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

src/compiler/bytecode-loop-analysis.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 "src/compiler/bytecode-loop-analysis.h"
+
+#include "src/compiler/bytecode-branch-analysis.h"
+#include "src/interpreter/bytecode-array-iterator.h"
+#include "src/objects-inl.h"
+
+namespace v8 {
+namespace internal {
+namespace compiler {
+
+BytecodeLoopAnalysis::BytecodeLoopAnalysis(
+    Handle<BytecodeArray> bytecode_array,
+    const BytecodeBranchAnalysis* branch_analysis, Zone* zone)
+    : bytecode_array_(bytecode_array),
+      branch_analysis_(branch_analysis),
+      zone_(zone),
+      backedge_to_header_(zone),
+      loop_header_to_parent_(zone) {}
+
+void BytecodeLoopAnalysis::Analyze() {
+  current_loop_offset_ = -1;
+  interpreter::BytecodeArrayIterator iterator(bytecode_array());
+  while (!iterator.done()) {
+    interpreter::Bytecode bytecode = iterator.current_bytecode();
+    int current_offset = iterator.current_offset();
+    if (branch_analysis_->backward_branches_target(current_offset)) {
+      AddLoopEntry(current_offset);
+    } else if (interpreter::Bytecodes::IsJump(bytecode)) {
+      AddBranch(current_offset, iterator.GetJumpTargetOffset());
+    }
+    iterator.Advance();
+  }
+}
+
+void BytecodeLoopAnalysis::AddLoopEntry(int entry_offset) {
+  loop_header_to_parent_[entry_offset] = current_loop_offset_;
+  current_loop_offset_ = entry_offset;
+}
+
+void BytecodeLoopAnalysis::AddBranch(int origin_offset, int target_offset) {
+  // If this is a backedge, record it and update the current loop to the parent.
+  if (target_offset < origin_offset) {
+    backedge_to_header_[origin_offset] = target_offset;
+    // Check that we are finishing the current loop. This assumes that
+    // there is one backedge for each loop.
+    DCHECK_EQ(target_offset, current_loop_offset_);
+    current_loop_offset_ = loop_header_to_parent_[target_offset];
+  }
+}
+
+int BytecodeLoopAnalysis::GetLoopOffsetFor(int offset) const {
+  auto next_backedge = backedge_to_header_.lower_bound(offset);
+  // If there is no next backedge => offset is not in a loop.
+  if (next_backedge == backedge_to_header_.end()) {
+    return -1;
+  }
+  // If the header preceeds the offset, it is the backedge of the containing
+  // loop.
+  if (next_backedge->second <= offset) {
+    return next_backedge->second;
+  }
+  // Otherwise there is a nested loop after this offset. We just return the
+  // parent of the next nested loop.
+  return loop_header_to_parent_.upper_bound(offset)->second;
+}
+
+int BytecodeLoopAnalysis::GetParentLoopFor(int header_offset) const {
+  auto parent = loop_header_to_parent_.find(header_offset);
+  DCHECK(parent != loop_header_to_parent_.end());
+  return parent->second;
+}
+
+}  // namespace compiler
+}  // namespace internal
+}  // namespace v8