Rename isPowerOfTwo to isKnownToBeAPowerOfTwo.

In a previous thread it was pointed out that isPowerOfTwo is not a very precise
name since it can return false for powers of two if it is unable to show that
they are powers of two.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@170093 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Analysis/InstructionSimplify.cpp b/lib/Analysis/InstructionSimplify.cpp
index 2bcd363..0b88f45 100644
--- a/lib/Analysis/InstructionSimplify.cpp
+++ b/lib/Analysis/InstructionSimplify.cpp
@@ -1457,9 +1457,9 @@
   // A & (-A) = A if A is a power of two or zero.
   if (match(Op0, m_Neg(m_Specific(Op1))) ||
       match(Op1, m_Neg(m_Specific(Op0)))) {
-    if (isPowerOfTwo(Op0, /*OrZero*/true))
+    if (isKnownToBeAPowerOfTwo(Op0, /*OrZero*/true))
       return Op0;
-    if (isPowerOfTwo(Op1, /*OrZero*/true))
+    if (isKnownToBeAPowerOfTwo(Op1, /*OrZero*/true))
       return Op1;
   }