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llvm-project/llvm/lib/IR/ModuleSummaryIndex.cpp

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//===-- ModuleSummaryIndex.cpp - Module Summary Index ---------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This file implements the module index and summary classes for the
// IR library.
//
//===----------------------------------------------------------------------===//
#include "llvm/IR/ModuleSummaryIndex.h"
#include "llvm/ADT/SCCIterator.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/StringMap.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Path.h"
#include "llvm/Support/raw_ostream.h"
using namespace llvm;
#define DEBUG_TYPE "module-summary-index"
STATISTIC(ReadOnlyLiveGVars,
"Number of live global variables marked read only");
STATISTIC(WriteOnlyLiveGVars,
"Number of live global variables marked write only");
static cl::opt<bool> PropagateAttrs("propagate-attrs", cl::init(true),
cl::Hidden,
cl::desc("Propagate attributes in index"));
static cl::opt<bool> ImportConstantsWithRefs(
"import-constants-with-refs", cl::init(true), cl::Hidden,
cl::desc("Import constant global variables with references"));
constexpr uint32_t FunctionSummary::ParamAccess::RangeWidth;
FunctionSummary FunctionSummary::ExternalNode =
FunctionSummary::makeDummyFunctionSummary({});
bool ValueInfo::isDSOLocal() const {
// Need to check all summaries are local in case of hash collisions.
return getSummaryList().size() &&
llvm::all_of(getSummaryList(),
[](const std::unique_ptr<GlobalValueSummary> &Summary) {
return Summary->isDSOLocal();
});
}
bool ValueInfo::canAutoHide() const {
// Can only auto hide if all copies are eligible to auto hide.
return getSummaryList().size() &&
llvm::all_of(getSummaryList(),
[](const std::unique_ptr<GlobalValueSummary> &Summary) {
return Summary->canAutoHide();
});
}
// Gets the number of readonly and writeonly refs in RefEdgeList
std::pair<unsigned, unsigned> FunctionSummary::specialRefCounts() const {
// Here we take advantage of having all readonly and writeonly references
// located in the end of the RefEdgeList.
auto Refs = refs();
unsigned RORefCnt = 0, WORefCnt = 0;
int I;
for (I = Refs.size() - 1; I >= 0 && Refs[I].isWriteOnly(); --I)
WORefCnt++;
for (; I >= 0 && Refs[I].isReadOnly(); --I)
RORefCnt++;
return {RORefCnt, WORefCnt};
}
constexpr uint64_t ModuleSummaryIndex::BitcodeSummaryVersion;
uint64_t ModuleSummaryIndex::getFlags() const {
uint64_t Flags = 0;
if (withGlobalValueDeadStripping())
Flags |= 0x1;
if (skipModuleByDistributedBackend())
Flags |= 0x2;
if (hasSyntheticEntryCounts())
Flags |= 0x4;
if (enableSplitLTOUnit())
Flags |= 0x8;
if (partiallySplitLTOUnits())
Flags |= 0x10;
if (withAttributePropagation())
Flags |= 0x20;
return Flags;
}
void ModuleSummaryIndex::setFlags(uint64_t Flags) {
assert(Flags <= 0x3f && "Unexpected bits in flag");
// 1 bit: WithGlobalValueDeadStripping flag.
// Set on combined index only.
if (Flags & 0x1)
setWithGlobalValueDeadStripping();
// 1 bit: SkipModuleByDistributedBackend flag.
// Set on combined index only.
if (Flags & 0x2)
setSkipModuleByDistributedBackend();
// 1 bit: HasSyntheticEntryCounts flag.
// Set on combined index only.
if (Flags & 0x4)
setHasSyntheticEntryCounts();
// 1 bit: DisableSplitLTOUnit flag.
// Set on per module indexes. It is up to the client to validate
// the consistency of this flag across modules being linked.
if (Flags & 0x8)
setEnableSplitLTOUnit();
// 1 bit: PartiallySplitLTOUnits flag.
// Set on combined index only.
if (Flags & 0x10)
setPartiallySplitLTOUnits();
// 1 bit: WithAttributePropagation flag.
// Set on combined index only.
if (Flags & 0x20)
setWithAttributePropagation();
}
// Collect for the given module the list of function it defines
// (GUID -> Summary).
void ModuleSummaryIndex::collectDefinedFunctionsForModule(
StringRef ModulePath, GVSummaryMapTy &GVSummaryMap) const {
for (auto &GlobalList : *this) {
auto GUID = GlobalList.first;
for (auto &GlobSummary : GlobalList.second.SummaryList) {
auto *Summary = dyn_cast_or_null<FunctionSummary>(GlobSummary.get());
if (!Summary)
// Ignore global variable, focus on functions
continue;
// Ignore summaries from other modules.
if (Summary->modulePath() != ModulePath)
continue;
GVSummaryMap[GUID] = Summary;
}
}
}
GlobalValueSummary *
ModuleSummaryIndex::getGlobalValueSummary(uint64_t ValueGUID,
bool PerModuleIndex) const {
auto VI = getValueInfo(ValueGUID);
assert(VI && "GlobalValue not found in index");
assert((!PerModuleIndex || VI.getSummaryList().size() == 1) &&
"Expected a single entry per global value in per-module index");
auto &Summary = VI.getSummaryList()[0];
return Summary.get();
}
bool ModuleSummaryIndex::isGUIDLive(GlobalValue::GUID GUID) const {
auto VI = getValueInfo(GUID);
if (!VI)
return true;
const auto &SummaryList = VI.getSummaryList();
if (SummaryList.empty())
return true;
for (auto &I : SummaryList)
if (isGlobalValueLive(I.get()))
return true;
return false;
}
static void propagateAttributesToRefs(GlobalValueSummary *S) {
// If reference is not readonly or writeonly then referenced summary is not
// read/writeonly either. Note that:
// - All references from GlobalVarSummary are conservatively considered as
// not readonly or writeonly. Tracking them properly requires more complex
// analysis then we have now.
//
// - AliasSummary objects have no refs at all so this function is a no-op
// for them.
for (auto &VI : S->refs()) {
assert(VI.getAccessSpecifier() == 0 || isa<FunctionSummary>(S));
for (auto &Ref : VI.getSummaryList())
// If references to alias is not read/writeonly then aliasee
// is not read/writeonly
if (auto *GVS = dyn_cast<GlobalVarSummary>(Ref->getBaseObject())) {
if (!VI.isReadOnly())
GVS->setReadOnly(false);
if (!VI.isWriteOnly())
GVS->setWriteOnly(false);
}
}
}
// Do the access attribute propagation in combined index.
// The goal of attribute propagation is internalization of readonly (RO)
// or writeonly (WO) variables. To determine which variables are RO or WO
// and which are not we take following steps:
// - During analysis we speculatively assign readonly and writeonly
// attribute to all variables which can be internalized. When computing
// function summary we also assign readonly or writeonly attribute to a
// reference if function doesn't modify referenced variable (readonly)
// or doesn't read it (writeonly).
//
// - After computing dead symbols in combined index we do the attribute
// propagation. During this step we:
// a. clear RO and WO attributes from variables which are preserved or
// can't be imported
// b. clear RO and WO attributes from variables referenced by any global
// variable initializer
// c. clear RO attribute from variable referenced by a function when
// reference is not readonly
// d. clear WO attribute from variable referenced by a function when
// reference is not writeonly
//
// Because of (c, d) we don't internalize variables read by function A
// and modified by function B.
//
// Internalization itself happens in the backend after import is finished
// See internalizeGVsAfterImport.
void ModuleSummaryIndex::propagateAttributes(
const DenseSet<GlobalValue::GUID> &GUIDPreservedSymbols) {
if (!PropagateAttrs)
return;
for (auto &P : *this)
for (auto &S : P.second.SummaryList) {
if (!isGlobalValueLive(S.get()))
// We don't examine references from dead objects
continue;
// Global variable can't be marked read/writeonly if it is not eligible
// to import since we need to ensure that all external references get
// a local (imported) copy. It also can't be marked read/writeonly if
// it or any alias (since alias points to the same memory) are preserved
// or notEligibleToImport, since either of those means there could be
// writes (or reads in case of writeonly) that are not visible (because
// preserved means it could have external to DSO writes or reads, and
// notEligibleToImport means it could have writes or reads via inline
// assembly leading it to be in the @llvm.*used).
if (auto *GVS = dyn_cast<GlobalVarSummary>(S->getBaseObject()))
// Here we intentionally pass S.get() not GVS, because S could be
// an alias. We don't analyze references here, because we have to
// know exactly if GV is readonly to do so.
if (!canImportGlobalVar(S.get(), /* AnalyzeRefs */ false) ||
GUIDPreservedSymbols.count(P.first)) {
GVS->setReadOnly(false);
GVS->setWriteOnly(false);
}
propagateAttributesToRefs(S.get());
}
setWithAttributePropagation();
if (llvm::AreStatisticsEnabled())
for (auto &P : *this)
if (P.second.SummaryList.size())
if (auto *GVS = dyn_cast<GlobalVarSummary>(
P.second.SummaryList[0]->getBaseObject()))
if (isGlobalValueLive(GVS)) {
if (GVS->maybeReadOnly())
ReadOnlyLiveGVars++;
if (GVS->maybeWriteOnly())
WriteOnlyLiveGVars++;
}
}
bool ModuleSummaryIndex::canImportGlobalVar(GlobalValueSummary *S,
bool AnalyzeRefs) const {
auto HasRefsPreventingImport = [this](const GlobalVarSummary *GVS) {
// We don't analyze GV references during attribute propagation, so
// GV with non-trivial initializer can be marked either read or
// write-only.
// Importing definiton of readonly GV with non-trivial initializer
// allows us doing some extra optimizations (like converting indirect
// calls to direct).
// Definition of writeonly GV with non-trivial initializer should also
// be imported. Not doing so will result in:
// a) GV internalization in source module (because it's writeonly)
// b) Importing of GV declaration to destination module as a result
// of promotion.
// c) Link error (external declaration with internal definition).
// However we do not promote objects referenced by writeonly GV
// initializer by means of converting it to 'zeroinitializer'
return !(ImportConstantsWithRefs && GVS->isConstant()) &&
!isReadOnly(GVS) && !isWriteOnly(GVS) && GVS->refs().size();
};
auto *GVS = cast<GlobalVarSummary>(S->getBaseObject());
// Global variable with non-trivial initializer can be imported
// if it's readonly. This gives us extra opportunities for constant
// folding and converting indirect calls to direct calls. We don't
// analyze GV references during attribute propagation, because we
// don't know yet if it is readonly or not.
return !GlobalValue::isInterposableLinkage(S->linkage()) &&
!S->notEligibleToImport() &&
(!AnalyzeRefs || !HasRefsPreventingImport(GVS));
}
// TODO: write a graphviz dumper for SCCs (see ModuleSummaryIndex::exportToDot)
// then delete this function and update its tests
LLVM_DUMP_METHOD
void ModuleSummaryIndex::dumpSCCs(raw_ostream &O) {
for (scc_iterator<ModuleSummaryIndex *> I =
scc_begin<ModuleSummaryIndex *>(this);
!I.isAtEnd(); ++I) {
O << "SCC (" << utostr(I->size()) << " node" << (I->size() == 1 ? "" : "s")
<< ") {\n";
for (const ValueInfo &V : *I) {
FunctionSummary *F = nullptr;
if (V.getSummaryList().size())
F = cast<FunctionSummary>(V.getSummaryList().front().get());
O << " " << (F == nullptr ? "External" : "") << " " << utostr(V.getGUID())
<< (I.hasCycle() ? " (has cycle)" : "") << "\n";
}
O << "}\n";
}
}
namespace {
struct Attributes {
void add(const Twine &Name, const Twine &Value,
const Twine &Comment = Twine());
void addComment(const Twine &Comment);
std::string getAsString() const;
std::vector<std::string> Attrs;
std::string Comments;
};
struct Edge {
uint64_t SrcMod;
int Hotness;
GlobalValue::GUID Src;
GlobalValue::GUID Dst;
};
}
void Attributes::add(const Twine &Name, const Twine &Value,
const Twine &Comment) {
std::string A = Name.str();
A += "=\"";
A += Value.str();
A += "\"";
Attrs.push_back(A);
addComment(Comment);
}
void Attributes::addComment(const Twine &Comment) {
if (!Comment.isTriviallyEmpty()) {
if (Comments.empty())
Comments = " // ";
else
Comments += ", ";
Comments += Comment.str();
}
}
std::string Attributes::getAsString() const {
if (Attrs.empty())
return "";
std::string Ret = "[";
for (auto &A : Attrs)
Ret += A + ",";
Ret.pop_back();
Ret += "];";
Ret += Comments;
return Ret;
}
static std::string linkageToString(GlobalValue::LinkageTypes LT) {
switch (LT) {
case GlobalValue::ExternalLinkage:
return "extern";
case GlobalValue::AvailableExternallyLinkage:
return "av_ext";
case GlobalValue::LinkOnceAnyLinkage:
return "linkonce";
case GlobalValue::LinkOnceODRLinkage:
return "linkonce_odr";
case GlobalValue::WeakAnyLinkage:
return "weak";
case GlobalValue::WeakODRLinkage:
return "weak_odr";
case GlobalValue::AppendingLinkage:
return "appending";
case GlobalValue::InternalLinkage:
return "internal";
case GlobalValue::PrivateLinkage:
return "private";
case GlobalValue::ExternalWeakLinkage:
return "extern_weak";
case GlobalValue::CommonLinkage:
return "common";
}
return "<unknown>";
}
static std::string fflagsToString(FunctionSummary::FFlags F) {
auto FlagValue = [](unsigned V) { return V ? '1' : '0'; };
char FlagRep[] = {FlagValue(F.ReadNone), FlagValue(F.ReadOnly),
FlagValue(F.NoRecurse), FlagValue(F.ReturnDoesNotAlias),
FlagValue(F.NoInline), FlagValue(F.AlwaysInline), 0};
return FlagRep;
}
// Get string representation of function instruction count and flags.
static std::string getSummaryAttributes(GlobalValueSummary* GVS) {
auto *FS = dyn_cast_or_null<FunctionSummary>(GVS);
if (!FS)
return "";
return std::string("inst: ") + std::to_string(FS->instCount()) +
", ffl: " + fflagsToString(FS->fflags());
}
static std::string getNodeVisualName(GlobalValue::GUID Id) {
return std::string("@") + std::to_string(Id);
}
static std::string getNodeVisualName(const ValueInfo &VI) {
return VI.name().empty() ? getNodeVisualName(VI.getGUID()) : VI.name().str();
}
static std::string getNodeLabel(const ValueInfo &VI, GlobalValueSummary *GVS) {
if (isa<AliasSummary>(GVS))
return getNodeVisualName(VI);
std::string Attrs = getSummaryAttributes(GVS);
std::string Label =
getNodeVisualName(VI) + "|" + linkageToString(GVS->linkage());
if (!Attrs.empty())
Label += std::string(" (") + Attrs + ")";
Label += "}";
return Label;
}
// Write definition of external node, which doesn't have any
// specific module associated with it. Typically this is function
// or variable defined in native object or library.
static void defineExternalNode(raw_ostream &OS, const char *Pfx,
const ValueInfo &VI, GlobalValue::GUID Id) {
auto StrId = std::to_string(Id);
OS << " " << StrId << " [label=\"";
if (VI) {
OS << getNodeVisualName(VI);
} else {
OS << getNodeVisualName(Id);
}
OS << "\"]; // defined externally\n";
}
static bool hasReadOnlyFlag(const GlobalValueSummary *S) {
if (auto *GVS = dyn_cast<GlobalVarSummary>(S))
return GVS->maybeReadOnly();
return false;
}
static bool hasWriteOnlyFlag(const GlobalValueSummary *S) {
if (auto *GVS = dyn_cast<GlobalVarSummary>(S))
return GVS->maybeWriteOnly();
return false;
}
static bool hasConstantFlag(const GlobalValueSummary *S) {
if (auto *GVS = dyn_cast<GlobalVarSummary>(S))
return GVS->isConstant();
return false;
}
void ModuleSummaryIndex::exportToDot(
raw_ostream &OS,
const DenseSet<GlobalValue::GUID> &GUIDPreservedSymbols) const {
std::vector<Edge> CrossModuleEdges;
DenseMap<GlobalValue::GUID, std::vector<uint64_t>> NodeMap;
using GVSOrderedMapTy = std::map<GlobalValue::GUID, GlobalValueSummary *>;
std::map<StringRef, GVSOrderedMapTy> ModuleToDefinedGVS;
collectDefinedGVSummariesPerModule(ModuleToDefinedGVS);
// Get node identifier in form MXXX_<GUID>. The MXXX prefix is required,
// because we may have multiple linkonce functions summaries.
auto NodeId = [](uint64_t ModId, GlobalValue::GUID Id) {
return ModId == (uint64_t)-1 ? std::to_string(Id)
: std::string("M") + std::to_string(ModId) +
"_" + std::to_string(Id);
};
auto DrawEdge = [&](const char *Pfx, uint64_t SrcMod, GlobalValue::GUID SrcId,
uint64_t DstMod, GlobalValue::GUID DstId,
int TypeOrHotness) {
// 0 - alias
// 1 - reference
// 2 - constant reference
// 3 - writeonly reference
// Other value: (hotness - 4).
TypeOrHotness += 4;
static const char *EdgeAttrs[] = {
" [style=dotted]; // alias",
" [style=dashed]; // ref",
" [style=dashed,color=forestgreen]; // const-ref",
" [style=dashed,color=violetred]; // writeOnly-ref",
" // call (hotness : Unknown)",
" [color=blue]; // call (hotness : Cold)",
" // call (hotness : None)",
" [color=brown]; // call (hotness : Hot)",
" [style=bold,color=red]; // call (hotness : Critical)"};
assert(static_cast<size_t>(TypeOrHotness) <
sizeof(EdgeAttrs) / sizeof(EdgeAttrs[0]));
OS << Pfx << NodeId(SrcMod, SrcId) << " -> " << NodeId(DstMod, DstId)
<< EdgeAttrs[TypeOrHotness] << "\n";
};
OS << "digraph Summary {\n";
for (auto &ModIt : ModuleToDefinedGVS) {
auto ModId = getModuleId(ModIt.first);
OS << " // Module: " << ModIt.first << "\n";
OS << " subgraph cluster_" << std::to_string(ModId) << " {\n";
OS << " style = filled;\n";
OS << " color = lightgrey;\n";
OS << " label = \"" << sys::path::filename(ModIt.first) << "\";\n";
OS << " node [style=filled,fillcolor=lightblue];\n";
auto &GVSMap = ModIt.second;
auto Draw = [&](GlobalValue::GUID IdFrom, GlobalValue::GUID IdTo, int Hotness) {
if (!GVSMap.count(IdTo)) {
CrossModuleEdges.push_back({ModId, Hotness, IdFrom, IdTo});
return;
}
DrawEdge(" ", ModId, IdFrom, ModId, IdTo, Hotness);
};
for (auto &SummaryIt : GVSMap) {
NodeMap[SummaryIt.first].push_back(ModId);
auto Flags = SummaryIt.second->flags();
Attributes A;
if (isa<FunctionSummary>(SummaryIt.second)) {
A.add("shape", "record", "function");
} else if (isa<AliasSummary>(SummaryIt.second)) {
A.add("style", "dotted,filled", "alias");
A.add("shape", "box");
} else {
A.add("shape", "Mrecord", "variable");
if (Flags.Live && hasReadOnlyFlag(SummaryIt.second))
A.addComment("immutable");
if (Flags.Live && hasWriteOnlyFlag(SummaryIt.second))
A.addComment("writeOnly");
if (Flags.Live && hasConstantFlag(SummaryIt.second))
A.addComment("constant");
}
if (Flags.DSOLocal)
A.addComment("dsoLocal");
if (Flags.CanAutoHide)
A.addComment("canAutoHide");
if (GUIDPreservedSymbols.count(SummaryIt.first))
A.addComment("preserved");
auto VI = getValueInfo(SummaryIt.first);
A.add("label", getNodeLabel(VI, SummaryIt.second));
if (!Flags.Live)
A.add("fillcolor", "red", "dead");
else if (Flags.NotEligibleToImport)
A.add("fillcolor", "yellow", "not eligible to import");
OS << " " << NodeId(ModId, SummaryIt.first) << " " << A.getAsString()
<< "\n";
}
OS << " // Edges:\n";
for (auto &SummaryIt : GVSMap) {
auto *GVS = SummaryIt.second;
for (auto &R : GVS->refs())
Draw(SummaryIt.first, R.getGUID(),
R.isWriteOnly() ? -1 : (R.isReadOnly() ? -2 : -3));
if (auto *AS = dyn_cast_or_null<AliasSummary>(SummaryIt.second)) {
Draw(SummaryIt.first, AS->getAliaseeGUID(), -4);
continue;
}
if (auto *FS = dyn_cast_or_null<FunctionSummary>(SummaryIt.second))
for (auto &CGEdge : FS->calls())
Draw(SummaryIt.first, CGEdge.first.getGUID(),
static_cast<int>(CGEdge.second.Hotness));
}
OS << " }\n";
}
OS << " // Cross-module edges:\n";
for (auto &E : CrossModuleEdges) {
auto &ModList = NodeMap[E.Dst];
if (ModList.empty()) {
defineExternalNode(OS, " ", getValueInfo(E.Dst), E.Dst);
// Add fake module to the list to draw an edge to an external node
// in the loop below.
ModList.push_back(-1);
}
for (auto DstMod : ModList)
// The edge representing call or ref is drawn to every module where target
// symbol is defined. When target is a linkonce symbol there can be
// multiple edges representing a single call or ref, both intra-module and
// cross-module. As we've already drawn all intra-module edges before we
// skip it here.
if (DstMod != E.SrcMod)
DrawEdge(" ", E.SrcMod, E.Src, DstMod, E.Dst, E.Hotness);
}
OS << "}";
}
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