Subzero: Initial O2 lowering

src/IceTargetLowering.h

Index: src/IceTargetLowering.h
diff --git a/src/IceTargetLowering.h b/src/IceTargetLowering.h
index 92a36af2938b3fdd317cf01eece892af512cef6d..7f798a89d62ab46fb2a828cd5cee5021c4f1d9db 100644
--- a/src/IceTargetLowering.h
+++ b/src/IceTargetLowering.h
@@ -109,6 +109,8 @@ public:
     Func->setError("Target doesn't specify O2 lowering steps.");
   }
 
+  // Tries to do address mode optimization on a single instruction.
+  void doAddressOpt();
   // Lowers a single instruction.
   void lower();
 
@@ -173,6 +175,8 @@ protected:
   virtual void lowerSwitch(const InstSwitch *Inst) = 0;
   virtual void lowerUnreachable(const InstUnreachable *Inst) = 0;
 
+  virtual void doAddressOptLoad() {}
+  virtual void doAddressOptStore() {}
   // This gives the target an opportunity to post-process the lowered
   // expansion before returning.  The primary intention is to do some
   // Register Manager activity as necessary, specifically to eagerly