codegen.c

#include "9cc.h"

static void gen_addr(Node *node) {
  if (node->kind == ND_VAR) {
    printf("  lea rax, [rbp-%d]\n", node->var->offset);
    printf("  push rax\n");
    return;
  }

  error("not an lvalue");
}

static void load(void) {
  printf("  pop rax\n");
  printf("  mov rax, [rax]\n");
  printf("  push rax\n");
}

static void store(void) {
  printf("  pop rdi\n");
  printf("  pop rax\n");
  printf("  mov [rax], rdi\n");
  printf("  push rdi\n");
}

static void gen(Node *node) {
  switch (node->kind) {
  case ND_NUM:
    printf("  push %ld\n", node->val);
    return;
  case ND_EXPR_STMT:
    gen(node->lhs);
    printf("  add rsp, 8\n");
    return;
  case ND_VAR:
    gen_addr(node);
    load();
    return;
  case ND_ASSIGN:
    gen_addr(node->lhs);
    gen(node->rhs);
    store();
    return;
  case ND_RETURN:
    gen(node->lhs);
    printf("  pop rax\n");
    printf("  jmp .L.return\n");
    return;
  }

  gen(node->lhs);
  gen(node->rhs);

  printf("  pop rdi\n");
  printf("  pop rax\n");

  switch (node->kind) {
  case ND_ADD:
    printf("  add rax, rdi\n");
    break;
  case ND_SUB:
    printf("  sub rax, rdi\n");
    break;
  case ND_MUL:
    printf("  imul rax, rdi\n");
    break;
  case ND_DIV:
    printf("  cqo\n");
    printf("  idiv rdi\n");
    break;
  case ND_EQ:
    printf("  cmp rax, rdi\n");
    printf("  sete al\n");
    printf("  movzb rax, al\n");
    break;
  case ND_NE:
    printf("  cmp rax, rdi\n");
    printf("  setne al\n");
    printf("  movzb rax, al\n");
    break;
  case ND_LT:
    printf("  cmp rax, rdi\n");
    printf("  setl al\n");
    printf("  movzb rax, al\n");
    break;
  case ND_LE:
    printf("  cmp rax, rdi\n");
    printf("  setle al\n");
    printf("  movzb rax, al\n");
    break;
  }

  printf("  push rax\n");
}

void codegen(Function *prog) {
  printf(".intel_syntax noprefix\n");
  printf(".global main\n");
  printf("main:\n");

  // Prologue
  printf("  push rbp\n");
  printf("  mov rbp, rsp\n");
  printf("  sub rsp, %d\n", prog->stack_size);

  for (Node *node = prog->node; node; node = node->next)
    gen(node);

  // Epilogue
  printf(".L.return:\n");
  printf("  mov rsp, rbp\n");
  printf("  pop rbp\n");

  printf("  ret\n");
}