[PATCH] D54415: [llvm-exegesis] InstructionBenchmarkClustering::rangeQuery(): reserve for the upper bound of Neighbors

[Roman Lebedev via Phabricator via llvm-commits]

lebedev.ri created this revision.
lebedev.ri added reviewers: courbet, MaskRay, RKSimon, gchatelet, john.brawn.
Herald added a subscriber: tschuett.

As it was pointed out in https://reviews.llvm.org/D54388+https://reviews.llvm.org/D54390, the maximal size of `Neighbors` is known,
it will contain at most Points_.size() minus one (the center of the cluster)

While that is the upper bound, meaning in the most cases, the actual count
will be much smaller, since https://reviews.llvm.org/D54390 made the allocation persistent,
we no longer have to worry about overly-optimistically `reserve()`ing.

Old: (https://reviews.llvm.org/D54393)

   Performance counter stats for './bin/llvm-exegesis -mode=analysis -analysis-epsilon=100000 -benchmarks-file=/tmp/benchmarks.yaml -analysis-inconsistencies-output-file=/tmp/clusters.html' (16 runs):
  
         6553.167456      task-clock (msec)         #    1.000 CPUs utilized            ( +-  0.21% )
  ...
              6.5547 +- 0.0134 seconds time elapsed  ( +-  0.20% )

New:

   Performance counter stats for './bin/llvm-exegesis -mode=analysis -analysis-epsilon=100000 -benchmarks-file=/tmp/benchmarks.yaml -analysis-inconsistencies-output-file=/tmp/clusters.html' (16 runs):
  
         6315.057872      task-clock (msec)         #    0.999 CPUs utilized            ( +-  0.24% )
  ...
              6.3187 +- 0.0160 seconds time elapsed  ( +-  0.25% )

And that is another -~4%.


Repository:
  rL LLVM

https://reviews.llvm.org/D54415

Files:
  tools/llvm-exegesis/lib/Clustering.cpp
  tools/llvm-exegesis/lib/Clustering.h


Index: tools/llvm-exegesis/lib/Clustering.h
===================================================================
--- tools/llvm-exegesis/lib/Clustering.h
+++ tools/llvm-exegesis/lib/Clustering.h
@@ -104,7 +104,7 @@
       const std::vector<InstructionBenchmark> &Points, double EpsilonSquared);
   llvm::Error validateAndSetup();
   void dbScan(size_t MinPts);
-  void rangeQuery(size_t Q, llvm::SmallVectorImpl<size_t> &Scratchpad) const;
+  void rangeQuery(size_t Q, std::vector<size_t> &Scratchpad) const;
 
   const std::vector<InstructionBenchmark> &Points_;
   const double EpsilonSquared_;
Index: tools/llvm-exegesis/lib/Clustering.cpp
===================================================================
--- tools/llvm-exegesis/lib/Clustering.cpp
+++ tools/llvm-exegesis/lib/Clustering.cpp
@@ -34,8 +34,9 @@
 // Finds the points at distance less than sqrt(EpsilonSquared) of Q (not
 // including Q).
 void InstructionBenchmarkClustering::rangeQuery(
-    const size_t Q, llvm::SmallVectorImpl<size_t> &Neighbors) const {
+    const size_t Q, std::vector<size_t> &Neighbors) const {
   Neighbors.clear();
+  Neighbors.reserve(Points_.size() - 1); // The Q itself isn't a neighbor.
   const auto &QMeasurements = Points_[Q].Measurements;
   for (size_t P = 0, NumPoints = Points_.size(); P < NumPoints; ++P) {
     if (P == Q)
@@ -91,7 +92,7 @@
 }
 
 void InstructionBenchmarkClustering::dbScan(const size_t MinPts) {
-  llvm::SmallVector<size_t, 0> Neighbors; // Persistent buffer to avoid allocs.
+  std::vector<size_t> Neighbors; // Persistent buffer to avoid allocs.
   for (size_t P = 0, NumPoints = Points_.size(); P < NumPoints; ++P) {
     if (!ClusterIdForPoint_[P].isUndef())
       continue; // Previously processed in inner loop.
@@ -136,6 +137,8 @@
       }
     }
   }
+  // assert(Neighbors.capacity() == (Points_.size() - 1));
+  // ^ True, but it is not quaranteed to be true in all the cases.
 
   // Add noisy points to noise cluster.
   for (size_t P = 0, NumPoints = Points_.size(); P < NumPoints; ++P) {


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