311 lines
11 KiB
C++
311 lines
11 KiB
C++
//===- BasicAliasAnalysis.h - Stateless, local Alias Analysis ---*- C++ -*-===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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/// \file
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/// This is the interface for LLVM's primary stateless and local alias analysis.
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///
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_ANALYSIS_BASICALIASANALYSIS_H
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#define LLVM_ANALYSIS_BASICALIASANALYSIS_H
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#include "llvm/ADT/DenseMap.h"
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#include "llvm/ADT/Optional.h"
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#include "llvm/ADT/SmallPtrSet.h"
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#include "llvm/ADT/SmallVector.h"
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#include "llvm/Analysis/AliasAnalysis.h"
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#include "llvm/IR/PassManager.h"
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#include "llvm/Pass.h"
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#include <algorithm>
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#include <cstdint>
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#include <memory>
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#include <utility>
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namespace llvm {
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struct AAMDNodes;
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class APInt;
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class AssumptionCache;
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class BasicBlock;
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class DataLayout;
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class DominatorTree;
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class Function;
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class GEPOperator;
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class LoopInfo;
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class PHINode;
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class SelectInst;
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class TargetLibraryInfo;
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class PhiValues;
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class Value;
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/// This is the AA result object for the basic, local, and stateless alias
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/// analysis. It implements the AA query interface in an entirely stateless
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/// manner. As one consequence, it is never invalidated due to IR changes.
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/// While it does retain some storage, that is used as an optimization and not
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/// to preserve information from query to query. However it does retain handles
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/// to various other analyses and must be recomputed when those analyses are.
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class BasicAAResult : public AAResultBase<BasicAAResult> {
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friend AAResultBase<BasicAAResult>;
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const DataLayout &DL;
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const Function &F;
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const TargetLibraryInfo &TLI;
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AssumptionCache &AC;
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DominatorTree *DT;
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LoopInfo *LI;
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PhiValues *PV;
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public:
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BasicAAResult(const DataLayout &DL, const Function &F,
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const TargetLibraryInfo &TLI, AssumptionCache &AC,
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DominatorTree *DT = nullptr, LoopInfo *LI = nullptr,
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PhiValues *PV = nullptr)
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: AAResultBase(), DL(DL), F(F), TLI(TLI), AC(AC), DT(DT), LI(LI), PV(PV)
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{}
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BasicAAResult(const BasicAAResult &Arg)
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: AAResultBase(Arg), DL(Arg.DL), F(Arg.F), TLI(Arg.TLI), AC(Arg.AC),
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DT(Arg.DT), LI(Arg.LI), PV(Arg.PV) {}
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BasicAAResult(BasicAAResult &&Arg)
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: AAResultBase(std::move(Arg)), DL(Arg.DL), F(Arg.F), TLI(Arg.TLI),
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AC(Arg.AC), DT(Arg.DT), LI(Arg.LI), PV(Arg.PV) {}
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/// Handle invalidation events in the new pass manager.
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bool invalidate(Function &Fn, const PreservedAnalyses &PA,
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FunctionAnalysisManager::Invalidator &Inv);
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AliasResult alias(const MemoryLocation &LocA, const MemoryLocation &LocB,
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AAQueryInfo &AAQI);
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ModRefInfo getModRefInfo(const CallBase *Call, const MemoryLocation &Loc,
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AAQueryInfo &AAQI);
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ModRefInfo getModRefInfo(const CallBase *Call1, const CallBase *Call2,
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AAQueryInfo &AAQI);
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/// Chases pointers until we find a (constant global) or not.
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bool pointsToConstantMemory(const MemoryLocation &Loc, AAQueryInfo &AAQI,
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bool OrLocal);
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/// Get the location associated with a pointer argument of a callsite.
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ModRefInfo getArgModRefInfo(const CallBase *Call, unsigned ArgIdx);
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/// Returns the behavior when calling the given call site.
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FunctionModRefBehavior getModRefBehavior(const CallBase *Call);
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/// Returns the behavior when calling the given function. For use when the
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/// call site is not known.
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FunctionModRefBehavior getModRefBehavior(const Function *Fn);
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private:
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// A linear transformation of a Value; this class represents ZExt(SExt(V,
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// SExtBits), ZExtBits) * Scale + Offset.
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struct VariableGEPIndex {
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// An opaque Value - we can't decompose this further.
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const Value *V;
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// We need to track what extensions we've done as we consider the same Value
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// with different extensions as different variables in a GEP's linear
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// expression;
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// e.g.: if V == -1, then sext(x) != zext(x).
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unsigned ZExtBits;
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unsigned SExtBits;
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APInt Scale;
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// Context instruction to use when querying information about this index.
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const Instruction *CxtI;
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bool operator==(const VariableGEPIndex &Other) const {
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return V == Other.V && ZExtBits == Other.ZExtBits &&
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SExtBits == Other.SExtBits && Scale == Other.Scale;
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}
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bool operator!=(const VariableGEPIndex &Other) const {
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return !operator==(Other);
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}
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void dump() const {
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print(dbgs());
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dbgs() << "\n";
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}
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void print(raw_ostream &OS) const {
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OS << "(V=" << V->getName()
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<< ", zextbits=" << ZExtBits
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<< ", sextbits=" << SExtBits
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<< ", scale=" << Scale << ")";
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}
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};
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// Represents the internal structure of a GEP, decomposed into a base pointer,
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// constant offsets, and variable scaled indices.
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struct DecomposedGEP {
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// Base pointer of the GEP
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const Value *Base;
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// Total constant offset from base.
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APInt Offset;
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// Scaled variable (non-constant) indices.
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SmallVector<VariableGEPIndex, 4> VarIndices;
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// Is GEP index scale compile-time constant.
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bool HasCompileTimeConstantScale;
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void dump() const {
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print(dbgs());
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dbgs() << "\n";
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}
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void print(raw_ostream &OS) const {
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OS << "(DecomposedGEP Base=" << Base->getName()
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<< ", Offset=" << Offset
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<< ", VarIndices=[";
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for (size_t i = 0; i < VarIndices.size(); i++) {
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if (i != 0)
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OS << ", ";
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VarIndices[i].print(OS);
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}
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OS << "], HasCompileTimeConstantScale=" << HasCompileTimeConstantScale
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<< ")";
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}
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};
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/// Tracks phi nodes we have visited.
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///
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/// When interpret "Value" pointer equality as value equality we need to make
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/// sure that the "Value" is not part of a cycle. Otherwise, two uses could
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/// come from different "iterations" of a cycle and see different values for
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/// the same "Value" pointer.
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///
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/// The following example shows the problem:
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/// %p = phi(%alloca1, %addr2)
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/// %l = load %ptr
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/// %addr1 = gep, %alloca2, 0, %l
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/// %addr2 = gep %alloca2, 0, (%l + 1)
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/// alias(%p, %addr1) -> MayAlias !
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/// store %l, ...
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SmallPtrSet<const BasicBlock *, 8> VisitedPhiBBs;
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/// Tracks instructions visited by pointsToConstantMemory.
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SmallPtrSet<const Value *, 16> Visited;
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static const Value *
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GetLinearExpression(const Value *V, APInt &Scale, APInt &Offset,
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unsigned &ZExtBits, unsigned &SExtBits,
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const DataLayout &DL, unsigned Depth, AssumptionCache *AC,
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DominatorTree *DT, bool &NSW, bool &NUW);
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static DecomposedGEP
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DecomposeGEPExpression(const Value *V, const DataLayout &DL,
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AssumptionCache *AC, DominatorTree *DT);
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static bool isGEPBaseAtNegativeOffset(const GEPOperator *GEPOp,
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const DecomposedGEP &DecompGEP, const DecomposedGEP &DecompObject,
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LocationSize ObjectAccessSize);
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/// A Heuristic for aliasGEP that searches for a constant offset
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/// between the variables.
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///
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/// GetLinearExpression has some limitations, as generally zext(%x + 1)
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/// != zext(%x) + zext(1) if the arithmetic overflows. GetLinearExpression
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/// will therefore conservatively refuse to decompose these expressions.
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/// However, we know that, for all %x, zext(%x) != zext(%x + 1), even if
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/// the addition overflows.
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bool
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constantOffsetHeuristic(const SmallVectorImpl<VariableGEPIndex> &VarIndices,
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LocationSize V1Size, LocationSize V2Size,
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const APInt &BaseOffset, AssumptionCache *AC,
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DominatorTree *DT);
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bool isValueEqualInPotentialCycles(const Value *V1, const Value *V2);
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void GetIndexDifference(SmallVectorImpl<VariableGEPIndex> &Dest,
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const SmallVectorImpl<VariableGEPIndex> &Src);
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AliasResult aliasGEP(const GEPOperator *V1, LocationSize V1Size,
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const AAMDNodes &V1AAInfo, const Value *V2,
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LocationSize V2Size, const AAMDNodes &V2AAInfo,
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const Value *UnderlyingV1, const Value *UnderlyingV2,
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AAQueryInfo &AAQI);
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AliasResult aliasPHI(const PHINode *PN, LocationSize PNSize,
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const AAMDNodes &PNAAInfo, const Value *V2,
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LocationSize V2Size, const AAMDNodes &V2AAInfo,
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AAQueryInfo &AAQI);
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AliasResult aliasSelect(const SelectInst *SI, LocationSize SISize,
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const AAMDNodes &SIAAInfo, const Value *V2,
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LocationSize V2Size, const AAMDNodes &V2AAInfo,
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AAQueryInfo &AAQI);
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AliasResult aliasCheck(const Value *V1, LocationSize V1Size,
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const AAMDNodes &V1AATag, const Value *V2,
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LocationSize V2Size, const AAMDNodes &V2AATag,
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AAQueryInfo &AAQI);
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AliasResult aliasCheckRecursive(const Value *V1, LocationSize V1Size,
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const AAMDNodes &V1AATag, const Value *V2,
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LocationSize V2Size, const AAMDNodes &V2AATag,
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AAQueryInfo &AAQI, const Value *O1,
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const Value *O2);
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};
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/// Analysis pass providing a never-invalidated alias analysis result.
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class BasicAA : public AnalysisInfoMixin<BasicAA> {
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friend AnalysisInfoMixin<BasicAA>;
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static AnalysisKey Key;
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public:
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using Result = BasicAAResult;
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BasicAAResult run(Function &F, FunctionAnalysisManager &AM);
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};
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/// Legacy wrapper pass to provide the BasicAAResult object.
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class BasicAAWrapperPass : public FunctionPass {
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std::unique_ptr<BasicAAResult> Result;
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virtual void anchor();
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public:
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static char ID;
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BasicAAWrapperPass();
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BasicAAResult &getResult() { return *Result; }
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const BasicAAResult &getResult() const { return *Result; }
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bool runOnFunction(Function &F) override;
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void getAnalysisUsage(AnalysisUsage &AU) const override;
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};
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FunctionPass *createBasicAAWrapperPass();
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/// A helper for the legacy pass manager to create a \c BasicAAResult object
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/// populated to the best of our ability for a particular function when inside
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/// of a \c ModulePass or a \c CallGraphSCCPass.
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BasicAAResult createLegacyPMBasicAAResult(Pass &P, Function &F);
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/// This class is a functor to be used in legacy module or SCC passes for
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/// computing AA results for a function. We store the results in fields so that
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/// they live long enough to be queried, but we re-use them each time.
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class LegacyAARGetter {
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Pass &P;
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Optional<BasicAAResult> BAR;
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Optional<AAResults> AAR;
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public:
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LegacyAARGetter(Pass &P) : P(P) {}
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AAResults &operator()(Function &F) {
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BAR.emplace(createLegacyPMBasicAAResult(P, F));
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AAR.emplace(createLegacyPMAAResults(P, F, *BAR));
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return *AAR;
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}
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};
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} // end namespace llvm
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#endif // LLVM_ANALYSIS_BASICALIASANALYSIS_H
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