[interpreter] Simplify BytecodeBranchAnalysis to minimum.

src/compiler/bytecode-branch-analysis.h

 // Copyright 2015 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_COMPILER_BYTECODE_BRANCH_ANALYSIS_H_
 #define V8_COMPILER_BYTECODE_BRANCH_ANALYSIS_H_
 
 #include "src/bit-vector.h"
 #include "src/handles.h"
-#include "src/zone-containers.h"
 
 namespace v8 {
 namespace internal {
 
 class BytecodeArray;
 
 namespace compiler {
 
-class BytecodeBranchInfo;
-
-// A class for identifying the branch targets and their branch sites
-// within a bytecode array. This information can be used to construct
-// the local control flow logic for high-level IR graphs built from
-// bytecode.
+// A class for identifying branch targets within a bytecode array.
+// This information can be used to construct the local control flow
+// logic for high-level IR graphs built from bytecode.
 //
-// NB This class relies on the only backwards branches in bytecode
-// being jumps back to loop headers.
+// N.B. If this class is used to determine loop headers, then such a
+// usage relies on the only backwards branches in bytecode being jumps
+// back to loop headers.
 class BytecodeBranchAnalysis BASE_EMBEDDED {
  public:
   BytecodeBranchAnalysis(Handle<BytecodeArray> bytecode_array, Zone* zone);
 
   // Analyze the bytecodes to find the branch sites and their
   // targets. No other methods in this class return valid information
   // until this has been called.
   void Analyze();
 
   // Returns true if there are any forward branches to the bytecode at
   // |offset|.
   bool forward_branches_target(int offset) const {
-    const ZoneVector<int>* sites = ForwardBranchesTargetting(offset);
-    return sites != nullptr && sites->size() > 0;
+    return is_forward_target_.Contains(offset);
   }
 
   // Returns true if there are any backward branches to the bytecode
   // at |offset|.
   bool backward_branches_target(int offset) const {
-    const ZoneVector<int>* sites = BackwardBranchesTargetting(offset);
-    return sites != nullptr && sites->size() > 0;
+    return is_backward_target_.Contains(offset);
   }
 
  private:
   void AddBranch(int origin_offset, int target_offset);
 
-  // Offsets of bytecodes having a backward branch to the bytecode at |offset|.
-  const ZoneVector<int>* BackwardBranchesTargetting(int offset) const;
-
-  // Offsets of bytecodes having a forward branch to the bytecode at |offset|.
-  const ZoneVector<int>* ForwardBranchesTargetting(int offset) const;
-
   Zone* zone() const { return zone_; }
   Handle<BytecodeArray> bytecode_array() const { return bytecode_array_; }
 
-  ZoneMap<int, BytecodeBranchInfo*> branch_infos_;
   Handle<BytecodeArray> bytecode_array_;
+  BitVector is_backward_target_;
+  BitVector is_forward_target_;
   Zone* zone_;
 
   DISALLOW_COPY_AND_ASSIGN(BytecodeBranchAnalysis);
 };
 
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_BYTECODE_BRANCH_ANALYSIS_H_