From 1faab48ecf83d31a4fd781f10f6f00acb681d2dd Mon Sep 17 00:00:00 2001
From: Rui Ueyama <ruiu@cs.stanford.edu>
Date: Fri, 24 Jul 2020 16:18:03 +0900
Subject: [PATCH] Add _Generic

---
 parse.c        | 47 +++++++++++++++++++++++++++++++++++++++++++++++
 test/generic.c | 12 ++++++++++++
 2 files changed, 59 insertions(+)
 create mode 100644 test/generic.c

diff --git a/parse.c b/parse.c
index ea6ff50..aed31d6 100644
--- a/parse.c
+++ b/parse.c
@@ -2605,12 +2605,56 @@ static Node *funcall(Token **rest, Token *tok, Node *fn) {
   return node;
 }
 
+// generic-selection = "(" assign "," generic-assoc ("," generic-assoc)* ")"
+//
+// generic-assoc = type-name ":" assign
+//               | "default" ":" assign
+static Node *generic_selection(Token **rest, Token *tok) {
+  Token *start = tok;
+  tok = skip(tok, "(");
+
+  Node *ctrl = assign(&tok, tok);
+  add_type(ctrl);
+
+  Type *t1 = ctrl->ty;
+  if (t1->kind == TY_FUNC)
+    t1 = pointer_to(t1);
+  else if (t1->kind == TY_ARRAY)
+    t1 = pointer_to(t1->base);
+
+  Node *ret = NULL;
+
+  while (!consume(rest, tok, ")")) {
+    tok = skip(tok, ",");
+
+    if (equal(tok, "default")) {
+      tok = skip(tok->next, ":");
+      Node *node = assign(&tok, tok);
+      if (!ret)
+        ret = node;
+      continue;
+    }
+
+    Type *t2 = typename(&tok, tok);
+    tok = skip(tok, ":");
+    Node *node = assign(&tok, tok);
+    if (is_compatible(t1, t2))
+      ret = node;
+  }
+
+  if (!ret)
+    error_tok(start, "controlling expression type not compatible with"
+              " any generic association type");
+  return ret;
+}
+
 // primary = "(" "{" stmt+ "}" ")"
 //         | "(" expr ")"
 //         | "sizeof" "(" type-name ")"
 //         | "sizeof" unary
 //         | "_Alignof" "(" type-name ")"
 //         | "_Alignof" unary
+//         | "_Generic" generic-selection
 //         | "__builtin_types_compatible_p" "(" type-name, type-name, ")"
 //         | "__builtin_reg_class" "(" type-name ")"
 //         | ident
@@ -2657,6 +2701,9 @@ static Node *primary(Token **rest, Token *tok) {
     return new_ulong(node->ty->align, tok);
   }
 
+  if (equal(tok, "_Generic"))
+    return generic_selection(rest, tok->next);
+
   if (equal(tok, "__builtin_types_compatible_p")) {
     tok = skip(tok->next, "(");
     Type *t1 = typename(&tok, tok);
diff --git a/test/generic.c b/test/generic.c
new file mode 100644
index 0000000..ac1fb9c
--- /dev/null
+++ b/test/generic.c
@@ -0,0 +1,12 @@
+#include "test.h"
+
+int main() {
+  ASSERT(1, _Generic(100.0, double: 1, int *: 2, int: 3, float: 4));
+  ASSERT(2, _Generic((int *)0, double: 1, int *: 2, int: 3, float: 4));
+  ASSERT(2, _Generic((int[3]){}, double: 1, int *: 2, int: 3, float: 4));
+  ASSERT(3, _Generic(100, double: 1, int *: 2, int: 3, float: 4));
+  ASSERT(4, _Generic(100f, double: 1, int *: 2, int: 3, float: 4));
+
+  printf("OK\n");
+  return 0;
+}