gh-140868: Don't rely on undefined left shift behavior in assert (#140869)

DinoV · web-flow · commit b1554146c291 · 2025-11-01T12:23:58.000-04:00
Don't rely on undefined left shift behavior in assert
diff --git a/Include/internal/pycore_stackref.h b/Include/internal/pycore_stackref.h
@@ -403,7 +403,8 @@ PyStackRef_IsTaggedInt(_PyStackRef i)
 static inline _PyStackRef
 PyStackRef_TagInt(intptr_t i)
 {
-    assert(Py_ARITHMETIC_RIGHT_SHIFT(intptr_t, (i << Py_TAGGED_SHIFT), Py_TAGGED_SHIFT) == i);
+    assert(Py_ARITHMETIC_RIGHT_SHIFT(intptr_t, (intptr_t)(((uintptr_t)i) << Py_TAGGED_SHIFT),
+                                     Py_TAGGED_SHIFT) == i);
     return (_PyStackRef){ .bits = ((((uintptr_t)i) << Py_TAGGED_SHIFT) | Py_INT_TAG) };
 }
 

Original file line number	Diff line number	Diff line change
`@@ -403,7 +403,8 @@ PyStackRef_IsTaggedInt(_PyStackRef i)`
`403`	`403`	`static inline _PyStackRef`
`404`	`404`	`PyStackRef_TagInt(intptr_t i)`
`405`	`405`	`{`
`406`		`- assert(Py_ARITHMETIC_RIGHT_SHIFT(intptr_t, (i << Py_TAGGED_SHIFT), Py_TAGGED_SHIFT) == i);`
	`406`	`+ assert(Py_ARITHMETIC_RIGHT_SHIFT(intptr_t, (intptr_t)(((uintptr_t)i) << Py_TAGGED_SHIFT),`
	`407`	`+ Py_TAGGED_SHIFT) == i);`
`407`	`408`	`return (_PyStackRef){ .bits = ((((uintptr_t)i) << Py_TAGGED_SHIFT) \| Py_INT_TAG) };`
`408`	`409`	`}`
`409`	`410`