forked from OSchip/llvm-project
247 lines
9.0 KiB
C++
247 lines
9.0 KiB
C++
//===- AliasAnalysis.cpp - Generic Alias Analysis Interface 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 the generic AliasAnalysis interface which is used as the
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// common interface used by all clients and implementations of alias analysis.
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//
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// This file also implements the default version of the AliasAnalysis interface
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// that is to be used when no other implementation is specified. This does some
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// simple tests that detect obvious cases: two different global pointers cannot
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// alias, a global cannot alias a malloc, two different mallocs cannot alias,
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// etc.
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//
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// This alias analysis implementation really isn't very good for anything, but
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// it is very fast, and makes a nice clean default implementation. Because it
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// handles lots of little corner cases, other, more complex, alias analysis
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// implementations may choose to rely on this pass to resolve these simple and
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// easy cases.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Analysis/AliasAnalysis.h"
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#include "llvm/Pass.h"
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#include "llvm/BasicBlock.h"
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#include "llvm/Function.h"
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#include "llvm/IntrinsicInst.h"
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#include "llvm/Instructions.h"
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#include "llvm/Type.h"
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#include "llvm/Target/TargetData.h"
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using namespace llvm;
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// Register the AliasAnalysis interface, providing a nice name to refer to.
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static RegisterAnalysisGroup<AliasAnalysis> Z("Alias Analysis");
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char AliasAnalysis::ID = 0;
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//===----------------------------------------------------------------------===//
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// Default chaining methods
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//===----------------------------------------------------------------------===//
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AliasAnalysis::AliasResult
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AliasAnalysis::alias(const Value *V1, unsigned V1Size,
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const Value *V2, unsigned V2Size) {
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assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!");
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return AA->alias(V1, V1Size, V2, V2Size);
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}
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bool AliasAnalysis::pointsToConstantMemory(const Value *P) {
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assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!");
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return AA->pointsToConstantMemory(P);
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}
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void AliasAnalysis::deleteValue(Value *V) {
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assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!");
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AA->deleteValue(V);
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}
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void AliasAnalysis::copyValue(Value *From, Value *To) {
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assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!");
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AA->copyValue(From, To);
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}
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AliasAnalysis::ModRefResult
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AliasAnalysis::getModRefInfo(CallSite CS1, CallSite CS2) {
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// FIXME: we can do better.
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assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!");
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return AA->getModRefInfo(CS1, CS2);
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}
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//===----------------------------------------------------------------------===//
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// AliasAnalysis non-virtual helper method implementation
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//===----------------------------------------------------------------------===//
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AliasAnalysis::ModRefResult
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AliasAnalysis::getModRefInfo(LoadInst *L, Value *P, unsigned Size) {
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return alias(L->getOperand(0), getTypeStoreSize(L->getType()),
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P, Size) ? Ref : NoModRef;
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}
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AliasAnalysis::ModRefResult
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AliasAnalysis::getModRefInfo(StoreInst *S, Value *P, unsigned Size) {
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// If the stored address cannot alias the pointer in question, then the
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// pointer cannot be modified by the store.
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if (!alias(S->getOperand(1),
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getTypeStoreSize(S->getOperand(0)->getType()), P, Size))
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return NoModRef;
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// If the pointer is a pointer to constant memory, then it could not have been
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// modified by this store.
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return pointsToConstantMemory(P) ? NoModRef : Mod;
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}
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AliasAnalysis::ModRefBehavior
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AliasAnalysis::getModRefBehavior(CallSite CS,
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std::vector<PointerAccessInfo> *Info) {
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if (CS.doesNotAccessMemory())
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// Can't do better than this.
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return DoesNotAccessMemory;
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ModRefBehavior MRB = getModRefBehavior(CS.getCalledFunction(), Info);
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if (MRB != DoesNotAccessMemory && CS.onlyReadsMemory())
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return OnlyReadsMemory;
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return MRB;
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}
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AliasAnalysis::ModRefBehavior
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AliasAnalysis::getModRefBehavior(Function *F,
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std::vector<PointerAccessInfo> *Info) {
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if (F) {
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if (F->doesNotAccessMemory())
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// Can't do better than this.
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return DoesNotAccessMemory;
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if (F->onlyReadsMemory())
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return OnlyReadsMemory;
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if (unsigned id = F->getIntrinsicID()) {
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#define GET_INTRINSIC_MODREF_BEHAVIOR
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#include "llvm/Intrinsics.gen"
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#undef GET_INTRINSIC_MODREF_BEHAVIOR
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}
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}
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return UnknownModRefBehavior;
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}
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AliasAnalysis::ModRefResult
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AliasAnalysis::getModRefInfo(CallSite CS, Value *P, unsigned Size) {
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ModRefBehavior MRB = getModRefBehavior(CS);
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if (MRB == DoesNotAccessMemory)
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return NoModRef;
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ModRefResult Mask = ModRef;
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if (MRB == OnlyReadsMemory)
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Mask = Ref;
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else if (MRB == AliasAnalysis::AccessesArguments) {
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bool doesAlias = false;
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for (CallSite::arg_iterator AI = CS.arg_begin(), AE = CS.arg_end();
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AI != AE; ++AI)
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if (!isNoAlias(*AI, ~0U, P, Size)) {
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doesAlias = true;
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break;
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}
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if (!doesAlias)
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return NoModRef;
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}
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if (!AA) return Mask;
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// If P points to a constant memory location, the call definitely could not
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// modify the memory location.
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if ((Mask & Mod) && AA->pointsToConstantMemory(P))
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Mask = ModRefResult(Mask & ~Mod);
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return ModRefResult(Mask & AA->getModRefInfo(CS, P, Size));
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}
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// AliasAnalysis destructor: DO NOT move this to the header file for
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// AliasAnalysis or else clients of the AliasAnalysis class may not depend on
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// the AliasAnalysis.o file in the current .a file, causing alias analysis
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// support to not be included in the tool correctly!
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//
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AliasAnalysis::~AliasAnalysis() {}
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/// InitializeAliasAnalysis - Subclasses must call this method to initialize the
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/// AliasAnalysis interface before any other methods are called.
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///
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void AliasAnalysis::InitializeAliasAnalysis(Pass *P) {
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TD = P->getAnalysisIfAvailable<TargetData>();
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AA = &P->getAnalysis<AliasAnalysis>();
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}
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// getAnalysisUsage - All alias analysis implementations should invoke this
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// directly (using AliasAnalysis::getAnalysisUsage(AU)).
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void AliasAnalysis::getAnalysisUsage(AnalysisUsage &AU) const {
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AU.addRequired<AliasAnalysis>(); // All AA's chain
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}
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/// getTypeStoreSize - Return the TargetData store size for the given type,
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/// if known, or a conservative value otherwise.
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///
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unsigned AliasAnalysis::getTypeStoreSize(const Type *Ty) {
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return TD ? TD->getTypeStoreSize(Ty) : ~0u;
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}
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/// canBasicBlockModify - Return true if it is possible for execution of the
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/// specified basic block to modify the value pointed to by Ptr.
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///
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bool AliasAnalysis::canBasicBlockModify(const BasicBlock &BB,
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const Value *Ptr, unsigned Size) {
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return canInstructionRangeModify(BB.front(), BB.back(), Ptr, Size);
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}
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/// canInstructionRangeModify - Return true if it is possible for the execution
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/// of the specified instructions to modify the value pointed to by Ptr. The
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/// instructions to consider are all of the instructions in the range of [I1,I2]
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/// INCLUSIVE. I1 and I2 must be in the same basic block.
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///
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bool AliasAnalysis::canInstructionRangeModify(const Instruction &I1,
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const Instruction &I2,
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const Value *Ptr, unsigned Size) {
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assert(I1.getParent() == I2.getParent() &&
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"Instructions not in same basic block!");
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BasicBlock::iterator I = const_cast<Instruction*>(&I1);
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BasicBlock::iterator E = const_cast<Instruction*>(&I2);
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++E; // Convert from inclusive to exclusive range.
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for (; I != E; ++I) // Check every instruction in range
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if (getModRefInfo(I, const_cast<Value*>(Ptr), Size) & Mod)
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return true;
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return false;
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}
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/// isNoAliasCall - Return true if this pointer is returned by a noalias
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/// function.
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bool llvm::isNoAliasCall(const Value *V) {
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if (isa<CallInst>(V) || isa<InvokeInst>(V))
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return CallSite(const_cast<Instruction*>(cast<Instruction>(V)))
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.paramHasAttr(0, Attribute::NoAlias);
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return false;
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}
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/// isIdentifiedObject - Return true if this pointer refers to a distinct and
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/// identifiable object. This returns true for:
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/// Global Variables and Functions (but not Global Aliases)
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/// Allocas and Mallocs
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/// ByVal and NoAlias Arguments
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/// NoAlias returns
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///
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bool llvm::isIdentifiedObject(const Value *V) {
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if (isa<AllocaInst>(V) || isNoAliasCall(V))
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return true;
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if (isa<GlobalValue>(V) && !isa<GlobalAlias>(V))
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return true;
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if (const Argument *A = dyn_cast<Argument>(V))
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return A->hasNoAliasAttr() || A->hasByValAttr();
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return false;
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}
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// Because of the way .a files work, we must force the BasicAA implementation to
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// be pulled in if the AliasAnalysis classes are pulled in. Otherwise we run
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// the risk of AliasAnalysis being used, but the default implementation not
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// being linked into the tool that uses it.
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DEFINING_FILE_FOR(AliasAnalysis)
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