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llvm/lib/Analysis/CFLAliasAnalysis.cpp
Hal Finkel 6a075f530a [CFL-AA] Update for handling of globals and more tests 
We used to return PartialAlias if *either* variable being queried interacted
with arguments or globals. AFAICT, we can change this to only returning
MayAlias iff *both* variables being queried interacted with arguments or
globals.

Also, adding some basic functionality tests: some basic IPA tests, checking
that we give conservative responses with arguments/globals thrown in the mix,
and ensuring that we trace values through stores and loads.

Note that saying that 'x' interacted with arguments or globals means that the
Attributes of the StratifiedSet that 'x' belongs to has any bits set.

Patch by George Burgess IV, thanks!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@219122 91177308-0d34-0410-b5e6-96231b3b80d8
2014-10-06 14:42:56 +00:00

1003 lines
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//===- CFLAliasAnalysis.cpp - CFL-Based Alias Analysis Implementation ------==//
//
// 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 context-insensitive alias analysis
// algorithm. It does not depend on types. The algorithm is a mixture of the one
// described in "Demand-driven alias analysis for C" by Xin Zheng and Radu
// Rugina, and "Fast algorithms for Dyck-CFL-reachability with applications to
// Alias Analysis" by Zhang Q, Lyu M R, Yuan H, and Su Z. -- to summarize the
// papers, we build a graph of the uses of a variable, where each node is a
// memory location, and each edge is an action that happened on that memory
// location. The "actions" can be one of Dereference, Reference, Assign, or
// Assign.
//
// Two variables are considered as aliasing iff you can reach one value's node
// from the other value's node and the language formed by concatenating all of
// the edge labels (actions) conforms to a context-free grammar.
//
// Because this algorithm requires a graph search on each query, we execute the
// algorithm outlined in "Fast algorithms..." (mentioned above)
// in order to transform the graph into sets of variables that may alias in
// ~nlogn time (n = number of variables.), which makes queries take constant
// time.
//===----------------------------------------------------------------------===//
#include "StratifiedSets.h"
#include "llvm/Analysis/Passes.h"
#include "llvm/ADT/BitVector.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/Optional.h"
#include "llvm/ADT/None.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/InstVisitor.h"
#include "llvm/IR/ValueHandle.h"
#include "llvm/Pass.h"
#include "llvm/Support/Allocator.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/ErrorHandling.h"
#include <algorithm>
#include <cassert>
#include <forward_list>
#include <tuple>
using namespace llvm;
// Try to go from a Value* to a Function*. Never returns nullptr.
static Optional<Function *> parentFunctionOfValue(Value *);
// Returns possible functions called by the Inst* into the given
// SmallVectorImpl. Returns true if targets found, false otherwise.
// This is templated because InvokeInst/CallInst give us the same
// set of functions that we care about, and I don't like repeating
// myself.
template <typename Inst>
static bool getPossibleTargets(Inst *, SmallVectorImpl<Function *> &);
// Some instructions need to have their users tracked. Instructions like
// `add` require you to get the users of the Instruction* itself, other
// instructions like `store` require you to get the users of the first
// operand. This function gets the "proper" value to track for each
// type of instruction we support.
static Optional<Value *> getTargetValue(Instruction *);
// There are certain instructions (i.e. FenceInst, etc.) that we ignore.
// This notes that we should ignore those.
static bool hasUsefulEdges(Instruction *);
const StratifiedIndex StratifiedLink::SetSentinel =
std::numeric_limits<StratifiedIndex>::max();
namespace {
// StratifiedInfo Attribute things.
typedef unsigned StratifiedAttr;
LLVM_CONSTEXPR unsigned MaxStratifiedAttrIndex = NumStratifiedAttrs;
LLVM_CONSTEXPR unsigned AttrAllIndex = 0;
LLVM_CONSTEXPR unsigned AttrGlobalIndex = 1;
LLVM_CONSTEXPR unsigned AttrFirstArgIndex = 2;
LLVM_CONSTEXPR unsigned AttrLastArgIndex = MaxStratifiedAttrIndex;
LLVM_CONSTEXPR unsigned AttrMaxNumArgs = AttrLastArgIndex - AttrFirstArgIndex;
LLVM_CONSTEXPR StratifiedAttr AttrNone = 0;
LLVM_CONSTEXPR StratifiedAttr AttrAll = ~AttrNone;
// \brief StratifiedSets call for knowledge of "direction", so this is how we
// represent that locally.
enum class Level { Same, Above, Below };
// \brief Edges can be one of four "weights" -- each weight must have an inverse
// weight (Assign has Assign; Reference has Dereference).
enum class EdgeType {
// The weight assigned when assigning from or to a value. For example, in:
// %b = getelementptr %a, 0
// ...The relationships are %b assign %a, and %a assign %b. This used to be
// two edges, but having a distinction bought us nothing.
Assign,
// The edge used when we have an edge going from some handle to a Value.
// Examples of this include:
// %b = load %a (%b Dereference %a)
// %b = extractelement %a, 0 (%a Dereference %b)
Dereference,
// The edge used when our edge goes from a value to a handle that may have
// contained it at some point. Examples:
// %b = load %a (%a Reference %b)
// %b = extractelement %a, 0 (%b Reference %a)
Reference
};
// \brief Encodes the notion of a "use"
struct Edge {
// \brief Which value the edge is coming from
Value *From;
// \brief Which value the edge is pointing to
Value *To;
// \brief Edge weight
EdgeType Weight;
// \brief Whether we aliased any external values along the way that may be
// invisible to the analysis (i.e. landingpad for exceptions, calls for
// interprocedural analysis, etc.)
StratifiedAttrs AdditionalAttrs;
Edge(Value *From, Value *To, EdgeType W, StratifiedAttrs A)
: From(From), To(To), Weight(W), AdditionalAttrs(A) {}
};
// \brief Information we have about a function and would like to keep around
struct FunctionInfo {
StratifiedSets<Value *> Sets;
// Lots of functions have < 4 returns. Adjust as necessary.
SmallVector<Value *, 4> ReturnedValues;
FunctionInfo(StratifiedSets<Value *> &&S,
SmallVector<Value *, 4> &&RV)
: Sets(std::move(S)), ReturnedValues(std::move(RV)) {}
};
struct CFLAliasAnalysis;
struct FunctionHandle : public CallbackVH {
FunctionHandle(Function *Fn, CFLAliasAnalysis *CFLAA)
: CallbackVH(Fn), CFLAA(CFLAA) {
assert(Fn != nullptr);
assert(CFLAA != nullptr);
}
virtual ~FunctionHandle() {}
virtual void deleted() override { removeSelfFromCache(); }
virtual void allUsesReplacedWith(Value *) override { removeSelfFromCache(); }
private:
CFLAliasAnalysis *CFLAA;
void removeSelfFromCache();
};
struct CFLAliasAnalysis : public ImmutablePass, public AliasAnalysis {
private:
/// \brief Cached mapping of Functions to their StratifiedSets.
/// If a function's sets are currently being built, it is marked
/// in the cache as an Optional without a value. This way, if we
/// have any kind of recursion, it is discernable from a function
/// that simply has empty sets.
DenseMap<Function *, Optional<FunctionInfo>> Cache;
std::forward_list<FunctionHandle> Handles;
public:
static char ID;
CFLAliasAnalysis() : ImmutablePass(ID) {
initializeCFLAliasAnalysisPass(*PassRegistry::getPassRegistry());
}
virtual ~CFLAliasAnalysis() {}
void getAnalysisUsage(AnalysisUsage &AU) const override {
AliasAnalysis::getAnalysisUsage(AU);
}
void *getAdjustedAnalysisPointer(const void *ID) override {
if (ID == &AliasAnalysis::ID)
return (AliasAnalysis *)this;
return this;
}
/// \brief Inserts the given Function into the cache.
void scan(Function *Fn);
void evict(Function *Fn) { Cache.erase(Fn); }
/// \brief Ensures that the given function is available in the cache.
/// Returns the appropriate entry from the cache.
const Optional<FunctionInfo> &ensureCached(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;
}
AliasResult query(const Location &LocA, const Location &LocB);
AliasResult alias(const Location &LocA, const Location &LocB) override {
if (LocA.Ptr == LocB.Ptr) {
if (LocA.Size == LocB.Size) {
return MustAlias;
} else {
return PartialAlias;
}
}
// Comparisons between global variables and other constants should be
// handled by BasicAA.
if (isa<Constant>(LocA.Ptr) && isa<Constant>(LocB.Ptr)) {
return MayAlias;
}
return query(LocA, LocB);
}
void initializePass() override { InitializeAliasAnalysis(this); }
};
void FunctionHandle::removeSelfFromCache() {
assert(CFLAA != nullptr);
auto *Val = getValPtr();
CFLAA->evict(cast<Function>(Val));
setValPtr(nullptr);
}
// \brief Gets the edges our graph should have, based on an Instruction*
class GetEdgesVisitor : public InstVisitor<GetEdgesVisitor, void> {
CFLAliasAnalysis &AA;
SmallVectorImpl<Edge> &Output;
public:
GetEdgesVisitor(CFLAliasAnalysis &AA, SmallVectorImpl<Edge> &Output)
: AA(AA), Output(Output) {}
void visitInstruction(Instruction &) {
llvm_unreachable("Unsupported instruction encountered");
}
void visitCastInst(CastInst &Inst) {
Output.push_back(Edge(&Inst, Inst.getOperand(0), EdgeType::Assign,
AttrNone));
}
void visitBinaryOperator(BinaryOperator &Inst) {
auto *Op1 = Inst.getOperand(0);
auto *Op2 = Inst.getOperand(1);
Output.push_back(Edge(&Inst, Op1, EdgeType::Assign, AttrNone));
Output.push_back(Edge(&Inst, Op2, EdgeType::Assign, AttrNone));
}
void visitAtomicCmpXchgInst(AtomicCmpXchgInst &Inst) {
auto *Ptr = Inst.getPointerOperand();
auto *Val = Inst.getNewValOperand();
Output.push_back(Edge(Ptr, Val, EdgeType::Dereference, AttrNone));
}
void visitAtomicRMWInst(AtomicRMWInst &Inst) {
auto *Ptr = Inst.getPointerOperand();
auto *Val = Inst.getValOperand();
Output.push_back(Edge(Ptr, Val, EdgeType::Dereference, AttrNone));
}
void visitPHINode(PHINode &Inst) {
for (unsigned I = 0, E = Inst.getNumIncomingValues(); I != E; ++I) {
Value *Val = Inst.getIncomingValue(I);
Output.push_back(Edge(&Inst, Val, EdgeType::Assign, AttrNone));
}
}
void visitGetElementPtrInst(GetElementPtrInst &Inst) {
auto *Op = Inst.getPointerOperand();
Output.push_back(Edge(&Inst, Op, EdgeType::Assign, AttrNone));
for (auto I = Inst.idx_begin(), E = Inst.idx_end(); I != E; ++I)
Output.push_back(Edge(&Inst, *I, EdgeType::Assign, AttrNone));
}
void visitSelectInst(SelectInst &Inst) {
auto *Condition = Inst.getCondition();
Output.push_back(Edge(&Inst, Condition, EdgeType::Assign, AttrNone));
auto *TrueVal = Inst.getTrueValue();
Output.push_back(Edge(&Inst, TrueVal, EdgeType::Assign, AttrNone));
auto *FalseVal = Inst.getFalseValue();
Output.push_back(Edge(&Inst, FalseVal, EdgeType::Assign, AttrNone));
}
void visitAllocaInst(AllocaInst &) {}
void visitLoadInst(LoadInst &Inst) {
auto *Ptr = Inst.getPointerOperand();
auto *Val = &Inst;
Output.push_back(Edge(Val, Ptr, EdgeType::Reference, AttrNone));
}
void visitStoreInst(StoreInst &Inst) {
auto *Ptr = Inst.getPointerOperand();
auto *Val = Inst.getValueOperand();
Output.push_back(Edge(Ptr, Val, EdgeType::Dereference, AttrNone));
}
static bool isFunctionExternal(Function *Fn) {
return Fn->isDeclaration() || !Fn->hasLocalLinkage();
}
// Gets whether the sets at Index1 above, below, or equal to the sets at
// Index2. Returns None if they are not in the same set chain.
static Optional<Level> getIndexRelation(const StratifiedSets<Value *> &Sets,
StratifiedIndex Index1,
StratifiedIndex Index2) {
if (Index1 == Index2)
return Level::Same;
const auto *Current = &Sets.getLink(Index1);
while (Current->hasBelow()) {
if (Current->Below == Index2)
return Level::Below;
Current = &Sets.getLink(Current->Below);
}
Current = &Sets.getLink(Index1);
while (Current->hasAbove()) {
if (Current->Above == Index2)
return Level::Above;
Current = &Sets.getLink(Current->Above);
}
return NoneType();
}
bool
tryInterproceduralAnalysis(const SmallVectorImpl<Function *> &Fns,
Value *FuncValue,
const iterator_range<User::op_iterator> &Args) {
const unsigned ExpectedMaxArgs = 8;
const unsigned MaxSupportedArgs = 50;
assert(Fns.size() > 0);
// I put this here to give us an upper bound on time taken by IPA. Is it
// really (realistically) needed? Keep in mind that we do have an n^2 algo.
if (std::distance(Args.begin(), Args.end()) > (int) MaxSupportedArgs)
return false;
// Exit early if we'll fail anyway
for (auto *Fn : Fns) {
if (isFunctionExternal(Fn) || Fn->isVarArg())
return false;
auto &MaybeInfo = AA.ensureCached(Fn);
if (!MaybeInfo.hasValue())
return false;
}
SmallVector<Value *, ExpectedMaxArgs> Arguments(Args.begin(), Args.end());
SmallVector<StratifiedInfo, ExpectedMaxArgs> Parameters;
for (auto *Fn : Fns) {
auto &Info = *AA.ensureCached(Fn);
auto &Sets = Info.Sets;
auto &RetVals = Info.ReturnedValues;
Parameters.clear();
for (auto &Param : Fn->args()) {
auto MaybeInfo = Sets.find(&Param);
// Did a new parameter somehow get added to the function/slip by?
if (!MaybeInfo.hasValue())
return false;
Parameters.push_back(*MaybeInfo);
}
// Adding an edge from argument -> return value for each parameter that
// may alias the return value
for (unsigned I = 0, E = Parameters.size(); I != E; ++I) {
auto &ParamInfo = Parameters[I];
auto &ArgVal = Arguments[I];
bool AddEdge = false;
StratifiedAttrs Externals;
for (unsigned X = 0, XE = RetVals.size(); X != XE; ++X) {
auto MaybeInfo = Sets.find(RetVals[X]);
if (!MaybeInfo.hasValue())
return false;
auto &RetInfo = *MaybeInfo;
auto RetAttrs = Sets.getLink(RetInfo.Index).Attrs;
auto ParamAttrs = Sets.getLink(ParamInfo.Index).Attrs;
auto MaybeRelation =
getIndexRelation(Sets, ParamInfo.Index, RetInfo.Index);
if (MaybeRelation.hasValue()) {
AddEdge = true;
Externals |= RetAttrs | ParamAttrs;
}
}
if (AddEdge)
Output.push_back(Edge(FuncValue, ArgVal, EdgeType::Assign,
StratifiedAttrs().flip()));
}
if (Parameters.size() != Arguments.size())
return false;
// Adding edges between arguments for arguments that may end up aliasing
// each other. This is necessary for functions such as
// void foo(int** a, int** b) { *a = *b; }
// (Technically, the proper sets for this would be those below
// Arguments[I] and Arguments[X], but our algorithm will produce
// extremely similar, and equally correct, results either way)
for (unsigned I = 0, E = Arguments.size(); I != E; ++I) {
auto &MainVal = Arguments[I];
auto &MainInfo = Parameters[I];
auto &MainAttrs = Sets.getLink(MainInfo.Index).Attrs;
for (unsigned X = I + 1; X != E; ++X) {
auto &SubInfo = Parameters[X];
auto &SubVal = Arguments[X];
auto &SubAttrs = Sets.getLink(SubInfo.Index).Attrs;
auto MaybeRelation =
getIndexRelation(Sets, MainInfo.Index, SubInfo.Index);
if (!MaybeRelation.hasValue())
continue;
auto NewAttrs = SubAttrs | MainAttrs;
Output.push_back(Edge(MainVal, SubVal, EdgeType::Assign, NewAttrs));
}
}
}
return true;
}
template <typename InstT> void visitCallLikeInst(InstT &Inst) {
SmallVector<Function *, 4> Targets;
if (getPossibleTargets(&Inst, Targets)) {
if (tryInterproceduralAnalysis(Targets, &Inst, Inst.arg_operands()))
return;
// Cleanup from interprocedural analysis
Output.clear();
}
for (Value *V : Inst.arg_operands())
Output.push_back(Edge(&Inst, V, EdgeType::Assign, AttrAll));
}
void visitCallInst(CallInst &Inst) { visitCallLikeInst(Inst); }
void visitInvokeInst(InvokeInst &Inst) { visitCallLikeInst(Inst); }
// Because vectors/aggregates are immutable and unaddressable,
// there's nothing we can do to coax a value out of them, other
// than calling Extract{Element,Value}. We can effectively treat
// them as pointers to arbitrary memory locations we can store in
// and load from.
void visitExtractElementInst(ExtractElementInst &Inst) {
auto *Ptr = Inst.getVectorOperand();
auto *Val = &Inst;
Output.push_back(Edge(Val, Ptr, EdgeType::Reference, AttrNone));
}
void visitInsertElementInst(InsertElementInst &Inst) {
auto *Vec = Inst.getOperand(0);
auto *Val = Inst.getOperand(1);
Output.push_back(Edge(&Inst, Vec, EdgeType::Assign, AttrNone));
Output.push_back(Edge(&Inst, Val, EdgeType::Dereference, AttrNone));
}
void visitLandingPadInst(LandingPadInst &Inst) {
// Exceptions come from "nowhere", from our analysis' perspective.
// So we place the instruction its own group, noting that said group may
// alias externals
Output.push_back(Edge(&Inst, &Inst, EdgeType::Assign, AttrAll));
}
void visitInsertValueInst(InsertValueInst &Inst) {
auto *Agg = Inst.getOperand(0);
auto *Val = Inst.getOperand(1);
Output.push_back(Edge(&Inst, Agg, EdgeType::Assign, AttrNone));
Output.push_back(Edge(&Inst, Val, EdgeType::Dereference, AttrNone));
}
void visitExtractValueInst(ExtractValueInst &Inst) {
auto *Ptr = Inst.getAggregateOperand();
Output.push_back(Edge(&Inst, Ptr, EdgeType::Reference, AttrNone));
}
void visitShuffleVectorInst(ShuffleVectorInst &Inst) {
auto *From1 = Inst.getOperand(0);
auto *From2 = Inst.getOperand(1);
Output.push_back(Edge(&Inst, From1, EdgeType::Assign, AttrNone));
Output.push_back(Edge(&Inst, From2, EdgeType::Assign, AttrNone));
}
};
// For a given instruction, we need to know which Value* to get the
// users of in order to build our graph. In some cases (i.e. add),
// we simply need the Instruction*. In other cases (i.e. store),
// finding the users of the Instruction* is useless; we need to find
// the users of the first operand. This handles determining which
// value to follow for us.
//
// Note: we *need* to keep this in sync with GetEdgesVisitor. Add
// something to GetEdgesVisitor, add it here -- remove something from
// GetEdgesVisitor, remove it here.
class GetTargetValueVisitor
: public InstVisitor<GetTargetValueVisitor, Value *> {
public:
Value *visitInstruction(Instruction &Inst) { return &Inst; }
Value *visitStoreInst(StoreInst &Inst) { return Inst.getPointerOperand(); }
Value *visitAtomicCmpXchgInst(AtomicCmpXchgInst &Inst) {
return Inst.getPointerOperand();
}
Value *visitAtomicRMWInst(AtomicRMWInst &Inst) {
return Inst.getPointerOperand();
}
Value *visitInsertElementInst(InsertElementInst &Inst) {
return Inst.getOperand(0);
}
Value *visitInsertValueInst(InsertValueInst &Inst) {
return Inst.getAggregateOperand();
}
};
// Set building requires a weighted bidirectional graph.
template <typename EdgeTypeT> class WeightedBidirectionalGraph {
public:
typedef std::size_t Node;
private:
const static Node StartNode = Node(0);
struct Edge {
EdgeTypeT Weight;
Node Other;
Edge(const EdgeTypeT &W, const Node &N)
: Weight(W), Other(N) {}
bool operator==(const Edge &E) const {
return Weight == E.Weight && Other == E.Other;
}
bool operator!=(const Edge &E) const { return !operator==(E); }
};
struct NodeImpl {
std::vector<Edge> Edges;
};
std::vector<NodeImpl> NodeImpls;
bool inbounds(Node NodeIndex) const { return NodeIndex < NodeImpls.size(); }
const NodeImpl &getNode(Node N) const { return NodeImpls[N]; }
NodeImpl &getNode(Node N) { return NodeImpls[N]; }
public:
// ----- Various Edge iterators for the graph ----- //
// \brief Iterator for edges. Because this graph is bidirected, we don't
// allow modificaiton of the edges using this iterator. Additionally, the
// iterator becomes invalid if you add edges to or from the node you're
// getting the edges of.
struct EdgeIterator : public std::iterator<std::forward_iterator_tag,
std::tuple<EdgeTypeT, Node *>> {
EdgeIterator(const typename std::vector<Edge>::const_iterator &Iter)
: Current(Iter) {}
EdgeIterator(NodeImpl &Impl) : Current(Impl.begin()) {}
EdgeIterator &operator++() {
++Current;
return *this;
}
EdgeIterator operator++(int) {
EdgeIterator Copy(Current);
operator++();
return Copy;
}
std::tuple<EdgeTypeT, Node> &operator*() {
Store = std::make_tuple(Current->Weight, Current->Other);
return Store;
}
bool operator==(const EdgeIterator &Other) const {
return Current == Other.Current;
}
bool operator!=(const EdgeIterator &Other) const {
return !operator==(Other);
}
private:
typename std::vector<Edge>::const_iterator Current;
std::tuple<EdgeTypeT, Node> Store;
};
// Wrapper for EdgeIterator with begin()/end() calls.
struct EdgeIterable {
EdgeIterable(const std::vector<Edge> &Edges)
: BeginIter(Edges.begin()), EndIter(Edges.end()) {}
EdgeIterator begin() { return EdgeIterator(BeginIter); }
EdgeIterator end() { return EdgeIterator(EndIter); }
private:
typename std::vector<Edge>::const_iterator BeginIter;
typename std::vector<Edge>::const_iterator EndIter;
};
// ----- Actual graph-related things ----- //
WeightedBidirectionalGraph() {}
WeightedBidirectionalGraph(WeightedBidirectionalGraph<EdgeTypeT> &&Other)
: NodeImpls(std::move(Other.NodeImpls)) {}
WeightedBidirectionalGraph<EdgeTypeT> &
operator=(WeightedBidirectionalGraph<EdgeTypeT> &&Other) {
NodeImpls = std::move(Other.NodeImpls);
return *this;
}
Node addNode() {
auto Index = NodeImpls.size();
auto NewNode = Node(Index);
NodeImpls.push_back(NodeImpl());
return NewNode;
}
void addEdge(Node From, Node To, const EdgeTypeT &Weight,
const EdgeTypeT &ReverseWeight) {
assert(inbounds(From));
assert(inbounds(To));
auto &FromNode = getNode(From);
auto &ToNode = getNode(To);
FromNode.Edges.push_back(Edge(Weight, To));
ToNode.Edges.push_back(Edge(ReverseWeight, From));
}
EdgeIterable edgesFor(const Node &N) const {
const auto &Node = getNode(N);
return EdgeIterable(Node.Edges);
}
bool empty() const { return NodeImpls.empty(); }
std::size_t size() const { return NodeImpls.size(); }
// \brief Gets an arbitrary node in the graph as a starting point for
// traversal.
Node getEntryNode() {
assert(inbounds(StartNode));
return StartNode;
}
};
typedef WeightedBidirectionalGraph<std::pair<EdgeType, StratifiedAttrs>> GraphT;
typedef DenseMap<Value *, GraphT::Node> NodeMapT;
}
// -- Setting up/registering CFLAA pass -- //
char CFLAliasAnalysis::ID = 0;
INITIALIZE_AG_PASS(CFLAliasAnalysis, AliasAnalysis, "cfl-aa",
"CFL-Based AA implementation", false, true, false)
ImmutablePass *llvm::createCFLAliasAnalysisPass() {
return new CFLAliasAnalysis();
}
//===----------------------------------------------------------------------===//
// Function declarations that require types defined in the namespace above
//===----------------------------------------------------------------------===//
// Given an argument number, returns the appropriate Attr index to set.
static StratifiedAttr argNumberToAttrIndex(StratifiedAttr);
// Given a Value, potentially return which AttrIndex it maps to.
static Optional<StratifiedAttr> valueToAttrIndex(Value *Val);
// Gets the inverse of a given EdgeType.
static EdgeType flipWeight(EdgeType);
// Gets edges of the given Instruction*, writing them to the SmallVector*.
static void argsToEdges(CFLAliasAnalysis &, Instruction *,
SmallVectorImpl<Edge> &);
// Gets the "Level" that one should travel in StratifiedSets
// given an EdgeType.
static Level directionOfEdgeType(EdgeType);
// Builds the graph needed for constructing the StratifiedSets for the
// given function
static void buildGraphFrom(CFLAliasAnalysis &, Function *,
SmallVectorImpl<Value *> &, NodeMapT &, GraphT &);
// Builds the graph + StratifiedSets for a function.
static FunctionInfo buildSetsFrom(CFLAliasAnalysis &, Function *);
static Optional<Function *> parentFunctionOfValue(Value *Val) {
if (auto *Inst = dyn_cast<Instruction>(Val)) {
auto *Bb = Inst->getParent();
return Bb->getParent();
}
if (auto *Arg = dyn_cast<Argument>(Val))
return Arg->getParent();
return NoneType();
}
template <typename Inst>
static bool getPossibleTargets(Inst *Call,
SmallVectorImpl<Function *> &Output) {
if (auto *Fn = Call->getCalledFunction()) {
Output.push_back(Fn);
return true;
}
// TODO: If the call is indirect, we might be able to enumerate all potential
// targets of the call and return them, rather than just failing.
return false;
}
static Optional<Value *> getTargetValue(Instruction *Inst) {
GetTargetValueVisitor V;
return V.visit(Inst);
}
static bool hasUsefulEdges(Instruction *Inst) {
bool IsNonInvokeTerminator =
isa<TerminatorInst>(Inst) && !isa<InvokeInst>(Inst);
return !isa<CmpInst>(Inst) && !isa<FenceInst>(Inst) && !IsNonInvokeTerminator;
}
static Optional<StratifiedAttr> valueToAttrIndex(Value *Val) {
if (isa<GlobalValue>(Val))
return AttrGlobalIndex;
if (auto *Arg = dyn_cast<Argument>(Val))
if (!Arg->hasNoAliasAttr())
return argNumberToAttrIndex(Arg->getArgNo());
return NoneType();
}
static StratifiedAttr argNumberToAttrIndex(unsigned ArgNum) {
if (ArgNum > AttrMaxNumArgs)
return AttrAllIndex;
return ArgNum + AttrFirstArgIndex;
}
static EdgeType flipWeight(EdgeType Initial) {
switch (Initial) {
case EdgeType::Assign:
return EdgeType::Assign;
case EdgeType::Dereference:
return EdgeType::Reference;
case EdgeType::Reference:
return EdgeType::Dereference;
}
llvm_unreachable("Incomplete coverage of EdgeType enum");
}
static void argsToEdges(CFLAliasAnalysis &Analysis, Instruction *Inst,
SmallVectorImpl<Edge> &Output) {
GetEdgesVisitor v(Analysis, Output);
v.visit(Inst);
}
static Level directionOfEdgeType(EdgeType Weight) {
switch (Weight) {
case EdgeType::Reference:
return Level::Above;
case EdgeType::Dereference:
return Level::Below;
case EdgeType::Assign:
return Level::Same;
}
llvm_unreachable("Incomplete switch coverage");
}
// Aside: We may remove graph construction entirely, because it doesn't really
// buy us much that we don't already have. I'd like to add interprocedural
// analysis prior to this however, in case that somehow requires the graph
// produced by this for efficient execution
static void buildGraphFrom(CFLAliasAnalysis &Analysis, Function *Fn,
SmallVectorImpl<Value *> &ReturnedValues,
NodeMapT &Map, GraphT &Graph) {
const auto findOrInsertNode = [&Map, &Graph](Value *Val) {
auto Pair = Map.insert(std::make_pair(Val, GraphT::Node()));
auto &Iter = Pair.first;
if (Pair.second) {
auto NewNode = Graph.addNode();
Iter->second = NewNode;
}
return Iter->second;
};
SmallVector<Edge, 8> Edges;
for (auto &Bb : Fn->getBasicBlockList()) {
for (auto &Inst : Bb.getInstList()) {
// We don't want the edges of most "return" instructions, but we *do* want
// to know what can be returned.
if (auto *Ret = dyn_cast<ReturnInst>(&Inst))
ReturnedValues.push_back(Ret);
if (!hasUsefulEdges(&Inst))
continue;
Edges.clear();
argsToEdges(Analysis, &Inst, Edges);
// In the case of an unused alloca (or similar), edges may be empty. Note
// that it exists so we can potentially answer NoAlias.
if (Edges.empty()) {
auto MaybeVal = getTargetValue(&Inst);
assert(MaybeVal.hasValue());
auto *Target = *MaybeVal;
findOrInsertNode(Target);
continue;
}
for (const Edge &E : Edges) {
auto To = findOrInsertNode(E.To);
auto From = findOrInsertNode(E.From);
auto FlippedWeight = flipWeight(E.Weight);
auto Attrs = E.AdditionalAttrs;
Graph.addEdge(From, To, std::make_pair(E.Weight, Attrs),
std::make_pair(FlippedWeight, Attrs));
}
}
}
}
static FunctionInfo buildSetsFrom(CFLAliasAnalysis &Analysis, Function *Fn) {
NodeMapT Map;
GraphT Graph;
SmallVector<Value *, 4> ReturnedValues;
buildGraphFrom(Analysis, Fn, ReturnedValues, Map, Graph);
DenseMap<GraphT::Node, Value *> NodeValueMap;
NodeValueMap.resize(Map.size());
for (const auto &Pair : Map)
NodeValueMap.insert(std::make_pair(Pair.second, Pair.first));
const auto findValueOrDie = [&NodeValueMap](GraphT::Node Node) {
auto ValIter = NodeValueMap.find(Node);
assert(ValIter != NodeValueMap.end());
return ValIter->second;
};
StratifiedSetsBuilder<Value *> Builder;
SmallVector<GraphT::Node, 16> Worklist;
for (auto &Pair : Map) {
Worklist.clear();
auto *Value = Pair.first;
Builder.add(Value);
auto InitialNode = Pair.second;
Worklist.push_back(InitialNode);
while (!Worklist.empty()) {
auto Node = Worklist.pop_back_val();
auto *CurValue = findValueOrDie(Node);
if (isa<Constant>(CurValue) && !isa<GlobalValue>(CurValue))
continue;
for (const auto &EdgeTuple : Graph.edgesFor(Node)) {
auto Weight = std::get<0>(EdgeTuple);
auto Label = Weight.first;
auto &OtherNode = std::get<1>(EdgeTuple);
auto *OtherValue = findValueOrDie(OtherNode);
if (isa<Constant>(OtherValue) && !isa<GlobalValue>(OtherValue))
continue;
bool Added;
switch (directionOfEdgeType(Label)) {
case Level::Above:
Added = Builder.addAbove(CurValue, OtherValue);
break;
case Level::Below:
Added = Builder.addBelow(CurValue, OtherValue);
break;
case Level::Same:
Added = Builder.addWith(CurValue, OtherValue);
break;
}
if (Added) {
auto Aliasing = Weight.second;
if (auto MaybeCurIndex = valueToAttrIndex(CurValue))
Aliasing.set(*MaybeCurIndex);
if (auto MaybeOtherIndex = valueToAttrIndex(OtherValue))
Aliasing.set(*MaybeOtherIndex);
Builder.noteAttributes(CurValue, Aliasing);
Builder.noteAttributes(OtherValue, Aliasing);
Worklist.push_back(OtherNode);
}
}
}
}
// There are times when we end up with parameters not in our graph (i.e. if
// it's only used as the condition of a branch). Other bits of code depend on
// things that were present during construction being present in the graph.
// So, we add all present arguments here.
for (auto &Arg : Fn->args()) {
Builder.add(&Arg);
}
return FunctionInfo(Builder.build(), std::move(ReturnedValues));
}
void CFLAliasAnalysis::scan(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");
FunctionInfo Info(buildSetsFrom(*this, Fn));
Cache[Fn] = std::move(Info);
Handles.push_front(FunctionHandle(Fn, this));
}
AliasAnalysis::AliasResult
CFLAliasAnalysis::query(const AliasAnalysis::Location &LocA,
const AliasAnalysis::Location &LocB) {
auto *ValA = const_cast<Value *>(LocA.Ptr);
auto *ValB = const_cast<Value *>(LocB.Ptr);
Function *Fn = nullptr;
auto MaybeFnA = parentFunctionOfValue(ValA);
auto MaybeFnB = parentFunctionOfValue(ValB);
if (!MaybeFnA.hasValue() && !MaybeFnB.hasValue()) {
llvm_unreachable("Don't know how to extract the parent function "
"from values A or B");
}
if (MaybeFnA.hasValue()) {
Fn = *MaybeFnA;
assert((!MaybeFnB.hasValue() || *MaybeFnB == *MaybeFnA) &&
"Interprocedural queries not supported");
} else {
Fn = *MaybeFnB;
}
assert(Fn != nullptr);
auto &MaybeInfo = ensureCached(Fn);
assert(MaybeInfo.hasValue());
auto &Sets = MaybeInfo->Sets;
auto MaybeA = Sets.find(ValA);
if (!MaybeA.hasValue())
return AliasAnalysis::MayAlias;
auto MaybeB = Sets.find(ValB);
if (!MaybeB.hasValue())
return AliasAnalysis::MayAlias;
auto SetA = *MaybeA;
auto SetB = *MaybeB;
if (SetA.Index == SetB.Index)
return AliasAnalysis::PartialAlias;
auto AttrsA = Sets.getLink(SetA.Index).Attrs;
auto AttrsB = Sets.getLink(SetB.Index).Attrs;
// Stratified set attributes are used as markets to signify whether a member
// of a StratifiedSet (or a member of a set above the current set) has
// interacted with either arguments or globals. "Interacted with" meaning
// its value may be different depending on the value of an argument or
// global. The thought behind this is that, because arguments and globals
// may alias each other, if AttrsA and AttrsB have touched args/globals,
// we must conservatively say that they alias. However, if at least one of
// the sets has no values that could legally be altered by changing the value
// of an argument or global, then we don't have to be as conservative.
if (AttrsA.any() && AttrsB.any())
return AliasAnalysis::MayAlias;
return AliasAnalysis::NoAlias;
}
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