[interpeter] Move to table based peephole optimizer.

src/interpreter/mkpeephole.cc

+// 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.
+
+#include <array>
+#include <fstream>
+#include <map>
+#include <string>
+#include <vector>
+
+#include "src/globals.h"
+#include "src/interpreter/bytecode-peephole-table.h"
+#include "src/interpreter/bytecodes.h"
+
+namespace v8 {
+namespace internal {
+
+// These flag definitions are used in bytecodes.cc, but not available
+// to the linker.
+bool FLAG_prepare_always_opt = false;
+bool FLAG_always_opt = false;

[rmcilroy, 2016/07/13 13:51:41]

I don't think these should be necessary any longer after your preceeding CL.

[oth, 2016/07/15 13:09:40]

Done. Thanks!

[rmcilroy, 2016/07/15 15:31:48]

Still there?

[oth, 2016/07/15 17:27:26]

Done...Again. Started removing hashing and decided to save it for later as not
wanting to introduce churn. Backed out the changes described as done here.

+
+namespace interpreter {
+
+const char* ActionName(PeepholeAction action) {
+  switch (action) {
+#define CASE(Name)              \
+  case PeepholeAction::k##Name: \
+    return "PeepholeAction::k" #Name;
+    PEEPHOLE_ACTION_LIST(CASE)
+#undef CASE
+    default:
+      UNREACHABLE();
+      return "";
+  }
+}
+
+std::string BytecodeName(Bytecode bytecode) {
+  return "Bytecode::k" + std::string(Bytecodes::ToString(bytecode));
+}
+
+class PeepholeActionTableWriter final {
+ public:
+  static const size_t kNumberOfBytecodes =
+      static_cast<size_t>(Bytecode::kLast) + 1;
+  typedef std::array<PeepholeActionAndData, kNumberOfBytecodes> Row;
+
+  void BuildTable();
+  void Write(std::ostream& os);
+
+ private:
+  static const char* kIndent;
+  static const char* kNamespaceElements[];
+
+  void WriteHeader(std::ostream& os);
+  void WriteIncludeFiles(std::ostream& os);
+  void WriteClassMethods(std::ostream& os);
+  void WriteUniqueRows(std::ostream& os);
+  void WriteRowMap(std::ostream& os);
+  void WriteRow(std::ostream& os, size_t row_index);
+  void WriteOpenNamespace(std::ostream& os);
+  void WriteCloseNamespace(std::ostream& os);
+
+  PeepholeActionAndData LookupActionAndData(Bytecode last, Bytecode current);
+  void BuildRow(Bytecode last, Row* row);
+  size_t HashRow(const Row* row);
+  void InsertRow(size_t row_index, const Row* const row, size_t row_hash,
+                 std::map<size_t, size_t>* hash_to_row_map);
+  bool RowsEqual(const Row* const first, const Row* const second);
+
+  std::vector<Row>* table() { return &table_; }
+
+  // Table of unique rows.
+  std::vector<Row> table_;
+
+  // Mapping of row index to unique row index.
+  std::array<size_t, kNumberOfBytecodes> row_map_;
+};
+
+const char* PeepholeActionTableWriter::kIndent = "  ";
+const char* PeepholeActionTableWriter::kNamespaceElements[] = {"v8", "internal",
+                                                               "interpreter"};
+
+// static
+PeepholeActionAndData PeepholeActionTableWriter::LookupActionAndData(
+    Bytecode last, Bytecode current) {
+  // Optimize various accumulator loads followed by store accumulator
+  // to an equivalent register load and loading the accumulator with
+  // the register. The latter accumulator load can often be elided as
+  // it is side-effect free and often followed by another accumulator
+  // load so can be elided.
+  if (current == Bytecode::kStar) {
+    switch (last) {
+      case Bytecode::kLdaNamedProperty:
+        return {PeepholeAction::kTransformLdaStarToLdrLdarAction,
+                Bytecode::kLdrNamedProperty};
+      case Bytecode::kLdaKeyedProperty:
+        return {PeepholeAction::kTransformLdaStarToLdrLdarAction,
+                Bytecode::kLdrKeyedProperty};
+      case Bytecode::kLdaGlobal:
+        return {PeepholeAction::kTransformLdaStarToLdrLdarAction,
+                Bytecode::kLdrGlobal};
+      case Bytecode::kLdaContextSlot:
+        return {PeepholeAction::kTransformLdaStarToLdrLdarAction,
+                Bytecode::kLdrContextSlot};
+      case Bytecode::kLdaUndefined:
+        return {PeepholeAction::kTransformLdaStarToLdrLdarAction,
+                Bytecode::kLdrUndefined};
+      default:
+        break;
+    }
+  }
+
+  // ToName optimizations: remove unnecessary ToName bytecodes.
+  if (current == Bytecode::kToName) {
+    if (last == Bytecode::kLdaConstant) {
+      return {PeepholeAction::kElideCurrentIfLoadingNameConstantAction,
+              Bytecode::kIllegal};
+    } else if (Bytecodes::PutsNameInAccumulator(last)) {
+      return {PeepholeAction::kElideCurrentAction, Bytecode::kIllegal};
+    }
+  }
+
+  // Nop are placeholders for holding source position information and can be
+  // elided if there is no source information.
+  if (last == Bytecode::kNop) {
+    if (Bytecodes::IsJump(current)) {
+      return {PeepholeAction::kElideLastBeforeJumpAction, Bytecode::kIllegal};
+    } else {
+      return {PeepholeAction::kElideLastAction, Bytecode::kIllegal};
+    }
+  }
+
+  // The accumulator is invisible to the debugger. If there is a sequence
+  // of consecutive accumulator loads (that don't have side effects) then
+  // only the final load is potentially visible.
+  if (Bytecodes::IsAccumulatorLoadWithoutEffects(last) &&
+      Bytecodes::IsAccumulatorLoadWithoutEffects(current)) {
+    return {PeepholeAction::kElideLastAction, Bytecode::kIllegal};
+  }
+
+  // The current instruction clobbers the accumulator without reading
+  // it. The load in the last instruction can be elided as it has no
+  // effect.
+  if (Bytecodes::IsAccumulatorLoadWithoutEffects(last) &&
+      Bytecodes::GetAccumulatorUse(current) == AccumulatorUse::kWrite) {
+    return {PeepholeAction::kElideLastAction, Bytecode::kIllegal};
+  }
+
+  // Ldar and Star make the accumulator and register hold equivalent
+  // values. Only the first bytecode is needed if there's a sequence
+  // of back-to-back Ldar and Star bytecodes with the same operand.
+  if (Bytecodes::IsLdarOrStar(last) && Bytecodes::IsLdarOrStar(current)) {
+    return {PeepholeAction::kElideCurrentIfOperand0MatchesAction,
+            Bytecode::kIllegal};
+  }
+
+  // Remove ToBoolean coercion from conditional jumps where possible.
+  if (Bytecodes::WritesBooleanToAccumulator(last)) {
+    if (Bytecodes::IsJumpIfToBoolean(current)) {
+      return {PeepholeAction::kChangeJumpBytecodeAction,
+              Bytecodes::GetJumpWithoutToBoolean(current)};
+    } else if (current == Bytecode::kToBooleanLogicalNot) {
+      return {PeepholeAction::kChangeBytecodeAction, Bytecode::kLogicalNot};
+    }
+  }
+
+  // Fuse LdaSmi followed by binary op to produce binary op with a
+  // zero immediate argument. This saves dispatches, but not size.

[rmcilroy, 2016/07/13 13:51:41]

second half of this comment is wrong (related to LdaZero I think).

[oth, 2016/07/15 13:09:40]

Done.

[rmcilroy, 2016/07/15 15:31:48]

Still there?

[oth, 2016/07/15 17:27:26]

Done.

+  if (last == Bytecode::kLdaSmi) {
+    switch (current) {
+      case Bytecode::kAdd:
+        return {PeepholeAction::kTransformLdaSmiBinaryOpToBinaryOpWithSmiAction,
+                Bytecode::kAddSmi};
+      case Bytecode::kSub:
+        return {PeepholeAction::kTransformLdaSmiBinaryOpToBinaryOpWithSmiAction,
+                Bytecode::kSubSmi};
+      case Bytecode::kBitwiseAnd:
+        return {PeepholeAction::kTransformLdaSmiBinaryOpToBinaryOpWithSmiAction,
+                Bytecode::kBitwiseAndSmi};
+      case Bytecode::kBitwiseOr:
+        return {PeepholeAction::kTransformLdaSmiBinaryOpToBinaryOpWithSmiAction,
+                Bytecode::kBitwiseOrSmi};
+      case Bytecode::kShiftLeft:
+        return {PeepholeAction::kTransformLdaSmiBinaryOpToBinaryOpWithSmiAction,
+                Bytecode::kShiftLeftSmi};
+      case Bytecode::kShiftRight:
+        return {PeepholeAction::kTransformLdaSmiBinaryOpToBinaryOpWithSmiAction,
+                Bytecode::kShiftRightSmi};
+      default:
+        break;
+    }
+  }
+
+  // Fuse LdaZero followed by binary op to produce binary op with a
+  // zero immediate argument. This saves dispatches, but not size.
+  if (last == Bytecode::kLdaZero) {
+    switch (current) {
+      case Bytecode::kAdd:
+        return {
+            PeepholeAction::kTransformLdaZeroBinaryOpToBinaryOpWithZeroAction,
+            Bytecode::kAddSmi};
+      case Bytecode::kSub:
+        return {
+            PeepholeAction::kTransformLdaZeroBinaryOpToBinaryOpWithZeroAction,
+            Bytecode::kSubSmi};
+      case Bytecode::kBitwiseAnd:
+        return {
+            PeepholeAction::kTransformLdaZeroBinaryOpToBinaryOpWithZeroAction,
+            Bytecode::kBitwiseAndSmi};
+      case Bytecode::kBitwiseOr:
+        return {
+            PeepholeAction::kTransformLdaZeroBinaryOpToBinaryOpWithZeroAction,
+            Bytecode::kBitwiseOrSmi};
+      case Bytecode::kShiftLeft:
+        return {
+            PeepholeAction::kTransformLdaZeroBinaryOpToBinaryOpWithZeroAction,
+            Bytecode::kShiftLeftSmi};
+      case Bytecode::kShiftRight:
+        return {
+            PeepholeAction::kTransformLdaZeroBinaryOpToBinaryOpWithZeroAction,
+            Bytecode::kShiftRightSmi};
+      default:
+        break;
+    }
+  }
+
+  // If there is no last bytecode to optimize against, store the incoming
+  // bytecode or for jumps emit incoming bytecode immediately.
+  if (last == Bytecode::kIllegal) {
+    if (Bytecodes::IsJump(current)) {
+      return {PeepholeAction::kUpdateLastJumpAction, Bytecode::kIllegal};
+    } else {
+      return {PeepholeAction::kUpdateLastAction, Bytecode::kIllegal};
+    }
+  }
+
+  // No matches, take the default action.
+  if (Bytecodes::IsJump(current)) {
+    return {PeepholeAction::kDefaultJumpAction, Bytecode::kIllegal};
+  } else {
+    return {PeepholeAction::kDefaultAction, Bytecode::kIllegal};
+  }
+}
+
+void PeepholeActionTableWriter::Write(std::ostream& os) {
+  WriteHeader(os);
+  WriteIncludeFiles(os);
+  WriteOpenNamespace(os);
+  WriteUniqueRows(os);
+  WriteRowMap(os);
+  WriteClassMethods(os);
+  WriteCloseNamespace(os);
+}
+
+void PeepholeActionTableWriter::WriteHeader(std::ostream& os) {
+  os << "// Copyright 2016 the V8 project authors. All rights reserved.\n"
+     << "// Use of this source code is governed by a BSD-style license that\n"
+     << "// can be found in the LICENSE file.\n\n"
+     << "// Autogenerated by " __FILE__ ". Do not edit.\n\n";
+}
+
+void PeepholeActionTableWriter::WriteIncludeFiles(std::ostream& os) {
+  os << "#include \"src/interpreter/bytecode-peephole-table.h\"\n\n";
+}
+
+void PeepholeActionTableWriter::WriteUniqueRows(std::ostream& os) {
+  os << "const PeepholeActionAndData PeepholeActionTable::row_data_["
+     << table_.size() << "][" << kNumberOfBytecodes << "] = {\n";
+  for (size_t i = 0; i < table_.size(); ++i) {
+    os << "{\n";
+    WriteRow(os, i);
+    os << "},\n";
+  }
+  os << "};\n\n";
+}
+
+void PeepholeActionTableWriter::WriteRowMap(std::ostream& os) {
+  os << "const PeepholeActionAndData* const PeepholeActionTable::row_["
+     << kNumberOfBytecodes << "] = {\n";
+  for (size_t i = 0; i < kNumberOfBytecodes; ++i) {
+    os << kIndent << " PeepholeActionTable::row_data_[" << row_map_[i]
+       << "], \n";
+  }
+  os << "};\n\n";
+}
+
+void PeepholeActionTableWriter::WriteRow(std::ostream& os, size_t row_index) {
+  const Row row = table_.at(row_index);
+  for (PeepholeActionAndData action_data : row) {
+    os << kIndent << "{" << ActionName(action_data.action) << ","
+       << BytecodeName(action_data.bytecode) << "},\n";
+  }
+}
+
+void PeepholeActionTableWriter::WriteOpenNamespace(std::ostream& os) {
+  for (auto element : kNamespaceElements) {
+    os << "namespace " << element << " {\n";
+  }
+  os << "\n";
+}
+
+void PeepholeActionTableWriter::WriteCloseNamespace(std::ostream& os) {
+  for (auto element : kNamespaceElements) {
+    os << "}  // namespace " << element << "\n";
+  }
+}
+
+void PeepholeActionTableWriter::WriteClassMethods(std::ostream& os) {
+  os << "// static\n"
+     << "const PeepholeActionAndData*\n"
+     << "PeepholeActionTable::Lookup(Bytecode last, Bytecode current) {\n"
+     << kIndent
+     << "return &row_[Bytecodes::ToByte(last)][Bytecodes::ToByte(current)];\n"
+     << "}\n\n";
+}
+
+void PeepholeActionTableWriter::BuildTable() {
+  std::map<size_t, size_t> hash_to_row_map;
+  Row row;
+  for (size_t i = 0; i < kNumberOfBytecodes; ++i) {
+    uint8_t byte_value = static_cast<uint8_t>(i);
+    Bytecode last = Bytecodes::FromByte(byte_value);
+    BuildRow(last, &row);
+    size_t row_hash = HashRow(&row);
+    InsertRow(i, &row, row_hash, &hash_to_row_map);
+  }
+}
+
+void PeepholeActionTableWriter::BuildRow(Bytecode last, Row* row) {
+  for (size_t i = 0; i < kNumberOfBytecodes; ++i) {
+    uint8_t byte_value = static_cast<uint8_t>(i);
+    Bytecode current = Bytecodes::FromByte(byte_value);
+    PeepholeActionAndData action_data = LookupActionAndData(last, current);
+    row->at(i) = action_data;
+  }
+}
+
+// static
+bool PeepholeActionTableWriter::RowsEqual(const Row* const first,
+                                          const Row* const second) {
+  return memcmp(first, second, sizeof(*first)) == 0;
+}
+
+// static
+void PeepholeActionTableWriter::InsertRow(
+    size_t row_index, const Row* const row, size_t row_hash,
+    std::map<size_t, size_t>* hash_to_row_map) {
+  // Insert row if no existing row matches, otherwise use existing row.
+  auto iter = hash_to_row_map->find(row_hash);
+  if (iter == hash_to_row_map->end()) {
+    row_map_[row_index] = table()->size();
+    hash_to_row_map->insert({row_hash, table()->size()});
+    table()->push_back(*row);
+  } else {
+    row_map_[row_index] = iter->second;
+    DCHECK(RowsEqual(&table()->at(iter->second), row));

[rmcilroy, 2016/07/13 13:51:41]

Could we have this be part of the check instead of being a DCHECK (e.g.,:
if (iter != hash_to_row_map->end() && RowsEqual(&table()->at(iter->second),
row)) {
  ...

[oth, 2016/07/15 13:09:40]

Added the comment above DCHECK to clarify as we discussed that changing the
check could allow de-duping to silently fail.

The hashing was more useful when this wasn't standalone. Considering removing
it.

[rmcilroy, 2016/07/15 15:31:49]

Can't see the comment, did you forget to add the changes to file to the commit?

[oth, 2016/07/15 17:27:26]

Done.

+  }
+}
+
+// static
+size_t PeepholeActionTableWriter::HashRow(const Row* row) {
+  static const size_t kHashShift = 3;
+  std::size_t result = (1u << 31) - 1u;
+  const uint8_t* raw_data = reinterpret_cast<const uint8_t*>(row);
+  for (size_t i = 0; i < sizeof(*row); ++i) {
+    size_t top_bits = result >> (kBitsPerByte * sizeof(size_t) - kHashShift);
+    result = (result << kHashShift) ^ top_bits ^ raw_data[i];
+  }
+  return result;
+}
+
+}  // namespace interpreter
+}  // namespace internal
+}  // namespace v8
+
+int main(int argc, const char* argv[]) {
+  CHECK_EQ(argc, 2);
+
+  std::ofstream ofs(argv[1], std::ofstream::trunc);
+  v8::internal::interpreter::PeepholeActionTableWriter writer;
+  writer.BuildTable();
+  writer.Write(ofs);
+  ofs.flush();
+  ofs.close();
+
+  return 0;
+}