1//==-- llvm/CodeGen/ExecutionDomainFix.h - Execution Domain Fix -*- 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 Execution Domain Fix pass.
10///
11/// Some X86 SSE instructions like mov, and, or, xor are available in different
12/// variants for different operand types. These variant instructions are
13/// equivalent, but on Nehalem and newer cpus there is extra latency
14/// transferring data between integer and floating point domains. ARM cores
15/// have similar issues when they are configured with both VFP and NEON
16/// pipelines.
17///
18/// This pass changes the variant instructions to minimize domain crossings.
19//
20//===----------------------------------------------------------------------===//
21
22#ifndef LLVM_CODEGEN_EXECUTIONDOMAINFIX_H
23#define LLVM_CODEGEN_EXECUTIONDOMAINFIX_H
24
25#include "llvm/ADT/SmallVector.h"
26#include "llvm/CodeGen/LoopTraversal.h"
27#include "llvm/CodeGen/MachineFunctionPass.h"
28#include "llvm/CodeGen/ReachingDefAnalysis.h"
29#include "llvm/CodeGen/TargetRegisterInfo.h"
30
31namespace llvm {
32
33class MachineInstr;
34class TargetInstrInfo;
35
36/// A DomainValue is a bit like LiveIntervals' ValNo, but it also keeps track
37/// of execution domains.
38///
39/// An open DomainValue represents a set of instructions that can still switch
40/// execution domain. Multiple registers may refer to the same open
41/// DomainValue - they will eventually be collapsed to the same execution
42/// domain.
43///
44/// A collapsed DomainValue represents a single register that has been forced
45/// into one of more execution domains. There is a separate collapsed
46/// DomainValue for each register, but it may contain multiple execution
47/// domains. A register value is initially created in a single execution
48/// domain, but if we were forced to pay the penalty of a domain crossing, we
49/// keep track of the fact that the register is now available in multiple
50/// domains.
51struct DomainValue {
52 /// Basic reference counting.
53 unsigned Refs = 0;
54
55 /// Bitmask of available domains. For an open DomainValue, it is the still
56 /// possible domains for collapsing. For a collapsed DomainValue it is the
57 /// domains where the register is available for free.
58 unsigned AvailableDomains;
59
60 /// Pointer to the next DomainValue in a chain. When two DomainValues are
61 /// merged, Victim.Next is set to point to Victor, so old DomainValue
62 /// references can be updated by following the chain.
63 DomainValue *Next;
64
65 /// Twiddleable instructions using or defining these registers.
66 SmallVector<MachineInstr *, 8> Instrs;
67
68 DomainValue() { clear(); }
69
70 /// A collapsed DomainValue has no instructions to twiddle - it simply keeps
71 /// track of the domains where the registers are already available.
72 bool isCollapsed() const { return Instrs.empty(); }
73
74 /// Is domain available?
75 bool hasDomain(unsigned domain) const {
76 assert(domain <
77 static_cast<unsigned>(std::numeric_limits<unsigned>::digits) &&
78 "undefined behavior");
79 return AvailableDomains & (1u << domain);
80 }
81
82 /// Mark domain as available.
83 void addDomain(unsigned domain) {
84 assert(domain <
85 static_cast<unsigned>(std::numeric_limits<unsigned>::digits) &&
86 "undefined behavior");
87 AvailableDomains |= 1u << domain;
88 }
89
90 // Restrict to a single domain available.
91 void setSingleDomain(unsigned domain) {
92 assert(domain <
93 static_cast<unsigned>(std::numeric_limits<unsigned>::digits) &&
94 "undefined behavior");
95 AvailableDomains = 1u << domain;
96 }
97
98 /// Return bitmask of domains that are available and in mask.
99 unsigned getCommonDomains(unsigned mask) const {
100 return AvailableDomains & mask;
101 }
102
103 /// First domain available.
104 unsigned getFirstDomain() const {
105 return llvm::countr_zero(Val: AvailableDomains);
106 }
107
108 /// Clear this DomainValue and point to next which has all its data.
109 void clear() {
110 AvailableDomains = 0;
111 Next = nullptr;
112 Instrs.clear();
113 }
114};
115
116class ExecutionDomainFix : public MachineFunctionPass {
117 SpecificBumpPtrAllocator<DomainValue> Allocator;
118 SmallVector<DomainValue *, 16> Avail;
119
120 const TargetRegisterClass *const RC;
121 MachineFunction *MF = nullptr;
122 const TargetInstrInfo *TII = nullptr;
123 const TargetRegisterInfo *TRI = nullptr;
124 std::vector<SmallVector<int, 1>> AliasMap;
125 const unsigned NumRegs;
126 /// Value currently in each register, or NULL when no value is being tracked.
127 /// This counts as a DomainValue reference.
128 using LiveRegsDVInfo = std::vector<DomainValue *>;
129 LiveRegsDVInfo LiveRegs;
130 /// Keeps domain information for all registers. Note that this
131 /// is different from the usual definition notion of liveness. The CPU
132 /// doesn't care whether or not we consider a register killed.
133 using OutRegsInfoMap = SmallVector<LiveRegsDVInfo, 4>;
134 OutRegsInfoMap MBBOutRegsInfos;
135
136 ReachingDefAnalysis *RDA = nullptr;
137
138public:
139 ExecutionDomainFix(char &PassID, const TargetRegisterClass &RC)
140 : MachineFunctionPass(PassID), RC(&RC), NumRegs(RC.getNumRegs()) {}
141
142 void getAnalysisUsage(AnalysisUsage &AU) const override {
143 AU.setPreservesAll();
144 AU.addRequired<ReachingDefAnalysis>();
145 MachineFunctionPass::getAnalysisUsage(AU);
146 }
147
148 bool runOnMachineFunction(MachineFunction &MF) override;
149
150 MachineFunctionProperties getRequiredProperties() const override {
151 return MachineFunctionProperties().set(
152 MachineFunctionProperties::Property::NoVRegs);
153 }
154
155private:
156 /// Translate TRI register number to a list of indices into our smaller tables
157 /// of interesting registers.
158 iterator_range<SmallVectorImpl<int>::const_iterator>
159 regIndices(unsigned Reg) const;
160
161 /// DomainValue allocation.
162 DomainValue *alloc(int domain = -1);
163
164 /// Add reference to DV.
165 DomainValue *retain(DomainValue *DV) {
166 if (DV)
167 ++DV->Refs;
168 return DV;
169 }
170
171 /// Release a reference to DV. When the last reference is released,
172 /// collapse if needed.
173 void release(DomainValue *);
174
175 /// Follow the chain of dead DomainValues until a live DomainValue is reached.
176 /// Update the referenced pointer when necessary.
177 DomainValue *resolve(DomainValue *&);
178
179 /// Set LiveRegs[rx] = dv, updating reference counts.
180 void setLiveReg(int rx, DomainValue *DV);
181
182 /// Kill register rx, recycle or collapse any DomainValue.
183 void kill(int rx);
184
185 /// Force register rx into domain.
186 void force(int rx, unsigned domain);
187
188 /// Collapse open DomainValue into given domain. If there are multiple
189 /// registers using dv, they each get a unique collapsed DomainValue.
190 void collapse(DomainValue *dv, unsigned domain);
191
192 /// All instructions and registers in B are moved to A, and B is released.
193 bool merge(DomainValue *A, DomainValue *B);
194
195 /// Set up LiveRegs by merging predecessor live-out values.
196 void enterBasicBlock(const LoopTraversal::TraversedMBBInfo &TraversedMBB);
197
198 /// Update live-out values.
199 void leaveBasicBlock(const LoopTraversal::TraversedMBBInfo &TraversedMBB);
200
201 /// Process he given basic block.
202 void processBasicBlock(const LoopTraversal::TraversedMBBInfo &TraversedMBB);
203
204 /// Visit given insturcion.
205 bool visitInstr(MachineInstr *);
206
207 /// Update def-ages for registers defined by MI.
208 /// If Kill is set, also kill off DomainValues clobbered by the defs.
209 void processDefs(MachineInstr *, bool Kill);
210
211 /// A soft instruction can be changed to work in other domains given by mask.
212 void visitSoftInstr(MachineInstr *, unsigned mask);
213
214 /// A hard instruction only works in one domain. All input registers will be
215 /// forced into that domain.
216 void visitHardInstr(MachineInstr *, unsigned domain);
217};
218
219} // namespace llvm
220
221#endif // LLVM_CODEGEN_EXECUTIONDOMAINFIX_H
222

source code of llvm/include/llvm/CodeGen/ExecutionDomainFix.h