Selectively invert ICMP operands for better address optimization

Results in lower code size and more loads folded into cmp instructions.

BUG=none
R=eholk@chromium.org, jpp@chromium.org, stichnot@chromium.org

Review URL: https://codereview.chromium.org/2124973005 .
diff --git a/src/IceTargetLowering.h b/src/IceTargetLowering.h
index dcba5ce..43f5e01 100644
--- a/src/IceTargetLowering.h
+++ b/src/IceTargetLowering.h
@@ -396,6 +396,8 @@
   virtual void genTargetHelperCallFor(Inst *Instr) = 0;
   virtual uint32_t getCallStackArgumentsSizeBytes(const InstCall *Instr) = 0;
 
+  /// Opportunity to modify other instructions to help Address Optimization
+  virtual void doAddressOptOther() {}
   virtual void doAddressOptLoad() {}
   virtual void doAddressOptStore() {}
   virtual void doMockBoundsCheck(Operand *) {}