1 //===-- llvm/CodeGen/LiveVariables.h - Live Variable Analysis ---*- C++ -*-===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file implements the LiveVariables 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 a 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/ADT/DenseMap.h"
33 #include "llvm/ADT/IndexedMap.h"
34 #include "llvm/ADT/SmallSet.h"
35 #include "llvm/ADT/SmallVector.h"
36 #include "llvm/ADT/SparseBitVector.h"
37 #include "llvm/CodeGen/MachineFunctionPass.h"
38 #include "llvm/CodeGen/MachineInstr.h"
39 #include "llvm/Target/TargetRegisterInfo.h"
43 class MachineBasicBlock;
44 class MachineRegisterInfo;
46 class LiveVariables : public MachineFunctionPass {
48 static char ID; // Pass identification, replacement for typeid
49 LiveVariables() : MachineFunctionPass(ID) {
50 initializeLiveVariablesPass(*PassRegistry::getPassRegistry());
53 /// VarInfo - This represents the regions where a virtual register is live in
54 /// the program. We represent this with three different pieces of
55 /// information: the set of blocks in which the instruction is live
56 /// throughout, the set of blocks in which the instruction is actually used,
57 /// and the set of non-phi instructions that are the last users of the value.
59 /// In the common case where a value is defined and killed in the same block,
60 /// There is one killing instruction, and AliveBlocks is empty.
62 /// Otherwise, the value is live out of the block. If the value is live
63 /// throughout any blocks, these blocks are listed in AliveBlocks. Blocks
64 /// where the liveness range ends are not included in AliveBlocks, instead
65 /// being captured by the Kills set. In these blocks, the value is live into
66 /// the block (unless the value is defined and killed in the same block) and
67 /// lives until the specified instruction. Note that there cannot ever be a
68 /// value whose Kills set contains two instructions from the same basic block.
70 /// PHI nodes complicate things a bit. If a PHI node is the last user of a
71 /// value in one of its predecessor blocks, it is not listed in the kills set,
72 /// but does include the predecessor block in the AliveBlocks set (unless that
73 /// block also defines the value). This leads to the (perfectly sensical)
74 /// situation where a value is defined in a block, and the last use is a phi
75 /// node in the successor. In this case, AliveBlocks is empty (the value is
76 /// not live across any blocks) and Kills is empty (phi nodes are not
77 /// included). This is sensical because the value must be live to the end of
78 /// the block, but is not live in any successor blocks.
80 /// AliveBlocks - Set of blocks in which this value is alive completely
81 /// through. This is a bit set which uses the basic block number as an
84 SparseBitVector<> AliveBlocks;
86 /// Kills - List of MachineInstruction's which are the last use of this
87 /// virtual register (kill it) in their basic block.
89 std::vector<MachineInstr*> Kills;
91 /// removeKill - Delete a kill corresponding to the specified
92 /// machine instruction. Returns true if there was a kill
93 /// corresponding to this instruction, false otherwise.
94 bool removeKill(MachineInstr *MI) {
95 std::vector<MachineInstr*>::iterator
96 I = std::find(Kills.begin(), Kills.end(), MI);
103 /// findKill - Find a kill instruction in MBB. Return NULL if none is found.
104 MachineInstr *findKill(const MachineBasicBlock *MBB) const;
106 /// isLiveIn - Is Reg live in to MBB? This means that Reg is live through
107 /// MBB, or it is killed in MBB. If Reg is only used by PHI instructions in
108 /// MBB, it is not considered live in.
109 bool isLiveIn(const MachineBasicBlock &MBB,
111 MachineRegisterInfo &MRI);
117 /// VirtRegInfo - This list is a mapping from virtual register number to
118 /// variable information.
120 IndexedMap<VarInfo, VirtReg2IndexFunctor> VirtRegInfo;
122 /// PHIJoins - list of virtual registers that are PHI joins. These registers
123 /// may have multiple definitions, and they require special handling when
124 /// building live intervals.
125 SparseBitVector<> PHIJoins;
127 private: // Intermediate data structures
130 MachineRegisterInfo* MRI;
132 const TargetRegisterInfo *TRI;
134 // PhysRegInfo - Keep track of which instruction was the last def of a
135 // physical register. This is a purely local property, because all physical
136 // register references are presumed dead across basic blocks.
137 std::vector<MachineInstr *> PhysRegDef;
139 // PhysRegInfo - Keep track of which instruction was the last use of a
140 // physical register. This is a purely local property, because all physical
141 // register references are presumed dead across basic blocks.
142 std::vector<MachineInstr *> PhysRegUse;
144 std::vector<SmallVector<unsigned, 4>> PHIVarInfo;
146 // DistanceMap - Keep track the distance of a MI from the start of the
147 // current basic block.
148 DenseMap<MachineInstr*, unsigned> DistanceMap;
150 /// HandlePhysRegKill - Add kills of Reg and its sub-registers to the
151 /// uses. Pay special attention to the sub-register uses which may come below
152 /// the last use of the whole register.
153 bool HandlePhysRegKill(unsigned Reg, MachineInstr *MI);
155 /// HandleRegMask - Call HandlePhysRegKill for all registers clobbered by Mask.
156 void HandleRegMask(const MachineOperand&);
158 void HandlePhysRegUse(unsigned Reg, MachineInstr *MI);
159 void HandlePhysRegDef(unsigned Reg, MachineInstr *MI,
160 SmallVectorImpl<unsigned> &Defs);
161 void UpdatePhysRegDefs(MachineInstr *MI, SmallVectorImpl<unsigned> &Defs);
163 /// FindLastRefOrPartRef - Return the last reference or partial reference of
164 /// the specified register.
165 MachineInstr *FindLastRefOrPartRef(unsigned Reg);
167 /// FindLastPartialDef - Return the last partial def of the specified
168 /// register. Also returns the sub-registers that're defined by the
170 MachineInstr *FindLastPartialDef(unsigned Reg,
171 SmallSet<unsigned,4> &PartDefRegs);
173 /// analyzePHINodes - Gather information about the PHI nodes in here. In
174 /// particular, we want to map the variable information of a virtual
175 /// register which is used in a PHI node. We map that to the BB the vreg
177 void analyzePHINodes(const MachineFunction& Fn);
179 void runOnInstr(MachineInstr *MI, SmallVectorImpl<unsigned> &Defs);
181 void runOnBlock(MachineBasicBlock *MBB, unsigned NumRegs);
184 bool runOnMachineFunction(MachineFunction &MF) override;
186 /// RegisterDefIsDead - Return true if the specified instruction defines the
187 /// specified register, but that definition is dead.
188 bool RegisterDefIsDead(MachineInstr *MI, unsigned Reg) const;
190 //===--------------------------------------------------------------------===//
191 // API to update live variable information
193 /// replaceKillInstruction - Update register kill info by replacing a kill
194 /// instruction with a new one.
195 void replaceKillInstruction(unsigned Reg, MachineInstr *OldMI,
196 MachineInstr *NewMI);
198 /// addVirtualRegisterKilled - Add information about the fact that the
199 /// specified register is killed after being used by the specified
200 /// instruction. If AddIfNotFound is true, add a implicit operand if it's
202 void addVirtualRegisterKilled(unsigned IncomingReg, MachineInstr *MI,
203 bool AddIfNotFound = false) {
204 if (MI->addRegisterKilled(IncomingReg, TRI, AddIfNotFound))
205 getVarInfo(IncomingReg).Kills.push_back(MI);
208 /// removeVirtualRegisterKilled - Remove the specified kill of the virtual
209 /// register from the live variable information. Returns true if the
210 /// variable was marked as killed by the specified instruction,
212 bool removeVirtualRegisterKilled(unsigned reg, MachineInstr *MI) {
213 if (!getVarInfo(reg).removeKill(MI))
216 bool Removed = false;
217 for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
218 MachineOperand &MO = MI->getOperand(i);
219 if (MO.isReg() && MO.isKill() && MO.getReg() == reg) {
226 assert(Removed && "Register is not used by this instruction!");
231 /// removeVirtualRegistersKilled - Remove all killed info for the specified
233 void removeVirtualRegistersKilled(MachineInstr *MI);
235 /// addVirtualRegisterDead - Add information about the fact that the specified
236 /// register is dead after being used by the specified instruction. If
237 /// AddIfNotFound is true, add a implicit operand if it's not found.
238 void addVirtualRegisterDead(unsigned IncomingReg, MachineInstr *MI,
239 bool AddIfNotFound = false) {
240 if (MI->addRegisterDead(IncomingReg, TRI, AddIfNotFound))
241 getVarInfo(IncomingReg).Kills.push_back(MI);
244 /// removeVirtualRegisterDead - Remove the specified kill of the virtual
245 /// register from the live variable information. Returns true if the
246 /// variable was marked dead at the specified instruction, false
248 bool removeVirtualRegisterDead(unsigned reg, MachineInstr *MI) {
249 if (!getVarInfo(reg).removeKill(MI))
252 bool Removed = false;
253 for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
254 MachineOperand &MO = MI->getOperand(i);
255 if (MO.isReg() && MO.isDef() && MO.getReg() == reg) {
261 assert(Removed && "Register is not defined by this instruction!");
266 void getAnalysisUsage(AnalysisUsage &AU) const override;
268 void releaseMemory() override {
272 /// getVarInfo - Return the VarInfo structure for the specified VIRTUAL
274 VarInfo &getVarInfo(unsigned RegIdx);
276 void MarkVirtRegAliveInBlock(VarInfo& VRInfo, MachineBasicBlock* DefBlock,
277 MachineBasicBlock *BB);
278 void MarkVirtRegAliveInBlock(VarInfo& VRInfo, MachineBasicBlock* DefBlock,
279 MachineBasicBlock *BB,
280 std::vector<MachineBasicBlock*> &WorkList);
281 void HandleVirtRegDef(unsigned reg, MachineInstr *MI);
282 void HandleVirtRegUse(unsigned reg, MachineBasicBlock *MBB,
285 bool isLiveIn(unsigned Reg, const MachineBasicBlock &MBB) {
286 return getVarInfo(Reg).isLiveIn(MBB, Reg, *MRI);
289 /// isLiveOut - Determine if Reg is live out from MBB, when not considering
290 /// PHI nodes. This means that Reg is either killed by a successor block or
291 /// passed through one.
292 bool isLiveOut(unsigned Reg, const MachineBasicBlock &MBB);
294 /// addNewBlock - Add a new basic block BB between DomBB and SuccBB. All
295 /// variables that are live out of DomBB and live into SuccBB will be marked
296 /// as passing live through BB. This method assumes that the machine code is
297 /// still in SSA form.
298 void addNewBlock(MachineBasicBlock *BB,
299 MachineBasicBlock *DomBB,
300 MachineBasicBlock *SuccBB);
302 /// isPHIJoin - Return true if Reg is a phi join register.
303 bool isPHIJoin(unsigned Reg) { return PHIJoins.test(Reg); }
305 /// setPHIJoin - Mark Reg as a phi join register.
306 void setPHIJoin(unsigned Reg) { PHIJoins.set(Reg); }
309 } // End llvm namespace