Optimize expressions of the form (expr === true) when expr has boolean type.

vm/intermediate_language.h

Index: vm/intermediate_language.h
===================================================================
--- vm/intermediate_language.h	(revision 10497)
+++ vm/intermediate_language.h	(working copy)
@@ -112,6 +112,7 @@
 class BranchInstr;
 class BufferFormatter;
 class ComparisonComp;
+class Definition;
 class Instruction;
 class PushArgumentInstr;
 class Value;
@@ -147,6 +148,10 @@
   // Returns true, if this computation can deoptimize.
   virtual bool CanDeoptimize() const  = 0;
 
+  // Optimize this computation. Returns a replacement for the instruction
+  // that wraps this computation or NULL if nothing to replace.
+  virtual Definition* TryReplace(BindInstr* instr) { return NULL; }
+
   // Compile time type of the computation, which typically depends on the
   // compile time types (and possibly propagated types) of its inputs.
   virtual RawAbstractType* CompileType() const = 0;
@@ -354,6 +359,8 @@
   UseVal* next_use_;
   UseVal* previous_use_;
 
+  friend class Definition;
+
   DISALLOW_COPY_AND_ASSIGN(UseVal);
 };
 
@@ -646,6 +653,8 @@
 
   virtual bool CanDeoptimize() const { return false; }
 
+  virtual Definition* TryReplace(BindInstr* instr);
+
  private:
   DISALLOW_COPY_AND_ASSIGN(StrictCompareComp);
 };
@@ -2374,6 +2383,8 @@
     use_list_ = head;
   }
 
+  void ReplaceUsesWith(Definition* other);
+
  private:
   intptr_t temp_index_;
   intptr_t ssa_temp_index_;