[APInt] Add a fastpath for the single word case of isOneValue to match isNullValue, isAllOnesValue, etc. NFCI

llvm-svn: 307430

1 files changed, 5 insertions, 1 deletions

diff --git a/llvm/include/llvm/ADT/APInt.h b/llvm/include/llvm/ADT/APInt.h
index e5f0c35534a..a1cce6e5fe1 100644
--- a/llvm/include/llvm/ADT/APInt.h
+++ b/llvm/include/llvm/ADT/APInt.h
@@ -401,7 +401,11 @@ public:
   /// \brief Determine if this is a value of 1.
   ///
   /// This checks to see if the value of this APInt is one.
-  bool isOneValue() const { return getActiveBits() == 1; }
+  bool isOneValue() const {
+    if (isSingleWord())
+      return U.VAL == 1;
+    return countLeadingZerosSlowCase() == BitWidth - 1;
+  }
 
   /// \brief Determine if this is the largest unsigned value.
   ///