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llvm-project/llvm/lib/Analysis/CFLAndersAliasAnalysis.cpp

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//===- CFLAndersAliasAnalysis.cpp - Unification-based Alias Analysis ------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements a CFL-based, summary-based alias analysis algorithm. It
// differs from CFLSteensAliasAnalysis in its inclusion-based nature while
// CFLSteensAliasAnalysis is unification-based. This pass has worse performance
// than CFLSteensAliasAnalysis (the worst case complexity of
// CFLAndersAliasAnalysis is cubic, while the worst case complexity of
// CFLSteensAliasAnalysis is almost linear), but it is able to yield more
// precise analysis result. The precision of this analysis is roughly the same
// as that of an one level context-sensitive Andersen's algorithm.
//
// The algorithm used here is based on recursive state machine matching scheme
// proposed in "Demand-driven alias analysis for C" by Xin Zheng and Radu
// Rugina. The general idea is to extend the traditional transitive closure
// algorithm to perform CFL matching along the way: instead of recording
// "whether X is reachable from Y", we keep track of "whether X is reachable
// from Y at state Z", where the "state" field indicates where we are in the CFL
// matching process. To understand the matching better, it is advisable to have
// the state machine shown in Figure 3 of the paper available when reading the
// codes: all we do here is to selectively expand the transitive closure by
// discarding edges that are not recognized by the state machine.
//
// There are two differences between our current implementation and the one
// described in the paper:
// - Our algorithm eagerly computes all alias pairs after the CFLGraph is built,
// while in the paper the authors did the computation in a demand-driven
// fashion. We did not implement the demand-driven algorithm due to the
// additional coding complexity and higher memory profile, but if we found it
// necessary we may switch to it eventually.
// - In the paper the authors use a state machine that does not distinguish
// value reads from value writes. For example, if Y is reachable from X at state
// S3, it may be the case that X is written into Y, or it may be the case that
// there's a third value Z that writes into both X and Y. To make that
// distinction (which is crucial in building function summary as well as
// retrieving mod-ref info), we choose to duplicate some of the states in the
// paper's proposed state machine. The duplication does not change the set the
// machine accepts. Given a pair of reachable values, it only provides more
// detailed information on which value is being written into and which is being
// read from.
//
//===----------------------------------------------------------------------===//
// N.B. AliasAnalysis as a whole is phrased as a FunctionPass at the moment, and
// CFLAndersAA is interprocedural. This is *technically* A Bad Thing, because
// FunctionPasses are only allowed to inspect the Function that they're being
// run on. Realistically, this likely isn't a problem until we allow
// FunctionPasses to run concurrently.
#include "llvm/Analysis/CFLAndersAliasAnalysis.h"
#include "AliasAnalysisSummary.h"
#include "CFLGraph.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/DenseMapInfo.h"
#include "llvm/ADT/DenseSet.h"
#include "llvm/ADT/None.h"
#include "llvm/ADT/Optional.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/iterator_range.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/MemoryLocation.h"
#include "llvm/IR/Argument.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/PassManager.h"
#include "llvm/IR/Type.h"
#include "llvm/Pass.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include <algorithm>
#include <bitset>
#include <cassert>
#include <cstddef>
#include <cstdint>
#include <functional>
#include <utility>
#include <vector>
using namespace llvm;
using namespace llvm::cflaa;
#define DEBUG_TYPE "cfl-anders-aa"
CFLAndersAAResult::CFLAndersAAResult(const TargetLibraryInfo &TLI) : TLI(TLI) {}
CFLAndersAAResult::CFLAndersAAResult(CFLAndersAAResult &&RHS)
: AAResultBase(std::move(RHS)), TLI(RHS.TLI) {}
CFLAndersAAResult::~CFLAndersAAResult() = default;
namespace {
enum class MatchState : uint8_t {
// The following state represents S1 in the paper.
FlowFromReadOnly = 0,
// The following two states together represent S2 in the paper.
// The 'NoReadWrite' suffix indicates that there exists an alias path that
// does not contain assignment and reverse assignment edges.
// The 'ReadOnly' suffix indicates that there exists an alias path that
// contains reverse assignment edges only.
FlowFromMemAliasNoReadWrite,
FlowFromMemAliasReadOnly,
// The following two states together represent S3 in the paper.
// The 'WriteOnly' suffix indicates that there exists an alias path that
// contains assignment edges only.
// The 'ReadWrite' suffix indicates that there exists an alias path that
// contains both assignment and reverse assignment edges. Note that if X and Y
// are reachable at 'ReadWrite' state, it does NOT mean X is both read from
// and written to Y. Instead, it means that a third value Z is written to both
// X and Y.
FlowToWriteOnly,
FlowToReadWrite,
// The following two states together represent S4 in the paper.
FlowToMemAliasWriteOnly,
FlowToMemAliasReadWrite,
};
using StateSet = std::bitset<7>;
const unsigned ReadOnlyStateMask =
(1U << static_cast<uint8_t>(MatchState::FlowFromReadOnly)) |
(1U << static_cast<uint8_t>(MatchState::FlowFromMemAliasReadOnly));
const unsigned WriteOnlyStateMask =
(1U << static_cast<uint8_t>(MatchState::FlowToWriteOnly)) |
(1U << static_cast<uint8_t>(MatchState::FlowToMemAliasWriteOnly));
// A pair that consists of a value and an offset
struct OffsetValue {
const Value *Val;
int64_t Offset;
};
bool operator==(OffsetValue LHS, OffsetValue RHS) {
return LHS.Val == RHS.Val && LHS.Offset == RHS.Offset;
}
bool operator<(OffsetValue LHS, OffsetValue RHS) {
return std::less<const Value *>()(LHS.Val, RHS.Val) ||
(LHS.Val == RHS.Val && LHS.Offset < RHS.Offset);
}
// A pair that consists of an InstantiatedValue and an offset
struct OffsetInstantiatedValue {
InstantiatedValue IVal;
int64_t Offset;
};
bool operator==(OffsetInstantiatedValue LHS, OffsetInstantiatedValue RHS) {
return LHS.IVal == RHS.IVal && LHS.Offset == RHS.Offset;
}
// We use ReachabilitySet to keep track of value aliases (The nonterminal "V" in
// the paper) during the analysis.
class ReachabilitySet {
using ValueStateMap = DenseMap<InstantiatedValue, StateSet>;
using ValueReachMap = DenseMap<InstantiatedValue, ValueStateMap>;
ValueReachMap ReachMap;
public:
using const_valuestate_iterator = ValueStateMap::const_iterator;
using const_value_iterator = ValueReachMap::const_iterator;
// Insert edge 'From->To' at state 'State'
bool insert(InstantiatedValue From, InstantiatedValue To, MatchState State) {
assert(From != To);
auto &States = ReachMap[To][From];
auto Idx = static_cast<size_t>(State);
if (!States.test(Idx)) {
States.set(Idx);
return true;
}
return false;
}
// Return the set of all ('From', 'State') pair for a given node 'To'
iterator_range<const_valuestate_iterator>
reachableValueAliases(InstantiatedValue V) const {
auto Itr = ReachMap.find(V);
if (Itr == ReachMap.end())
return make_range<const_valuestate_iterator>(const_valuestate_iterator(),
const_valuestate_iterator());
return make_range<const_valuestate_iterator>(Itr->second.begin(),
Itr->second.end());
}
iterator_range<const_value_iterator> value_mappings() const {
return make_range<const_value_iterator>(ReachMap.begin(), ReachMap.end());
}
};
// We use AliasMemSet to keep track of all memory aliases (the nonterminal "M"
// in the paper) during the analysis.
class AliasMemSet {
using MemSet = DenseSet<InstantiatedValue>;
using MemMapType = DenseMap<InstantiatedValue, MemSet>;
MemMapType MemMap;
public:
using const_mem_iterator = MemSet::const_iterator;
bool insert(InstantiatedValue LHS, InstantiatedValue RHS) {
// Top-level values can never be memory aliases because one cannot take the
// addresses of them
assert(LHS.DerefLevel > 0 && RHS.DerefLevel > 0);
return MemMap[LHS].insert(RHS).second;
}
const MemSet *getMemoryAliases(InstantiatedValue V) const {
auto Itr = MemMap.find(V);
if (Itr == MemMap.end())
return nullptr;
return &Itr->second;
}
};
// We use AliasAttrMap to keep track of the AliasAttr of each node.
class AliasAttrMap {
using MapType = DenseMap<InstantiatedValue, AliasAttrs>;
MapType AttrMap;
public:
using const_iterator = MapType::const_iterator;
bool add(InstantiatedValue V, AliasAttrs Attr) {
auto &OldAttr = AttrMap[V];
auto NewAttr = OldAttr | Attr;
if (OldAttr == NewAttr)
return false;
OldAttr = NewAttr;
return true;
}
AliasAttrs getAttrs(InstantiatedValue V) const {
AliasAttrs Attr;
auto Itr = AttrMap.find(V);
if (Itr != AttrMap.end())
Attr = Itr->second;
return Attr;
}
iterator_range<const_iterator> mappings() const {
return make_range<const_iterator>(AttrMap.begin(), AttrMap.end());
}
};
struct WorkListItem {
InstantiatedValue From;
InstantiatedValue To;
MatchState State;
};
struct ValueSummary {
struct Record {
InterfaceValue IValue;
unsigned DerefLevel;
};
SmallVector<Record, 4> FromRecords, ToRecords;
};
} // end anonymous namespace
namespace llvm {
// Specialize DenseMapInfo for OffsetValue.
template <> struct DenseMapInfo<OffsetValue> {
static OffsetValue getEmptyKey() {
return OffsetValue{DenseMapInfo<const Value *>::getEmptyKey(),
DenseMapInfo<int64_t>::getEmptyKey()};
}
static OffsetValue getTombstoneKey() {
return OffsetValue{DenseMapInfo<const Value *>::getTombstoneKey(),
DenseMapInfo<int64_t>::getEmptyKey()};
}
static unsigned getHashValue(const OffsetValue &OVal) {
return DenseMapInfo<std::pair<const Value *, int64_t>>::getHashValue(
std::make_pair(OVal.Val, OVal.Offset));
}
static bool isEqual(const OffsetValue &LHS, const OffsetValue &RHS) {
return LHS == RHS;
}
};
// Specialize DenseMapInfo for OffsetInstantiatedValue.
template <> struct DenseMapInfo<OffsetInstantiatedValue> {
static OffsetInstantiatedValue getEmptyKey() {
return OffsetInstantiatedValue{
DenseMapInfo<InstantiatedValue>::getEmptyKey(),
DenseMapInfo<int64_t>::getEmptyKey()};
}
static OffsetInstantiatedValue getTombstoneKey() {
return OffsetInstantiatedValue{
DenseMapInfo<InstantiatedValue>::getTombstoneKey(),
DenseMapInfo<int64_t>::getEmptyKey()};
}
static unsigned getHashValue(const OffsetInstantiatedValue &OVal) {
return DenseMapInfo<std::pair<InstantiatedValue, int64_t>>::getHashValue(
std::make_pair(OVal.IVal, OVal.Offset));
}
static bool isEqual(const OffsetInstantiatedValue &LHS,
const OffsetInstantiatedValue &RHS) {
return LHS == RHS;
}
};
} // end namespace llvm
class CFLAndersAAResult::FunctionInfo {
/// Map a value to other values that may alias it
/// Since the alias relation is symmetric, to save some space we assume values
/// are properly ordered: if a and b alias each other, and a < b, then b is in
/// AliasMap[a] but not vice versa.
DenseMap<const Value *, std::vector<OffsetValue>> AliasMap;
/// Map a value to its corresponding AliasAttrs
DenseMap<const Value *, AliasAttrs> AttrMap;
/// Summary of externally visible effects.
AliasSummary Summary;
Optional<AliasAttrs> getAttrs(const Value *) const;
public:
FunctionInfo(const Function &, const SmallVectorImpl<Value *> &,
const ReachabilitySet &, const AliasAttrMap &);
bool mayAlias(const Value *, uint64_t, const Value *, uint64_t) const;
const AliasSummary &getAliasSummary() const { return Summary; }
};
static bool hasReadOnlyState(StateSet Set) {
return (Set & StateSet(ReadOnlyStateMask)).any();
}
static bool hasWriteOnlyState(StateSet Set) {
return (Set & StateSet(WriteOnlyStateMask)).any();
}
static Optional<InterfaceValue>
getInterfaceValue(InstantiatedValue IValue,
const SmallVectorImpl<Value *> &RetVals) {
auto Val = IValue.Val;
Optional<unsigned> Index;
if (auto Arg = dyn_cast<Argument>(Val))
Index = Arg->getArgNo() + 1;
else if (is_contained(RetVals, Val))
Index = 0;
if (Index)
return InterfaceValue{*Index, IValue.DerefLevel};
return None;
}
static void populateAttrMap(DenseMap<const Value *, AliasAttrs> &AttrMap,
const AliasAttrMap &AMap) {
for (const auto &Mapping : AMap.mappings()) {
auto IVal = Mapping.first;
// Insert IVal into the map
auto &Attr = AttrMap[IVal.Val];
// AttrMap only cares about top-level values
if (IVal.DerefLevel == 0)
Attr |= Mapping.second;
}
}
static void
populateAliasMap(DenseMap<const Value *, std::vector<OffsetValue>> &AliasMap,
const ReachabilitySet &ReachSet) {
for (const auto &OuterMapping : ReachSet.value_mappings()) {
// AliasMap only cares about top-level values
if (OuterMapping.first.DerefLevel > 0)
continue;
auto Val = OuterMapping.first.Val;
auto &AliasList = AliasMap[Val];
for (const auto &InnerMapping : OuterMapping.second) {
// Again, AliasMap only cares about top-level values
if (InnerMapping.first.DerefLevel == 0)
AliasList.push_back(OffsetValue{InnerMapping.first.Val, UnknownOffset});
}
// Sort AliasList for faster lookup
std::sort(AliasList.begin(), AliasList.end());
}
}
static void populateExternalRelations(
SmallVectorImpl<ExternalRelation> &ExtRelations, const Function &Fn,
const SmallVectorImpl<Value *> &RetVals, const ReachabilitySet &ReachSet) {
// If a function only returns one of its argument X, then X will be both an
// argument and a return value at the same time. This is an edge case that
// needs special handling here.
for (const auto &Arg : Fn.args()) {
if (is_contained(RetVals, &Arg)) {
auto ArgVal = InterfaceValue{Arg.getArgNo() + 1, 0};
auto RetVal = InterfaceValue{0, 0};
ExtRelations.push_back(ExternalRelation{ArgVal, RetVal, 0});
}
}
// Below is the core summary construction logic.
// A naive solution of adding only the value aliases that are parameters or
// return values in ReachSet to the summary won't work: It is possible that a
// parameter P is written into an intermediate value I, and the function
// subsequently returns *I. In that case, *I is does not value alias anything
// in ReachSet, and the naive solution will miss a summary edge from (P, 1) to
// (I, 1).
// To account for the aforementioned case, we need to check each non-parameter
// and non-return value for the possibility of acting as an intermediate.
// 'ValueMap' here records, for each value, which InterfaceValues read from or
// write into it. If both the read list and the write list of a given value
// are non-empty, we know that a particular value is an intermidate and we
// need to add summary edges from the writes to the reads.
DenseMap<Value *, ValueSummary> ValueMap;
for (const auto &OuterMapping : ReachSet.value_mappings()) {
if (auto Dst = getInterfaceValue(OuterMapping.first, RetVals)) {
for (const auto &InnerMapping : OuterMapping.second) {
// If Src is a param/return value, we get a same-level assignment.
if (auto Src = getInterfaceValue(InnerMapping.first, RetVals)) {
// This may happen if both Dst and Src are return values
if (*Dst == *Src)
continue;
if (hasReadOnlyState(InnerMapping.second))
ExtRelations.push_back(ExternalRelation{*Dst, *Src, UnknownOffset});
// No need to check for WriteOnly state, since ReachSet is symmetric
} else {
// If Src is not a param/return, add it to ValueMap
auto SrcIVal = InnerMapping.first;
if (hasReadOnlyState(InnerMapping.second))
ValueMap[SrcIVal.Val].FromRecords.push_back(
ValueSummary::Record{*Dst, SrcIVal.DerefLevel});
if (hasWriteOnlyState(InnerMapping.second))
ValueMap[SrcIVal.Val].ToRecords.push_back(
ValueSummary::Record{*Dst, SrcIVal.DerefLevel});
}
}
}
}
for (const auto &Mapping : ValueMap) {
for (const auto &FromRecord : Mapping.second.FromRecords) {
for (const auto &ToRecord : Mapping.second.ToRecords) {
auto ToLevel = ToRecord.DerefLevel;
auto FromLevel = FromRecord.DerefLevel;
// Same-level assignments should have already been processed by now
if (ToLevel == FromLevel)
continue;
auto SrcIndex = FromRecord.IValue.Index;
auto SrcLevel = FromRecord.IValue.DerefLevel;
auto DstIndex = ToRecord.IValue.Index;
auto DstLevel = ToRecord.IValue.DerefLevel;
if (ToLevel > FromLevel)
SrcLevel += ToLevel - FromLevel;
else
DstLevel += FromLevel - ToLevel;
ExtRelations.push_back(ExternalRelation{
InterfaceValue{SrcIndex, SrcLevel},
InterfaceValue{DstIndex, DstLevel}, UnknownOffset});
}
}
}
// Remove duplicates in ExtRelations
std::sort(ExtRelations.begin(), ExtRelations.end());
ExtRelations.erase(std::unique(ExtRelations.begin(), ExtRelations.end()),
ExtRelations.end());
}
static void populateExternalAttributes(
SmallVectorImpl<ExternalAttribute> &ExtAttributes, const Function &Fn,
const SmallVectorImpl<Value *> &RetVals, const AliasAttrMap &AMap) {
for (const auto &Mapping : AMap.mappings()) {
if (auto IVal = getInterfaceValue(Mapping.first, RetVals)) {
auto Attr = getExternallyVisibleAttrs(Mapping.second);
if (Attr.any())
ExtAttributes.push_back(ExternalAttribute{*IVal, Attr});
}
}
}
CFLAndersAAResult::FunctionInfo::FunctionInfo(
const Function &Fn, const SmallVectorImpl<Value *> &RetVals,
const ReachabilitySet &ReachSet, const AliasAttrMap &AMap) {
populateAttrMap(AttrMap, AMap);
populateExternalAttributes(Summary.RetParamAttributes, Fn, RetVals, AMap);
populateAliasMap(AliasMap, ReachSet);
populateExternalRelations(Summary.RetParamRelations, Fn, RetVals, ReachSet);
}
Optional<AliasAttrs>
CFLAndersAAResult::FunctionInfo::getAttrs(const Value *V) const {
assert(V != nullptr);
auto Itr = AttrMap.find(V);
if (Itr != AttrMap.end())
return Itr->second;
return None;
}
bool CFLAndersAAResult::FunctionInfo::mayAlias(const Value *LHS,
uint64_t LHSSize,
const Value *RHS,
uint64_t RHSSize) const {
assert(LHS && RHS);
// Check if we've seen LHS and RHS before. Sometimes LHS or RHS can be created
// after the analysis gets executed, and we want to be conservative in those
// cases.
auto MaybeAttrsA = getAttrs(LHS);
auto MaybeAttrsB = getAttrs(RHS);
if (!MaybeAttrsA || !MaybeAttrsB)
return true;
// Check AliasAttrs before AliasMap lookup since it's cheaper
auto AttrsA = *MaybeAttrsA;
auto AttrsB = *MaybeAttrsB;
if (hasUnknownOrCallerAttr(AttrsA))
return AttrsB.any();
if (hasUnknownOrCallerAttr(AttrsB))
return AttrsA.any();
if (isGlobalOrArgAttr(AttrsA))
return isGlobalOrArgAttr(AttrsB);
if (isGlobalOrArgAttr(AttrsB))
return isGlobalOrArgAttr(AttrsA);
// At this point both LHS and RHS should point to locally allocated objects
auto Itr = AliasMap.find(LHS);
if (Itr != AliasMap.end()) {
// Find out all (X, Offset) where X == RHS
auto Comparator = [](OffsetValue LHS, OffsetValue RHS) {
return std::less<const Value *>()(LHS.Val, RHS.Val);
};
#ifdef EXPENSIVE_CHECKS
assert(std::is_sorted(Itr->second.begin(), Itr->second.end(), Comparator));
#endif
auto RangePair = std::equal_range(Itr->second.begin(), Itr->second.end(),
OffsetValue{RHS, 0}, Comparator);
if (RangePair.first != RangePair.second) {
// Be conservative about UnknownSize
if (LHSSize == MemoryLocation::UnknownSize ||
RHSSize == MemoryLocation::UnknownSize)
return true;
for (const auto &OVal : make_range(RangePair)) {
// Be conservative about UnknownOffset
if (OVal.Offset == UnknownOffset)
return true;
// We know that LHS aliases (RHS + OVal.Offset) if the control flow
// reaches here. The may-alias query essentially becomes integer
// range-overlap queries over two ranges [OVal.Offset, OVal.Offset +
// LHSSize) and [0, RHSSize).
// Try to be conservative on super large offsets
if (LLVM_UNLIKELY(LHSSize > INT64_MAX || RHSSize > INT64_MAX))
return true;
auto LHSStart = OVal.Offset;
// FIXME: Do we need to guard against integer overflow?
auto LHSEnd = OVal.Offset + static_cast<int64_t>(LHSSize);
auto RHSStart = 0;
auto RHSEnd = static_cast<int64_t>(RHSSize);
if (LHSEnd > RHSStart && LHSStart < RHSEnd)
return true;
}
}
}
return false;
}
static void propagate(InstantiatedValue From, InstantiatedValue To,
MatchState State, ReachabilitySet &ReachSet,
std::vector<WorkListItem> &WorkList) {
if (From == To)
return;
if (ReachSet.insert(From, To, State))
WorkList.push_back(WorkListItem{From, To, State});
}
static void initializeWorkList(std::vector<WorkListItem> &WorkList,
ReachabilitySet &ReachSet,
const CFLGraph &Graph) {
for (const auto &Mapping : Graph.value_mappings()) {
auto Val = Mapping.first;
auto &ValueInfo = Mapping.second;
assert(ValueInfo.getNumLevels() > 0);
// Insert all immediate assignment neighbors to the worklist
for (unsigned I = 0, E = ValueInfo.getNumLevels(); I < E; ++I) {
auto Src = InstantiatedValue{Val, I};
// If there's an assignment edge from X to Y, it means Y is reachable from
// X at S2 and X is reachable from Y at S1
for (auto &Edge : ValueInfo.getNodeInfoAtLevel(I).Edges) {
propagate(Edge.Other, Src, MatchState::FlowFromReadOnly, ReachSet,
WorkList);
propagate(Src, Edge.Other, MatchState::FlowToWriteOnly, ReachSet,
WorkList);
}
}
}
}
static Optional<InstantiatedValue> getNodeBelow(const CFLGraph &Graph,
InstantiatedValue V) {
auto NodeBelow = InstantiatedValue{V.Val, V.DerefLevel + 1};
if (Graph.getNode(NodeBelow))
return NodeBelow;
return None;
}
static void processWorkListItem(const WorkListItem &Item, const CFLGraph &Graph,
ReachabilitySet &ReachSet, AliasMemSet &MemSet,
std::vector<WorkListItem> &WorkList) {
auto FromNode = Item.From;
auto ToNode = Item.To;
auto NodeInfo = Graph.getNode(ToNode);
assert(NodeInfo != nullptr);
// TODO: propagate field offsets
// FIXME: Here is a neat trick we can do: since both ReachSet and MemSet holds
// relations that are symmetric, we could actually cut the storage by half by
// sorting FromNode and ToNode before insertion happens.
// The newly added value alias pair may potentially generate more memory
// alias pairs. Check for them here.
auto FromNodeBelow = getNodeBelow(Graph, FromNode);
auto ToNodeBelow = getNodeBelow(Graph, ToNode);
if (FromNodeBelow && ToNodeBelow &&
MemSet.insert(*FromNodeBelow, *ToNodeBelow)) {
propagate(*FromNodeBelow, *ToNodeBelow,
MatchState::FlowFromMemAliasNoReadWrite, ReachSet, WorkList);
for (const auto &Mapping : ReachSet.reachableValueAliases(*FromNodeBelow)) {
auto Src = Mapping.first;
auto MemAliasPropagate = [&](MatchState FromState, MatchState ToState) {
if (Mapping.second.test(static_cast<size_t>(FromState)))
propagate(Src, *ToNodeBelow, ToState, ReachSet, WorkList);
};
MemAliasPropagate(MatchState::FlowFromReadOnly,
MatchState::FlowFromMemAliasReadOnly);
MemAliasPropagate(MatchState::FlowToWriteOnly,
MatchState::FlowToMemAliasWriteOnly);
MemAliasPropagate(MatchState::FlowToReadWrite,
MatchState::FlowToMemAliasReadWrite);
}
}
// This is the core of the state machine walking algorithm. We expand ReachSet
// based on which state we are at (which in turn dictates what edges we
// should examine)
// From a high-level point of view, the state machine here guarantees two
// properties:
// - If *X and *Y are memory aliases, then X and Y are value aliases
// - If Y is an alias of X, then reverse assignment edges (if there is any)
// should precede any assignment edges on the path from X to Y.
auto NextAssignState = [&](MatchState State) {
for (const auto &AssignEdge : NodeInfo->Edges)
propagate(FromNode, AssignEdge.Other, State, ReachSet, WorkList);
};
auto NextRevAssignState = [&](MatchState State) {
for (const auto &RevAssignEdge : NodeInfo->ReverseEdges)
propagate(FromNode, RevAssignEdge.Other, State, ReachSet, WorkList);
};
auto NextMemState = [&](MatchState State) {
if (auto AliasSet = MemSet.getMemoryAliases(ToNode)) {
for (const auto &MemAlias : *AliasSet)
propagate(FromNode, MemAlias, State, ReachSet, WorkList);
}
};
switch (Item.State) {
case MatchState::FlowFromReadOnly:
NextRevAssignState(MatchState::FlowFromReadOnly);
NextAssignState(MatchState::FlowToReadWrite);
NextMemState(MatchState::FlowFromMemAliasReadOnly);
break;
case MatchState::FlowFromMemAliasNoReadWrite:
NextRevAssignState(MatchState::FlowFromReadOnly);
NextAssignState(MatchState::FlowToWriteOnly);
break;
case MatchState::FlowFromMemAliasReadOnly:
NextRevAssignState(MatchState::FlowFromReadOnly);
NextAssignState(MatchState::FlowToReadWrite);
break;
case MatchState::FlowToWriteOnly:
NextAssignState(MatchState::FlowToWriteOnly);
NextMemState(MatchState::FlowToMemAliasWriteOnly);
break;
case MatchState::FlowToReadWrite:
NextAssignState(MatchState::FlowToReadWrite);
NextMemState(MatchState::FlowToMemAliasReadWrite);
break;
case MatchState::FlowToMemAliasWriteOnly:
NextAssignState(MatchState::FlowToWriteOnly);
break;
case MatchState::FlowToMemAliasReadWrite:
NextAssignState(MatchState::FlowToReadWrite);
break;
}
}
static AliasAttrMap buildAttrMap(const CFLGraph &Graph,
const ReachabilitySet &ReachSet) {
AliasAttrMap AttrMap;
std::vector<InstantiatedValue> WorkList, NextList;
// Initialize each node with its original AliasAttrs in CFLGraph
for (const auto &Mapping : Graph.value_mappings()) {
auto Val = Mapping.first;
auto &ValueInfo = Mapping.second;
for (unsigned I = 0, E = ValueInfo.getNumLevels(); I < E; ++I) {
auto Node = InstantiatedValue{Val, I};
AttrMap.add(Node, ValueInfo.getNodeInfoAtLevel(I).Attr);
WorkList.push_back(Node);
}
}
while (!WorkList.empty()) {
for (const auto &Dst : WorkList) {
auto DstAttr = AttrMap.getAttrs(Dst);
if (DstAttr.none())
continue;
// Propagate attr on the same level
for (const auto &Mapping : ReachSet.reachableValueAliases(Dst)) {
auto Src = Mapping.first;
if (AttrMap.add(Src, DstAttr))
NextList.push_back(Src);
}
// Propagate attr to the levels below
auto DstBelow = getNodeBelow(Graph, Dst);
while (DstBelow) {
if (AttrMap.add(*DstBelow, DstAttr)) {
NextList.push_back(*DstBelow);
break;
}
DstBelow = getNodeBelow(Graph, *DstBelow);
}
}
WorkList.swap(NextList);
NextList.clear();
}
return AttrMap;
}
CFLAndersAAResult::FunctionInfo
CFLAndersAAResult::buildInfoFrom(const Function &Fn) {
CFLGraphBuilder<CFLAndersAAResult> GraphBuilder(
*this, TLI,
// Cast away the constness here due to GraphBuilder's API requirement
const_cast<Function &>(Fn));
auto &Graph = GraphBuilder.getCFLGraph();
ReachabilitySet ReachSet;
AliasMemSet MemSet;
std::vector<WorkListItem> WorkList, NextList;
initializeWorkList(WorkList, ReachSet, Graph);
// TODO: make sure we don't stop before the fix point is reached
while (!WorkList.empty()) {
for (const auto &Item : WorkList)
processWorkListItem(Item, Graph, ReachSet, MemSet, NextList);
NextList.swap(WorkList);
NextList.clear();
}
// Now that we have all the reachability info, propagate AliasAttrs according
// to it
auto IValueAttrMap = buildAttrMap(Graph, ReachSet);
return FunctionInfo(Fn, GraphBuilder.getReturnValues(), ReachSet,
std::move(IValueAttrMap));
}
void CFLAndersAAResult::scan(const Function &Fn) {
auto InsertPair = Cache.insert(std::make_pair(&Fn, Optional<FunctionInfo>()));
(void)InsertPair;
assert(InsertPair.second &&
"Trying to scan a function that has already been cached");
// Note that we can't do Cache[Fn] = buildSetsFrom(Fn) here: the function call
// may get evaluated after operator[], potentially triggering a DenseMap
// resize and invalidating the reference returned by operator[]
auto FunInfo = buildInfoFrom(Fn);
Cache[&Fn] = std::move(FunInfo);
Handles.emplace_front(const_cast<Function *>(&Fn), this);
}
void CFLAndersAAResult::evict(const Function *Fn) { Cache.erase(Fn); }
const Optional<CFLAndersAAResult::FunctionInfo> &
CFLAndersAAResult::ensureCached(const Function &Fn) {
auto Iter = Cache.find(&Fn);
if (Iter == Cache.end()) {
scan(Fn);
Iter = Cache.find(&Fn);
assert(Iter != Cache.end());
assert(Iter->second.hasValue());
}
return Iter->second;
}
const AliasSummary *CFLAndersAAResult::getAliasSummary(const Function &Fn) {
auto &FunInfo = ensureCached(Fn);
if (FunInfo.hasValue())
return &FunInfo->getAliasSummary();
else
return nullptr;
}
AliasResult CFLAndersAAResult::query(const MemoryLocation &LocA,
const MemoryLocation &LocB) {
auto *ValA = LocA.Ptr;
auto *ValB = LocB.Ptr;
if (!ValA->getType()->isPointerTy() || !ValB->getType()->isPointerTy())
return NoAlias;
auto *Fn = parentFunctionOfValue(ValA);
if (!Fn) {
Fn = parentFunctionOfValue(ValB);
if (!Fn) {
// The only times this is known to happen are when globals + InlineAsm are
// involved
DEBUG(dbgs()
<< "CFLAndersAA: could not extract parent function information.\n");
return MayAlias;
}
} else {
assert(!parentFunctionOfValue(ValB) || parentFunctionOfValue(ValB) == Fn);
}
assert(Fn != nullptr);
auto &FunInfo = ensureCached(*Fn);
// AliasMap lookup
if (FunInfo->mayAlias(ValA, LocA.Size, ValB, LocB.Size))
return MayAlias;
return NoAlias;
}
AliasResult CFLAndersAAResult::alias(const MemoryLocation &LocA,
const MemoryLocation &LocB) {
if (LocA.Ptr == LocB.Ptr)
return MustAlias;
// Comparisons between global variables and other constants should be
// handled by BasicAA.
// CFLAndersAA may report NoAlias when comparing a GlobalValue and
// ConstantExpr, but every query needs to have at least one Value tied to a
// Function, and neither GlobalValues nor ConstantExprs are.
if (isa<Constant>(LocA.Ptr) && isa<Constant>(LocB.Ptr))
return AAResultBase::alias(LocA, LocB);
AliasResult QueryResult = query(LocA, LocB);
if (QueryResult == MayAlias)
return AAResultBase::alias(LocA, LocB);
return QueryResult;
}
AnalysisKey CFLAndersAA::Key;
CFLAndersAAResult CFLAndersAA::run(Function &F, FunctionAnalysisManager &AM) {
return CFLAndersAAResult(AM.getResult<TargetLibraryAnalysis>(F));
}
char CFLAndersAAWrapperPass::ID = 0;
INITIALIZE_PASS(CFLAndersAAWrapperPass, "cfl-anders-aa",
"Inclusion-Based CFL Alias Analysis", false, true)
ImmutablePass *llvm::createCFLAndersAAWrapperPass() {
return new CFLAndersAAWrapperPass();
}
CFLAndersAAWrapperPass::CFLAndersAAWrapperPass() : ImmutablePass(ID) {
initializeCFLAndersAAWrapperPassPass(*PassRegistry::getPassRegistry());
}
void CFLAndersAAWrapperPass::initializePass() {
auto &TLIWP = getAnalysis<TargetLibraryInfoWrapperPass>();
Result.reset(new CFLAndersAAResult(TLIWP.getTLI()));
}
void CFLAndersAAWrapperPass::getAnalysisUsage(AnalysisUsage &AU) const {
AU.setPreservesAll();
AU.addRequired<TargetLibraryInfoWrapperPass>();
}
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