py: Split RAISE_VARARGS opcode into 3 separate ones.

From the beginning of this project the RAISE_VARARGS opcode was named and
implemented following CPython, where it has an argument (to the opcode)
counting how many args the raise takes:

    raise # 0 args (re-raise previous exception)
    raise exc # 1 arg
    raise exc from exc2 # 2 args (chained raise)

In the bytecode this operation therefore takes 2 bytes, one for
RAISE_VARARGS and one for the number of args.

This patch splits this opcode into 3, where each is now a single byte.
This reduces bytecode size by 1 byte for each use of raise.  Every byte
counts!  It also has the benefit of reducing code size (on all ports except
nanbox).

py/bc0.h

@@ -46,7 +46,7 @@
 #define MP_BC_BASE_VINT_O                   (0x30) // UUMMCCCC--------
 #define MP_BC_BASE_JUMP_E                   (0x40) // J-JJJJJEEEEF----
 #define MP_BC_BASE_BYTE_O                   (0x50) // LLLLSSDTTTTTEEFF
-#define MP_BC_BASE_BYTE_E                   (0x60) // E-BRYYI---------
+#define MP_BC_BASE_BYTE_E                   (0x60) // --BREEEYYI------
 #define MP_BC_LOAD_CONST_SMALL_INT_MULTI    (0x70) // LLLLLLLLLLLLLLLL
                                          // (0x80) // LLLLLLLLLLLLLLLL
                                          // (0x90) // LLLLLLLLLLLLLLLL
@@ -128,9 +128,11 @@
 #define MP_BC_UNPACK_EX                     (MP_BC_BASE_VINT_O + 0x01) // uint
 
 #define MP_BC_RETURN_VALUE                  (MP_BC_BASE_BYTE_E + 0x03)
-#define MP_BC_RAISE_VARARGS                 (MP_BC_BASE_BYTE_E + 0x00) // extra byte
-#define MP_BC_YIELD_VALUE                   (MP_BC_BASE_BYTE_E + 0x04)
-#define MP_BC_YIELD_FROM                    (MP_BC_BASE_BYTE_E + 0x05)
+#define MP_BC_RAISE_LAST                    (MP_BC_BASE_BYTE_E + 0x04)
+#define MP_BC_RAISE_OBJ                     (MP_BC_BASE_BYTE_E + 0x05)
+#define MP_BC_RAISE_FROM                    (MP_BC_BASE_BYTE_E + 0x06)
+#define MP_BC_YIELD_VALUE                   (MP_BC_BASE_BYTE_E + 0x07)
+#define MP_BC_YIELD_FROM                    (MP_BC_BASE_BYTE_E + 0x08)
 
 #define MP_BC_MAKE_FUNCTION                 (MP_BC_BASE_VINT_O + 0x02) // uint
 #define MP_BC_MAKE_FUNCTION_DEFARGS         (MP_BC_BASE_VINT_O + 0x03) // uint
@@ -143,6 +145,6 @@
 
 #define MP_BC_IMPORT_NAME                   (MP_BC_BASE_QSTR_O + 0x0b) // qstr
 #define MP_BC_IMPORT_FROM                   (MP_BC_BASE_QSTR_O + 0x0c) // qstr
-#define MP_BC_IMPORT_STAR                   (MP_BC_BASE_BYTE_E + 0x06)
+#define MP_BC_IMPORT_STAR                   (MP_BC_BASE_BYTE_E + 0x09)
 
 #endif // MICROPY_INCLUDED_PY_BC0_H

py/emitbc.c

@@ -193,13 +193,6 @@ STATIC void emit_write_bytecode_byte(emit_t *emit, int stack_adj, byte b1) {
     c[0] = b1;
 }
 
-STATIC void emit_write_bytecode_byte_byte(emit_t* emit, int stack_adj, byte b1, byte b2) {
-    mp_emit_bc_adjust_stack_size(emit, stack_adj);
-    byte *c = emit_get_cur_to_write_bytecode(emit, 2);
-    c[0] = b1;
-    c[1] = b2;
-}
-
 // Similar to emit_write_bytecode_uint(), just some extra handling to encode sign
 STATIC void emit_write_bytecode_byte_int(emit_t *emit, int stack_adj, byte b1, mp_int_t num) {
     emit_write_bytecode_byte(emit, stack_adj, b1);
@@ -848,8 +841,10 @@ void mp_emit_bc_return_value(emit_t *emit) {
 }
 
 void mp_emit_bc_raise_varargs(emit_t *emit, mp_uint_t n_args) {
+    MP_STATIC_ASSERT(MP_BC_RAISE_LAST + 1 == MP_BC_RAISE_OBJ);
+    MP_STATIC_ASSERT(MP_BC_RAISE_LAST + 2 == MP_BC_RAISE_FROM);
     assert(n_args <= 2);
-    emit_write_bytecode_byte_byte(emit, -n_args, MP_BC_RAISE_VARARGS, n_args);
+    emit_write_bytecode_byte(emit, -n_args, MP_BC_RAISE_LAST + n_args);
 }
 
 void mp_emit_bc_yield(emit_t *emit, int kind) {

py/showbc.c

@@ -500,9 +500,16 @@ const byte *mp_bytecode_print_str(const byte *ip) {
             printf("RETURN_VALUE");
             break;
 
-        case MP_BC_RAISE_VARARGS:
-            unum = *ip++;
-            printf("RAISE_VARARGS " UINT_FMT, unum);
+        case MP_BC_RAISE_LAST:
+            printf("RAISE_LAST");
+            break;
+
+        case MP_BC_RAISE_OBJ:
+            printf("RAISE_OBJ");
+            break;
+
+        case MP_BC_RAISE_FROM:
+            printf("RAISE_FROM");
             break;
 
         case MP_BC_YIELD_VALUE:

py/vm.c

@@ -1162,32 +1162,33 @@ unwind_return:
                     FRAME_LEAVE();
                     return MP_VM_RETURN_NORMAL;
 
-                ENTRY(MP_BC_RAISE_VARARGS): {
+                ENTRY(MP_BC_RAISE_LAST): {
                     MARK_EXC_IP_SELECTIVE();
-                    mp_uint_t unum = *ip;
-                    mp_obj_t obj;
-                    if (unum == 2) {
-                        mp_warning(NULL, "exception chaining not supported");
-                        // ignore (pop) "from" argument
-                        sp--;
-                    }
-                    if (unum == 0) {
-                        // search for the inner-most previous exception, to reraise it
-                        obj = MP_OBJ_NULL;
-                        for (mp_exc_stack_t *e = exc_sp; e >= exc_stack; e--) {
-                            if (e->prev_exc != NULL) {
-                                obj = MP_OBJ_FROM_PTR(e->prev_exc);
-                                break;
-                            }
-                        }
-                        if (obj == MP_OBJ_NULL) {
-                            obj = mp_obj_new_exception_msg(&mp_type_RuntimeError, "no active exception to reraise");
-                            RAISE(obj);
+                    // search for the inner-most previous exception, to reraise it
+                    mp_obj_t obj = MP_OBJ_NULL;
+                    for (mp_exc_stack_t *e = exc_sp; e >= exc_stack; --e) {
+                        if (e->prev_exc != NULL) {
+                            obj = MP_OBJ_FROM_PTR(e->prev_exc);
+                            break;
                         }
-                    } else {
-                        obj = TOP();
                     }
-                    obj = mp_make_raise_obj(obj);
+                    if (obj == MP_OBJ_NULL) {
+                        obj = mp_obj_new_exception_msg(&mp_type_RuntimeError, "no active exception to reraise");
+                    }
+                    RAISE(obj);
+                }
+
+                ENTRY(MP_BC_RAISE_OBJ): {
+                    MARK_EXC_IP_SELECTIVE();
+                    mp_obj_t obj = mp_make_raise_obj(TOP());
+                    RAISE(obj);
+                }
+
+                ENTRY(MP_BC_RAISE_FROM): {
+                    MARK_EXC_IP_SELECTIVE();
+                    mp_warning(NULL, "exception chaining not supported");
+                    sp--; // ignore (pop) "from" argument
+                    mp_obj_t obj = mp_make_raise_obj(TOP());
                     RAISE(obj);
                 }
 
@@ -1437,7 +1438,7 @@ unwind_loop:
             // - exceptions re-raised explicitly by "raise"
             if (nlr.ret_val != &mp_const_GeneratorExit_obj
                 && *code_state->ip != MP_BC_END_FINALLY
-                && !(*code_state->ip == MP_BC_RAISE_VARARGS && code_state->ip[1] == 0)) {
+                && *code_state->ip != MP_BC_RAISE_LAST) {
                 const byte *ip = code_state->fun_bc->bytecode;
                 ip = mp_decode_uint_skip(ip); // skip n_state
                 ip = mp_decode_uint_skip(ip); // skip n_exc_stack

py/vmentrytable.h

@@ -99,7 +99,9 @@ static const void *const entry_table[256] = {
     [MP_BC_CALL_METHOD] = &&entry_MP_BC_CALL_METHOD,
     [MP_BC_CALL_METHOD_VAR_KW] = &&entry_MP_BC_CALL_METHOD_VAR_KW,
     [MP_BC_RETURN_VALUE] = &&entry_MP_BC_RETURN_VALUE,
-    [MP_BC_RAISE_VARARGS] = &&entry_MP_BC_RAISE_VARARGS,
+    [MP_BC_RAISE_LAST] = &&entry_MP_BC_RAISE_LAST,
+    [MP_BC_RAISE_OBJ] = &&entry_MP_BC_RAISE_OBJ,
+    [MP_BC_RAISE_FROM] = &&entry_MP_BC_RAISE_FROM,
     [MP_BC_YIELD_VALUE] = &&entry_MP_BC_YIELD_VALUE,
     [MP_BC_YIELD_FROM] = &&entry_MP_BC_YIELD_FROM,
     [MP_BC_IMPORT_NAME] = &&entry_MP_BC_IMPORT_NAME,

tests/cmdline/cmd_showbc.py.exp

@@ -305,9 +305,9 @@ Raw bytecode (code_info_size=\\d\+, bytecode_size=\\d\+):
 \\d\+ BUILD_TUPLE 1
 \\d\+ IMPORT_NAME 'a'
 \\d\+ IMPORT_STAR
-\\d\+ RAISE_VARARGS 0
+\\d\+ RAISE_LAST
 \\d\+ LOAD_CONST_SMALL_INT 1
-\\d\+ RAISE_VARARGS 1
+\\d\+ RAISE_OBJ
 \\d\+ LOAD_CONST_NONE
 \\d\+ RETURN_VALUE
 \\d\+ LOAD_CONST_SMALL_INT 1