Refactor synthetic profile count computation. NFC.

Summary:
Instead of using two separate callbacks to return the entry count and the
relative block frequency, use a single callback to return callsite
count. This would allow better supporting hybrid mode in the future as
the count of callsite need not always be derived from entry count (as in
sample PGO).

Reviewers: davidxl

Subscribers: mehdi_amini, steven_wu, dexonsmith, dang, llvm-commits

Differential Revision: https://reviews.llvm.org/D56464

llvm-svn: 350755

3 files changed, 41 insertions, 37 deletions

diff --git a/llvm/lib/Analysis/SyntheticCountsUtils.cpp b/llvm/lib/Analysis/SyntheticCountsUtils.cpp
index 386396bcff3..c2d7bb11a4c 100644
--- a/llvm/lib/Analysis/SyntheticCountsUtils.cpp
+++ b/llvm/lib/Analysis/SyntheticCountsUtils.cpp
@@ -26,8 +26,7 @@ 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, GetRelBBFreqTy GetRelBBFreq, GetCountTy GetCount,
-    AddCountTy AddCount) {
+    const SccTy &SCC, GetProfCountTy GetProfCount, AddCountTy AddCount) {
 
   DenseSet<NodeRef> SCCNodes;
   SmallVector<std::pair<NodeRef, EdgeRef>, 8> SCCEdges, NonSCCEdges;
@@ -54,17 +53,13 @@ void SyntheticCountsUtils<CallGraphType>::propagateFromSCC(
   // This ensures that the order of
   // traversal of nodes within the SCC doesn't affect the final result.
 
-  DenseMap<NodeRef, uint64_t> AdditionalCounts;
+  DenseMap<NodeRef, Scaled64> AdditionalCounts;
   for (auto &E : SCCEdges) {
-    auto OptRelFreq = GetRelBBFreq(E.second);
-    if (!OptRelFreq)
+    auto OptProfCount = GetProfCount(E.first, E.second);
+    if (!OptProfCount)
       continue;
-    Scaled64 RelFreq = OptRelFreq.getValue();
-    auto Caller = E.first;
     auto Callee = CGT::edge_dest(E.second);
-    RelFreq *= Scaled64(GetCount(Caller), 0);
-    uint64_t AdditionalCount = RelFreq.toInt<uint64_t>();
-    AdditionalCounts[Callee] += AdditionalCount;
+    AdditionalCounts[Callee] += OptProfCount.getValue();
   }
 
   // Update the counts for the nodes in the SCC.
@@ -73,14 +68,11 @@ void SyntheticCountsUtils<CallGraphType>::propagateFromSCC(
 
   // Now update the counts for nodes outside the SCC.
   for (auto &E : NonSCCEdges) {
-    auto OptRelFreq = GetRelBBFreq(E.second);
-    if (!OptRelFreq)
+    auto OptProfCount = GetProfCount(E.first, E.second);
+    if (!OptProfCount)
       continue;
-    Scaled64 RelFreq = OptRelFreq.getValue();
-    auto Caller = E.first;
     auto Callee = CGT::edge_dest(E.second);
-    RelFreq *= Scaled64(GetCount(Caller), 0);
-    AddCount(Callee, RelFreq.toInt<uint64_t>());
+    AddCount(Callee, OptProfCount.getValue());
   }
 }
 
@@ -94,8 +86,7 @@ void SyntheticCountsUtils<CallGraphType>::propagateFromSCC(
 
 template <typename CallGraphType>
 void SyntheticCountsUtils<CallGraphType>::propagate(const CallGraphType &CG,
-                                                    GetRelBBFreqTy GetRelBBFreq,
-                                                    GetCountTy GetCount,
+                                                    GetProfCountTy GetProfCount,
                                                     AddCountTy AddCount) {
   std::vector<SccTy> SCCs;
 
@@ -107,7 +98,7 @@ void SyntheticCountsUtils<CallGraphType>::propagate(const CallGraphType &CG,
   // The scc iterator returns the scc in bottom-up order, so reverse the SCCs
   // and call propagateFromSCC.
   for (auto &SCC : reverse(SCCs))
-    propagateFromSCC(SCC, GetRelBBFreq, GetCount, AddCount);
+    propagateFromSCC(SCC, GetProfCount, AddCount);
 }
 
 template class llvm::SyntheticCountsUtils<const CallGraph *>;
diff --git a/llvm/lib/LTO/SummaryBasedOptimizations.cpp b/llvm/lib/LTO/SummaryBasedOptimizations.cpp
index 8b1abb78462..bcdd984daa5 100644
--- a/llvm/lib/LTO/SummaryBasedOptimizations.cpp
+++ b/llvm/lib/LTO/SummaryBasedOptimizations.cpp
@@ -60,21 +60,27 @@ void llvm::computeSyntheticCounts(ModuleSummaryIndex &Index) {
       return UINT64_C(0);
     }
   };
-  auto AddToEntryCount = [](ValueInfo V, uint64_t New) {
+  auto AddToEntryCount = [](ValueInfo V, Scaled64 New) {
     if (!V.getSummaryList().size())
       return;
     for (auto &GVS : V.getSummaryList()) {
       auto S = GVS.get()->getBaseObject();
       auto *F = cast<FunctionSummary>(S);
-      F->setEntryCount(SaturatingAdd(F->entryCount(), New));
+      F->setEntryCount(
+          SaturatingAdd(F->entryCount(), New.template toInt<uint64_t>()));
     }
   };
 
+  auto GetProfileCount = [&](ValueInfo V, FunctionSummary::EdgeTy &Edge) {
+    auto RelFreq = GetCallSiteRelFreq(Edge);
+    Scaled64 EC(GetEntryCount(V), 0);
+    return RelFreq * EC;
+  };
   // After initializing the counts in initializeCounts above, the counts have to
   // be propagated across the combined callgraph.
   // SyntheticCountsUtils::propagate takes care of this propagation on any
   // callgraph that specialized GraphTraits.
-  SyntheticCountsUtils<ModuleSummaryIndex *>::propagate(
-      &Index, GetCallSiteRelFreq, GetEntryCount, AddToEntryCount);
+  SyntheticCountsUtils<ModuleSummaryIndex *>::propagate(&Index, GetProfileCount,
+                                                        AddToEntryCount);
   Index.setHasSyntheticEntryCounts();
 }
diff --git a/llvm/lib/Transforms/IPO/SyntheticCountsPropagation.cpp b/llvm/lib/Transforms/IPO/SyntheticCountsPropagation.cpp
index 64837d4f5d6..ba4efb3ff60 100644
--- a/llvm/lib/Transforms/IPO/SyntheticCountsPropagation.cpp
+++ b/llvm/lib/Transforms/IPO/SyntheticCountsPropagation.cpp
@@ -30,6 +30,7 @@
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/Analysis/BlockFrequencyInfo.h"
 #include "llvm/Analysis/CallGraph.h"
+#include "llvm/Analysis/ProfileSummaryInfo.h"
 #include "llvm/Analysis/SyntheticCountsUtils.h"
 #include "llvm/IR/CallSite.h"
 #include "llvm/IR/Function.h"
@@ -98,13 +99,15 @@ PreservedAnalyses SyntheticCountsPropagation::run(Module &M,
                                                   ModuleAnalysisManager &MAM) {
   FunctionAnalysisManager &FAM =
       MAM.getResult<FunctionAnalysisManagerModuleProxy>(M).getManager();
-  DenseMap<Function *, uint64_t> Counts;
+  DenseMap<Function *, Scaled64> Counts;
   // Set initial entry counts.
-  initializeCounts(M, [&](Function *F, uint64_t Count) { Counts[F] = Count; });
+  initializeCounts(
+      M, [&](Function *F, uint64_t Count) { Counts[F] = Scaled64(Count, 0); });
 
-  // Compute the relative block frequency for a call edge. Use scaled numbers
-  // and not integers since the relative block frequency could be less than 1.
-  auto GetCallSiteRelFreq = [&](const CallGraphNode::CallRecord &Edge) {
+  // Edge includes information about the source. Hence ignore the first
+  // parameter.
+  auto GetCallSiteProfCount = [&](const CallGraphNode *,
+                                  const CallGraphNode::CallRecord &Edge) {
     Optional<Scaled64> Res = None;
     if (!Edge.first)
       return Res;
@@ -112,29 +115,33 @@ PreservedAnalyses SyntheticCountsPropagation::run(Module &M,
     CallSite CS(cast<Instruction>(Edge.first));
     Function *Caller = CS.getCaller();
     auto &BFI = FAM.getResult<BlockFrequencyAnalysis>(*Caller);
+
+    // Now compute the callsite count from relative frequency and
+    // entry count:
     BasicBlock *CSBB = CS.getInstruction()->getParent();
     Scaled64 EntryFreq(BFI.getEntryFreq(), 0);
-    Scaled64 BBFreq(BFI.getBlockFreq(CSBB).getFrequency(), 0);
-    BBFreq /= EntryFreq;
-    return Optional<Scaled64>(BBFreq);
+    Scaled64 BBCount(BFI.getBlockFreq(CSBB).getFrequency(), 0);
+    BBCount /= EntryFreq;
+    BBCount *= Counts[Caller];
+    return Optional<Scaled64>(BBCount);
   };
 
   CallGraph CG(M);
   // Propgate the entry counts on the callgraph.
   SyntheticCountsUtils<const CallGraph *>::propagate(
-      &CG, GetCallSiteRelFreq,
-      [&](const CallGraphNode *N) { return Counts[N->getFunction()]; },
-      [&](const CallGraphNode *N, uint64_t New) {
+      &CG, GetCallSiteProfCount, [&](const CallGraphNode *N, Scaled64 New) {
         auto F = N->getFunction();
         if (!F || F->isDeclaration())
           return;
+
         Counts[F] += New;
       });
 
   // Set the counts as metadata.
-  for (auto Entry : Counts)
-    Entry.first->setEntryCount(
-        ProfileCount(Entry.second, Function::PCT_Synthetic));
+  for (auto Entry : Counts) {
+    Entry.first->setEntryCount(ProfileCount(
+        Entry.second.template toInt<uint64_t>(), Function::PCT_Synthetic));
+  }
 
   return PreservedAnalyses::all();
 }