IR: MDNode => Value: Instruction::getMetadata()

Change `Instruction::getMetadata()` to return `Value` as part of
PR21433.

Update most callers to use `Instruction::getMDNode()`, which wraps the
result in a `cast_or_null<MDNode>`.

llvm-svn: 221024
diff --git a/llvm/lib/Analysis/BranchProbabilityInfo.cpp b/llvm/lib/Analysis/BranchProbabilityInfo.cpp
index bbd8750..4e083d2 100644
--- a/llvm/lib/Analysis/BranchProbabilityInfo.cpp
+++ b/llvm/lib/Analysis/BranchProbabilityInfo.cpp
@@ -180,7 +180,7 @@
   if (!isa<BranchInst>(TI) && !isa<SwitchInst>(TI))
     return false;
 
-  MDNode *WeightsNode = TI->getMetadata(LLVMContext::MD_prof);
+  MDNode *WeightsNode = TI->getMDNode(LLVMContext::MD_prof);
   if (!WeightsNode)
     return false;