Check in LLVM r95781.

1 files changed, 302 insertions, 0 deletions

diff --git a/include/llvm/CodeGen/LiveVariables.h b/include/llvm/CodeGen/LiveVariables.h
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+//===-- llvm/CodeGen/LiveVariables.h - Live Variable Analysis ---*- C++ -*-===//
+//
+//                     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 LiveVariables analysis pass.  For each machine
+// instruction in the function, this pass calculates the set of registers that
+// are immediately dead after the instruction (i.e., the instruction calculates
+// the value, but it is never used) and the set of registers that are used by
+// the instruction, but are never used after the instruction (i.e., they are
+// killed).
+//
+// This class computes live variables using a sparse implementation based on
+// the machine code SSA form.  This class computes live variable information for
+// each virtual and _register allocatable_ physical register in a function.  It
+// uses the dominance properties of SSA form to efficiently compute live
+// variables for virtual registers, and assumes that physical registers are only
+// live within a single basic block (allowing it to do a single local analysis
+// to resolve physical register lifetimes in each basic block).  If a physical
+// register is not register allocatable, it is not tracked.  This is useful for
+// things like the stack pointer and condition codes.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CODEGEN_LIVEVARIABLES_H
+#define LLVM_CODEGEN_LIVEVARIABLES_H
+
+#include "llvm/CodeGen/MachineBasicBlock.h"
+#include "llvm/CodeGen/MachineFunctionPass.h"
+#include "llvm/CodeGen/MachineInstr.h"
+#include "llvm/ADT/BitVector.h"
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/SmallSet.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/SparseBitVector.h"
+
+namespace llvm {
+
+class MachineRegisterInfo;
+class TargetRegisterInfo;
+
+class LiveVariables : public MachineFunctionPass {
+public:
+  static char ID; // Pass identification, replacement for typeid
+  LiveVariables() : MachineFunctionPass(&ID) {}
+
+  /// VarInfo - This represents the regions where a virtual register is live in
+  /// the program.  We represent this with three different pieces of
+  /// information: the set of blocks in which the instruction is live
+  /// throughout, the set of blocks in which the instruction is actually used,
+  /// and the set of non-phi instructions that are the last users of the value.
+  ///
+  /// In the common case where a value is defined and killed in the same block,
+  /// There is one killing instruction, and AliveBlocks is empty.
+  ///
+  /// Otherwise, the value is live out of the block.  If the value is live
+  /// throughout any blocks, these blocks are listed in AliveBlocks.  Blocks
+  /// where the liveness range ends are not included in AliveBlocks, instead
+  /// being captured by the Kills set.  In these blocks, the value is live into
+  /// the block (unless the value is defined and killed in the same block) and
+  /// lives until the specified instruction.  Note that there cannot ever be a
+  /// value whose Kills set contains two instructions from the same basic block.
+  ///
+  /// PHI nodes complicate things a bit.  If a PHI node is the last user of a
+  /// value in one of its predecessor blocks, it is not listed in the kills set,
+  /// but does include the predecessor block in the AliveBlocks set (unless that
+  /// block also defines the value).  This leads to the (perfectly sensical)
+  /// situation where a value is defined in a block, and the last use is a phi
+  /// node in the successor.  In this case, AliveBlocks is empty (the value is
+  /// not live across any  blocks) and Kills is empty (phi nodes are not
+  /// included). This is sensical because the value must be live to the end of
+  /// the block, but is not live in any successor blocks.
+  struct VarInfo {
+    /// AliveBlocks - Set of blocks in which this value is alive completely
+    /// through.  This is a bit set which uses the basic block number as an
+    /// index.
+    ///
+    SparseBitVector<> AliveBlocks;
+
+    /// NumUses - Number of uses of this register across the entire function.
+    ///
+    unsigned NumUses;
+
+    /// Kills - List of MachineInstruction's which are the last use of this
+    /// virtual register (kill it) in their basic block.
+    ///
+    std::vector<MachineInstr*> Kills;
+
+    VarInfo() : NumUses(0) {}
+
+    /// removeKill - Delete a kill corresponding to the specified
+    /// machine instruction. Returns true if there was a kill
+    /// corresponding to this instruction, false otherwise.
+    bool removeKill(MachineInstr *MI) {
+      std::vector<MachineInstr*>::iterator
+        I = std::find(Kills.begin(), Kills.end(), MI);
+      if (I == Kills.end())
+        return false;
+      Kills.erase(I);
+      return true;
+    }
+
+    /// findKill - Find a kill instruction in MBB. Return NULL if none is found.
+    MachineInstr *findKill(const MachineBasicBlock *MBB) const;
+
+    /// isLiveIn - Is Reg live in to MBB? This means that Reg is live through
+    /// MBB, or it is killed in MBB. If Reg is only used by PHI instructions in
+    /// MBB, it is not considered live in.
+    bool isLiveIn(const MachineBasicBlock &MBB,
+                  unsigned Reg,
+                  MachineRegisterInfo &MRI);
+
+    void dump() const;
+  };
+
+private:
+  /// VirtRegInfo - This list is a mapping from virtual register number to
+  /// variable information.  FirstVirtualRegister is subtracted from the virtual
+  /// register number before indexing into this list.
+  ///
+  std::vector<VarInfo> VirtRegInfo;
+
+  /// ReservedRegisters - This vector keeps track of which registers
+  /// are reserved register which are not allocatable by the target machine.
+  /// We can not track liveness for values that are in this set.
+  ///
+  BitVector ReservedRegisters;
+
+private:   // Intermediate data structures
+  MachineFunction *MF;
+
+  MachineRegisterInfo* MRI;
+
+  const TargetRegisterInfo *TRI;
+
+  // PhysRegInfo - Keep track of which instruction was the last def of a
+  // physical register. This is a purely local property, because all physical
+  // register references are presumed dead across basic blocks.
+  MachineInstr **PhysRegDef;
+
+  // PhysRegInfo - Keep track of which instruction was the last use of a
+  // physical register. This is a purely local property, because all physical
+  // register references are presumed dead across basic blocks.
+  MachineInstr **PhysRegUse;
+
+  SmallVector<unsigned, 4> *PHIVarInfo;
+
+  // DistanceMap - Keep track the distance of a MI from the start of the
+  // current basic block.
+  DenseMap<MachineInstr*, unsigned> DistanceMap;
+
+  /// HandlePhysRegKill - Add kills of Reg and its sub-registers to the
+  /// uses. Pay special attention to the sub-register uses which may come below
+  /// the last use of the whole register.
+  bool HandlePhysRegKill(unsigned Reg, MachineInstr *MI);
+
+  void HandlePhysRegUse(unsigned Reg, MachineInstr *MI);
+  void HandlePhysRegDef(unsigned Reg, MachineInstr *MI,
+                        SmallVector<unsigned, 4> &Defs);
+  void UpdatePhysRegDefs(MachineInstr *MI, SmallVector<unsigned, 4> &Defs);
+
+  /// FindLastRefOrPartRef - Return the last reference or partial reference of
+  /// the specified register.
+  MachineInstr *FindLastRefOrPartRef(unsigned Reg);
+
+  /// FindLastPartialDef - Return the last partial def of the specified
+  /// register. Also returns the sub-registers that're defined by the
+  /// instruction.
+  MachineInstr *FindLastPartialDef(unsigned Reg,
+                                   SmallSet<unsigned,4> &PartDefRegs);
+
+  /// analyzePHINodes - Gather information about the PHI nodes in here. In
+  /// particular, we want to map the variable information of a virtual
+  /// register which is used in a PHI node. We map that to the BB the vreg
+  /// is coming from.
+  void analyzePHINodes(const MachineFunction& Fn);
+public:
+
+  virtual bool runOnMachineFunction(MachineFunction &MF);
+
+  /// RegisterDefIsDead - Return true if the specified instruction defines the
+  /// specified register, but that definition is dead.
+  bool RegisterDefIsDead(MachineInstr *MI, unsigned Reg) const;
+
+  //===--------------------------------------------------------------------===//
+  //  API to update live variable information
+
+  /// replaceKillInstruction - Update register kill info by replacing a kill
+  /// instruction with a new one.
+  void replaceKillInstruction(unsigned Reg, MachineInstr *OldMI,
+                              MachineInstr *NewMI);
+
+  /// addVirtualRegisterKilled - Add information about the fact that the
+  /// specified register is killed after being used by the specified
+  /// instruction. If AddIfNotFound is true, add a implicit operand if it's
+  /// not found.
+  void addVirtualRegisterKilled(unsigned IncomingReg, MachineInstr *MI,
+                                bool AddIfNotFound = false) {
+    if (MI->addRegisterKilled(IncomingReg, TRI, AddIfNotFound))
+      getVarInfo(IncomingReg).Kills.push_back(MI); 
+  }
+
+  /// removeVirtualRegisterKilled - Remove the specified kill of the virtual
+  /// register from the live variable information. Returns true if the
+  /// variable was marked as killed by the specified instruction,
+  /// false otherwise.
+  bool removeVirtualRegisterKilled(unsigned reg, MachineInstr *MI) {
+    if (!getVarInfo(reg).removeKill(MI))
+      return false;
+
+    bool Removed = false;
+    for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
+      MachineOperand &MO = MI->getOperand(i);
+      if (MO.isReg() && MO.isKill() && MO.getReg() == reg) {
+        MO.setIsKill(false);
+        Removed = true;
+        break;
+      }
+    }
+
+    assert(Removed && "Register is not used by this instruction!");
+    return true;
+  }
+
+  /// removeVirtualRegistersKilled - Remove all killed info for the specified
+  /// instruction.
+  void removeVirtualRegistersKilled(MachineInstr *MI);
+
+  /// addVirtualRegisterDead - Add information about the fact that the specified
+  /// register is dead after being used by the specified instruction. If
+  /// AddIfNotFound is true, add a implicit operand if it's not found.
+  void addVirtualRegisterDead(unsigned IncomingReg, MachineInstr *MI,
+                              bool AddIfNotFound = false) {
+    if (MI->addRegisterDead(IncomingReg, TRI, AddIfNotFound))
+      getVarInfo(IncomingReg).Kills.push_back(MI);
+  }
+
+  /// removeVirtualRegisterDead - Remove the specified kill of the virtual
+  /// register from the live variable information. Returns true if the
+  /// variable was marked dead at the specified instruction, false
+  /// otherwise.
+  bool removeVirtualRegisterDead(unsigned reg, MachineInstr *MI) {
+    if (!getVarInfo(reg).removeKill(MI))
+      return false;
+
+    bool Removed = false;
+    for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
+      MachineOperand &MO = MI->getOperand(i);
+      if (MO.isReg() && MO.isDef() && MO.getReg() == reg) {
+        MO.setIsDead(false);
+        Removed = true;
+        break;
+      }
+    }
+    assert(Removed && "Register is not defined by this instruction!");
+    return true;
+  }
+  
+  void getAnalysisUsage(AnalysisUsage &AU) const;
+
+  virtual void releaseMemory() {
+    VirtRegInfo.clear();
+  }
+
+  /// getVarInfo - Return the VarInfo structure for the specified VIRTUAL
+  /// register.
+  VarInfo &getVarInfo(unsigned RegIdx);
+
+  void MarkVirtRegAliveInBlock(VarInfo& VRInfo, MachineBasicBlock* DefBlock,
+                               MachineBasicBlock *BB);
+  void MarkVirtRegAliveInBlock(VarInfo& VRInfo, MachineBasicBlock* DefBlock,
+                               MachineBasicBlock *BB,
+                               std::vector<MachineBasicBlock*> &WorkList);
+  void HandleVirtRegDef(unsigned reg, MachineInstr *MI);
+  void HandleVirtRegUse(unsigned reg, MachineBasicBlock *MBB,
+                        MachineInstr *MI);
+
+  bool isLiveIn(unsigned Reg, const MachineBasicBlock &MBB) {
+    return getVarInfo(Reg).isLiveIn(MBB, Reg, *MRI);
+  }
+
+  /// isLiveOut - Determine if Reg is live out from MBB, when not considering
+  /// PHI nodes. This means that Reg is either killed by a successor block or
+  /// passed through one.
+  bool isLiveOut(unsigned Reg, const MachineBasicBlock &MBB);
+
+  /// addNewBlock - Add a new basic block BB between DomBB and SuccBB. All
+  /// variables that are live out of DomBB and live into SuccBB will be marked
+  /// as passing live through BB. This method assumes that the machine code is
+  /// still in SSA form.
+  void addNewBlock(MachineBasicBlock *BB,
+                   MachineBasicBlock *DomBB,
+                   MachineBasicBlock *SuccBB);
+};
+
+} // End llvm namespace
+
+#endif