86 lines
3.1 KiB
C++
86 lines
3.1 KiB
C++
//==-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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using namespace llvm;
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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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extern cl::opt<int> InitialSyntheticCount;
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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().get()->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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