1//===- SIPreAllocateWWMRegs.cpp - WWM Register Pre-allocation -------------===//
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/// Pass to pre-allocated WWM registers
11//
12//===----------------------------------------------------------------------===//
13
14#include "AMDGPU.h"
15#include "GCNSubtarget.h"
16#include "MCTargetDesc/AMDGPUMCTargetDesc.h"
17#include "SIMachineFunctionInfo.h"
18#include "llvm/ADT/PostOrderIterator.h"
19#include "llvm/CodeGen/LiveIntervals.h"
20#include "llvm/CodeGen/LiveRegMatrix.h"
21#include "llvm/CodeGen/MachineFrameInfo.h"
22#include "llvm/CodeGen/MachineFunctionPass.h"
23#include "llvm/CodeGen/RegisterClassInfo.h"
24#include "llvm/CodeGen/VirtRegMap.h"
25#include "llvm/InitializePasses.h"
26
27using namespace llvm;
28
29#define DEBUG_TYPE "si-pre-allocate-wwm-regs"
30
31static cl::opt<bool>
32 EnablePreallocateSGPRSpillVGPRs("amdgpu-prealloc-sgpr-spill-vgprs",
33 cl::init(Val: false), cl::Hidden);
34
35namespace {
36
37class SIPreAllocateWWMRegs : public MachineFunctionPass {
38private:
39 const SIInstrInfo *TII;
40 const SIRegisterInfo *TRI;
41 MachineRegisterInfo *MRI;
42 LiveIntervals *LIS;
43 LiveRegMatrix *Matrix;
44 VirtRegMap *VRM;
45 RegisterClassInfo RegClassInfo;
46
47 std::vector<unsigned> RegsToRewrite;
48#ifndef NDEBUG
49 void printWWMInfo(const MachineInstr &MI);
50#endif
51
52public:
53 static char ID;
54
55 SIPreAllocateWWMRegs() : MachineFunctionPass(ID) {
56 initializeSIPreAllocateWWMRegsPass(*PassRegistry::getPassRegistry());
57 }
58
59 bool runOnMachineFunction(MachineFunction &MF) override;
60
61 void getAnalysisUsage(AnalysisUsage &AU) const override {
62 AU.addRequired<LiveIntervalsWrapperPass>();
63 AU.addRequired<VirtRegMap>();
64 AU.addRequired<LiveRegMatrix>();
65 AU.setPreservesAll();
66 MachineFunctionPass::getAnalysisUsage(AU);
67 }
68
69private:
70 bool processDef(MachineOperand &MO);
71 void rewriteRegs(MachineFunction &MF);
72};
73
74} // End anonymous namespace.
75
76INITIALIZE_PASS_BEGIN(SIPreAllocateWWMRegs, DEBUG_TYPE,
77 "SI Pre-allocate WWM Registers", false, false)
78INITIALIZE_PASS_DEPENDENCY(LiveIntervalsWrapperPass)
79INITIALIZE_PASS_DEPENDENCY(VirtRegMap)
80INITIALIZE_PASS_DEPENDENCY(LiveRegMatrix)
81INITIALIZE_PASS_END(SIPreAllocateWWMRegs, DEBUG_TYPE,
82 "SI Pre-allocate WWM Registers", false, false)
83
84char SIPreAllocateWWMRegs::ID = 0;
85
86char &llvm::SIPreAllocateWWMRegsID = SIPreAllocateWWMRegs::ID;
87
88FunctionPass *llvm::createSIPreAllocateWWMRegsPass() {
89 return new SIPreAllocateWWMRegs();
90}
91
92bool SIPreAllocateWWMRegs::processDef(MachineOperand &MO) {
93 Register Reg = MO.getReg();
94 if (Reg.isPhysical())
95 return false;
96
97 if (!TRI->isVGPR(MRI: *MRI, Reg))
98 return false;
99
100 if (VRM->hasPhys(virtReg: Reg))
101 return false;
102
103 LiveInterval &LI = LIS->getInterval(Reg);
104
105 for (MCRegister PhysReg : RegClassInfo.getOrder(RC: MRI->getRegClass(Reg))) {
106 if (!MRI->isPhysRegUsed(PhysReg, /*SkipRegMaskTest=*/true) &&
107 Matrix->checkInterference(VirtReg: LI, PhysReg) == LiveRegMatrix::IK_Free) {
108 Matrix->assign(VirtReg: LI, PhysReg);
109 assert(PhysReg != 0);
110 RegsToRewrite.push_back(x: Reg);
111 return true;
112 }
113 }
114
115 llvm_unreachable("physreg not found for WWM expression");
116}
117
118void SIPreAllocateWWMRegs::rewriteRegs(MachineFunction &MF) {
119 for (MachineBasicBlock &MBB : MF) {
120 for (MachineInstr &MI : MBB) {
121 for (MachineOperand &MO : MI.operands()) {
122 if (!MO.isReg())
123 continue;
124
125 const Register VirtReg = MO.getReg();
126 if (VirtReg.isPhysical())
127 continue;
128
129 if (!VRM->hasPhys(virtReg: VirtReg))
130 continue;
131
132 Register PhysReg = VRM->getPhys(virtReg: VirtReg);
133 const unsigned SubReg = MO.getSubReg();
134 if (SubReg != 0) {
135 PhysReg = TRI->getSubReg(Reg: PhysReg, Idx: SubReg);
136 MO.setSubReg(0);
137 }
138
139 MO.setReg(PhysReg);
140 MO.setIsRenamable(false);
141 }
142 }
143 }
144
145 SIMachineFunctionInfo *MFI = MF.getInfo<SIMachineFunctionInfo>();
146
147 for (unsigned Reg : RegsToRewrite) {
148 LIS->removeInterval(Reg);
149
150 const Register PhysReg = VRM->getPhys(virtReg: Reg);
151 assert(PhysReg != 0);
152
153 MFI->reserveWWMRegister(Reg: PhysReg);
154 }
155
156 RegsToRewrite.clear();
157
158 // Update the set of reserved registers to include WWM ones.
159 MRI->freezeReservedRegs();
160}
161
162#ifndef NDEBUG
163LLVM_DUMP_METHOD void
164SIPreAllocateWWMRegs::printWWMInfo(const MachineInstr &MI) {
165
166 unsigned Opc = MI.getOpcode();
167
168 if (Opc == AMDGPU::ENTER_STRICT_WWM || Opc == AMDGPU::ENTER_STRICT_WQM) {
169 dbgs() << "Entering ";
170 } else {
171 assert(Opc == AMDGPU::EXIT_STRICT_WWM || Opc == AMDGPU::EXIT_STRICT_WQM);
172 dbgs() << "Exiting ";
173 }
174
175 if (Opc == AMDGPU::ENTER_STRICT_WWM || Opc == AMDGPU::EXIT_STRICT_WWM) {
176 dbgs() << "Strict WWM ";
177 } else {
178 assert(Opc == AMDGPU::ENTER_STRICT_WQM || Opc == AMDGPU::EXIT_STRICT_WQM);
179 dbgs() << "Strict WQM ";
180 }
181
182 dbgs() << "region: " << MI;
183}
184
185#endif
186
187bool SIPreAllocateWWMRegs::runOnMachineFunction(MachineFunction &MF) {
188 LLVM_DEBUG(dbgs() << "SIPreAllocateWWMRegs: function " << MF.getName() << "\n");
189
190 const GCNSubtarget &ST = MF.getSubtarget<GCNSubtarget>();
191
192 TII = ST.getInstrInfo();
193 TRI = &TII->getRegisterInfo();
194 MRI = &MF.getRegInfo();
195
196 LIS = &getAnalysis<LiveIntervalsWrapperPass>().getLIS();
197 Matrix = &getAnalysis<LiveRegMatrix>();
198 VRM = &getAnalysis<VirtRegMap>();
199
200 RegClassInfo.runOnMachineFunction(MF);
201
202 bool PreallocateSGPRSpillVGPRs =
203 EnablePreallocateSGPRSpillVGPRs ||
204 MF.getFunction().hasFnAttribute(Kind: "amdgpu-prealloc-sgpr-spill-vgprs");
205
206 bool RegsAssigned = false;
207
208 // We use a reverse post-order traversal of the control-flow graph to
209 // guarantee that we visit definitions in dominance order. Since WWM
210 // expressions are guaranteed to never involve phi nodes, and we can only
211 // escape WWM through the special WWM instruction, this means that this is a
212 // perfect elimination order, so we can never do any better.
213 ReversePostOrderTraversal<MachineFunction*> RPOT(&MF);
214
215 for (MachineBasicBlock *MBB : RPOT) {
216 bool InWWM = false;
217 for (MachineInstr &MI : *MBB) {
218 if (MI.getOpcode() == AMDGPU::V_SET_INACTIVE_B32 ||
219 MI.getOpcode() == AMDGPU::V_SET_INACTIVE_B64)
220 RegsAssigned |= processDef(MO&: MI.getOperand(i: 0));
221
222 if (MI.getOpcode() == AMDGPU::SI_SPILL_S32_TO_VGPR) {
223 if (!PreallocateSGPRSpillVGPRs)
224 continue;
225 RegsAssigned |= processDef(MO&: MI.getOperand(i: 0));
226 }
227
228 if (MI.getOpcode() == AMDGPU::ENTER_STRICT_WWM ||
229 MI.getOpcode() == AMDGPU::ENTER_STRICT_WQM) {
230 LLVM_DEBUG(printWWMInfo(MI));
231 InWWM = true;
232 continue;
233 }
234
235 if (MI.getOpcode() == AMDGPU::EXIT_STRICT_WWM ||
236 MI.getOpcode() == AMDGPU::EXIT_STRICT_WQM) {
237 LLVM_DEBUG(printWWMInfo(MI));
238 InWWM = false;
239 }
240
241 if (!InWWM)
242 continue;
243
244 LLVM_DEBUG(dbgs() << "Processing " << MI);
245
246 for (MachineOperand &DefOpnd : MI.defs()) {
247 RegsAssigned |= processDef(MO&: DefOpnd);
248 }
249 }
250 }
251
252 if (!RegsAssigned)
253 return false;
254
255 rewriteRegs(MF);
256 return true;
257}
258