1 //===- llvm/CodeGen/LivePhysRegs.h - Live Physical Register Set -*- C++ -*-===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 /// \file
10 /// This file implements the LivePhysRegs utility for tracking liveness of
11 /// physical registers. This can be used for ad-hoc liveness tracking after
12 /// register allocation. You can start with the live-ins/live-outs at the
13 /// beginning/end of a block and update the information while walking the
14 /// instructions inside the block. This implementation tracks the liveness on a
15 /// sub-register granularity.
16 ///
17 /// We assume that the high bits of a physical super-register are not preserved
18 /// unless the instruction has an implicit-use operand reading the super-
19 /// register.
20 ///
21 /// X86 Example:
22 /// %ymm0 = ...
23 /// %xmm0 = ... (Kills %xmm0, all %xmm0s sub-registers, and %ymm0)
24 ///
25 /// %ymm0 = ...
26 /// %xmm0 = ..., implicit %ymm0 (%ymm0 and all its sub-registers are alive)
27 //===----------------------------------------------------------------------===//
28
29 #ifndef LLVM_CODEGEN_LIVEPHYSREGS_H
30 #define LLVM_CODEGEN_LIVEPHYSREGS_H
31
32 #include "llvm/ADT/SparseSet.h"
33 #include "llvm/CodeGen/MachineBasicBlock.h"
34 #include "llvm/CodeGen/TargetRegisterInfo.h"
35 #include "llvm/MC/MCRegister.h"
36 #include "llvm/MC/MCRegisterInfo.h"
37 #include <cassert>
38 #include <utility>
39
40 namespace llvm {
41
42 class MachineInstr;
43 class MachineFunction;
44 class MachineOperand;
45 class MachineRegisterInfo;
46 class raw_ostream;
47
48 /// A set of physical registers with utility functions to track liveness
49 /// when walking backward/forward through a basic block.
50 class LivePhysRegs {
51 const TargetRegisterInfo *TRI = nullptr;
52 using RegisterSet = SparseSet<MCPhysReg, identity<MCPhysReg>>;
53 RegisterSet LiveRegs;
54
55 public:
56 /// Constructs an unitialized set. init() needs to be called to initialize it.
57 LivePhysRegs() = default;
58
59 /// Constructs and initializes an empty set.
LivePhysRegs(const TargetRegisterInfo & TRI)60 LivePhysRegs(const TargetRegisterInfo &TRI) : TRI(&TRI) {
61 LiveRegs.setUniverse(TRI.getNumRegs());
62 }
63
64 LivePhysRegs(const LivePhysRegs&) = delete;
65 LivePhysRegs &operator=(const LivePhysRegs&) = delete;
66
67 /// (re-)initializes and clears the set.
init(const TargetRegisterInfo & TRI)68 void init(const TargetRegisterInfo &TRI) {
69 this->TRI = &TRI;
70 LiveRegs.clear();
71 LiveRegs.setUniverse(TRI.getNumRegs());
72 }
73
74 /// Clears the set.
clear()75 void clear() { LiveRegs.clear(); }
76
77 /// Returns true if the set is empty.
empty()78 bool empty() const { return LiveRegs.empty(); }
79
80 /// Adds a physical register and all its sub-registers to the set.
addReg(MCPhysReg Reg)81 void addReg(MCPhysReg Reg) {
82 assert(TRI && "LivePhysRegs is not initialized.");
83 assert(Reg <= TRI->getNumRegs() && "Expected a physical register.");
84 for (MCPhysReg SubReg : TRI->subregs_inclusive(Reg))
85 LiveRegs.insert(SubReg);
86 }
87
88 /// Removes a physical register, all its sub-registers, and all its
89 /// super-registers from the set.
removeReg(MCPhysReg Reg)90 void removeReg(MCPhysReg Reg) {
91 assert(TRI && "LivePhysRegs is not initialized.");
92 assert(Reg <= TRI->getNumRegs() && "Expected a physical register.");
93 for (MCRegAliasIterator R(Reg, TRI, true); R.isValid(); ++R)
94 LiveRegs.erase(*R);
95 }
96
97 /// Removes physical registers clobbered by the regmask operand \p MO.
98 void removeRegsInMask(const MachineOperand &MO,
99 SmallVectorImpl<std::pair<MCPhysReg, const MachineOperand*>> *Clobbers =
100 nullptr);
101
102 /// Returns true if register \p Reg is contained in the set. This also
103 /// works if only the super register of \p Reg has been defined, because
104 /// addReg() always adds all sub-registers to the set as well.
105 /// Note: Returns false if just some sub registers are live, use available()
106 /// when searching a free register.
contains(MCPhysReg Reg)107 bool contains(MCPhysReg Reg) const { return LiveRegs.count(Reg); }
108
109 /// Returns true if register \p Reg and no aliasing register is in the set.
110 bool available(const MachineRegisterInfo &MRI, MCPhysReg Reg) const;
111
112 /// Remove defined registers and regmask kills from the set.
113 void removeDefs(const MachineInstr &MI);
114
115 /// Add uses to the set.
116 void addUses(const MachineInstr &MI);
117
118 /// Simulates liveness when stepping backwards over an instruction(bundle).
119 /// Remove Defs, add uses. This is the recommended way of calculating
120 /// liveness.
121 void stepBackward(const MachineInstr &MI);
122
123 /// Simulates liveness when stepping forward over an instruction(bundle).
124 /// Remove killed-uses, add defs. This is the not recommended way, because it
125 /// depends on accurate kill flags. If possible use stepBackward() instead of
126 /// this function. The clobbers set will be the list of registers either
127 /// defined or clobbered by a regmask. The operand will identify whether this
128 /// is a regmask or register operand.
129 void stepForward(const MachineInstr &MI,
130 SmallVectorImpl<std::pair<MCPhysReg, const MachineOperand*>> &Clobbers);
131
132 /// Adds all live-in registers of basic block \p MBB.
133 /// Live in registers are the registers in the blocks live-in list and the
134 /// pristine registers.
135 void addLiveIns(const MachineBasicBlock &MBB);
136
137 /// Adds all live-in registers of basic block \p MBB but skips pristine
138 /// registers.
139 void addLiveInsNoPristines(const MachineBasicBlock &MBB);
140
141 /// Adds all live-out registers of basic block \p MBB.
142 /// Live out registers are the union of the live-in registers of the successor
143 /// blocks and pristine registers. Live out registers of the end block are the
144 /// callee saved registers.
145 /// If a register is not added by this method, it is guaranteed to not be
146 /// live out from MBB, although a sub-register may be. This is true
147 /// both before and after regalloc.
148 void addLiveOuts(const MachineBasicBlock &MBB);
149
150 /// Adds all live-out registers of basic block \p MBB but skips pristine
151 /// registers.
152 void addLiveOutsNoPristines(const MachineBasicBlock &MBB);
153
154 using const_iterator = RegisterSet::const_iterator;
155
begin()156 const_iterator begin() const { return LiveRegs.begin(); }
end()157 const_iterator end() const { return LiveRegs.end(); }
158
159 /// Prints the currently live registers to \p OS.
160 void print(raw_ostream &OS) const;
161
162 /// Dumps the currently live registers to the debug output.
163 void dump() const;
164
165 private:
166 /// Adds live-in registers from basic block \p MBB, taking associated
167 /// lane masks into consideration.
168 void addBlockLiveIns(const MachineBasicBlock &MBB);
169
170 /// Adds pristine registers. Pristine registers are callee saved registers
171 /// that are unused in the function.
172 void addPristines(const MachineFunction &MF);
173 };
174
175 inline raw_ostream &operator<<(raw_ostream &OS, const LivePhysRegs& LR) {
176 LR.print(OS);
177 return OS;
178 }
179
180 /// Computes registers live-in to \p MBB assuming all of its successors
181 /// live-in lists are up-to-date. Puts the result into the given LivePhysReg
182 /// instance \p LiveRegs.
183 void computeLiveIns(LivePhysRegs &LiveRegs, const MachineBasicBlock &MBB);
184
185 /// Recomputes dead and kill flags in \p MBB.
186 void recomputeLivenessFlags(MachineBasicBlock &MBB);
187
188 /// Adds registers contained in \p LiveRegs to the block live-in list of \p MBB.
189 /// Does not add reserved registers.
190 void addLiveIns(MachineBasicBlock &MBB, const LivePhysRegs &LiveRegs);
191
192 /// Convenience function combining computeLiveIns() and addLiveIns().
193 void computeAndAddLiveIns(LivePhysRegs &LiveRegs,
194 MachineBasicBlock &MBB);
195
196 /// Convenience function for recomputing live-in's for \p MBB.
recomputeLiveIns(MachineBasicBlock & MBB)197 static inline void recomputeLiveIns(MachineBasicBlock &MBB) {
198 LivePhysRegs LPR;
199 MBB.clearLiveIns();
200 computeAndAddLiveIns(LPR, MBB);
201 }
202
203 } // end namespace llvm
204
205 #endif // LLVM_CODEGEN_LIVEPHYSREGS_H
206