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
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
index 56b6cd3..1505ff0 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -1204,7 +1204,7 @@
       II->addAttribute(AttributeSet::ReturnIndex, Attribute::NonNull);
 
     // isDereferenceablePointer -> deref attribute
-    if (DerivedPtr->isDereferenceablePointer(DL)) {
+    if (isDereferenceablePointer(DerivedPtr, DL)) {
       if (Argument *A = dyn_cast<Argument>(DerivedPtr)) {
         uint64_t Bytes = A->getDereferenceableBytes();
         II->addDereferenceableAttr(AttributeSet::ReturnIndex, Bytes);