cgen: remove tos3() call: part 1

Author: medvednikov

vlib/v/gen/cgen.v

@@ -1127,6 +1127,12 @@ fn (mut g Gen) expr(node ast.Expr) {
 				// `C.printf("hi")` => `printf("hi");`
 				g.write('"$escaped_val"')
 			} else {
+				// TODO calculate the literal's length in V, it's a bit tricky with all the
+				// escape characters.
+				// Clang and GCC optimize `strlen("lorem ipsum")` to `11`
+				// g.write('tos4("$escaped_val", strlen("$escaped_val"))')
+				// g.write('tos4("$escaped_val", $it.val.len)')
+				// g.write('_SLIT("$escaped_val")')
 				g.write('tos3("$escaped_val")')
 			}
 		}
@@ -2727,7 +2733,7 @@ fn (g Gen) type_default(typ table.Type) string {
 	}
 	*/
 	match sym.name {
-		'string' { return 'tos3("")' }
+		'string' { return '(string){.str=""}' }
 		'rune' { return '0' }
 		else {}
 	}

vlib/v/gen/cheaders.v

@@ -173,6 +173,8 @@ extern wchar_t **_wenviron;
 
 
 //============================== HELPER C MACROS =============================*/
+//#define tos4(s, slen) ((string){.str=(s), .len=(slen)})
+#define _SLIT(s) ((string){.str=(s), .len=(strlen(s))})
 #define _PUSH_MANY(arr, val, tmp, tmp_typ) {tmp_typ tmp = (val); array_push_many(arr, tmp.data, tmp.len);}
 #define _IN(typ, val, arr) array_##typ##_contains(arr, val)
 #define _IN_MAP(val, m) map_exists(m, val)