Add a getNumSignBits() method to APInt.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@126379 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index 2fb2f2d..0b7cbcc 100644
--- a/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -2088,12 +2088,7 @@
 
   case ISD::Constant: {
     const APInt &Val = cast<ConstantSDNode>(Op)->getAPIntValue();
-    // If negative, return # leading ones.
-    if (Val.isNegative())
-      return Val.countLeadingOnes();
-
-    // Return # leading zeros.
-    return Val.countLeadingZeros();
+    return Val.getNumSignBits();
   }
 
   case ISD::SIGN_EXTEND: