NFC. Introduce Value::getPointerDerferecnceableBytes

Extract a part of isDereferenceableAndAlignedPointer functionality to Value::getPointerDerferecnceableBytes. Currently it's a NFC, but in future I'm going to accumulate all the logic about value dereferenceability in this function similarly to Value::getPointerAlignment function (D16144).

Reviewed By: reames

Differential Revision: http://reviews.llvm.org/D17572

llvm-svn: 267708

llvm/include/llvm/IR/Value.h

@@ -504,6 +504,13 @@ public:
     return const_cast<Value*>(this)->stripInBoundsOffsets();
   }
 
+  /// \brief Returns the number of bytes known to be dereferenceable for the
+  /// pointer value.
+  ///
+  /// If CanBeNull is set by this function the pointer can either be null or be
+  /// dereferenceable up to the returned number of bytes.
+  unsigned getPointerDereferenceableBytes(bool &CanBeNull) const;
+
   /// \brief Returns an alignment of the pointer value.
   ///
   /// Returns an alignment which is either specified explicitly, e.g. via

llvm/lib/Analysis/Loads.cpp

@@ -33,34 +33,9 @@ static bool isDereferenceableFromAttribute(const Value *BV, APInt Offset,
   assert(Offset.isNonNegative() && "offset can't be negative");
   assert(Ty->isSized() && "must be sized");
 
-  APInt DerefBytes(Offset.getBitWidth(), 0);
   bool CheckForNonNull = false;
-  if (const Argument *A = dyn_cast<Argument>(BV)) {
+  APInt DerefBytes(Offset.getBitWidth(),
-    DerefBytes = A->getDereferenceableBytes();
+                   BV->getPointerDereferenceableBytes(CheckForNonNull));
-    if (!DerefBytes.getBoolValue()) {
-      DerefBytes = A->getDereferenceableOrNullBytes();
-      CheckForNonNull = true;
-    }
-  } else if (auto CS = ImmutableCallSite(BV)) {
-    DerefBytes = CS.getDereferenceableBytes(0);
-    if (!DerefBytes.getBoolValue()) {
-      DerefBytes = CS.getDereferenceableOrNullBytes(0);
-      CheckForNonNull = true;
-    }
-  } else if (const LoadInst *LI = dyn_cast<LoadInst>(BV)) {
-    if (MDNode *MD = LI->getMetadata(LLVMContext::MD_dereferenceable)) {
-      ConstantInt *CI = mdconst::extract<ConstantInt>(MD->getOperand(0));
-      DerefBytes = CI->getLimitedValue();
-    }
-    if (!DerefBytes.getBoolValue()) {
-      if (MDNode *MD =
-              LI->getMetadata(LLVMContext::MD_dereferenceable_or_null)) {
-        ConstantInt *CI = mdconst::extract<ConstantInt>(MD->getOperand(0));
-        DerefBytes = CI->getLimitedValue();
-      }
-      CheckForNonNull = true;
-    }
-  }
 
   if (DerefBytes.getBoolValue())
     if (DerefBytes.uge(Offset + DL.getTypeStoreSize(Ty)))

llvm/lib/IR/Value.cpp

@@ -525,6 +525,40 @@ Value *Value::stripInBoundsOffsets() {
   return stripPointerCastsAndOffsets<PSK_InBounds>(this);
 }
 
+unsigned Value::getPointerDereferenceableBytes(bool &CanBeNull) const {
+  assert(getType()->isPointerTy() && "must be pointer");
+
+  unsigned DerefBytes = 0;
+  CanBeNull = false;
+  if (const Argument *A = dyn_cast<Argument>(this)) {
+    DerefBytes = A->getDereferenceableBytes();
+    if (DerefBytes == 0) {
+      DerefBytes = A->getDereferenceableOrNullBytes();
+      CanBeNull = true;
+    }
+  } else if (auto CS = ImmutableCallSite(this)) {
+    DerefBytes = CS.getDereferenceableBytes(0);
+    if (DerefBytes == 0) {
+      DerefBytes = CS.getDereferenceableOrNullBytes(0);
+      CanBeNull = true;
+    }
+  } else if (const LoadInst *LI = dyn_cast<LoadInst>(this)) {
+    if (MDNode *MD = LI->getMetadata(LLVMContext::MD_dereferenceable)) {
+      ConstantInt *CI = mdconst::extract<ConstantInt>(MD->getOperand(0));
+      DerefBytes = CI->getLimitedValue();
+    }
+    if (DerefBytes == 0) {
+      if (MDNode *MD =
+              LI->getMetadata(LLVMContext::MD_dereferenceable_or_null)) {
+        ConstantInt *CI = mdconst::extract<ConstantInt>(MD->getOperand(0));
+        DerefBytes = CI->getLimitedValue();
+      }
+      CanBeNull = true;
+    }
+  }
+  return DerefBytes;
+}
+
 unsigned Value::getPointerAlignment(const DataLayout &DL) const {
   assert(getType()->isPointerTy() && "must be pointer");