[BOLT][NFCI] Simplify DataAggregator using traces (#143289)

Consistently apply traces as defined in #127125 for branch profile
aggregation. This combines branches and fall-through records into one.

With large input binaries/profiles, the speed up in aggregation time
(`-time-aggr`, wall time):
- perf.data, pre-BOLT input: 154.5528s -> 144.0767s
- pre-aggregated data, pre-BOLT input: 15.1026s -> 9.0711s
- pre-aggregated data, BOLTed input: 15.4871s -> 10.0077s

Test Plan: NFC

Author: aaupov

bolt/include/bolt/Profile/DataAggregator.h

@@ -99,24 +99,28 @@ class DataAggregator : public DataReader {
     uint64_t Addr;
   };
 
+  /// Container for the unit of branch data.
+  /// Backwards compatible with legacy use for branches and fall-throughs:
+  /// - if \p Branch is FT_ONLY or FT_EXTERNAL_ORIGIN, the trace only
+  ///   contains fall-through data,
+  /// - if \p To is BR_ONLY, the trace only contains branch data.
   struct Trace {
+    static constexpr const uint64_t EXTERNAL = 0ULL;
+    static constexpr const uint64_t BR_ONLY = -1ULL;
+    static constexpr const uint64_t FT_ONLY = -1ULL;
+    static constexpr const uint64_t FT_EXTERNAL_ORIGIN = -2ULL;
+
+    uint64_t Branch;
     uint64_t From;
     uint64_t To;
-    Trace(uint64_t From, uint64_t To) : From(From), To(To) {}
-    bool operator==(const Trace &Other) const {
-      return From == Other.From && To == Other.To;
-    }
+    auto tie() const { return std::tie(Branch, From, To); }
+    bool operator==(const Trace &Other) const { return tie() == Other.tie(); }
+    bool operator<(const Trace &Other) const { return tie() < Other.tie(); }
   };
+  friend raw_ostream &operator<<(raw_ostream &OS, const Trace &);
 
   struct TraceHash {
-    size_t operator()(const Trace &L) const {
-      return std::hash<uint64_t>()(L.From << 32 | L.To);
-    }
-  };
-
-  struct FTInfo {
-    uint64_t InternCount{0};
-    uint64_t ExternCount{0};
+    size_t operator()(const Trace &L) const { return hash_combine(L.tie()); }
   };
 
   struct TakenBranchInfo {
@@ -126,8 +130,8 @@ class DataAggregator : public DataReader {
 
   /// Intermediate storage for profile data. We save the results of parsing
   /// and use them later for processing and assigning profile.
-  std::unordered_map<Trace, TakenBranchInfo, TraceHash> BranchLBRs;
-  std::unordered_map<Trace, FTInfo, TraceHash> FallthroughLBRs;
+  std::unordered_map<Trace, TakenBranchInfo, TraceHash> TraceMap;
+  std::vector<std::pair<Trace, TakenBranchInfo>> Traces;
   std::unordered_map<uint64_t, uint64_t> BasicSamples;
   std::vector<PerfMemSample> MemSamples;
 
@@ -200,8 +204,8 @@ class DataAggregator : public DataReader {
   /// Return a vector of offsets corresponding to a trace in a function
   /// if the trace is valid, std::nullopt otherwise.
   std::optional<SmallVector<std::pair<uint64_t, uint64_t>, 16>>
-  getFallthroughsInTrace(BinaryFunction &BF, const LBREntry &First,
-                         const LBREntry &Second, uint64_t Count = 1) const;
+  getFallthroughsInTrace(BinaryFunction &BF, const Trace &Trace,
+                         uint64_t Count) const;
 
   /// Record external entry into the function \p BF.
   ///
@@ -265,8 +269,7 @@ class DataAggregator : public DataReader {
   bool doBranch(uint64_t From, uint64_t To, uint64_t Count, uint64_t Mispreds);
 
   /// Register a trace between two LBR entries supplied in execution order.
-  bool doTrace(const LBREntry &First, const LBREntry &Second,
-               uint64_t Count = 1);
+  bool doTrace(const Trace &Trace, uint64_t Count);
 
   /// Parser helpers
   /// Return false if we exhausted our parser buffer and finished parsing
@@ -516,6 +519,21 @@ inline raw_ostream &operator<<(raw_ostream &OS,
   OS << formatv("{0:x} -> {1:x}/{2}", L.From, L.To, L.Mispred ? 'M' : 'P');
   return OS;
 }
+
+inline raw_ostream &operator<<(raw_ostream &OS,
+                               const DataAggregator::Trace &T) {
+  switch (T.Branch) {
+  case DataAggregator::Trace::FT_ONLY:
+  case DataAggregator::Trace::FT_EXTERNAL_ORIGIN:
+    break;
+  default:
+    OS << Twine::utohexstr(T.Branch) << " -> ";
+  }
+  OS << Twine::utohexstr(T.From);
+  if (T.To != DataAggregator::Trace::BR_ONLY)
+    OS << " ... " << Twine::utohexstr(T.To);
+  return OS;
+}
 } // namespace bolt
 } // namespace llvm