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 (MCSubRegIterator SubRegs(Reg, TRI, /*IncludeSelf=*/true);
85 SubRegs.isValid(); ++SubRegs)
86 LiveRegs.insert(*SubRegs);
87 }
88
89 /// Removes a physical register, all its sub-registers, and all its
90 /// super-registers from the set.
removeReg(MCPhysReg Reg)91 void removeReg(MCPhysReg Reg) {
92 assert(TRI && "LivePhysRegs is not initialized.");
93 assert(Reg <= TRI->getNumRegs() && "Expected a physical register.");
94 for (MCRegAliasIterator R(Reg, TRI, true); R.isValid(); ++R)
95 LiveRegs.erase(*R);
96 }
97
98 /// Removes physical registers clobbered by the regmask operand \p MO.
99 void removeRegsInMask(const MachineOperand &MO,
100 SmallVectorImpl<std::pair<MCPhysReg, const MachineOperand*>> *Clobbers =
101 nullptr);
102
103 /// Returns true if register \p Reg is contained in the set. This also
104 /// works if only the super register of \p Reg has been defined, because
105 /// addReg() always adds all sub-registers to the set as well.
106 /// Note: Returns false if just some sub registers are live, use available()
107 /// when searching a free register.
contains(MCPhysReg Reg)108 bool contains(MCPhysReg Reg) const { return LiveRegs.count(Reg); }
109
110 /// Returns true if register \p Reg and no aliasing register is in the set.
111 bool available(const MachineRegisterInfo &MRI, MCPhysReg Reg) const;
112
113 /// Remove defined registers and regmask kills from the set.
114 void removeDefs(const MachineInstr &MI);
115
116 /// Add uses to the set.
117 void addUses(const MachineInstr &MI);
118
119 /// Simulates liveness when stepping backwards over an instruction(bundle).
120 /// Remove Defs, add uses. This is the recommended way of calculating
121 /// liveness.
122 void stepBackward(const MachineInstr &MI);
123
124 /// Simulates liveness when stepping forward over an instruction(bundle).
125 /// Remove killed-uses, add defs. This is the not recommended way, because it
126 /// depends on accurate kill flags. If possible use stepBackward() instead of
127 /// this function. The clobbers set will be the list of registers either
128 /// defined or clobbered by a regmask. The operand will identify whether this
129 /// is a regmask or register operand.
130 void stepForward(const MachineInstr &MI,
131 SmallVectorImpl<std::pair<MCPhysReg, const MachineOperand*>> &Clobbers);
132
133 /// Adds all live-in registers of basic block \p MBB.
134 /// Live in registers are the registers in the blocks live-in list and the
135 /// pristine registers.
136 void addLiveIns(const MachineBasicBlock &MBB);
137
138 /// Adds all live-in registers of basic block \p MBB but skips pristine
139 /// registers.
140 void addLiveInsNoPristines(const MachineBasicBlock &MBB);
141
142 /// Adds all live-out registers of basic block \p MBB.
143 /// Live out registers are the union of the live-in registers of the successor
144 /// blocks and pristine registers. Live out registers of the end block are the
145 /// callee saved registers.
146 /// If a register is not added by this method, it is guaranteed to not be
147 /// live out from MBB, although a sub-register may be. This is true
148 /// both before and after regalloc.
149 void addLiveOuts(const MachineBasicBlock &MBB);
150
151 /// Adds all live-out registers of basic block \p MBB but skips pristine
152 /// registers.
153 void addLiveOutsNoPristines(const MachineBasicBlock &MBB);
154
155 using const_iterator = RegisterSet::const_iterator;
156
begin()157 const_iterator begin() const { return LiveRegs.begin(); }
end()158 const_iterator end() const { return LiveRegs.end(); }
159
160 /// Prints the currently live registers to \p OS.
161 void print(raw_ostream &OS) const;
162
163 /// Dumps the currently live registers to the debug output.
164 void dump() const;
165
166 private:
167 /// Adds live-in registers from basic block \p MBB, taking associated
168 /// lane masks into consideration.
169 void addBlockLiveIns(const MachineBasicBlock &MBB);
170
171 /// Adds pristine registers. Pristine registers are callee saved registers
172 /// that are unused in the function.
173 void addPristines(const MachineFunction &MF);
174 };
175
176 inline raw_ostream &operator<<(raw_ostream &OS, const LivePhysRegs& LR) {
177 LR.print(OS);
178 return OS;
179 }
180
181 /// Computes registers live-in to \p MBB assuming all of its successors
182 /// live-in lists are up-to-date. Puts the result into the given LivePhysReg
183 /// instance \p LiveRegs.
184 void computeLiveIns(LivePhysRegs &LiveRegs, const MachineBasicBlock &MBB);
185
186 /// Recomputes dead and kill flags in \p MBB.
187 void recomputeLivenessFlags(MachineBasicBlock &MBB);
188
189 /// Adds registers contained in \p LiveRegs to the block live-in list of \p MBB.
190 /// Does not add reserved registers.
191 void addLiveIns(MachineBasicBlock &MBB, const LivePhysRegs &LiveRegs);
192
193 /// Convenience function combining computeLiveIns() and addLiveIns().
194 void computeAndAddLiveIns(LivePhysRegs &LiveRegs,
195 MachineBasicBlock &MBB);
196
197 /// Convenience function for recomputing live-in's for \p MBB.
recomputeLiveIns(MachineBasicBlock & MBB)198 static inline void recomputeLiveIns(MachineBasicBlock &MBB) {
199 LivePhysRegs LPR;
200 MBB.clearLiveIns();
201 computeAndAddLiveIns(LPR, MBB);
202 }
203
204 } // end namespace llvm
205
206 #endif // LLVM_CODEGEN_LIVEPHYSREGS_H
207