[thinlto] Basic thinlto fdo heuristic

Summary:
This patch improves thinlto importer
by importing 3x larger functions that are called from hot block.

I compared performance with the trunk on spec, and there
were about 2% on povray and 3.33% on milc. These results seems
to be consistant and match the results Teresa got with her simple
heuristic. Some benchmarks got slower but I think they are just
noisy (mcf, xalancbmki, omnetpp)- running the benchmarks again with
more iterations to confirm. Geomean of all benchmarks including the noisy ones
were about +0.02%.

I see much better improvement on google branch with Easwaran patch
for pgo callsite inlining (the inliner actually inline those big functions)
Over all I see +0.5% improvement, and I get +8.65% on povray.
So I guess we will see much bigger change when Easwaran patch will land
(it depends on new pass manager), but it is still worth putting this to trunk
before it.

Implementation details changes:
- Removed CallsiteCount.
- ProfileCount got replaced by Hotness
- hot-import-multiplier is set to 3.0 for now,
didn't have time to tune it up, but I see that we get most of the interesting
functions with 3, so there is no much performance difference with higher, and
binary size doesn't grow as much as with 10.0.

Reviewers: eraman, mehdi_amini, tejohnson

Subscribers: mehdi_amini, llvm-commits

Differential Revision: https://reviews.llvm.org/D24638

llvm-svn: 282437

5 files changed, 102 insertions, 48 deletions

diff --git a/llvm/lib/Analysis/ModuleSummaryAnalysis.cpp b/llvm/lib/Analysis/ModuleSummaryAnalysis.cpp
index 1a8872adeb8..c736c6aa169 100644
--- a/llvm/lib/Analysis/ModuleSummaryAnalysis.cpp
+++ b/llvm/lib/Analysis/ModuleSummaryAnalysis.cpp
@@ -18,6 +18,7 @@
 #include "llvm/Analysis/BranchProbabilityInfo.h"
 #include "llvm/Analysis/IndirectCallPromotionAnalysis.h"
 #include "llvm/Analysis/LoopInfo.h"
+#include "llvm/Analysis/ProfileSummaryInfo.h"
 #include "llvm/IR/CallSite.h"
 #include "llvm/IR/Dominators.h"
 #include "llvm/IR/InstIterator.h"
@@ -63,8 +64,20 @@ static void findRefEdges(const User *CurUser, DenseSet<const Value *> &RefEdges,
   }
 }
 
+static CalleeInfo::HotnessType getHotness(uint64_t ProfileCount,
+                                          ProfileSummaryInfo *PSI) {
+  if (!PSI)
+    return CalleeInfo::HotnessType::Unknown;
+  if (PSI->isHotCount(ProfileCount))
+    return CalleeInfo::HotnessType::Hot;
+  if (PSI->isColdCount(ProfileCount))
+    return CalleeInfo::HotnessType::Cold;
+  return CalleeInfo::HotnessType::None;
+}
+
 static void computeFunctionSummary(ModuleSummaryIndex &Index, const Module &M,
-                                   const Function &F, BlockFrequencyInfo *BFI) {
+                                   const Function &F, BlockFrequencyInfo *BFI,
+                                   ProfileSummaryInfo *PSI) {
   // Summary not currently supported for anonymous functions, they must
   // be renamed.
   if (!F.hasName())
@@ -97,7 +110,10 @@ static void computeFunctionSummary(ModuleSummaryIndex &Index, const Module &M,
         auto ScaledCount = BFI ? BFI->getBlockProfileCount(&BB) : None;
         auto *CalleeId =
             M.getValueSymbolTable().lookup(CalledFunction->getName());
-        CallGraphEdges[CalleeId] += (ScaledCount ? ScaledCount.getValue() : 0);
+
+        auto Hotness = ScaledCount ? getHotness(ScaledCount.getValue(), PSI)
+                                   : CalleeInfo::HotnessType::Unknown;
+        CallGraphEdges[CalleeId].updateHotness(Hotness);
       } else {
         const auto *CI = dyn_cast<CallInst>(&I);
         // Skip inline assembly calls.
@@ -113,7 +129,8 @@ static void computeFunctionSummary(ModuleSummaryIndex &Index, const Module &M,
             ICallAnalysis.getPromotionCandidatesForInstruction(
                 &I, NumVals, TotalCount, NumCandidates);
         for (auto &Candidate : CandidateProfileData)
-          IndirectCallEdges[Candidate.Value] += Candidate.Count;
+          IndirectCallEdges[Candidate.Value].updateHotness(
+              getHotness(Candidate.Count, PSI));
       }
     }
 
@@ -140,7 +157,8 @@ static void computeVariableSummary(ModuleSummaryIndex &Index,
 
 ModuleSummaryIndex llvm::buildModuleSummaryIndex(
     const Module &M,
-    std::function<BlockFrequencyInfo *(const Function &F)> GetBFICallback) {
+    std::function<BlockFrequencyInfo *(const Function &F)> GetBFICallback,
+    ProfileSummaryInfo *PSI) {
   ModuleSummaryIndex Index;
   // Check if the module can be promoted, otherwise just disable importing from
   // it by not emitting any summary.
@@ -165,7 +183,7 @@ ModuleSummaryIndex llvm::buildModuleSummaryIndex(
       BFI = BFIPtr.get();
     }
 
-    computeFunctionSummary(Index, M, F, BFI);
+    computeFunctionSummary(Index, M, F, BFI, PSI);
   }
 
   // Compute summaries for all variables defined in module, and save in the
@@ -182,10 +200,15 @@ char ModuleSummaryIndexAnalysis::PassID;
 
 ModuleSummaryIndex
 ModuleSummaryIndexAnalysis::run(Module &M, ModuleAnalysisManager &AM) {
+  ProfileSummaryInfo &PSI = AM.getResult<ProfileSummaryAnalysis>(M);
   auto &FAM = AM.getResult<FunctionAnalysisManagerModuleProxy>(M).getManager();
-  return buildModuleSummaryIndex(M, [&FAM](const Function &F) {
-    return &FAM.getResult<BlockFrequencyAnalysis>(*const_cast<Function *>(&F));
-  });
+  return buildModuleSummaryIndex(
+      M,
+      [&FAM](const Function &F) {
+        return &FAM.getResult<BlockFrequencyAnalysis>(
+            *const_cast<Function *>(&F));
+      },
+      &PSI);
 }
 
 char ModuleSummaryIndexWrapperPass::ID = 0;
@@ -205,11 +228,15 @@ ModuleSummaryIndexWrapperPass::ModuleSummaryIndexWrapperPass()
 }
 
 bool ModuleSummaryIndexWrapperPass::runOnModule(Module &M) {
-  Index = buildModuleSummaryIndex(M, [this](const Function &F) {
-    return &(this->getAnalysis<BlockFrequencyInfoWrapperPass>(
-                     *const_cast<Function *>(&F))
-                 .getBFI());
-  });
+  auto &PSI = *getAnalysis<ProfileSummaryInfoWrapperPass>().getPSI(M);
+  Index = buildModuleSummaryIndex(
+      M,
+      [this](const Function &F) {
+        return &(this->getAnalysis<BlockFrequencyInfoWrapperPass>(
+                         *const_cast<Function *>(&F))
+                     .getBFI());
+      },
+      &PSI);
   return false;
 }
 
@@ -221,6 +248,7 @@ bool ModuleSummaryIndexWrapperPass::doFinalization(Module &M) {
 void ModuleSummaryIndexWrapperPass::getAnalysisUsage(AnalysisUsage &AU) const {
   AU.setPreservesAll();
   AU.addRequired<BlockFrequencyInfoWrapperPass>();
+  AU.addRequired<ProfileSummaryInfoWrapperPass>();
 }
 
 bool llvm::moduleCanBeRenamedForThinLTO(const Module &M) {
diff --git a/llvm/lib/Bitcode/Reader/BitcodeReader.cpp b/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
index 49bf8136f4e..101e8eba6b1 100644
--- a/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
+++ b/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
@@ -651,6 +651,9 @@ private:
   std::pair<GlobalValue::GUID, GlobalValue::GUID>
 
   getGUIDFromValueId(unsigned ValueId);
+  std::pair<GlobalValue::GUID, CalleeInfo::HotnessType>
+  readCallGraphEdge(const SmallVector<uint64_t, 64> &Record, unsigned int &I,
+                    bool IsOldProfileFormat, bool HasProfile);
 };
 
 } // end anonymous namespace
@@ -6218,8 +6221,10 @@ std::error_code ModuleSummaryIndexBitcodeReader::parseEntireSummary() {
       return error("Invalid Summary Block: version expected");
   }
   const uint64_t Version = Record[0];
-  if (Version != 1)
-    return error("Invalid summary version " + Twine(Version) + ", 1 expected");
+  const bool IsOldProfileFormat = Version == 1;
+  if (!IsOldProfileFormat && Version != 2)
+    return error("Invalid summary version " + Twine(Version) +
+                 ", 1 or 2 expected");
   Record.clear();
 
   // Keep around the last seen summary to be used when we see an optional
@@ -6264,10 +6269,10 @@ std::error_code ModuleSummaryIndexBitcodeReader::parseEntireSummary() {
     default: // Default behavior: ignore.
       break;
     // FS_PERMODULE: [valueid, flags, instcount, numrefs, numrefs x valueid,
-    //                n x (valueid, callsitecount)]
+    //                n x (valueid)]
     // FS_PERMODULE_PROFILE: [valueid, flags, instcount, numrefs,
     //                        numrefs x valueid,
-    //                        n x (valueid, callsitecount, profilecount)]
+    //                        n x (valueid, hotness)]
     case bitc::FS_PERMODULE:
     case bitc::FS_PERMODULE_PROFILE: {
       unsigned ValueID = Record[0];
@@ -6296,12 +6301,11 @@ std::error_code ModuleSummaryIndexBitcodeReader::parseEntireSummary() {
       bool HasProfile = (BitCode == bitc::FS_PERMODULE_PROFILE);
       for (unsigned I = CallGraphEdgeStartIndex, E = Record.size(); I != E;
            ++I) {
-        unsigned CalleeValueId = Record[I];
-        unsigned CallsiteCount = Record[++I];
-        uint64_t ProfileCount = HasProfile ? Record[++I] : 0;
-        GlobalValue::GUID CalleeGUID = getGUIDFromValueId(CalleeValueId).first;
-        FS->addCallGraphEdge(CalleeGUID,
-                             CalleeInfo(CallsiteCount, ProfileCount));
+        CalleeInfo::HotnessType Hotness;
+        GlobalValue::GUID CalleeGUID;
+        std::tie(CalleeGUID, Hotness) =
+            readCallGraphEdge(Record, I, IsOldProfileFormat, HasProfile);
+        FS->addCallGraphEdge(CalleeGUID, CalleeInfo(Hotness));
       }
       auto GUID = getGUIDFromValueId(ValueID);
       FS->setOriginalName(GUID.second);
@@ -6356,10 +6360,9 @@ std::error_code ModuleSummaryIndexBitcodeReader::parseEntireSummary() {
       break;
     }
     // FS_COMBINED: [valueid, modid, flags, instcount, numrefs,
-    //               numrefs x valueid, n x (valueid, callsitecount)]
+    //               numrefs x valueid, n x (valueid)]
     // FS_COMBINED_PROFILE: [valueid, modid, flags, instcount, numrefs,
-    //                       numrefs x valueid,
-    //                       n x (valueid, callsitecount, profilecount)]
+    //                       numrefs x valueid, n x (valueid, hotness)]
     case bitc::FS_COMBINED:
     case bitc::FS_COMBINED_PROFILE: {
       unsigned ValueID = Record[0];
@@ -6385,12 +6388,11 @@ std::error_code ModuleSummaryIndexBitcodeReader::parseEntireSummary() {
       bool HasProfile = (BitCode == bitc::FS_COMBINED_PROFILE);
       for (unsigned I = CallGraphEdgeStartIndex, E = Record.size(); I != E;
            ++I) {
-        unsigned CalleeValueId = Record[I];
-        unsigned CallsiteCount = Record[++I];
-        uint64_t ProfileCount = HasProfile ? Record[++I] : 0;
-        GlobalValue::GUID CalleeGUID = getGUIDFromValueId(CalleeValueId).first;
-        FS->addCallGraphEdge(CalleeGUID,
-                             CalleeInfo(CallsiteCount, ProfileCount));
+        CalleeInfo::HotnessType Hotness;
+        GlobalValue::GUID CalleeGUID;
+        std::tie(CalleeGUID, Hotness) =
+            readCallGraphEdge(Record, I, IsOldProfileFormat, HasProfile);
+        FS->addCallGraphEdge(CalleeGUID, CalleeInfo(Hotness));
       }
       GlobalValue::GUID GUID = getGUIDFromValueId(ValueID).first;
       TheIndex->addGlobalValueSummary(GUID, std::move(FS));
@@ -6456,6 +6458,23 @@ std::error_code ModuleSummaryIndexBitcodeReader::parseEntireSummary() {
   llvm_unreachable("Exit infinite loop");
 }
 
+std::pair<GlobalValue::GUID, CalleeInfo::HotnessType>
+ModuleSummaryIndexBitcodeReader::readCallGraphEdge(
+    const SmallVector<uint64_t, 64> &Record, unsigned int &I,
+    const bool IsOldProfileFormat, const bool HasProfile) {
+
+  auto Hotness = CalleeInfo::HotnessType::Unknown;
+  unsigned CalleeValueId = Record[I];
+  GlobalValue::GUID CalleeGUID = getGUIDFromValueId(CalleeValueId).first;
+  if (IsOldProfileFormat) {
+    I += 1; // Skip old callsitecount field
+    if (HasProfile)
+      I += 1; // Skip old profilecount field
+  } else if (HasProfile)
+    Hotness = static_cast<CalleeInfo::HotnessType>(Record[++I]);
+  return {CalleeGUID, Hotness};
+}
+
 // Parse the  module string table block into the Index.
 // This populates the ModulePathStringTable map in the index.
 std::error_code ModuleSummaryIndexBitcodeReader::parseModuleStringTable() {
diff --git a/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp b/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
index a353edf7aec..af722723845 100644
--- a/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
+++ b/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
@@ -3293,10 +3293,8 @@ void ModuleBitcodeWriter::writePerModuleFunctionSummaryRecord(
   bool HasProfileData = F.getEntryCount().hasValue();
   for (auto &ECI : Calls) {
     NameVals.push_back(getValueId(ECI.first));
-    assert(ECI.second.CallsiteCount > 0 && "Expected at least one callsite");
-    NameVals.push_back(ECI.second.CallsiteCount);
     if (HasProfileData)
-      NameVals.push_back(ECI.second.ProfileCount);
+      NameVals.push_back(static_cast<uint8_t>(ECI.second.Hotness));
   }
 
   unsigned FSAbbrev = (HasProfileData ? FSCallsProfileAbbrev : FSCallsAbbrev);
@@ -3336,7 +3334,7 @@ void ModuleBitcodeWriter::writeModuleLevelReferences(
 // Current version for the summary.
 // This is bumped whenever we introduce changes in the way some record are
 // interpreted, like flags for instance.
-static const uint64_t INDEX_VERSION = 1;
+static const uint64_t INDEX_VERSION = 2;
 
 /// Emit the per-module summary section alongside the rest of
 /// the module's bitcode.
@@ -3357,7 +3355,7 @@ void ModuleBitcodeWriter::writePerModuleGlobalValueSummary() {
   Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6));   // flags
   Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8));   // instcount
   Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 4));   // numrefs
-  // numrefs x valueid, n x (valueid, callsitecount)
+  // numrefs x valueid, n x (valueid)
   Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Array));
   Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8));
   unsigned FSCallsAbbrev = Stream.EmitAbbrev(Abbv);
@@ -3369,7 +3367,7 @@ void ModuleBitcodeWriter::writePerModuleGlobalValueSummary() {
   Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6));   // flags
   Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8));   // instcount
   Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 4));   // numrefs
-  // numrefs x valueid, n x (valueid, callsitecount, profilecount)
+  // numrefs x valueid, n x (valueid, hotness)
   Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Array));
   Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8));
   unsigned FSCallsProfileAbbrev = Stream.EmitAbbrev(Abbv);
@@ -3442,7 +3440,7 @@ void IndexBitcodeWriter::writeCombinedGlobalValueSummary() {
   Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6));   // flags
   Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8));   // instcount
   Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 4));   // numrefs
-  // numrefs x valueid, n x (valueid, callsitecount)
+  // numrefs x valueid, n x (valueid)
   Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Array));
   Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8));
   unsigned FSCallsAbbrev = Stream.EmitAbbrev(Abbv);
@@ -3455,7 +3453,7 @@ void IndexBitcodeWriter::writeCombinedGlobalValueSummary() {
   Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6));   // flags
   Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8));   // instcount
   Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 4));   // numrefs
-  // numrefs x valueid, n x (valueid, callsitecount, profilecount)
+  // numrefs x valueid, n x (valueid, hotness)
   Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Array));
   Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8));
   unsigned FSCallsProfileAbbrev = Stream.EmitAbbrev(Abbv);
@@ -3542,7 +3540,7 @@ void IndexBitcodeWriter::writeCombinedGlobalValueSummary() {
 
     bool HasProfileData = false;
     for (auto &EI : FS->calls()) {
-      HasProfileData |= EI.second.ProfileCount != 0;
+      HasProfileData |= EI.second.Hotness != CalleeInfo::HotnessType::Unknown;
       if (HasProfileData)
         break;
     }
@@ -3553,10 +3551,8 @@ void IndexBitcodeWriter::writeCombinedGlobalValueSummary() {
       if (!hasValueId(EI.first.getGUID()))
         continue;
       NameVals.push_back(getValueId(EI.first.getGUID()));
-      assert(EI.second.CallsiteCount > 0 && "Expected at least one callsite");
-      NameVals.push_back(EI.second.CallsiteCount);
       if (HasProfileData)
-        NameVals.push_back(EI.second.ProfileCount);
+        NameVals.push_back(static_cast<uint8_t>(EI.second.Hotness));
     }
 
     unsigned FSAbbrev = (HasProfileData ? FSCallsProfileAbbrev : FSCallsAbbrev);
diff --git a/llvm/lib/LTO/ThinLTOCodeGenerator.cpp b/llvm/lib/LTO/ThinLTOCodeGenerator.cpp
index ae646b7347a..f4232dc2f89 100644
--- a/llvm/lib/LTO/ThinLTOCodeGenerator.cpp
+++ b/llvm/lib/LTO/ThinLTOCodeGenerator.cpp
@@ -21,6 +21,7 @@
 #include "llvm/ADT/Statistic.h"
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/Analysis/ModuleSummaryAnalysis.h"
+#include "llvm/Analysis/ProfileSummaryInfo.h"
 #include "llvm/Analysis/TargetLibraryInfo.h"
 #include "llvm/Analysis/TargetTransformInfo.h"
 #include "llvm/Bitcode/BitcodeWriterPass.h"
@@ -377,7 +378,8 @@ ProcessThinLTOModule(Module &TheModule, ModuleSummaryIndex &Index,
     SmallVector<char, 128> OutputBuffer;
     {
       raw_svector_ostream OS(OutputBuffer);
-      auto Index = buildModuleSummaryIndex(TheModule);
+      ProfileSummaryInfo PSI(TheModule);
+      auto Index = buildModuleSummaryIndex(TheModule, nullptr, nullptr);
       WriteBitcodeToFile(&TheModule, OS, true, &Index);
     }
     return make_unique<ObjectMemoryBuffer>(std::move(OutputBuffer));
diff --git a/llvm/lib/Transforms/IPO/FunctionImport.cpp b/llvm/lib/Transforms/IPO/FunctionImport.cpp
index 81d9ca5638d..6c43b780870 100644
--- a/llvm/lib/Transforms/IPO/FunctionImport.cpp
+++ b/llvm/lib/Transforms/IPO/FunctionImport.cpp
@@ -48,6 +48,10 @@ static cl::opt<float>
                       cl::desc("As we import functions, multiply the "
                                "`import-instr-limit` threshold by this factor "
                                "before processing newly imported functions"));
+static cl::opt<float> ImportHotMultiplier(
+    "import-hot-multiplier", cl::init(3.0), cl::Hidden, cl::value_desc("x"),
+    cl::ZeroOrMore, cl::desc("Multiply the `import-instr-limit` threshold for "
+                             "hot callsites"));
 
 static cl::opt<bool> PrintImports("print-imports", cl::init(false), cl::Hidden,
                                   cl::desc("Print imported functions"));
@@ -268,7 +272,7 @@ using EdgeInfo = std::pair<const FunctionSummary *, unsigned /* Threshold */>;
 /// exported from their source module.
 static void computeImportForFunction(
     const FunctionSummary &Summary, const ModuleSummaryIndex &Index,
-    unsigned Threshold, const GVSummaryMapTy &DefinedGVSummaries,
+    const unsigned Threshold, const GVSummaryMapTy &DefinedGVSummaries,
     SmallVectorImpl<EdgeInfo> &Worklist,
     FunctionImporter::ImportMapTy &ImportList,
     StringMap<FunctionImporter::ExportSetTy> *ExportLists = nullptr) {
@@ -281,7 +285,12 @@ static void computeImportForFunction(
       continue;
     }
 
-    auto *CalleeSummary = selectCallee(GUID, Threshold, Index);
+    // FIXME: Also lower the threshold for cold callsites.
+    const auto NewThreshold =
+        Edge.second.Hotness == CalleeInfo::HotnessType::Hot
+            ? Threshold * ImportHotMultiplier
+            : Threshold;
+    auto *CalleeSummary = selectCallee(GUID, NewThreshold, Index);
     if (!CalleeSummary) {
       DEBUG(dbgs() << "ignored! No qualifying callee with summary found.\n");
       continue;
@@ -297,7 +306,7 @@ static void computeImportForFunction(
     } else
       ResolvedCalleeSummary = cast<FunctionSummary>(CalleeSummary);
 
-    assert(ResolvedCalleeSummary->instCount() <= Threshold &&
+    assert(ResolvedCalleeSummary->instCount() <= NewThreshold &&
            "selectCallee() didn't honor the threshold");
 
     auto ExportModulePath = ResolvedCalleeSummary->modulePath();