Simplify source position calculation.

src/objects.cc

 // 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.
 
 #include "src/objects.h"
 
 #include <cmath>
 #include <iomanip>
 #include <sstream>
 
@@ skipping 13487 matching lines @@
     }
   }
   Assembler::FlushICache(GetIsolate(), instruction_start(), instruction_size());
 }
 
 // Locate the source position which is closest to the code offset. This is
 // using the source position information embedded in the relocation info.
 // The position returned is relative to the beginning of the script where the
 // source for this function is found.
 int Code::SourcePosition(int code_offset) {
-  Address pc = instruction_start() + code_offset;
-  int distance = kMaxInt;
+  // Subtract one because the current PC is one instruction after the call site.
+  Address pc = instruction_start() + code_offset - 1;
   int position = RelocInfo::kNoPosition;  // Initially no position found.
-  // Run through all the relocation info to find the best matching source
-  // position. All the code needs to be considered as the sequence of the
-  // instructions in the code does not necessarily follow the same order as the
-  // source.
-  RelocIterator it(this, RelocInfo::kPositionMask);
-  while (!it.done()) {
-    // Only look at positions after the current pc.
-    if (it.rinfo()->pc() < pc) {
-      // Get position and distance.
-
-      int dist = static_cast<int>(pc - it.rinfo()->pc());
-      int pos = static_cast<int>(it.rinfo()->data());
-      // If this position is closer than the current candidate or if it has the
-      // same distance as the current candidate and the position is higher then
-      // this position is the new candidate.
-      if ((dist < distance) ||
-          (dist == distance && pos > position)) {
-        position = pos;
-        distance = dist;
-      }
-    }
-    it.next();
+  // Find the closest position attached to a pc lower or equal to the current.
+  // Note that the pc of reloc infos grow monotonically.
+  for (RelocIterator it(this, RelocInfo::kPositionMask);
+       !it.done() && it.rinfo()->pc() <= pc; it.next()) {
+    position = static_cast<int>(it.rinfo()->data());
   }
   DCHECK(kind() == FUNCTION || (is_optimized_code() && is_turbofanned()) ||
          is_wasm_code() || position == RelocInfo::kNoPosition);
   return position;
 }
 
 
 // Same as Code::SourcePosition above except it only looks for statement
 // positions.
 int Code::SourceStatementPosition(int code_offset) {
-  // First find the position as close as possible using all position
-  // information.
+  // First find the closest position.
   int position = SourcePosition(code_offset);
   // Now find the closest statement position before the position.
   int statement_position = 0;
-  RelocIterator it(this, RelocInfo::kPositionMask);
-  while (!it.done()) {
+  for (RelocIterator it(this, RelocInfo::kPositionMask); !it.done();
+       it.next()) {
     if (RelocInfo::IsStatementPosition(it.rinfo()->rmode())) {
       int p = static_cast<int>(it.rinfo()->data());
       if (statement_position < p && p <= position) {
         statement_position = p;
       }
     }
-    it.next();
   }
   return statement_position;
 }
 
 
 SafepointEntry Code::GetSafepointEntry(Address pc) {
   SafepointTable table(this);
   return table.FindEntry(pc);
 }
 
@@ skipping 788 matching lines @@
   for (interpreter::SourcePositionTableIterator iterator(
            source_position_table());
        !iterator.done() && iterator.bytecode_offset() <= offset;
        iterator.Advance()) {
     last_position = iterator.source_position();
   }
   return last_position;
 }
 
 int BytecodeArray::SourceStatementPosition(int offset) {
-  // First find the position as close as possible using all position
-  // information.
+  // First find the closest position.
   int position = SourcePosition(offset);
   // Now find the closest statement position before the position.
   int statement_position = 0;
-  interpreter::SourcePositionTableIterator iterator(source_position_table());
-  while (!iterator.done()) {
-    if (iterator.is_statement()) {
-      int p = iterator.source_position();
+  for (interpreter::SourcePositionTableIterator it(source_position_table());
+       !it.done(); it.Advance()) {
+    if (it.is_statement()) {
+      int p = it.source_position();
       if (statement_position < p && p <= position) {
         statement_position = p;
       }
     }
-    iterator.Advance();
   }
   return statement_position;
 }
 
 void BytecodeArray::Disassemble(std::ostream& os) {
   os << "Parameter count " << parameter_count() << "\n";
   os << "Frame size " << frame_size() << "\n";
 
   const uint8_t* base_address = GetFirstBytecodeAddress();
   interpreter::SourcePositionTableIterator source_positions(
@@ skipping 4466 matching lines @@
   } else {
     // Old-style generators.
     int offset = continuation();
     CHECK(0 <= offset && offset < function()->code()->instruction_size());
     return function()->code()->SourcePosition(offset);
   }
 }
 
 }  // namespace internal
 }  // namespace v8