[Interpreter] Local flow control in the bytecode graph builder.

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/compiler.h"

[Michael Starzinger, 2015/12/16 12:40:11]

nit: Can we get by without including the compiler.h grab-bag header here? AFAICT
the handles.h header and a forward declare of "BytecodeArray" should suffice,
but with V8 you never know. :)

[oth, 2015/12/16 14:17:06]

Done.

+#include "src/zone-containers.h"
+
+namespace v8 {
+namespace internal {
+namespace compiler {
+
+class BytecodeBranchInfo;
+
+// A class for identifying the branch targets and their branch sites
+// within a bytecode array and also identifying which bytecodes are
+// reachable. This information can be used to construct the local
+// control flow logic for turbofan graphs built from bytecode.

[Michael Starzinger, 2015/12/16 12:40:11]

nit: s/turbofan graphs/high-level IR graphs/

[oth, 2015/12/16 14:17:06]

Done.

+//
+// NB This class 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)
+      : branch_infos_(zone),
+        bytecode_array_(bytecode_array),
+        reachable_(bytecode_array->length(), zone),

[Michael Starzinger, 2015/12/16 12:40:11]

nit: Can we move this constructor into the .cc file, otherwise a whole slew of
headers needs to be included for the BytecodeArray::length function.

[oth, 2015/12/16 14:17:06]

Done.

+        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();
+
+  // 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;
+
+  // Returns true if the bytecode at |offset| is reachable.
+  bool is_reachable(int offset) const { return reachable_.Contains(offset); }
+
+  // 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;
+  }
+
+  // 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;
+  }
+
+ private:
+  void AddBranch(int origin_offset, int target_offset);
+
+  Zone* zone() const { return zone_; }
+  Handle<BytecodeArray> bytecode_array() const { return bytecode_array_; }
+
+  ZoneMap<int, BytecodeBranchInfo*> branch_infos_;
+  Handle<BytecodeArray> bytecode_array_;
+  BitVector reachable_;
+  Zone* zone_;
+
+  DISALLOW_COPY_AND_ASSIGN(BytecodeBranchAnalysis);
+};
+
+
+}  // namespace compiler
+}  // namespace internal
+}  // namespace v8
+
+#endif  // V8_COMPILER_BYTECODE_BRANCH_ANALYSIS_H_