bpo-45753: Make recursion checks more efficient. (GH-29524)

* Uses recursion remaining, instead of recursion depth to speed up check against recursion limit.

2 files changed, 6 insertions, 6 deletions

diff --git a/Include/cpython/pystate.h b/Include/cpython/pystate.h
index cf69c72028..9ac0a298ba 100644
--- a/Include/cpython/pystate.h
+++ b/Include/cpython/pystate.h
@@ -79,9 +79,9 @@ struct _ts {
     struct _ts *next;
     PyInterpreterState *interp;
 
-    int recursion_depth;
+    int recursion_remaining;
+    int recursion_limit;
     int recursion_headroom; /* Allow 50 more calls to handle any errors. */
-    int stackcheck_counter;
 
     /* 'tracing' keeps track of the execution depth when tracing/profiling.
        This is to prevent the actual trace/profile code from being recorded in
diff --git a/Include/internal/pycore_ceval.h b/Include/internal/pycore_ceval.h
index 53580b99d3..c2251b04be 100644
--- a/Include/internal/pycore_ceval.h
+++ b/Include/internal/pycore_ceval.h
@@ -75,12 +75,12 @@ extern void _PyEval_DeactivateOpCache(void);
 /* With USE_STACKCHECK macro defined, trigger stack checks in
    _Py_CheckRecursiveCall() on every 64th call to Py_EnterRecursiveCall. */
 static inline int _Py_MakeRecCheck(PyThreadState *tstate)  {
-    return (++tstate->recursion_depth > tstate->interp->ceval.recursion_limit
-            || ++tstate->stackcheck_counter > 64);
+    return (tstate->recursion_remaining-- <= 0
+            || (tstate->recursion_remaining & 63) == 0);
 }
 #else
 static inline int _Py_MakeRecCheck(PyThreadState *tstate) {
-    return (++tstate->recursion_depth > tstate->interp->ceval.recursion_limit);
+    return tstate->recursion_remaining-- <= 0;
 }
 #endif
 
@@ -101,7 +101,7 @@ static inline int _Py_EnterRecursiveCall_inline(const char *where) {
 #define Py_EnterRecursiveCall(where) _Py_EnterRecursiveCall_inline(where)
 
 static inline void _Py_LeaveRecursiveCall(PyThreadState *tstate)  {
-    tstate->recursion_depth--;
+    tstate->recursion_remaining++;
 }
 
 static inline void _Py_LeaveRecursiveCall_inline(void)  {