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llvm-project/llvm/lib/Analysis/AliasAnalysis.cpp

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//===- AliasAnalysis.cpp - Generic Alias Analysis Interface Implementation -==//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements the generic AliasAnalysis interface which is used as the
// common interface used by all clients and implementations of alias analysis.
//
// This file also implements the default version of the AliasAnalysis interface
// that is to be used when no other implementation is specified. This does some
// simple tests that detect obvious cases: two different global pointers cannot
// alias, a global cannot alias a malloc, two different mallocs cannot alias,
// etc.
//
// This alias analysis implementation really isn't very good for anything, but
// it is very fast, and makes a nice clean default implementation. Because it
// handles lots of little corner cases, other, more complex, alias analysis
// implementations may choose to rely on this pass to resolve these simple and
// easy cases.
//
//===----------------------------------------------------------------------===//
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Pass.h"
#include "llvm/BasicBlock.h"
#include "llvm/Function.h"
#include "llvm/IntrinsicInst.h"
#include "llvm/Instructions.h"
#include "llvm/Type.h"
#include "llvm/Target/TargetData.h"
using namespace llvm;
// Register the AliasAnalysis interface, providing a nice name to refer to.
static RegisterAnalysisGroup<AliasAnalysis> Z("Alias Analysis");
char AliasAnalysis::ID = 0;
//===----------------------------------------------------------------------===//
// Default chaining methods
//===----------------------------------------------------------------------===//
AliasAnalysis::AliasResult
AliasAnalysis::alias(const Value *V1, unsigned V1Size,
const Value *V2, unsigned V2Size) {
assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!");
return AA->alias(V1, V1Size, V2, V2Size);
}
bool AliasAnalysis::pointsToConstantMemory(const Value *P) {
assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!");
return AA->pointsToConstantMemory(P);
}
void AliasAnalysis::deleteValue(Value *V) {
assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!");
AA->deleteValue(V);
}
void AliasAnalysis::copyValue(Value *From, Value *To) {
assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!");
AA->copyValue(From, To);
}
AliasAnalysis::ModRefResult
AliasAnalysis::getModRefInfo(ImmutableCallSite CS,
const Value *P, unsigned Size) {
// Don't assert AA because BasicAA calls us in order to make use of the
// logic here.
ModRefBehavior MRB = getModRefBehavior(CS);
if (MRB == DoesNotAccessMemory)
return NoModRef;
ModRefResult Mask = ModRef;
if (MRB == OnlyReadsMemory)
Mask = Ref;
else if (MRB == AliasAnalysis::AccessesArguments) {
bool doesAlias = false;
for (ImmutableCallSite::arg_iterator AI = CS.arg_begin(), AE = CS.arg_end();
AI != AE; ++AI)
if (!isNoAlias(*AI, ~0U, P, Size)) {
doesAlias = true;
break;
}
if (!doesAlias)
return NoModRef;
}
// If P points to a constant memory location, the call definitely could not
// modify the memory location.
if ((Mask & Mod) && pointsToConstantMemory(P))
Mask = ModRefResult(Mask & ~Mod);
// If this is BasicAA, don't forward.
if (!AA) return Mask;
// Otherwise, fall back to the next AA in the chain. But we can merge
// in any mask we've managed to compute.
return ModRefResult(AA->getModRefInfo(CS, P, Size) & Mask);
}
AliasAnalysis::ModRefResult
AliasAnalysis::getModRefInfo(ImmutableCallSite CS1, ImmutableCallSite CS2) {
// Don't assert AA because BasicAA calls us in order to make use of the
// logic here.
// If CS1 or CS2 are readnone, they don't interact.
ModRefBehavior CS1B = getModRefBehavior(CS1);
if (CS1B == DoesNotAccessMemory) return NoModRef;
ModRefBehavior CS2B = getModRefBehavior(CS2);
if (CS2B == DoesNotAccessMemory) return NoModRef;
// If they both only read from memory, there is no dependence.
if (CS1B == OnlyReadsMemory && CS2B == OnlyReadsMemory)
return NoModRef;
AliasAnalysis::ModRefResult Mask = ModRef;
// If CS1 only reads memory, the only dependence on CS2 can be
// from CS1 reading memory written by CS2.
if (CS1B == OnlyReadsMemory)
Mask = ModRefResult(Mask & Ref);
// If CS2 only access memory through arguments, accumulate the mod/ref
// information from CS1's references to the memory referenced by
// CS2's arguments.
if (CS2B == AccessesArguments) {
AliasAnalysis::ModRefResult R = NoModRef;
for (ImmutableCallSite::arg_iterator
I = CS2.arg_begin(), E = CS2.arg_end(); I != E; ++I) {
R = ModRefResult((R | getModRefInfo(CS1, *I, UnknownSize)) & Mask);
if (R == Mask)
break;
}
return R;
}
// If CS1 only accesses memory through arguments, check if CS2 references
// any of the memory referenced by CS1's arguments. If not, return NoModRef.
if (CS1B == AccessesArguments) {
AliasAnalysis::ModRefResult R = NoModRef;
for (ImmutableCallSite::arg_iterator
I = CS1.arg_begin(), E = CS1.arg_end(); I != E; ++I)
if (getModRefInfo(CS2, *I, UnknownSize) != NoModRef) {
R = Mask;
break;
}
if (R == NoModRef)
return R;
}
// If this is BasicAA, don't forward.
if (!AA) return Mask;
// Otherwise, fall back to the next AA in the chain. But we can merge
// in any mask we've managed to compute.
return ModRefResult(AA->getModRefInfo(CS1, CS2) & Mask);
}
AliasAnalysis::ModRefBehavior
AliasAnalysis::getModRefBehavior(ImmutableCallSite CS) {
// Don't assert AA because BasicAA calls us in order to make use of the
// logic here.
ModRefBehavior Min = UnknownModRefBehavior;
// Call back into the alias analysis with the other form of getModRefBehavior
// to see if it can give a better response.
if (const Function *F = CS.getCalledFunction())
Min = getModRefBehavior(F);
// If this is BasicAA, don't forward.
if (!AA) return Min;
// Otherwise, fall back to the next AA in the chain. But we can merge
// in any result we've managed to compute.
return std::min(AA->getModRefBehavior(CS), Min);
}
AliasAnalysis::ModRefBehavior
AliasAnalysis::getModRefBehavior(const Function *F) {
assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!");
return AA->getModRefBehavior(F);
}
AliasAnalysis::DependenceResult
AliasAnalysis::getDependence(const Instruction *First,
const Value *FirstPHITranslatedAddr,
DependenceQueryFlags FirstFlags,
const Instruction *Second,
const Value *SecondPHITranslatedAddr,
DependenceQueryFlags SecondFlags) {
assert(AA && "AA didn't call InitializeAliasAnalyais in its run method!");
return AA->getDependence(First, FirstPHITranslatedAddr, FirstFlags,
Second, SecondPHITranslatedAddr, SecondFlags);
}
//===----------------------------------------------------------------------===//
// AliasAnalysis non-virtual helper method implementation
//===----------------------------------------------------------------------===//
AliasAnalysis::ModRefResult
AliasAnalysis::getModRefInfo(const LoadInst *L, const Value *P, unsigned Size) {
// Be conservative in the face of volatile.
if (L->isVolatile())
return ModRef;
// If the load address doesn't alias the given address, it doesn't read
// or write the specified memory.
if (!alias(L->getOperand(0), getTypeStoreSize(L->getType()), P, Size))
return NoModRef;
// Otherwise, a load just reads.
return Ref;
}
AliasAnalysis::ModRefResult
AliasAnalysis::getModRefInfo(const StoreInst *S, const Value *P, unsigned Size) {
// Be conservative in the face of volatile.
if (S->isVolatile())
return ModRef;
// If the store address cannot alias the pointer in question, then the
// specified memory cannot be modified by the store.
if (!alias(S->getOperand(1),
getTypeStoreSize(S->getOperand(0)->getType()), P, Size))
return NoModRef;
// If the pointer is a pointer to constant memory, then it could not have been
// modified by this store.
if (pointsToConstantMemory(P))
return NoModRef;
// Otherwise, a store just writes.
return Mod;
}
AliasAnalysis::ModRefResult
AliasAnalysis::getModRefInfo(const VAArgInst *V, const Value *P, unsigned Size) {
// If the va_arg address cannot alias the pointer in question, then the
// specified memory cannot be accessed by the va_arg.
if (!alias(V->getOperand(0), UnknownSize, P, Size))
return NoModRef;
// If the pointer is a pointer to constant memory, then it could not have been
// modified by this va_arg.
if (pointsToConstantMemory(P))
return NoModRef;
// Otherwise, a va_arg reads and writes.
return ModRef;
}
AliasAnalysis::DependenceResult
AliasAnalysis::getDependenceViaModRefInfo(const Instruction *First,
const Value *FirstPHITranslatedAddr,
DependenceQueryFlags FirstFlags,
const Instruction *Second,
const Value *SecondPHITranslatedAddr,
DependenceQueryFlags SecondFlags) {
if (const LoadInst *L = dyn_cast<LoadInst>(First)) {
// Be over-conservative with volatile for now.
if (L->isVolatile())
return Unknown;
// If we don't have a phi-translated address, use the actual one.
if (!FirstPHITranslatedAddr)
FirstPHITranslatedAddr = L->getPointerOperand();
// Forward this query to getModRefInfo.
switch (getModRefInfo(Second,
FirstPHITranslatedAddr,
getTypeStoreSize(L->getType()))) {
case NoModRef:
// Second doesn't reference First's memory, so they're independent.
return Independent;
case Ref:
// Second only reads from the memory read from by First. If it
// also writes to any other memory, be conservative.
if (Second->mayWriteToMemory())
return Unknown;
// If it's loading the same size from the same address, we can
// give a more precise result.
if (const LoadInst *SecondL = dyn_cast<LoadInst>(Second)) {
// If we don't have a phi-translated address, use the actual one.
if (!SecondPHITranslatedAddr)
SecondPHITranslatedAddr = SecondL->getPointerOperand();
unsigned LSize = getTypeStoreSize(L->getType());
unsigned SecondLSize = getTypeStoreSize(SecondL->getType());
if (alias(FirstPHITranslatedAddr, LSize,
SecondPHITranslatedAddr, SecondLSize) ==
MustAlias) {
// If the loads are the same size, it's ReadThenRead.
if (LSize == SecondLSize)
return ReadThenRead;
// If the second load is smaller, it's only ReadThenReadSome.
if (LSize > SecondLSize)
return ReadThenReadSome;
}
}
// Otherwise it's just two loads.
return Independent;
case Mod:
// Second only writes to the memory read from by First. If it
// also reads from any other memory, be conservative.
if (Second->mayReadFromMemory())
return Unknown;
// If it's storing the same size to the same address, we can
// give a more precise result.
if (const StoreInst *SecondS = dyn_cast<StoreInst>(Second)) {
// If we don't have a phi-translated address, use the actual one.
if (!SecondPHITranslatedAddr)
SecondPHITranslatedAddr = SecondS->getPointerOperand();
unsigned LSize = getTypeStoreSize(L->getType());
unsigned SecondSSize = getTypeStoreSize(SecondS->getType());
if (alias(FirstPHITranslatedAddr, LSize,
SecondPHITranslatedAddr, SecondSSize) ==
MustAlias) {
// If the load and the store are the same size, it's ReadThenWrite.
if (LSize == SecondSSize)
return ReadThenWrite;
}
}
// Otherwise we don't know if it could be writing to other memory.
return Unknown;
case ModRef:
// Second reads and writes to the memory read from by First.
// We don't have a way to express that.
return Unknown;
}
} else if (const StoreInst *S = dyn_cast<StoreInst>(First)) {
// Be over-conservative with volatile for now.
if (S->isVolatile())
return Unknown;
// If we don't have a phi-translated address, use the actual one.
if (!FirstPHITranslatedAddr)
FirstPHITranslatedAddr = S->getPointerOperand();
// Forward this query to getModRefInfo.
switch (getModRefInfo(Second,
FirstPHITranslatedAddr,
getTypeStoreSize(S->getValueOperand()->getType()))) {
case NoModRef:
// Second doesn't reference First's memory, so they're independent.
return Independent;
case Ref:
// Second only reads from the memory written to by First. If it
// also writes to any other memory, be conservative.
if (Second->mayWriteToMemory())
return Unknown;
// If it's loading the same size from the same address, we can
// give a more precise result.
if (const LoadInst *SecondL = dyn_cast<LoadInst>(Second)) {
// If we don't have a phi-translated address, use the actual one.
if (!SecondPHITranslatedAddr)
SecondPHITranslatedAddr = SecondL->getPointerOperand();
unsigned SSize = getTypeStoreSize(S->getValueOperand()->getType());
unsigned SecondLSize = getTypeStoreSize(SecondL->getType());
if (alias(FirstPHITranslatedAddr, SSize,
SecondPHITranslatedAddr, SecondLSize) ==
MustAlias) {
// If the store and the load are the same size, it's WriteThenRead.
if (SSize == SecondLSize)
return WriteThenRead;
// If the load is smaller, it's only WriteThenReadSome.
if (SSize > SecondLSize)
return WriteThenReadSome;
}
}
// Otherwise we don't know if it could be reading from other memory.
return Unknown;
case Mod:
// Second only writes to the memory written to by First. If it
// also reads from any other memory, be conservative.
if (Second->mayReadFromMemory())
return Unknown;
// If it's storing the same size to the same address, we can
// give a more precise result.
if (const StoreInst *SecondS = dyn_cast<StoreInst>(Second)) {
// If we don't have a phi-translated address, use the actual one.
if (!SecondPHITranslatedAddr)
SecondPHITranslatedAddr = SecondS->getPointerOperand();
unsigned SSize = getTypeStoreSize(S->getValueOperand()->getType());
unsigned SecondSSize = getTypeStoreSize(SecondS->getType());
if (alias(FirstPHITranslatedAddr, SSize,
SecondPHITranslatedAddr, SecondSSize) ==
MustAlias) {
// If the stores are the same size, it's WriteThenWrite.
if (SSize == SecondSSize)
return WriteThenWrite;
// If the second store is larger, it's only WriteSomeThenWrite.
if (SSize < SecondSSize)
return WriteSomeThenWrite;
}
}
// Otherwise we don't know if it could be writing to other memory.
return Unknown;
case ModRef:
// Second reads and writes to the memory written to by First.
// We don't have a way to express that.
return Unknown;
}
} else if (const VAArgInst *V = dyn_cast<VAArgInst>(First)) {
// If we don't have a phi-translated address, use the actual one.
if (!FirstPHITranslatedAddr)
FirstPHITranslatedAddr = V->getPointerOperand();
// Forward this query to getModRefInfo.
if (getModRefInfo(Second, FirstPHITranslatedAddr, UnknownSize) == NoModRef)
// Second doesn't reference First's memory, so they're independent.
return Independent;
} else if (ImmutableCallSite FirstCS = cast<Value>(First)) {
assert(!FirstPHITranslatedAddr &&
!SecondPHITranslatedAddr &&
"PHI translation with calls not supported yet!");
// If both instructions are calls/invokes we can use the two-callsite
// form of getModRefInfo.
if (ImmutableCallSite SecondCS = cast<Value>(Second))
// getModRefInfo's arguments are backwards from intuition.
switch (getModRefInfo(SecondCS, FirstCS)) {
case NoModRef:
// Second doesn't reference First's memory, so they're independent.
return Independent;
case Ref:
// If they're both read-only, there's no dependence.
if (FirstCS.onlyReadsMemory() && SecondCS.onlyReadsMemory())
return Independent;
// Otherwise it's not obvious what we can do here.
return Unknown;
case Mod:
// It's not obvious what we can do here.
return Unknown;
case ModRef:
// I know, right?
return Unknown;
}
}
// For anything else, be conservative.
return Unknown;
}
AliasAnalysis::ModRefBehavior
AliasAnalysis::getIntrinsicModRefBehavior(unsigned iid) {
#define GET_INTRINSIC_MODREF_BEHAVIOR
#include "llvm/Intrinsics.gen"
#undef GET_INTRINSIC_MODREF_BEHAVIOR
}
// AliasAnalysis destructor: DO NOT move this to the header file for
// AliasAnalysis or else clients of the AliasAnalysis class may not depend on
// the AliasAnalysis.o file in the current .a file, causing alias analysis
// support to not be included in the tool correctly!
//
AliasAnalysis::~AliasAnalysis() {}
/// InitializeAliasAnalysis - Subclasses must call this method to initialize the
/// AliasAnalysis interface before any other methods are called.
///
void AliasAnalysis::InitializeAliasAnalysis(Pass *P) {
TD = P->getAnalysisIfAvailable<TargetData>();
AA = &P->getAnalysis<AliasAnalysis>();
}
// getAnalysisUsage - All alias analysis implementations should invoke this
// directly (using AliasAnalysis::getAnalysisUsage(AU)).
void AliasAnalysis::getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequired<AliasAnalysis>(); // All AA's chain
}
/// getTypeStoreSize - Return the TargetData store size for the given type,
/// if known, or a conservative value otherwise.
///
unsigned AliasAnalysis::getTypeStoreSize(const Type *Ty) {
return TD ? TD->getTypeStoreSize(Ty) : ~0u;
}
/// canBasicBlockModify - Return true if it is possible for execution of the
/// specified basic block to modify the value pointed to by Ptr.
///
bool AliasAnalysis::canBasicBlockModify(const BasicBlock &BB,
const Value *Ptr, unsigned Size) {
return canInstructionRangeModify(BB.front(), BB.back(), Ptr, Size);
}
/// canInstructionRangeModify - Return true if it is possible for the execution
/// of the specified instructions to modify the value pointed to by Ptr. The
/// instructions to consider are all of the instructions in the range of [I1,I2]
/// INCLUSIVE. I1 and I2 must be in the same basic block.
///
bool AliasAnalysis::canInstructionRangeModify(const Instruction &I1,
const Instruction &I2,
const Value *Ptr, unsigned Size) {
assert(I1.getParent() == I2.getParent() &&
"Instructions not in same basic block!");
BasicBlock::const_iterator I = &I1;
BasicBlock::const_iterator E = &I2;
++E; // Convert from inclusive to exclusive range.
for (; I != E; ++I) // Check every instruction in range
if (getModRefInfo(I, Ptr, Size) & Mod)
return true;
return false;
}
/// isNoAliasCall - Return true if this pointer is returned by a noalias
/// function.
bool llvm::isNoAliasCall(const Value *V) {
if (isa<CallInst>(V) || isa<InvokeInst>(V))
return ImmutableCallSite(cast<Instruction>(V))
.paramHasAttr(0, Attribute::NoAlias);
return false;
}
/// isIdentifiedObject - Return true if this pointer refers to a distinct and
/// identifiable object. This returns true for:
/// Global Variables and Functions (but not Global Aliases)
/// Allocas and Mallocs
/// ByVal and NoAlias Arguments
/// NoAlias returns
///
bool llvm::isIdentifiedObject(const Value *V) {
if (isa<AllocaInst>(V))
return true;
if (isa<GlobalValue>(V) && !isa<GlobalAlias>(V))
return true;
if (isNoAliasCall(V))
return true;
if (const Argument *A = dyn_cast<Argument>(V))
return A->hasNoAliasAttr() || A->hasByValAttr();
return false;
}
// Because of the way .a files work, we must force the BasicAA implementation to
// be pulled in if the AliasAnalysis classes are pulled in. Otherwise we run
// the risk of AliasAnalysis being used, but the default implementation not
// being linked into the tool that uses it.
DEFINING_FILE_FOR(AliasAnalysis)
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