Stub out a new LiveDebugVariables pass.

This analysis is going to run immediately after LiveIntervals. It will stay
alive during register allocation and keep track of user variables mentioned in
DBG_VALUE instructions.

When the register allocator is moving values between registers and the stack, it
is very hard to keep track of DBG_VALUE instructions. We usually get it wrong.
This analysis maintains a data structure that makes it easy to update DBG_VALUE
instructions.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@120385 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/LiveDebugVariables.h

@@ -0,0 +1,57 @@
+//===- LiveDebugVariables.h - Tracking debug info variables ----*- c++ -*--===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file provides the interface to the LiveDebugVariables analysis.
+//
+// The analysis removes DBG_VALUE instructions for virtual registers and tracks
+// live user variables in a data structure that can be updated during register
+// allocation.
+//
+// After register allocation new DBG_VALUE instructions are emitted to reflect
+// the new locations of user variables.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CODEGEN_LIVEDEBUGVARIABLES_H
+#define LLVM_CODEGEN_LIVEDEBUGVARIABLES_H
+
+#include "llvm/CodeGen/MachineFunctionPass.h"
+
+namespace llvm {
+
+class LiveDebugVariables : public MachineFunctionPass {
+  void *pImpl;
+public:
+  static char ID; // Pass identification, replacement for typeid
+
+  LiveDebugVariables();
+
+  /// renameRegister - Move any user variables in OldReg to NewReg:SubIdx.
+  /// @param OldReg Old virtual register that is going away.
+  /// @param NewReg New register holding the user variables.
+  /// @param SubIdx If NewReg is a virtual register, SubIdx may indicate a sub-
+  ///               register.
+  void renameRegister(unsigned OldReg, unsigned NewReg, unsigned SubIdx);
+
+  /// emitDebugValues - Emit new DBG_VALUE instructions reflecting the changes
+  /// that happened during register allocation.
+  void emitDebugValues();
+
+private:
+
+  /// runOnMachineFunction - Analyze and remove DBG_VALUE instructions.
+  virtual bool runOnMachineFunction(MachineFunction &);
+
+  virtual void getAnalysisUsage(AnalysisUsage &) const;
+
+};
+
+} // namespace llvm
+
+#endif // LLVM_CODEGEN_LIVEDEBUGVARIABLES_H