KOS_OP_FAST_ITEM_FAST_INPLACE

• Style: EXTRA (OPCOUNT, FASTVAR, FASTVAR, NOARG).

• Stack: [..., v0 .. v_{n-1}] → [...]. Reduce obj[key] in place with the count values left to right and store it back with the object read from a fast slot and the key read from a fast slot.

• Cache: one KOS_CACHE_ITEM slot; the site elects a body for the container kind it first sees through the shared helper in eval/eval_item.c (see the items section of the VM reference).

• Compiler form: The lowering of VAR_ITEM_VAR_INPLACE: every named operand has a fast slot.

• Implementation: koskari/lib/opcode/FAST_ITEM_FAST_INPLACE.c