BalancedPartitioning: minor updates (#77568)

When LargestTraceSize is a power of two, createBPFunctionNodes does not
allocate a group ID for Trace[LargestTraceSize-1] (as N is off by 1).
Fix
this and change floor+log2 to Log2_64.

BalancedPartitioning::bisect can use unstable sort because `Nodes`
contains distinct `InputOrderIndex`s.

BalancedPartitioning::runIterations: use one DenseMap and simplify the
node renumbering code.

Author: MaskRay

llvm/lib/ProfileData/InstrProf.cpp

@@ -921,24 +921,24 @@ std::vector<BPFunctionNode> TemporalProfTraceTy::createBPFunctionNodes(
       if (Timestamp < Trace.FunctionNameRefs.size())
         FunctionIds.insert(Trace.FunctionNameRefs[Timestamp]);
 
-  int N = std::ceil(std::log2(LargestTraceSize));
+  const int N = Log2_64(LargestTraceSize) + 1;
 
   // TODO: We need to use the Trace.Weight field to give more weight to more
   // important utilities
   DenseMap<IDT, SmallVector<UtilityNodeT, 4>> FuncGroups;
   for (size_t TraceIdx = 0; TraceIdx < Traces.size(); TraceIdx++) {
     auto &Trace = Traces[TraceIdx].FunctionNameRefs;
     for (size_t Timestamp = 0; Timestamp < Trace.size(); Timestamp++) {
-      for (int I = std::floor(std::log2(Timestamp + 1)); I < N; I++) {
-        auto &FunctionId = Trace[Timestamp];
+      for (int I = Log2_64(Timestamp + 1); I < N; I++) {
+        auto FunctionId = Trace[Timestamp];
         UtilityNodeT GroupId = TraceIdx * N + I;
         FuncGroups[FunctionId].push_back(GroupId);
       }
     }
   }
 
   std::vector<BPFunctionNode> Nodes;
-  for (auto &Id : FunctionIds) {
+  for (auto Id : FunctionIds) {
     auto &UNs = FuncGroups[Id];
     llvm::sort(UNs);
     UNs.erase(std::unique(UNs.begin(), UNs.end()), UNs.end());

llvm/lib/Support/BalancedPartitioning.cpp

@@ -117,7 +117,7 @@ void BalancedPartitioning::bisect(const FunctionNodeRange Nodes,
   if (NumNodes <= 1 || RecDepth >= Config.SplitDepth) {
     // We've reach the lowest level of the recursion tree. Fall back to the
     // original order and assign to buckets.
-    llvm::stable_sort(Nodes, [](const auto &L, const auto &R) {
+    llvm::sort(Nodes, [](const auto &L, const auto &R) {
       return L.InputOrderIndex < R.InputOrderIndex;
     });
     for (auto &N : Nodes)
@@ -167,26 +167,22 @@ void BalancedPartitioning::runIterations(const FunctionNodeRange Nodes,
                                          unsigned RightBucket,
                                          std::mt19937 &RNG) const {
   unsigned NumNodes = std::distance(Nodes.begin(), Nodes.end());
-  DenseMap<BPFunctionNode::UtilityNodeT, unsigned> UtilityNodeDegree;
+  DenseMap<BPFunctionNode::UtilityNodeT, unsigned> UtilityNodeIndex;
   for (auto &N : Nodes)
     for (auto &UN : N.UtilityNodes)
-      ++UtilityNodeDegree[UN];
+      ++UtilityNodeIndex[UN];
   // Remove utility nodes if they have just one edge or are connected to all
   // functions
   for (auto &N : Nodes)
     llvm::erase_if(N.UtilityNodes, [&](auto &UN) {
-      return UtilityNodeDegree[UN] <= 1 || UtilityNodeDegree[UN] >= NumNodes;
+      return UtilityNodeIndex[UN] == 1 || UtilityNodeIndex[UN] == NumNodes;
     });
 
   // Renumber utility nodes so they can be used to index into Signatures
-  DenseMap<BPFunctionNode::UtilityNodeT, unsigned> UtilityNodeIndex;
-  for (auto &N : Nodes)
-    for (auto &UN : N.UtilityNodes)
-      if (!UtilityNodeIndex.count(UN))
-        UtilityNodeIndex[UN] = UtilityNodeIndex.size();
+  UtilityNodeIndex.clear();
   for (auto &N : Nodes)
     for (auto &UN : N.UtilityNodes)
-      UN = UtilityNodeIndex[UN];
+      UN = UtilityNodeIndex.insert({UN, UtilityNodeIndex.size()}).first->second;
 
   // Initialize signatures
   SignaturesT Signatures(/*Size=*/UtilityNodeIndex.size());

llvm/unittests/ProfileData/BPFunctionNodeTest.cpp

@@ -24,18 +24,25 @@ void PrintTo(const BPFunctionNode &Node, std::ostream *OS) {
 }
 
 TEST(BPFunctionNodeTest, Basic) {
-  auto Nodes = TemporalProfTraceTy::createBPFunctionNodes({
-      TemporalProfTraceTy({0, 1, 2, 3, 4}),
-      TemporalProfTraceTy({4, 2}),
-  });
-
   auto NodeIs = [](BPFunctionNode::IDT Id,
                    ArrayRef<BPFunctionNode::UtilityNodeT> UNs) {
     return AllOf(Field("Id", &BPFunctionNode::Id, Id),
                  Field("UtilityNodes", &BPFunctionNode::UtilityNodes,
                        UnorderedElementsAreArray(UNs)));
   };
 
+  auto Nodes = TemporalProfTraceTy::createBPFunctionNodes({
+      TemporalProfTraceTy({0, 1, 2, 3}),
+  });
+  EXPECT_THAT(Nodes,
+              UnorderedElementsAre(NodeIs(0, {0, 1, 2}), NodeIs(1, {1, 2}),
+                                   NodeIs(2, {1, 2}), NodeIs(3, {2})));
+
+  Nodes = TemporalProfTraceTy::createBPFunctionNodes({
+      TemporalProfTraceTy({0, 1, 2, 3, 4}),
+      TemporalProfTraceTy({4, 2}),
+  });
+
   EXPECT_THAT(Nodes,
               UnorderedElementsAre(NodeIs(0, {0, 1, 2}), NodeIs(1, {1, 2}),
                                    NodeIs(2, {1, 2, 4, 5}), NodeIs(3, {2}),