py/parse: Allow const types other than int to optimise as true/false.

Allows optimisation of cases like:

    import micropython
    _DEBUG = micropython.const(False)
    if _DEBUG:
        print('Debugging info')

Previously the 'if' statement was only optimised out if the type of the
const() argument was integer.

The change is implemented in a way that makes the compiler slightly smaller
(-16 bytes on PYBV11) but compilation will also be very slightly slower.

As a bonus, if const support is enabled then the compiler can now optimise
const truthy/falsey expressions of other types, like:

    while "something":
        pass

... unclear if that is useful, but perhaps it could be.

Signed-off-by: Angus Gratton <angus@redyak.com.au>

1 files changed, 18 insertions, 10 deletions

diff --git a/py/parse.c b/py/parse.c
index d58098af2e..62de3282b3 100644
--- a/py/parse.c
+++ b/py/parse.c
@@ -334,16 +334,6 @@ STATIC uint8_t peek_rule(parser_t *parser, size_t n) {
 }
 #endif
 
-bool mp_parse_node_is_const_false(mp_parse_node_t pn) {
-    return MP_PARSE_NODE_IS_TOKEN_KIND(pn, MP_TOKEN_KW_FALSE)
-           || (MP_PARSE_NODE_IS_SMALL_INT(pn) && MP_PARSE_NODE_LEAF_SMALL_INT(pn) == 0);
-}
-
-bool mp_parse_node_is_const_true(mp_parse_node_t pn) {
-    return MP_PARSE_NODE_IS_TOKEN_KIND(pn, MP_TOKEN_KW_TRUE)
-           || (MP_PARSE_NODE_IS_SMALL_INT(pn) && MP_PARSE_NODE_LEAF_SMALL_INT(pn) != 0);
-}
-
 bool mp_parse_node_get_int_maybe(mp_parse_node_t pn, mp_obj_t *o) {
     if (MP_PARSE_NODE_IS_SMALL_INT(pn)) {
         *o = MP_OBJ_NEW_SMALL_INT(MP_PARSE_NODE_LEAF_SMALL_INT(pn));
@@ -427,6 +417,24 @@ STATIC mp_obj_t mp_parse_node_convert_to_obj(mp_parse_node_t pn) {
 }
 #endif
 
+STATIC bool parse_node_is_const_bool(mp_parse_node_t pn, bool value) {
+    // Returns true if 'pn' is a constant whose boolean value is equivalent to 'value'
+    #if MICROPY_COMP_CONST_TUPLE || MICROPY_COMP_CONST
+    return mp_parse_node_is_const(pn) && mp_obj_is_true(mp_parse_node_convert_to_obj(pn)) == value;
+    #else
+    return MP_PARSE_NODE_IS_TOKEN_KIND(pn, value ? MP_TOKEN_KW_TRUE : MP_TOKEN_KW_FALSE)
+           || (MP_PARSE_NODE_IS_SMALL_INT(pn) && !!MP_PARSE_NODE_LEAF_SMALL_INT(pn) == value);
+    #endif
+}
+
+bool mp_parse_node_is_const_false(mp_parse_node_t pn) {
+    return parse_node_is_const_bool(pn, false);
+}
+
+bool mp_parse_node_is_const_true(mp_parse_node_t pn) {
+    return parse_node_is_const_bool(pn, true);
+}
+
 size_t mp_parse_node_extract_list(mp_parse_node_t *pn, size_t pn_kind, mp_parse_node_t **nodes) {
     if (MP_PARSE_NODE_IS_NULL(*pn)) {
         *nodes = NULL;