Revert rL349136: [llvm-exegesis] Optimize ToProcess in dbScan

Summary:
Use `vector<char> Added + vector<size_t> ToProcess` to replace `SetVector ToProcess`

We also check `Added[P]` to enqueueing a point more than once, which
also saves us a `ClusterIdForPoint_[Q].isUndef()` check.

Reviewers: courbet, RKSimon, gchatelet, john.brawn, lebedev.ri

Subscribers: tschuett, llvm-commits

Differential Revision: https://reviews.llvm.org/D54442
........
Patch wasn't approved and breaks buildbots

llvm-svn: 349139

1 files changed, 14 insertions, 24 deletions

diff --git a/llvm/tools/llvm-exegesis/lib/Clustering.cpp b/llvm/tools/llvm-exegesis/lib/Clustering.cpp
index 508068ef667..b2cd97c12eb 100644
--- a/llvm/tools/llvm-exegesis/lib/Clustering.cpp
+++ b/llvm/tools/llvm-exegesis/lib/Clustering.cpp
@@ -8,6 +8,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "Clustering.h"
+#include "llvm/ADT/SetVector.h"
 #include "llvm/ADT/SmallVector.h"
 #include <string>
 
@@ -91,14 +92,8 @@ llvm::Error InstructionBenchmarkClustering::validateAndSetup() {
 }
 
 void InstructionBenchmarkClustering::dbScan(const size_t MinPts) {
-  const size_t NumPoints = Points_.size();
-
-  // Persistent buffers to avoid allocs.
-  std::vector<size_t> Neighbors;
-  std::vector<size_t> ToProcess(NumPoints);
-  std::vector<char> Added(NumPoints);
-
-  for (size_t P = 0; P < NumPoints; ++P) {
+  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.
     rangeQuery(P, Neighbors);
@@ -114,18 +109,14 @@ void InstructionBenchmarkClustering::dbScan(const size_t MinPts) {
     Cluster &CurrentCluster = Clusters_.back();
     ClusterIdForPoint_[P] = CurrentCluster.Id; /* Label initial point */
     CurrentCluster.PointIndices.push_back(P);
-    Added[P] = 1;
 
     // Process P's neighbors.
-    size_t Tail = 0;
-    for (size_t Q : Neighbors)
-      if (!Added[Q]) {
-        ToProcess[Tail++] = P;
-        Added[Q] = 1;
-      }
-    for (size_t Head = 0; Head < Tail; ++Head) {
+    llvm::SetVector<size_t, std::deque<size_t>> ToProcess;
+    ToProcess.insert(Neighbors.begin(), Neighbors.end());
+    while (!ToProcess.empty()) {
       // Retrieve a point from the set.
-      size_t Q = ToProcess[Head];
+      const size_t Q = *ToProcess.begin();
+      ToProcess.erase(ToProcess.begin());
 
       if (ClusterIdForPoint_[Q].isNoise()) {
         // Change noise point to border point.
@@ -133,18 +124,17 @@ void InstructionBenchmarkClustering::dbScan(const size_t MinPts) {
         CurrentCluster.PointIndices.push_back(Q);
         continue;
       }
-      assert(ClusterIdForPoint_[Q].isUndef());
+      if (!ClusterIdForPoint_[Q].isUndef()) {
+        continue; // Previously processed.
+      }
       // Add Q to the current custer.
       ClusterIdForPoint_[Q] = CurrentCluster.Id;
       CurrentCluster.PointIndices.push_back(Q);
       // And extend to the neighbors of Q if the region is dense enough.
       rangeQuery(Q, Neighbors);
-      if (Neighbors.size() + 1 >= MinPts)
-        for (size_t P : Neighbors)
-          if (!Added[P]) {
-            ToProcess[Tail++] = P;
-            Added[P] = 1;
-          }
+      if (Neighbors.size() + 1 >= MinPts) {
+        ToProcess.insert(Neighbors.begin(), Neighbors.end());
+      }
     }
   }
   // assert(Neighbors.capacity() == (Points_.size() - 1));