Rename Instruction::dropUnknownMetadata() to dropUnknownNonDebugMetadata()
and make it always preserve debug locations, since all callers wanted this
behavior anyway.

This is addressing a post-commit review feedback for r245589.

NFC (inside the LLVM tree).

llvm-svn: 245622
diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index 02e17d3..db260b6 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -1093,7 +1093,6 @@
       I2->replaceAllUsesWith(I1);
     I1->intersectOptionalDataWith(I2);
     unsigned KnownIDs[] = {
-      LLVMContext::MD_dbg,
       LLVMContext::MD_tbaa,
       LLVMContext::MD_range,
       LLVMContext::MD_fpmath,
@@ -2200,7 +2199,7 @@
       // only given the branch precondition.
       // For an analogous reason, we must also drop all the metadata whose
       // semantics we don't understand.
-      NewBonusInst->dropUnknownMetadata(LLVMContext::MD_dbg);
+      NewBonusInst->dropUnknownNonDebugMetadata();
 
       PredBlock->getInstList().insert(PBI, NewBonusInst);
       NewBonusInst->takeName(BonusInst);