path: root/lib/Analysis/BasicAliasAnalysis.cpp

//===- BasicAliasAnalysis.cpp - Stateless Alias Analysis Impl -------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file defines the primary stateless implementation of the
// Alias Analysis interface that implements identities (two different
// globals cannot alias, etc), but does no stateful analysis.
//
//===----------------------------------------------------------------------===//

#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/Passes.h"
#include "llvm/Constants.h"
#include "llvm/DerivedTypes.h"
#include "llvm/Function.h"
#include "llvm/GlobalAlias.h"
#include "llvm/GlobalVariable.h"
#include "llvm/Instructions.h"
#include "llvm/IntrinsicInst.h"
#include "llvm/LLVMContext.h"
#include "llvm/Operator.h"
#include "llvm/Pass.h"
#include "llvm/Analysis/CaptureTracking.h"
#include "llvm/Analysis/MemoryBuiltins.h"
#include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/Target/TargetData.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/GetElementPtrTypeIterator.h"
#include <algorithm>
using namespace llvm;

//===----------------------------------------------------------------------===//
// Useful predicates
//===----------------------------------------------------------------------===//

/// isKnownNonNull - Return true if we know that the specified value is never
/// null.
static bool isKnownNonNull(const Value *V) {
  // Alloca never returns null, malloc might.
  if (isa<AllocaInst>(V)) return true;
  
  // A byval argument is never null.
  if (const Argument *A = dyn_cast<Argument>(V))
    return A->hasByValAttr();

  // Global values are not null unless extern weak.
  if (const GlobalValue *GV = dyn_cast<GlobalValue>(V))
    return !GV->hasExternalWeakLinkage();
  return false;
}

/// areAllUsesInOneFunction - Return true if all the uses of the given value
/// are in the same function. Note that this returns false if any of the uses
/// are from non-instruction values.
static bool areAllUsesInOneFunction(const Value *V) {
  const llvm::Function *Fn = 0;

  for (Value::const_use_iterator UI = V->use_begin(), E = V->use_end(); 
       UI != E; ++UI) {
    if (const Instruction *I = dyn_cast<Instruction>(*UI)) {
      if (!Fn) {
        Fn = I->getParent()->getParent();
        continue;
      } 
      
      if (Fn != I->getParent()->getParent())
        return false;
    } else
      return false;
  }

  return true;
}

/// isNonEscapingLocalObject - Return true if the pointer is to a function-local
/// object that never escapes from the function.
static bool isNonEscapingLocalObject(const Value *V) {
  // If this is a local allocation, check to see if it escapes.
  if (isa<AllocaInst>(V) || isNoAliasCall(V))
    // Set StoreCaptures to True so that we can assume in our callers that the
    // pointer is not the result of a load instruction. Currently
    // PointerMayBeCaptured doesn't have any special analysis for the
    // StoreCaptures=false case; if it did, our callers could be refined to be
    // more precise.
    return !PointerMayBeCaptured(V, false, /*StoreCaptures=*/true);

  // If this is an argument that corresponds to a byval or noalias argument,
  // then it has not escaped before entering the function.  Check if it escapes
  // inside the function.
  if (const Argument *A = dyn_cast<Argument