[llvm] Add a pass to collect dropped var statistics for MIR (PR #126686)

[Nikita Popov via llvm-commits]

================
@@ -0,0 +1,59 @@
+///===- DroppedVariableStatsMIR.h - Opt Diagnostics -*- C++ -*-------------===//
+///
+/// Part of the LLVM Project, under the Apache License v2.0 with LLVM
+/// Exceptions. See https://llvm.org/LICENSE.txt for license information.
+/// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+///
+///===---------------------------------------------------------------------===//
+/// \file
+/// Dropped Variable Statistics for Debug Information. Reports any number
+/// of DBG_VALUEs that get dropped due to an optimization pass.
+///
+///===---------------------------------------------------------------------===//
+
+#ifndef LLVM_CODEGEN_DROPPEDVARIABLESTATSMIR_H
+#define LLVM_CODEGEN_DROPPEDVARIABLESTATSMIR_H
+
+#include "llvm/CodeGen/MachineFunction.h"
+#include "llvm/IR/DroppedVariableStats.h"
+
+namespace llvm {
+
+/// A class to collect and print dropped debug information due to MIR
+/// optimization passes. After every MIR pass is run, it will print how many
+/// #DBG_VALUEs were dropped due to that pass.
+class DroppedVariableStatsMIR : public DroppedVariableStats {
+public:
+  DroppedVariableStatsMIR() : llvm::DroppedVariableStats(false) {}
----------------
nikic wrote:

```suggestion
  DroppedVariableStatsMIR() : DroppedVariableStats(false) {}
```
Avoid `llvm::` prefix in llvm/.

https://github.com/llvm/llvm-project/pull/126686