Simple input-output stack effects

No arrays; no conitionals; no types; no cache effects.

Author: gvanrossum

Python/bytecodes.c

@@ -69,6 +69,7 @@ do { \
 #define DISPATCH() ((void)0)
 
 #define inst(name) case name:
+#define instr(name, arg) case name:
 #define family(name) static int family_##name
 
 #define NAME_ERROR_MSG \
@@ -103,58 +104,46 @@ dummy_func(
            and that all operation that succeed call DISPATCH() ! */
 
 // BEGIN BYTECODES //
-        // stack effect: ( -- )
-        inst(NOP) {
+        instr(NOP, (--)) {
         }
 
-        // stack effect: ( -- )
-        inst(RESUME) {
+        instr(RESUME, (--)) {
             assert(tstate->cframe == &cframe);
             assert(frame == cframe.current_frame);
             if (_Py_atomic_load_relaxed_int32(eval_breaker) && oparg < 2) {
                 goto handle_eval_breaker;
             }
         }
 
-        // stack effect: ( -- __0)
-        inst(LOAD_CLOSURE) {
+        instr(LOAD_CLOSURE, (-- value)) {
             /* We keep LOAD_CLOSURE so that the bytecode stays more readable. */
-            PyObject *value = GETLOCAL(oparg);
+            value = GETLOCAL(oparg);
             if (value == NULL) {
                 goto unbound_local_error;
             }
             Py_INCREF(value);
-            PUSH(value);
         }
 
-        // stack effect: ( -- __0)
-        inst(LOAD_FAST_CHECK) {
-            PyObject *value = GETLOCAL(oparg);
+        instr(LOAD_FAST_CHECK, (-- value)) {
+            value = GETLOCAL(oparg);
             if (value == NULL) {
                 goto unbound_local_error;
             }
             Py_INCREF(value);
-            PUSH(value);
         }
 
-        // stack effect: ( -- __0)
-        inst(LOAD_FAST) {
-            PyObject *value = GETLOCAL(oparg);
+        instr(LOAD_FAST, (-- value)) {
+            value = GETLOCAL(oparg);
             assert(value != NULL);
             Py_INCREF(value);
-            PUSH(value);
         }
 
-        // stack effect: ( -- __0)
-        inst(LOAD_CONST) {
-            PyObject *value = GETITEM(consts, oparg);
+        instr(LOAD_CONST, (-- value)) {
+            value = GETITEM(consts, oparg);
             Py_INCREF(value);
-            PUSH(value);
         }
 
-        // stack effect: (__0 -- )
-        inst(STORE_FAST) {
-            PyObject *value = POP();
+        inst(STORE_FAST, (value --)) {
             SETLOCAL(oparg, value);
         }
 
@@ -220,9 +209,7 @@ dummy_func(
             PUSH(value);
         }
 
-        // stack effect: (__0 -- )
-        inst(POP_TOP) {
-            PyObject *value = POP();
+        instr(POP_TOP, (value --)) {
             Py_DECREF(value);
         }
 
@@ -232,59 +219,43 @@ dummy_func(
             BASIC_PUSH(NULL);
         }
 
-        // stack effect: (__0, __1 -- )
-        inst(END_FOR) {
-            PyObject *value = POP();
-            Py_DECREF(value);
-            value = POP();
-            Py_DECREF(value);
+        instr(END_FOR, (value1, value2 --)) {
+            Py_DECREF(value1);
+            Py_DECREF(value2);
         }
 
-        // stack effect: ( -- )
-        inst(UNARY_POSITIVE) {
-            PyObject *value = TOP();
-            PyObject *res = PyNumber_Positive(value);
+        instr(UNARY_POSITIVE, (value -- res)) {
+            res = PyNumber_Positive(value);
             Py_DECREF(value);
-            SET_TOP(res);
             if (res == NULL)
                 goto error;
         }
 
-        // stack effect: ( -- )
-        inst(UNARY_NEGATIVE) {
-            PyObject *value = TOP();
-            PyObject *res = PyNumber_Negative(value);
+        instr(UNARY_NEGATIVE, (value -- res)) {
+            res = PyNumber_Negative(value);
             Py_DECREF(value);
-            SET_TOP(res);
             if (res == NULL)
                 goto error;
         }
 
-        // stack effect: ( -- )
-        inst(UNARY_NOT) {
-            PyObject *value = TOP();
+        instr(UNARY_NOT, (value -- res)) {
             int err = PyObject_IsTrue(value);
             Py_DECREF(value);
             if (err == 0) {
-                Py_INCREF(Py_True);
-                SET_TOP(Py_True);
-                DISPATCH();
+                res = Py_True;
             }
             else if (err > 0) {
-                Py_INCREF(Py_False);
-                SET_TOP(Py_False);
-                DISPATCH();
+                res = Py_False;
             }
-            STACK_SHRINK(1);
-            goto error;
+            else {
+                goto error;
+            }
+            Py_INCREF(res);
         }
 
-        // stack effect: ( -- )
-        inst(UNARY_INVERT) {
-            PyObject *value = TOP();
-            PyObject *res = PyNumber_Invert(value);
+        inst(UNARY_INVERT, (value -- res)) {
+            res = PyNumber_Invert(value);
             Py_DECREF(value);
-            SET_TOP(res);
             if (res == NULL)
                 goto error;
         }

Python/generated_cases.c.h

@@ -73,6 +73,10 @@ def write_cases(f: io.TextIOBase, instrs: list[InstDef]):
     for instr in instrs:
         assert isinstance(instr, InstDef)
         f.write(f"\n{indent}TARGET({instr.name}) {{\n")
+        for input in instr.inputs or ():
+            f.write(f"{indent}    PyObject *{input} = POP();\n")
+        for output in instr.outputs or ():
+            f.write(f"{indent}    PyObject *{output};\n")
         if instr.name in predictions:
             f.write(f"{indent}    PREDICTED({instr.name});\n")
         # input = ", ".join(instr.inputs)
@@ -96,6 +100,8 @@ def write_cases(f: io.TextIOBase, instrs: list[InstDef]):
         # Write the body
         for line in blocklines:
             f.write(line)
+        for output in instr.outputs or ():
+            f.write(f"{indent}    PUSH({output});\n")
         assert instr.block
         if not always_exits(instr.block):
             f.write(f"{indent}    DISPATCH();\n")

Tools/cases_generator/generate_cases.py

@@ -83,7 +83,7 @@ def inst_header(self):
         # inst(NAME) | inst(NAME, (inputs -- outputs))
         # TODO: Error out when there is something unexpected.
         # TODO: Make INST a keyword in the lexer.
-        if (tkn := self.expect(lx.IDENTIFIER)) and tkn.text == "inst":
+        if (tkn := self.expect(lx.IDENTIFIER)) and tkn.text in ("inst", "instr"):
             if (self.expect(lx.LPAREN)
                     and (tkn := self.expect(lx.IDENTIFIER))):
                 name = tkn.text