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//===- 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.
//
// 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/BasicBlock.h"
#include "llvm/iMemory.h"
#include "llvm/Target/TargetData.h"
using namespace llvm;
// Register the AliasAnalysis interface, providing a nice name to refer to.
namespace {
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;
}
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;
}
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;
}
// 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
// support to not be included in the tool correctly!
//
AliasAnalysis::~AliasAnalysis() {}
/// setTargetData - Subclasses must call this method to initialize the
/// AliasAnalysis interface before any other methods are called.
///
void AliasAnalysis::InitializeAliasAnalysis(Pass *P) {
TD = &P->getAnalysis<TargetData>();
}
// 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.
}
/// 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::iterator I = const_cast<Instruction*>(&I1);
BasicBlock::iterator E = const_cast<Instruction*>(&I2);
++E; // Convert from inclusive to exclusive range.
for (; I != E; ++I) // Check every instruction in range
if (getModRefInfo(I, const_cast<Value*>(Ptr), Size) & Mod)
return true;
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.
//
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<NoAA>
X("no-aa", "No Alias Analysis (always returns 'may' alias)");
// Declare that we implement the AliasAnalysis interface
RegisterAnalysisGroup<AliasAnalysis, NoAA> Y;
} // End of anonymous namespace
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