[llvm] [DLCov][NFC] Propagate annotated DebugLocs through transformations (PR #138047)

[Stephen Tozer via llvm-commits]

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@@ -251,8 +259,12 @@ class IRBuilderBase {
   /// not on \p Src will be dropped from MetadataToCopy.
   void CollectMetadataToCopy(Instruction *Src,
                              ArrayRef<unsigned> MetadataKinds) {
-    for (unsigned K : MetadataKinds)
-      AddOrRemoveMetadataToCopy(K, Src->getMetadata(K));
+    for (unsigned K : MetadataKinds) {
+      if (K == LLVMContext::MD_dbg)
+        SetCurrentDebugLocation(Src->getDebugLoc());
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SLTozer wrote:

It should not, if `MetadataKinds` contains `MD_dbg` and `Src` has no loc, then we would call `AddOrRemoveMetadataToCopy(LLVMContext::MD_dbg, nullptr)`, which will remove any `MD_dbg` entry in `MetadataToCopy` - effectively the same thing as this, which overwrites any existing `StoredDL` with an empty debug loc.

https://github.com/llvm/llvm-project/pull/138047