Ensure full init of IR_NOP instructions.

src/lj_ir.h

@@ -548,4 +548,12 @@ static LJ_AINLINE int ir_sideeff(IRIns *ir)
 
 LJ_STATIC_ASSERT((int)IRT_GUARD == (int)IRM_W);
 
+/* Replace IR instruction with NOP. */
+static LJ_AINLINE void lj_ir_nop(IRIns *ir)
+{
+  ir->ot = IRT(IR_NOP, IRT_NIL);
+  ir->op1 = ir->op2 = 0;
+  ir->prev = 0;
+}
+
 #endif