Add _Bool type

_Bool isn't just a 1-bit integer because when you convert a value
to bool, the result is 1 if the original value is non-zero. This
is contrary to the other small integral types, e.g. char, as you
can see below:

  char x  = 256; // x is 0
  _Bool y = 256; // y is 1

chibicc.h

@@ -156,6 +156,7 @@ Obj *parse(Token *tok);
 
 typedef enum {
   TY_VOID,
+  TY_BOOL,
   TY_CHAR,
   TY_SHORT,
   TY_INT,
@@ -206,6 +207,7 @@ struct Member {
 };
 
 extern Type *ty_void;
+extern Type *ty_bool;
 
 extern Type *ty_char;
 extern Type *ty_short;

codegen.c

@@ -118,6 +118,13 @@ static void store(Type *ty) {
     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 };
 
 static int getTypeId(Type *ty) {
@@ -148,6 +155,13 @@ 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])

parse.c

@@ -236,7 +236,7 @@ static void push_tag_scope(Token *tok, Type *ty) {
   scope->tags = sc;
 }
 
-// declspec = ("void" | "char" | "short" | "int" | "long"
+// declspec = ("void" | "_Bool" | "char" | "short" | "int" | "long"
 //             | "typedef"
 //             | struct-decl | union-decl | typedef-name)+
 //
@@ -258,11 +258,12 @@ static Type *declspec(Token **rest, Token *tok, VarAttr *attr) {
   // as you can see below.
   enum {
     VOID  = 1 << 0,
-    CHAR  = 1 << 2,
-    SHORT = 1 << 4,
-    INT   = 1 << 6,
-    LONG  = 1 << 8,
-    OTHER = 1 << 10,
+    BOOL  = 1 << 2,
+    CHAR  = 1 << 4,
+    SHORT = 1 << 6,
+    INT   = 1 << 8,
+    LONG  = 1 << 10,
+    OTHER = 1 << 12,
   };
 
   Type *ty = ty_int;
@@ -300,6 +301,8 @@ static Type *declspec(Token **rest, Token *tok, VarAttr *attr) {
     // Handle built-in types.
     if (equal(tok, "void"))
       counter += VOID;
+    else if (equal(tok, "_Bool"))
+      counter += BOOL;
     else if (equal(tok, "char"))
       counter += CHAR;
     else if (equal(tok, "short"))
@@ -315,6 +318,9 @@ static Type *declspec(Token **rest, Token *tok, VarAttr *attr) {
     case VOID:
       ty = ty_void;
       break;
+    case BOOL:
+      ty = ty_bool;
+      break;
     case CHAR:
       ty = ty_char;
       break;
@@ -460,7 +466,7 @@ static Node *declaration(Token **rest, Token *tok, Type *basety) {
 // Returns true if a given token represents a type.
 static bool is_typename(Token *tok) {
   static char *kw[] = {
-    "void", "char", "short", "int", "long", "struct", "union",
+    "void", "_Bool", "char", "short", "int", "long", "struct", "union",
     "typedef",
   };
 

test/decl.c

@@ -10,6 +10,13 @@ int main() {
 
   ASSERT(8, ({ long long x; sizeof(x); }));
 
+  ASSERT(0, ({ _Bool x=0; x; }));
+  ASSERT(1, ({ _Bool x=1; x; }));
+  ASSERT(1, ({ _Bool x=2; x; }));
+  ASSERT(1, (_Bool)1);
+  ASSERT(1, (_Bool)2);
+  ASSERT(0, (_Bool)(char)256);
+
   printf("OK\n");
   return 0;
 }

test/function.c

@@ -48,6 +48,9 @@ int div_long(long a, long b) {
   return a / b;
 }
 
+_Bool bool_fn_add(_Bool x) { return x + 1; }
+_Bool bool_fn_sub(_Bool x) { return x - 1; }
+
 int main() {
   ASSERT(3, ret3());
   ASSERT(8, add2(3, 5));
@@ -72,6 +75,13 @@ int main() {
   ASSERT(5, int_to_char(261));
   ASSERT(-5, div_long(-10, 2));
 
+  ASSERT(1, bool_fn_add(3));
+  ASSERT(0, bool_fn_sub(3));
+  ASSERT(1, bool_fn_add(-3));
+  ASSERT(0, bool_fn_sub(-3));
+  ASSERT(1, bool_fn_add(0));
+  ASSERT(1, bool_fn_sub(0));
+
   printf("OK\n");
   return 0;
 }

tokenize.c

@@ -127,7 +127,7 @@ static int read_punct(char *p) {
 static bool is_keyword(Token *tok) {
   static char *kw[] = {
     "return", "if", "else", "for", "while", "int", "sizeof", "char",
-    "struct", "union", "short", "long", "void", "typedef",
+    "struct", "union", "short", "long", "void", "typedef", "_Bool",
   };
 
   for (int i = 0; i < sizeof(kw) / sizeof(*kw); i++)

type.c

@@ -1,6 +1,7 @@
 #include "chibicc.h"
 
 Type *ty_void = &(Type){TY_VOID, 1, 1};
+Type *ty_bool = &(Type){TY_BOOL, 1, 1};
 
 Type *ty_char = &(Type){TY_CHAR, 1, 1};
 Type *ty_short = &(Type){TY_SHORT, 2, 2};
@@ -17,8 +18,8 @@ static Type *new_type(TypeKind kind, int size, int align) {
 
 bool is_integer(Type *ty) {
   TypeKind k = ty->kind;
-  return k == TY_CHAR || k == TY_SHORT || k == TY_INT ||
-         k == TY_LONG;
+  return k == TY_BOOL || k == TY_CHAR || k == TY_SHORT ||
+         k == TY_INT  || k == TY_LONG;
 }
 
 Type *copy_type(Type *ty) {