Extend CPU profiler with mapping ticks to source lines

src/log.h

Index: src/log.h
diff --git a/src/log.h b/src/log.h
index 51597ddda93a902d3c7ffd73b2974d47ec0706fd..0be085395ed1fa3225ac9e7ec10f505f0d450b93 100644
--- a/src/log.h
+++ b/src/log.h
@@ -149,6 +149,76 @@ class LowLevelLogger;
 class PerfJitLogger;
 class Sampler;
 
+// Mapping from the offset within generated code to source line number.
+class JITLineInfoTable : public Malloced {
+ public:
+  JITLineInfoTable() : pc_offset_infos_(20) {}
+
+  void SetPosition(unsigned int pc_offset, unsigned int src_line) {
+    AddPcOffsetInfo(PcOffsetInfo(pc_offset, src_line));
+  }
+
+  int GetSourceLineNumber(unsigned int pc_offset) const {
+    int length = pc_offset_infos_.length();

[danno, 2014/07/29 09:24:51]

Why not use binary_search/lower_bound here?

+    if (0 == length) return 0;

[alph, 2014/07/29 12:55:56]

nit style: the v8 code doesn't seem to use const at the left in comparisons.

+
+    int low = 0;
+    int high = length - 1;
+
+    if (pc_offset > pc_offset_infos_[high].pc_offset_) {
+      return 0;  // out of range
+    }
+
+    while (low < high) {
+      int mid = (low + high) / 2;
+      const JITLineInfoTable::PcOffsetInfo& elem = pc_offset_infos_[mid];
+      if (elem.pc_offset_ > pc_offset) {
+        high = mid;
+        continue;
+      }
+      if (elem.pc_offset_ < pc_offset) {
+        low = mid + 1;
+        continue;
+      }
+      return elem.line_;  // found the element
+    }
+
+    int line = pc_offset_infos_[high].line_;
+    return line;
+  }
+
+  struct PcOffsetInfo {
+    PcOffsetInfo(unsigned int pc_offset, unsigned int src_line)
+      : pc_offset_(pc_offset), line_(src_line) { }
+
+      unsigned int pc_offset_;
+      unsigned int line_;
+  };
+
+  List<PcOffsetInfo>* entries() { return &pc_offset_infos_; }
+  const List<PcOffsetInfo>* entries() const { return &pc_offset_infos_; }
+
+  JITLineInfoTable& operator=(const JITLineInfoTable& other) {
+    if (this != &other) {
+      const List<PcOffsetInfo>* entries = other.entries();
+      if (entries) {
+        pc_offset_infos_.Clear();
+        pc_offset_infos_.AddAll(*entries);
+      }
+    }
+    return *this;
+  }
+
+ private:
+  void AddPcOffsetInfo(const PcOffsetInfo& pc_offset_info) {
+    pc_offset_infos_.Add(pc_offset_info);

[alph, 2014/07/29 12:55:56]

As long as the algo expects the entries are sorted by pc_offset, could you
please add the corresponding ASSERT here to be on the safe side?

+  }
+
+  // The data reported by code generator.
+  List<PcOffsetInfo> pc_offset_infos_;
+};
+
+
 class Logger {
  public:
   enum StartEnd { START = 0, END = 1 };