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//===--- SyntheticCountsUtils.cpp - synthetic counts propagation utils ---===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This file defines utilities for propagating synthetic counts.
//
//===----------------------------------------------------------------------===//
#include "llvm/Analysis/SyntheticCountsUtils.h"
#include "llvm/ADT/DenseSet.h"
#include "llvm/ADT/SCCIterator.h"
#include "llvm/Analysis/CallGraph.h"
#include "llvm/IR/ModuleSummaryIndex.h"
using namespace llvm;
// Given an SCC, propagate entry counts along the edge of the SCC nodes.
template <typename CallGraphType>
void SyntheticCountsUtils<CallGraphType>::propagateFromSCC(
const SccTy &SCC, GetProfCountTy GetProfCount, AddCountTy AddCount) {
DenseSet<NodeRef> SCCNodes;
SmallVector<std::pair<NodeRef, EdgeRef>, 8> SCCEdges, NonSCCEdges;
for (auto &Node : SCC)
SCCNodes.insert(Node);
// Partition the edges coming out of the SCC into those whose destination is
// in the SCC and the rest.
for (const auto &Node : SCCNodes) {
for (auto &E : children_edges<CallGraphType>(Node)) {
if (SCCNodes.count(CGT::edge_dest(E)))
SCCEdges.emplace_back(Node, E);
else
NonSCCEdges.emplace_back(Node, E);
}
}
// For nodes in the same SCC, update the counts in two steps:
// 1. Compute the additional count for each node by propagating the counts
// along all incoming edges to the node that originate from within the same
// SCC and summing them up.
// 2. Add the additional counts to the nodes in the SCC.
// This ensures that the order of
// traversal of nodes within the SCC doesn't affect the final result.
DenseMap<NodeRef, Scaled64> AdditionalCounts;
for (auto &E : SCCEdges) {
auto OptProfCount = GetProfCount(E.first, E.second);
if (!OptProfCount)
continue;
auto Callee = CGT::edge_dest(E.second);
AdditionalCounts[Callee] += *OptProfCount;
}
// Update the counts for the nodes in the SCC.
for (auto &Entry : AdditionalCounts)
AddCount(Entry.first, Entry.second);
// Now update the counts for nodes outside the SCC.
for (auto &E : NonSCCEdges) {
auto OptProfCount = GetProfCount(E.first, E.second);
if (!OptProfCount)
continue;
auto Callee = CGT::edge_dest(E.second);
AddCount(Callee, *OptProfCount);
}
}
/// Propgate synthetic entry counts on a callgraph \p CG.
///
/// This performs a reverse post-order traversal of the callgraph SCC. For each
/// SCC, it first propagates the entry counts to the nodes within the SCC
/// through call edges and updates them in one shot. Then the entry counts are
/// propagated to nodes outside the SCC. This requires \p GraphTraits
/// to have a specialization for \p CallGraphType.
template <typename CallGraphType>
void SyntheticCountsUtils<CallGraphType>::propagate(const CallGraphType &CG,
GetProfCountTy GetProfCount,
AddCountTy AddCount) {
std::vector<SccTy> SCCs;
// Collect all the SCCs.
for (auto I = scc_begin(CG); !I.isAtEnd(); ++I)
SCCs.push_back(*I);
// The callgraph-scc needs to be visited in top-down order for propagation.
// The scc iterator returns the scc in bottom-up order, so reverse the SCCs
// and call propagateFromSCC.
for (auto &SCC : reverse(SCCs))
propagateFromSCC(SCC, GetProfCount, AddCount);
}
template class llvm::SyntheticCountsUtils<const CallGraph *>;
template class llvm::SyntheticCountsUtils<ModuleSummaryIndex *>;
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