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f23c6af13d
We already had a method to iterate over all the incoming values of a PHI. This just changes all eligible code to use it. Ineligible code included anything which cared about the index, or was also trying to get the i'th incoming BB. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@237169 91177308-0d34-0410-b5e6-96231b3b80d8
1155 lines
39 KiB
C++
1155 lines
39 KiB
C++
//===- CFLAliasAnalysis.cpp - CFL-Based Alias Analysis Implementation ------==//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file implements a CFL-based context-insensitive alias analysis
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// algorithm. It does not depend on types. The algorithm is a mixture of the one
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// described in "Demand-driven alias analysis for C" by Xin Zheng and Radu
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// Rugina, and "Fast algorithms for Dyck-CFL-reachability with applications to
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// Alias Analysis" by Zhang Q, Lyu M R, Yuan H, and Su Z. -- to summarize the
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// papers, we build a graph of the uses of a variable, where each node is a
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// memory location, and each edge is an action that happened on that memory
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// location. The "actions" can be one of Dereference, Reference, Assign, or
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// Assign.
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//
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// Two variables are considered as aliasing iff you can reach one value's node
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// from the other value's node and the language formed by concatenating all of
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// the edge labels (actions) conforms to a context-free grammar.
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//
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// Because this algorithm requires a graph search on each query, we execute the
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// algorithm outlined in "Fast algorithms..." (mentioned above)
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// in order to transform the graph into sets of variables that may alias in
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// ~nlogn time (n = number of variables.), which makes queries take constant
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// time.
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//===----------------------------------------------------------------------===//
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#include "StratifiedSets.h"
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#include "llvm/ADT/BitVector.h"
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#include "llvm/ADT/DenseMap.h"
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#include "llvm/ADT/None.h"
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#include "llvm/ADT/Optional.h"
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#include "llvm/Analysis/AliasAnalysis.h"
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#include "llvm/Analysis/Passes.h"
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#include "llvm/IR/Constants.h"
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#include "llvm/IR/Function.h"
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#include "llvm/IR/InstVisitor.h"
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#include "llvm/IR/Instructions.h"
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#include "llvm/IR/ValueHandle.h"
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#include "llvm/Pass.h"
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#include "llvm/Support/Allocator.h"
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#include "llvm/Support/Compiler.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/ErrorHandling.h"
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#include "llvm/Support/raw_ostream.h"
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#include <algorithm>
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#include <cassert>
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#include <forward_list>
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#include <memory>
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#include <tuple>
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using namespace llvm;
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#define DEBUG_TYPE "cfl-aa"
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// Try to go from a Value* to a Function*. Never returns nullptr.
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static Optional<Function *> parentFunctionOfValue(Value *);
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// Returns possible functions called by the Inst* into the given
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// SmallVectorImpl. Returns true if targets found, false otherwise.
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// This is templated because InvokeInst/CallInst give us the same
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// set of functions that we care about, and I don't like repeating
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// myself.
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template <typename Inst>
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static bool getPossibleTargets(Inst *, SmallVectorImpl<Function *> &);
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// Some instructions need to have their users tracked. Instructions like
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// `add` require you to get the users of the Instruction* itself, other
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// instructions like `store` require you to get the users of the first
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// operand. This function gets the "proper" value to track for each
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// type of instruction we support.
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static Optional<Value *> getTargetValue(Instruction *);
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// There are certain instructions (i.e. FenceInst, etc.) that we ignore.
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// This notes that we should ignore those.
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static bool hasUsefulEdges(Instruction *);
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const StratifiedIndex StratifiedLink::SetSentinel =
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std::numeric_limits<StratifiedIndex>::max();
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namespace {
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// StratifiedInfo Attribute things.
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typedef unsigned StratifiedAttr;
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LLVM_CONSTEXPR unsigned MaxStratifiedAttrIndex = NumStratifiedAttrs;
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LLVM_CONSTEXPR unsigned AttrAllIndex = 0;
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LLVM_CONSTEXPR unsigned AttrGlobalIndex = 1;
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LLVM_CONSTEXPR unsigned AttrUnknownIndex = 2;
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LLVM_CONSTEXPR unsigned AttrFirstArgIndex = 3;
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LLVM_CONSTEXPR unsigned AttrLastArgIndex = MaxStratifiedAttrIndex;
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LLVM_CONSTEXPR unsigned AttrMaxNumArgs = AttrLastArgIndex - AttrFirstArgIndex;
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LLVM_CONSTEXPR StratifiedAttr AttrNone = 0;
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LLVM_CONSTEXPR StratifiedAttr AttrUnknown = 1 << AttrUnknownIndex;
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LLVM_CONSTEXPR StratifiedAttr AttrAll = ~AttrNone;
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// \brief StratifiedSets call for knowledge of "direction", so this is how we
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// represent that locally.
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enum class Level { Same, Above, Below };
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// \brief Edges can be one of four "weights" -- each weight must have an inverse
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// weight (Assign has Assign; Reference has Dereference).
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enum class EdgeType {
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// The weight assigned when assigning from or to a value. For example, in:
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// %b = getelementptr %a, 0
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// ...The relationships are %b assign %a, and %a assign %b. This used to be
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// two edges, but having a distinction bought us nothing.
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Assign,
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// The edge used when we have an edge going from some handle to a Value.
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// Examples of this include:
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// %b = load %a (%b Dereference %a)
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// %b = extractelement %a, 0 (%a Dereference %b)
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Dereference,
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// The edge used when our edge goes from a value to a handle that may have
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// contained it at some point. Examples:
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// %b = load %a (%a Reference %b)
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// %b = extractelement %a, 0 (%b Reference %a)
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Reference
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};
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// \brief Encodes the notion of a "use"
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struct Edge {
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// \brief Which value the edge is coming from
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Value *From;
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// \brief Which value the edge is pointing to
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Value *To;
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// \brief Edge weight
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EdgeType Weight;
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// \brief Whether we aliased any external values along the way that may be
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// invisible to the analysis (i.e. landingpad for exceptions, calls for
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// interprocedural analysis, etc.)
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StratifiedAttrs AdditionalAttrs;
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Edge(Value *From, Value *To, EdgeType W, StratifiedAttrs A)
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: From(From), To(To), Weight(W), AdditionalAttrs(A) {}
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};
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// \brief Information we have about a function and would like to keep around
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struct FunctionInfo {
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StratifiedSets<Value *> Sets;
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// Lots of functions have < 4 returns. Adjust as necessary.
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SmallVector<Value *, 4> ReturnedValues;
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FunctionInfo(StratifiedSets<Value *> &&S, SmallVector<Value *, 4> &&RV)
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: Sets(std::move(S)), ReturnedValues(std::move(RV)) {}
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};
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struct CFLAliasAnalysis;
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struct FunctionHandle : public CallbackVH {
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FunctionHandle(Function *Fn, CFLAliasAnalysis *CFLAA)
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: CallbackVH(Fn), CFLAA(CFLAA) {
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assert(Fn != nullptr);
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assert(CFLAA != nullptr);
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}
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~FunctionHandle() override {}
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void deleted() override { removeSelfFromCache(); }
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void allUsesReplacedWith(Value *) override { removeSelfFromCache(); }
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private:
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CFLAliasAnalysis *CFLAA;
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void removeSelfFromCache();
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};
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struct CFLAliasAnalysis : public ImmutablePass, public AliasAnalysis {
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private:
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/// \brief Cached mapping of Functions to their StratifiedSets.
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/// If a function's sets are currently being built, it is marked
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/// in the cache as an Optional without a value. This way, if we
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/// have any kind of recursion, it is discernable from a function
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/// that simply has empty sets.
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DenseMap<Function *, Optional<FunctionInfo>> Cache;
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std::forward_list<FunctionHandle> Handles;
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public:
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static char ID;
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CFLAliasAnalysis() : ImmutablePass(ID) {
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initializeCFLAliasAnalysisPass(*PassRegistry::getPassRegistry());
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}
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~CFLAliasAnalysis() override {}
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void getAnalysisUsage(AnalysisUsage &AU) const override {
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AliasAnalysis::getAnalysisUsage(AU);
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}
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void *getAdjustedAnalysisPointer(const void *ID) override {
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if (ID == &AliasAnalysis::ID)
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return (AliasAnalysis *)this;
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return this;
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}
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/// \brief Inserts the given Function into the cache.
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void scan(Function *Fn);
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void evict(Function *Fn) { Cache.erase(Fn); }
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/// \brief Ensures that the given function is available in the cache.
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/// Returns the appropriate entry from the cache.
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const Optional<FunctionInfo> &ensureCached(Function *Fn) {
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auto Iter = Cache.find(Fn);
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if (Iter == Cache.end()) {
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scan(Fn);
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Iter = Cache.find(Fn);
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assert(Iter != Cache.end());
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assert(Iter->second.hasValue());
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}
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return Iter->second;
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}
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AliasResult query(const Location &LocA, const Location &LocB);
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AliasResult alias(const Location &LocA, const Location &LocB) override {
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if (LocA.Ptr == LocB.Ptr) {
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if (LocA.Size == LocB.Size) {
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return MustAlias;
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} else {
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return PartialAlias;
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}
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}
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// Comparisons between global variables and other constants should be
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// handled by BasicAA.
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// TODO: ConstantExpr handling -- CFLAA may report NoAlias when comparing
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// a GlobalValue and ConstantExpr, but every query needs to have at least
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// one Value tied to a Function, and neither GlobalValues nor ConstantExprs
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// are.
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if (isa<Constant>(LocA.Ptr) && isa<Constant>(LocB.Ptr)) {
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return AliasAnalysis::alias(LocA, LocB);
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}
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AliasResult QueryResult = query(LocA, LocB);
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if (QueryResult == MayAlias)
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return AliasAnalysis::alias(LocA, LocB);
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return QueryResult;
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}
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bool doInitialization(Module &M) override;
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};
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void FunctionHandle::removeSelfFromCache() {
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assert(CFLAA != nullptr);
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auto *Val = getValPtr();
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CFLAA->evict(cast<Function>(Val));
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setValPtr(nullptr);
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}
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// \brief Gets the edges our graph should have, based on an Instruction*
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class GetEdgesVisitor : public InstVisitor<GetEdgesVisitor, void> {
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CFLAliasAnalysis &AA;
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SmallVectorImpl<Edge> &Output;
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public:
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GetEdgesVisitor(CFLAliasAnalysis &AA, SmallVectorImpl<Edge> &Output)
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: AA(AA), Output(Output) {}
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void visitInstruction(Instruction &) {
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llvm_unreachable("Unsupported instruction encountered");
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}
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void visitPtrToIntInst(PtrToIntInst &Inst) {
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auto *Ptr = Inst.getOperand(0);
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Output.push_back(Edge(Ptr, Ptr, EdgeType::Assign, AttrUnknown));
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}
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void visitIntToPtrInst(IntToPtrInst &Inst) {
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auto *Ptr = &Inst;
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Output.push_back(Edge(Ptr, Ptr, EdgeType::Assign, AttrUnknown));
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}
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void visitCastInst(CastInst &Inst) {
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Output.push_back(
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Edge(&Inst, Inst.getOperand(0), EdgeType::Assign, AttrNone));
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}
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void visitBinaryOperator(BinaryOperator &Inst) {
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auto *Op1 = Inst.getOperand(0);
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auto *Op2 = Inst.getOperand(1);
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Output.push_back(Edge(&Inst, Op1, EdgeType::Assign, AttrNone));
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Output.push_back(Edge(&Inst, Op2, EdgeType::Assign, AttrNone));
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}
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void visitAtomicCmpXchgInst(AtomicCmpXchgInst &Inst) {
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auto *Ptr = Inst.getPointerOperand();
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auto *Val = Inst.getNewValOperand();
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Output.push_back(Edge(Ptr, Val, EdgeType::Dereference, AttrNone));
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}
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void visitAtomicRMWInst(AtomicRMWInst &Inst) {
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auto *Ptr = Inst.getPointerOperand();
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auto *Val = Inst.getValOperand();
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Output.push_back(Edge(Ptr, Val, EdgeType::Dereference, AttrNone));
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}
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void visitPHINode(PHINode &Inst) {
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for (Value *Val : Inst.incoming_values()) {
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Output.push_back(Edge(&Inst, Val, EdgeType::Assign, AttrNone));
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}
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}
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void visitGetElementPtrInst(GetElementPtrInst &Inst) {
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auto *Op = Inst.getPointerOperand();
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Output.push_back(Edge(&Inst, Op, EdgeType::Assign, AttrNone));
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for (auto I = Inst.idx_begin(), E = Inst.idx_end(); I != E; ++I)
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Output.push_back(Edge(&Inst, *I, EdgeType::Assign, AttrNone));
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}
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void visitSelectInst(SelectInst &Inst) {
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// Condition is not processed here (The actual statement producing
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// the condition result is processed elsewhere). For select, the
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// condition is evaluated, but not loaded, stored, or assigned
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// simply as a result of being the condition of a select.
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auto *TrueVal = Inst.getTrueValue();
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Output.push_back(Edge(&Inst, TrueVal, EdgeType::Assign, AttrNone));
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auto *FalseVal = Inst.getFalseValue();
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Output.push_back(Edge(&Inst, FalseVal, EdgeType::Assign, AttrNone));
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}
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void visitAllocaInst(AllocaInst &) {}
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void visitLoadInst(LoadInst &Inst) {
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auto *Ptr = Inst.getPointerOperand();
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auto *Val = &Inst;
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Output.push_back(Edge(Val, Ptr, EdgeType::Reference, AttrNone));
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}
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void visitStoreInst(StoreInst &Inst) {
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auto *Ptr = Inst.getPointerOperand();
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auto *Val = Inst.getValueOperand();
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Output.push_back(Edge(Ptr, Val, EdgeType::Dereference, AttrNone));
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}
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void visitVAArgInst(VAArgInst &Inst) {
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// We can't fully model va_arg here. For *Ptr = Inst.getOperand(0), it does
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// two things:
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// 1. Loads a value from *((T*)*Ptr).
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// 2. Increments (stores to) *Ptr by some target-specific amount.
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// For now, we'll handle this like a landingpad instruction (by placing the
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// result in its own group, and having that group alias externals).
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auto *Val = &Inst;
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Output.push_back(Edge(Val, Val, EdgeType::Assign, AttrAll));
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}
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static bool isFunctionExternal(Function *Fn) {
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return Fn->isDeclaration() || !Fn->hasLocalLinkage();
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}
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// Gets whether the sets at Index1 above, below, or equal to the sets at
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// Index2. Returns None if they are not in the same set chain.
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static Optional<Level> getIndexRelation(const StratifiedSets<Value *> &Sets,
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StratifiedIndex Index1,
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StratifiedIndex Index2) {
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if (Index1 == Index2)
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return Level::Same;
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const auto *Current = &Sets.getLink(Index1);
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while (Current->hasBelow()) {
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if (Current->Below == Index2)
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return Level::Below;
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Current = &Sets.getLink(Current->Below);
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}
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Current = &Sets.getLink(Index1);
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while (Current->hasAbove()) {
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if (Current->Above == Index2)
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return Level::Above;
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Current = &Sets.getLink(Current->Above);
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}
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return NoneType();
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}
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bool
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tryInterproceduralAnalysis(const SmallVectorImpl<Function *> &Fns,
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Value *FuncValue,
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const iterator_range<User::op_iterator> &Args) {
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const unsigned ExpectedMaxArgs = 8;
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const unsigned MaxSupportedArgs = 50;
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assert(Fns.size() > 0);
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// I put this here to give us an upper bound on time taken by IPA. Is it
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// really (realistically) needed? Keep in mind that we do have an n^2 algo.
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if (std::distance(Args.begin(), Args.end()) > (int)MaxSupportedArgs)
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return false;
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// Exit early if we'll fail anyway
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for (auto *Fn : Fns) {
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if (isFunctionExternal(Fn) || Fn->isVarArg())
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return false;
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auto &MaybeInfo = AA.ensureCached(Fn);
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if (!MaybeInfo.hasValue())
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return false;
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}
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SmallVector<Value *, ExpectedMaxArgs> Arguments(Args.begin(), Args.end());
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SmallVector<StratifiedInfo, ExpectedMaxArgs> Parameters;
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for (auto *Fn : Fns) {
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auto &Info = *AA.ensureCached(Fn);
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auto &Sets = Info.Sets;
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auto &RetVals = Info.ReturnedValues;
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Parameters.clear();
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for (auto &Param : Fn->args()) {
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auto MaybeInfo = Sets.find(&Param);
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// Did a new parameter somehow get added to the function/slip by?
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if (!MaybeInfo.hasValue())
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return false;
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Parameters.push_back(*MaybeInfo);
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}
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// Adding an edge from argument -> return value for each parameter that
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// may alias the return value
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for (unsigned I = 0, E = Parameters.size(); I != E; ++I) {
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auto &ParamInfo = Parameters[I];
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auto &ArgVal = Arguments[I];
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bool AddEdge = false;
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StratifiedAttrs Externals;
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for (unsigned X = 0, XE = RetVals.size(); X != XE; ++X) {
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auto MaybeInfo = Sets.find(RetVals[X]);
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if (!MaybeInfo.hasValue())
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return false;
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auto &RetInfo = *MaybeInfo;
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auto RetAttrs = Sets.getLink(RetInfo.Index).Attrs;
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auto ParamAttrs = Sets.getLink(ParamInfo.Index).Attrs;
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auto MaybeRelation =
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getIndexRelation(Sets, ParamInfo.Index, RetInfo.Index);
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if (MaybeRelation.hasValue()) {
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AddEdge = true;
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Externals |= RetAttrs | ParamAttrs;
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}
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}
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if (AddEdge)
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Output.push_back(Edge(FuncValue, ArgVal, EdgeType::Assign,
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StratifiedAttrs().flip()));
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}
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if (Parameters.size() != Arguments.size())
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return false;
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// Adding edges between arguments for arguments that may end up aliasing
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// each other. This is necessary for functions such as
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// void foo(int** a, int** b) { *a = *b; }
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// (Technically, the proper sets for this would be those below
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// Arguments[I] and Arguments[X], but our algorithm will produce
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// extremely similar, and equally correct, results either way)
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for (unsigned I = 0, E = Arguments.size(); I != E; ++I) {
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auto &MainVal = Arguments[I];
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auto &MainInfo = Parameters[I];
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auto &MainAttrs = Sets.getLink(MainInfo.Index).Attrs;
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for (unsigned X = I + 1; X != E; ++X) {
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auto &SubInfo = Parameters[X];
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auto &SubVal = Arguments[X];
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auto &SubAttrs = Sets.getLink(SubInfo.Index).Attrs;
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auto MaybeRelation =
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getIndexRelation(Sets, MainInfo.Index, SubInfo.Index);
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if (!MaybeRelation.hasValue())
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continue;
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auto NewAttrs = SubAttrs | MainAttrs;
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Output.push_back(Edge(MainVal, SubVal, EdgeType::Assign, NewAttrs));
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}
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}
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}
|
|
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 &);
|
|
|
|
// 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(CFLAliasAnalysis &, 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(CFLAliasAnalysis &, Instruction &,
|
|
SmallVectorImpl<Value *> &, NodeMapT &,
|
|
GraphT &);
|
|
|
|
// Notes whether it would be pointless to add the given Value to our sets.
|
|
static bool canSkipAddingToSets(Value *Val);
|
|
|
|
// 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))
|
|
// 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(CFLAliasAnalysis &Analysis, Instruction *Inst,
|
|
SmallVectorImpl<Edge> &Output) {
|
|
assert(hasUsefulEdges(Inst) &&
|
|
"Expected instructions to have 'useful' edges");
|
|
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");
|
|
}
|
|
|
|
static void constexprToEdges(CFLAliasAnalysis &Analysis,
|
|
ConstantExpr &CExprToCollapse,
|
|
SmallVectorImpl<Edge> &Results) {
|
|
SmallVector<ConstantExpr *, 4> Worklist;
|
|
Worklist.push_back(&CExprToCollapse);
|
|
|
|
SmallVector<Edge, 8> ConstexprEdges;
|
|
while (!Worklist.empty()) {
|
|
auto *CExpr = Worklist.pop_back_val();
|
|
std::unique_ptr<Instruction> Inst(CExpr->getAsInstruction());
|
|
|
|
if (!hasUsefulEdges(Inst.get()))
|
|
continue;
|
|
|
|
ConstexprEdges.clear();
|
|
argsToEdges(Analysis, Inst.get(), ConstexprEdges);
|
|
for (auto &Edge : ConstexprEdges) {
|
|
if (Edge.From == Inst.get())
|
|
Edge.From = CExpr;
|
|
else if (auto *Nested = dyn_cast<ConstantExpr>(Edge.From))
|
|
Worklist.push_back(Nested);
|
|
|
|
if (Edge.To == Inst.get())
|
|
Edge.To = CExpr;
|
|
else if (auto *Nested = dyn_cast<ConstantExpr>(Edge.To))
|
|
Worklist.push_back(Nested);
|
|
}
|
|
|
|
Results.append(ConstexprEdges.begin(), ConstexprEdges.end());
|
|
}
|
|
}
|
|
|
|
static void addInstructionToGraph(CFLAliasAnalysis &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(CFLAliasAnalysis &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;
|
|
}
|
|
|
|
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 (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 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()) {
|
|
// 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 AliasAnalysis::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 AliasAnalysis::MayAlias;
|
|
|
|
auto MaybeB = Sets.find(ValB);
|
|
if (!MaybeB.hasValue())
|
|
return AliasAnalysis::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 AliasAnalysis::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 AliasAnalysis::MayAlias;
|
|
|
|
return AliasAnalysis::NoAlias;
|
|
}
|
|
|
|
bool CFLAliasAnalysis::doInitialization(Module &M) {
|
|
InitializeAliasAnalysis(this, &M.getDataLayout());
|
|
return true;
|
|
}
|