Revert "Use implicit null checks inside try blocks."

Fails gcstress tests.

This reverts commit 7aa7560683626c7893011271c241b3265ded1dc3.

Change-Id: I4f5c89048b9ffddbafa02f3001e329ff87058ca2
diff --git a/compiler/optimizing/code_generator.h b/compiler/optimizing/code_generator.h
index b4d4b9b..0c60a98 100644
--- a/compiler/optimizing/code_generator.h
+++ b/compiler/optimizing/code_generator.h
@@ -313,7 +313,6 @@
 
   bool CanMoveNullCheckToUser(HNullCheck* null_check);
   void MaybeRecordImplicitNullCheck(HInstruction* instruction);
-  LocationSummary* CreateNullCheckLocations(HNullCheck* null_check);
   void GenerateNullCheck(HNullCheck* null_check);
   virtual void GenerateImplicitNullCheck(HNullCheck* null_check) = 0;
   virtual void GenerateExplicitNullCheck(HNullCheck* null_check) = 0;
@@ -323,6 +322,12 @@
   // TODO: Replace with a catch-entering instruction that records the environment.
   void RecordCatchBlockInfo();
 
+  // Returns true if implicit null checks are allowed in the compiler options
+  // and if the null check is not inside a try block. We currently cannot do
+  // implicit null checks in that case because we need the NullCheckSlowPath to
+  // save live registers, which may be needed by the runtime to set catch phis.
+  bool IsImplicitNullCheckAllowed(HNullCheck* null_check) const;
+
   // TODO: Avoid creating the `std::unique_ptr` here.
   void AddSlowPath(SlowPathCode* slow_path) {
     slow_paths_.push_back(std::unique_ptr<SlowPathCode>(slow_path));
@@ -708,8 +713,6 @@
   bool is_leaf_;
 
   // Whether an instruction in the graph accesses the current method.
-  // TODO: Rename: this actually indicates that some instruction in the method
-  // needs the environment including a valid stack frame.
   bool requires_current_method_;
 
   friend class OptimizingCFITest;