py: Add option to cache map lookup results in bytecode.

This is a simple optimisation inspired by JITing technology: we cache in
the bytecode (using 1 byte) the offset of the last successful lookup in
a map. This allows us next time round to check in that location in the
hash table (mp_map_t) for the desired entry, and if it's there use that
entry straight away.  Otherwise fallback to a normal map lookup.

Works for LOAD_NAME, LOAD_GLOBAL, LOAD_ATTR and STORE_ATTR opcodes.

On a few tests it gives >90% cache hit and greatly improves speed of
code.

Disabled by default.  Enabled for unix and stmhal ports.

1 files changed, 12 insertions, 0 deletions

diff --git a/py/emitbc.c b/py/emitbc.c
index a93c03e7e..4560d1ec6 100644
--- a/py/emitbc.c
+++ b/py/emitbc.c
@@ -510,16 +510,25 @@ STATIC void emit_bc_load_deref(emit_t *emit, qstr qst, mp_uint_t local_num) {
 STATIC void emit_bc_load_name(emit_t *emit, qstr qst) {
     emit_bc_pre(emit, 1);
     emit_write_bytecode_byte_qstr(emit, MP_BC_LOAD_NAME, qst);
+    if (MICROPY_OPT_CACHE_MAP_LOOKUP_IN_BYTECODE) {
+        emit_write_bytecode_byte(emit, 0);
+    }
 }
 
 STATIC void emit_bc_load_global(emit_t *emit, qstr qst) {
     emit_bc_pre(emit, 1);
     emit_write_bytecode_byte_qstr(emit, MP_BC_LOAD_GLOBAL, qst);
+    if (MICROPY_OPT_CACHE_MAP_LOOKUP_IN_BYTECODE) {
+        emit_write_bytecode_byte(emit, 0);
+    }
 }
 
 STATIC void emit_bc_load_attr(emit_t *emit, qstr qst) {
     emit_bc_pre(emit, 0);
     emit_write_bytecode_byte_qstr(emit, MP_BC_LOAD_ATTR, qst);
+    if (MICROPY_OPT_CACHE_MAP_LOOKUP_IN_BYTECODE) {
+        emit_write_bytecode_byte(emit, 0);
+    }
 }
 
 STATIC void emit_bc_load_method(emit_t *emit, qstr qst) {
@@ -565,6 +574,9 @@ STATIC void emit_bc_store_global(emit_t *emit, qstr qst) {
 STATIC void emit_bc_store_attr(emit_t *emit, qstr qst) {
     emit_bc_pre(emit, -2);
     emit_write_bytecode_byte_qstr(emit, MP_BC_STORE_ATTR, qst);
+    if (MICROPY_OPT_CACHE_MAP_LOOKUP_IN_BYTECODE) {
+        emit_write_bytecode_byte(emit, 0);
+    }
 }
 
 STATIC void emit_bc_store_subscr(emit_t *emit) {