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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@11707 91177308-0d34-0410-b5e6-96231b3b80d8
524 lines
22 KiB
C++
524 lines
22 KiB
C++
//===- BasicAliasAnalysis.cpp - Local Alias Analysis Impl -----------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file was developed by the LLVM research group and is distributed under
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// the University of Illinois Open Source License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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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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// FIXME: This could be extended for a very simple form of mod/ref information.
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// If a pointer is locally allocated (either malloc or alloca) and never passed
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// into a call or stored to memory, then we know that calls will not mod/ref the
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// memory. This can be important for tailcallelim.
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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/Argument.h"
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#include "llvm/iOther.h"
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#include "llvm/iMemory.h"
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#include "llvm/Constants.h"
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#include "llvm/GlobalVariable.h"
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#include "llvm/DerivedTypes.h"
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#include "llvm/Target/TargetData.h"
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#include "llvm/Support/GetElementPtrTypeIterator.h"
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using namespace llvm;
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// Make sure that anything that uses AliasAnalysis pulls in this file...
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void llvm::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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AliasResult alias(const Value *V1, unsigned V1Size,
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const Value *V2, unsigned V2Size);
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/// pointsToConstantMemory - Chase pointers until we find a (constant
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/// global) or not.
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bool pointsToConstantMemory(const Value *P);
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private:
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// CheckGEPInstructions - Check two GEP instructions with known
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// must-aliasing base pointers. This checks to see if the index expressions
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// preclude the pointers from aliasing...
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AliasResult
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CheckGEPInstructions(const Type* BasePtr1Ty, std::vector<Value*> &GEP1Ops,
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unsigned G1Size,
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const Type *BasePtr2Ty, std::vector<Value*> &GEP2Ops,
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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 specified value points to something
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// with a unique, discernable, address.
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static inline bool hasUniqueAddress(const Value *V) {
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return isa<GlobalValue>(V) || isa<AllocationInst>(V);
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}
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// getUnderlyingObject - This traverses the use chain to figure out what object
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// the specified value points to. If the value points to, or is derived from, a
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// unique object or an argument, return it.
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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) || isa<Argument>(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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} else if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
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if (CE->getOpcode() == Instruction::Cast ||
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CE->getOpcode() == Instruction::GetElementPtr)
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return getUnderlyingObject(CE->getOperand(0));
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} else if (const ConstantPointerRef *CPR = dyn_cast<ConstantPointerRef>(V)) {
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return CPR->getValue();
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}
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return 0;
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}
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static const User *isGEP(const Value *V) {
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if (isa<GetElementPtrInst>(V) ||
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(isa<ConstantExpr>(V) &&
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cast<ConstantExpr>(V)->getOpcode() == Instruction::GetElementPtr))
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return cast<User>(V);
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return 0;
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}
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static const Value *GetGEPOperands(const Value *V, std::vector<Value*> &GEPOps){
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assert(GEPOps.empty() && "Expect empty list to populate!");
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GEPOps.insert(GEPOps.end(), cast<User>(V)->op_begin()+1,
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cast<User>(V)->op_end());
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// Accumulate all of the chained indexes into the operand array
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V = cast<User>(V)->getOperand(0);
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while (const User *G = isGEP(V)) {
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if (!isa<Constant>(GEPOps[0]) ||
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!cast<Constant>(GEPOps[0])->isNullValue())
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break; // Don't handle folding arbitrary pointer offsets yet...
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GEPOps.erase(GEPOps.begin()); // Drop the zero index
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GEPOps.insert(GEPOps.begin(), G->op_begin()+1, G->op_end());
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V = G->getOperand(0);
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}
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return V;
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}
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/// pointsToConstantMemory - Chase pointers until we find a (constant
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/// global) or not.
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bool BasicAliasAnalysis::pointsToConstantMemory(const Value *P) {
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if (const Value *V = getUnderlyingObject(P))
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if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(V))
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return GV->isConstant();
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return false;
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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 any constant expression casts if they exist
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if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V1))
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if (CE->getOpcode() == Instruction::Cast)
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V1 = CE->getOperand(0);
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if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V2))
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if (CE->getOpcode() == Instruction::Cast)
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V2 = CE->getOperand(0);
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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 discernible object?
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if (O1 && O2) {
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if (isa<Argument>(O1)) {
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// Incoming argument cannot alias locally allocated object!
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if (isa<AllocationInst>(O2)) return NoAlias;
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// Otherwise, nothing is known...
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} else if (isa<Argument>(O2)) {
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// Incoming argument cannot alias locally allocated object!
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if (isa<AllocationInst>(O1)) return NoAlias;
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// Otherwise, nothing is known...
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} else {
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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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}
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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<Argument>(O1) && isa<ConstantPointerNull>(V2)) {
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return NoAlias; // Unique values don't alias null
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} else if (O2 && !isa<Argument>(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 must-alias'ing base pointers, figure
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// out if the indexes to the GEP tell us anything about the derived pointer.
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// Note that we also handle chains of getelementptr instructions as well as
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// constant expression getelementptrs here.
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//
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if (isGEP(V1) && isGEP(V2)) {
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// Drill down into the first non-gep value, to test for must-aliasing of
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// the base pointers.
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const Value *BasePtr1 = V1, *BasePtr2 = V2;
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do {
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BasePtr1 = cast<User>(BasePtr1)->getOperand(0);
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} while (isGEP(BasePtr1) &&
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cast<User>(BasePtr1)->getOperand(1) ==
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Constant::getNullValue(cast<User>(BasePtr1)->getOperand(1)->getType()));
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do {
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BasePtr2 = cast<User>(BasePtr2)->getOperand(0);
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} while (isGEP(BasePtr2) &&
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cast<User>(BasePtr2)->getOperand(1) ==
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Constant::getNullValue(cast<User>(BasePtr2)->getOperand(1)->getType()));
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// Do the base pointers alias?
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AliasResult BaseAlias = alias(BasePtr1, V1Size, BasePtr2, V2Size);
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if (BaseAlias == NoAlias) return NoAlias;
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if (BaseAlias == MustAlias) {
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// If the base pointers alias each other exactly, check to see if we can
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// figure out anything about the resultant pointers, to try to prove
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// non-aliasing.
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// Collect all of the chained GEP operands together into one simple place
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std::vector<Value*> GEP1Ops, GEP2Ops;
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BasePtr1 = GetGEPOperands(V1, GEP1Ops);
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BasePtr2 = GetGEPOperands(V2, GEP2Ops);
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AliasResult GAlias =
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CheckGEPInstructions(BasePtr1->getType(), GEP1Ops, V1Size,
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BasePtr2->getType(), GEP2Ops, V2Size);
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if (GAlias != MayAlias)
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return GAlias;
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}
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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 (isGEP(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 User *GEP = isGEP(V1)) {
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std::vector<Value*> GEPOperands;
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const Value *BasePtr = GetGEPOperands(V1, GEPOperands);
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AliasResult R = alias(BasePtr, 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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bool AllZerosFound = true;
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for (unsigned i = 0, e = GEPOperands.size(); i != e; ++i)
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if (const Constant *C = dyn_cast<Constant>(GEPOperands[i])) {
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if (!C->isNullValue()) {
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ConstantFound = true;
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AllZerosFound = false;
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break;
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}
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} else {
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AllZerosFound = false;
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}
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// If we have getelementptr <ptr>, 0, 0, 0, 0, ... and V2 must aliases
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// the ptr, the end result is a must alias also.
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if (AllZerosFound)
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return MustAlias;
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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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for (unsigned i = 0; i != GEPOperands.size(); ++i)
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if (!isa<Constant>(GEPOperands[i]) ||
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isa<ConstantExpr>(GEPOperands[i]))
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GEPOperands[i] =Constant::getNullValue(GEPOperands[i]->getType());
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int64_t Offset = getTargetData().getIndexedOffset(BasePtr->getType(),
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GEPOperands);
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if (Offset >= (int64_t)V2Size || Offset <= -(int64_t)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 with known must-aliasing
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/// base pointers. This checks to see if the index expressions preclude the
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/// pointers from aliasing...
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AliasAnalysis::AliasResult BasicAliasAnalysis::
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CheckGEPInstructions(const Type* BasePtr1Ty, std::vector<Value*> &GEP1Ops,
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unsigned G1S,
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const Type *BasePtr2Ty, std::vector<Value*> &GEP2Ops,
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unsigned G2S) {
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// We currently can't handle the case when the base pointers have different
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// primitive types. Since this is uncommon anyway, we are happy being
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// extremely conservative.
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if (BasePtr1Ty != BasePtr2Ty)
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return MayAlias;
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const Type *GEPPointerTy = BasePtr1Ty;
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// Find the (possibly empty) initial sequence of equal values... which are not
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// necessarily constants.
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unsigned NumGEP1Operands = GEP1Ops.size(), NumGEP2Operands = GEP2Ops.size();
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unsigned MinOperands = std::min(NumGEP1Operands, NumGEP2Operands);
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unsigned MaxOperands = std::max(NumGEP1Operands, NumGEP2Operands);
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unsigned UnequalOper = 0;
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while (UnequalOper != MinOperands &&
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GEP1Ops[UnequalOper] == GEP2Ops[UnequalOper]) {
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// Advance through the type as we go...
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++UnequalOper;
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if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr1Ty))
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BasePtr1Ty = CT->getTypeAtIndex(GEP1Ops[UnequalOper-1]);
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else {
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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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BasePtr1Ty = 0;
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assert(UnequalOper == NumGEP1Operands && UnequalOper == NumGEP2Operands &&
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"Ran out of type nesting, but not out of operands?");
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return MustAlias;
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}
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}
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// If we have seen all constant operands, and run out of indexes on one of the
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// getelementptrs, check to see if the tail of the leftover one is all zeros.
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// If so, return mustalias.
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if (UnequalOper == MinOperands) {
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if (GEP1Ops.size() < GEP2Ops.size()) std::swap(GEP1Ops, GEP2Ops);
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bool AllAreZeros = true;
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for (unsigned i = UnequalOper; i != MaxOperands; ++i)
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if (!isa<Constant>(GEP1Ops[i]) ||
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!cast<Constant>(GEP1Ops[i])->isNullValue()) {
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AllAreZeros = false;
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break;
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}
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if (AllAreZeros) return MustAlias;
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}
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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 != MinOperands; ++FirstConstantOper) {
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const Value *G1Oper = GEP1Ops[FirstConstantOper];
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const Value *G2Oper = GEP2Ops[FirstConstantOper];
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if (G1Oper != G2Oper) // Found non-equal constant indexes...
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if (Constant *G1OC = dyn_cast<Constant>(const_cast<Value*>(G1Oper)))
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if (Constant *G2OC = dyn_cast<Constant>(const_cast<Value*>(G2Oper))) {
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// Make sure they are comparable (ie, not constant expressions)...
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// and make sure the GEP with the smaller leading constant is GEP1.
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Constant *Compare = ConstantExpr::get(Instruction::SetGT, G1OC, G2OC);
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if (ConstantBool *CV = dyn_cast<ConstantBool>(Compare)) {
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if (CV->getValue()) // If they are comparable and G2 > G1
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std::swap(GEP1Ops, GEP2Ops); // Make GEP1 < GEP2
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break;
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}
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}
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BasePtr1Ty = cast<CompositeType>(BasePtr1Ty)->getTypeAtIndex(G1Oper);
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}
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// No shared constant operands, and we ran out of common operands. At this
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// point, the GEP instructions have run through all of their operands, and we
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// haven't found evidence that there are any deltas between the GEP's.
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// However, one GEP may have more operands than the other. If this is the
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// case, there may still be hope. This this now.
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if (FirstConstantOper == MinOperands) {
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// Make GEP1Ops be the longer one if there is a longer one.
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if (GEP1Ops.size() < GEP2Ops.size())
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std::swap(GEP1Ops, GEP2Ops);
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// Is there anything to check?
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if (GEP1Ops.size() > MinOperands) {
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for (unsigned i = FirstConstantOper; i != MaxOperands; ++i)
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if (isa<Constant>(GEP1Ops[i]) && !isa<ConstantExpr>(GEP1Ops[i]) &&
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!cast<Constant>(GEP1Ops[i])->isNullValue()) {
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// Yup, there's a constant in the tail. Set all variables to
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// constants in the GEP instruction to make it suiteable for
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// TargetData::getIndexedOffset.
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for (i = 0; i != MaxOperands; ++i)
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if (!isa<Constant>(GEP1Ops[i]) || isa<ConstantExpr>(GEP1Ops[i]))
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GEP1Ops[i] = Constant::getNullValue(GEP1Ops[i]->getType());
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// Okay, now get the offset. This is the relative offset for the full
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// instruction.
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const TargetData &TD = getTargetData();
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int64_t Offset1 = TD.getIndexedOffset(GEPPointerTy, GEP1Ops);
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// Now crop off any constants from the end...
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GEP1Ops.resize(MinOperands);
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int64_t Offset2 = TD.getIndexedOffset(GEPPointerTy, GEP1Ops);
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// If the tail provided a bit enough offset, return noalias!
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if ((uint64_t)(Offset2-Offset1) >= SizeMax)
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return NoAlias;
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}
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}
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// Couldn't find anything useful.
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return MayAlias;
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}
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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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// Advance BasePtr[12]Ty over this first differing constant operand.
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BasePtr2Ty = cast<CompositeType>(BasePtr1Ty)->getTypeAtIndex(GEP2Ops[FirstConstantOper]);
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BasePtr1Ty = cast<CompositeType>(BasePtr1Ty)->getTypeAtIndex(GEP1Ops[FirstConstantOper]);
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// We are going to be using TargetData::getIndexedOffset to determine the
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// offset that each of the GEP's is reaching. To do this, we have to convert
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// all variable references to constant references. To do this, we convert the
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// initial equal sequence of variables into constant zeros to start with.
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for (unsigned i = 0; i != FirstConstantOper; ++i) {
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if (!isa<Constant>(GEP1Ops[i]) || isa<ConstantExpr>(GEP1Ops[i]) ||
|
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!isa<Constant>(GEP2Ops[i]) || isa<ConstantExpr>(GEP2Ops[i])) {
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GEP1Ops[i] = Constant::getNullValue(GEP1Ops[i]->getType());
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|
GEP2Ops[i] = Constant::getNullValue(GEP2Ops[i]->getType());
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|
}
|
|
}
|
|
|
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// We know that GEP1Ops[FirstConstantOper] & GEP2Ops[FirstConstantOper] are ok
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|
|
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// Loop over the rest of the operands...
|
|
for (unsigned i = FirstConstantOper+1; i != MaxOperands; ++i) {
|
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const Value *Op1 = i < GEP1Ops.size() ? GEP1Ops[i] : 0;
|
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const Value *Op2 = i < GEP2Ops.size() ? GEP2Ops[i] : 0;
|
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// If they are equal, use a zero index...
|
|
if (Op1 == Op2 && BasePtr1Ty == BasePtr2Ty) {
|
|
if (!isa<Constant>(Op1) || isa<ConstantExpr>(Op1))
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|
GEP1Ops[i] = GEP2Ops[i] = Constant::getNullValue(Op1->getType());
|
|
// Otherwise, just keep the constants we have.
|
|
} else {
|
|
if (Op1) {
|
|
if (const ConstantInt *Op1C = dyn_cast<ConstantInt>(Op1)) {
|
|
// If this is an array index, make sure the array element is in range.
|
|
if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty))
|
|
if (Op1C->getRawValue() >= AT->getNumElements())
|
|
return MayAlias; // Be conservative with out-of-range accesses
|
|
|
|
} else {
|
|
// GEP1 is known to produce a value less than GEP2. To be
|
|
// conservatively correct, we must assume the largest possible
|
|
// constant is used in this position. This cannot be the initial
|
|
// index to the GEP instructions (because we know we have at least one
|
|
// element before this one with the different constant arguments), so
|
|
// we know that the current index must be into either a struct or
|
|
// array. Because we know it's not constant, this cannot be a
|
|
// structure index. Because of this, we can calculate the maximum
|
|
// value possible.
|
|
//
|
|
if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty))
|
|
GEP1Ops[i] = ConstantSInt::get(Type::LongTy,AT->getNumElements()-1);
|
|
}
|
|
}
|
|
|
|
if (Op2) {
|
|
if (const ConstantInt *Op2C = dyn_cast<ConstantInt>(Op2)) {
|
|
// If this is an array index, make sure the array element is in range.
|
|
if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty))
|
|
if (Op2C->getRawValue() >= AT->getNumElements())
|
|
return MayAlias; // Be conservative with out-of-range accesses
|
|
} else { // Conservatively assume the minimum value for this index
|
|
GEP2Ops[i] = Constant::getNullValue(Op2->getType());
|
|
}
|
|
}
|
|
}
|
|
|
|
if (BasePtr1Ty && Op1) {
|
|
if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr1Ty))
|
|
BasePtr1Ty = CT->getTypeAtIndex(GEP1Ops[i]);
|
|
else
|
|
BasePtr1Ty = 0;
|
|
}
|
|
|
|
if (BasePtr2Ty && Op2) {
|
|
if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr2Ty))
|
|
BasePtr2Ty = CT->getTypeAtIndex(GEP2Ops[i]);
|
|
else
|
|
BasePtr2Ty = 0;
|
|
}
|
|
}
|
|
|
|
int64_t Offset1 = getTargetData().getIndexedOffset(GEPPointerTy, GEP1Ops);
|
|
int64_t Offset2 = getTargetData().getIndexedOffset(GEPPointerTy, GEP2Ops);
|
|
assert(Offset1 < Offset2 &&"There is at least one different constant here!");
|
|
|
|
if ((uint64_t)(Offset2-Offset1) >= SizeMax) {
|
|
//std::cerr << "Determined that these two GEP's don't alias ["
|
|
// << SizeMax << " bytes]: \n" << *GEP1 << *GEP2;
|
|
return NoAlias;
|
|
}
|
|
return MayAlias;
|
|
}
|
|
|