[RemoveDIs] Add DPLabels support [3a/3] (#82633)

Patch 2 of 3 to add llvm.dbg.label support to the RemoveDIs project. The
patch stack adds the DPLabel class, which is the RemoveDIs llvm.dbg.label
equivalent.

   1. Add DbgRecord base class for DPValue and the not-yet-added
       DPLabel class.
   2. Add the DPLabel class.
-> 3. Add support to passes.

The next patch, #82639, will enable conversion between dbg.labels and DPLabels.

AssignemntTrackingAnalysis support could have gone two ways:

1. Have the analysis store a DPLabel representation in its results -
   SelectionDAGBuilder reads the analysis results and ignores all DbgRecord
   kinds.
2. Ignore DPLabels in the analysis - SelectionDAGBuilder reads the analysis
   results but still needs to iterate over DPLabels from the IR.

I went with option 2 because it's less work and is no less correct than 1. It's
worth noting that causes labels to sink to the bottom of packs of debug records.
e.g., [value, label, value] becomes [value, value, label]. This shouldn't be a
problem because labels and variable locations don't have an ordering requirement.
The ordering between variable locations is maintained and the label movement is
deterministic

1 files changed, 9 insertions, 1 deletions

diff --git a/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp b/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp
index 7fd6759..5bb109a 100644
--- a/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp
+++ b/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp
@@ -386,7 +386,15 @@ static bool DPValuesRemoveRedundantDbgInstrsUsingBackwardScan(BasicBlock *BB) {
   SmallVector<DPValue *, 8> ToBeRemoved;
   SmallDenseSet<DebugVariable> VariableSet;
   for (auto &I : reverse(*BB)) {
-    for (DPValue &DPV : reverse(DPValue::filter(I.getDbgValueRange()))) {
+    for (DbgRecord &DR : reverse(I.getDbgValueRange())) {
+      if (isa<DPLabel>(DR)) {
+        // Emulate existing behaviour (see comment below for dbg.declares).
+        // FIXME: Don't do this.
+        VariableSet.clear();
+        continue;
+      }
+
+      DPValue &DPV = cast<DPValue>(DR);
       // Skip declare-type records, as the debug intrinsic method only works
       // on dbg.value intrinsics.
       if (DPV.getType() == DPValue::LocationType::Declare) {