codegen.c

#include "9cc.h"

static int labelseq = 1;
static char *argreg1[] = {"dil", "sil", "dl", "cl", "r8b", "r9b"};
static char *argreg8[] = {"rdi", "rsi", "rdx", "rcx", "r8", "r9"};
static char *funcname;

void gen_lvar(Node *node)
{
  switch (node->kind)
  {
  case ND_VAR:
  {
    Var *var = node->var;
    if (var->is_local)
    {
      // NOTE: can be written as `printf("  lea rax, [rbp-%d]\n", node->var->offset)`
      printf("  mov rax, rbp\n");
      printf("  sub rax, %d\n", var->offset);
      printf("  push rax\n");
    }
    else
      printf("  push offset %s\n", var->name);
    return;
  }
  case ND_DEREF:
    gen(node->lhs);
    return;
  }
  error_tok(node->tok, "左辺値が変数ではありません");
}

static void gen_lval(Node *node)
{
  if (node->ty->kind == TY_ARRAY)
    error_tok(node->tok, "not a lvalue");
  gen_lvar(node);
}

static void load(Type *ty)
{
  printf("  pop rax\n");
  if (ty->size == 1)
    printf("  movsx rax, byte ptr [rax]\n");
  else
    printf("  mov rax, [rax]\n");
  printf("  push rax\n");
}

static void store(Type *ty)
{
  printf("  pop rdi\n");
  printf("  pop rax\n");
  if (ty->size == 1)
    printf("  mov [rax], dil\n");
  else
    printf("  mov [rax], rdi\n");
  printf("  push rdi\n");
}

void gen(Node *node)
{
  switch (node->kind)
  {
  case ND_NULL:
    return;
  case ND_EXPR_STMT:
    gen(node->lhs);
    printf("  add rsp, 8\n");
    return;
  case ND_IF:
  {
    int seq = labelseq++;
    if (node->els)
    {
      gen(node->cond);
      printf("  pop rax\n");
      printf("  cmp rax, 0\n");
      printf("  je .L.else.%d\n", seq);
      gen(node->then);
      printf("  jmp .L.end.%d\n", seq);
      printf(".L.else.%d:\n", seq);
      gen(node->els);
      printf(".L.end.%d:\n", seq);
    }
    else
    {
      gen(node->cond);
      printf("  pop rax\n");
      printf("  cmp rax, 0\n");
      printf("  je .L.end.%d\n", seq);
      gen(node->then);
      printf(".L.end.%d:\n", seq);
    }
    return;
  }
  case ND_WHILE:
  {
    int seq = labelseq++;
    printf(".L.continue.%d:\n", seq);
    gen(node->cond);
    printf("  pop rax\n");
    printf("  cmp rax, 0\n");
    printf("  je .L.break.%d\n", seq);
    gen(node->then);
    printf("  jmp .L.continue.%d\n", seq);
    printf(".L.break.%d:\n", seq);
    return;
  }
  case ND_FOR:
  {
    int seq = labelseq++;
    if (node->init)
      gen(node->init);
    printf(".L.begin.%d:\n", seq);
    if (node->cond)
    {
      gen(node->cond);
      printf("  pop rax\n");
      printf("  cmp rax, 0\n");
      printf("  je .L.break.%d\n", seq);
    }
    gen(node->then);
    if (node->inc)
      gen(node->inc);
    printf("  jmp .L.begin.%d\n", seq);
    printf(".L.break.%d:\n", seq);
    return;
  }
  case ND_BLOCK:
  case ND_STMT_EXPR:
    for (Node *var = node->body; var; var = var->next)
      gen(var);
    return;
  case ND_FUNCALL:
  {
    int nargs = 0;
    for (Node *arg = node->args; arg; arg = arg->next)
    {
      gen(arg);
      nargs++;
    }

    for (int i = nargs - 1; i >= 0; i--)
      printf("  pop %s\n", argreg8[i]);

    // We need to align RSP to a 16 byte boundary before
    // calling a function to meet ABI requirement.
    // RAX is set to 0 for variadic function.
    int seq = labelseq++;
    printf("  mov rax, rsp\n");
    printf("  and rax, 15\n");
    printf("  jnz .L.call.%d\n", seq);
    printf("  mov rax, 0\n");
    printf("  call %s\n", node->funcname);
    printf("  jmp .L.end.%d\n", seq);
    printf(".L.call.%d:\n", seq);
    printf("  sub rsp, 8\n");
    printf("  mov rax, 0\n");
    printf("  call %s\n", node->funcname);
    printf("  add rsp, 8\n");
    printf(".L.end.%d:\n", seq);
    printf("  push rax\n");
    return;
  }
  case ND_RETURN:
    gen(node->lhs);
    printf("  pop rax\n");
    printf("  jmp .L.return.%s\n", funcname);
    return;
  case ND_NUM:
    printf("  push %d\n", node->val);
    return;
  case ND_VAR:
    gen_lvar(node);
    if (node->ty->kind != TY_ARRAY)
      load(node->ty);
    return;
  case ND_ASSIGN:
    gen_lval(node->lhs);
    gen(node->rhs);
    store(node->ty);
    return;
  case ND_ADDR:
    gen_lvar(node->lhs);
    return;
  case ND_DEREF:
    gen(node->lhs);
    if (node->ty->kind != TY_ARRAY)
      load(node->ty);
    return;
  }

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

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

  switch (node->kind)
  {
  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;
  case ND_ADD:
    printf("  add rax, rdi\n");
    break;
  case ND_PTR_ADD:
    printf("  imul rdi, %ld\n", node->ty->base->size);
    printf("  add rax, rdi\n");
    break;
  case ND_SUB:
    printf("  sub rax, rdi\n");
    break;
  case ND_PTR_SUB:
    printf("  imul rdi, %ld\n", node->ty->base->size);
    printf("  sub rax, rdi\n");
    break;
  case ND_PTR_DIFF:
    printf("  sub rax, rdi\n");
    printf("  cqo\n");
    printf("  mov rdi, %ld\n", node->lhs->ty->base->size);
    printf("  idiv rdi\n");
    break;
  case ND_MUL:
    printf("  imul rax, rdi\n");
    break;
  case ND_DIV:
    printf("  cqo\n");
    printf("  idiv rdi\n");
    break;
  default:
    error_tok(node->tok, "No effective NodeKind found for the token");
  }

  printf("  push rax\n");
}

static void emit_data(Program *prog)
{
  printf(".data\n");
  for (VarList *vl = prog->globals; vl; vl = vl->next)
  {
    Var *var = vl->var;
    printf("%s:\n", var->name);
    if (!var->contents)
    {
      printf("  .zero %ld\n", var->ty->size);
      continue;
    }

    for (int i = 0; i < var->cont_len; i++)
      printf("  .byte %d\n", var->contents[i]);
  }
}

static void load_arg(Var *var, int idx)
{
  int sz = var->ty->size;
  if (sz == 1)
    printf("  mov [rbp-%d], %s\n", var->offset, argreg1[idx]);
  else
  {
    assert(sz == 8);
    printf("  mov [rbp-%d], %s\n", var->offset, argreg8[idx]);
  }
}

static void emit_text(Program *prog)
{
  printf(".text\n");
  for (Function *fn = prog->fns; fn; fn = fn->next)
  {
    printf(".global %s\n", fn->name);
    printf("%s:\n", fn->name);
    funcname = fn->name;

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

    int i = 0;
    for (VarList *vl = fn->params; vl; vl = vl->next)
      load_arg(vl->var, i++);

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

    // Epilogue
    printf(".L.return.%s:\n", funcname);
    printf("  mov rsp, rbp\n");
    printf("  pop rbp\n");
    printf("  ret\n");
  }
}

void codegen(Program *prog)
{
  printf(".intel_syntax noprefix\n");
  emit_data(prog);
  emit_text(prog);
}