Replace a hand-coded leading one counting loop with the magic from MathExtras.h.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@152545 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Support/APInt.cpp b/lib/Support/APInt.cpp
index 031bbb8..a60bff3 100644
--- a/lib/Support/APInt.cpp
+++ b/lib/Support/APInt.cpp
@@ -723,14 +723,7 @@
 }
 
 static unsigned countLeadingOnes_64(uint64_t V, unsigned skip) {
-  unsigned Count = 0;
-  if (skip)
-    V <<= skip;
-  while (V && (V & (1ULL << 63))) {
-    Count++;
-    V <<= 1;
-  }
-  return Count;
+  return CountLeadingOnes_64(V << skip);
 }
 
 unsigned APInt::countLeadingOnes() const {