[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, 4 insertions, 5 deletions

diff --git a/llvm/lib/CodeGen/AssignmentTrackingAnalysis.cpp b/llvm/lib/CodeGen/AssignmentTrackingAnalysis.cpp
index 7b66a85..3b84624 100644
--- a/llvm/lib/CodeGen/AssignmentTrackingAnalysis.cpp
+++ b/llvm/lib/CodeGen/AssignmentTrackingAnalysis.cpp
@@ -829,11 +829,7 @@ class MemLocFragmentFill {
   void process(BasicBlock &BB, VarFragMap &LiveSet) {
     BBInsertBeforeMap[&BB].clear();
     for (auto &I : BB) {
-      for (DbgRecord &DR : I.getDbgValueRange()) {
-        // FIXME: DPValue::filter usage needs attention in this file; we need
-        // to make sure dbg.labels are handled correctly in RemoveDIs mode.
-        // Cast below to ensure this gets fixed when DPLabels are introduced.
-        DPValue &DPV = cast<DPValue>(DR);
+      for (DPValue &DPV : DPValue::filter(I.getDbgValueRange())) {
         if (const auto *Locs = FnVarLocs->getWedge(&DPV)) {
           for (const VarLocInfo &Loc : *Locs) {
             addDef(Loc, &DPV, *I.getParent(), LiveSet);
@@ -1919,6 +1915,9 @@ void AssignmentTrackingLowering::process(BasicBlock &BB, BlockInfo *LiveSet) {
     // attached DPValues, or a non-debug instruction with attached unprocessed
     // DPValues.
     if (II != EI && II->hasDbgValues()) {
+      // Skip over non-variable debug records (i.e., labels). They're going to
+      // be read from IR (possibly re-ordering them within the debug record
+      // range) rather than from the analysis results.
       for (DPValue &DPV : DPValue::filter(II->getDbgValueRange())) {
         resetInsertionPoint(DPV);
         processDPValue(DPV, LiveSet);