/****************************************************//* File: cgen.c                                     *//* The code generator implementation                *//* for the TINY compiler                            *//* (generates code for the TM machine)              *//* Compiler Construction: Principles and Practice   *//* Kenneth C. Louden                                *//****************************************************/#include "globals.h"#include "symtab.h"#include "code.h"#include "cgen.h"/* tmpOffset is the memory offset for temps   It is decremented each time a temp is   stored, and incremeted when loaded again*/static int tmpOffset = 0;/* prototype for internal recursive code generator */static void cGen (TreeNode * tree);/* Procedure genStmt generates code at a statement node */static void genStmt( TreeNode * tree){ TreeNode * p1, * p2, * p3;  int savedLoc1,savedLoc2,currentLoc;  int loc;  switch (tree->kind.stmt) {      case IfK :         if (TraceCode) emitComment("-> if") ;         p1 = tree->child[0] ;         p2 = tree->child[1] ;         p3 = tree->child[2] ;         /* generate code for test expression */         cGen(p1);         savedLoc1 = emitSkip(1) ;         emitComment("if: jump to else belongs here");         /* recurse on then part */         cGen(p2);         savedLoc2 = emitSkip(1) ;         emitComment("if: jump to end belongs here");         currentLoc = emitSkip(0) ;         emitBackup(savedLoc1) ;         emitRM_Abs("JEQ",ac,currentLoc,"if: jmp to else");         emitRestore() ;         /* recurse on else part */         cGen(p3);         currentLoc = emitSkip(0) ;         emitBackup(savedLoc2) ;         emitRM_Abs("LDA",pc,currentLoc,"jmp to end") ;         emitRestore() ;         if (TraceCode)  emitComment("<- if") ;         break; /* if_k */      case RepeatK:         if (TraceCode) emitComment("-> repeat") ;         p1 = tree->child[0] ;         p2 = tree->child[1] ;         savedLoc1 = emitSkip(0);         emitComment("repeat: jump after body comes back here");         /* generate code for body */         cGen(p1);         /* generate code for test */         cGen(p2);         emitRM_Abs("JEQ",ac,savedLoc1,"repeat: jmp back to body");         if (TraceCode)  emitComment("<- repeat") ;         break; /* repeat */      case AssignK:         if (TraceCode) emitComment("-> assign") ;         /* generate code for rhs */         cGen(tree->child[0]);         /* now store value */         loc = st_lookup(tree->attr.name);         emitRM("ST",ac,loc,gp,"assign: store value");         if (TraceCode)  emitComment("<- assign") ;         break; /* assign_k */      case ReadK:         emitRO("IN",ac,0,0,"read integer value");         loc = st_lookup(tree->attr.name);         emitRM("ST",ac,loc,gp,"read: store value");         break;      case WriteK:         /* generate code for expression to write */         cGen(tree->child[0]);         /* now output it */         emitRO("OUT",ac,0,0,"write ac");         break;      default:         break;    }} /* genStmt *//* Procedure genExp generates code at an expression node */static void genExp( TreeNode * tree){ int loc;  TreeNode * p1, * p2;  switch (tree->kind.exp) {    case ConstK :      if (TraceCode) emitComment("-> Const") ;      /* gen code to load integer constant using LDC */      emitRM("LDC",ac,tree->attr.val,0,"load const");      if (TraceCode)  emitComment("<- Const") ;      break; /* ConstK */        case IdK :      if (TraceCode) emitComment("-> Id") ;      loc = st_lookup(tree->attr.name);      emitRM("LD",ac,loc,gp,"load id value");      if (TraceCode)  emitComment("<- Id") ;      break; /* IdK */    case OpK :         if (TraceCode) emitComment("-> Op") ;         p1 = tree->child[0];         p2 = tree->child[1];         /* gen code for ac = left arg */         cGen(p1);         /* gen code to push left operand */         emitRM("ST",ac,tmpOffset--,mp,"op: push left");         /* gen code for ac = right operand */         cGen(p2);         /* now load left operand */         emitRM("LD",ac1,++tmpOffset,mp,"op: load left");         switch (tree->attr.op) {            case PLUS :               emitRO("ADD",ac,ac1,ac,"op +");               break;            case MINUS :               emitRO("SUB",ac,ac1,ac,"op -");               break;            case TIMES :               emitRO("MUL",ac,ac1,ac,"op *");               break;            case OVER :               emitRO("DIV",ac,ac1,ac,"op /");               break;            case LT :               emitRO("SUB",ac,ac1,ac,"op <") ;               emitRM("JLT",ac,2,pc,"br if true") ;               emitRM("LDC",ac,0,ac,"false case") ;               emitRM("LDA",pc,1,pc,"unconditional jmp") ;               emitRM("LDC",ac,1,ac,"true case") ;               break;            case EQ :               emitRO("SUB",ac,ac1,ac,"op ==") ;               emitRM("JEQ",ac,2,pc,"br if true");               emitRM("LDC",ac,0,ac,"false case") ;               emitRM("LDA",pc,1,pc,"unconditional jmp") ;               emitRM("LDC",ac,1,ac,"true case") ;               break;            default:               emitComment("BUG: Unknown operator");               break;         } /* case op */         if (TraceCode)  emitComment("<- Op") ;         break; /* OpK */    default:      break;  }} /* genExp *//* Procedure cGen recursively generates code by * tree traversal */static void cGen( TreeNode * tree){ if (tree != NULL)  { switch (tree->nodekind) {      case StmtK:        genStmt(tree);        break;      case ExpK:        genExp(tree);        break;      default:        break;    }    cGen(tree->sibling);  }}/**********************************************//* the primary function of the code generator *//**********************************************//* Procedure codeGen generates code to a code * file by traversal of the syntax tree. The * second parameter (codefile) is the file name * of the code file, and is used to print the * file name as a comment in the code file */void codeGen(TreeNode * syntaxTree, char * codefile){  char * s = malloc(strlen(codefile)+7);   strcpy(s,"File: ");   strcat(s,codefile);   emitComment("TINY Compilation to TM Code");   emitComment(s);   /* generate standard prelude */   emitComment("Standard prelude:");   emitRM("LD",mp,0,ac,"load maxaddress from location 0");   emitRM("ST",ac,0,ac,"clear location 0");   emitComment("End of standard prelude.");   /* generate code for TINY program */   cGen(syntaxTree);   /* finish */   emitComment("End of execution.");   emitRO("HALT",0,0,0,"");}