From beaea6105cdb4e3c96ba313dc5d211b644ef0e1c Mon Sep 17 00:00:00 2001
From: Guido van Rossum <guido@python.org>
Date: Mon, 12 Dec 2022 17:02:55 -0800
Subject: [PATCH] Add DECREF_INPUTS(), expanding to DECREF() each stack input

The presence of this macro indicates that a particular instruction
may be considered for conversion to a register-based format
(see https://github.com/faster-cpython/ideas/issues/485).

An invariant (currently unchecked) is that `DEOPT_IF()` may only
occur *before* `DECREF_INPUTS()`, and `ERROR_IF()` may only occur
*after* it. One reason not to check this is that there are a few
places where we insert *two* `DECREF_INPUTS()` calls, in different
branches of the code. The invariant checking would have to be able
to do some flow control analysis to understand this.

Note that many instructions, especially specialized ones,
can't be converted to use this macro straightforwardly.
This is because the generator currently only generates plain
`Py_DECREF(variable)` statements, and cannot generate
things like `_Py_DECREF_SPECIALIZED()` let alone deal with
`_PyList_AppendTakeRef()`.
---
 Python/bytecodes.c                      | 31 +++++++++++--------------
 Tools/cases_generator/generate_cases.py |  6 ++++-
 2 files changed, 18 insertions(+), 19 deletions(-)

diff --git a/Python/bytecodes.c b/Python/bytecodes.c
index c56f1d3ef9f498..a827b35fc078b5 100644
--- a/Python/bytecodes.c
+++ b/Python/bytecodes.c
@@ -161,7 +161,7 @@ dummy_func(
         super(LOAD_CONST__LOAD_FAST) = LOAD_CONST + LOAD_FAST;
 
         inst(POP_TOP, (value --)) {
-            Py_DECREF(value);
+            DECREF_INPUTS();
         }
 
         inst(PUSH_NULL, (-- res)) {
@@ -172,19 +172,19 @@ dummy_func(
 
         inst(UNARY_POSITIVE, (value -- res)) {
             res = PyNumber_Positive(value);
-            Py_DECREF(value);
+            DECREF_INPUTS();
             ERROR_IF(res == NULL, error);
         }
 
         inst(UNARY_NEGATIVE, (value -- res)) {
             res = PyNumber_Negative(value);
-            Py_DECREF(value);
+            DECREF_INPUTS();
             ERROR_IF(res == NULL, error);
         }
 
         inst(UNARY_NOT, (value -- res)) {
             int err = PyObject_IsTrue(value);
-            Py_DECREF(value);
+            DECREF_INPUTS();
             ERROR_IF(err < 0, error);
             if (err == 0) {
                 res = Py_True;
@@ -197,7 +197,7 @@ dummy_func(
 
         inst(UNARY_INVERT, (value -- res)) {
             res = PyNumber_Invert(value);
-            Py_DECREF(value);
+            DECREF_INPUTS();
             ERROR_IF(res == NULL, error);
         }
 
@@ -351,8 +351,7 @@ dummy_func(
             STAT_INC(BINARY_SUBSCR, deferred);
             DECREMENT_ADAPTIVE_COUNTER(cache->counter);
             res = PyObject_GetItem(container, sub);
-            Py_DECREF(container);
-            Py_DECREF(sub);
+            DECREF_INPUTS();
             ERROR_IF(res == NULL, error);
         }
 
@@ -438,8 +437,7 @@ dummy_func(
                 ERROR_IF(true, error);
             }
             Py_INCREF(res);  // Do this before DECREF'ing dict, sub
-            Py_DECREF(dict);
-            Py_DECREF(sub);
+            DECREF_INPUTS();
         }
 
         inst(BINARY_SUBSCR_GETITEM, (unused/1, type_version/2, func_version/1, container, sub -- unused)) {
@@ -500,9 +498,7 @@ dummy_func(
             DECREMENT_ADAPTIVE_COUNTER(cache->counter);
             /* container[sub] = v */
             int err = PyObject_SetItem(container, sub, v);
-            Py_DECREF(v);
-            Py_DECREF(container);
-            Py_DECREF(sub);
+            DECREF_INPUTS();
             ERROR_IF(err, error);
         }
 
@@ -538,8 +534,7 @@ dummy_func(
         inst(DELETE_SUBSCR, (container, sub --)) {
             /* del container[sub] */
             int err = PyObject_DelItem(container, sub);
-            Py_DECREF(container);
-            Py_DECREF(sub);
+            DECREF_INPUTS();
             ERROR_IF(err, error);
         }
 
@@ -550,11 +545,11 @@ dummy_func(
             if (hook == NULL) {
                 _PyErr_SetString(tstate, PyExc_RuntimeError,
                                  "lost sys.displayhook");
-                Py_DECREF(value);
+                DECREF_INPUTS();
                 ERROR_IF(true, error);
             }
             res = PyObject_CallOneArg(hook, value);
-            Py_DECREF(value);
+            DECREF_INPUTS();
             ERROR_IF(res == NULL, error);
             Py_DECREF(res);
         }
@@ -625,12 +620,12 @@ dummy_func(
                               "'async for' requires an object with "
                               "__aiter__ method, got %.100s",
                               type->tp_name);
-                Py_DECREF(obj);
+                DECREF_INPUTS();
                 ERROR_IF(true, error);
             }
 
             iter = (*getter)(obj);
-            Py_DECREF(obj);
+            DECREF_INPUTS();
             ERROR_IF(iter == NULL, error);
 
             if (Py_TYPE(iter)->tp_as_async == NULL ||
diff --git a/Tools/cases_generator/generate_cases.py b/Tools/cases_generator/generate_cases.py
index 5930c797b8a4d3..3f2bad824c80a6 100644
--- a/Tools/cases_generator/generate_cases.py
+++ b/Tools/cases_generator/generate_cases.py
@@ -209,7 +209,7 @@ def write_body(self, out: Formatter, dedent: int, cache_adjust: int = 0) -> None
             cache_offset += ceffect.size
         assert cache_offset == self.cache_offset + cache_adjust
 
-        # Write the body, substituting a goto for ERROR_IF()
+        # Write the body, substituting a goto for ERROR_IF() and other stuff
         assert dedent <= 0
         extra = " " * -dedent
         for line in self.block_text:
@@ -232,6 +232,10 @@ def write_body(self, out: Formatter, dedent: int, cache_adjust: int = 0) -> None
                     )
                 else:
                     out.write_raw(f"{extra}{space}if ({cond}) goto {label};\n")
+            elif m := re.match(r"(\s*)DECREF_INPUTS\(\);\s*$", line):
+                space = m.group(1)
+                for ieff in self.input_effects:
+                    out.write_raw(f"{extra}{space}Py_DECREF({ieff.name});\n")
             else:
                 out.write_raw(extra + line)