Add NOP to ARM IR lowering.

src/IceInstARM32.h

Index: src/IceInstARM32.h
diff --git a/src/IceInstARM32.h b/src/IceInstARM32.h
index bce1aca787ddd3b6484855fc2e2be4a6a82ad9ad..62af449c7168814e4fb5f7720c65fb7629c3869d 100644
--- a/src/IceInstARM32.h
+++ b/src/IceInstARM32.h
@@ -394,6 +394,7 @@ public:
     Ldrex,
     Lsl,
     Lsr,
+    Nop,
     Mla,
     Mls,
     Mov,
@@ -1434,6 +1435,24 @@ private:
   explicit InstARM32Dmb(Cfg *Func);
 };
 
+class InstARM32Nop final : public InstARM32Pred {

[Eric Holk, 2016/02/08 17:29:43]

Does it make sense to have Nop derive from a predicable instruction?

[Karl, 2016/02/08 17:55:55]

The ARM instruction allows predicates, and so like other instructions, I made it
a subclass of this.

[Eric Holk, 2016/02/08 17:58:15]

That seems reasonable.

+  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.