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// 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 "test/cctest/interpreter/source-position-matcher.h"
#include "src/objects-inl.h"
#include "src/objects.h"
namespace v8 {
namespace internal {
namespace interpreter {
// Comparer for PositionTableEntry instances.
struct PositionTableEntryComparer {
bool operator()(const PositionTableEntry& lhs,
const PositionTableEntry& rhs) const {
int lhs_type_score = type_score(lhs);
int rhs_type_score = type_score(rhs);
if (lhs_type_score == rhs_type_score) {
return lhs.source_position < rhs.source_position;
} else {
return lhs_type_score < rhs_type_score;
}
}
int type_score(const PositionTableEntry& entry) const {
return entry.is_statement ? 1 : 0;
}
};
//
// The principles for comparing source positions in bytecode arrays
// are:
//
// 1. The number of statement positions must be the same in both.
//
// 2. Statement positions may be moved provide they do not affect the
// debuggers causal view of the v8 heap and local state. This means
// statement positions may be moved when their initial position is
// on bytecodes that manipulate the accumulator and temporary
// registers.
//
// 3. When duplicate expression positions are present, either may
// be dropped.
//
// 4. Expression positions may be applied to later bytecodes in the
// bytecode array if the current bytecode does not throw.
//
// 5. Expression positions may be dropped when they are applied to
// bytecodes that manipulate local frame state and immediately
// proceeded by another source position.
//
// 6. The relative ordering of source positions must be preserved.
//
bool SourcePositionMatcher::Match(Handle<BytecodeArray> original_bytecode,
Handle<BytecodeArray> optimized_bytecode) {
SourcePositionTableIterator original(
original_bytecode->SourcePositionTable());
SourcePositionTableIterator optimized(
optimized_bytecode->SourcePositionTable());
int last_original_bytecode_offset = 0;
int last_optimized_bytecode_offset = 0;
// Ordered lists of expression positions immediately before the
// latest statements in each bytecode array.
std::vector<PositionTableEntry> original_expression_entries;
std::vector<PositionTableEntry> optimized_expression_entries;
while (true) {
MoveToNextStatement(&original, &original_expression_entries);
MoveToNextStatement(&optimized, &optimized_expression_entries);
if (original.done() && optimized.done()) {
return true;
} else if (original.done()) {
return false;
} else if (optimized.done()) {
return false;
}
if (HasNewExpressionPositionsInOptimized(&original_expression_entries,
&optimized_expression_entries)) {
return false;
}
StripUnneededExpressionPositions(original_bytecode,
&original_expression_entries,
original.code_offset());
StripUnneededExpressionPositions(optimized_bytecode,
&optimized_expression_entries,
optimized.code_offset());
if (!CompareExpressionPositions(&original_expression_entries,
&optimized_expression_entries)) {
// Message logged in CompareExpressionPositions().
return false;
}
// Check original and optimized have matching source positions.
if (original.source_position() != optimized.source_position()) {
return false;
}
if (original.code_offset() < last_original_bytecode_offset) {
return false;
}
last_original_bytecode_offset = original.code_offset();
if (optimized.code_offset() < last_optimized_bytecode_offset) {
return false;
}
last_optimized_bytecode_offset = optimized.code_offset();
// TODO(oth): Can we compare statement positions are semantically
// equivalent? e.g. before a bytecode that has debugger observable
// effects. This is likely non-trivial.
}
return true;
}
bool SourcePositionMatcher::HasNewExpressionPositionsInOptimized(
const std::vector<PositionTableEntry>* const original_positions,
const std::vector<PositionTableEntry>* const optimized_positions) {
std::set<PositionTableEntry, PositionTableEntryComparer> original_set(
original_positions->begin(), original_positions->end());
bool retval = false;
for (auto optimized_position : *optimized_positions) {
if (original_set.find(optimized_position) == original_set.end()) {
retval = true;
}
}
return retval;
}
bool SourcePositionMatcher::CompareExpressionPositions(
const std::vector<PositionTableEntry>* const original_positions,
const std::vector<PositionTableEntry>* const optimized_positions) {
if (original_positions->size() != optimized_positions->size()) {
return false;
}
if (original_positions->size() == 0) {
return true;
}
for (size_t i = 0; i < original_positions->size(); ++i) {
PositionTableEntry original = original_positions->at(i);
PositionTableEntry optimized = original_positions->at(i);
CHECK(original.source_position > 0);
if ((original.is_statement || optimized.is_statement) ||
(original.source_position != optimized.source_position) ||
(original.source_position < 0)) {
return false;
}
}
return true;
}
void SourcePositionMatcher::StripUnneededExpressionPositions(
Handle<BytecodeArray> bytecode_array,
std::vector<PositionTableEntry>* expression_positions,
int next_statement_bytecode_offset) {
size_t j = 0;
for (size_t i = 0; i < expression_positions->size(); ++i) {
CHECK(expression_positions->at(i).source_position > 0 &&
!expression_positions->at(i).is_statement);
int bytecode_end = (i == expression_positions->size() - 1)
? next_statement_bytecode_offset
: expression_positions->at(i + 1).code_offset;
if (ExpressionPositionIsNeeded(bytecode_array,
expression_positions->at(i).code_offset,
bytecode_end)) {
expression_positions->at(j++) = expression_positions->at(i);
}
}
expression_positions->resize(j);
}
void SourcePositionMatcher::AdvanceBytecodeIterator(
BytecodeArrayIterator* iterator, int bytecode_offset) {
while (iterator->current_offset() != bytecode_offset) {
iterator->Advance();
}
}
bool SourcePositionMatcher::ExpressionPositionIsNeeded(
Handle<BytecodeArray> bytecode_array, int start_offset, int end_offset) {
CHECK_GT(end_offset, start_offset);
BytecodeArrayIterator iterator(bytecode_array);
AdvanceBytecodeIterator(&iterator, start_offset);
while (iterator.current_offset() != end_offset) {
if (Bytecodes::IsWithoutExternalSideEffects(iterator.current_bytecode())) {
iterator.Advance();
} else {
// Bytecode could throw so need an expression position.
return true;
}
}
return false;
}
void SourcePositionMatcher::MoveToNextStatement(
SourcePositionTableIterator* iterator,
std::vector<PositionTableEntry>* positions) {
iterator->Advance();
positions->clear();
while (!iterator->done()) {
if (iterator->is_statement()) {
break;
}
positions->push_back({iterator->code_offset(),
iterator->source_position().raw(),
iterator->is_statement()});
iterator->Advance();
}
}
} // namespace interpreter
} // namespace internal
} // namespace v8
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