Add NOP to ARM IR lowering.

src/IceInstARM32.h

Index: src/IceInstARM32.h
diff --git a/src/IceInstARM32.h b/src/IceInstARM32.h
index 504123b630f794de85e5f79a26a7c1fd174c7220..4d8f02b5b712e21d1f6ddf0a88f6cce172cfe286 100644
--- a/src/IceInstARM32.h
+++ b/src/IceInstARM32.h
@@ -397,6 +397,7 @@ public:
     Ldrex,
     Lsl,
     Lsr,
+    Nop,
     Mla,
     Mls,
     Mov,
@@ -1494,6 +1495,24 @@ private:
   explicit InstARM32Dmb(Cfg *Func);
 };
 
+class InstARM32Nop final : public InstARM32Pred {
+  InstARM32Nop() = delete;
+  InstARM32Nop(const InstARM32Nop &) = delete;
+  InstARM32Nop &operator=(const InstARM32Nop &) = delete;
+
+public:
+  static InstARM32Nop *create(Cfg *Func) {
+    return new (Func->allocate<InstARM32Nop>()) InstARM32Nop(Func);
+  }
+  void emit(const Cfg *Func) const override;
+  void emitIAS(const Cfg *Func) const override;
+  void dump(const Cfg *Func) const override;
+  static bool classof(const Inst *Instr) { return isClassof(Instr, Nop); }
+
+private:
+  explicit InstARM32Nop(Cfg *Func);
+};
+
 // Declare partial template specializations of emit() methods that already have
 // default implementations. Without this, there is the possibility of ODR
 // violations and link errors.