From d94bc675e8f3bcf37acf2d88d7c0ce0d9de68672 Mon Sep 17 00:00:00 2001
From: Damien George <damien.p.george@gmail.com>
Date: Thu, 22 Jun 2017 15:05:58 +1000
Subject: [PATCH] py/compile: Optimise emitter label indices to save a word of
 heap.

Previous to this patch, a label with value "0" was used to indicate an
invalid label, but that meant a wasted word (at slot 0) in the array of
label offsets.  This patch adjusts the label indices so the first one
starts at 0, and the maximum value indicates an invalid label.
---
 py/compile.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/py/compile.c b/py/compile.c
index 1511786ae9..e0a7711121 100644
--- a/py/compile.c
+++ b/py/compile.c
@@ -40,6 +40,8 @@
 
 // TODO need to mangle __attr names
 
+#define INVALID_LABEL (0xffff)
+
 typedef enum {
 // define rules with a compile function
 #define DEF_RULE(rule, comp, kind, ...) PN_##rule,
@@ -954,7 +956,7 @@ STATIC void compile_del_stmt(compiler_t *comp, mp_parse_node_struct_t *pns) {
 }
 
 STATIC void compile_break_stmt(compiler_t *comp, mp_parse_node_struct_t *pns) {
-    if (comp->break_label == 0) {
+    if (comp->break_label == INVALID_LABEL) {
         compile_syntax_error(comp, (mp_parse_node_t)pns, "'break' outside loop");
     }
     assert(comp->cur_except_level >= comp->break_continue_except_level);
@@ -962,7 +964,7 @@ STATIC void compile_break_stmt(compiler_t *comp, mp_parse_node_struct_t *pns) {
 }
 
 STATIC void compile_continue_stmt(compiler_t *comp, mp_parse_node_struct_t *pns) {
-    if (comp->continue_label == 0) {
+    if (comp->continue_label == INVALID_LABEL) {
         compile_syntax_error(comp, (mp_parse_node_t)pns, "'continue' outside loop");
     }
     assert(comp->cur_except_level >= comp->break_continue_except_level);
@@ -2960,7 +2962,7 @@ STATIC void check_for_doc_string(compiler_t *comp, mp_parse_node_t pn) {
 STATIC void compile_scope(compiler_t *comp, scope_t *scope, pass_kind_t pass) {
     comp->pass = pass;
     comp->scope_cur = scope;
-    comp->next_label = 1;
+    comp->next_label = 0;
     EMIT_ARG(start_pass, pass, scope);
 
     if (comp->pass == MP_PASS_SCOPE) {
@@ -3135,7 +3137,7 @@ STATIC void compile_scope(compiler_t *comp, scope_t *scope, pass_kind_t pass) {
 STATIC void compile_scope_inline_asm(compiler_t *comp, scope_t *scope, pass_kind_t pass) {
     comp->pass = pass;
     comp->scope_cur = scope;
-    comp->next_label = 1;
+    comp->next_label = 0;
 
     if (scope->kind != SCOPE_FUNCTION) {
         compile_syntax_error(comp, MP_PARSE_NODE_NULL, "inline assembler must be a function");
@@ -3381,6 +3383,8 @@ mp_raw_code_t *mp_compile_to_raw_code(mp_parse_tree_t *parse_tree, qstr source_f
 
     comp->source_file = source_file;
     comp->is_repl = is_repl;
+    comp->break_label = INVALID_LABEL;
+    comp->continue_label = INVALID_LABEL;
 
     // create the module scope
     scope_t *module_scope = scope_new_and_link(comp, SCOPE_MODULE, parse_tree->root, emit_opt);