chibicc/codegen.c

#include "chibicc.h"

static FILE *output_file;
static int depth;
static char *argreg8[] = {"%dil", "%sil", "%dl", "%cl", "%r8b", "%r9b"};
static char *argreg16[] = {"%di", "%si", "%dx", "%cx", "%r8w", "%r9w"};
static char *argreg32[] = {"%edi", "%esi", "%edx", "%ecx", "%r8d", "%r9d"};
static char *argreg64[] = {"%rdi", "%rsi", "%rdx", "%rcx", "%r8", "%r9"};
static Obj *current_fn;

static void gen_expr(Node *node);
static void gen_stmt(Node *node);

static void println(char *fmt, ...) {
  va_list ap;
  va_start(ap, fmt);
  vfprintf(output_file, fmt, ap);
  va_end(ap);
  fprintf(output_file, "\n");
}

static int count(void) {
  static int i = 1;
  return i++;
}

static void push(void) {
  println("  push %%rax");
  depth++;
}

static void pop(char *arg) {
  println("  pop %s", arg);
  depth--;
}

// Round up `n` to the nearest multiple of `align`. For instance,
// align_to(5, 8) returns 8 and align_to(11, 8) returns 16.
int align_to(int n, int align) {
  return (n + align - 1) / align * align;
}

// Compute the absolute address of a given node.
// It's an error if a given node does not reside in memory.
static void gen_addr(Node *node) {
  switch (node->kind) {
  case ND_VAR:
    if (node->var->is_local) {
      // Local variable
      println("  lea %d(%%rbp), %%rax", node->var->offset);
    } else {
      // Global variable
      println("  lea %s(%%rip), %%rax", node->var->name);
    }
    return;
  case ND_DEREF:
    gen_expr(node->lhs);
    return;
  case ND_COMMA:
    gen_expr(node->lhs);
    gen_addr(node->rhs);
    return;
  case ND_MEMBER:
    gen_addr(node->lhs);
    println("  add $%d, %%rax", node->member->offset);
    return;
  }

  error_tok(node->tok, "not an lvalue");
}

// Load a value from where %rax is pointing to.
static void load(Type *ty) {
  if (ty->kind == TY_ARRAY || ty->kind == TY_STRUCT || ty->kind == TY_UNION) {
    // If it is an array, do not attempt to load a value to the
    // register because in general we can't load an entire array to a
    // register. As a result, the result of an evaluation of an array
    // becomes not the array itself but the address of the array.
    // This is where "array is automatically converted to a pointer to
    // the first element of the array in C" occurs.
    return;
  }

  char *insn = ty->is_unsigned ? "movz" : "movs";

  // When we load a char or a short value to a register, we always
  // extend them to the size of int, so we can assume the lower half of
  // a register always contains a valid value. The upper half of a
  // register for char, short and int may contain garbage. When we load
  // a long value to a register, it simply occupies the entire register.
  if (ty->size == 1)
    println("  %sbl (%%rax), %%eax", insn);
  else if (ty->size == 2)
    println("  %swl (%%rax), %%eax", insn);
  else if (ty->size == 4)
    println("  movsxd (%%rax), %%rax");
  else
    println("  mov (%%rax), %%rax");
}

// Store %rax to an address that the stack top is pointing to.
static void store(Type *ty) {
  pop("%rdi");

  if (ty->kind == TY_STRUCT || ty->kind == TY_UNION) {
    for (int i = 0; i < ty->size; i++) {
      println("  mov %d(%%rax), %%r8b", i);
      println("  mov %%r8b, %d(%%rdi)", i);
    }
    return;
  }

  if (ty->size == 1)
    println("  mov %%al, (%%rdi)");
  else if (ty->size == 2)
    println("  mov %%ax, (%%rdi)");
  else if (ty->size == 4)
    println("  mov %%eax, (%%rdi)");
  else
    println("  mov %%rax, (%%rdi)");
}

static void cmp_zero(Type *ty) {
  if (is_integer(ty) && ty->size <= 4)
    println("  cmp $0, %%eax");
  else
    println("  cmp $0, %%rax");
}

enum { I8, I16, I32, I64, U8, U16, U32, U64 };

static int getTypeId(Type *ty) {
  switch (ty->kind) {
  case TY_CHAR:
    return ty->is_unsigned ? U8 : I8;
  case TY_SHORT:
    return ty->is_unsigned ? U16 : I16;
  case TY_INT:
    return ty->is_unsigned ? U32 : I32;
  case TY_LONG:
    return ty->is_unsigned ? U64 : I64;
  }
  return U64;
}

// The table for type casts
static char i32i8[] = "movsbl %al, %eax";
static char i32u8[] = "movzbl %al, %eax";
static char i32i16[] = "movswl %ax, %eax";
static char i32u16[] = "movzwl %ax, %eax";
static char i32i64[] = "movsxd %eax, %rax";
static char u32i64[] = "mov %eax, %eax";

static char *cast_table[][10] = {
  // i8   i16     i32   i64     u8     u16     u32   u64
  {NULL,  NULL,   NULL, i32i64, i32u8, i32u16, NULL, i32i64}, // i8
  {i32i8, NULL,   NULL, i32i64, i32u8, i32u16, NULL, i32i64}, // i16
  {i32i8, i32i16, NULL, i32i64, i32u8, i32u16, NULL, i32i64}, // i32
  {i32i8, i32i16, NULL, NULL,   i32u8, i32u16, NULL, NULL},   // i64
  {i32i8, NULL,   NULL, i32i64, NULL,  NULL,   NULL, i32i64}, // u8
  {i32i8, i32i16, NULL, i32i64, i32u8, NULL,   NULL, i32i64}, // u16
  {i32i8, i32i16, NULL, u32i64, i32u8, i32u16, NULL, u32i64}, // u32
  {i32i8, i32i16, NULL, NULL,   i32u8, i32u16, NULL, NULL},   // u64
};

static void cast(Type *from, Type *to) {
  if (to->kind == TY_VOID)
    return;

  if (to->kind == TY_BOOL) {
    cmp_zero(from);
    println("  setne %%al");
    println("  movzx %%al, %%eax");
    return;
  }

  int t1 = getTypeId(from);
  int t2 = getTypeId(to);
  if (cast_table[t1][t2])
    println("  %s", cast_table[t1][t2]);
}

// Generate code for a given node.
static void gen_expr(Node *node) {
  println("  .loc 1 %d", node->tok->line_no);

  switch (node->kind) {
  case ND_NULL_EXPR:
    return;
  case ND_NUM: {
    union { float f32; double f64; uint32_t u32; uint64_t u64; } u;

    switch (node->ty->kind) {
    case TY_FLOAT:
      u.f32 = node->fval;
      println("  mov $%u, %%eax  # float %f", u.u32, node->fval);
      println("  movq %%rax, %%xmm0");
      return;
    case TY_DOUBLE:
      u.f64 = node->fval;
      println("  mov $%lu, %%rax  # double %f", u.u64, node->fval);
      println("  movq %%rax, %%xmm0");
      return;
    }

    println("  mov $%ld, %%rax", node->val);
    return;
  }
  case ND_NEG:
    gen_expr(node->lhs);
    println("  neg %%rax");
    return;
  case ND_VAR:
  case ND_MEMBER:
    gen_addr(node);
    load(node->ty);
    return;
  case ND_DEREF:
    gen_expr(node->lhs);
    load(node->ty);
    return;
  case ND_ADDR:
    gen_addr(node->lhs);
    return;
  case ND_ASSIGN:
    gen_addr(node->lhs);
    push();
    gen_expr(node->rhs);
    store(node->ty);
    return;
  case ND_STMT_EXPR:
    for (Node *n = node->body; n; n = n->next)
      gen_stmt(n);
    return;
  case ND_COMMA:
    gen_expr(node->lhs);
    gen_expr(node->rhs);
    return;
  case ND_CAST:
    gen_expr(node->lhs);
    cast(node->lhs->ty, node->ty);
    return;
  case ND_MEMZERO:
    // `rep stosb` is equivalent to `memset(%rdi, %al, %rcx)`.
    println("  mov $%d, %%rcx", node->var->ty->size);
    println("  lea %d(%%rbp), %%rdi", node->var->offset);
    println("  mov $0, %%al");
    println("  rep stosb");
    return;
  case ND_COND: {
    int c = count();
    gen_expr(node->cond);
    println("  cmp $0, %%rax");
    println("  je .L.else.%d", c);
    gen_expr(node->then);
    println("  jmp .L.end.%d", c);
    println(".L.else.%d:", c);
    gen_expr(node->els);
    println(".L.end.%d:", c);
    return;
  }
  case ND_NOT:
    gen_expr(node->lhs);
    println("  cmp $0, %%rax");
    println("  sete %%al");
    println("  movzx %%al, %%rax");
    return;
  case ND_BITNOT:
    gen_expr(node->lhs);
    println("  not %%rax");
    return;
  case ND_LOGAND: {
    int c = count();
    gen_expr(node->lhs);
    println("  cmp $0, %%rax");
    println("  je .L.false.%d", c);
    gen_expr(node->rhs);
    println("  cmp $0, %%rax");
    println("  je .L.false.%d", c);
    println("  mov $1, %%rax");
    println("  jmp .L.end.%d", c);
    println(".L.false.%d:", c);
    println("  mov $0, %%rax");
    println(".L.end.%d:", c);
    return;
  }
  case ND_LOGOR: {
    int c = count();
    gen_expr(node->lhs);
    println("  cmp $0, %%rax");
    println("  jne .L.true.%d", c);
    gen_expr(node->rhs);
    println("  cmp $0, %%rax");
    println("  jne .L.true.%d", c);
    println("  mov $0, %%rax");
    println("  jmp .L.end.%d", c);
    println(".L.true.%d:", c);
    println("  mov $1, %%rax");
    println(".L.end.%d:", c);
    return;
  }
  case ND_FUNCALL: {
    int nargs = 0;
    for (Node *arg = node->args; arg; arg = arg->next) {
      gen_expr(arg);
      push();
      nargs++;
    }

    for (int i = nargs - 1; i >= 0; i--)
      pop(argreg64[i]);

    println("  mov $0, %%rax");

    if (depth % 2 == 0) {
      println("  call %s", node->funcname);
    } else {
      println("  sub $8, %%rsp");
      println("  call %s", node->funcname);
      println("  add $8, %%rsp");
    }

    // It looks like the most significant 48 or 56 bits in RAX may
    // contain garbage if a function return type is short or bool/char,
    // respectively. We clear the upper bits here.
    switch (node->ty->kind) {
    case TY_BOOL:
      println("  movzx %%al, %%eax");
      return;
    case TY_CHAR:
      if (node->ty->is_unsigned)
        println("  movzbl %%al, %%eax");
      else
        println("  movsbl %%al, %%eax");
      return;
    case TY_SHORT:
      if (node->ty->is_unsigned)
        println("  movzwl %%ax, %%eax");
      else
        println("  movswl %%ax, %%eax");
      return;
    }
    return;
  }
  }

  gen_expr(node->rhs);
  push();
  gen_expr(node->lhs);
  pop("%rdi");

  char *ax, *di, *dx;

  if (node->lhs->ty->kind == TY_LONG || node->lhs->ty->base) {
    ax = "%rax";
    di = "%rdi";
    dx = "%rdx";
  } else {
    ax = "%eax";
    di = "%edi";
    dx = "%edx";
  }

  switch (node->kind) {
  case ND_ADD:
    println("  add %s, %s", di, ax);
    return;
  case ND_SUB:
    println("  sub %s, %s", di, ax);
    return;
  case ND_MUL:
    println("  imul %s, %s", di, ax);
    return;
  case ND_DIV:
  case ND_MOD:
    if (node->ty->is_unsigned) {
      println("  mov $0, %s", dx);
      println("  div %s", di);
    } else {
      if (node->lhs->ty->size == 8)
        println("  cqo");
      else
        println("  cdq");
      println("  idiv %s", di);
    }

    if (node->kind == ND_MOD)
      println("  mov %%rdx, %%rax");
    return;
  case ND_BITAND:
    println("  and %%rdi, %%rax");
    return;
  case ND_BITOR:
    println("  or %%rdi, %%rax");
    return;
  case ND_BITXOR:
    println("  xor %%rdi, %%rax");
    return;
  case ND_EQ:
  case ND_NE:
  case ND_LT:
  case ND_LE:
    println("  cmp %s, %s", di, ax);

    if (node->kind == ND_EQ) {
      println("  sete %%al");
    } else if (node->kind == ND_NE) {
      println("  setne %%al");
    } else if (node->kind == ND_LT) {
      if (node->lhs->ty->is_unsigned)
        println("  setb %%al");
      else
        println("  setl %%al");
    } else if (node->kind == ND_LE) {
      if (node->lhs->ty->is_unsigned)
        println("  setbe %%al");
      else
        println("  setle %%al");
    }

    println("  movzb %%al, %%rax");
    return;
  case ND_SHL:
    println("  mov %%rdi, %%rcx");
    println("  shl %%cl, %s", ax);
    return;
  case ND_SHR:
    println("  mov %%rdi, %%rcx");
    if (node->lhs->ty->is_unsigned)
      println("  shr %%cl, %s", ax);
    else
      println("  sar %%cl, %s", ax);
    return;
  }

  error_tok(node->tok, "invalid expression");
}

static void gen_stmt(Node *node) {
  println("  .loc 1 %d", node->tok->line_no);

  switch (node->kind) {
  case ND_IF: {
    int c = count();
    gen_expr(node->cond);
    println("  cmp $0, %%rax");
    println("  je  .L.else.%d", c);
    gen_stmt(node->then);
    println("  jmp .L.end.%d", c);
    println(".L.else.%d:", c);
    if (node->els)
      gen_stmt(node->els);
    println(".L.end.%d:", c);
    return;
  }
  case ND_FOR: {
    int c = count();
    if (node->init)
      gen_stmt(node->init);
    println(".L.begin.%d:", c);
    if (node->cond) {
      gen_expr(node->cond);
      println("  cmp $0, %%rax");
      println("  je %s", node->brk_label);
    }
    gen_stmt(node->then);
    println("%s:", node->cont_label);
    if (node->inc)
      gen_expr(node->inc);
    println("  jmp .L.begin.%d", c);
    println("%s:", node->brk_label);
    return;
  }
  case ND_DO: {
    int c = count();
    println(".L.begin.%d:", c);
    gen_stmt(node->then);
    println("%s:", node->cont_label);
    gen_expr(node->cond);
    println("  cmp $0, %%rax");
    println("  jne .L.begin.%d", c);
    println("%s:", node->brk_label);
    return;
  }
  case ND_SWITCH:
    gen_expr(node->cond);

    for (Node *n = node->case_next; n; n = n->case_next) {
      char *reg = (node->cond->ty->size == 8) ? "%rax" : "%eax";
      println("  cmp $%ld, %s", n->val, reg);
      println("  je %s", n->label);
    }

    if (node->default_case)
      println("  jmp %s", node->default_case->label);

    println("  jmp %s", node->brk_label);
    gen_stmt(node->then);
    println("%s:", node->brk_label);
    return;
  case ND_CASE:
    println("%s:", node->label);
    gen_stmt(node->lhs);
    return;
  case ND_BLOCK:
    for (Node *n = node->body; n; n = n->next)
      gen_stmt(n);
    return;
  case ND_GOTO:
    println("  jmp %s", node->unique_label);
    return;
  case ND_LABEL:
    println("%s:", node->unique_label);
    gen_stmt(node->lhs);
    return;
  case ND_RETURN:
    if (node->lhs)
      gen_expr(node->lhs);
    println("  jmp .L.return.%s", current_fn->name);
    return;
  case ND_EXPR_STMT:
    gen_expr(node->lhs);
    return;
  }

  error_tok(node->tok, "invalid statement");
}

// Assign offsets to local variables.
static void assign_lvar_offsets(Obj *prog) {
  for (Obj *fn = prog; fn; fn = fn->next) {
    if (!fn->is_function)
      continue;

    int offset = 0;
    for (Obj *var = fn->locals; var; var = var->next) {
      offset += var->ty->size;
      offset = align_to(offset, var->align);
      var->offset = -offset;
    }
    fn->stack_size = align_to(offset, 16);
  }
}

static void emit_data(Obj *prog) {
  for (Obj *var = prog; var; var = var->next) {
    if (var->is_function || !var->is_definition)
      continue;

    if (var->is_static)
      println("  .local %s", var->name);
    else
      println("  .globl %s", var->name);

    println("  .align %d", var->align);

    if (var->init_data) {
      println("  .data");
      println("%s:", var->name);

      Relocation *rel = var->rel;
      int pos = 0;
      while (pos < var->ty->size) {
        if (rel && rel->offset == pos) {
          println("  .quad %s%+ld", rel->label, rel->addend);
          rel = rel->next;
          pos += 8;
        } else {
          println("  .byte %d", var->init_data[pos++]);
        }
      }
      continue;
    }

    println("  .bss");
    println("%s:", var->name);
    println("  .zero %d", var->ty->size);
  }
}

static void store_gp(int r, int offset, int sz) {
  switch (sz) {
  case 1:
    println("  mov %s, %d(%%rbp)", argreg8[r], offset);
    return;
  case 2:
    println("  mov %s, %d(%%rbp)", argreg16[r], offset);
    return;
  case 4:
    println("  mov %s, %d(%%rbp)", argreg32[r], offset);
    return;
  case 8:
    println("  mov %s, %d(%%rbp)", argreg64[r], offset);
    return;
  }
  unreachable();
}

static void emit_text(Obj *prog) {
  for (Obj *fn = prog; fn; fn = fn->next) {
    if (!fn->is_function || !fn->is_definition)
      continue;

    if (fn->is_static)
      println("  .local %s", fn->name);
    else
      println("  .globl %s", fn->name);

    println("  .text");
    println("%s:", fn->name);
    current_fn = fn;

    // Prologue
    println("  push %%rbp");
    println("  mov %%rsp, %%rbp");
    println("  sub $%d, %%rsp", fn->stack_size);

    // Save arg registers if function is variadic
    if (fn->va_area) {
      int gp = 0;
      for (Obj *var = fn->params; var; var = var->next)
        gp++;
      int off = fn->va_area->offset;

      // va_elem
      println("  movl $%d, %d(%%rbp)", gp * 8, off);
      println("  movl $0, %d(%%rbp)", off + 4);
      println("  movq %%rbp, %d(%%rbp)", off + 16);
      println("  addq $%d, %d(%%rbp)", off + 24, off + 16);

      // __reg_save_area__
      println("  movq %%rdi, %d(%%rbp)", off + 24);
      println("  movq %%rsi, %d(%%rbp)", off + 32);
      println("  movq %%rdx, %d(%%rbp)", off + 40);
      println("  movq %%rcx, %d(%%rbp)", off + 48);
      println("  movq %%r8, %d(%%rbp)", off + 56);
      println("  movq %%r9, %d(%%rbp)", off + 64);
      println("  movsd %%xmm0, %d(%%rbp)", off + 72);
      println("  movsd %%xmm1, %d(%%rbp)", off + 80);
      println("  movsd %%xmm2, %d(%%rbp)", off + 88);
      println("  movsd %%xmm3, %d(%%rbp)", off + 96);
      println("  movsd %%xmm4, %d(%%rbp)", off + 104);
      println("  movsd %%xmm5, %d(%%rbp)", off + 112);
      println("  movsd %%xmm6, %d(%%rbp)", off + 120);
      println("  movsd %%xmm7, %d(%%rbp)", off + 128);
    }

    // Save passed-by-register arguments to the stack
    int i = 0;
    for (Obj *var = fn->params; var; var = var->next)
      store_gp(i++, var->offset, var->ty->size);

    // Emit code
    gen_stmt(fn->body);
    assert(depth == 0);

    // Epilogue
    println(".L.return.%s:", fn->name);
    println("  mov %%rbp, %%rsp");
    println("  pop %%rbp");
    println("  ret");
  }
}

void codegen(Obj *prog, FILE *out) {
  output_file = out;

  assign_lvar_offsets(prog);
  emit_data(prog);
  emit_text(prog);
}