Move Value.isDereferenceablePointer to ValueTracking [NFC]

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

llvm-svn: 235611

1 files changed, 0 insertions, 131 deletions

diff --git a/llvm/lib/IR/Value.cpp b/llvm/lib/IR/Value.cpp
index f6eb427..18f6b1e 100644
--- a/llvm/lib/IR/Value.cpp
+++ b/llvm/lib/IR/Value.cpp
@@ -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);