gh-117045: Add code object to function version cache (#117028)

Changes to the function version cache:

- In addition to the function object, also store the code object,
  and allow the latter to be retrieved even if the function has been evicted.
- Stop assigning new function versions after a critical attribute (e.g. `__code__`)
  has been modified; the version is permanently reset to zero in this case.
- Changes to `__annotations__` are no longer considered critical. (This fixes gh-109998.)

Changes to the Tier 2 optimization machinery:

- If we cannot map a function version to a function, but it is still mapped to a code object,
  we continue projecting the trace.
  The operand of the `_PUSH_FRAME` and `_POP_FRAME` opcodes can be either NULL,
  a function object, or a code object with the lowest bit set.

This allows us to trace through code that calls an ephemeral function,
i.e., a function that may not be alive when we are constructing the executor,
e.g. a generator expression or certain nested functions.
We will lose globals removal inside such functions,
but we can still do other peephole operations
(and even possibly [call inlining](https://github.com/python/cpython/pull/116290),
if we decide to do it), which only need the code object.
As before, if we cannot retrieve the code object from the cache, we stop projecting.

1 files changed, 19 insertions, 8 deletions

diff --git a/Python/optimizer_bytecodes.c b/Python/optimizer_bytecodes.c
index a1ef644..e761b1b 100644
--- a/Python/optimizer_bytecodes.c
+++ b/Python/optimizer_bytecodes.c
@@ -543,14 +543,25 @@ dummy_func(void) {
 
         (void)callable;
 
-        PyFunctionObject *func = (PyFunctionObject *)(this_instr + 2)->operand;
-        DPRINTF(3, "func: %p ", func);
-        if (func == NULL) {
-            DPRINTF(3, "\n");
-            DPRINTF(1, "Missing function\n");
-            goto done;
-        }
-        PyCodeObject *co = (PyCodeObject *)func->func_code;
+        PyCodeObject *co = NULL;
+        assert((this_instr + 2)->opcode == _PUSH_FRAME);
+        uintptr_t push_operand = (this_instr + 2)->operand;
+        if (push_operand & 1) {
+            co = (PyCodeObject *)(push_operand & ~1);
+            DPRINTF(3, "code=%p ", co);
+            assert(PyCode_Check(co));
+        }
+        else {
+            PyFunctionObject *func = (PyFunctionObject *)push_operand;
+            DPRINTF(3, "func=%p ", func);
+            if (func == NULL) {
+                DPRINTF(3, "\n");
+                DPRINTF(1, "Missing function\n");
+                goto done;
+            }
+            co = (PyCodeObject *)func->func_code;
+            DPRINTF(3, "code=%p ", co);
+        }
 
         assert(self_or_null != NULL);
         assert(args != NULL);