gh-127022: Simplify `PyStackRef_FromPyObjectSteal` (#127024)

This gets rid of the immortal check in `PyStackRef_FromPyObjectSteal()`.
Overall, this improves performance about 2% in the free threading
build.

This also renames `PyStackRef_Is()` to `PyStackRef_IsExactly()` because
the macro requires that the tag bits of the arguments match, which is
only true in certain special cases.

1 files changed, 10 insertions, 4 deletions

diff --git a/Include/internal/pycore_stackref.h b/Include/internal/pycore_stackref.h
index 588e57f..90a3118 100644
--- a/Include/internal/pycore_stackref.h
+++ b/Include/internal/pycore_stackref.h
@@ -99,8 +99,7 @@ _PyStackRef_FromPyObjectSteal(PyObject *obj)
     assert(obj != NULL);
     // Make sure we don't take an already tagged value.
     assert(((uintptr_t)obj & Py_TAG_BITS) == 0);
-    unsigned int tag = _Py_IsImmortal(obj) ? (Py_TAG_DEFERRED) : Py_TAG_PTR;
-    return ((_PyStackRef){.bits = ((uintptr_t)(obj)) | tag});
+    return (_PyStackRef){ .bits = (uintptr_t)obj };
 }
 #   define PyStackRef_FromPyObjectSteal(obj) _PyStackRef_FromPyObjectSteal(_PyObject_CAST(obj))
 
@@ -190,9 +189,16 @@ static const _PyStackRef PyStackRef_NULL = { .bits = 0 };
 
 #endif // Py_GIL_DISABLED
 
-// Note: this is a macro because MSVC (Windows) has trouble inlining it.
+// Check if a stackref is exactly the same as another stackref, including the
+// the deferred bit. This can only be used safely if you know that the deferred
+// bits of `a` and `b` match.
+#define PyStackRef_IsExactly(a, b) \
+    (assert(((a).bits & Py_TAG_BITS) == ((b).bits & Py_TAG_BITS)), (a).bits == (b).bits)
 
-#define PyStackRef_Is(a, b) ((a).bits == (b).bits)
+// Checks that mask out the deferred bit in the free threading build.
+#define PyStackRef_IsNone(ref) (PyStackRef_AsPyObjectBorrow(ref) == Py_None)
+#define PyStackRef_IsTrue(ref) (PyStackRef_AsPyObjectBorrow(ref) == Py_True)
+#define PyStackRef_IsFalse(ref) (PyStackRef_AsPyObjectBorrow(ref) == Py_False)
 
 // Converts a PyStackRef back to a PyObject *, converting the
 // stackref to a new reference.