[3.14]: gh-148284: Move stackref buffer to per-eval loop, and don't override PGO data.

Misc/NEWS.d/next/Core_and_Builtins/2026-04-09-20-02-06.gh-issue-148284.DTBhaX.rst

@@ -0,0 +1 @@
+Reduce C stack usage in the Python interpreter on recent versions of Clang.

Python/ceval.c

@@ -1141,12 +1141,29 @@ typedef struct {
     _PyStackRef stack[1];
 } _PyEntryFrame;
 
-PyObject* _Py_HOT_FUNCTION DONT_SLP_VECTORIZE
+/* gh-148284: *Do not* mark this function as _Py_HOT_FUNCTION.
+ * On certain compilers (Clang), this overrides PGO information
+ * leading possibly to miss-optimization and over-inlining.
+ * On GCC, _Py_HOT_FUNCTION is ignored when PGO is enabled.
+ */
+PyObject* DONT_SLP_VECTORIZE
 _PyEval_EvalFrameDefault(PyThreadState *tstate, _PyInterpreterFrame *frame, int throwflag)
 {
+    /* +1 because vectorcall might use -1 to write self */
+    /* gh-138115: This must not be in individual cases for
+       non-tail-call interpreters, as it results in excessive
+       stack usage in some compilers.
+       This must also be placed before any branches to avoid
+       interaction with other optimization passes.
+    */
+#if !Py_TAIL_CALL_INTERP
+    PyObject *STACKREF_SCRATCH[MAX_STACKREF_SCRATCH+1];
+#endif
+
     _Py_EnsureTstateNotNULL(tstate);
     CALL_STAT_INC(pyeval_calls);
 
+
 #if USE_COMPUTED_GOTOS && !Py_TAIL_CALL_INTERP
 /* Import the static jump table */
 #include "opcode_targets.h"
@@ -1168,6 +1185,7 @@ _PyEval_EvalFrameDefault(PyThreadState *tstate, _PyInterpreterFrame *frame, int
         return NULL;
     }
 
+
     /* Local "register" variables.
      * These are cached values from the frame and code object.  */
     _Py_CODEUNIT *next_instr;

Python/ceval_macros.h

@@ -427,10 +427,16 @@ do { \
 /* How much scratch space to give stackref to PyObject* conversion. */
 #define MAX_STACKREF_SCRATCH 10
 
+#if Py_TAIL_CALL_INTERP
 #define STACKREFS_TO_PYOBJECTS(ARGS, ARG_COUNT, NAME) \
     /* +1 because vectorcall might use -1 to write self */ \
     PyObject *NAME##_temp[MAX_STACKREF_SCRATCH+1]; \
     PyObject **NAME = _PyObjectArray_FromStackRefArray(ARGS, ARG_COUNT, NAME##_temp + 1);
+#else
+#define STACKREFS_TO_PYOBJECTS(ARGS, ARG_COUNT, NAME) \
+    PyObject **NAME##_temp = (PyObject **)&STACKREF_SCRATCH; \
+    PyObject **NAME = _PyObjectArray_FromStackRefArray(ARGS, ARG_COUNT, NAME##_temp + 1);
+#endif
 
 #define STACKREFS_TO_PYOBJECTS_CLEANUP(NAME) \
     /* +1 because we +1 previously */ \