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Move Value.isDereferenceablePointer to ValueTracking [NFC]

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Move isDereferenceablePointer function to Analysis. This function recursively tracks dereferencability over a chain of values like other functions in ValueTracking.

This refactoring is motivated by further changes to support dereferenceable_or_null attribute (http://reviews.llvm.org/D8650). isDereferenceablePointer will be extended to perform context-sensitive analysis and IR is not a good place to have such functionality.

Patch by: Artur Pilipenko <apilipenko@azulsystems.com>
Differential Revision: reviews.llvm.org/D9075




git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@235611 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Philip Reames
2015-04-23 17:36:48 +00:00
parent dab5145cb3
commit 1aa9710c60
9 changed files with 159 additions and 147 deletions
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131
lib/IR/Value.cpp
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@ -477,137 +477,6 @@ Value *Value::stripInBoundsOffsets() {
return stripPointerCastsAndOffsets<PSK_InBounds>(this);
}
/// \brief Check if Value is always a dereferenceable pointer.
///
/// Test if V is always a pointer to allocated and suitably aligned memory for
/// a simple load or store.
static bool isDereferenceablePointer(const Value *V, const DataLayout &DL,
SmallPtrSetImpl<const Value *> &Visited) {
// Note that it is not safe to speculate into a malloc'd region because
// malloc may return null.
// These are obviously ok.
if (isa<AllocaInst>(V)) return true;
// It's not always safe to follow a bitcast, for example:
// bitcast i8* (alloca i8) to i32*
// would result in a 4-byte load from a 1-byte alloca. However,
// if we're casting from a pointer from a type of larger size
// to a type of smaller size (or the same size), and the alignment
// is at least as large as for the resulting pointer type, then
// we can look through the bitcast.
if (const BitCastOperator *BC = dyn_cast<BitCastOperator>(V)) {
Type *STy = BC->getSrcTy()->getPointerElementType(),
*DTy = BC->getDestTy()->getPointerElementType();
if (STy->isSized() && DTy->isSized() &&
(DL.getTypeStoreSize(STy) >= DL.getTypeStoreSize(DTy)) &&
(DL.getABITypeAlignment(STy) >= DL.getABITypeAlignment(DTy)))
return isDereferenceablePointer(BC->getOperand(0), DL, Visited);
}
// Global variables which can't collapse to null are ok.
if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(V))
return !GV->hasExternalWeakLinkage();
// byval arguments are okay. Arguments specifically marked as
// dereferenceable are okay too.
if (const Argument *A = dyn_cast<Argument>(V)) {
if (A->hasByValAttr())
return true;
else if (uint64_t Bytes = A->getDereferenceableBytes()) {
Type *Ty = V->getType()->getPointerElementType();
if (Ty->isSized() && DL.getTypeStoreSize(Ty) <= Bytes)
return true;
}
return false;
}
// Return values from call sites specifically marked as dereferenceable are
// also okay.
if (auto CS = ImmutableCallSite(V)) {
if (uint64_t Bytes = CS.getDereferenceableBytes(0)) {
Type *Ty = V->getType()->getPointerElementType();
if (Ty->isSized() && DL.getTypeStoreSize(Ty) <= Bytes)
return true;
}
}
// For GEPs, determine if the indexing lands within the allocated object.
if (const GEPOperator *GEP = dyn_cast<GEPOperator>(V)) {
// Conservatively require that the base pointer be fully dereferenceable.
if (!Visited.insert(GEP->getOperand(0)).second)
return false;
if (!isDereferenceablePointer(GEP->getOperand(0), DL, Visited))
return false;
// Check the indices.
gep_type_iterator GTI = gep_type_begin(GEP);
for (User::const_op_iterator I = GEP->op_begin()+1,
E = GEP->op_end(); I != E; ++I) {
Value *Index = *I;
Type *Ty = *GTI++;
// Struct indices can't be out of bounds.
if (isa<StructType>(Ty))
continue;
ConstantInt *CI = dyn_cast<ConstantInt>(Index);
if (!CI)
return false;
// Zero is always ok.
if (CI->isZero())
continue;
// Check to see that it's within the bounds of an array.
ArrayType *ATy = dyn_cast<ArrayType>(Ty);
if (!ATy)
return false;
if (CI->getValue().getActiveBits() > 64)
return false;
if (CI->getZExtValue() >= ATy->getNumElements())
return false;
}
// Indices check out; this is dereferenceable.
return true;
}
// For gc.relocate, look through relocations
if (const IntrinsicInst *I = dyn_cast<IntrinsicInst>(V))
if (I->getIntrinsicID() == Intrinsic::experimental_gc_relocate) {
GCRelocateOperands RelocateInst(I);
return isDereferenceablePointer(RelocateInst.derivedPtr(), DL, Visited);
}
if (const AddrSpaceCastInst *ASC = dyn_cast<AddrSpaceCastInst>(V))
return isDereferenceablePointer(ASC->getOperand(0), DL, Visited);
// If we don't know, assume the worst.
return false;
}
bool Value::isDereferenceablePointer(const DataLayout &DL) const {
// When dereferenceability information is provided by a dereferenceable
// attribute, we know exactly how many bytes are dereferenceable. If we can
// determine the exact offset to the attributed variable, we can use that
// information here.
Type *Ty = getType()->getPointerElementType();
if (Ty->isSized()) {
APInt Offset(DL.getTypeStoreSizeInBits(getType()), 0);
const Value *BV = stripAndAccumulateInBoundsConstantOffsets(DL, Offset);
APInt DerefBytes(Offset.getBitWidth(), 0);
if (const Argument *A = dyn_cast<Argument>(BV))
DerefBytes = A->getDereferenceableBytes();
else if (auto CS = ImmutableCallSite(BV))
DerefBytes = CS.getDereferenceableBytes(0);
if (DerefBytes.getBoolValue() && Offset.isNonNegative()) {
if (DerefBytes.uge(Offset + DL.getTypeStoreSize(Ty)))
return true;
}
}
SmallPtrSet<const Value *, 32> Visited;
return ::isDereferenceablePointer(this, DL, Visited);
}
Value *Value::DoPHITranslation(const BasicBlock *CurBB,
const BasicBlock *PredBB) {
PHINode *PN = dyn_cast<PHINode>(this);