gh-123923: Defer refcounting for `f_funcobj` in `_PyInterpreterFrame` (#124026)

Use a `_PyStackRef` and defer the reference to `f_funcobj` when
possible. This avoids some reference count contention in the common case
of executing the same code object from multiple threads concurrently in
the free-threaded build.

2 files changed, 17 insertions, 4 deletions

diff --git a/Tools/cases_generator/analyzer.py b/Tools/cases_generator/analyzer.py
index 3cc36b6..0680c21 100644
--- a/Tools/cases_generator/analyzer.py
+++ b/Tools/cases_generator/analyzer.py
@@ -365,12 +365,24 @@ def analyze_deferred_refs(node: parser.InstDef) -> dict[lexer.Token, str | None]
             offset += 1
         return []
 
+    def in_frame_push(idx: int) -> bool:
+        for tkn in reversed(node.block.tokens[: idx - 1]):
+            if tkn.kind == "SEMI" or tkn.kind == "LBRACE" or tkn.kind == "RBRACE":
+                return False
+            if tkn.kind == "IDENTIFIER" and tkn.text == "_PyFrame_PushUnchecked":
+                return True
+        return False
+
     refs: dict[lexer.Token, str | None] = {}
     for idx, tkn in enumerate(node.block.tokens):
         if tkn.kind != "IDENTIFIER" or tkn.text != "PyStackRef_FromPyObjectNew":
             continue
 
         if idx == 0 or node.block.tokens[idx - 1].kind != "EQUALS":
+            if in_frame_push(idx):
+                # PyStackRef_FromPyObjectNew() is called in _PyFrame_PushUnchecked()
+                refs[tkn] = None
+                continue
             raise analysis_error("Expected '=' before PyStackRef_FromPyObjectNew", tkn)
 
         lhs = find_assignment_target(idx)
diff --git a/Tools/cases_generator/generators_common.py b/Tools/cases_generator/generators_common.py
index 2f8fcce..4cfd4ad 100644
--- a/Tools/cases_generator/generators_common.py
+++ b/Tools/cases_generator/generators_common.py
@@ -200,15 +200,16 @@ class Emitter:
         stack: Stack,
         inst: Instruction | None,
     ) -> None:
-        self.out.emit(tkn)
-        emit_to(self.out, tkn_iter, "SEMI")
-        self.out.emit(";\n")
-
         target = uop.deferred_refs[tkn]
         if target is None:
             # An assignment we don't handle, such as to a pointer or array.
+            self.out.emit(tkn)
             return
 
+        self.out.emit(tkn)
+        emit_to(self.out, tkn_iter, "SEMI")
+        self.out.emit(";\n")
+
         # Flush the assignment to the stack.  Note that we don't flush the
         # stack pointer here, and instead are currently relying on initializing
         # unused portions of the stack to NULL.