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llvm-mirror/lib/Analysis/LazyValueInfo.cpp
Dan Gohman 6968f40e37 Move isKnownNonNull out of AliasAnalysis.h and into ValueTracking.cpp since 
it isn't really an AliasAnalysis concept, and ValueTracking has similar things
that it could plausibly share code with some day.

llvm-svn: 174027
2013-01-31 02:40:59 +00:00

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//===- LazyValueInfo.cpp - Value constraint analysis ----------------------===//
//
// 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 interface for lazy computation of value constraint
// information.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "lazy-value-info"
#include "llvm/Analysis/LazyValueInfo.h"
#include "llvm/ADT/DenseSet.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/Analysis/ConstantFolding.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/Support/CFG.h"
#include "llvm/Support/ConstantRange.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/PatternMatch.h"
#include "llvm/Support/ValueHandle.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Target/TargetLibraryInfo.h"
#include <map>
#include <stack>
using namespace llvm;
using namespace PatternMatch;
char LazyValueInfo::ID = 0;
INITIALIZE_PASS_BEGIN(LazyValueInfo, "lazy-value-info",
"Lazy Value Information Analysis", false, true)
INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfo)
INITIALIZE_PASS_END(LazyValueInfo, "lazy-value-info",
"Lazy Value Information Analysis", false, true)
namespace llvm {
FunctionPass *createLazyValueInfoPass() { return new LazyValueInfo(); }
}
//===----------------------------------------------------------------------===//
// LVILatticeVal
//===----------------------------------------------------------------------===//
/// LVILatticeVal - This is the information tracked by LazyValueInfo for each
/// value.
///
/// FIXME: This is basically just for bringup, this can be made a lot more rich
/// in the future.
///
namespace {
class LVILatticeVal {
enum LatticeValueTy {
/// undefined - This Value has no known value yet.
undefined,
/// constant - This Value has a specific constant value.
constant,
/// notconstant - This Value is known to not have the specified value.
notconstant,
/// constantrange - The Value falls within this range.
constantrange,
/// overdefined - This value is not known to be constant, and we know that
/// it has a value.
overdefined
};
/// Val: This stores the current lattice value along with the Constant* for
/// the constant if this is a 'constant' or 'notconstant' value.
LatticeValueTy Tag;
Constant *Val;
ConstantRange Range;
public:
LVILatticeVal() : Tag(undefined), Val(0), Range(1, true) {}
static LVILatticeVal get(Constant *C) {
LVILatticeVal Res;
if (!isa<UndefValue>(C))
Res.markConstant(C);
return Res;
}
static LVILatticeVal getNot(Constant *C) {
LVILatticeVal Res;
if (!isa<UndefValue>(C))
Res.markNotConstant(C);
return Res;
}
static LVILatticeVal getRange(ConstantRange CR) {
LVILatticeVal Res;
Res.markConstantRange(CR);
return Res;
}
bool isUndefined() const { return Tag == undefined; }
bool isConstant() const { return Tag == constant; }
bool isNotConstant() const { return Tag == notconstant; }
bool isConstantRange() const { return Tag == constantrange; }
bool isOverdefined() const { return Tag == overdefined; }
Constant *getConstant() const {
assert(isConstant() && "Cannot get the constant of a non-constant!");
return Val;
}
Constant *getNotConstant() const {
assert(isNotConstant() && "Cannot get the constant of a non-notconstant!");
return Val;
}
ConstantRange getConstantRange() const {
assert(isConstantRange() &&
"Cannot get the constant-range of a non-constant-range!");
return Range;
}
/// markOverdefined - Return true if this is a change in status.
bool markOverdefined() {
if (isOverdefined())
return false;
Tag = overdefined;
return true;
}
/// markConstant - Return true if this is a change in status.
bool markConstant(Constant *V) {
assert(V && "Marking constant with NULL");
if (ConstantInt *CI = dyn_cast<ConstantInt>(V))
return markConstantRange(ConstantRange(CI->getValue()));
if (isa<UndefValue>(V))
return false;
assert((!isConstant() || getConstant() == V) &&
"Marking constant with different value");
assert(isUndefined());
Tag = constant;
Val = V;
return true;
}
/// markNotConstant - Return true if this is a change in status.
bool markNotConstant(Constant *V) {
assert(V && "Marking constant with NULL");
if (ConstantInt *CI = dyn_cast<ConstantInt>(V))
return markConstantRange(ConstantRange(CI->getValue()+1, CI->getValue()));
if (isa<UndefValue>(V))
return false;
assert((!isConstant() || getConstant() != V) &&
"Marking constant !constant with same value");
assert((!isNotConstant() || getNotConstant() == V) &&
"Marking !constant with different value");
assert(isUndefined() || isConstant());
Tag = notconstant;
Val = V;
return true;
}
/// markConstantRange - Return true if this is a change in status.
bool markConstantRange(const ConstantRange NewR) {
if (isConstantRange()) {
if (NewR.isEmptySet())
return markOverdefined();
bool changed = Range != NewR;
Range = NewR;
return changed;
}
assert(isUndefined());
if (NewR.isEmptySet())
return markOverdefined();
Tag = constantrange;
Range = NewR;
return true;
}
/// mergeIn - Merge the specified lattice value into this one, updating this
/// one and returning true if anything changed.
bool mergeIn(const LVILatticeVal &RHS) {
if (RHS.isUndefined() || isOverdefined()) return false;
if (RHS.isOverdefined()) return markOverdefined();
if (isUndefined()) {
Tag = RHS.Tag;
Val = RHS.Val;
Range = RHS.Range;
return true;
}
if (isConstant()) {
if (RHS.isConstant()) {
if (Val == RHS.Val)
return false;
return markOverdefined();
}
if (RHS.isNotConstant()) {
if (Val == RHS.Val)
return markOverdefined();
// Unless we can prove that the two Constants are different, we must
// move to overdefined.
// FIXME: use DataLayout/TargetLibraryInfo for smarter constant folding.
if (ConstantInt *Res = dyn_cast<ConstantInt>(
ConstantFoldCompareInstOperands(CmpInst::ICMP_NE,
getConstant(),
RHS.getNotConstant())))
if (Res->isOne())
return markNotConstant(RHS.getNotConstant());
return markOverdefined();
}
// RHS is a ConstantRange, LHS is a non-integer Constant.
// FIXME: consider the case where RHS is a range [1, 0) and LHS is
// a function. The correct result is to pick up RHS.
return markOverdefined();
}
if (isNotConstant()) {
if (RHS.isConstant()) {
if (Val == RHS.Val)
return markOverdefined();
// Unless we can prove that the two Constants are different, we must
// move to overdefined.
// FIXME: use DataLayout/TargetLibraryInfo for smarter constant folding.
if (ConstantInt *Res = dyn_cast<ConstantInt>(
ConstantFoldCompareInstOperands(CmpInst::ICMP_NE,
getNotConstant(),
RHS.getConstant())))
if (Res->isOne())
return false;
return markOverdefined();
}
if (RHS.isNotConstant()) {
if (Val == RHS.Val)
return false;
return markOverdefined();
}
return markOverdefined();
}
assert(isConstantRange() && "New LVILattice type?");
if (!RHS.isConstantRange())
return markOverdefined();
ConstantRange NewR = Range.unionWith(RHS.getConstantRange());
if (NewR.isFullSet())
return markOverdefined();
return markConstantRange(NewR);
}
};
} // end anonymous namespace.
namespace llvm {
raw_ostream &operator<<(raw_ostream &OS, const LVILatticeVal &Val)
LLVM_ATTRIBUTE_USED;
raw_ostream &operator<<(raw_ostream &OS, const LVILatticeVal &Val) {
if (Val.isUndefined())
return OS << "undefined";
if (Val.isOverdefined())
return OS << "overdefined";
if (Val.isNotConstant())
return OS << "notconstant<" << *Val.getNotConstant() << '>';
else if (Val.isConstantRange())
return OS << "constantrange<" << Val.getConstantRange().getLower() << ", "
<< Val.getConstantRange().getUpper() << '>';
return OS << "constant<" << *Val.getConstant() << '>';
}
}
//===----------------------------------------------------------------------===//
// LazyValueInfoCache Decl
//===----------------------------------------------------------------------===//
namespace {
/// LVIValueHandle - A callback value handle updates the cache when
/// values are erased.
class LazyValueInfoCache;
struct LVIValueHandle : public CallbackVH {
LazyValueInfoCache *Parent;
LVIValueHandle(Value *V, LazyValueInfoCache *P)
: CallbackVH(V), Parent(P) { }
void deleted();
void allUsesReplacedWith(Value *V) {
deleted();
}
};
}
namespace {
/// LazyValueInfoCache - This is the cache kept by LazyValueInfo which
/// maintains information about queries across the clients' queries.
class LazyValueInfoCache {
/// ValueCacheEntryTy - This is all of the cached block information for
/// exactly one Value*. The entries are sorted by the BasicBlock* of the
/// entries, allowing us to do a lookup with a binary search.
typedef std::map<AssertingVH<BasicBlock>, LVILatticeVal> ValueCacheEntryTy;
/// ValueCache - This is all of the cached information for all values,
/// mapped from Value* to key information.
std::map<LVIValueHandle, ValueCacheEntryTy> ValueCache;
/// OverDefinedCache - This tracks, on a per-block basis, the set of
/// values that are over-defined at the end of that block. This is required
/// for cache updating.
typedef std::pair<AssertingVH<BasicBlock>, Value*> OverDefinedPairTy;
DenseSet<OverDefinedPairTy> OverDefinedCache;
/// SeenBlocks - Keep track of all blocks that we have ever seen, so we
/// don't spend time removing unused blocks from our caches.
DenseSet<AssertingVH<BasicBlock> > SeenBlocks;
/// BlockValueStack - This stack holds the state of the value solver
/// during a query. It basically emulates the callstack of the naive
/// recursive value lookup process.
std::stack<std::pair<BasicBlock*, Value*> > BlockValueStack;
friend struct LVIValueHandle;
/// OverDefinedCacheUpdater - A helper object that ensures that the
/// OverDefinedCache is updated whenever solveBlockValue returns.
struct OverDefinedCacheUpdater {
LazyValueInfoCache *Parent;
Value *Val;
BasicBlock *BB;
LVILatticeVal &BBLV;
OverDefinedCacheUpdater(Value *V, BasicBlock *B, LVILatticeVal &LV,
LazyValueInfoCache *P)
: Parent(P), Val(V), BB(B), BBLV(LV) { }
bool markResult(bool changed) {
if (changed && BBLV.isOverdefined())
Parent->OverDefinedCache.insert(std::make_pair(BB, Val));
return changed;
}
};
LVILatticeVal getBlockValue(Value *Val, BasicBlock *BB);
bool getEdgeValue(Value *V, BasicBlock *F, BasicBlock *T,
LVILatticeVal &Result);
bool hasBlockValue(Value *Val, BasicBlock *BB);
// These methods process one work item and may add more. A false value
// returned means that the work item was not completely processed and must
// be revisited after going through the new items.
bool solveBlockValue(Value *Val, BasicBlock *BB);
bool solveBlockValueNonLocal(LVILatticeVal &BBLV,
Value *Val, BasicBlock *BB);
bool solveBlockValuePHINode(LVILatticeVal &BBLV,
PHINode *PN, BasicBlock *BB);
bool solveBlockValueConstantRange(LVILatticeVal &BBLV,
Instruction *BBI, BasicBlock *BB);
void solve();
ValueCacheEntryTy &lookup(Value *V) {
return ValueCache[LVIValueHandle(V, this)];
}
public:
/// getValueInBlock - This is the query interface to determine the lattice
/// value for the specified Value* at the end of the specified block.
LVILatticeVal getValueInBlock(Value *V, BasicBlock *BB);
/// getValueOnEdge - This is the query interface to determine the lattice
/// value for the specified Value* that is true on the specified edge.
LVILatticeVal getValueOnEdge(Value *V, BasicBlock *FromBB,BasicBlock *ToBB);
/// threadEdge - This is the update interface to inform the cache that an
/// edge from PredBB to OldSucc has been threaded to be from PredBB to
/// NewSucc.
void threadEdge(BasicBlock *PredBB,BasicBlock *OldSucc,BasicBlock *NewSucc);
/// eraseBlock - This is part of the update interface to inform the cache
/// that a block has been deleted.
void eraseBlock(BasicBlock *BB);
/// clear - Empty the cache.
void clear() {
SeenBlocks.clear();
ValueCache.clear();
OverDefinedCache.clear();
}
};
} // end anonymous namespace
void LVIValueHandle::deleted() {
typedef std::pair<AssertingVH<BasicBlock>, Value*> OverDefinedPairTy;
SmallVector<OverDefinedPairTy, 4> ToErase;
for (DenseSet<OverDefinedPairTy>::iterator
I = Parent->OverDefinedCache.begin(),
E = Parent->OverDefinedCache.end();
I != E; ++I) {
if (I->second == getValPtr())
ToErase.push_back(*I);
}
for (SmallVector<OverDefinedPairTy, 4>::iterator I = ToErase.begin(),
E = ToErase.end(); I != E; ++I)
Parent->OverDefinedCache.erase(*I);
// This erasure deallocates *this, so it MUST happen after we're done
// using any and all members of *this.
Parent->ValueCache.erase(*this);
}
void LazyValueInfoCache::eraseBlock(BasicBlock *BB) {
// Shortcut if we have never seen this block.
DenseSet<AssertingVH<BasicBlock> >::iterator I = SeenBlocks.find(BB);
if (I == SeenBlocks.end())
return;
SeenBlocks.erase(I);
SmallVector<OverDefinedPairTy, 4> ToErase;
for (DenseSet<OverDefinedPairTy>::iterator I = OverDefinedCache.begin(),
E = OverDefinedCache.end(); I != E; ++I) {
if (I->first == BB)
ToErase.push_back(*I);
}
for (SmallVector<OverDefinedPairTy, 4>::iterator I = ToErase.begin(),
E = ToErase.end(); I != E; ++I)
OverDefinedCache.erase(*I);
for (std::map<LVIValueHandle, ValueCacheEntryTy>::iterator
I = ValueCache.begin(), E = ValueCache.end(); I != E; ++I)
I->second.erase(BB);
}
void LazyValueInfoCache::solve() {
while (!BlockValueStack.empty()) {
std::pair<BasicBlock*, Value*> &e = BlockValueStack.top();
if (solveBlockValue(e.second, e.first)) {
assert(BlockValueStack.top() == e);
BlockValueStack.pop();
}
}
}
bool LazyValueInfoCache::hasBlockValue(Value *Val, BasicBlock *BB) {
// If already a constant, there is nothing to compute.
if (isa<Constant>(Val))
return true;
LVIValueHandle ValHandle(Val, this);
std::map<LVIValueHandle, ValueCacheEntryTy>::iterator I =
ValueCache.find(ValHandle);
if (I == ValueCache.end()) return false;
return I->second.count(BB);
}
LVILatticeVal LazyValueInfoCache::getBlockValue(Value *Val, BasicBlock *BB) {
// If already a constant, there is nothing to compute.
if (Constant *VC = dyn_cast<Constant>(Val))
return LVILatticeVal::get(VC);
SeenBlocks.insert(BB);
return lookup(Val)[BB];
}
bool LazyValueInfoCache::solveBlockValue(Value *Val, BasicBlock *BB) {
if (isa<Constant>(Val))
return true;
ValueCacheEntryTy &Cache = lookup(Val);
SeenBlocks.insert(BB);
LVILatticeVal &BBLV = Cache[BB];
// OverDefinedCacheUpdater is a helper object that will update
// the OverDefinedCache for us when this method exits. Make sure to
// call markResult on it as we exist, passing a bool to indicate if the
// cache needs updating, i.e. if we have solve a new value or not.
OverDefinedCacheUpdater ODCacheUpdater(Val, BB, BBLV, this);
// If we've already computed this block's value, return it.
if (!BBLV.isUndefined()) {
DEBUG(dbgs() << " reuse BB '" << BB->getName() << "' val=" << BBLV <<'\n');
// Since we're reusing a cached value here, we don't need to update the
// OverDefinedCahce. The cache will have been properly updated
// whenever the cached value was inserted.
ODCacheUpdater.markResult(false);
return true;
}
// Otherwise, this is the first time we're seeing this block. Reset the
// lattice value to overdefined, so that cycles will terminate and be
// conservatively correct.
BBLV.markOverdefined();
Instruction *BBI = dyn_cast<Instruction>(Val);
if (BBI == 0 || BBI->getParent() != BB) {
return ODCacheUpdater.markResult(solveBlockValueNonLocal(BBLV, Val, BB));
}
if (PHINode *PN = dyn_cast<PHINode>(BBI)) {
return ODCacheUpdater.markResult(solveBlockValuePHINode(BBLV, PN, BB));
}
if (AllocaInst *AI = dyn_cast<AllocaInst>(BBI)) {
BBLV = LVILatticeVal::getNot(ConstantPointerNull::get(AI->getType()));
return ODCacheUpdater.markResult(true);
}
// We can only analyze the definitions of certain classes of instructions
// (integral binops and casts at the moment), so bail if this isn't one.
LVILatticeVal Result;
if ((!isa<BinaryOperator>(BBI) && !isa<CastInst>(BBI)) ||
!BBI->getType()->isIntegerTy()) {
DEBUG(dbgs() << " compute BB '" << BB->getName()
<< "' - overdefined because inst def found.\n");
BBLV.markOverdefined();
return ODCacheUpdater.markResult(true);
}
// FIXME: We're currently limited to binops with a constant RHS. This should
// be improved.
BinaryOperator *BO = dyn_cast<BinaryOperator>(BBI);
if (BO && !isa<ConstantInt>(BO->getOperand(1))) {
DEBUG(dbgs() << " compute BB '" << BB->getName()
<< "' - overdefined because inst def found.\n");
BBLV.markOverdefined();
return ODCacheUpdater.markResult(true);
}
return ODCacheUpdater.markResult(solveBlockValueConstantRange(BBLV, BBI, BB));
}
static bool InstructionDereferencesPointer(Instruction *I, Value *Ptr) {
if (LoadInst *L = dyn_cast<LoadInst>(I)) {
return L->getPointerAddressSpace() == 0 &&
GetUnderlyingObject(L->getPointerOperand()) == Ptr;
}
if (StoreInst *S = dyn_cast<StoreInst>(I)) {
return S->getPointerAddressSpace() == 0 &&
GetUnderlyingObject(S->getPointerOperand()) == Ptr;
}
if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(I)) {
if (MI->isVolatile()) return false;
// FIXME: check whether it has a valuerange that excludes zero?
ConstantInt *Len = dyn_cast<ConstantInt>(MI->getLength());
if (!Len || Len->isZero()) return false;
if (MI->getDestAddressSpace() == 0)
if (GetUnderlyingObject(MI->getRawDest()) == Ptr)
return true;
if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(MI))
if (MTI->getSourceAddressSpace() == 0)
if (GetUnderlyingObject(MTI->getRawSource()) == Ptr)
return true;
}
return false;
}
bool LazyValueInfoCache::solveBlockValueNonLocal(LVILatticeVal &BBLV,
Value *Val, BasicBlock *BB) {
LVILatticeVal Result; // Start Undefined.
// If this is a pointer, and there's a load from that pointer in this BB,
// then we know that the pointer can't be NULL.
bool NotNull = false;
if (Val->getType()->isPointerTy()) {
if (isKnownNonNull(Val)) {
NotNull = true;
} else {
Value *UnderlyingVal = GetUnderlyingObject(Val);
// If 'GetUnderlyingObject' didn't converge, skip it. It won't converge
// inside InstructionDereferencesPointer either.
if (UnderlyingVal == GetUnderlyingObject(UnderlyingVal, NULL, 1)) {
for (BasicBlock::iterator BI = BB->begin(), BE = BB->end();
BI != BE; ++BI) {
if (InstructionDereferencesPointer(BI, UnderlyingVal)) {
NotNull = true;
break;
}
}
}
}
}
// If this is the entry block, we must be asking about an argument. The
// value is overdefined.
if (BB == &BB->getParent()->getEntryBlock()) {
assert(isa<Argument>(Val) && "Unknown live-in to the entry block");
if (NotNull) {
PointerType *PTy = cast<PointerType>(Val->getType());
Result = LVILatticeVal::getNot(ConstantPointerNull::get(PTy));
} else {
Result.markOverdefined();
}
BBLV = Result;
return true;
}
// Loop over all of our predecessors, merging what we know from them into
// result.
bool EdgesMissing = false;
for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
LVILatticeVal EdgeResult;
EdgesMissing |= !getEdgeValue(Val, *PI, BB, EdgeResult);
if (EdgesMissing)
continue;
Result.mergeIn(EdgeResult);
// If we hit overdefined, exit early. The BlockVals entry is already set
// to overdefined.
if (Result.isOverdefined()) {
DEBUG(dbgs() << " compute BB '" << BB->getName()
<< "' - overdefined because of pred.\n");
// If we previously determined that this is a pointer that can't be null
// then return that rather than giving up entirely.
if (NotNull) {
PointerType *PTy = cast<PointerType>(Val->getType());
Result = LVILatticeVal::getNot(ConstantPointerNull::get(PTy));
}
BBLV = Result;
return true;
}
}
if (EdgesMissing)
return false;
// Return the merged value, which is more precise than 'overdefined'.
assert(!Result.isOverdefined());
BBLV = Result;
return true;
}
bool LazyValueInfoCache::solveBlockValuePHINode(LVILatticeVal &BBLV,
PHINode *PN, BasicBlock *BB) {
LVILatticeVal Result; // Start Undefined.
// Loop over all of our predecessors, merging what we know from them into
// result.
bool EdgesMissing = false;
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
BasicBlock *PhiBB = PN->getIncomingBlock(i);
Value *PhiVal = PN->getIncomingValue(i);
LVILatticeVal EdgeResult;
EdgesMissing |= !getEdgeValue(PhiVal, PhiBB, BB, EdgeResult);
if (EdgesMissing)
continue;
Result.mergeIn(EdgeResult);
// If we hit overdefined, exit early. The BlockVals entry is already set
// to overdefined.
if (Result.isOverdefined()) {
DEBUG(dbgs() << " compute BB '" << BB->getName()
<< "' - overdefined because of pred.\n");
BBLV = Result;
return true;
}
}
if (EdgesMissing)
return false;
// Return the merged value, which is more precise than 'overdefined'.
assert(!Result.isOverdefined() && "Possible PHI in entry block?");
BBLV = Result;
return true;
}
bool LazyValueInfoCache::solveBlockValueConstantRange(LVILatticeVal &BBLV,
Instruction *BBI,
BasicBlock *BB) {
// Figure out the range of the LHS. If that fails, bail.
if (!hasBlockValue(BBI->getOperand(0), BB)) {
BlockValueStack.push(std::make_pair(BB, BBI->getOperand(0)));
return false;
}
LVILatticeVal LHSVal = getBlockValue(BBI->getOperand(0), BB);
if (!LHSVal.isConstantRange()) {
BBLV.markOverdefined();
return true;
}
ConstantRange LHSRange = LHSVal.getConstantRange();
ConstantRange RHSRange(1);
IntegerType *ResultTy = cast<IntegerType>(BBI->getType());
if (isa<BinaryOperator>(BBI)) {
if (ConstantInt *RHS = dyn_cast<ConstantInt>(BBI->getOperand(1))) {
RHSRange = ConstantRange(RHS->getValue());
} else {
BBLV.markOverdefined();
return true;
}
}
// NOTE: We're currently limited by the set of operations that ConstantRange
// can evaluate symbolically. Enhancing that set will allows us to analyze
// more definitions.
LVILatticeVal Result;
switch (BBI->getOpcode()) {
case Instruction::Add:
Result.markConstantRange(LHSRange.add(RHSRange));
break;
case Instruction::Sub:
Result.markConstantRange(LHSRange.sub(RHSRange));
break;
case Instruction::Mul:
Result.markConstantRange(LHSRange.multiply(RHSRange));
break;
case Instruction::UDiv:
Result.markConstantRange(LHSRange.udiv(RHSRange));
break;
case Instruction::Shl:
Result.markConstantRange(LHSRange.shl(RHSRange));
break;
case Instruction::LShr:
Result.markConstantRange(LHSRange.lshr(RHSRange));
break;
case Instruction::Trunc:
Result.markConstantRange(LHSRange.truncate(ResultTy->getBitWidth()));
break;
case Instruction::SExt:
Result.markConstantRange(LHSRange.signExtend(ResultTy->getBitWidth()));
break;
case Instruction::ZExt:
Result.markConstantRange(LHSRange.zeroExtend(ResultTy->getBitWidth()));
break;
case Instruction::BitCast:
Result.markConstantRange(LHSRange);
break;
case Instruction::And:
Result.markConstantRange(LHSRange.binaryAnd(RHSRange));
break;
case Instruction::Or:
Result.markConstantRange(LHSRange.binaryOr(RHSRange));
break;
// Unhandled instructions are overdefined.
default:
DEBUG(dbgs() << " compute BB '" << BB->getName()
<< "' - overdefined because inst def found.\n");
Result.markOverdefined();
break;
}
BBLV = Result;
return true;
}
/// \brief Compute the value of Val on the edge BBFrom -> BBTo. Returns false if
/// Val is not constrained on the edge.
static bool getEdgeValueLocal(Value *Val, BasicBlock *BBFrom,
BasicBlock *BBTo, LVILatticeVal &Result) {
// TODO: Handle more complex conditionals. If (v == 0 || v2 < 1) is false, we
// know that v != 0.
if (BranchInst *BI = dyn_cast<BranchInst>(BBFrom->getTerminator())) {
// If this is a conditional branch and only one successor goes to BBTo, then
// we maybe able to infer something from the condition.
if (BI->isConditional() &&
BI->getSuccessor(0) != BI->getSuccessor(1)) {
bool isTrueDest = BI->getSuccessor(0) == BBTo;
assert(BI->getSuccessor(!isTrueDest) == BBTo &&
"BBTo isn't a successor of BBFrom");
// If V is the condition of the branch itself, then we know exactly what
// it is.
if (BI->getCondition() == Val) {
Result = LVILatticeVal::get(ConstantInt::get(
Type::getInt1Ty(Val->getContext()), isTrueDest));
return true;
}
// If the condition of the branch is an equality comparison, we may be
// able to infer the value.
ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition());
if (ICI && isa<Constant>(ICI->getOperand(1))) {
if (ICI->isEquality() && ICI->getOperand(0) == Val) {
// We know that V has the RHS constant if this is a true SETEQ or
// false SETNE.
if (isTrueDest == (ICI->getPredicate() == ICmpInst::ICMP_EQ))
Result = LVILatticeVal::get(cast<Constant>(ICI->getOperand(1)));
else
Result = LVILatticeVal::getNot(cast<Constant>(ICI->getOperand(1)));
return true;
}
// Recognize the range checking idiom that InstCombine produces.
// (X-C1) u< C2 --> [C1, C1+C2)
ConstantInt *NegOffset = 0;
if (ICI->getPredicate() == ICmpInst::ICMP_ULT)
match(ICI->getOperand(0), m_Add(m_Specific(Val),
m_ConstantInt(NegOffset)));
ConstantInt *CI = dyn_cast<ConstantInt>(ICI->getOperand(1));
if (CI && (ICI->getOperand(0) == Val || NegOffset)) {
// Calculate the range of values that would satisfy the comparison.
ConstantRange CmpRange(CI->getValue());
ConstantRange TrueValues =
ConstantRange::makeICmpRegion(ICI->getPredicate(), CmpRange);
if (NegOffset) // Apply the offset from above.
TrueValues = TrueValues.subtract(NegOffset->getValue());
// If we're interested in the false dest, invert the condition.
if (!isTrueDest) TrueValues = TrueValues.inverse();
Result = LVILatticeVal::getRange(TrueValues);
return true;
}
}
}
}
// If the edge was formed by a switch on the value, then we may know exactly
// what it is.
if (SwitchInst *SI = dyn_cast<SwitchInst>(BBFrom->getTerminator())) {
if (SI->getCondition() != Val)
return false;
bool DefaultCase = SI->getDefaultDest() == BBTo;
unsigned BitWidth = Val->getType()->getIntegerBitWidth();
ConstantRange EdgesVals(BitWidth, DefaultCase/*isFullSet*/);
for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end();
i != e; ++i) {
ConstantRange EdgeVal(i.getCaseValue()->getValue());
if (DefaultCase) {
// It is possible that the default destination is the destination of
// some cases. There is no need to perform difference for those cases.
if (i.getCaseSuccessor() != BBTo)
EdgesVals = EdgesVals.difference(EdgeVal);
} else if (i.getCaseSuccessor() == BBTo)
EdgesVals = EdgesVals.unionWith(EdgeVal);
}
Result = LVILatticeVal::getRange(EdgesVals);
return true;
}
return false;
}
/// \brief Compute the value of Val on the edge BBFrom -> BBTo, or the value at
/// the basic block if the edge does not constraint Val.
bool LazyValueInfoCache::getEdgeValue(Value *Val, BasicBlock *BBFrom,
BasicBlock *BBTo, LVILatticeVal &Result) {
// If already a constant, there is nothing to compute.
if (Constant *VC = dyn_cast<Constant>(Val)) {
Result = LVILatticeVal::get(VC);
return true;
}
if (getEdgeValueLocal(Val, BBFrom, BBTo, Result)) {
if (!Result.isConstantRange() ||
Result.getConstantRange().getSingleElement())
return true;
// FIXME: this check should be moved to the beginning of the function when
// LVI better supports recursive values. Even for the single value case, we
// can intersect to detect dead code (an empty range).
if (!hasBlockValue(Val, BBFrom)) {
BlockValueStack.push(std::make_pair(BBFrom, Val));
return false;
}
// Try to intersect ranges of the BB and the constraint on the edge.
LVILatticeVal InBlock = getBlockValue(Val, BBFrom);
if (!InBlock.isConstantRange())
return true;
ConstantRange Range =
Result.getConstantRange().intersectWith(InBlock.getConstantRange());
Result = LVILatticeVal::getRange(Range);
return true;
}
if (!hasBlockValue(Val, BBFrom)) {
BlockValueStack.push(std::make_pair(BBFrom, Val));
return false;
}
// if we couldn't compute the value on the edge, use the value from the BB
Result = getBlockValue(Val, BBFrom);
return true;
}
LVILatticeVal LazyValueInfoCache::getValueInBlock(Value *V, BasicBlock *BB) {
DEBUG(dbgs() << "LVI Getting block end value " << *V << " at '"
<< BB->getName() << "'\n");
BlockValueStack.push(std::make_pair(BB, V));
solve();
LVILatticeVal Result = getBlockValue(V, BB);
DEBUG(dbgs() << " Result = " << Result << "\n");
return Result;
}
LVILatticeVal LazyValueInfoCache::
getValueOnEdge(Value *V, BasicBlock *FromBB, BasicBlock *ToBB) {
DEBUG(dbgs() << "LVI Getting edge value " << *V << " from '"
<< FromBB->getName() << "' to '" << ToBB->getName() << "'\n");
LVILatticeVal Result;
if (!getEdgeValue(V, FromBB, ToBB, Result)) {
solve();
bool WasFastQuery = getEdgeValue(V, FromBB, ToBB, Result);
(void)WasFastQuery;
assert(WasFastQuery && "More work to do after problem solved?");
}
DEBUG(dbgs() << " Result = " << Result << "\n");
return Result;
}
void LazyValueInfoCache::threadEdge(BasicBlock *PredBB, BasicBlock *OldSucc,
BasicBlock *NewSucc) {
// When an edge in the graph has been threaded, values that we could not
// determine a value for before (i.e. were marked overdefined) may be possible
// to solve now. We do NOT try to proactively update these values. Instead,
// we clear their entries from the cache, and allow lazy updating to recompute
// them when needed.
// The updating process is fairly simple: we need to dropped cached info
// for all values that were marked overdefined in OldSucc, and for those same
// values in any successor of OldSucc (except NewSucc) in which they were
// also marked overdefined.
std::vector<BasicBlock*> worklist;
worklist.push_back(OldSucc);
DenseSet<Value*> ClearSet;
for (DenseSet<OverDefinedPairTy>::iterator I = OverDefinedCache.begin(),
E = OverDefinedCache.end(); I != E; ++I) {
if (I->first == OldSucc)
ClearSet.insert(I->second);
}
// Use a worklist to perform a depth-first search of OldSucc's successors.
// NOTE: We do not need a visited list since any blocks we have already
// visited will have had their overdefined markers cleared already, and we
// thus won't loop to their successors.
while (!worklist.empty()) {
BasicBlock *ToUpdate = worklist.back();
worklist.pop_back();
// Skip blocks only accessible through NewSucc.
if (ToUpdate == NewSucc) continue;
bool changed = false;
for (DenseSet<Value*>::iterator I = ClearSet.begin(), E = ClearSet.end();
I != E; ++I) {
// If a value was marked overdefined in OldSucc, and is here too...
DenseSet<OverDefinedPairTy>::iterator OI =
OverDefinedCache.find(std::make_pair(ToUpdate, *I));
if (OI == OverDefinedCache.end()) continue;
// Remove it from the caches.
ValueCacheEntryTy &Entry = ValueCache[LVIValueHandle(*I, this)];
ValueCacheEntryTy::iterator CI = Entry.find(ToUpdate);
assert(CI != Entry.end() && "Couldn't find entry to update?");
Entry.erase(CI);
OverDefinedCache.erase(OI);
// If we removed anything, then we potentially need to update
// blocks successors too.
changed = true;
}
if (!changed) continue;
worklist.insert(worklist.end(), succ_begin(ToUpdate), succ_end(ToUpdate));
}
}
//===----------------------------------------------------------------------===//
// LazyValueInfo Impl
//===----------------------------------------------------------------------===//
/// getCache - This lazily constructs the LazyValueInfoCache.
static LazyValueInfoCache &getCache(void *&PImpl) {
if (!PImpl)
PImpl = new LazyValueInfoCache();
return *static_cast<LazyValueInfoCache*>(PImpl);
}
bool LazyValueInfo::runOnFunction(Function &F) {
if (PImpl)
getCache(PImpl).clear();
TD = getAnalysisIfAvailable<DataLayout>();
TLI = &getAnalysis<TargetLibraryInfo>();
// Fully lazy.
return false;
}
void LazyValueInfo::getAnalysisUsage(AnalysisUsage &AU) const {
AU.setPreservesAll();
AU.addRequired<TargetLibraryInfo>();
}
void LazyValueInfo::releaseMemory() {
// If the cache was allocated, free it.
if (PImpl) {
delete &getCache(PImpl);
PImpl = 0;
}
}
Constant *LazyValueInfo::getConstant(Value *V, BasicBlock *BB) {
LVILatticeVal Result = getCache(PImpl).getValueInBlock(V, BB);
if (Result.isConstant())
return Result.getConstant();
if (Result.isConstantRange()) {
ConstantRange CR = Result.getConstantRange();
if (const APInt *SingleVal = CR.getSingleElement())
return ConstantInt::get(V->getContext(), *SingleVal);
}
return 0;
}
/// getConstantOnEdge - Determine whether the specified value is known to be a
/// constant on the specified edge. Return null if not.
Constant *LazyValueInfo::getConstantOnEdge(Value *V, BasicBlock *FromBB,
BasicBlock *ToBB) {
LVILatticeVal Result = getCache(PImpl).getValueOnEdge(V, FromBB, ToBB);
if (Result.isConstant())
return Result.getConstant();
if (Result.isConstantRange()) {
ConstantRange CR = Result.getConstantRange();
if (const APInt *SingleVal = CR.getSingleElement())
return ConstantInt::get(V->getContext(), *SingleVal);
}
return 0;
}
/// getPredicateOnEdge - Determine whether the specified value comparison
/// with a constant is known to be true or false on the specified CFG edge.
/// Pred is a CmpInst predicate.
LazyValueInfo::Tristate
LazyValueInfo::getPredicateOnEdge(unsigned Pred, Value *V, Constant *C,
BasicBlock *FromBB, BasicBlock *ToBB) {
LVILatticeVal Result = getCache(PImpl).getValueOnEdge(V, FromBB, ToBB);
// If we know the value is a constant, evaluate the conditional.
Constant *Res = 0;
if (Result.isConstant()) {
Res = ConstantFoldCompareInstOperands(Pred, Result.getConstant(), C, TD,
TLI);
if (ConstantInt *ResCI = dyn_cast<ConstantInt>(Res))
return ResCI->isZero() ? False : True;
return Unknown;
}
if (Result.isConstantRange()) {
ConstantInt *CI = dyn_cast<ConstantInt>(C);
if (!CI) return Unknown;
ConstantRange CR = Result.getConstantRange();
if (Pred == ICmpInst::ICMP_EQ) {
if (!CR.contains(CI->getValue()))
return False;
if (CR.isSingleElement() && CR.contains(CI->getValue()))
return True;
} else if (Pred == ICmpInst::ICMP_NE) {
if (!CR.contains(CI->getValue()))
return True;
if (CR.isSingleElement() && CR.contains(CI->getValue()))
return False;
}
// Handle more complex predicates.
ConstantRange TrueValues =
ICmpInst::makeConstantRange((ICmpInst::Predicate)Pred, CI->getValue());
if (TrueValues.contains(CR))
return True;
if (TrueValues.inverse().contains(CR))
return False;
return Unknown;
}
if (Result.isNotConstant()) {
// If this is an equality comparison, we can try to fold it knowing that
// "V != C1".
if (Pred == ICmpInst::ICMP_EQ) {
// !C1 == C -> false iff C1 == C.
Res = ConstantFoldCompareInstOperands(ICmpInst::ICMP_NE,
Result.getNotConstant(), C, TD,
TLI);
if (Res->isNullValue())
return False;
} else if (Pred == ICmpInst::ICMP_NE) {
// !C1 != C -> true iff C1 == C.
Res = ConstantFoldCompareInstOperands(ICmpInst::ICMP_NE,
Result.getNotConstant(), C, TD,
TLI);
if (Res->isNullValue())
return True;
}
return Unknown;
}
return Unknown;
}
void LazyValueInfo::threadEdge(BasicBlock *PredBB, BasicBlock *OldSucc,
BasicBlock *NewSucc) {
if (PImpl) getCache(PImpl).threadEdge(PredBB, OldSucc, NewSucc);
}
void LazyValueInfo::eraseBlock(BasicBlock *BB) {
if (PImpl) getCache(PImpl).eraseBlock(BB);
}
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