1 //===-- llvm/CodeGen/LiveVariables.h - Live Variable Analysis ---*- C++ -*-===//
3 // The LLVM Compiler Infrastructure
5 // This file was developed by the LLVM research group and is distributed under
6 // the University of Illinois Open Source License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file implements the LiveVariable analysis pass. For each machine
11 // instruction in the function, this pass calculates the set of registers that
12 // are immediately dead after the instruction (i.e., the instruction calculates
13 // the value, but it is never used) and the set of registers that are used by
14 // the instruction, but are never used after the instruction (i.e., they are
17 // This class computes live variables using are sparse implementation based on
18 // the machine code SSA form. This class computes live variable information for
19 // each virtual and _register allocatable_ physical register in a function. It
20 // uses the dominance properties of SSA form to efficiently compute live
21 // variables for virtual registers, and assumes that physical registers are only
22 // live within a single basic block (allowing it to do a single local analysis
23 // to resolve physical register lifetimes in each basic block). If a physical
24 // register is not register allocatable, it is not tracked. This is useful for
25 // things like the stack pointer and condition codes.
27 //===----------------------------------------------------------------------===//
29 #ifndef LLVM_CODEGEN_LIVEVARIABLES_H
30 #define LLVM_CODEGEN_LIVEVARIABLES_H
32 #include "llvm/CodeGen/MachineFunctionPass.h"
39 class LiveVariables : public MachineFunctionPass {
42 /// DefBlock - The basic block which defines this value...
43 MachineBasicBlock *DefBlock;
44 MachineInstr *DefInst;
46 /// AliveBlocks - Set of blocks of which this value is alive completely
47 /// through. This is a bit set which uses the basic block number as an
50 std::vector<bool> AliveBlocks;
52 /// Kills - List of MachineBasicblock's which contain the last use of this
53 /// virtual register (kill it). This also includes the specific instruction
54 /// which kills the value.
56 std::vector<std::pair<MachineBasicBlock*, MachineInstr*> > Kills;
58 VarInfo() : DefBlock(0), DefInst(0) {}
60 /// removeKill - Delete a kill corresponding to the specified
61 /// machine instruction. Returns true if there was a kill
62 /// corresponding to this instruction, false otherwise.
63 bool removeKill(MachineInstr *MI) {
64 for (std::vector<std::pair<MachineBasicBlock*, MachineInstr*> >::iterator
65 i = Kills.begin(); i != Kills.end(); ++i) {
66 if (i->second == MI) {
76 /// VirtRegInfo - This list is a mapping from virtual register number to
77 /// variable information. FirstVirtualRegister is subtracted from the virtual
78 /// register number before indexing into this list.
80 std::vector<VarInfo> VirtRegInfo;
82 /// RegistersKilled - This multimap keeps track of all of the registers that
83 /// are dead immediately after an instruction reads its operands. If an
84 /// instruction does not have an entry in this map, it kills no registers.
86 std::multimap<MachineInstr*, unsigned> RegistersKilled;
88 /// RegistersDead - This multimap keeps track of all of the registers that are
89 /// dead immediately after an instruction executes, which are not dead after
90 /// the operands are evaluated. In practice, this only contains registers
91 /// which are defined by an instruction, but never used.
93 std::multimap<MachineInstr*, unsigned> RegistersDead;
95 /// AllocatablePhysicalRegisters - This vector keeps track of which registers
96 /// are actually register allocatable by the target machine. We can not track
97 /// liveness for values that are not in this set.
99 std::vector<bool> AllocatablePhysicalRegisters;
101 private: // Intermediate data structures
103 /// BBMap - This provides a numbering of the basic blocks in the function.
105 std::map<MachineBasicBlock*, unsigned> BBMap;
107 /// BBIdxMap - This contains the inverse mapping of BBMap, going from block ID
108 /// numbers to the corresponding MachineBasicBlock. This is lazily computed
109 /// when the getIndexMachineBasicBlock() method is called.
110 std::vector<MachineBasicBlock*> BBIdxMap;
112 const MRegisterInfo *RegInfo;
114 MachineInstr **PhysRegInfo;
117 void HandlePhysRegUse(unsigned Reg, MachineInstr *MI);
118 void HandlePhysRegDef(unsigned Reg, MachineInstr *MI);
122 virtual bool runOnMachineFunction(MachineFunction &MF);
124 /// getMachineBasicBlockIndex - Turn a MachineBasicBlock into an index number
125 /// suitable for use with VarInfo's.
127 unsigned getMachineBasicBlockIndex(MachineBasicBlock *MBB) const {
128 return BBMap.find(MBB)->second;
131 /// getIndexMachineBasicBlock() - Given a block index, return the
132 /// MachineBasicBlock corresponding to it.
133 MachineBasicBlock *getIndexMachineBasicBlock(unsigned Idx);
135 /// killed_iterator - Iterate over registers killed by a machine instruction
137 typedef std::multimap<MachineInstr*, unsigned>::iterator killed_iterator;
139 /// killed_begin/end - Get access to the range of registers killed by a
140 /// machine instruction.
141 killed_iterator killed_begin(MachineInstr *MI) {
142 return RegistersKilled.lower_bound(MI);
144 killed_iterator killed_end(MachineInstr *MI) {
145 return RegistersKilled.upper_bound(MI);
147 std::pair<killed_iterator, killed_iterator>
148 killed_range(MachineInstr *MI) {
149 return RegistersKilled.equal_range(MI);
152 killed_iterator dead_begin(MachineInstr *MI) {
153 return RegistersDead.lower_bound(MI);
155 killed_iterator dead_end(MachineInstr *MI) {
156 return RegistersDead.upper_bound(MI);
158 std::pair<killed_iterator, killed_iterator>
159 dead_range(MachineInstr *MI) {
160 return RegistersDead.equal_range(MI);
163 //===--------------------------------------------------------------------===//
164 // API to update live variable information
166 /// instructionChanged - When the address of an instruction changes, this
167 /// method should be called so that live variables can update its internal
168 /// data structures. This removes the records for OldMI, transfering them to
169 /// the records for NewMI.
170 void instructionChanged(MachineInstr *OldMI, MachineInstr *NewMI);
172 /// addVirtualRegisterKilled - Add information about the fact that the
173 /// specified register is killed after being used by the specified
176 void addVirtualRegisterKilled(unsigned IncomingReg,
177 MachineBasicBlock *MBB,
179 RegistersKilled.insert(std::make_pair(MI, IncomingReg));
180 getVarInfo(IncomingReg).Kills.push_back(std::make_pair(MBB, MI));
183 /// removeVirtualRegisterKilled - Remove the specified virtual
184 /// register from the live variable information. Returns true if the
185 /// variable was marked as killed by the specified instruction,
187 bool removeVirtualRegisterKilled(unsigned reg,
188 MachineBasicBlock *MBB,
190 if (!getVarInfo(reg).removeKill(MI))
192 for (killed_iterator i = killed_begin(MI), e = killed_end(MI); i != e; ) {
193 if (i->second == reg)
194 RegistersKilled.erase(i++);
201 /// removeVirtualRegistersKilled - Remove all of the specified killed
202 /// registers from the live variable information.
203 void removeVirtualRegistersKilled(killed_iterator B, killed_iterator E) {
204 for (killed_iterator I = B; I != E; ++I) { // Remove VarInfo entries...
205 bool removed = getVarInfo(I->second).removeKill(I->first);
206 assert(removed && "kill not in register's VarInfo?");
208 RegistersKilled.erase(B, E);
211 /// addVirtualRegisterDead - Add information about the fact that the specified
212 /// register is dead after being used by the specified instruction.
214 void addVirtualRegisterDead(unsigned IncomingReg,
215 MachineBasicBlock *MBB,
217 RegistersDead.insert(std::make_pair(MI, IncomingReg));
218 getVarInfo(IncomingReg).Kills.push_back(std::make_pair(MBB, MI));
221 /// removeVirtualRegisterDead - Remove the specified virtual
222 /// register from the live variable information. Returns true if the
223 /// variable was marked dead at the specified instruction, false
225 bool removeVirtualRegisterDead(unsigned reg,
226 MachineBasicBlock *MBB,
228 if (!getVarInfo(reg).removeKill(MI))
231 for (killed_iterator i = killed_begin(MI), e = killed_end(MI); i != e; ) {
232 if (i->second == reg)
233 RegistersKilled.erase(i++);
240 /// removeVirtualRegistersDead - Remove all of the specified dead
241 /// registers from the live variable information.
242 void removeVirtualRegistersDead(killed_iterator B, killed_iterator E) {
243 for (killed_iterator I = B; I != E; ++I) // Remove VarInfo entries...
244 getVarInfo(I->second).removeKill(I->first);
245 RegistersDead.erase(B, E);
248 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
249 AU.setPreservesAll();
252 virtual void releaseMemory() {
254 RegistersKilled.clear();
255 RegistersDead.clear();
260 /// getVarInfo - Return the VarInfo structure for the specified VIRTUAL
262 VarInfo &getVarInfo(unsigned RegIdx);
264 const std::vector<bool>& getAllocatablePhysicalRegisters() const {
265 return AllocatablePhysicalRegisters;
268 void MarkVirtRegAliveInBlock(VarInfo &VRInfo, MachineBasicBlock *BB);
269 void HandleVirtRegUse(VarInfo &VRInfo, MachineBasicBlock *MBB,
273 } // End llvm namespace