1 //===--- SyntheticCountsUtils.cpp - synthetic counts propagation utils ---===//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This file defines utilities for propagating synthetic counts.
11 //
12 //===----------------------------------------------------------------------===//
13
14 #include "llvm/Analysis/SyntheticCountsUtils.h"
15 #include "llvm/ADT/DenseSet.h"
16 #include "llvm/ADT/SCCIterator.h"
17 #include "llvm/Analysis/CallGraph.h"
18 #include "llvm/IR/CallSite.h"
19 #include "llvm/IR/Function.h"
20 #include "llvm/IR/InstIterator.h"
21 #include "llvm/IR/Instructions.h"
22 #include "llvm/IR/ModuleSummaryIndex.h"
23
24 using namespace llvm;
25
26 // Given an SCC, propagate entry counts along the edge of the SCC nodes.
27 template <typename CallGraphType>
propagateFromSCC(const SccTy & SCC,GetProfCountTy GetProfCount,AddCountTy AddCount)28 void SyntheticCountsUtils<CallGraphType>::propagateFromSCC(
29 const SccTy &SCC, GetProfCountTy GetProfCount, AddCountTy AddCount) {
30
31 DenseSet<NodeRef> SCCNodes;
32 SmallVector<std::pair<NodeRef, EdgeRef>, 8> SCCEdges, NonSCCEdges;
33
34 for (auto &Node : SCC)
35 SCCNodes.insert(Node);
36
37 // Partition the edges coming out of the SCC into those whose destination is
38 // in the SCC and the rest.
39 for (const auto &Node : SCCNodes) {
40 for (auto &E : children_edges<CallGraphType>(Node)) {
41 if (SCCNodes.count(CGT::edge_dest(E)))
42 SCCEdges.emplace_back(Node, E);
43 else
44 NonSCCEdges.emplace_back(Node, E);
45 }
46 }
47
48 // For nodes in the same SCC, update the counts in two steps:
49 // 1. Compute the additional count for each node by propagating the counts
50 // along all incoming edges to the node that originate from within the same
51 // SCC and summing them up.
52 // 2. Add the additional counts to the nodes in the SCC.
53 // This ensures that the order of
54 // traversal of nodes within the SCC doesn't affect the final result.
55
56 DenseMap<NodeRef, Scaled64> AdditionalCounts;
57 for (auto &E : SCCEdges) {
58 auto OptProfCount = GetProfCount(E.first, E.second);
59 if (!OptProfCount)
60 continue;
61 auto Callee = CGT::edge_dest(E.second);
62 AdditionalCounts[Callee] += OptProfCount.getValue();
63 }
64
65 // Update the counts for the nodes in the SCC.
66 for (auto &Entry : AdditionalCounts)
67 AddCount(Entry.first, Entry.second);
68
69 // Now update the counts for nodes outside the SCC.
70 for (auto &E : NonSCCEdges) {
71 auto OptProfCount = GetProfCount(E.first, E.second);
72 if (!OptProfCount)
73 continue;
74 auto Callee = CGT::edge_dest(E.second);
75 AddCount(Callee, OptProfCount.getValue());
76 }
77 }
78
79 /// Propgate synthetic entry counts on a callgraph \p CG.
80 ///
81 /// This performs a reverse post-order traversal of the callgraph SCC. For each
82 /// SCC, it first propagates the entry counts to the nodes within the SCC
83 /// through call edges and updates them in one shot. Then the entry counts are
84 /// propagated to nodes outside the SCC. This requires \p GraphTraits
85 /// to have a specialization for \p CallGraphType.
86
87 template <typename CallGraphType>
propagate(const CallGraphType & CG,GetProfCountTy GetProfCount,AddCountTy AddCount)88 void SyntheticCountsUtils<CallGraphType>::propagate(const CallGraphType &CG,
89 GetProfCountTy GetProfCount,
90 AddCountTy AddCount) {
91 std::vector<SccTy> SCCs;
92
93 // Collect all the SCCs.
94 for (auto I = scc_begin(CG); !I.isAtEnd(); ++I)
95 SCCs.push_back(*I);
96
97 // The callgraph-scc needs to be visited in top-down order for propagation.
98 // The scc iterator returns the scc in bottom-up order, so reverse the SCCs
99 // and call propagateFromSCC.
100 for (auto &SCC : reverse(SCCs))
101 propagateFromSCC(SCC, GetProfCount, AddCount);
102 }
103
104 template class llvm::SyntheticCountsUtils<const CallGraph *>;
105 template class llvm::SyntheticCountsUtils<ModuleSummaryIndex *>;
106