BitcodeWriter: Refactor common computation of bits required for a type index.

Suggested by Duncan. Happy to bikeshed the name, cache the result, etc.

llvm-svn: 230410
diff --git a/llvm/lib/Bitcode/Writer/ValueEnumerator.cpp b/llvm/lib/Bitcode/Writer/ValueEnumerator.cpp
index 24b077b..549e94f 100644
--- a/llvm/lib/Bitcode/Writer/ValueEnumerator.cpp
+++ b/llvm/lib/Bitcode/Writer/ValueEnumerator.cpp
@@ -803,3 +803,7 @@
   IncorporateFunctionInfoGlobalBBIDs(BB->getParent(), GlobalBasicBlockIDs);
   return getGlobalBasicBlockID(BB);
 }
+
+uint64_t ValueEnumerator::computeBitsRequiredForTypeIndicies() const {
+  return Log2_32_Ceil(getTypes().size() + 1);
+}