refactor: Vm 状态分组、dispatch 拆分为分发表、IC 辅助函数独立成模块

crates/oxide_vm/src/ic_helper.rs

@@ -0,0 +1,37 @@
+//! Inline-cache (IC) bytecode-stream helpers.
+//!
+//! These operate purely on the bytecode `Instr` slice — they read/clear/write
+//! the IC extension words embedded after IC-bearing opcodes. They take no `Vm`
+//! state, so they live outside `Vm` for clearer ownership and to ease the future
+//! IC side-table migration.
+
+use oxide_bytecode::opcode::{self, Instr};
+
+/// Write a resolved `(shape_id, slot)` back into the three IC extension words
+/// that precede the current `pc`. Called on an IC miss after resolving a
+/// property, so the next execution of this site hits the cache.
+pub(crate) fn write_ic_back(bytecode: &mut [Instr], pc: usize, shape_id: u32, slot_index: u32) {
+    debug_assert!(pc >= 3, "IC write-back requires 3 extension words before pc");
+    bytecode[pc - 3] = shape_id & 0x00FF_FFFF;
+    bytecode[pc - 2] = slot_index;
+    bytecode[pc - 1] = 0;
+}
+
+/// Zero every IC extension word in the stream, invalidating all cached shapes.
+/// Used on `rerun()` so re-execution never derefs a stale cached pointer.
+pub(crate) fn clear_ic_caches(bytecode: &mut [Instr]) {
+    let mut i = 0;
+    while i < bytecode.len() {
+        let op = opcode::opcode(bytecode[i]);
+        if op.has_ic_ext_words() {
+            if i + 3 < bytecode.len() {
+                bytecode[i + 1] = 0;
+                bytecode[i + 2] = 0;
+                bytecode[i + 3] = 0;
+            }
+            i += 4;
+        } else {
+            i += 1;
+        }
+    }
+}