gh-100146: Steal references from stack when building a list (#100147)

When executing the BUILD_LIST opcode, steal the references from the stack,
in a manner similar to the BUILD_TUPLE opcode.  Implement this by offloading
the logic to a new private API, _PyList_FromArraySteal(), that works similarly
to _PyTuple_FromArraySteal().

This way, instead of performing multiple stack pointer adjustments while the
list is being initialized, the stack is adjusted only once and a fast memory
copy operation is performed in one fell swoop.

2 files changed, 4 insertions, 10 deletions

diff --git a/Python/bytecodes.c b/Python/bytecodes.c
index e1c73ab..839fac3 100644
--- a/Python/bytecodes.c
+++ b/Python/bytecodes.c
@@ -1390,13 +1390,10 @@ dummy_func(
 
         // stack effect: (__array[oparg] -- __0)
         inst(BUILD_LIST) {
-            PyObject *list =  PyList_New(oparg);
+            STACK_SHRINK(oparg);
+            PyObject *list = _PyList_FromArraySteal(stack_pointer, oparg);
             if (list == NULL)
                 goto error;
-            while (--oparg >= 0) {
-                PyObject *item = POP();
-                PyList_SET_ITEM(list, oparg, item);
-            }
             PUSH(list);
         }
 
diff --git a/Python/generated_cases.c.h b/Python/generated_cases.c.h
index 1179bdf..ed89e90 100644
--- a/Python/generated_cases.c.h
+++ b/Python/generated_cases.c.h
@@ -1608,13 +1608,10 @@
         }
 
         TARGET(BUILD_LIST) {
-            PyObject *list =  PyList_New(oparg);
+            STACK_SHRINK(oparg);
+            PyObject *list = _PyList_FromArraySteal(stack_pointer, oparg);
             if (list == NULL)
                 goto error;
-            while (--oparg >= 0) {
-                PyObject *item = POP();
-                PyList_SET_ITEM(list, oparg, item);
-            }
             PUSH(list);
             DISPATCH();
         }