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https://github.com/c64scene-ar/llvm-6502.git
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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@6270 91177308-0d34-0410-b5e6-96231b3b80d8
309 lines
12 KiB
C++
309 lines
12 KiB
C++
//===- llvm/Analysis/BasicAliasAnalysis.h - Alias Analysis Impl -*- C++ -*-===//
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//
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// This file defines the default implementation of the Alias Analysis interface
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// that simply implements a few identities (two different globals cannot alias,
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// etc), but otherwise does no analysis.
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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/iMemory.h"
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#include "llvm/iOther.h"
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#include "llvm/ConstantHandling.h"
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#include "llvm/GlobalValue.h"
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#include "llvm/DerivedTypes.h"
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#include "llvm/Target/TargetData.h"
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// Make sure that anything that uses AliasAnalysis pulls in this file...
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void BasicAAStub() {}
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namespace {
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struct BasicAliasAnalysis : public ImmutablePass, public AliasAnalysis {
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virtual void getAnalysisUsage(AnalysisUsage &AU) const {
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AliasAnalysis::getAnalysisUsage(AU);
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}
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virtual void initializePass();
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// alias - This is the only method here that does anything interesting...
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//
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AliasResult alias(const Value *V1, unsigned V1Size,
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const Value *V2, unsigned V2Size);
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private:
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// CheckGEPInstructions - Check two GEP instructions of compatible types and
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// equal number of arguments. This checks to see if the index expressions
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// preclude the pointers from aliasing...
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AliasResult CheckGEPInstructions(GetElementPtrInst *GEP1, unsigned G1Size,
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GetElementPtrInst *GEP2, unsigned G2Size);
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};
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// Register this pass...
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RegisterOpt<BasicAliasAnalysis>
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X("basicaa", "Basic Alias Analysis (default AA impl)");
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// Declare that we implement the AliasAnalysis interface
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RegisterAnalysisGroup<AliasAnalysis, BasicAliasAnalysis, true> Y;
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} // End of anonymous namespace
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void BasicAliasAnalysis::initializePass() {
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InitializeAliasAnalysis(this);
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}
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// hasUniqueAddress - Return true if the
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static inline bool hasUniqueAddress(const Value *V) {
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return isa<GlobalValue>(V) || isa<MallocInst>(V) || isa<AllocaInst>(V);
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}
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static const Value *getUnderlyingObject(const Value *V) {
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if (!isa<PointerType>(V->getType())) return 0;
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// If we are at some type of object... return it.
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if (hasUniqueAddress(V)) return V;
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// Traverse through different addressing mechanisms...
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if (const Instruction *I = dyn_cast<Instruction>(V)) {
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if (isa<CastInst>(I) || isa<GetElementPtrInst>(I))
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return getUnderlyingObject(I->getOperand(0));
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}
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return 0;
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}
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// alias - Provide a bunch of ad-hoc rules to disambiguate in common cases, such
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// as array references. Note that this function is heavily tail recursive.
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// Hopefully we have a smart C++ compiler. :)
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//
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AliasAnalysis::AliasResult
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BasicAliasAnalysis::alias(const Value *V1, unsigned V1Size,
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const Value *V2, unsigned V2Size) {
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// Strip off constant pointer refs if they exist
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if (const ConstantPointerRef *CPR = dyn_cast<ConstantPointerRef>(V1))
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V1 = CPR->getValue();
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if (const ConstantPointerRef *CPR = dyn_cast<ConstantPointerRef>(V2))
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V2 = CPR->getValue();
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// Are we checking for alias of the same value?
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if (V1 == V2) return MustAlias;
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if ((!isa<PointerType>(V1->getType()) || !isa<PointerType>(V2->getType())) &&
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V1->getType() != Type::LongTy && V2->getType() != Type::LongTy)
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return NoAlias; // Scalars cannot alias each other
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// Strip off cast instructions...
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if (const Instruction *I = dyn_cast<CastInst>(V1))
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return alias(I->getOperand(0), V1Size, V2, V2Size);
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if (const Instruction *I = dyn_cast<CastInst>(V2))
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return alias(V1, V1Size, I->getOperand(0), V2Size);
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// Figure out what objects these things are pointing to if we can...
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const Value *O1 = getUnderlyingObject(V1);
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const Value *O2 = getUnderlyingObject(V2);
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// Pointing at a discernable object?
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if (O1 && O2) {
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// If they are two different objects, we know that we have no alias...
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if (O1 != O2) return NoAlias;
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// If they are the same object, they we can look at the indexes. If they
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// index off of the object is the same for both pointers, they must alias.
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// If they are provably different, they must not alias. Otherwise, we can't
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// tell anything.
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} else if (O1 && isa<ConstantPointerNull>(V2)) {
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return NoAlias; // Unique values don't alias null
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} else if (O2 && isa<ConstantPointerNull>(V1)) {
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return NoAlias; // Unique values don't alias null
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}
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// If we have two gep instructions with identical indices, return an alias
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// result equal to the alias result of the original pointer...
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//
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if (const GetElementPtrInst *GEP1 = dyn_cast<GetElementPtrInst>(V1))
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if (const GetElementPtrInst *GEP2 = dyn_cast<GetElementPtrInst>(V2))
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if (GEP1->getNumOperands() == GEP2->getNumOperands() &&
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GEP1->getOperand(0)->getType() == GEP2->getOperand(0)->getType()) {
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AliasResult GAlias =
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CheckGEPInstructions((GetElementPtrInst*)GEP1, V1Size,
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(GetElementPtrInst*)GEP2, V2Size);
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if (GAlias != MayAlias)
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return GAlias;
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}
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// Check to see if these two pointers are related by a getelementptr
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// instruction. If one pointer is a GEP with a non-zero index of the other
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// pointer, we know they cannot alias.
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//
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if (isa<GetElementPtrInst>(V2)) {
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std::swap(V1, V2);
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std::swap(V1Size, V2Size);
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}
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if (V1Size != ~0U && V2Size != ~0U)
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if (const GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(V1)) {
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AliasResult R = alias(GEP->getOperand(0), V1Size, V2, V2Size);
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if (R == MustAlias) {
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// If there is at least one non-zero constant index, we know they cannot
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// alias.
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bool ConstantFound = false;
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for (unsigned i = 1, e = GEP->getNumOperands(); i != e; ++i)
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if (const Constant *C = dyn_cast<Constant>(GEP->getOperand(i)))
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if (!C->isNullValue()) {
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ConstantFound = true;
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break;
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}
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if (ConstantFound) {
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if (V2Size <= 1 && V1Size <= 1) // Just pointer check?
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return NoAlias;
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// Otherwise we have to check to see that the distance is more than
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// the size of the argument... build an index vector that is equal to
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// the arguments provided, except substitute 0's for any variable
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// indexes we find...
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std::vector<Value*> Indices;
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Indices.reserve(GEP->getNumOperands()-1);
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for (unsigned i = 1; i != GEP->getNumOperands(); ++i)
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if (const Constant *C = dyn_cast<Constant>(GEP->getOperand(i)))
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Indices.push_back((Value*)C);
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else
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Indices.push_back(Constant::getNullValue(Type::LongTy));
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const Type *Ty = GEP->getOperand(0)->getType();
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int Offset = getTargetData().getIndexedOffset(Ty, Indices);
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if (Offset >= (int)V2Size || Offset <= -(int)V1Size)
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return NoAlias;
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}
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}
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}
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return MayAlias;
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}
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// CheckGEPInstructions - Check two GEP instructions of compatible types and
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// equal number of arguments. This checks to see if the index expressions
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// preclude the pointers from aliasing...
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//
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AliasAnalysis::AliasResult
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BasicAliasAnalysis::CheckGEPInstructions(GetElementPtrInst *GEP1, unsigned G1S,
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GetElementPtrInst *GEP2, unsigned G2S){
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// Do the base pointers alias?
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AliasResult BaseAlias = alias(GEP1->getOperand(0), G1S,
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GEP2->getOperand(0), G2S);
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if (BaseAlias != MustAlias) // No or May alias: We cannot add anything...
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return BaseAlias;
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// Find the (possibly empty) initial sequence of equal values...
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unsigned NumGEPOperands = GEP1->getNumOperands();
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unsigned UnequalOper = 1;
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while (UnequalOper != NumGEPOperands &&
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GEP1->getOperand(UnequalOper) == GEP2->getOperand(UnequalOper))
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++UnequalOper;
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// If all operands equal each other, then the derived pointers must
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// alias each other...
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if (UnequalOper == NumGEPOperands) return MustAlias;
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// So now we know that the indexes derived from the base pointers,
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// which are known to alias, are different. We can still determine a
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// no-alias result if there are differing constant pairs in the index
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// chain. For example:
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// A[i][0] != A[j][1] iff (&A[0][1]-&A[0][0] >= std::max(G1S, G2S))
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//
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unsigned SizeMax = std::max(G1S, G2S);
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if (SizeMax == ~0U) return MayAlias; // Avoid frivolous work...
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// Scan for the first operand that is constant and unequal in the
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// two getelemenptrs...
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unsigned FirstConstantOper = UnequalOper;
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for (; FirstConstantOper != NumGEPOperands; ++FirstConstantOper) {
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const Value *G1Oper = GEP1->getOperand(FirstConstantOper);
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const Value *G2Oper = GEP2->getOperand(FirstConstantOper);
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if (G1Oper != G2Oper && // Found non-equal constant indexes...
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isa<Constant>(G1Oper) && isa<Constant>(G2Oper)) {
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// Make sure they are comparable... and make sure the GEP with
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// the smaller leading constant is GEP1.
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ConstantBool *Compare =
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*cast<Constant>(GEP1->getOperand(FirstConstantOper)) >
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*cast<Constant>(GEP2->getOperand(FirstConstantOper));
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if (Compare) { // If they are comparable...
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if (Compare->getValue())
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std::swap(GEP1, GEP2); // Make GEP1 < GEP2
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break;
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}
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}
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}
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// No constant operands, we cannot tell anything...
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if (FirstConstantOper == NumGEPOperands) return MayAlias;
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// If there are non-equal constants arguments, then we can figure
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// out a minimum known delta between the two index expressions... at
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// this point we know that the first constant index of GEP1 is less
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// than the first constant index of GEP2.
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//
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std::vector<Value*> Indices1;
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Indices1.reserve(NumGEPOperands-1);
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for (unsigned i = 1; i != FirstConstantOper; ++i)
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if (GEP1->getOperand(i)->getType() == Type::UByteTy)
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Indices1.push_back(GEP1->getOperand(i));
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else
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Indices1.push_back(Constant::getNullValue(Type::LongTy));
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std::vector<Value*> Indices2;
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Indices2.reserve(NumGEPOperands-1);
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Indices2 = Indices1; // Copy the zeros prefix...
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// Add the two known constant operands...
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Indices1.push_back((Value*)GEP1->getOperand(FirstConstantOper));
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Indices2.push_back((Value*)GEP2->getOperand(FirstConstantOper));
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const Type *GEPPointerTy = GEP1->getOperand(0)->getType();
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// Loop over the rest of the operands...
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for (unsigned i = FirstConstantOper+1; i!=NumGEPOperands; ++i){
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const Value *Op1 = GEP1->getOperand(i);
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const Value *Op2 = GEP2->getOperand(i);
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if (Op1 == Op2) { // If they are equal, use a zero index...
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Indices1.push_back(Constant::getNullValue(Op1->getType()));
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Indices2.push_back(Indices1.back());
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} else {
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if (isa<Constant>(Op1))
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Indices1.push_back((Value*)Op1);
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else {
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// GEP1 is known to produce a value less than GEP2. To be
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// conservatively correct, we must assume the largest possible constant
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// is used in this position. This cannot be the initial index to the
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// GEP instructions (because we know we have at least one element before
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// this one with the different constant arguments), so we know that the
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// current index must be into either a struct or array. Because we know
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// it's not constant, this cannot be a structure index. Because of
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// this, we can calculate the maximum value possible.
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//
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const ArrayType *ElTy =
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cast<ArrayType>(GEP1->getIndexedType(GEPPointerTy, Indices1, true));
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Indices1.push_back(ConstantSInt::get(Type::LongTy,
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ElTy->getNumElements()-1));
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}
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if (isa<Constant>(Op2))
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Indices2.push_back((Value*)Op2);
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else // Conservatively assume the minimum value for this index
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Indices2.push_back(Constant::getNullValue(Op2->getType()));
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}
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}
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int64_t Offset1 = getTargetData().getIndexedOffset(GEPPointerTy, Indices1);
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int64_t Offset2 = getTargetData().getIndexedOffset(GEPPointerTy, Indices2);
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assert(Offset1 < Offset2 &&"There is at least one different constant here!");
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if ((uint64_t)(Offset2-Offset1) >= SizeMax) {
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//std::cerr << "Determined that these two GEP's don't alias ["
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// << SizeMax << " bytes]: \n" << *GEP1 << *GEP2;
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return NoAlias;
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}
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return MayAlias;
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}
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