1 files changed, 628 insertions, 0 deletions
diff --git a/contrib/llvm/lib/DebugInfo/DWARFDebugLine.cpp b/contrib/llvm/lib/DebugInfo/DWARFDebugLine.cpp
new file mode 100644
index 0000000..192381c
--- /dev/null
+++ b/contrib/llvm/lib/DebugInfo/DWARFDebugLine.cpp
@@ -0,0 +1,628 @@
+//===-- DWARFDebugLine.cpp ------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "DWARFDebugLine.h"
+#include "llvm/Support/Dwarf.h"
+#include "llvm/Support/Format.h"
+#include "llvm/Support/Path.h"
+#include "llvm/Support/raw_ostream.h"
+#include <algorithm>
+using namespace llvm;
+using namespace dwarf;
+
+void DWARFDebugLine::Prologue::dump(raw_ostream &OS) const {
+  OS << "Line table prologue:\n"
+     << format("   total_length: 0x%8.8x\n", TotalLength)
+     << format("        version: %u\n", Version)
+     << format("prologue_length: 0x%8.8x\n", PrologueLength)
+     << format("min_inst_length: %u\n", MinInstLength)
+     << format("default_is_stmt: %u\n", DefaultIsStmt)
+     << format("      line_base: %i\n", LineBase)
+     << format("     line_range: %u\n", LineRange)
+     << format("    opcode_base: %u\n", OpcodeBase);
+
+  for (uint32_t i = 0; i < StandardOpcodeLengths.size(); ++i)
+    OS << format("standard_opcode_lengths[%s] = %u\n", LNStandardString(i+1),
+                 StandardOpcodeLengths[i]);
+
+  if (!IncludeDirectories.empty())
+    for (uint32_t i = 0; i < IncludeDirectories.size(); ++i)
+      OS << format("include_directories[%3u] = '", i+1)
+         << IncludeDirectories[i] << "'\n";
+
+  if (!FileNames.empty()) {
+    OS << "                Dir  Mod Time   File Len   File Name\n"
+       << "                ---- ---------- ---------- -----------"
+          "----------------\n";
+    for (uint32_t i = 0; i < FileNames.size(); ++i) {
+      const FileNameEntry& fileEntry = FileNames[i];
+      OS << format("file_names[%3u] %4" PRIu64 " ", i+1, fileEntry.DirIdx)
+         << format("0x%8.8" PRIx64 " 0x%8.8" PRIx64 " ",
+                   fileEntry.ModTime, fileEntry.Length)
+         << fileEntry.Name << '\n';
+    }
+  }
+}
+
+void DWARFDebugLine::Row::postAppend() {
+  BasicBlock = false;
+  PrologueEnd = false;
+  EpilogueBegin = false;
+}
+
+void DWARFDebugLine::Row::reset(bool default_is_stmt) {
+  Address = 0;
+  Line = 1;
+  Column = 0;
+  File = 1;
+  Isa = 0;
+  IsStmt = default_is_stmt;
+  BasicBlock = false;
+  EndSequence = false;
+  PrologueEnd = false;
+  EpilogueBegin = false;
+}
+
+void DWARFDebugLine::Row::dump(raw_ostream &OS) const {
+  OS << format("0x%16.16" PRIx64 " %6u %6u", Address, Line, Column)
+     << format(" %6u %3u ", File, Isa)
+     << (IsStmt ? " is_stmt" : "")
+     << (BasicBlock ? " basic_block" : "")
+     << (PrologueEnd ? " prologue_end" : "")
+     << (EpilogueBegin ? " epilogue_begin" : "")
+     << (EndSequence ? " end_sequence" : "")
+     << '\n';
+}
+
+void DWARFDebugLine::LineTable::dump(raw_ostream &OS) const {
+  Prologue.dump(OS);
+  OS << '\n';
+
+  if (!Rows.empty()) {
+    OS << "Address            Line   Column File   ISA Flags\n"
+       << "------------------ ------ ------ ------ --- -------------\n";
+    for (std::vector<Row>::const_iterator pos = Rows.begin(),
+         end = Rows.end(); pos != end; ++pos)
+      pos->dump(OS);
+  }
+}
+
+DWARFDebugLine::State::~State() {}
+
+void DWARFDebugLine::State::appendRowToMatrix(uint32_t offset) {
+  if (Sequence::Empty) {
+    // Record the beginning of instruction sequence.
+    Sequence::Empty = false;
+    Sequence::LowPC = Address;
+    Sequence::FirstRowIndex = row;
+  }
+  ++row;  // Increase the row number.
+  LineTable::appendRow(*this);
+  if (EndSequence) {
+    // Record the end of instruction sequence.
+    Sequence::HighPC = Address;
+    Sequence::LastRowIndex = row;
+    if (Sequence::isValid())
+      LineTable::appendSequence(*this);
+    Sequence::reset();
+  }
+  Row::postAppend();
+}
+
+void DWARFDebugLine::State::finalize() {
+  row = DoneParsingLineTable;
+  if (!Sequence::Empty) {
+    fprintf(stderr, "warning: last sequence in debug line table is not"
+                    "terminated!\n");
+  }
+  // Sort all sequences so that address lookup will work faster.
+  if (!Sequences.empty()) {
+    std::sort(Sequences.begin(), Sequences.end(), Sequence::orderByLowPC);
+    // Note: actually, instruction address ranges of sequences should not
+    // overlap (in shared objects and executables). If they do, the address
+    // lookup would still work, though, but result would be ambiguous.
+    // We don't report warning in this case. For example,
+    // sometimes .so compiled from multiple object files contains a few
+    // rudimentary sequences for address ranges [0x0, 0xsomething).
+  }
+}
+
+DWARFDebugLine::DumpingState::~DumpingState() {}
+
+void DWARFDebugLine::DumpingState::finalize() {
+  LineTable::dump(OS);
+}
+
+const DWARFDebugLine::LineTable *
+DWARFDebugLine::getLineTable(uint32_t offset) const {
+  LineTableConstIter pos = LineTableMap.find(offset);
+  if (pos != LineTableMap.end())
+    return &pos->second;
+  return 0;
+}
+
+const DWARFDebugLine::LineTable *
+DWARFDebugLine::getOrParseLineTable(DataExtractor debug_line_data,
+                                    uint32_t offset) {
+  std::pair<LineTableIter, bool> pos =
+    LineTableMap.insert(LineTableMapTy::value_type(offset, LineTable()));
+  if (pos.second) {
+    // Parse and cache the line table for at this offset.
+    State state;
+    if (!parseStatementTable(debug_line_data, RelocMap, &offset, state))
+      return 0;
+    pos.first->second = state;
+  }
+  return &pos.first->second;
+}
+
+bool
+DWARFDebugLine::parsePrologue(DataExtractor debug_line_data,
+                              uint32_t *offset_ptr, Prologue *prologue) {
+  const uint32_t prologue_offset = *offset_ptr;
+
+  prologue->clear();
+  prologue->TotalLength = debug_line_data.getU32(offset_ptr);
+  prologue->Version = debug_line_data.getU16(offset_ptr);
+  if (prologue->Version != 2)
+    return false;
+
+  prologue->PrologueLength = debug_line_data.getU32(offset_ptr);
+  const uint32_t end_prologue_offset = prologue->PrologueLength + *offset_ptr;
+  prologue->MinInstLength = debug_line_data.getU8(offset_ptr);
+  prologue->DefaultIsStmt = debug_line_data.getU8(offset_ptr);
+  prologue->LineBase = debug_line_data.getU8(offset_ptr);
+  prologue->LineRange = debug_line_data.getU8(offset_ptr);
+  prologue->OpcodeBase = debug_line_data.getU8(offset_ptr);
+
+  prologue->StandardOpcodeLengths.reserve(prologue->OpcodeBase-1);
+  for (uint32_t i = 1; i < prologue->OpcodeBase; ++i) {
+    uint8_t op_len = debug_line_data.getU8(offset_ptr);
+    prologue->StandardOpcodeLengths.push_back(op_len);
+  }
+
+  while (*offset_ptr < end_prologue_offset) {
+    const char *s = debug_line_data.getCStr(offset_ptr);
+    if (s && s[0])
+      prologue->IncludeDirectories.push_back(s);
+    else
+      break;
+  }
+
+  while (*offset_ptr < end_prologue_offset) {
+    const char *name = debug_line_data.getCStr(offset_ptr);
+    if (name && name[0]) {
+      FileNameEntry fileEntry;
+      fileEntry.Name = name;
+      fileEntry.DirIdx = debug_line_data.getULEB128(offset_ptr);
+      fileEntry.ModTime = debug_line_data.getULEB128(offset_ptr);
+      fileEntry.Length = debug_line_data.getULEB128(offset_ptr);
+      prologue->FileNames.push_back(fileEntry);
+    } else {
+      break;
+    }
+  }
+
+  if (*offset_ptr != end_prologue_offset) {
+    fprintf(stderr, "warning: parsing line table prologue at 0x%8.8x should"
+                    " have ended at 0x%8.8x but it ended ad 0x%8.8x\n",
+            prologue_offset, end_prologue_offset, *offset_ptr);
+    return false;
+  }
+  return true;
+}
+
+bool
+DWARFDebugLine::parseStatementTable(DataExtractor debug_line_data, 
+                                    const RelocAddrMap *RMap,
+                                    uint32_t *offset_ptr, State &state) {
+  const uint32_t debug_line_offset = *offset_ptr;
+
+  Prologue *prologue = &state.Prologue;
+
+  if (!parsePrologue(debug_line_data, offset_ptr, prologue)) {
+    // Restore our offset and return false to indicate failure!
+    *offset_ptr = debug_line_offset;
+    return false;
+  }
+
+  const uint32_t end_offset = debug_line_offset + prologue->TotalLength +
+                              sizeof(prologue->TotalLength);
+
+  state.reset();
+
+  while (*offset_ptr < end_offset) {
+    uint8_t opcode = debug_line_data.getU8(offset_ptr);
+
+    if (opcode == 0) {
+      // Extended Opcodes always start with a zero opcode followed by
+      // a uleb128 length so you can skip ones you don't know about
+      uint32_t ext_offset = *offset_ptr;
+      uint64_t len = debug_line_data.getULEB128(offset_ptr);
+      uint32_t arg_size = len - (*offset_ptr - ext_offset);
+
+      uint8_t sub_opcode = debug_line_data.getU8(offset_ptr);
+      switch (sub_opcode) {
+      case DW_LNE_end_sequence:
+        // Set the end_sequence register of the state machine to true and
+        // append a row to the matrix using the current values of the
+        // state-machine registers. Then reset the registers to the initial
+        // values specified above. Every statement program sequence must end
+        // with a DW_LNE_end_sequence instruction which creates a row whose
+        // address is that of the byte after the last target machine instruction
+        // of the sequence.
+        state.EndSequence = true;
+        state.appendRowToMatrix(*offset_ptr);
+        state.reset();
+        break;
+
+      case DW_LNE_set_address:
+        // Takes a single relocatable address as an operand. The size of the
+        // operand is the size appropriate to hold an address on the target
+        // machine. Set the address register to the value given by the
+        // relocatable address. All of the other statement program opcodes
+        // that affect the address register add a delta to it. This instruction
+        // stores a relocatable value into it instead.
+        {
+          // If this address is in our relocation map, apply the relocation.
+          RelocAddrMap::const_iterator AI = RMap->find(*offset_ptr);
+          if (AI != RMap->end()) {
+             const std::pair<uint8_t, int64_t> &R = AI->second;
+             state.Address = debug_line_data.getAddress(offset_ptr) + R.second;
+          } else
+            state.Address = debug_line_data.getAddress(offset_ptr);
+        }
+        break;
+
+      case DW_LNE_define_file:
+        // Takes 4 arguments. The first is a null terminated string containing
+        // a source file name. The second is an unsigned LEB128 number
+        // representing the directory index of the directory in which the file
+        // was found. The third is an unsigned LEB128 number representing the
+        // time of last modification of the file. The fourth is an unsigned
+        // LEB128 number representing the length in bytes of the file. The time
+        // and length fields may contain LEB128(0) if the information is not
+        // available.
+        //
+        // The directory index represents an entry in the include_directories
+        // section of the statement program prologue. The index is LEB128(0)
+        // if the file was found in the current directory of the compilation,
+        // LEB128(1) if it was found in the first directory in the
+        // include_directories section, and so on. The directory index is
+        // ignored for file names that represent full path names.
+        //
+        // The files are numbered, starting at 1, in the order in which they
+        // appear; the names in the prologue come before names defined by
+        // the DW_LNE_define_file instruction. These numbers are used in the
+        // the file register of the state machine.
+        {
+          FileNameEntry fileEntry;
+          fileEntry.Name = debug_line_data.getCStr(offset_ptr);
+          fileEntry.DirIdx = debug_line_data.getULEB128(offset_ptr);
+          fileEntry.ModTime = debug_line_data.getULEB128(offset_ptr);
+          fileEntry.Length = debug_line_data.getULEB128(offset_ptr);
+          prologue->FileNames.push_back(fileEntry);
+        }
+        break;
+
+      default:
+        // Length doesn't include the zero opcode byte or the length itself, but
+        // it does include the sub_opcode, so we have to adjust for that below
+        (*offset_ptr) += arg_size;
+        break;
+      }
+    } else if (opcode < prologue->OpcodeBase) {
+      switch (opcode) {
+      // Standard Opcodes
+      case DW_LNS_copy:
+        // Takes no arguments. Append a row to the matrix using the
+        // current values of the state-machine registers. Then set
+        // the basic_block register to false.
+        state.appendRowToMatrix(*offset_ptr);
+        break;
+
+      case DW_LNS_advance_pc:
+        // Takes a single unsigned LEB128 operand, multiplies it by the
+        // min_inst_length field of the prologue, and adds the
+        // result to the address register of the state machine.
+        state.Address += debug_line_data.getULEB128(offset_ptr) *
+                         prologue->MinInstLength;
+        break;
+
+      case DW_LNS_advance_line:
+        // Takes a single signed LEB128 operand and adds that value to
+        // the line register of the state machine.
+        state.Line += debug_line_data.getSLEB128(offset_ptr);
+        break;
+
+      case DW_LNS_set_file:
+        // Takes a single unsigned LEB128 operand and stores it in the file
+        // register of the state machine.
+        state.File = debug_line_data.getULEB128(offset_ptr);
+        break;
+
+      case DW_LNS_set_column:
+        // Takes a single unsigned LEB128 operand and stores it in the
+        // column register of the state machine.
+        state.Column = debug_line_data.getULEB128(offset_ptr);
+        break;
+
+      case DW_LNS_negate_stmt:
+        // Takes no arguments. Set the is_stmt register of the state
+        // machine to the logical negation of its current value.
+        state.IsStmt = !state.IsStmt;
+        break;
+
+      case DW_LNS_set_basic_block:
+        // Takes no arguments. Set the basic_block register of the
+        // state machine to true
+        state.BasicBlock = true;
+        break;
+
+      case DW_LNS_const_add_pc:
+        // Takes no arguments. Add to the address register of the state
+        // machine the address increment value corresponding to special
+        // opcode 255. The motivation for DW_LNS_const_add_pc is this:
+        // when the statement program needs to advance the address by a
+        // small amount, it can use a single special opcode, which occupies
+        // a single byte. When it needs to advance the address by up to
+        // twice the range of the last special opcode, it can use
+        // DW_LNS_const_add_pc followed by a special opcode, for a total
+        // of two bytes. Only if it needs to advance the address by more
+        // than twice that range will it need to use both DW_LNS_advance_pc
+        // and a special opcode, requiring three or more bytes.
+        {
+          uint8_t adjust_opcode = 255 - prologue->OpcodeBase;
+          uint64_t addr_offset = (adjust_opcode / prologue->LineRange) *
+                                 prologue->MinInstLength;
+          state.Address += addr_offset;
+        }
+        break;
+
+      case DW_LNS_fixed_advance_pc:
+        // Takes a single uhalf operand. Add to the address register of
+        // the state machine the value of the (unencoded) operand. This
+        // is the only extended opcode that takes an argument that is not
+        // a variable length number. The motivation for DW_LNS_fixed_advance_pc
+        // is this: existing assemblers cannot emit DW_LNS_advance_pc or
+        // special opcodes because they cannot encode LEB128 numbers or
+        // judge when the computation of a special opcode overflows and
+        // requires the use of DW_LNS_advance_pc. Such assemblers, however,
+        // can use DW_LNS_fixed_advance_pc instead, sacrificing compression.
+        state.Address += debug_line_data.getU16(offset_ptr);
+        break;
+
+      case DW_LNS_set_prologue_end:
+        // Takes no arguments. Set the prologue_end register of the
+        // state machine to true
+        state.PrologueEnd = true;
+        break;
+
+      case DW_LNS_set_epilogue_begin:
+        // Takes no arguments. Set the basic_block register of the
+        // state machine to true
+        state.EpilogueBegin = true;
+        break;
+
+      case DW_LNS_set_isa:
+        // Takes a single unsigned LEB128 operand and stores it in the
+        // column register of the state machine.
+        state.Isa = debug_line_data.getULEB128(offset_ptr);
+        break;
+
+      default:
+        // Handle any unknown standard opcodes here. We know the lengths
+        // of such opcodes because they are specified in the prologue
+        // as a multiple of LEB128 operands for each opcode.
+        {
+          assert(opcode - 1U < prologue->StandardOpcodeLengths.size());
+          uint8_t opcode_length = prologue->StandardOpcodeLengths[opcode - 1];
+          for (uint8_t i=0; i<opcode_length; ++i)
+            debug_line_data.getULEB128(offset_ptr);
+        }
+        break;
+      }
+    } else {
+      // Special Opcodes
+
+      // A special opcode value is chosen based on the amount that needs
+      // to be added to the line and address registers. The maximum line
+      // increment for a special opcode is the value of the line_base
+      // field in the header, plus the value of the line_range field,
+      // minus 1 (line base + line range - 1). If the desired line
+      // increment is greater than the maximum line increment, a standard
+      // opcode must be used instead of a special opcode. The "address
+      // advance" is calculated by dividing the desired address increment
+      // by the minimum_instruction_length field from the header. The
+      // special opcode is then calculated using the following formula:
+      //
+      //  opcode = (desired line increment - line_base) +
+      //           (line_range * address advance) + opcode_base
+      //
+      // If the resulting opcode is greater than 255, a standard opcode
+      // must be used instead.
+      //
+      // To decode a special opcode, subtract the opcode_base from the
+      // opcode itself to give the adjusted opcode. The amount to
+      // increment the address register is the result of the adjusted
+      // opcode divided by the line_range multiplied by the
+      // minimum_instruction_length field from the header. That is:
+      //
+      //  address increment = (adjusted opcode / line_range) *
+      //                      minimum_instruction_length
+      //
+      // The amount to increment the line register is the line_base plus
+      // the result of the adjusted opcode modulo the line_range. That is:
+      //
+      // line increment = line_base + (adjusted opcode % line_range)
+
+      uint8_t adjust_opcode = opcode - prologue->OpcodeBase;
+      uint64_t addr_offset = (adjust_opcode / prologue->LineRange) *
+                             prologue->MinInstLength;
+      int32_t line_offset = prologue->LineBase +
+                            (adjust_opcode % prologue->LineRange);
+      state.Line += line_offset;
+      state.Address += addr_offset;
+      state.appendRowToMatrix(*offset_ptr);
+    }
+  }
+
+  state.finalize();
+
+  return end_offset;
+}
+
+uint32_t
+DWARFDebugLine::LineTable::lookupAddress(uint64_t address) const {
+  uint32_t unknown_index = UINT32_MAX;
+  if (Sequences.empty())
+    return unknown_index;
+  // First, find an instruction sequence containing the given address.
+  DWARFDebugLine::Sequence sequence;
+  sequence.LowPC = address;
+  SequenceIter first_seq = Sequences.begin();
+  SequenceIter last_seq = Sequences.end();
+  SequenceIter seq_pos = std::lower_bound(first_seq, last_seq, sequence,
+      DWARFDebugLine::Sequence::orderByLowPC);
+  DWARFDebugLine::Sequence found_seq;
+  if (seq_pos == last_seq) {
+    found_seq = Sequences.back();
+  } else if (seq_pos->LowPC == address) {
+    found_seq = *seq_pos;
+  } else {
+    if (seq_pos == first_seq)
+      return unknown_index;
+    found_seq = *(seq_pos - 1);
+  }
+  if (!found_seq.containsPC(address))
+    return unknown_index;
+  // Search for instruction address in the rows describing the sequence.
+  // Rows are stored in a vector, so we may use arithmetical operations with
+  // iterators.
+  DWARFDebugLine::Row row;
+  row.Address = address;
+  RowIter first_row = Rows.begin() + found_seq.FirstRowIndex;
+  RowIter last_row = Rows.begin() + found_seq.LastRowIndex;
+  RowIter row_pos = std::lower_bound(first_row, last_row, row,
+      DWARFDebugLine::Row::orderByAddress);
+  if (row_pos == last_row) {
+    return found_seq.LastRowIndex - 1;
+  }
+  uint32_t index = found_seq.FirstRowIndex + (row_pos - first_row);
+  if (row_pos->Address > address) {
+    if (row_pos == first_row)
+      return unknown_index;
+    else
+      index--;
+  }
+  return index;
+}
+
+bool
+DWARFDebugLine::LineTable::lookupAddressRange(uint64_t address,
+                                       uint64_t size, 
+                                       std::vector<uint32_t>& result) const {
+  if (Sequences.empty())
+    return false;
+  uint64_t end_addr = address + size;
+  // First, find an instruction sequence containing the given address.
+  DWARFDebugLine::Sequence sequence;
+  sequence.LowPC = address;
+  SequenceIter first_seq = Sequences.begin();
+  SequenceIter last_seq = Sequences.end();
+  SequenceIter seq_pos = std::lower_bound(first_seq, last_seq, sequence,
+      DWARFDebugLine::Sequence::orderByLowPC);
+  if (seq_pos == last_seq || seq_pos->LowPC != address) {
+    if (seq_pos == first_seq)
+      return false;
+    seq_pos--;
+  }
+  if (!seq_pos->containsPC(address))
+    return false;
+
+  SequenceIter start_pos = seq_pos;
+
+  // Add the rows from the first sequence to the vector, starting with the
+  // index we just calculated
+
+  while (seq_pos != last_seq && seq_pos->LowPC < end_addr) {
+    DWARFDebugLine::Sequence cur_seq = *seq_pos;
+    uint32_t first_row_index;
+    uint32_t last_row_index;
+    if (seq_pos == start_pos) {
+      // For the first sequence, we need to find which row in the sequence is the
+      // first in our range. Rows are stored in a vector, so we may use
+      // arithmetical operations with iterators.
+      DWARFDebugLine::Row row;
+      row.Address = address;
+      RowIter first_row = Rows.begin() + cur_seq.FirstRowIndex;
+      RowIter last_row = Rows.begin() + cur_seq.LastRowIndex;
+      RowIter row_pos = std::upper_bound(first_row, last_row, row,
+                                         DWARFDebugLine::Row::orderByAddress);
+      // The 'row_pos' iterator references the first row that is greater than
+      // our start address. Unless that's the first row, we want to start at
+      // the row before that.
+      first_row_index = cur_seq.FirstRowIndex + (row_pos - first_row);
+      if (row_pos != first_row)
+        --first_row_index;
+    } else
+      first_row_index = cur_seq.FirstRowIndex;
+
+    // For the last sequence in our range, we need to figure out the last row in
+    // range.  For all other sequences we can go to the end of the sequence.
+    if (cur_seq.HighPC > end_addr) {
+      DWARFDebugLine::Row row;
+      row.Address = end_addr;
+      RowIter first_row = Rows.begin() + cur_seq.FirstRowIndex;
+      RowIter last_row = Rows.begin() + cur_seq.LastRowIndex;
+      RowIter row_pos = std::upper_bound(first_row, last_row, row,
+                                         DWARFDebugLine::Row::orderByAddress);
+      // The 'row_pos' iterator references the first row that is greater than
+      // our end address.  The row before that is the last row we want.
+      last_row_index = cur_seq.FirstRowIndex + (row_pos - first_row) - 1;
+    } else
+      // Contrary to what you might expect, DWARFDebugLine::SequenceLastRowIndex
+      // isn't a valid index within the current sequence.  It's that plus one.
+      last_row_index = cur_seq.LastRowIndex - 1;
+
+    for (uint32_t i = first_row_index; i <= last_row_index; ++i) {
+      result.push_back(i);
+    }
+
+    ++seq_pos;
+  }
+
+  return true;
+}
+
+bool
+DWARFDebugLine::LineTable::getFileNameByIndex(uint64_t FileIndex,
+                                              bool NeedsAbsoluteFilePath,
+                                              std::string &Result) const {
+  if (FileIndex == 0 || FileIndex > Prologue.FileNames.size())
+    return false;
+  const FileNameEntry &Entry = Prologue.FileNames[FileIndex - 1];
+  const char *FileName = Entry.Name;
+  if (!NeedsAbsoluteFilePath ||
+      sys::path::is_absolute(FileName)) {
+    Result = FileName;
+    return true;
+  }
+  SmallString<16> FilePath;
+  uint64_t IncludeDirIndex = Entry.DirIdx;
+  // Be defensive about the contents of Entry.
+  if (IncludeDirIndex > 0 &&
+      IncludeDirIndex <= Prologue.IncludeDirectories.size()) {
+    const char *IncludeDir = Prologue.IncludeDirectories[IncludeDirIndex - 1];
+    sys::path::append(FilePath, IncludeDir);
+  }
+  sys::path::append(FilePath, FileName);
+  Result = FilePath.str();
+  return true;
+}