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;
}
LVILatticeVal LVIQuery::getBlockValue(BasicBlock *BB) {
// See if we already have a value for this block.
LVILatticeVal BBLV = getCachedEntryForBlock(BB);
// If we've already computed this block's value, return it.
if (!BBLV.isUndefined()) {
DEBUG(dbgs() << " reuse BB '" << BB->getName() << "' val=" << BBLV <<'\n');
return BBLV;
}
// 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();
Cache[BB] = BBLV;
Instruction *BBI = dyn_cast<Instruction>(Val);
if (BBI == 0 || BBI->getParent() != 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()) {
for (BasicBlock::iterator BI = BB->begin(), BE = BB->end();BI != BE;++BI){
LoadInst *L = dyn_cast<LoadInst>(BI);
if (L && L->getPointerAddressSpace() == 0 &&
L->getPointerOperand()->getUnderlyingObject() ==
Val->getUnderlyingObject()) {
NotNull = true;
break;
}
}
}
unsigned NumPreds = 0;
// Loop over all of our predecessors, merging what we know from them into
// result.
for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
Result.mergeIn(getEdgeValue(*PI, BB));
// 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) {
const PointerType *PTy = cast<PointerType>(Val->getType());
Result = LVILatticeVal::getNot(ConstantPointerNull::get(PTy));
}
return Result;
}
++NumPreds;
}
// If this is the entry block, we must be asking about an argument. The
// value is overdefined.
if (NumPreds == 0 && BB == &BB->getParent()->front()) {
assert(isa<Argument>(Val) && "Unknown live-in to the entry block");
Result.markOverdefined();
return Result;
}
// Return the merged value, which is more precise than 'overdefined'.
assert(!Result.isOverdefined());
return Cache[BB] = Result;
}
// If this value is defined by an instruction in this block, we have to
// process it here somehow or return overdefined.
if (PHINode *PN = dyn_cast<PHINode>(BBI)) {
LVILatticeVal Result; // Start Undefined.
// Loop over all of our predecessors, merging what we know from them into
// result.
for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
Value* PhiVal = PN->getIncomingValueForBlock(*PI);
Result.mergeIn(Parent.getValueOnEdge(PhiVal, *PI, BB));
// 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");
return Result;
}
}
// Return the merged value, which is more precise than 'overdefined'.
assert(!Result.isOverdefined());
return Cache[BB] = Result;
}
assert(Cache[BB].isOverdefined() && "Recursive query changed our cache?");
// 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");
Result.markOverdefined();
return Result;
}
// 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");
Result.markOverdefined();
return Result;
}
// Figure out the range of the LHS. If that fails, bail.
LVILatticeVal LHSVal = Parent.getValueInBlock(BBI->getOperand(0), BB);
if (!LHSVal.isConstantRange()) {
Result.markOverdefined();
return Result;
}
ConstantInt *RHS = 0;
ConstantRange LHSRange = LHSVal.getConstantRange();
ConstantRange RHSRange(1);
const IntegerType *ResultTy = cast<IntegerType>(BBI->getType());
if (isa<BinaryOperator>(BBI)) {
RHS = dyn_cast<ConstantInt>(BBI->getOperand(1));
if (!RHS) {
Result.markOverdefined();
return Result;
}
RHSRange = ConstantRange(RHS->getValue(), RHS->getValue()+1);
}
// 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.
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;
}
return Cache[BB] = Result;
}
