llvm-project

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//==-SummaryBasedOptimizations.cpp - Optimizations based on ThinLTO summary-==//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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//
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// This file implements optimizations that are based on the module summaries.
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// These optimizations are performed during the thinlink phase of the
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// compilation.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/LTO/SummaryBasedOptimizations.h"
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#include "llvm/Analysis/SyntheticCountsUtils.h"
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#include "llvm/IR/ModuleSummaryIndex.h"
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#include "llvm/Support/CommandLine.h"
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using namespace llvm;
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static cl::opt<bool> ThinLTOSynthesizeEntryCounts(
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    "thinlto-synthesize-entry-counts", cl::init(false), cl::Hidden,
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    cl::desc("Synthesize entry counts based on the summary"));
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namespace llvm {
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extern cl::opt<int> InitialSyntheticCount;
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}
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static void initializeCounts(ModuleSummaryIndex &Index) {
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  auto Root = Index.calculateCallGraphRoot();
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  // Root is a fake node. All its successors are the actual roots of the
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  // callgraph.
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  // FIXME: This initializes the entry counts of only the root nodes. This makes
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  // sense when compiling a binary with ThinLTO, but for libraries any of the
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  // non-root nodes could be called from outside.
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  for (auto &C : Root.calls()) {
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    auto &V = C.first;
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    for (auto &GVS : V.getSummaryList()) {
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      auto S = GVS.get()->getBaseObject();
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      auto *F = cast<FunctionSummary>(S);
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      F->setEntryCount(InitialSyntheticCount);
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    }
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  }
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}
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void llvm::computeSyntheticCounts(ModuleSummaryIndex &Index) {
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  if (!ThinLTOSynthesizeEntryCounts)
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    return;
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  using Scaled64 = ScaledNumber<uint64_t>;
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  initializeCounts(Index);
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  auto GetCallSiteRelFreq = [](FunctionSummary::EdgeTy &Edge) {
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    return Scaled64(Edge.second.RelBlockFreq, -CalleeInfo::ScaleShift);
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  };
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  auto GetEntryCount = [](ValueInfo V) {
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    if (V.getSummaryList().size()) {
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      auto S = V.getSummaryList().front()->getBaseObject();
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      auto *F = cast<FunctionSummary>(S);
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      return F->entryCount();
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    } else {
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      return UINT64_C(0);
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    }
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  };
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  auto AddToEntryCount = [](ValueInfo V, Scaled64 New) {
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    if (!V.getSummaryList().size())
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      return;
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    for (auto &GVS : V.getSummaryList()) {
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      auto S = GVS.get()->getBaseObject();
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      auto *F = cast<FunctionSummary>(S);
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      F->setEntryCount(
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          SaturatingAdd(F->entryCount(), New.template toInt<uint64_t>()));
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    }
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  };
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  auto GetProfileCount = [&](ValueInfo V, FunctionSummary::EdgeTy &Edge) {
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    auto RelFreq = GetCallSiteRelFreq(Edge);
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    Scaled64 EC(GetEntryCount(V), 0);
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    return RelFreq * EC;
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  };
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  // After initializing the counts in initializeCounts above, the counts have to
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  // be propagated across the combined callgraph.
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  // SyntheticCountsUtils::propagate takes care of this propagation on any
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  // callgraph that specialized GraphTraits.
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  SyntheticCountsUtils<ModuleSummaryIndex *>::propagate(&Index, GetProfileCount,
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                                                        AddToEntryCount);
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  Index.setHasSyntheticEntryCounts();
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}
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