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Add support for inferring that a load from a pointer implies that it is not null. 

llvm-svn: 111959
This commit is contained in:
Owen Anderson 2010-08-24 20:47:29 +00:00
parent 6b900c5dcd
commit da34de1599
1 changed files with 17 additions and 4 deletions
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21
llvm/lib/Analysis/LazyValueInfo.cpp
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@ -367,6 +367,7 @@ namespace {
/// NewBlocks - This is a mapping of the new BasicBlocks which have been
/// added to cache but that are not in sorted order.
DenseSet<BasicBlock*> NewBlockInfo;
public:
LVIQuery(Value *V, LazyValueInfoCache &P,
@ -448,12 +449,24 @@ LVILatticeVal LVIQuery::getBlockValue(BasicBlock *BB) {
BBLV.markOverdefined();
Cache[BB] = BBLV;
// If V is live into BB, see if our predecessors know anything about it.
Instruction *BBI = dyn_cast<Instruction>(Val);
if (BBI == 0 || BBI->getParent() != BB) {
LVILatticeVal Result; // Start Undefined.
unsigned NumPreds = 0;
// 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.
if (Val->getType()->isPointerTy()) {
const PointerType *PTy = cast<PointerType>(Val->getType());
for (Value::use_iterator UI = Val->use_begin(), UE = Val->use_end();
UI != UE; ++UI) {
LoadInst *L = dyn_cast<LoadInst>(*UI);
if (L && L->getParent() == BB) {
return LVILatticeVal::getNot(ConstantPointerNull::get(PTy));
}
}
}
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) {
@ -694,8 +707,8 @@ LVILatticeVal LazyValueInfoCache::getValueInBlock(Value *V, BasicBlock *BB) {
<< BB->getName() << "'\n");
LVILatticeVal Result = LVIQuery(V, *this,
ValueCache[LVIValueHandle(V, this)],
OverDefinedCache).getBlockValue(BB);
ValueCache[LVIValueHandle(V, this)],
OverDefinedCache).getBlockValue(BB);
DEBUG(dbgs() << " Result = " << Result << "\n");
return Result;