//===- AliasAnalysis.cpp - Generic Alias Analysis Interface Implementation -==//
+//
+// The LLVM Compiler Infrastructure
+//
+// This file was developed by the LLVM research group and 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.
//
//===----------------------------------------------------------------------===//
-#include "llvm/Analysis/BasicAliasAnalysis.h"
+#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/BasicBlock.h"
-#include "llvm/Support/InstVisitor.h"
#include "llvm/iMemory.h"
-#include "llvm/Constants.h"
-#include "llvm/GlobalValue.h"
-#include "llvm/DerivedTypes.h"
-#include "llvm/Pass.h"
+#include "llvm/Target/TargetData.h"
+using namespace llvm;
// Register the AliasAnalysis interface, providing a nice name to refer to.
-static RegisterAnalysisGroup<AliasAnalysis> X("Alias Analysis");
-
-// CanModify - Define a little visitor class that is used to check to see if
-// arbitrary chunks of code can modify a specified pointer.
-//
namespace {
- struct CanModify : public InstVisitor<CanModify, bool> {
- const AliasAnalysis &AA;
- const Value *Ptr;
+ RegisterAnalysisGroup<AliasAnalysis> Z("Alias Analysis");
+}
+
+AliasAnalysis::ModRefResult
+AliasAnalysis::getModRefInfo(LoadInst *L, Value *P, unsigned Size) {
+ return alias(L->getOperand(0), TD->getTypeSize(L->getType()),
+ P, Size) ? Ref : NoModRef;
+}
- CanModify(const AliasAnalysis *aa, const Value *ptr)
- : AA(*aa), Ptr(ptr) {}
+AliasAnalysis::ModRefResult
+AliasAnalysis::getModRefInfo(StoreInst *S, Value *P, unsigned Size) {
+ // If the stored address cannot alias the pointer in question, then the
+ // pointer cannot be modified by the store.
+ if (!alias(S->getOperand(1), TD->getTypeSize(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.
+ return pointsToConstantMemory(P) ? NoModRef : Mod;
+}
- bool visitInvokeInst(InvokeInst &II) {
- return AA.canInvokeModify(II, Ptr);
- }
- bool visitCallInst(CallInst &CI) {
- return AA.canCallModify(CI, Ptr);
- }
- bool visitStoreInst(StoreInst &SI) {
- return AA.alias(Ptr, SI.getOperand(1));
+AliasAnalysis::ModRefResult
+AliasAnalysis::getModRefInfo(CallSite CS, Value *P, unsigned Size) {
+ if (Function *F = CS.getCalledFunction())
+ if (onlyReadsMemory(F)) {
+ if (doesNotAccessMemory(F)) return NoModRef;
+ return Ref;
}
- // Other instructions do not alias anything.
- bool visitInstruction(Instruction &I) { return false; }
- };
+ // If P points to a constant memory location, the call definitely could not
+ // modify the memory location.
+ return pointsToConstantMemory(P) ? Ref : ModRef;
}
+AliasAnalysis::ModRefResult
+AliasAnalysis::getModRefInfo(CallSite CS1, CallSite CS2) {
+ // FIXME: could probably do better.
+ return ModRef;
+}
+
+
// 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
//
AliasAnalysis::~AliasAnalysis() {}
-/// canBasicBlockModify - Return true if it is possible for execution of the
-/// specified basic block to modify the value pointed to by Ptr.
+/// setTargetData - Subclasses must call this method to initialize the
+/// AliasAnalysis interface before any other methods are called.
///
-bool AliasAnalysis::canBasicBlockModify(const BasicBlock &bb,
- const Value *Ptr) const {
- CanModify CM(this, Ptr);
- BasicBlock &BB = const_cast<BasicBlock&>(bb);
+void AliasAnalysis::InitializeAliasAnalysis(Pass *P) {
+ TD = &P->getAnalysis<TargetData>();
+}
- for (BasicBlock::iterator I = BB.begin(), E = BB.end(); I != E; ++I)
- if (CM.visit(I)) // Check every instruction in the basic block...
- return true;
+// getAnalysisUsage - All alias analysis implementations should invoke this
+// directly (using AliasAnalysis::getAnalysisUsage(AU)) to make sure that
+// TargetData is required by the pass.
+void AliasAnalysis::getAnalysisUsage(AnalysisUsage &AU) const {
+ AU.addRequired<TargetData>(); // All AA's need TargetData.
+}
- return false;
+/// 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
///
bool AliasAnalysis::canInstructionRangeModify(const Instruction &I1,
const Instruction &I2,
- const Value *Ptr) const {
+ const Value *Ptr, unsigned Size) {
assert(I1.getParent() == I2.getParent() &&
"Instructions not in same basic block!");
- CanModify CM(this, Ptr);
BasicBlock::iterator I = const_cast<Instruction*>(&I1);
BasicBlock::iterator E = const_cast<Instruction*>(&I2);
++E; // Convert from inclusive to exclusive range.
- for (; I != E; ++I)
- if (CM.visit(I)) // Check every instruction in the basic block...
+ for (; I != E; ++I) // Check every instruction in range
+ if (getModRefInfo(I, const_cast<Value*>(Ptr), Size) & Mod)
return true;
-
return false;
}
-//===----------------------------------------------------------------------===//
-// BasicAliasAnalysis Pass Implementation
-//===----------------------------------------------------------------------===//
-//
-// Because of the way .a files work, the implementation of the
-// BasicAliasAnalysis class MUST be in the AliasAnalysis file itself, or else we
-// run the risk of AliasAnalysis being used, but the default implementation not
-// being linked into the tool that uses it. As such, we register and implement
-// the class here.
+// 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.
//
+extern void llvm::BasicAAStub();
+static IncludeFile INCLUDE_BASICAA_CPP((void*)&BasicAAStub);
+
+
namespace {
+ struct NoAA : public ImmutablePass, public AliasAnalysis {
+ virtual void getAnalysisUsage(AnalysisUsage &AU) const {
+ AliasAnalysis::getAnalysisUsage(AU);
+ }
+
+ virtual void initializePass() {
+ InitializeAliasAnalysis(this);
+ }
+ };
+
// Register this pass...
- RegisterOpt<BasicAliasAnalysis>
- X("basicaa", "Basic Alias Analysis (default AA impl)");
+ RegisterOpt<NoAA>
+ X("no-aa", "No Alias Analysis (always returns 'may' alias)");
// Declare that we implement the AliasAnalysis interface
- RegisterAnalysisGroup<AliasAnalysis, BasicAliasAnalysis, true> Y;
+ RegisterAnalysisGroup<AliasAnalysis, NoAA> Y;
} // End of anonymous namespace
-
-
-
-// hasUniqueAddress - Return true if the
-static inline bool hasUniqueAddress(const Value *V) {
- return isa<GlobalValue>(V) || isa<MallocInst>(V) || isa<AllocaInst>(V);
-}
-
-AliasAnalysis::Result BasicAliasAnalysis::alias(const Value *V1,
- const Value *V2) const {
- // Strip off constant pointer refs if they exist
- if (const ConstantPointerRef *CPR = dyn_cast<ConstantPointerRef>(V1))
- V1 = CPR->getValue();
- if (const ConstantPointerRef *CPR = dyn_cast<ConstantPointerRef>(V2))
- V2 = CPR->getValue();
-
- // Are we checking for alias of the same value?
- if (V1 == V2) return MustAlias;
-
- if (!isa<PointerType>(V1->getType()) || !isa<PointerType>(V2->getType()))
- return NoAlias; // Scalars cannot alias each other
-
- bool V1Unique = hasUniqueAddress(V1);
- bool V2Unique = hasUniqueAddress(V2);
-
- if (V1Unique && V2Unique)
- return NoAlias; // Can't alias if they are different unique values
-
- if ((V1Unique && isa<ConstantPointerNull>(V2)) ||
- (V2Unique && isa<ConstantPointerNull>(V1)))
- return NoAlias; // Unique values don't alias null
-
- // TODO: Handle getelementptr with nonzero offset
-
- return MayAlias;
-}
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