diff --git a/mlir/lib/Dialect/LLVMIR/IR/LLVMMemorySlot.cpp b/mlir/lib/Dialect/LLVMIR/IR/LLVMMemorySlot.cpp
--- a/mlir/lib/Dialect/LLVMIR/IR/LLVMMemorySlot.cpp
+++ b/mlir/lib/Dialect/LLVMIR/IR/LLVMMemorySlot.cpp
@@ -263,12 +263,25 @@
 bool LLVM::DbgValueOp::canUsesBeRemoved(
     const SmallPtrSetImpl<OpOperand *> &blockingUses,
     SmallVectorImpl<OpOperand *> &newBlockingUses) {
-  return true;
+  // There is only one operand that we can remove the use of.
+  if (blockingUses.size() != 1)
+    return false;
+
+  return (*blockingUses.begin())->get() == getValue();
 }
 
 DeletionKind LLVM::DbgValueOp::removeBlockingUses(
     const SmallPtrSetImpl<OpOperand *> &blockingUses, RewriterBase &rewriter) {
-  return DeletionKind::Delete;
+  // Rewriter by default is after '*this', but we need it before '*this'.
+  rewriter.setInsertionPoint(*this);
+
+  // Rather than dropping the debug value, replace it with undef to preserve the
+  // debug local variable info. This allows the debugger to inform the user that
+  // the variable has been optimized out.
+  auto undef =
+      rewriter.create<UndefOp>(getValue().getLoc(), getValue().getType());
+  rewriter.updateRootInPlace(*this, [&] { getValueMutable().assign(undef); });
+  return DeletionKind::Keep;
 }
 
 //===----------------------------------------------------------------------===//
diff --git a/mlir/test/Dialect/LLVMIR/mem2reg-dbginfo.mlir b/mlir/test/Dialect/LLVMIR/mem2reg-dbginfo.mlir
--- a/mlir/test/Dialect/LLVMIR/mem2reg-dbginfo.mlir
+++ b/mlir/test/Dialect/LLVMIR/mem2reg-dbginfo.mlir
@@ -76,9 +76,10 @@
 }
 
 // CHECK-LABEL: llvm.func @always_drop_promoted_declare
+// CHECK: %[[UNDEF:.*]] = llvm.mlir.undef
 // CHECK-NOT: = llvm.alloca
 // CHECK-NOT: llvm.intr.dbg.declare
-// CHECK-NOT: llvm.intr.dbg.value
+// CHECK: llvm.intr.dbg.value #{{.*}} = %[[UNDEF]]
 llvm.func @always_drop_promoted_declare() {
   %0 = llvm.mlir.constant(1 : i32) : i32
   %1 = llvm.alloca %0 x i64 {alignment = 8 : i64} : (i32) -> !llvm.ptr