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

4 files changed, 109 insertions, 0 deletions

diff --git a/lib/CodeGen/CMakeLists.txt b/lib/CodeGen/CMakeLists.txt
index 7a36c5137a..ed7ec6ea50 100644
--- a/lib/CodeGen/CMakeLists.txt
+++ b/lib/CodeGen/CMakeLists.txt
@@ -20,6 +20,7 @@ add_llvm_library(LLVMCodeGen
   IntrinsicLowering.cpp
   LLVMTargetMachine.cpp
   LatencyPriorityQueue.cpp
+  LiveDebugVariables.cpp
   LiveInterval.cpp
   LiveIntervalAnalysis.cpp
   LiveIntervalUnion.cpp
diff --git a/lib/CodeGen/CodeGen.cpp b/lib/CodeGen/CodeGen.cpp
index fec98d26a1..515e6f9fde 100644
--- a/lib/CodeGen/CodeGen.cpp
+++ b/lib/CodeGen/CodeGen.cpp
@@ -23,6 +23,7 @@ void llvm::initializeCodeGen(PassRegistry &Registry) {
   initializeDeadMachineInstructionElimPass(Registry);
   initializeGCModuleInfoPass(Registry);
   initializeIfConverterPass(Registry);
+  initializeLiveDebugVariablesPass(Registry);
   initializeLiveIntervalsPass(Registry);
   initializeLiveStacksPass(Registry);
   initializeLiveVariablesPass(Registry);
diff --git a/lib/CodeGen/LiveDebugVariables.cpp b/lib/CodeGen/LiveDebugVariables.cpp
new file mode 100644
index 0000000000..2ca0bee68e
--- /dev/null
+++ b/lib/CodeGen/LiveDebugVariables.cpp
@@ -0,0 +1,50 @@
+//===- LiveDebugVariables.cpp - Tracking debug info variables -------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements the LiveDebugVariables analysis.
+//
+// Remove all DBG_VALUE instructions referencing virtual registers and replace
+// them with a data structure tracking where live user variables are kept - in a
+// virtual register or in a stack slot.
+//
+// Allow the data structure to be updated during register allocation when values
+// are moved between registers and stack slots. Finally emit new DBG_VALUE
+// instructions after register allocation is complete.
+//
+//===----------------------------------------------------------------------===//
+
+#include "LiveDebugVariables.h"
+#include "llvm/CodeGen/LiveIntervalAnalysis.h"
+#include "llvm/CodeGen/MachineFunction.h"
+#include "llvm/CodeGen/Passes.h"
+#include "llvm/Target/TargetMachine.h"
+
+using namespace llvm;
+
+char LiveDebugVariables::ID = 0;
+
+INITIALIZE_PASS_BEGIN(LiveDebugVariables, "livedebugvars",
+                "Debug Variable Analysis", false, false)
+INITIALIZE_PASS_DEPENDENCY(LiveIntervals)
+INITIALIZE_PASS_END(LiveDebugVariables, "livedebugvars",
+                "Debug Variable Analysis", false, false)
+
+void LiveDebugVariables::getAnalysisUsage(AnalysisUsage &AU) const {
+  AU.addRequiredTransitive<LiveIntervals>();
+  AU.setPreservesAll();
+  MachineFunctionPass::getAnalysisUsage(AU);
+}
+
+LiveDebugVariables::LiveDebugVariables() : MachineFunctionPass(ID) {
+  initializeLiveDebugVariablesPass(*PassRegistry::getPassRegistry());
+}
+
+bool LiveDebugVariables::runOnMachineFunction(MachineFunction &mf) {
+  return false;
+}
diff --git a/lib/CodeGen/LiveDebugVariables.h b/lib/CodeGen/LiveDebugVariables.h
new file mode 100644
index 0000000000..eba4fbede2
--- /dev/null
+++ b/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