llvm/lib/Analysis/CFLAliasAnalysis.cpp
Chandler Carruth 9146833fa3 [PM/AA] Rebuild LLVM's alias analysis infrastructure in a way compatible
with the new pass manager, and no longer relying on analysis groups.

This builds essentially a ground-up new AA infrastructure stack for
LLVM. The core ideas are the same that are used throughout the new pass
manager: type erased polymorphism and direct composition. The design is
as follows:

- FunctionAAResults is a type-erasing alias analysis results aggregation
  interface to walk a single query across a range of results from
  different alias analyses. Currently this is function-specific as we
  always assume that aliasing queries are *within* a function.

- AAResultBase is a CRTP utility providing stub implementations of
  various parts of the alias analysis result concept, notably in several
  cases in terms of other more general parts of the interface. This can
  be used to implement only a narrow part of the interface rather than
  the entire interface. This isn't really ideal, this logic should be
  hoisted into FunctionAAResults as currently it will cause
  a significant amount of redundant work, but it faithfully models the
  behavior of the prior infrastructure.

- All the alias analysis passes are ported to be wrapper passes for the
  legacy PM and new-style analysis passes for the new PM with a shared
  result object. In some cases (most notably CFL), this is an extremely
  naive approach that we should revisit when we can specialize for the
  new pass manager.

- BasicAA has been restructured to reflect that it is much more
  fundamentally a function analysis because it uses dominator trees and
  loop info that need to be constructed for each function.

All of the references to getting alias analysis results have been
updated to use the new aggregation interface. All the preservation and
other pass management code has been updated accordingly.

The way the FunctionAAResultsWrapperPass works is to detect the
available alias analyses when run, and add them to the results object.
This means that we should be able to continue to respect when various
passes are added to the pipeline, for example adding CFL or adding TBAA
passes should just cause their results to be available and to get folded
into this. The exception to this rule is BasicAA which really needs to
be a function pass due to using dominator trees and loop info. As
a consequence, the FunctionAAResultsWrapperPass directly depends on
BasicAA and always includes it in the aggregation.

This has significant implications for preserving analyses. Generally,
most passes shouldn't bother preserving FunctionAAResultsWrapperPass
because rebuilding the results just updates the set of known AA passes.
The exception to this rule are LoopPass instances which need to preserve
all the function analyses that the loop pass manager will end up
needing. This means preserving both BasicAAWrapperPass and the
aggregating FunctionAAResultsWrapperPass.

Now, when preserving an alias analysis, you do so by directly preserving
that analysis. This is only necessary for non-immutable-pass-provided
alias analyses though, and there are only three of interest: BasicAA,
GlobalsAA (formerly GlobalsModRef), and SCEVAA. Usually BasicAA is
preserved when needed because it (like DominatorTree and LoopInfo) is
marked as a CFG-only pass. I've expanded GlobalsAA into the preserved
set everywhere we previously were preserving all of AliasAnalysis, and
I've added SCEVAA in the intersection of that with where we preserve
SCEV itself.

One significant challenge to all of this is that the CGSCC passes were
actually using the alias analysis implementations by taking advantage of
a pretty amazing set of loop holes in the old pass manager's analysis
management code which allowed analysis groups to slide through in many
cases. Moving away from analysis groups makes this problem much more
obvious. To fix it, I've leveraged the flexibility the design of the new
PM components provides to just directly construct the relevant alias
analyses for the relevant functions in the IPO passes that need them.
This is a bit hacky, but should go away with the new pass manager, and
is already in many ways cleaner than the prior state.

Another significant challenge is that various facilities of the old
alias analysis infrastructure just don't fit any more. The most
significant of these is the alias analysis 'counter' pass. That pass
relied on the ability to snoop on AA queries at different points in the
analysis group chain. Instead, I'm planning to build printing
functionality directly into the aggregation layer. I've not included
that in this patch merely to keep it smaller.

Note that all of this needs a nearly complete rewrite of the AA
documentation. I'm planning to do that, but I'd like to make sure the
new design settles, and to flesh out a bit more of what it looks like in
the new pass manager first.

Differential Revision: http://reviews.llvm.org/D12080

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@247167 91177308-0d34-0410-b5e6-96231b3b80d8
2015-09-09 17:55:00 +00:00

1120 lines
39 KiB
C++

//===- 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, 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 "llvm/Analysis/CFLAliasAnalysis.h"
#include "StratifiedSets.h"
#include "llvm/ADT/BitVector.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/None.h"
#include "llvm/ADT/Optional.h"
#include "llvm/Analysis/TargetLibraryInfo.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/InstVisitor.h"
#include "llvm/IR/Instructions.h"
#include "llvm/Pass.h"
#include "llvm/Support/Allocator.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"
#include <algorithm>
#include <cassert>
#include <memory>
#include <tuple>
using namespace llvm;
#define DEBUG_TYPE "cfl-aa"
CFLAAResult::CFLAAResult(const TargetLibraryInfo &TLI) : AAResultBase(TLI) {}
CFLAAResult::CFLAAResult(CFLAAResult &&Arg) : AAResultBase(std::move(Arg)) {}
// \brief Information we have about a function and would like to keep around
struct CFLAAResult::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)) {}
};
// 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 AttrUnknownIndex = 2;
LLVM_CONSTEXPR unsigned AttrFirstArgIndex = 3;
LLVM_CONSTEXPR unsigned AttrLastArgIndex = MaxStratifiedAttrIndex;
LLVM_CONSTEXPR unsigned AttrMaxNumArgs = AttrLastArgIndex - AttrFirstArgIndex;
LLVM_CONSTEXPR StratifiedAttr AttrNone = 0;
LLVM_CONSTEXPR StratifiedAttr AttrUnknown = 1 << AttrUnknownIndex;
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 Gets the edges our graph should have, based on an Instruction*
class GetEdgesVisitor : public InstVisitor<GetEdgesVisitor, void> {
CFLAAResult &AA;
SmallVectorImpl<Edge> &Output;
public:
GetEdgesVisitor(CFLAAResult &AA, SmallVectorImpl<Edge> &Output)
: AA(AA), Output(Output) {}
void visitInstruction(Instruction &) {
llvm_unreachable("Unsupported instruction encountered");
}
void visitPtrToIntInst(PtrToIntInst &Inst) {
auto *Ptr = Inst.getOperand(0);
Output.push_back(Edge(Ptr, Ptr, EdgeType::Assign, AttrUnknown));
}
void visitIntToPtrInst(IntToPtrInst &Inst) {
auto *Ptr = &Inst;
Output.push_back(Edge(Ptr, Ptr, EdgeType::Assign, AttrUnknown));
}
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 (Value *Val : Inst.incoming_values()) {
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) {
// Condition is not processed here (The actual statement producing
// the condition result is processed elsewhere). For select, the
// condition is evaluated, but not loaded, stored, or assigned
// simply as a result of being the condition of a select.
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));
}
void visitVAArgInst(VAArgInst &Inst) {
// We can't fully model va_arg here. For *Ptr = Inst.getOperand(0), it does
// two things:
// 1. Loads a value from *((T*)*Ptr).
// 2. Increments (stores to) *Ptr by some target-specific amount.
// For now, we'll handle this like a landingpad instruction (by placing the
// result in its own group, and having that group alias externals).
auto *Val = &Inst;
Output.push_back(Edge(Val, Val, EdgeType::Assign, AttrAll));
}
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) {
// TODO: Add support for noalias args/all the other fun function attributes
// that we can tack on.
SmallVector<Function *, 4> Targets;
if (getPossibleTargets(&Inst, Targets)) {
if (tryInterproceduralAnalysis(Targets, &Inst, Inst.arg_operands()))
return;
// Cleanup from interprocedural analysis
Output.clear();
}
// Because the function is opaque, we need to note that anything
// could have happened to the arguments, and that the result could alias
// just about anything, too.
// The goal of the loop is in part to unify many Values into one set, so we
// don't care if the function is void there.
for (Value *V : Inst.arg_operands())
Output.push_back(Edge(&Inst, V, EdgeType::Assign, AttrAll));
if (Inst.getNumArgOperands() == 0 &&
Inst.getType() != Type::getVoidTy(Inst.getContext()))
Output.push_back(Edge(&Inst, &Inst, 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));
}
void visitConstantExpr(ConstantExpr *CE) {
switch (CE->getOpcode()) {
default:
llvm_unreachable("Unknown instruction type encountered!");
// Build the switch statement using the Instruction.def file.
#define HANDLE_INST(NUM, OPCODE, CLASS) \
case Instruction::OPCODE: \
visit##OPCODE(*(CLASS *)CE); \
break;
#include "llvm/IR/Instruction.def"
}
}
};
// 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 modification 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;
}
//===----------------------------------------------------------------------===//
// 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(CFLAAResult &, Instruction *, SmallVectorImpl<Edge> &);
// Gets edges of the given ConstantExpr*, writing them to the SmallVector*.
static void argsToEdges(CFLAAResult &, ConstantExpr *, 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(CFLAAResult &, Function *,
SmallVectorImpl<Value *> &, NodeMapT &, GraphT &);
// Gets the edges of a ConstantExpr as if it was an Instruction. This
// function also acts on any nested ConstantExprs, adding the edges
// of those to the given SmallVector as well.
static void constexprToEdges(CFLAAResult &, ConstantExpr &,
SmallVectorImpl<Edge> &);
// Given an Instruction, this will add it to the graph, along with any
// Instructions that are potentially only available from said Instruction
// For example, given the following line:
// %0 = load i16* getelementptr ([1 x i16]* @a, 0, 0), align 2
// addInstructionToGraph would add both the `load` and `getelementptr`
// instructions to the graph appropriately.
static void addInstructionToGraph(CFLAAResult &, Instruction &,
SmallVectorImpl<Value *> &, NodeMapT &,
GraphT &);
// Notes whether it would be pointless to add the given Value to our sets.
static bool canSkipAddingToSets(Value *Val);
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 bool hasUsefulEdges(ConstantExpr *CE) {
// ConstantExpr doesn't have terminators, invokes, or fences, so only needs
// to check for compares.
return CE->getOpcode() != Instruction::ICmp &&
CE->getOpcode() != Instruction::FCmp;
}
static Optional<StratifiedAttr> valueToAttrIndex(Value *Val) {
if (isa<GlobalValue>(Val))
return AttrGlobalIndex;
if (auto *Arg = dyn_cast<Argument>(Val))
// Only pointer arguments should have the argument attribute,
// because things can't escape through scalars without us seeing a
// cast, and thus, interaction with them doesn't matter.
if (!Arg->hasNoAliasAttr() && Arg->getType()->isPointerTy())
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(CFLAAResult &Analysis, Instruction *Inst,
SmallVectorImpl<Edge> &Output) {
assert(hasUsefulEdges(Inst) &&
"Expected instructions to have 'useful' edges");
GetEdgesVisitor v(Analysis, Output);
v.visit(Inst);
}
static void argsToEdges(CFLAAResult &Analysis, ConstantExpr *CE,
SmallVectorImpl<Edge> &Output) {
assert(hasUsefulEdges(CE) && "Expected constant expr to have 'useful' edges");
GetEdgesVisitor v(Analysis, Output);
v.visitConstantExpr(CE);
}
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");
}
static void constexprToEdges(CFLAAResult &Analysis,
ConstantExpr &CExprToCollapse,
SmallVectorImpl<Edge> &Results) {
SmallVector<ConstantExpr *, 4> Worklist;
Worklist.push_back(&CExprToCollapse);
SmallVector<Edge, 8> ConstexprEdges;
SmallPtrSet<ConstantExpr *, 4> Visited;
while (!Worklist.empty()) {
auto *CExpr = Worklist.pop_back_val();
if (!hasUsefulEdges(CExpr))
continue;
ConstexprEdges.clear();
argsToEdges(Analysis, CExpr, ConstexprEdges);
for (auto &Edge : ConstexprEdges) {
if (auto *Nested = dyn_cast<ConstantExpr>(Edge.From))
if (Visited.insert(Nested).second)
Worklist.push_back(Nested);
if (auto *Nested = dyn_cast<ConstantExpr>(Edge.To))
if (Visited.insert(Nested).second)
Worklist.push_back(Nested);
}
Results.append(ConstexprEdges.begin(), ConstexprEdges.end());
}
}
static void addInstructionToGraph(CFLAAResult &Analysis, Instruction &Inst,
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;
};
// We don't want the edges of most "return" instructions, but we *do* want
// to know what can be returned.
if (isa<ReturnInst>(&Inst))
ReturnedValues.push_back(&Inst);
if (!hasUsefulEdges(&Inst))
return;
SmallVector<Edge, 8> Edges;
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);
return;
}
const auto addEdgeToGraph = [&Graph, &findOrInsertNode](const Edge &E) {
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));
};
SmallVector<ConstantExpr *, 4> ConstantExprs;
for (const Edge &E : Edges) {
addEdgeToGraph(E);
if (auto *Constexpr = dyn_cast<ConstantExpr>(E.To))
ConstantExprs.push_back(Constexpr);
if (auto *Constexpr = dyn_cast<ConstantExpr>(E.From))
ConstantExprs.push_back(Constexpr);
}
for (ConstantExpr *CE : ConstantExprs) {
Edges.clear();
constexprToEdges(Analysis, *CE, Edges);
std::for_each(Edges.begin(), Edges.end(), addEdgeToGraph);
}
}
// 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(CFLAAResult &Analysis, Function *Fn,
SmallVectorImpl<Value *> &ReturnedValues,
NodeMapT &Map, GraphT &Graph) {
for (auto &Bb : Fn->getBasicBlockList())
for (auto &Inst : Bb.getInstList())
addInstructionToGraph(Analysis, Inst, ReturnedValues, Map, Graph);
}
static bool canSkipAddingToSets(Value *Val) {
// Constants can share instances, which may falsely unify multiple
// sets, e.g. in
// store i32* null, i32** %ptr1
// store i32* null, i32** %ptr2
// clearly ptr1 and ptr2 should not be unified into the same set, so
// we should filter out the (potentially shared) instance to
// i32* null.
if (isa<Constant>(Val)) {
bool Container = isa<ConstantVector>(Val) || isa<ConstantArray>(Val) ||
isa<ConstantStruct>(Val);
// TODO: Because all of these things are constant, we can determine whether
// the data is *actually* mutable at graph building time. This will probably
// come for free/cheap with offset awareness.
bool CanStoreMutableData =
isa<GlobalValue>(Val) || isa<ConstantExpr>(Val) || Container;
return !CanStoreMutableData;
}
return false;
}
// Builds the graph + StratifiedSets for a function.
CFLAAResult::FunctionInfo CFLAAResult::buildSetsFrom(Function *Fn) {
NodeMapT Map;
GraphT Graph;
SmallVector<Value *, 4> ReturnedValues;
buildGraphFrom(*this, 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 (canSkipAddingToSets(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 (canSkipAddingToSets(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;
}
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);
if (Added)
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()) {
if (!Builder.add(&Arg))
continue;
auto Attrs = valueToAttrIndex(&Arg);
if (Attrs.hasValue())
Builder.noteAttributes(&Arg, *Attrs);
}
return FunctionInfo(Builder.build(), std::move(ReturnedValues));
}
void CFLAAResult::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(Fn));
Cache[Fn] = std::move(Info);
Handles.push_front(FunctionHandle(Fn, this));
}
void CFLAAResult::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<CFLAAResult::FunctionInfo> &
CFLAAResult::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 CFLAAResult::query(const MemoryLocation &LocA,
const MemoryLocation &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()) {
// The only times this is known to happen are when globals + InlineAsm
// are involved
DEBUG(dbgs() << "CFLAA: could not extract parent function information.\n");
return MayAlias;
}
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 MayAlias;
auto MaybeB = Sets.find(ValB);
if (!MaybeB.hasValue())
return MayAlias;
auto SetA = *MaybeA;
auto SetB = *MaybeB;
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 MayAlias;
// We currently unify things even if the accesses to them may not be in
// bounds, so we can't return partial alias here because we don't
// know whether the pointer is really within the object or not.
// IE Given an out of bounds GEP and an alloca'd pointer, we may
// unify the two. We can't return partial alias for this case.
// Since we do not currently track enough information to
// differentiate
if (SetA.Index == SetB.Index)
return MayAlias;
return NoAlias;
}
CFLAAResult CFLAA::run(Function &F, AnalysisManager<Function> *AM) {
return CFLAAResult(AM->getResult<TargetLibraryAnalysis>(F));
}
char CFLAA::PassID;
char CFLAAWrapperPass::ID = 0;
INITIALIZE_PASS_BEGIN(CFLAAWrapperPass, "cfl-aa", "CFL-Based Alias Analysis",
false, true)
INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
INITIALIZE_PASS_END(CFLAAWrapperPass, "cfl-aa", "CFL-Based Alias Analysis",
false, true)
ImmutablePass *llvm::createCFLAAWrapperPass() { return new CFLAAWrapperPass(); }
CFLAAWrapperPass::CFLAAWrapperPass() : ImmutablePass(ID) {
initializeCFLAAWrapperPassPass(*PassRegistry::getPassRegistry());
}
bool CFLAAWrapperPass::doInitialization(Module &M) {
Result.reset(
new CFLAAResult(getAnalysis<TargetLibraryInfoWrapperPass>().getTLI()));
return false;
}
bool CFLAAWrapperPass::doFinalization(Module &M) {
Result.reset();
return false;
}
void CFLAAWrapperPass::getAnalysisUsage(AnalysisUsage &AU) const {
AU.setPreservesAll();
AU.addRequired<TargetLibraryInfoWrapperPass>();
}