Revert "change unpacking semantics for genexps: no delegation"

This reverts commit a2b7a69.

Author: adqm

Python/codegen.c

@@ -4488,18 +4488,11 @@ codegen_sync_comprehension_generator(compiler *c, location loc,
         switch (type) {
         case COMP_GENEXP:
             if (elt->kind == Starred_kind){
-                NEW_JUMP_TARGET_LABEL(c, unpack_start);
-                NEW_JUMP_TARGET_LABEL(c, unpack_end);
                 VISIT(c, expr, elt->v.Starred.value);
-                ADDOP(c, elt_loc, GET_ITER);
-                USE_LABEL(c, unpack_start);
-                ADDOP_JUMP(c, elt_loc, FOR_ITER, unpack_end);
-                ADDOP_YIELD(c, elt_loc);
+                ADDOP(c, elt_loc, GET_YIELD_FROM_ITER);
+                ADDOP_LOAD_CONST(c, elt_loc, Py_None);
+                ADD_YIELD_FROM(c, elt_loc, 0);
                 ADDOP(c, elt_loc, POP_TOP);
-                ADDOP_JUMP(c, NO_LOCATION, JUMP, unpack_start);
-                USE_LABEL(c, unpack_end);
-                ADDOP(c, NO_LOCATION, END_FOR);
-                ADDOP(c, NO_LOCATION, POP_ITER);
             }
             else{
                 VISIT(c, expr, elt);
@@ -4628,16 +4621,19 @@ codegen_async_comprehension_generator(compiler *c, location loc,
         switch (type) {
         case COMP_GENEXP:
             if (elt->kind == Starred_kind){
-                NEW_JUMP_TARGET_LABEL(c, unpack_start);
-                NEW_JUMP_TARGET_LABEL(c, unpack_end);
+                /* async generators don't support `yield from`, so use an
+                explicit loop to mimic the bytecode for (z async for y in x for
+                z in y). */
+                NEW_JUMP_TARGET_LABEL(c, async_unpack_start);
+                NEW_JUMP_TARGET_LABEL(c, async_unpack_end);
                 VISIT(c, expr, elt->v.Starred.value);
                 ADDOP(c, elt_loc, GET_ITER);
-                USE_LABEL(c, unpack_start);
-                ADDOP_JUMP(c, elt_loc, FOR_ITER, unpack_end);
+                USE_LABEL(c, async_unpack_start);
+                ADDOP_JUMP(c, elt_loc, FOR_ITER, async_unpack_end);
                 ADDOP_YIELD(c, elt_loc);
                 ADDOP(c, elt_loc, POP_TOP);
-                ADDOP_JUMP(c, NO_LOCATION, JUMP, unpack_start);
-                USE_LABEL(c, unpack_end);
+                ADDOP_JUMP(c, NO_LOCATION, JUMP, async_unpack_start);
+                USE_LABEL(c, async_unpack_end);
                 ADDOP(c, NO_LOCATION, END_FOR);
                 ADDOP(c, NO_LOCATION, POP_ITER);
             }