403 lines
14 KiB
C++
403 lines
14 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/LLVMContext.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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INITIALIZE_ANALYSIS_GROUP(AliasAnalysis, "Alias Analysis", NoAA)
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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 Location &LocA, const Location &LocB) {
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assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!");
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return AA->alias(LocA, LocB);
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}
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bool AliasAnalysis::pointsToConstantMemory(const Location &Loc,
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bool OrLocal) {
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assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!");
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return AA->pointsToConstantMemory(Loc, OrLocal);
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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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void AliasAnalysis::addEscapingUse(Use &U) {
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assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!");
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AA->addEscapingUse(U);
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}
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AliasAnalysis::ModRefResult
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AliasAnalysis::getModRefInfo(ImmutableCallSite CS,
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const Location &Loc) {
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assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!");
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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 (onlyReadsMemory(MRB))
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Mask = Ref;
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if (onlyAccessesArgPointees(MRB)) {
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bool doesAlias = false;
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if (doesAccessArgPointees(MRB)) {
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MDNode *CSTag = CS.getInstruction()->getMetadata(LLVMContext::MD_tbaa);
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for (ImmutableCallSite::arg_iterator AI = CS.arg_begin(), AE = CS.arg_end();
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AI != AE; ++AI) {
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const Value *Arg = *AI;
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if (!Arg->getType()->isPointerTy())
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continue;
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Location CSLoc(Arg, UnknownSize, CSTag);
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if (!isNoAlias(CSLoc, Loc)) {
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doesAlias = true;
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break;
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}
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}
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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 Loc is a constant memory location, the call definitely could not
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// modify the memory location.
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if ((Mask & Mod) && pointsToConstantMemory(Loc))
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Mask = ModRefResult(Mask & ~Mod);
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// If this is the end of the chain, don't forward.
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if (!AA) return Mask;
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// Otherwise, fall back to the next AA in the chain. But we can merge
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// in any mask we've managed to compute.
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return ModRefResult(AA->getModRefInfo(CS, Loc) & Mask);
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}
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AliasAnalysis::ModRefResult
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AliasAnalysis::getModRefInfo(ImmutableCallSite CS1, ImmutableCallSite CS2) {
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assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!");
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// If CS1 or CS2 are readnone, they don't interact.
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ModRefBehavior CS1B = getModRefBehavior(CS1);
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if (CS1B == DoesNotAccessMemory) return NoModRef;
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ModRefBehavior CS2B = getModRefBehavior(CS2);
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if (CS2B == DoesNotAccessMemory) return NoModRef;
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// If they both only read from memory, there is no dependence.
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if (onlyReadsMemory(CS1B) && onlyReadsMemory(CS2B))
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return NoModRef;
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AliasAnalysis::ModRefResult Mask = ModRef;
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// If CS1 only reads memory, the only dependence on CS2 can be
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// from CS1 reading memory written by CS2.
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if (onlyReadsMemory(CS1B))
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Mask = ModRefResult(Mask & Ref);
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// If CS2 only access memory through arguments, accumulate the mod/ref
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// information from CS1's references to the memory referenced by
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// CS2's arguments.
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if (onlyAccessesArgPointees(CS2B)) {
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AliasAnalysis::ModRefResult R = NoModRef;
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if (doesAccessArgPointees(CS2B)) {
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MDNode *CS2Tag = CS2.getInstruction()->getMetadata(LLVMContext::MD_tbaa);
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for (ImmutableCallSite::arg_iterator
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I = CS2.arg_begin(), E = CS2.arg_end(); I != E; ++I) {
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const Value *Arg = *I;
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if (!Arg->getType()->isPointerTy())
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continue;
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Location CS2Loc(Arg, UnknownSize, CS2Tag);
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R = ModRefResult((R | getModRefInfo(CS1, CS2Loc)) & Mask);
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if (R == Mask)
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break;
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}
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}
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return R;
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}
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// If CS1 only accesses memory through arguments, check if CS2 references
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// any of the memory referenced by CS1's arguments. If not, return NoModRef.
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if (onlyAccessesArgPointees(CS1B)) {
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AliasAnalysis::ModRefResult R = NoModRef;
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if (doesAccessArgPointees(CS1B)) {
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MDNode *CS1Tag = CS1.getInstruction()->getMetadata(LLVMContext::MD_tbaa);
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for (ImmutableCallSite::arg_iterator
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I = CS1.arg_begin(), E = CS1.arg_end(); I != E; ++I) {
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const Value *Arg = *I;
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if (!Arg->getType()->isPointerTy())
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continue;
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Location CS1Loc(Arg, UnknownSize, CS1Tag);
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if (getModRefInfo(CS2, CS1Loc) != NoModRef) {
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R = Mask;
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break;
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}
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}
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}
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if (R == NoModRef)
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return R;
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}
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// If this is the end of the chain, don't forward.
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if (!AA) return Mask;
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// Otherwise, fall back to the next AA in the chain. But we can merge
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// in any mask we've managed to compute.
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return ModRefResult(AA->getModRefInfo(CS1, CS2) & Mask);
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}
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AliasAnalysis::ModRefBehavior
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AliasAnalysis::getModRefBehavior(ImmutableCallSite CS) {
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assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!");
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ModRefBehavior Min = UnknownModRefBehavior;
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// Call back into the alias analysis with the other form of getModRefBehavior
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// to see if it can give a better response.
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if (const Function *F = CS.getCalledFunction())
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Min = getModRefBehavior(F);
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// If this is the end of the chain, don't forward.
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if (!AA) return Min;
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// Otherwise, fall back to the next AA in the chain. But we can merge
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// in any result we've managed to compute.
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return ModRefBehavior(AA->getModRefBehavior(CS) & Min);
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}
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AliasAnalysis::ModRefBehavior
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AliasAnalysis::getModRefBehavior(const Function *F) {
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assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!");
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return AA->getModRefBehavior(F);
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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::Location AliasAnalysis::getLocation(const LoadInst *LI) {
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return Location(LI->getPointerOperand(),
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getTypeStoreSize(LI->getType()),
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LI->getMetadata(LLVMContext::MD_tbaa));
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}
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AliasAnalysis::Location AliasAnalysis::getLocation(const StoreInst *SI) {
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return Location(SI->getPointerOperand(),
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getTypeStoreSize(SI->getValueOperand()->getType()),
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SI->getMetadata(LLVMContext::MD_tbaa));
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}
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AliasAnalysis::Location AliasAnalysis::getLocation(const VAArgInst *VI) {
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return Location(VI->getPointerOperand(),
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UnknownSize,
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VI->getMetadata(LLVMContext::MD_tbaa));
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}
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AliasAnalysis::Location
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AliasAnalysis::getLocationForSource(const MemTransferInst *MTI) {
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uint64_t Size = UnknownSize;
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if (ConstantInt *C = dyn_cast<ConstantInt>(MTI->getLength()))
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Size = C->getValue().getZExtValue();
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// memcpy/memmove can have TBAA tags. For memcpy, they apply
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// to both the source and the destination.
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MDNode *TBAATag = MTI->getMetadata(LLVMContext::MD_tbaa);
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return Location(MTI->getRawSource(), Size, TBAATag);
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}
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AliasAnalysis::Location
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AliasAnalysis::getLocationForDest(const MemIntrinsic *MTI) {
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uint64_t Size = UnknownSize;
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if (ConstantInt *C = dyn_cast<ConstantInt>(MTI->getLength()))
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Size = C->getValue().getZExtValue();
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// memcpy/memmove can have TBAA tags. For memcpy, they apply
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// to both the source and the destination.
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MDNode *TBAATag = MTI->getMetadata(LLVMContext::MD_tbaa);
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return Location(MTI->getRawDest(), Size, TBAATag);
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}
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AliasAnalysis::ModRefResult
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AliasAnalysis::getModRefInfo(const LoadInst *L, const Location &Loc) {
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// Be conservative in the face of volatile.
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if (L->isVolatile())
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return ModRef;
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// If the load address doesn't alias the given address, it doesn't read
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// or write the specified memory.
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if (!alias(getLocation(L), Loc))
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return NoModRef;
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// Otherwise, a load just reads.
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return Ref;
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}
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AliasAnalysis::ModRefResult
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AliasAnalysis::getModRefInfo(const StoreInst *S, const Location &Loc) {
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// Be conservative in the face of volatile.
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if (S->isVolatile())
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return ModRef;
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// If the store address cannot alias the pointer in question, then the
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// specified memory cannot be modified by the store.
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if (!alias(getLocation(S), Loc))
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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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if (pointsToConstantMemory(Loc))
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return NoModRef;
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// Otherwise, a store just writes.
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return Mod;
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}
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AliasAnalysis::ModRefResult
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AliasAnalysis::getModRefInfo(const VAArgInst *V, const Location &Loc) {
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// If the va_arg address cannot alias the pointer in question, then the
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// specified memory cannot be accessed by the va_arg.
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if (!alias(getLocation(V), Loc))
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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 va_arg.
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if (pointsToConstantMemory(Loc))
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return NoModRef;
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// Otherwise, a va_arg reads and writes.
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return ModRef;
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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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uint64_t AliasAnalysis::getTypeStoreSize(const Type *Ty) {
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return TD ? TD->getTypeStoreSize(Ty) : UnknownSize;
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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 Location &Loc) {
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return canInstructionRangeModify(BB.front(), BB.back(), Loc);
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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 Location &Loc) {
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assert(I1.getParent() == I2.getParent() &&
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"Instructions not in same basic block!");
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BasicBlock::const_iterator I = &I1;
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BasicBlock::const_iterator E = &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, Loc) & 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 ImmutableCallSite(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))
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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 (isNoAliasCall(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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