Don't bother to chain NOPs.

src/lj_opt_dce.c

@@ -47,17 +47,15 @@ static void dce_propagate(jit_State *J)
       pchain[ir->o] = &ir->prev;
     } else if (!ir_sideeff(ir)) {
       *pchain[ir->o] = ir->prev;  /* Reroute original instruction chain. */
-      *pchain[IR_NOP] = (IRRef1)ins;
       ir->t.irt = IRT_NIL;
       ir->o = IR_NOP;  /* Replace instruction with NOP. */
       ir->op1 = ir->op2 = 0;
-      pchain[IR_NOP] = &ir->prev;
+      ir->prev = 0;
       continue;
     }
     if (ir->op1 >= REF_FIRST) irt_setmark(IR(ir->op1)->t);
     if (ir->op2 >= REF_FIRST) irt_setmark(IR(ir->op2)->t);
   }
-  *pchain[IR_NOP] = 0;  /* Terminate NOP chain. */
 }
 
 /* Dead Code Elimination.

src/lj_opt_mem.c

@@ -323,7 +323,7 @@ TRef LJ_FASTCALL lj_opt_dse_ahstore(jit_State *J)
 	    goto doemit;  /* No elimination possible. */
 	/* Remove redundant store from chain and replace with NOP. */
 	*refp = store->prev;
-	store->o = IR_NOP;  /* Unchained NOP -- does anybody care? */
+	store->o = IR_NOP;
 	store->t.irt = IRT_NIL;
 	store->op1 = store->op2 = 0;
 	store->prev = 0;
@@ -418,7 +418,7 @@ TRef LJ_FASTCALL lj_opt_dse_ustore(jit_State *J)
 	    goto doemit;  /* No elimination possible. */
 	/* Remove redundant store from chain and replace with NOP. */
 	*refp = store->prev;
-	store->o = IR_NOP;  /* Unchained NOP -- does anybody care? */
+	store->o = IR_NOP;
 	store->t.irt = IRT_NIL;
 	store->op1 = store->op2 = 0;
 	store->prev = 0;
@@ -511,7 +511,7 @@ TRef LJ_FASTCALL lj_opt_dse_fstore(jit_State *J)
 	    goto doemit;  /* No elimination possible. */
 	/* Remove redundant store from chain and replace with NOP. */
 	*refp = store->prev;
-	store->o = IR_NOP;  /* Unchained NOP -- does anybody care? */
+	store->o = IR_NOP;
 	store->t.irt = IRT_NIL;
 	store->op1 = store->op2 = 0;
 	store->prev = 0;
@@ -761,7 +761,7 @@ TRef LJ_FASTCALL lj_opt_dse_xstore(jit_State *J)
 	    goto doemit;  /* No elimination possible. */
 	/* Remove redundant store from chain and replace with NOP. */
 	*refp = store->prev;
-	store->o = IR_NOP;  /* Unchained NOP -- does anybody care? */
+	store->o = IR_NOP;
 	store->t.irt = IRT_NIL;
 	store->op1 = store->op2 = 0;
 	store->prev = 0;

src/lj_record.c

@@ -67,7 +67,7 @@ static void rec_check_ir(jit_State *J)
     if (ir->prev) {
       lua_assert(ir->prev >= nk);
       lua_assert(i >= REF_BIAS ? ir->prev < i : ir->prev > i);
-      lua_assert(IR(ir->prev)->o == ir->o);
+      lua_assert(ir->o == IR_NOP || IR(ir->prev)->o == ir->o);
     }
   }
 }