py: Make UNARY_OP_NOT a first-class op, to agree with Py not semantics.

Fixes #1684 and makes "not" match Python semantics.  The code is also
simplified (the separate MP_BC_NOT opcode is removed) and the patch saves
68 bytes for bare-arm/ and 52 bytes for minimal/.

Previously "not x" was implemented as !mp_unary_op(x, MP_UNARY_OP_BOOL),
so any given object only needs to implement MP_UNARY_OP_BOOL (and the VM
had a special opcode to do the ! bit).

With this patch "not x" is implemented as mp_unary_op(x, MP_UNARY_OP_NOT),
but this operation is caught at the start of mp_unary_op and dispatched as
!mp_obj_is_true(x).  mp_obj_is_true has special logic to test for
truthness, and is the correct way to handle the not operation.

1 files changed, 3 insertions, 10 deletions

diff --git a/py/emitbc.c b/py/emitbc.c
index c08501b3f8..7957a21314 100644
--- a/py/emitbc.c
+++ b/py/emitbc.c
@@ -801,15 +801,8 @@ void mp_emit_bc_pop_except(emit_t *emit) {
 }
 
 void mp_emit_bc_unary_op(emit_t *emit, mp_unary_op_t op) {
-    if (op == MP_UNARY_OP_NOT) {
-        emit_bc_pre(emit, 0);
-        emit_write_bytecode_byte(emit, MP_BC_UNARY_OP_MULTI + MP_UNARY_OP_BOOL);
-        emit_bc_pre(emit, 0);
-        emit_write_bytecode_byte(emit, MP_BC_NOT);
-    } else {
-        emit_bc_pre(emit, 0);
-        emit_write_bytecode_byte(emit, MP_BC_UNARY_OP_MULTI + op);
-    }
+    emit_bc_pre(emit, 0);
+    emit_write_bytecode_byte(emit, MP_BC_UNARY_OP_MULTI + op);
 }
 
 void mp_emit_bc_binary_op(emit_t *emit, mp_binary_op_t op) {
@@ -825,7 +818,7 @@ void mp_emit_bc_binary_op(emit_t *emit, mp_binary_op_t op) {
     emit_write_bytecode_byte(emit, MP_BC_BINARY_OP_MULTI + op);
     if (invert) {
         emit_bc_pre(emit, 0);
-        emit_write_bytecode_byte(emit, MP_BC_NOT);
+        emit_write_bytecode_byte(emit, MP_BC_UNARY_OP_MULTI + MP_UNARY_OP_NOT);
     }
 }