Added COLD_EXPR() and HOT_EXPR() macros that (ab)use label attrs. Not sure of a better way to mark blocks/expressions as `cold` :/ I dunno if `if(UNLIKELY(1))` would work.

Fortune for naka's current commit: Great blessing − 大吉

include/macros.h

@@ -16,6 +16,9 @@
 #define _pure     __attribute__((const))
 #define _readonly __attribute__((pure))
 
+#define _cold __attribute__((cold))
+#define _hot __attribute__((hot))
+
 #ifndef __cplusplus
 #define noreturn __attribute__((noreturn))
 #define deprecated __attribute__((deprecated))
@@ -71,6 +74,21 @@
 #define ifL(x) if(LIKELY((x)))
 #define ifU(x) if(UNLIKELY((x)))
 
+#define COLD_EXPR(expr) ({ \
+		goto _cold_expr; \
+		UNREACHABLE_UNSAFE(); \
+		_cold_expr: \
+		__attribute__((cold)); \
+		expr; \
+	})
+#define HOT_EXPR(expr) ({ \
+		goto _hot_expr; \
+		UNREACHABLE_UNSAFE(); \
+		_hot_expr: \
+		__attribute__((hot)); \
+		expr; \
+	})
+
 /// Equivalent to GNU C `x ?: y` operator. 
 #define TERN_OR(x, y) ({ let _x = (x); _x ? _x : (y); })
 
@@ -100,6 +118,14 @@ _mixin void _drain_val(void* x, ...) { IGNORE(x); } // This compiles to no-op on
 
 #define assert_msg(expr, ...) ( (expr) ? 1 : FATAL(__VA_ARGS__))
 
+#define UNREACHABLE_UNSAFE() __builtin_unreachable()
+
+#ifdef DEBUG
+#define UNREACHABLE() do { COLD_EXPR(FATAL("unreachable code entered")); } while(0)
+#else
+#define UNREACHABLE() UNREACHABLE_UNSAFE()
+#endif
+
 #ifdef DEBUG
 #define debug_assert(x) assert((x))
 #elif defined(_EVAL_DEBUG_ONLY_STMTS)

include/map.h

@@ -68,6 +68,7 @@ _mixin int _map_handle_err(const char* stmt, const char* file, int line, const c
 				return 0;
 		}
 	}
+	UNREACHABLE();
 }
 #define map_handle_err(stmt) _map_handle_err(#stmt, __FILE__, __LINE__, __func__, stmt)