mirror of
https://github.com/c64scene-ar/llvm-6502.git
synced 2024-08-19 19:29:31 +00:00
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@4569 91177308-0d34-0410-b5e6-96231b3b80d8
222 lines
8.8 KiB
C++
222 lines
8.8 KiB
C++
//===- AliasAnalysis.cpp - Generic Alias Analysis Interface Implementation -==//
|
|
//
|
|
// 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/BasicAliasAnalysis.h"
|
|
#include "llvm/BasicBlock.h"
|
|
#include "llvm/Support/InstVisitor.h"
|
|
#include "llvm/iMemory.h"
|
|
#include "llvm/iOther.h"
|
|
#include "llvm/Constants.h"
|
|
#include "llvm/GlobalValue.h"
|
|
#include "llvm/DerivedTypes.h"
|
|
|
|
// 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> {
|
|
AliasAnalysis &AA;
|
|
const Value *Ptr;
|
|
|
|
CanModify(AliasAnalysis *aa, const Value *ptr)
|
|
: AA(*aa), Ptr(ptr) {}
|
|
|
|
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));
|
|
}
|
|
|
|
// Other instructions do not alias anything.
|
|
bool visitInstruction(Instruction &I) { return false; }
|
|
};
|
|
}
|
|
|
|
// 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() {}
|
|
|
|
/// 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) {
|
|
CanModify CM(this, Ptr);
|
|
BasicBlock &BB = const_cast<BasicBlock&>(bb);
|
|
|
|
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;
|
|
|
|
return false;
|
|
}
|
|
|
|
/// 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) {
|
|
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...
|
|
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.
|
|
//
|
|
namespace {
|
|
// Register this pass...
|
|
RegisterOpt<BasicAliasAnalysis>
|
|
X("basicaa", "Basic Alias Analysis (default AA impl)");
|
|
|
|
// Declare that we implement the AliasAnalysis interface
|
|
RegisterAnalysisGroup<AliasAnalysis, BasicAliasAnalysis, true> 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);
|
|
}
|
|
|
|
static const Value *getUnderlyingObject(const Value *V) {
|
|
if (!isa<PointerType>(V->getType())) return 0;
|
|
|
|
// If we are at some type of object... return it.
|
|
if (hasUniqueAddress(V)) return V;
|
|
|
|
// Traverse through different addressing mechanisms...
|
|
if (const Instruction *I = dyn_cast<Instruction>(V)) {
|
|
if (isa<CastInst>(I) || isa<GetElementPtrInst>(I))
|
|
return getUnderlyingObject(I->getOperand(0));
|
|
}
|
|
return 0;
|
|
}
|
|
|
|
// alias - Provide a bunch of ad-hoc rules to disambiguate in common cases, such
|
|
// as array references. Note that this function is heavily tail recursive.
|
|
// Hopefully we have a smart C++ compiler. :)
|
|
//
|
|
AliasAnalysis::Result BasicAliasAnalysis::alias(const Value *V1,
|
|
const Value *V2) {
|
|
// 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())) &&
|
|
V1->getType() != Type::LongTy && V2->getType() != Type::LongTy)
|
|
return NoAlias; // Scalars cannot alias each other
|
|
|
|
// Strip off cast instructions...
|
|
if (const Instruction *I = dyn_cast<CastInst>(V1))
|
|
return alias(I->getOperand(0), V2);
|
|
if (const Instruction *I = dyn_cast<CastInst>(V2))
|
|
return alias(I->getOperand(0), V1);
|
|
|
|
// If we have two gep instructions with identical indices, return an alias
|
|
// result equal to the alias result of the original pointer...
|
|
//
|
|
if (const GetElementPtrInst *GEP1 = dyn_cast<GetElementPtrInst>(V1))
|
|
if (const GetElementPtrInst *GEP2 = dyn_cast<GetElementPtrInst>(V2))
|
|
if (GEP1->getNumOperands() == GEP2->getNumOperands() &&
|
|
GEP1->getOperand(0)->getType() == GEP2->getOperand(0)->getType()) {
|
|
if (std::equal(GEP1->op_begin()+1, GEP1->op_end(), GEP2->op_begin()+1))
|
|
return alias(GEP1->getOperand(0), GEP2->getOperand(0));
|
|
|
|
// If all of the indexes to the getelementptr are constant, but
|
|
// different (well we already know they are different), then we know
|
|
// that there cannot be an alias here if the two base pointers DO alias.
|
|
//
|
|
bool AllConstant = true;
|
|
for (unsigned i = 1, e = GEP1->getNumOperands(); i != e; ++i)
|
|
if (!isa<Constant>(GEP1->getOperand(i)) ||
|
|
!isa<Constant>(GEP2->getOperand(i))) {
|
|
AllConstant = false;
|
|
break;
|
|
}
|
|
|
|
// If we are all constant, then look at where the the base pointers
|
|
// alias. If they are known not to alias, then we are dealing with two
|
|
// different arrays or something, so no alias is possible. If they are
|
|
// known to be the same object, then we cannot alias because we are
|
|
// indexing into a different part of the object. As usual, MayAlias
|
|
// doesn't tell us anything.
|
|
//
|
|
if (AllConstant &&
|
|
alias(GEP1->getOperand(0), GEP2->getOperand(1)) != MayAlias)
|
|
return NoAlias;
|
|
}
|
|
|
|
// Figure out what objects these things are pointing to if we can...
|
|
const Value *O1 = getUnderlyingObject(V1);
|
|
const Value *O2 = getUnderlyingObject(V2);
|
|
|
|
// Pointing at a discernable object?
|
|
if (O1 && O2) {
|
|
// If they are two different objects, we know that we have no alias...
|
|
if (O1 != O2) return NoAlias;
|
|
|
|
// If they are the same object, they we can look at the indexes. If they
|
|
// index off of the object is the same for both pointers, they must alias.
|
|
// If they are provably different, they must not alias. Otherwise, we can't
|
|
// tell anything.
|
|
} else if (O1 && isa<ConstantPointerNull>(V2)) {
|
|
return NoAlias; // Unique values don't alias null
|
|
} else if (O2 && isa<ConstantPointerNull>(V1)) {
|
|
return NoAlias; // Unique values don't alias null
|
|
}
|
|
|
|
return MayAlias;
|
|
}
|