[turbofan] Generate loop exits in the bytecode graph builder.

src/compiler/bytecode-loop-analysis.h

+// Copyright 2016 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_LOOP_ANALYSIS_H_
+#define V8_COMPILER_BYTECODE_LOOP_ANALYSIS_H_
+
+#include "src/bit-vector.h"

[Michael Starzinger, 2016/07/29 08:54:46]

nit: Seems the BitVector is not needed in the header?

[Jarin, 2016/07/29 11:36:46]

Done.

+#include "src/handles.h"
+#include "src/zone-containers.h"
+
+namespace v8 {
+namespace internal {
+
+class BytecodeArray;
+
+namespace compiler {
+
+class BytecodeBranchAnalysis;
+
+class BytecodeLoopAnalysis BASE_EMBEDDED {
+ public:
+  BytecodeLoopAnalysis(Handle<BytecodeArray> bytecode_array,
+                       const BytecodeBranchAnalysis* branch_analysis,
+                       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();
+
+  // Get the loop header offset of the containing loop for arbitrary
+  // {offset}, or -1 if the {offset} is not inside any loop.
+  int GetLoopOffsetFor(int offset) const;
+  // Gets the loop header offset of the parent loop of the loop header
+  // at {header_offset}, or -1 for outer-most loops.
+  int GetParentLoopFor(int header_offset) const;
+
+ private:
+  void AddLoopEntry(int entry_offset);
+  void AddBranch(int origin_offset, int target_offset);
+
+  Zone* zone() const { return zone_; }
+  Handle<BytecodeArray> bytecode_array() const { return bytecode_array_; }
+
+  Handle<BytecodeArray> bytecode_array_;
+  const BytecodeBranchAnalysis* branch_analysis_;
+  Zone* zone_;
+
+  int current_loop_offset_;
+
+  ZoneMap<int, int> backedge_to_header_;

[Michael Starzinger, 2016/07/29 08:54:46]

nit: Can we leave a comment here that both of these maps will contain one entry
per loop? That would clarify that they both take just O(n) space where n is the
number of loops. Also might we worth mentioning that both key and value
represent bytecode offsets.

[Jarin, 2016/07/29 11:36:46]

Done.

+  ZoneMap<int, int> loop_header_to_parent_;
+
+  DISALLOW_COPY_AND_ASSIGN(BytecodeLoopAnalysis);
+};
+
+}  // namespace compiler
+}  // namespace internal
+}  // namespace v8
+
+#endif  // V8_COMPILER_BYTECODE_LOOP_ANALYSIS_H_