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argument to the outer function, this isn't correct. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@49731 91177308-0d34-0410-b5e6-96231b3b80d8
834 lines
33 KiB
C++
834 lines
33 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 is distributed under the University of Illinois Open Source
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// 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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//===----------------------------------------------------------------------===//
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#include "llvm/Analysis/AliasAnalysis.h"
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#include "llvm/Analysis/Passes.h"
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#include "llvm/Constants.h"
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#include "llvm/DerivedTypes.h"
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#include "llvm/Function.h"
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#include "llvm/ParameterAttributes.h"
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#include "llvm/GlobalVariable.h"
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#include "llvm/Instructions.h"
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#include "llvm/IntrinsicInst.h"
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#include "llvm/Pass.h"
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#include "llvm/Target/TargetData.h"
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#include "llvm/ADT/SmallVector.h"
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#include "llvm/ADT/STLExtras.h"
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#include "llvm/Support/Compiler.h"
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#include "llvm/Support/GetElementPtrTypeIterator.h"
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#include "llvm/Support/ManagedStatic.h"
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#include <algorithm>
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using namespace llvm;
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namespace {
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/// NoAA - This class implements the -no-aa pass, which always returns "I
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/// don't know" for alias queries. NoAA is unlike other alias analysis
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/// implementations, in that it does not chain to a previous analysis. As
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/// such it doesn't follow many of the rules that other alias analyses must.
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///
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struct VISIBILITY_HIDDEN NoAA : public ImmutablePass, public AliasAnalysis {
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static char ID; // Class identification, replacement for typeinfo
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NoAA() : ImmutablePass((intptr_t)&ID) {}
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explicit NoAA(intptr_t PID) : ImmutablePass(PID) { }
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virtual void getAnalysisUsage(AnalysisUsage &AU) const {
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AU.addRequired<TargetData>();
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}
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virtual void initializePass() {
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TD = &getAnalysis<TargetData>();
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}
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virtual AliasResult alias(const Value *V1, unsigned V1Size,
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const Value *V2, unsigned V2Size) {
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return MayAlias;
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}
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virtual ModRefBehavior getModRefBehavior(Function *F, CallSite CS,
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std::vector<PointerAccessInfo> *Info) {
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return UnknownModRefBehavior;
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}
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virtual void getArgumentAccesses(Function *F, CallSite CS,
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std::vector<PointerAccessInfo> &Info) {
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assert(0 && "This method may not be called on this function!");
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}
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virtual void getMustAliases(Value *P, std::vector<Value*> &RetVals) { }
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virtual bool pointsToConstantMemory(const Value *P) { return false; }
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virtual ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size) {
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return ModRef;
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}
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virtual ModRefResult getModRefInfo(CallSite CS1, CallSite CS2) {
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return ModRef;
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}
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virtual bool hasNoModRefInfoForCalls() const { return true; }
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virtual void deleteValue(Value *V) {}
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virtual void copyValue(Value *From, Value *To) {}
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};
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// Register this pass...
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char NoAA::ID = 0;
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RegisterPass<NoAA>
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U("no-aa", "No Alias Analysis (always returns 'may' alias)", true, true);
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// Declare that we implement the AliasAnalysis interface
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RegisterAnalysisGroup<AliasAnalysis> V(U);
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} // End of anonymous namespace
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ImmutablePass *llvm::createNoAAPass() { return new NoAA(); }
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namespace {
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/// BasicAliasAnalysis - This is the default alias analysis implementation.
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/// Because it doesn't chain to a previous alias analysis (like -no-aa), it
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/// derives from the NoAA class.
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struct VISIBILITY_HIDDEN BasicAliasAnalysis : public NoAA {
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static char ID; // Class identification, replacement for typeinfo
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BasicAliasAnalysis() : NoAA((intptr_t)&ID) { }
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AliasResult alias(const Value *V1, unsigned V1Size,
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const Value *V2, unsigned V2Size);
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ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size);
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ModRefResult getModRefInfo(CallSite CS1, CallSite CS2) {
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return NoAA::getModRefInfo(CS1,CS2);
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}
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/// hasNoModRefInfoForCalls - We can provide mod/ref information against
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/// non-escaping allocations.
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virtual bool hasNoModRefInfoForCalls() const { return false; }
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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,
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Value **GEP1Ops, unsigned NumGEP1Ops, unsigned G1Size,
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const Type *BasePtr2Ty,
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Value **GEP2Ops, unsigned NumGEP2Ops, unsigned G2Size);
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};
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// Register this pass...
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char BasicAliasAnalysis::ID = 0;
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RegisterPass<BasicAliasAnalysis>
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X("basicaa", "Basic Alias Analysis (default AA impl)", false, true);
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// Declare that we implement the AliasAnalysis interface
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RegisterAnalysisGroup<AliasAnalysis, true> Y(X);
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} // End of anonymous namespace
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ImmutablePass *llvm::createBasicAliasAnalysisPass() {
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return new BasicAliasAnalysis();
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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,
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/// a unique object or an argument, return it. This returns:
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/// Arguments, GlobalVariables, Functions, Allocas, Mallocs.
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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. GlobalValues and Allocations
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// have unique addresses.
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if (isa<GlobalValue>(V) || isa<AllocationInst>(V) || isa<Argument>(V))
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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<BitCastInst>(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::BitCast ||
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CE->getOpcode() == Instruction::GetElementPtr)
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return getUnderlyingObject(CE->getOperand(0));
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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,
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SmallVector<Value*, 16> &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]) || isa<GlobalValue>(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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// Determine if an AllocationInst instruction escapes from the function it is
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// contained in. If it does not escape, there is no way for another function to
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// mod/ref it. We do this by looking at its uses and determining if the uses
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// can escape (recursively).
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static bool AddressMightEscape(const Value *V) {
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for (Value::use_const_iterator UI = V->use_begin(), E = V->use_end();
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UI != E; ++UI) {
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const Instruction *I = cast<Instruction>(*UI);
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switch (I->getOpcode()) {
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case Instruction::Load:
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break; //next use.
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case Instruction::Store:
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if (I->getOperand(0) == V)
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return true; // Escapes if the pointer is stored.
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break; // next use.
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case Instruction::GetElementPtr:
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if (AddressMightEscape(I))
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return true;
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break; // next use.
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case Instruction::BitCast:
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if (AddressMightEscape(I))
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return true;
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break; // next use
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case Instruction::Ret:
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// If returned, the address will escape to calling functions, but no
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// callees could modify it.
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break; // next use
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case Instruction::Call:
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// If the call is to a few known safe intrinsics, we know that it does
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// not escape
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if (!isa<MemIntrinsic>(I))
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return true;
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break; // next use
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default:
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return true;
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}
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}
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return false;
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}
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// getModRefInfo - Check to see if the specified callsite can clobber the
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// specified memory object. Since we only look at local properties of this
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// function, we really can't say much about this query. We do, however, use
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// simple "address taken" analysis on local objects.
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//
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AliasAnalysis::ModRefResult
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BasicAliasAnalysis::getModRefInfo(CallSite CS, Value *P, unsigned Size) {
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if (!isa<Constant>(P)) {
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const Value *Object = getUnderlyingObject(P);
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// Allocations and byval arguments are "new" objects.
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if (Object &&
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(isa<AllocationInst>(Object) || isa<Argument>(Object))) {
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// Okay, the pointer is to a stack allocated (or effectively so, for
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// for noalias parameters) object. If the address of this object doesn't
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// escape from this function body to a callee, then we know that no
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// callees can mod/ref it unless they are actually passed it.
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if (isa<AllocationInst>(Object) ||
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cast<Argument>(Object)->hasByValAttr() ||
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cast<Argument>(Object)->hasNoAliasAttr())
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if (!AddressMightEscape(Object)) {
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bool passedAsArg = false;
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for (CallSite::arg_iterator CI = CS.arg_begin(), CE = CS.arg_end();
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CI != CE; ++CI)
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if (isa<PointerType>((*CI)->getType()) &&
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( getUnderlyingObject(*CI) == P ||
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alias(cast<Value>(CI), ~0UL, P, ~0UL) != NoAlias) )
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passedAsArg = true;
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if (!passedAsArg)
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return NoModRef;
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}
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// If this is a tail call and P points to a stack location, we know that
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// the tail call cannot access or modify the local stack.
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// We cannot exclude byval arguments here; these belong to the caller of
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// the current function not to the current function, and a tail callee
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// may reference them.
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if (isa<AllocaInst>(Object))
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if (CallInst *CI = dyn_cast<CallInst>(CS.getInstruction()))
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if (CI->isTailCall())
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return NoModRef;
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}
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}
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// The AliasAnalysis base class has some smarts, lets use them.
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return AliasAnalysis::getModRefInfo(CS, P, Size);
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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->isCast() && isa<PointerType>(CE->getOperand(0)->getType()))
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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->isCast() && isa<PointerType>(CE->getOperand(0)->getType()))
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V2 = CE->getOperand(0);
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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::Int64Ty && V2->getType() != Type::Int64Ty)
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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 BitCastInst *I = dyn_cast<BitCastInst>(V1))
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return alias(I->getOperand(0), V1Size, V2, V2Size);
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if (const BitCastInst *I = dyn_cast<BitCastInst>(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) {
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if (O2) {
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if (const Argument *O1Arg = dyn_cast<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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// If they are two different objects, and one is a noalias argument
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// then they do not alias.
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if (O1 != O2 && O1Arg->hasNoAliasAttr())
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return NoAlias;
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// Byval arguments can't alias globals or other arguments.
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if (O1 != O2 && O1Arg->hasByValAttr()) return NoAlias;
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// Otherwise, nothing is known...
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}
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if (const Argument *O2Arg = dyn_cast<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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// If they are two different objects, and one is a noalias argument
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// then they do not alias.
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if (O1 != O2 && O2Arg->hasNoAliasAttr())
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return NoAlias;
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// Byval arguments can't alias globals or other arguments.
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if (O1 != O2 && O2Arg->hasByValAttr()) return NoAlias;
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// Otherwise, nothing is known...
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} else if (O1 != O2 && !isa<Argument>(O1)) {
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// If they are two different objects, and neither is an argument,
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// we know that we have no alias.
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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
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// can't tell anything.
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}
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// Unique values don't alias null, except non-byval arguments.
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if (isa<ConstantPointerNull>(V2)) {
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if (const Argument *O1Arg = dyn_cast<Argument>(O1)) {
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if (O1Arg->hasByValAttr())
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return NoAlias;
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} else {
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return NoAlias;
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}
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}
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if (isa<GlobalVariable>(O1) ||
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(isa<AllocationInst>(O1) &&
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!cast<AllocationInst>(O1)->isArrayAllocation()))
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if (cast<PointerType>(O1->getType())->getElementType()->isSized()) {
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// If the size of the other access is larger than the total size of the
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// global/alloca/malloc, it cannot be accessing the global (it's
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// undefined to load or store bytes before or after an object).
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const Type *ElTy = cast<PointerType>(O1->getType())->getElementType();
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unsigned GlobalSize = getTargetData().getABITypeSize(ElTy);
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if (GlobalSize < V2Size && V2Size != ~0U)
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return NoAlias;
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}
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}
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if (O2) {
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if (!isa<Argument>(O2) && isa<ConstantPointerNull>(V1))
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return NoAlias; // Unique values don't alias null
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if (isa<GlobalVariable>(O2) ||
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(isa<AllocationInst>(O2) &&
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!cast<AllocationInst>(O2)->isArrayAllocation()))
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if (cast<PointerType>(O2->getType())->getElementType()->isSized()) {
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// If the size of the other access is larger than the total size of the
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// global/alloca/malloc, it cannot be accessing the object (it's
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// undefined to load or store bytes before or after an object).
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const Type *ElTy = cast<PointerType>(O2->getType())->getElementType();
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unsigned GlobalSize = getTargetData().getABITypeSize(ElTy);
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if (GlobalSize < V1Size && V1Size != ~0U)
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return NoAlias;
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}
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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 User *G = cast<User>(V1);
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while (isGEP(G->getOperand(0)) &&
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G->getOperand(1) ==
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Constant::getNullValue(G->getOperand(1)->getType()))
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G = cast<User>(G->getOperand(0));
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const Value *BasePtr1 = G->getOperand(0);
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G = cast<User>(V2);
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while (isGEP(G->getOperand(0)) &&
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G->getOperand(1) ==
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Constant::getNullValue(G->getOperand(1)->getType()))
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G = cast<User>(G->getOperand(0));
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const Value *BasePtr2 = G->getOperand(0);
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// Do the base pointers alias?
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AliasResult BaseAlias = alias(BasePtr1, ~0U, BasePtr2, ~0U);
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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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SmallVector<Value*, 16> GEP1Ops, GEP2Ops;
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BasePtr1 = GetGEPOperands(V1, GEP1Ops);
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BasePtr2 = GetGEPOperands(V2, GEP2Ops);
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// If GetGEPOperands were able to fold to the same must-aliased pointer,
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// do the comparison.
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if (BasePtr1 == BasePtr2) {
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AliasResult GAlias =
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CheckGEPInstructions(BasePtr1->getType(),
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&GEP1Ops[0], GEP1Ops.size(), V1Size,
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BasePtr2->getType(),
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&GEP2Ops[0], GEP2Ops.size(), 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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}
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// Check to see if these two pointers are related by a getelementptr
|
|
// instruction. If one pointer is a GEP with a non-zero index of the other
|
|
// pointer, we know they cannot alias.
|
|
//
|
|
if (isGEP(V2)) {
|
|
std::swap(V1, V2);
|
|
std::swap(V1Size, V2Size);
|
|
}
|
|
|
|
if (V1Size != ~0U && V2Size != ~0U)
|
|
if (isGEP(V1)) {
|
|
SmallVector<Value*, 16> GEPOperands;
|
|
const Value *BasePtr = GetGEPOperands(V1, GEPOperands);
|
|
|
|
AliasResult R = alias(BasePtr, V1Size, V2, V2Size);
|
|
if (R == MustAlias) {
|
|
// If there is at least one non-zero constant index, we know they cannot
|
|
// alias.
|
|
bool ConstantFound = false;
|
|
bool AllZerosFound = true;
|
|
for (unsigned i = 0, e = GEPOperands.size(); i != e; ++i)
|
|
if (const Constant *C = dyn_cast<Constant>(GEPOperands[i])) {
|
|
if (!C->isNullValue()) {
|
|
ConstantFound = true;
|
|
AllZerosFound = false;
|
|
break;
|
|
}
|
|
} else {
|
|
AllZerosFound = false;
|
|
}
|
|
|
|
// If we have getelementptr <ptr>, 0, 0, 0, 0, ... and V2 must aliases
|
|
// the ptr, the end result is a must alias also.
|
|
if (AllZerosFound)
|
|
return MustAlias;
|
|
|
|
if (ConstantFound) {
|
|
if (V2Size <= 1 && V1Size <= 1) // Just pointer check?
|
|
return NoAlias;
|
|
|
|
// Otherwise we have to check to see that the distance is more than
|
|
// the size of the argument... build an index vector that is equal to
|
|
// the arguments provided, except substitute 0's for any variable
|
|
// indexes we find...
|
|
if (cast<PointerType>(
|
|
BasePtr->getType())->getElementType()->isSized()) {
|
|
for (unsigned i = 0; i != GEPOperands.size(); ++i)
|
|
if (!isa<ConstantInt>(GEPOperands[i]))
|
|
GEPOperands[i] =
|
|
Constant::getNullValue(GEPOperands[i]->getType());
|
|
int64_t Offset =
|
|
getTargetData().getIndexedOffset(BasePtr->getType(),
|
|
&GEPOperands[0],
|
|
GEPOperands.size());
|
|
|
|
if (Offset >= (int64_t)V2Size || Offset <= -(int64_t)V1Size)
|
|
return NoAlias;
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
return MayAlias;
|
|
}
|
|
|
|
// This function is used to determin if the indices of two GEP instructions are
|
|
// equal. V1 and V2 are the indices.
|
|
static bool IndexOperandsEqual(Value *V1, Value *V2) {
|
|
if (V1->getType() == V2->getType())
|
|
return V1 == V2;
|
|
if (Constant *C1 = dyn_cast<Constant>(V1))
|
|
if (Constant *C2 = dyn_cast<Constant>(V2)) {
|
|
// Sign extend the constants to long types, if necessary
|
|
if (C1->getType() != Type::Int64Ty)
|
|
C1 = ConstantExpr::getSExt(C1, Type::Int64Ty);
|
|
if (C2->getType() != Type::Int64Ty)
|
|
C2 = ConstantExpr::getSExt(C2, Type::Int64Ty);
|
|
return C1 == C2;
|
|
}
|
|
return false;
|
|
}
|
|
|
|
/// CheckGEPInstructions - Check two GEP instructions with known must-aliasing
|
|
/// base pointers. This checks to see if the index expressions preclude the
|
|
/// pointers from aliasing...
|
|
AliasAnalysis::AliasResult
|
|
BasicAliasAnalysis::CheckGEPInstructions(
|
|
const Type* BasePtr1Ty, Value **GEP1Ops, unsigned NumGEP1Ops, unsigned G1S,
|
|
const Type *BasePtr2Ty, Value **GEP2Ops, unsigned NumGEP2Ops, unsigned G2S) {
|
|
// We currently can't handle the case when the base pointers have different
|
|
// primitive types. Since this is uncommon anyway, we are happy being
|
|
// extremely conservative.
|
|
if (BasePtr1Ty != BasePtr2Ty)
|
|
return MayAlias;
|
|
|
|
const PointerType *GEPPointerTy = cast<PointerType>(BasePtr1Ty);
|
|
|
|
// Find the (possibly empty) initial sequence of equal values... which are not
|
|
// necessarily constants.
|
|
unsigned NumGEP1Operands = NumGEP1Ops, NumGEP2Operands = NumGEP2Ops;
|
|
unsigned MinOperands = std::min(NumGEP1Operands, NumGEP2Operands);
|
|
unsigned MaxOperands = std::max(NumGEP1Operands, NumGEP2Operands);
|
|
unsigned UnequalOper = 0;
|
|
while (UnequalOper != MinOperands &&
|
|
IndexOperandsEqual(GEP1Ops[UnequalOper], GEP2Ops[UnequalOper])) {
|
|
// Advance through the type as we go...
|
|
++UnequalOper;
|
|
if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr1Ty))
|
|
BasePtr1Ty = CT->getTypeAtIndex(GEP1Ops[UnequalOper-1]);
|
|
else {
|
|
// If all operands equal each other, then the derived pointers must
|
|
// alias each other...
|
|
BasePtr1Ty = 0;
|
|
assert(UnequalOper == NumGEP1Operands && UnequalOper == NumGEP2Operands &&
|
|
"Ran out of type nesting, but not out of operands?");
|
|
return MustAlias;
|
|
}
|
|
}
|
|
|
|
// If we have seen all constant operands, and run out of indexes on one of the
|
|
// getelementptrs, check to see if the tail of the leftover one is all zeros.
|
|
// If so, return mustalias.
|
|
if (UnequalOper == MinOperands) {
|
|
if (NumGEP1Ops < NumGEP2Ops) {
|
|
std::swap(GEP1Ops, GEP2Ops);
|
|
std::swap(NumGEP1Ops, NumGEP2Ops);
|
|
}
|
|
|
|
bool AllAreZeros = true;
|
|
for (unsigned i = UnequalOper; i != MaxOperands; ++i)
|
|
if (!isa<Constant>(GEP1Ops[i]) ||
|
|
!cast<Constant>(GEP1Ops[i])->isNullValue()) {
|
|
AllAreZeros = false;
|
|
break;
|
|
}
|
|
if (AllAreZeros) return MustAlias;
|
|
}
|
|
|
|
|
|
// So now we know that the indexes derived from the base pointers,
|
|
// which are known to alias, are different. We can still determine a
|
|
// no-alias result if there are differing constant pairs in the index
|
|
// chain. For example:
|
|
// A[i][0] != A[j][1] iff (&A[0][1]-&A[0][0] >= std::max(G1S, G2S))
|
|
//
|
|
// We have to be careful here about array accesses. In particular, consider:
|
|
// A[1][0] vs A[0][i]
|
|
// In this case, we don't *know* that the array will be accessed in bounds:
|
|
// the index could even be negative. Because of this, we have to
|
|
// conservatively *give up* and return may alias. We disregard differing
|
|
// array subscripts that are followed by a variable index without going
|
|
// through a struct.
|
|
//
|
|
unsigned SizeMax = std::max(G1S, G2S);
|
|
if (SizeMax == ~0U) return MayAlias; // Avoid frivolous work.
|
|
|
|
// Scan for the first operand that is constant and unequal in the
|
|
// two getelementptrs...
|
|
unsigned FirstConstantOper = UnequalOper;
|
|
for (; FirstConstantOper != MinOperands; ++FirstConstantOper) {
|
|
const Value *G1Oper = GEP1Ops[FirstConstantOper];
|
|
const Value *G2Oper = GEP2Ops[FirstConstantOper];
|
|
|
|
if (G1Oper != G2Oper) // Found non-equal constant indexes...
|
|
if (Constant *G1OC = dyn_cast<ConstantInt>(const_cast<Value*>(G1Oper)))
|
|
if (Constant *G2OC = dyn_cast<ConstantInt>(const_cast<Value*>(G2Oper))){
|
|
if (G1OC->getType() != G2OC->getType()) {
|
|
// Sign extend both operands to long.
|
|
if (G1OC->getType() != Type::Int64Ty)
|
|
G1OC = ConstantExpr::getSExt(G1OC, Type::Int64Ty);
|
|
if (G2OC->getType() != Type::Int64Ty)
|
|
G2OC = ConstantExpr::getSExt(G2OC, Type::Int64Ty);
|
|
GEP1Ops[FirstConstantOper] = G1OC;
|
|
GEP2Ops[FirstConstantOper] = G2OC;
|
|
}
|
|
|
|
if (G1OC != G2OC) {
|
|
// Handle the "be careful" case above: if this is an array/vector
|
|
// subscript, scan for a subsequent variable array index.
|
|
if (isa<SequentialType>(BasePtr1Ty)) {
|
|
const Type *NextTy =
|
|
cast<SequentialType>(BasePtr1Ty)->getElementType();
|
|
bool isBadCase = false;
|
|
|
|
for (unsigned Idx = FirstConstantOper+1;
|
|
Idx != MinOperands && isa<SequentialType>(NextTy); ++Idx) {
|
|
const Value *V1 = GEP1Ops[Idx], *V2 = GEP2Ops[Idx];
|
|
if (!isa<Constant>(V1) || !isa<Constant>(V2)) {
|
|
isBadCase = true;
|
|
break;
|
|
}
|
|
NextTy = cast<SequentialType>(NextTy)->getElementType();
|
|
}
|
|
|
|
if (isBadCase) G1OC = 0;
|
|
}
|
|
|
|
// Make sure they are comparable (ie, not constant expressions), and
|
|
// make sure the GEP with the smaller leading constant is GEP1.
|
|
if (G1OC) {
|
|
Constant *Compare = ConstantExpr::getICmp(ICmpInst::ICMP_SGT,
|
|
G1OC, G2OC);
|
|
if (ConstantInt *CV = dyn_cast<ConstantInt>(Compare)) {
|
|
if (CV->getZExtValue()) { // If they are comparable and G2 > G1
|
|
std::swap(GEP1Ops, GEP2Ops); // Make GEP1 < GEP2
|
|
std::swap(NumGEP1Ops, NumGEP2Ops);
|
|
}
|
|
break;
|
|
}
|
|
}
|
|
}
|
|
}
|
|
BasePtr1Ty = cast<CompositeType>(BasePtr1Ty)->getTypeAtIndex(G1Oper);
|
|
}
|
|
|
|
// No shared constant operands, and we ran out of common operands. At this
|
|
// point, the GEP instructions have run through all of their operands, and we
|
|
// haven't found evidence that there are any deltas between the GEP's.
|
|
// However, one GEP may have more operands than the other. If this is the
|
|
// case, there may still be hope. Check this now.
|
|
if (FirstConstantOper == MinOperands) {
|
|
// Make GEP1Ops be the longer one if there is a longer one.
|
|
if (NumGEP1Ops < NumGEP2Ops) {
|
|
std::swap(GEP1Ops, GEP2Ops);
|
|
std::swap(NumGEP1Ops, NumGEP2Ops);
|
|
}
|
|
|
|
// Is there anything to check?
|
|
if (NumGEP1Ops > MinOperands) {
|
|
for (unsigned i = FirstConstantOper; i != MaxOperands; ++i)
|
|
if (isa<ConstantInt>(GEP1Ops[i]) &&
|
|
!cast<ConstantInt>(GEP1Ops[i])->isZero()) {
|
|
// Yup, there's a constant in the tail. Set all variables to
|
|
// constants in the GEP instruction to make it suiteable for
|
|
// TargetData::getIndexedOffset.
|
|
for (i = 0; i != MaxOperands; ++i)
|
|
if (!isa<ConstantInt>(GEP1Ops[i]))
|
|
GEP1Ops[i] = Constant::getNullValue(GEP1Ops[i]->getType());
|
|
// Okay, now get the offset. This is the relative offset for the full
|
|
// instruction.
|
|
const TargetData &TD = getTargetData();
|
|
int64_t Offset1 = TD.getIndexedOffset(GEPPointerTy, GEP1Ops,
|
|
NumGEP1Ops);
|
|
|
|
// Now check without any constants at the end.
|
|
int64_t Offset2 = TD.getIndexedOffset(GEPPointerTy, GEP1Ops,
|
|
MinOperands);
|
|
|
|
// If the tail provided a bit enough offset, return noalias!
|
|
if ((uint64_t)(Offset2-Offset1) >= SizeMax)
|
|
return NoAlias;
|
|
}
|
|
}
|
|
|
|
// Couldn't find anything useful.
|
|
return MayAlias;
|
|
}
|
|
|
|
// If there are non-equal constants arguments, then we can figure
|
|
// out a minimum known delta between the two index expressions... at
|
|
// this point we know that the first constant index of GEP1 is less
|
|
// than the first constant index of GEP2.
|
|
|
|
// Advance BasePtr[12]Ty over this first differing constant operand.
|
|
BasePtr2Ty = cast<CompositeType>(BasePtr1Ty)->
|
|
getTypeAtIndex(GEP2Ops[FirstConstantOper]);
|
|
BasePtr1Ty = cast<CompositeType>(BasePtr1Ty)->
|
|
getTypeAtIndex(GEP1Ops[FirstConstantOper]);
|
|
|
|
// We are going to be using TargetData::getIndexedOffset to determine the
|
|
// offset that each of the GEP's is reaching. To do this, we have to convert
|
|
// all variable references to constant references. To do this, we convert the
|
|
// initial sequence of array subscripts into constant zeros to start with.
|
|
const Type *ZeroIdxTy = GEPPointerTy;
|
|
for (unsigned i = 0; i != FirstConstantOper; ++i) {
|
|
if (!isa<StructType>(ZeroIdxTy))
|
|
GEP1Ops[i] = GEP2Ops[i] = Constant::getNullValue(Type::Int32Ty);
|
|
|
|
if (const CompositeType *CT = dyn_cast<CompositeType>(ZeroIdxTy))
|
|
ZeroIdxTy = CT->getTypeAtIndex(GEP1Ops[i]);
|
|
}
|
|
|
|
// We know that GEP1Ops[FirstConstantOper] & GEP2Ops[FirstConstantOper] are ok
|
|
|
|
// Loop over the rest of the operands...
|
|
for (unsigned i = FirstConstantOper+1; i != MaxOperands; ++i) {
|
|
const Value *Op1 = i < NumGEP1Ops ? GEP1Ops[i] : 0;
|
|
const Value *Op2 = i < NumGEP2Ops ? GEP2Ops[i] : 0;
|
|
// If they are equal, use a zero index...
|
|
if (Op1 == Op2 && BasePtr1Ty == BasePtr2Ty) {
|
|
if (!isa<ConstantInt>(Op1))
|
|
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->getZExtValue() >= AT->getNumElements())
|
|
return MayAlias; // Be conservative with out-of-range accesses
|
|
} else if (const VectorType *VT = dyn_cast<VectorType>(BasePtr1Ty)) {
|
|
if (Op1C->getZExtValue() >= VT->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] = ConstantInt::get(Type::Int64Ty,AT->getNumElements()-1);
|
|
else if (const VectorType *VT = dyn_cast<VectorType>(BasePtr1Ty))
|
|
GEP1Ops[i] = ConstantInt::get(Type::Int64Ty,VT->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>(BasePtr2Ty)) {
|
|
if (Op2C->getZExtValue() >= AT->getNumElements())
|
|
return MayAlias; // Be conservative with out-of-range accesses
|
|
} else if (const VectorType *VT = dyn_cast<VectorType>(BasePtr2Ty)) {
|
|
if (Op2C->getZExtValue() >= VT->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;
|
|
}
|
|
}
|
|
|
|
if (GEPPointerTy->getElementType()->isSized()) {
|
|
int64_t Offset1 =
|
|
getTargetData().getIndexedOffset(GEPPointerTy, GEP1Ops, NumGEP1Ops);
|
|
int64_t Offset2 =
|
|
getTargetData().getIndexedOffset(GEPPointerTy, GEP2Ops, NumGEP2Ops);
|
|
assert(Offset1 != Offset2 &&
|
|
"There is at least one different constant here!");
|
|
|
|
// Make sure we compare the absolute difference.
|
|
if (Offset1 > Offset2)
|
|
std::swap(Offset1, Offset2);
|
|
|
|
if ((uint64_t)(Offset2-Offset1) >= SizeMax) {
|
|
//cerr << "Determined that these two GEP's don't alias ["
|
|
// << SizeMax << " bytes]: \n" << *GEP1 << *GEP2;
|
|
return NoAlias;
|
|
}
|
|
}
|
|
return MayAlias;
|
|
}
|
|
|
|
// Make sure that anything that uses AliasAnalysis pulls in this file...
|
|
DEFINING_FILE_FOR(BasicAliasAnalysis)
|