Codegen: Factor tail duplication into a utility class. NFC

This is in preparation for tail duplication during block placement. See D18226.
This needs to be a utility class for 2 reasons. No passes may run after block
placement, and also, tail-duplication affects subsequent layout decisions, so
it must be interleaved with placement, and can't be separated out into its own
pass. The original pass is still useful, and now runs by delegating to the
utility class.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@265842 91177308-0d34-0410-b5e6-96231b3b80d8

Author: Kyle Butt

include/llvm/CodeGen/TailDuplicator.h

@@ -0,0 +1,88 @@
+//===-- llvm/CodeGen/TailDuplicator.h ---------------------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file defines the TailDuplicator class. Used by the
+// TailDuplication pass, and MachineBlockPlacement.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CODEGEN_TAILDUPLICATOR_H
+#define LLVM_CODEGEN_TAILDUPLICATOR_H
+
+#include "llvm/CodeGen/MachineBranchProbabilityInfo.h"
+#include "llvm/CodeGen/MachineModuleInfo.h"
+#include "llvm/CodeGen/MachineRegisterInfo.h"
+#include "llvm/CodeGen/MachineSSAUpdater.h"
+#include "llvm/CodeGen/RegisterScavenging.h"
+#include "llvm/Target/TargetInstrInfo.h"
+#include "llvm/Target/TargetRegisterInfo.h"
+#include "llvm/Target/TargetSubtargetInfo.h"
+
+namespace llvm {
+
+/// Utility class to perform tail duplication.
+class TailDuplicator {
+  const TargetInstrInfo *TII;
+  const TargetRegisterInfo *TRI;
+  const MachineBranchProbabilityInfo *MBPI;
+  const MachineModuleInfo *MMI;
+  MachineRegisterInfo *MRI;
+  std::unique_ptr<RegScavenger> RS;
+  bool PreRegAlloc;
+
+  // A list of virtual registers for which to update SSA form.
+  SmallVector<unsigned, 16> SSAUpdateVRs;
+
+  // For each virtual register in SSAUpdateVals keep a list of source virtual
+  // registers.
+  typedef std::vector<std::pair<MachineBasicBlock *, unsigned>> AvailableValsTy;
+
+  DenseMap<unsigned, AvailableValsTy> SSAUpdateVals;
+
+public:
+  void initMF(MachineFunction &MF, const MachineModuleInfo *MMI,
+              const MachineBranchProbabilityInfo *MBPI);
+  bool tailDuplicateBlocks(MachineFunction &MF);
+  static bool isSimpleBB(MachineBasicBlock *TailBB);
+  bool shouldTailDuplicate(const MachineFunction &MF, bool IsSimple,
+                           MachineBasicBlock &TailBB);
+  bool tailDuplicateAndUpdate(MachineFunction &MF, bool IsSimple,
+                              MachineBasicBlock *MBB);
+
+private:
+  void addSSAUpdateEntry(unsigned OrigReg, unsigned NewReg,
+                         MachineBasicBlock *BB);
+  void processPHI(MachineInstr *MI, MachineBasicBlock *TailBB,
+                  MachineBasicBlock *PredBB,
+                  DenseMap<unsigned, unsigned> &LocalVRMap,
+                  SmallVectorImpl<std::pair<unsigned, unsigned>> &Copies,
+                  const DenseSet<unsigned> &UsedByPhi, bool Remove);
+  void duplicateInstruction(MachineInstr *MI, MachineBasicBlock *TailBB,
+                            MachineBasicBlock *PredBB, MachineFunction &MF,
+                            DenseMap<unsigned, unsigned> &LocalVRMap,
+                            const DenseSet<unsigned> &UsedByPhi);
+  void updateSuccessorsPHIs(MachineBasicBlock *FromBB, bool isDead,
+                            SmallVectorImpl<MachineBasicBlock *> &TDBBs,
+                            SmallSetVector<MachineBasicBlock *, 8> &Succs);
+  bool canCompletelyDuplicateBB(MachineBasicBlock &BB);
+  bool duplicateSimpleBB(MachineBasicBlock *TailBB,
+                         SmallVectorImpl<MachineBasicBlock *> &TDBBs,
+                         const DenseSet<unsigned> &RegsUsedByPhi,
+                         SmallVectorImpl<MachineInstr *> &Copies);
+  bool tailDuplicate(MachineFunction &MF, bool IsSimple,
+                     MachineBasicBlock *TailBB,
+                     SmallVectorImpl<MachineBasicBlock *> &TDBBs,
+                     SmallVectorImpl<MachineInstr *> &Copies);
+
+  void removeDeadBlock(MachineBasicBlock *MBB);
+};
+
+} // End llvm namespace
+
+#endif

lib/CodeGen/CMakeLists.txt

@@ -114,6 +114,7 @@ add_llvm_library(LLVMCodeGen
   StackProtector.cpp
   StackSlotColoring.cpp
   TailDuplication.cpp
+  TailDuplicator.cpp
   TargetFrameLoweringImpl.cpp
   TargetInstrInfo.cpp
   TargetLoweringBase.cpp