[KnownBits] Add methods for determining if KnownBits is a constant value

This patch adds isConstant and getConstant for determining if KnownBits represents a constant value and to retrieve the value. Use them to simplify code.

Differential Revision: https://reviews.llvm.org/D32785

llvm-svn: 302091
diff --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp
index 7aa6abf..5e4801d 100644
--- a/llvm/lib/Analysis/InstructionSimplify.cpp
+++ b/llvm/lib/Analysis/InstructionSimplify.cpp
@@ -4595,8 +4595,8 @@
     unsigned BitWidth = I->getType()->getScalarSizeInBits();
     KnownBits Known(BitWidth);
     computeKnownBits(I, Known, Q.DL, /*Depth*/ 0, Q.AC, I, Q.DT, ORE);
-    if ((Known.Zero | Known.One).isAllOnesValue())
-      Result = ConstantInt::get(I->getType(), Known.One);
+    if (Known.isConstant())
+      Result = ConstantInt::get(I->getType(), Known.getConstant());
   }
 
   /// If called on unreachable code, the above logic may report that the