cg.c

#include "defs.h"
#include "data.h"
#include "decl.h"

// Code generator for x86-64
// Copyright (c) 2019 Warren Toomey, GPL3


// List of available registers
// and their names
static int freereg[4];
static char *reglist[4]= { "%r8", "%r9", "%r10", "%r11" };

// Set all registers as available
void freeall_registers(void)
{
  freereg[0]= freereg[1]= freereg[2]= freereg[3]= 1;
}

// Allocate a free register. Return the number of
// the register. Die if no available registers.
static int alloc_register(void)
{
  for (int i=0; i<4; i++) {
    if (freereg[i]) {
      freereg[i]= 0;
      return(i);
    }
  }
  fprintf(stderr, "Out of registers!\n");
  exit(1);
}

// Return a register to the list of available registers.
// Check to see if it's not already there.
static void free_register(int reg)
{
  if (freereg[reg] != 0) {
    fprintf(stderr, "Error trying to free register %d\n", reg);
    exit(1);
  }
  freereg[reg]= 1;
}

// Print out the assembly preamble
void cgpreamble()
{
  freeall_registers();
  fputs(
	"\t.text\n"
	".LC0:\n"
	"\t.string\t\"%d\\n\"\n"
	"printint:\n"
	"\tpushq\t%rbp\n"
	"\tmovq\t%rsp, %rbp\n"
	"\tsubq\t$16, %rsp\n"
	"\tmovl\t%edi, -4(%rbp)\n"
	"\tmovl\t-4(%rbp), %eax\n"
	"\tmovl\t%eax, %esi\n"
	"\tleaq	.LC0(%rip), %rdi\n"
	"\tmovl	$0, %eax\n"
	"\tcall	printf@PLT\n"
	"\tnop\n"
	"\tleave\n"
	"\tret\n"
	"\n"
	"\t.globl\tmain\n"
	"\t.type\tmain, @function\n"
	"main:\n"
	"\tpushq\t%rbp\n"
	"\tmovq	%rsp, %rbp\n",
  Outfile);
}

// Print out the assembly postamble
void cgpostamble()
{
  fputs(
	"\tmovl	$0, %eax\n"
	"\tpopq	%rbp\n"
	"\tret\n",
  Outfile);
}

// Load an integer literal value into a register.
// Return the number of the register
int cgload(int value) {

  // Get a new register
  int r= alloc_register();

  // Print out the code to initialise it
  fprintf(Outfile, "\tmovq\t$%d, %s\n", value, reglist[r]);
  return(r);
}

// Add two registers together and return
// the number of the register with the result
int cgadd(int r1, int r2) {
  fprintf(Outfile, "\taddq\t%s, %s\n", reglist[r1], reglist[r2]);
  free_register(r1);
  return(r2);
}

// Subtract the second register from the first and
// return the number of the register with the result
int cgsub(int r1, int r2) {
  fprintf(Outfile, "\tsubq\t%s, %s\n", reglist[r2], reglist[r1]);
  free_register(r2);
  return(r1);
}

// Multiply two registers together and return
// the number of the register with the result
int cgmul(int r1, int r2) {
  fprintf(Outfile, "\timulq\t%s, %s\n", reglist[r1], reglist[r2]);
  free_register(r1);
  return(r2);
}

// Divide the first register by the second and
// return the number of the register with the result
int cgdiv(int r1, int r2) {
  fprintf(Outfile, "\tmovq\t%s,%%rax\n", reglist[r1]);
  fprintf(Outfile, "\tcqo\n");
  fprintf(Outfile, "\tidivq\t%s\n", reglist[r2]);
  fprintf(Outfile, "\tmovq\t%%rax,%s\n", reglist[r1]);
  free_register(r2);
  return(r1);
}

// Call printint() with the given register
void cgprintint(int r) {
  fprintf(Outfile, "\tmovq\t%s, %%rdi\n", reglist[r]);
  fprintf(Outfile, "\tcall\tprintint\n");
  free_register(r);
}