[RemoveDIs] Fix spliceDebugInfo splice-to-end edge case (#105671)

Fix #105571 which demonstrates an end() iterator dereference when
performing a non-empty splice to end() from a region that ends at
Src::end().

Rather than calling Instruction::adoptDbgRecords from Dest, create a marker
(which takes an iterator) and absorbDebugValues onto that. The "absorb" variant
doesn't clean up the source marker, which in this case we know is a trailing
marker, so we have to do that manually.

1 files changed, 10 insertions, 2 deletions

diff --git a/llvm/lib/IR/BasicBlock.cpp b/llvm/lib/IR/BasicBlock.cpp
index e259ec5..39cefa5 100644
--- a/llvm/lib/IR/BasicBlock.cpp
+++ b/llvm/lib/IR/BasicBlock.cpp
@@ -975,8 +975,16 @@ void BasicBlock::spliceDebugInfoImpl(BasicBlock::iterator Dest, BasicBlock *Src,
   if (ReadFromTail && Src->getMarker(Last)) {
     DbgMarker *FromLast = Src->getMarker(Last);
     if (LastIsEnd) {
-      Dest->adoptDbgRecords(Src, Last, true);
-      // adoptDbgRecords will release any trailers.
+      if (Dest == end()) {
+        // Abosrb the trailing markers from Src.
+        assert(FromLast == Src->getTrailingDbgRecords());
+        createMarker(Dest)->absorbDebugValues(*FromLast, true);
+        FromLast->eraseFromParent();
+        Src->deleteTrailingDbgRecords();
+      } else {
+        // adoptDbgRecords will release any trailers.
+        Dest->adoptDbgRecords(Src, Last, true);
+      }
       assert(!Src->getTrailingDbgRecords());
     } else {
       // FIXME: can we use adoptDbgRecords here to reduce allocations?