DISPOSE. *)
  VAR dt, at, et2, bt: SymTab.TypeIndex; dk: INTEGER;
      qd, qv, qe, qn2, qstep, qm: QbeGen.QVal;
      qn: SymTab.Name; sfx, isInc: BOOLEAN;
  BEGIN
    IF SymTab.Equal(nm, "INC") OR SymTab.Equal(nm, "DEC") THEN
      isInc := SymTab.Equal(nm, "INC");
      QbeGen.CopyOp("1", qstep);
      LowerDesign(AST.Child(n, 1), dt, dk, qd, qn, sfx);
      IF AST.NChild(n) > 2 THEN LowerExpr(AST.Child(n, 2), et2, qstep) END;
      IF dt = SymTab.InvalidType THEN
      ELSE
        IF sfx OR (dk = SymTab.KindField) THEN QbeGen.ElemLoad(qd, dt, qv)
        ELSE QbeGen.LoadVar(qn, FALSE, qv)
        END;
        QbeGen.NewTemp(qn2);
        IF isInc THEN QbeGen.Op3("add", qn2, qv, qstep, FALSE)
        ELSE QbeGen.Op3("sub", qn2, qv, qstep, FALSE)
        END;
        IF sfx OR (dk = SymTab.KindField) THEN QbeGen.ElemStore(qd, qn2, dt)
        ELSE QbeGen.StoreVar(qn, qn2, FALSE)
        END
      END
    ELSIF SymTab.Equal(nm, "INCL") OR SymTab.Equal(nm, "EXCL") THEN
      isInc := SymTab.Equal(nm, "INCL");
      LowerDesign(AST.Child(n, 1), at, dk, qd, qn, sfx);
      LowerExpr(AST.Child(n, 2), et2, qe);
      IF at = SymTab.InvalidType THEN
      ELSIF SymTab.ClassOf(at) # SymTab.ClSet THEN
      ELSE
        IF isInc THEN QbeGen.SetBit(qd, qe, SymTab.SetBaseLo(at), SymTab.SetCount(at))
        ELSE QbeGen.SetClearBit(qd, qe, SymTab.SetBaseLo(at), SymTab.SetCount(at))
        END
      END
    ELSIF SymTab.Equal(nm, "NEW") THEN
      LowerDesign(AST.Child(n, 1), dt, dk, qd, qn, sfx);
      IF dt = SymTab.InvalidType THEN
      ELSIF SymTab.ClassOf(dt) # SymTab.ClPtr THEN
      ELSE
        bt := SymTab.PtrBase(dt);
        IF bt # SymTab.InvalidType THEN
          QbeGen.NewHeap(bt, qm); QbeGen.InitHeap(qm, bt);
          IF sfx OR (dk = SymTab.KindField) THEN QbeGen.ElemStore(qd, qm, dt)
          ELSE QbeGen.StorePtr(qn, qm)
          END
        END
      END
    ELSIF SymTab.Equal(nm, "DISPOSE") THEN
      LowerDesign(AST.Child(n, 1), dt, dk, qd, qn, sfx);
      IF dt = SymTab.InvalidType THEN
      ELSIF SymTab.ClassOf(dt) # SymTab.ClPtr THEN
      ELSE
        IF sfx OR (dk = SymTab.KindField) THEN QbeGen.ElemLoad(qd, dt, qv)
        ELSE QbeGen.LoadPtr(qn, qv)
        END;
        QbeGen.FreeHeap(qv);
        IF sfx OR (dk = SymTab.KindField) THEN QbeGen.ElemStore(qd, "0", dt)
        ELSE QbeGen.StorePtr(qn, "0")
        END
      END
    END
  END LowerBuiltinStmt;

PROCEDURE LowerCase (n: AST.Node);
(* CASE as a compare-chain (mirrors CaseStat/CaseAlt/CaseLabel). *)
  VAR i, j: CARDINAL; arm, lab: AST.Node; tsel, t2, t3: SymTab.TypeIndex;
      qsel, q2, q3, qc, qd, qe, lEnd, lBody, lAfter, lNext: QbeGen.QVal;
  BEGIN
    LowerExpr(AST.Child(n, 0), tsel, qsel);
    QbeGen.NewLabel(lEnd);
    i := 1;
    WHILE i < AST.NChild(n) DO
      arm := AST.Child(n, i);
      IF AST.Op(arm) = 1 THEN
        (* ELSE arm: emitted after the alternatives *)
      ELSE
        QbeGen.NewLabel(lBody); QbeGen.NewLabel(lAfter);
        j := 0;
        WHILE j + 1 < AST.NChild(arm) DO
          lab := AST.Child(arm, j);
          IF AST.Kind(lab) = AST.NkSubrange THEN
            LowerExpr(AST.Child(lab, 0), t2, q2);
            QbeGen.NewLabel(lNext);
            QbeGen.Cmp(SymTab.OpEq, qsel, q2, qc, FALSE);
            QbeGen.Jnz(qc, lBody, lNext);
            QbeGen.EmitLabel(lNext);
            LowerExpr(AST.Child(lab, 1), t3, q3);
            QbeGen.Cmp(SymTab.OpGe, qsel, q2, qc, FALSE);
            QbeGen.Cmp(SymTab.OpLe, qsel, q3, qd, FALSE);
            QbeGen.NewTemp(qe);
            QbeGen.Op3("and", qe, qc, qd, FALSE);
            QbeGen.NewLabel(lNext);
            QbeGen.Jnz(qe, lBody, lNext);
            QbeGen.EmitLabel(lNext)
          ELSE
            LowerExpr(lab, t2, q2);
            QbeGen.NewLabel(lNext);
            QbeGen.Cmp(SymTab.OpEq, qsel, q2, qc, FALSE);
            QbeGen.Jnz(qc, lBody, lNext);
            QbeGen.EmitLabel(lNext)
          END;
          INC(j)
        END;
        QbeGen.Jmp(lAfter);
        QbeGen.EmitLabel(lBody);
        LowerStmt(AST.Child(arm, AST.NChild(arm) - 1));
        QbeGen.Jmp(lEnd);
        QbeGen.EmitLabel(lAfter)
      END;
      INC(i)
    END;
    i := 1;
    WHILE i < AST.NChild(n) DO
      arm := AST.Child(n, i);
      IF AST.Op(arm) = 1 THEN LowerStmt(AST.Child(arm, 0)) END;
      INC(i)
    END;
    QbeGen.EmitLabel(lEnd)
  END LowerCase;

PROCEDURE LowerWith (n: AST.Node);
(* WITH: push each record's base address, lower the body, pop. *)
  VAR i: CARDINAL; dt: SymTab.TypeIndex; dk: INTEGER; qd: QbeGen.QVal;
      qn: SymTab.Name; sfx: BOOLEAN;
  BEGIN
    i := 0;
    WHILE i + 1 < AST.NChild(n) DO
      LowerDesign(AST.Child(n, i), dt, dk, qd, qn, sfx);
      QbeGen.PushWith(qd);
      IF withTop <= HIGH(withRec) THEN
        withRec[withTop] := dt; INC(withTop)
      END;
      INC(i)
    END;
    LowerStmt(AST.Child(n, AST.NChild(n) - 1));
    WHILE withTop > 0 DO DEC(withTop); QbeGen.PopWith END
  END LowerWith;

PROCEDURE LowerExprFull (n: AST.Node; VAR t: SymTab.TypeIndex;
                         VAR q: QbeGen.QVal; VAR k: INTEGER;
                         VAR qn: SymTab.Name; VAR sfx: BOOLEAN;
                         asAddr: BOOLEAN);
  VAR t2: SymTab.TypeIndex; q2, qt, qf, qs, qr: QbeGen.QVal;
      lNext, lFalse, lTrue, lDone: QbeGen.QVal;
      kind, op, rop: INTEGER;
      folded, isR, isCh: BOOLEAN;
      i: CARDINAL; el: AST.Node;
      lw, rw, mw: CARDINAL; idx: INTEGER; fok, isL: BOOLEAN;
      lt, rt: SymTab.TypeIndex; qw: QbeGen.QVal;
  BEGIN
    IF AST.Kind(n) = AST.NkDesignator THEN
      LowerDesign(n, t, k, q, qn, sfx);
      IF NOT asAddr THEN FinalLoad(t, sfx, q) END;
      RETURN
    END;
    k := -1; qn[0] := CHR(0); sfx := FALSE;
    IF AST.Kind(n) = AST.NkIntLit THEN
      Name(n, qn); QbeGen.NormInt(qn, q); t := SymTab.IntType()
    ELSIF AST.Kind(n) = AST.NkCharLit THEN
      Name(n, qn); QbeGen.NormLit(qn, q, isCh); t := SymTab.CharType()
    ELSIF AST.Kind(n) = AST.NkRealLit THEN
      Name(n, qn); QbeGen.NormReal(qn, q); t := SymTab.RealType()
    ELSIF AST.Kind(n) = AST.NkStrLit THEN
      Name(n, qn);
      IF SymTab.StrLen(qn) = 3 THEN
        t := SymTab.CharType(); QbeGen.IntStr(QbeGen.CharVal(qn), q)
      ELSE
        t := SymTab.NewStr(); QbeGen.DeclStr(qn, q); QbeGen.NoteAddr(q, q)
      END
    ELSIF AST.Kind(n) = AST.NkSetLit THEN
      t := SymTab.NewSet(SymTab.NewSubR(0, 255));
      QbeGen.NewSetTemp(8, q); QbeGen.SetZero(q, 8);
      i := 0;
      WHILE i < AST.NChild(n) DO
        el := AST.Child(n, i);
        IF AST.Kind(el) = AST.NkSubrange THEN
          LowerExpr(AST.Child(el, 0), t2, q2);
          LowerExpr(AST.Child(el, 1), t2, qt);
          QbeGen.SetRange(q, q2, qt, SymTab.SetBaseLo(t), SymTab.SetCount(t))
        ELSE
          LowerExpr(el, t2, q2);
          QbeGen.SetBit(q, q2, SymTab.SetBaseLo(t), SymTab.SetCount(t))
        END;
        INC(i)
      END
    ELSIF AST.Kind(n) = AST.NkDesignator THEN
      LowerDesign(n, t, k, q, qn, sfx)
    ELSIF AST.Kind(n) = AST.NkCall THEN
      CalleeName(n, qn);
      IF IsBuiltin(qn) THEN LowerBuiltinExpr(n, qn, t, q)
      ELSE LowerCall(n, t, q, TRUE)
      END
    ELSIF AST.Kind(n) = AST.NkUnary THEN
      LowerExpr(AST.Child(n, 0), t, q);
      IF AST.Op(n) = AST.OpSub THEN
        IF QbeGen.IsImm(q) THEN QbeGen.NegFold(q, q)
        ELSE QbeGen.NewTemp(qt); QbeGen.NegQ(q, qt, FALSE); QbeGen.CopyOp(qt, q)
        END
      ELSE
        QbeGen.NotQ(q, qt); QbeGen.CopyOp(qt, q); t := SymTab.BoolType()
      END
    ELSIF AST.Kind(n) = AST.NkBinExpr THEN
      op := AST.Op(n);
      IF IsRel(op) THEN
        LowerExpr(AST.Child(n, 0), t, q);
        LowerExpr(AST.Child(n, 1), t2, q2);
        rop := SymTab.OpEq; folded := RelSym(op, rop);
        IF op = AST.OpIn THEN
          QbeGen.InSet(q, q2, SymTab.SetBaseLo(t2), SymTab.SetCount(t2), qt);
          t := SymTab.BoolType(); QbeGen.CopyOp(qt, q)
        ELSIF (SymTab.ClassOf(t) = SymTab.ClPtr)
           OR (SymTab.ClassOf(t2) = SymTab.ClPtr) THEN
          QbeGen.CmpL(rop, q, q2, qt);
          t := SymTab.BoolType(); QbeGen.CopyOp(qt, q)
        ELSIF (SymTab.ClassOf(t) = SymTab.ClSet)
           OR (SymTab.ClassOf(t2) = SymTab.ClSet) THEN
          QbeGen.CmpSet(rop, q, q2, SymTab.SetWords(t), SymTab.SetWords(t2), qt);
          t := SymTab.BoolType(); QbeGen.CopyOp(qt, q)
        ELSIF SymTab.StrCompat(t, t2) THEN
          QbeGen.StrEq(rop, q, q2, qt);
          t := SymTab.BoolType(); QbeGen.CopyOp(qt, q)
        ELSIF SymTab.IsLongFamily(t) OR SymTab.IsLongFamily(t2) THEN
          IF SymTab.IsIntFamily(t) THEN QbeGen.WidenLong(q, qf); QbeGen.CopyOp(qf, q) END;
          IF SymTab.IsIntFamily(t2) THEN QbeGen.WidenLong(q2, qf); QbeGen.CopyOp(qf, q2) END;
          QbeGen.CmpLong(rop, q, q2, qt);
          t := SymTab.BoolType(); QbeGen.CopyOp(qt, q)
        ELSE
          isR := (t # SymTab.InvalidType) AND (SymTab.ClassOf(t) = SymTab.ClReal);
          t := SymTab.BoolType();
          QbeGen.Cmp(rop, q, q2, qt, isR);
          QbeGen.CopyOp(qt, q)
        END
      ELSIF op = AST.OpAnd THEN
        LowerExpr(AST.Child(n, 0), t, q);
        QbeGen.DelayBegin;
        LowerExpr(AST.Child(n, 1), t2, q2);
        QbeGen.DelayEnd;
        QbeGen.Slot4(qs);
        QbeGen.NewLabel(lNext); QbeGen.NewLabel(lFalse); QbeGen.NewLabel(lDone);
        QbeGen.Jnz(q, lNext, lFalse);
        QbeGen.EmitLabel(lNext);
        QbeGen.DelayFlush;
        QbeGen.StoreW(qs, q2);
        QbeGen.Jmp(lDone);
        QbeGen.EmitLabel(lFalse);
        QbeGen.StoreW(qs, "0");
        QbeGen.Jmp(lDone);
        QbeGen.EmitLabel(lDone);
        QbeGen.LoadW(qs, qr);
        QbeGen.CopyOp(qr, q);
        t := SymTab.BoolType()
      ELSIF op = AST.OpOr THEN
        LowerExpr(AST.Child(n, 0), t, q);
        QbeGen.DelayBegin;
        LowerExpr(AST.Child(n, 1), t2, q2);
        QbeGen.DelayEnd;
        QbeGen.Slot4(qs);
        QbeGen.NewLabel(lTrue); QbeGen.NewLabel(lNext); QbeGen.NewLabel(lDone);
        QbeGen.Jnz(q, lTrue, lNext);
        QbeGen.EmitLabel(lTrue);
        QbeGen.StoreW(qs, "1");
        QbeGen.Jmp(lDone);
        QbeGen.EmitLabel(lNext);
        QbeGen.DelayFlush;
        QbeGen.StoreW(qs, q2);
        QbeGen.Jmp(lDone);
        QbeGen.EmitLabel(lDone);
        QbeGen.LoadW(qs, qr);
        QbeGen.CopyOp(qr, q);
        t := SymTab.BoolType()
      ELSE
        LowerExpr(AST.Child(n, 0), t, q);
        LowerExpr(AST.Child(n, 1), t2, q2);
        IF (t # SymTab.InvalidType) AND (t2 # SymTab.InvalidType)
           AND (SymTab.ClassOf(t) = SymTab.ClSet)
           AND (SymTab.ClassOf(t2) = SymTab.ClSet) THEN
          (* set union/diff (Add/Sub) or intersection/symdiff (Mul/Div) *)
          lw := SymTab.SetWords(t); rw := SymTab.SetWords(t2);
          mw := lw; IF rw > mw THEN mw := rw END;
          IF op = AST.OpAdd THEN idx := 0
          ELSIF op = AST.OpSub THEN idx := 2
          ELSIF op = AST.OpMul THEN idx := 1
          ELSE idx := 3
          END;
          QbeGen.SetBinOp(idx, q, q2, lw, rw, qt);
          t := SymTab.NewSet(SymTab.NewSubR(0, VAL(INTEGER, mw) * 32 - 1));
          QbeGen.CopyOp(qt, q)
        ELSIF (op = AST.OpAdd)
           AND (SymTab.StrCompat(t, t2)
                OR (SymTab.IsStrType(t) AND (SymTab.ClassOf(t2) = SymTab.ClChar))
                OR ((SymTab.ClassOf(t) = SymTab.ClChar) AND SymTab.IsStrType(t2))) THEN
          QbeGen.StrFold(q, q2, SymTab.ClassOf(t), SymTab.ClassOf(t2), qt, fok);
          IF NOT fok THEN
            IF SymTab.StrCompat(t, t2) THEN QbeGen.StrCat(q, q2, qt)
            ELSIF SymTab.IsStrType(t) THEN
              QbeGen.DeclCharStr(q2, qs); QbeGen.StrCat(q, qs, qt)
            ELSE
              QbeGen.DeclCharStr(q, qs); QbeGen.StrCat(qs, q2, qt)
            END
          END;
          t := SymTab.NewStr(); QbeGen.CopyOp(qt, q)
        ELSE
          lt := t; rt := t2;
          IF (SymTab.ClassOf(lt) = SymTab.ClReal)
             OR (SymTab.ClassOf(rt) = SymTab.ClReal) THEN
            t := SymTab.RealType()
          ELSIF SymTab.IsLongFamily(lt) OR SymTab.IsLongFamily(rt) THEN
            t := SymTab.LongType()
          ELSE t := SymTab.IntType()
          END;
          isL := SymTab.IsLongFamily(t);
          isR := SymTab.ClassOf(t) = SymTab.ClReal;
          kind := 0;
          IF op = AST.OpSub THEN kind := 1
          ELSIF op = AST.OpMul THEN kind := 2
          ELSIF op = AST.OpDiv THEN kind := 3
          ELSIF op = AST.OpMod THEN kind := 4
          END;
          folded := FALSE;
          IF (NOT isL) AND (NOT isR) AND QbeGen.IsImm(q) AND QbeGen.IsImm(q2) THEN
            folded := QbeGen.Fold2(kind, q, q2, qf)
          END;
          IF folded THEN QbeGen.CopyOp(qf, q)
          ELSE
            IF isL THEN
              IF SymTab.IsIntFamily(lt) THEN
                QbeGen.WidenLong(q, qw); QbeGen.CopyOp(qw, q)
              END;
              IF SymTab.IsIntFamily(rt) THEN
                QbeGen.WidenLong(q2, qw); QbeGen.CopyOp(qw, q2)
              END;
              QbeGen.NewTemp(qt);
              IF op = AST.OpAdd THEN QbeGen.Op3L("add", qt, q, q2)
              ELSIF op = AST.OpSub THEN QbeGen.Op3L("sub", qt, q, q2)
              ELSIF op = AST.OpMul THEN QbeGen.Op3L("mul", qt, q, q2)
              ELSE QbeGen.Op3L("div", qt, q, q2)
              END
            ELSE
              QbeGen.NewTemp(qt);
              IF op = AST.OpAdd THEN QbeGen.Op3("add", qt, q, q2, isR)
              ELSIF op = AST.OpSub THEN QbeGen.Op3("sub", qt, q, q2, isR)
              ELSIF op = AST.OpMul THEN QbeGen.Op3("mul", qt, q, q2, isR)
              ELSIF op = AST.OpDiv THEN QbeGen.Op3("div", qt, q, q2, isR)
              ELSE QbeGen.Op3("rem", qt, q, q2, isR)
              END
            END;
            QbeGen.CopyOp(qt, q)
          END
        END
      END
    END
  END LowerExprFull;

PROCEDURE LowerExpr (n: AST.Node; VAR t: SymTab.TypeIndex;
                     VAR q: QbeGen.QVal);
  VAR k: INTEGER; qn: SymTab.Name; sfx: BOOLEAN;
  BEGIN
    LowerExprFull(n, t, q, k, qn, sfx, FALSE)
  END LowerExpr;

PROCEDURE LowerStmt (seq: AST.Node);
  VAR i: CARDINAL; c, els, by: AST.Node; k: INTEGER;
      t, t2, dt, et: SymTab.TypeIndex;
      q, q2, qt, qf, qd, qe: QbeGen.QVal;
      qlo, qhi, qk, qb, ql: QbeGen.QVal;
      lTop, lBody, lEnd, lThen, lElse, lNext, lFalse, lDone, lx: QbeGen.QVal;
      qn, lv: SymTab.Name;
      kind, op, rop, cls: INTEGER;
      sfx, folded, isR, conv, wconv, hasElse: BOOLEAN;
  BEGIN
    IF seq = AST.NoNode THEN RETURN END;
    k := AST.Kind(seq);

    IF k = AST.NkBlock THEN
      i := 0;
      WHILE i < AST.NChild(seq) DO
        LowerStmt(AST.Child(seq, i)); INC(i)
      END
    ELSIF k = AST.NkAssign THEN
      LowerDesign(AST.Child(seq, 0), dt, cls, qd, qn, sfx);
      LowerExpr(AST.Child(seq, 1), et, qe);
      isR := (dt # SymTab.InvalidType) AND (SymTab.ClassOf(dt) = SymTab.ClReal);
      conv := isR AND SymTab.IsIntFamily(et);
      wconv := (dt # SymTab.InvalidType) AND SymTab.IsLongFamily(dt)
               AND SymTab.IsIntFamily(et);
      IF sfx OR (cls = SymTab.KindField) THEN
        IF SymTab.ClassOf(dt) = SymTab.ClArray THEN
          IF (et # SymTab.InvalidType) AND (SymTab.ClassOf(et) = SymTab.ClUStr)
             AND SymTab.IsUCharArray(dt) THEN QbeGen.UAssign(qd, qe)
          ELSIF SymTab.StrCompat(dt, et) THEN QbeGen.StrAssign(qd, qe)
          ELSE QbeGen.CopyArray(qd, qe, dt)
          END
        ELSIF SymTab.ClassOf(dt) = SymTab.ClSet THEN
          QbeGen.CopySet(qd, qe, SymTab.SetWords(dt), SymTab.SetWords(et))
        ELSIF SymTab.ClassOf(dt) = SymTab.ClRecord THEN
          QbeGen.CopyRecord(qd, qe, dt)
        ELSIF SymTab.IsLongFamily(dt) THEN
          IF wconv THEN QbeGen.WidenLong(qe, ql); QbeGen.ElemStore(qd, ql, dt)
          ELSE QbeGen.ElemStore(qd, qe, dt)
          END
        ELSIF conv THEN QbeGen.ConvIR(qe, qt); QbeGen.ElemStore(qd, qt, dt)
        ELSE QbeGen.ElemStore(qd, qe, dt)
        END
      ELSE
        IF SymTab.ClassOf(dt) = SymTab.ClArray THEN
          IF (et # SymTab.InvalidType) AND (SymTab.ClassOf(et) = SymTab.ClUStr)
             AND SymTab.IsUCharArray(dt) THEN QbeGen.UAssign(qd, qe)
          ELSIF SymTab.StrCompat(dt, et) THEN QbeGen.StrAssign(qd, qe)
          ELSE QbeGen.CopyArray(qd, qe, dt)
          END
        ELSIF SymTab.ClassOf(dt) = SymTab.ClSet THEN
          QbeGen.CopySet(qd, qe, SymTab.SetWords(dt), SymTab.SetWords(et))
        ELSIF SymTab.ClassOf(dt) = SymTab.ClRecord THEN
          QbeGen.CopyRecord(qd, qe, dt)
        ELSIF (SymTab.ClassOf(dt) = SymTab.ClPtr)
           OR (SymTab.ClassOf(dt) = SymTab.ClProc) THEN
          QbeGen.StorePtr(qn, qe)
        ELSIF SymTab.IsLongFamily(dt) THEN
          IF wconv THEN QbeGen.WidenLong(qe, ql); QbeGen.StoreLong(qn, ql)
          ELSE QbeGen.StoreLong(qn, qe)
          END
        ELSIF conv THEN QbeGen.ConvIR(qe, qt); QbeGen.StoreVar(qn, qt, TRUE)
        ELSE QbeGen.StoreVar(qn, qe, isR)
        END
      END
    ELSIF k = AST.NkIf THEN
      LowerExpr(AST.Child(seq, 0), t, q);
      QbeGen.NewLabel(lThen); QbeGen.NewLabel(lElse); QbeGen.NewLabel(lEnd);
      QbeGen.Jnz(q, lThen, lElse); QbeGen.EmitLabel(lThen);
      LowerStmt(AST.Child(seq, 1));
      QbeGen.Jmp(lEnd);
      els := AST.Child(seq, 2); hasElse := FALSE;
      WHILE (els # AST.NoNode) AND (AST.Kind(els) = AST.NkIf) DO
        QbeGen.EmitLabel(lElse); QbeGen.NewLabel(lElse);
        LowerExpr(AST.Child(els, 0), t, q);
        QbeGen.NewLabel(lThen); QbeGen.Jnz(q, lThen, lElse);
        QbeGen.EmitLabel(lThen);
        LowerStmt(AST.Child(els, 1));
        QbeGen.Jmp(lEnd);
        els := AST.Child(els, 2)
      END;
      IF els # AST.NoNode THEN
        QbeGen.EmitLabel(lElse); hasElse := TRUE; LowerStmt(els)
      END;
      IF hasElse THEN QbeGen.EmitLabel(lEnd)
      ELSE QbeGen.EmitLabel(lElse); QbeGen.EmitLabel(lEnd)
      END
    ELSIF k = AST.NkWhile THEN
      QbeGen.NewLabel(lTop); QbeGen.NewLabel(lBody); QbeGen.NewLabel(lEnd);
      QbeGen.EmitLabel(lTop);
      LowerExpr(AST.Child(seq, 0), t, q);
      QbeGen.Jnz(q, lBody, lEnd); QbeGen.EmitLabel(lBody);
      LowerStmt(AST.Child(seq, 1));
      QbeGen.Jmp(lTop); QbeGen.EmitLabel(lEnd)
    ELSIF k = AST.NkRepeat THEN
      QbeGen.NewLabel(lTop); QbeGen.NewLabel(lEnd); QbeGen.EmitLabel(lTop);
      LowerStmt(AST.Child(seq, 0));
      LowerExpr(AST.Child(seq, 1), t, q);
      QbeGen.Jnz(q, lEnd, lTop); QbeGen.EmitLabel(lEnd)
    ELSIF k = AST.NkLoop THEN
      QbeGen.NewLabel(lTop); QbeGen.NewLabel(lEnd);
      QbeGen.PushLoop(lEnd); QbeGen.EmitLabel(lTop);
      LowerStmt(AST.Child(seq, 0));
      QbeGen.Jmp(lTop); QbeGen.PopLoop; QbeGen.EmitLabel(lEnd)
    ELSIF k = AST.NkExit THEN
      IF QbeGen.TopLoop(lx) THEN QbeGen.Jmp(lx) END
    ELSIF k = AST.NkFor THEN
      Name(AST.Child(seq, 0), lv);
      LowerExpr(AST.Child(seq, 1), t, qlo);
      LowerExpr(AST.Child(seq, 2), t2, qhi);
      QbeGen.StoreVar(lv, qlo, FALSE);
      QbeGen.NewLabel(lTop); QbeGen.NewLabel(lBody); QbeGen.NewLabel(lEnd);
      QbeGen.EmitLabel(lTop);
      QbeGen.LoadVar(lv, FALSE, qt);
      QbeGen.NewTemp(qk);
      QbeGen.Op3("cslew", qk, qt, qhi, FALSE);
      QbeGen.Jnz(qk, lBody, lEnd);
      QbeGen.EmitLabel(lBody);
      LowerStmt(AST.Child(seq, 4));
      QbeGen.LoadVar(lv, FALSE, qt);
      QbeGen.IntStr(1, qb);
      QbeGen.NewTemp(qk);
      QbeGen.Op3("add", qk, qt, qb, FALSE);
      QbeGen.StoreVar(lv, qk, FALSE);
      QbeGen.Jmp(lTop); QbeGen.EmitLabel(lEnd)
    ELSIF k = AST.NkHalt THEN
      IF AST.Child(seq, 0) # AST.NoNode THEN
        LowerExpr(AST.Child(seq, 0), t, q) END;
      QbeGen.HaltQ
    ELSIF k = AST.NkReturn THEN
      IF AST.Child(seq, 0) = AST.NoNode THEN
        QbeGen.EmitRet(q, FALSE)
      ELSE
        LowerExpr(AST.Child(seq, 0), t, q);
        conv := (SymTab.ClassOf(SymTab.CurRes()) = SymTab.ClReal)
                AND SymTab.IsIntFamily(t);
        IF conv THEN QbeGen.ConvIR(q, qt); QbeGen.EmitRet(qt, TRUE)
        ELSE QbeGen.EmitRet(q, TRUE)
        END
      END
    ELSIF k = AST.NkCase THEN LowerCase(seq)
    ELSIF k = AST.NkWith THEN LowerWith(seq)
    ELSIF k = AST.NkCall THEN
      CalleeName(seq, qn);
      IF IsBuiltin(qn) THEN LowerBuiltinStmt(seq, qn)
      ELSE LowerCall(seq, t, q, FALSE)
      END
    END
  END LowerStmt;

PROCEDURE LowerDecls (seq: AST.Node);
  VAR i, j: CARDINAL; c: AST.Node; nm, txt: SymTab.Name; qv: QbeGen.QVal;
      mg: QbeGen.QVal; uid, depth, np: CARDINAL; res, pt: SymTab.TypeIndex;
      ext, pv: BOOLEAN;
  BEGIN
    IF seq = AST.NoNode THEN RETURN END;
    i := 0;
    WHILE i < AST.NChild(seq) DO
      c := AST.Child(seq, i);
      IF i = AST.MaxChild - 1 THEN LowerDecls(c)
      ELSIF AST.Kind(c) = AST.NkDeclSeq THEN LowerDecls(c)
      ELSIF AST.Kind(c) = AST.NkVarDecl THEN
        j := 0;
        WHILE j < AST.NChild(c) DO
          Name(AST.Child(c, j), nm);
          QbeGen.DeclVar(nm, AST.Ty(c));
          INC(j)
        END
      ELSIF AST.Kind(c) = AST.NkConstDecl THEN
        Name(AST.Child(c, 0), nm);
        Name(AST.Child(c, 1), txt);
        QbeGen.NormInt(txt, qv);
        QbeGen.DeclConst(nm, qv, AST.Ty(c))
      ELSIF AST.Kind(c) = AST.NkProcDecl THEN
        Name(AST.Child(c, 0), nm);
        IF NOT ProcInfo(nm, uid, res, depth, ext, np) THEN END;
        QbeGen.Mangled(nm, uid, mg);
        QbeGen.BeginFunc(mg);
        j := 0;
        WHILE j < np DO
          IF NOT ParamInfo(nm, j, pt, pv, txt) THEN END;
          IF NOT QbeGen.FuncParam(txt, pv, pt) THEN END;
          INC(j)
        END;
        QbeGen.SetFuncRes(res);
        QbeGen.EndFuncHeader;
        LowerDecls(AST.Child(c, 2));
        LowerStmt(AST.Child(c, 1));
        QbeGen.EndFunc(res)
      END;
      INC(i)
    END
  END LowerDecls;

PROCEDURE LowerUnit (unit: AST.Node);
  VAR nm: SymTab.Name; out: ARRAY [0 .. 255] OF CHAR; i: CARDINAL;
  BEGIN
    withTop := 0;
    Name(AST.Child(unit, 0), nm);
    i := 0;
    WHILE (i <= 254) AND (i <= HIGH(nm)) AND (nm[i] # CHR(0)) DO
      out[i] := nm[i]; INC(i)
    END;
    out[i] := "L"; INC(i); out[i] := CHR(0);
    QbeGen.OpenModule(nm);
    QbeGen.SetOutName(out);
    QbeGen.SetModule(nm);
    LowerDecls(AST.Child(unit, 1));
    QbeGen.BeginBody;
    LowerStmt(AST.Child(unit, 2));
    QbeGen.EndModule(nm)
  END LowerUnit;

BEGIN
END Lower.