lib/Analysis/SyntheticCountsUtils.cpp

   1 //===--- SyntheticCountsUtils.cpp - synthetic counts propagation utils ---===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 //
   9 // This file defines utilities for propagating synthetic counts.
  10 //
  11 //===----------------------------------------------------------------------===//
  12
  13 #include "llvm/Analysis/SyntheticCountsUtils.h"
  14 #include "llvm/ADT/DenseSet.h"
  15 #include "llvm/ADT/SCCIterator.h"
  16 #include "llvm/Analysis/CallGraph.h"
  17 #include "llvm/IR/CallSite.h"
  18 #include "llvm/IR/Function.h"
  19 #include "llvm/IR/InstIterator.h"
  20 #include "llvm/IR/Instructions.h"
  21 #include "llvm/IR/ModuleSummaryIndex.h"
  22
  23 using namespace llvm;
  24
  25 // Given an SCC, propagate entry counts along the edge of the SCC nodes.
  26 template <typename CallGraphType>
  27 void SyntheticCountsUtils<CallGraphType>::propagateFromSCC(
  28     const SccTy &SCC, GetProfCountTy GetProfCount, AddCountTy AddCount) {
  29
  30   DenseSet<NodeRef> SCCNodes;
  31   SmallVector<std::pair<NodeRef, EdgeRef>, 8> SCCEdges, NonSCCEdges;
  32
  33   for (auto &Node : SCC)
  34     SCCNodes.insert(Node);
  35
  36   // Partition the edges coming out of the SCC into those whose destination is
  37   // in the SCC and the rest.
  38   for (const auto &Node : SCCNodes) {
  39     for (auto &E : children_edges<CallGraphType>(Node)) {
  40       if (SCCNodes.count(CGT::edge_dest(E)))
  41         SCCEdges.emplace_back(Node, E);
  42       else
  43         NonSCCEdges.emplace_back(Node, E);
  44     }
  45   }
  46
  47   // For nodes in the same SCC, update the counts in two steps:
  48   // 1. Compute the additional count for each node by propagating the counts
  49   // along all incoming edges to the node that originate from within the same
  50   // SCC and summing them up.
  51   // 2. Add the additional counts to the nodes in the SCC.
  52   // This ensures that the order of
  53   // traversal of nodes within the SCC doesn't affect the final result.
  54
  55   DenseMap<NodeRef, Scaled64> AdditionalCounts;
  56   for (auto &E : SCCEdges) {
  57     auto OptProfCount = GetProfCount(E.first, E.second);
  58     if (!OptProfCount)
  59       continue;
  60     auto Callee = CGT::edge_dest(E.second);
  61     AdditionalCounts[Callee] += OptProfCount.getValue();
  62   }
  63
  64   // Update the counts for the nodes in the SCC.
  65   for (auto &Entry : AdditionalCounts)
  66     AddCount(Entry.first, Entry.second);
  67
  68   // Now update the counts for nodes outside the SCC.
  69   for (auto &E : NonSCCEdges) {
  70     auto OptProfCount = GetProfCount(E.first, E.second);
  71     if (!OptProfCount)
  72       continue;
  73     auto Callee = CGT::edge_dest(E.second);
  74     AddCount(Callee, OptProfCount.getValue());
  75   }
  76 }
  77
  78 /// Propgate synthetic entry counts on a callgraph \p CG.
  79 ///
  80 /// This performs a reverse post-order traversal of the callgraph SCC. For each
  81 /// SCC, it first propagates the entry counts to the nodes within the SCC
  82 /// through call edges and updates them in one shot. Then the entry counts are
  83 /// propagated to nodes outside the SCC. This requires \p GraphTraits
  84 /// to have a specialization for \p CallGraphType.
  85
  86 template <typename CallGraphType>
  87 void SyntheticCountsUtils<CallGraphType>::propagate(const CallGraphType &CG,
  88                                                     GetProfCountTy GetProfCount,
  89                                                     AddCountTy AddCount) {
  90   std::vector<SccTy> SCCs;
  91
  92   // Collect all the SCCs.
  93   for (auto I = scc_begin(CG); !I.isAtEnd(); ++I)
  94     SCCs.push_back(*I);
  95
  96   // The callgraph-scc needs to be visited in top-down order for propagation.
  97   // The scc iterator returns the scc in bottom-up order, so reverse the SCCs
  98   // and call propagateFromSCC.
  99   for (auto &SCC : reverse(SCCs))
 100     propagateFromSCC(SCC, GetProfCount, AddCount);
 101 }
 102
 103 template class llvm::SyntheticCountsUtils<const CallGraph *>;
 104 template class llvm::SyntheticCountsUtils<ModuleSummaryIndex *>;