1 //===-- GCNPreRAOptimizations.cpp -----------------------------------------===//
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 pass combines split register tuple initialization into a single pseudo:
11 ///
12 /// undef %0.sub1:sreg_64 = S_MOV_B32 1
13 /// %0.sub0:sreg_64 = S_MOV_B32 2
14 /// =>
15 /// %0:sreg_64 = S_MOV_B64_IMM_PSEUDO 0x200000001
16 ///
17 /// This is to allow rematerialization of a value instead of spilling. It is
18 /// supposed to be done after register coalescer to allow it to do its job and
19 /// before actual register allocation to allow rematerialization.
20 ///
21 /// Right now the pass only handles 64 bit SGPRs with immediate initializers,
22 /// although the same shall be possible with other register classes and
23 /// instructions if necessary.
24 ///
25 //===----------------------------------------------------------------------===//
26
27 #include "AMDGPU.h"
28 #include "GCNSubtarget.h"
29 #include "MCTargetDesc/AMDGPUMCTargetDesc.h"
30 #include "llvm/CodeGen/LiveIntervals.h"
31 #include "llvm/CodeGen/MachineFunctionPass.h"
32 #include "llvm/InitializePasses.h"
33
34 using namespace llvm;
35
36 #define DEBUG_TYPE "amdgpu-pre-ra-optimizations"
37
38 namespace {
39
40 class GCNPreRAOptimizations : public MachineFunctionPass {
41 private:
42 const SIInstrInfo *TII;
43 const SIRegisterInfo *TRI;
44 MachineRegisterInfo *MRI;
45 LiveIntervals *LIS;
46
47 bool processReg(Register Reg);
48
49 public:
50 static char ID;
51
GCNPreRAOptimizations()52 GCNPreRAOptimizations() : MachineFunctionPass(ID) {
53 initializeGCNPreRAOptimizationsPass(*PassRegistry::getPassRegistry());
54 }
55
56 bool runOnMachineFunction(MachineFunction &MF) override;
57
getPassName() const58 StringRef getPassName() const override {
59 return "AMDGPU Pre-RA optimizations";
60 }
61
getAnalysisUsage(AnalysisUsage & AU) const62 void getAnalysisUsage(AnalysisUsage &AU) const override {
63 AU.addRequired<LiveIntervalsWrapperPass>();
64 AU.setPreservesAll();
65 MachineFunctionPass::getAnalysisUsage(AU);
66 }
67 };
68
69 } // End anonymous namespace.
70
71 INITIALIZE_PASS_BEGIN(GCNPreRAOptimizations, DEBUG_TYPE,
72 "AMDGPU Pre-RA optimizations", false, false)
73 INITIALIZE_PASS_DEPENDENCY(LiveIntervalsWrapperPass)
74 INITIALIZE_PASS_END(GCNPreRAOptimizations, DEBUG_TYPE, "Pre-RA optimizations",
75 false, false)
76
77 char GCNPreRAOptimizations::ID = 0;
78
79 char &llvm::GCNPreRAOptimizationsID = GCNPreRAOptimizations::ID;
80
createGCNPreRAOptimizationsPass()81 FunctionPass *llvm::createGCNPreRAOptimizationsPass() {
82 return new GCNPreRAOptimizations();
83 }
84
processReg(Register Reg)85 bool GCNPreRAOptimizations::processReg(Register Reg) {
86 MachineInstr *Def0 = nullptr;
87 MachineInstr *Def1 = nullptr;
88 uint64_t Init = 0;
89 bool Changed = false;
90 SmallSet<Register, 32> ModifiedRegs;
91 bool IsAGPRDst = TRI->isAGPRClass(MRI->getRegClass(Reg));
92
93 for (MachineInstr &I : MRI->def_instructions(Reg)) {
94 switch (I.getOpcode()) {
95 default:
96 return false;
97 case AMDGPU::V_ACCVGPR_WRITE_B32_e64:
98 break;
99 case AMDGPU::COPY: {
100 // Some subtargets cannot do an AGPR to AGPR copy directly, and need an
101 // intermdiate temporary VGPR register. Try to find the defining
102 // accvgpr_write to avoid temporary registers.
103
104 if (!IsAGPRDst)
105 return false;
106
107 Register SrcReg = I.getOperand(1).getReg();
108
109 if (!SrcReg.isVirtual())
110 break;
111
112 // Check if source of copy is from another AGPR.
113 bool IsAGPRSrc = TRI->isAGPRClass(MRI->getRegClass(SrcReg));
114 if (!IsAGPRSrc)
115 break;
116
117 // def_instructions() does not look at subregs so it may give us a
118 // different instruction that defines the same vreg but different subreg
119 // so we have to manually check subreg.
120 Register SrcSubReg = I.getOperand(1).getSubReg();
121 for (auto &Def : MRI->def_instructions(SrcReg)) {
122 if (SrcSubReg != Def.getOperand(0).getSubReg())
123 continue;
124
125 if (Def.getOpcode() == AMDGPU::V_ACCVGPR_WRITE_B32_e64) {
126 MachineOperand DefSrcMO = Def.getOperand(1);
127
128 // Immediates are not an issue and can be propagated in
129 // postrapseudos pass. Only handle cases where defining
130 // accvgpr_write source is a vreg.
131 if (DefSrcMO.isReg() && DefSrcMO.getReg().isVirtual()) {
132 // Propagate source reg of accvgpr write to this copy instruction
133 I.getOperand(1).setReg(DefSrcMO.getReg());
134 I.getOperand(1).setSubReg(DefSrcMO.getSubReg());
135
136 // Reg uses were changed, collect unique set of registers to update
137 // live intervals at the end.
138 ModifiedRegs.insert(DefSrcMO.getReg());
139 ModifiedRegs.insert(SrcReg);
140
141 Changed = true;
142 }
143
144 // Found the defining accvgpr_write, stop looking any further.
145 break;
146 }
147 }
148 break;
149 }
150 case AMDGPU::S_MOV_B32:
151 if (I.getOperand(0).getReg() != Reg || !I.getOperand(1).isImm() ||
152 I.getNumOperands() != 2)
153 return false;
154
155 switch (I.getOperand(0).getSubReg()) {
156 default:
157 return false;
158 case AMDGPU::sub0:
159 if (Def0)
160 return false;
161 Def0 = &I;
162 Init |= I.getOperand(1).getImm() & 0xffffffff;
163 break;
164 case AMDGPU::sub1:
165 if (Def1)
166 return false;
167 Def1 = &I;
168 Init |= static_cast<uint64_t>(I.getOperand(1).getImm()) << 32;
169 break;
170 }
171 break;
172 }
173 }
174
175 // For AGPR reg, check if live intervals need to be updated.
176 if (IsAGPRDst) {
177 if (Changed) {
178 for (Register RegToUpdate : ModifiedRegs) {
179 LIS->removeInterval(RegToUpdate);
180 LIS->createAndComputeVirtRegInterval(RegToUpdate);
181 }
182 }
183
184 return Changed;
185 }
186
187 // For SGPR reg, check if we can combine instructions.
188 if (!Def0 || !Def1 || Def0->getParent() != Def1->getParent())
189 return Changed;
190
191 LLVM_DEBUG(dbgs() << "Combining:\n " << *Def0 << " " << *Def1
192 << " =>\n");
193
194 if (SlotIndex::isEarlierInstr(LIS->getInstructionIndex(*Def1),
195 LIS->getInstructionIndex(*Def0)))
196 std::swap(Def0, Def1);
197
198 LIS->RemoveMachineInstrFromMaps(*Def0);
199 LIS->RemoveMachineInstrFromMaps(*Def1);
200 auto NewI = BuildMI(*Def0->getParent(), *Def0, Def0->getDebugLoc(),
201 TII->get(AMDGPU::S_MOV_B64_IMM_PSEUDO), Reg)
202 .addImm(Init);
203
204 Def0->eraseFromParent();
205 Def1->eraseFromParent();
206 LIS->InsertMachineInstrInMaps(*NewI);
207 LIS->removeInterval(Reg);
208 LIS->createAndComputeVirtRegInterval(Reg);
209
210 LLVM_DEBUG(dbgs() << " " << *NewI);
211
212 return true;
213 }
214
runOnMachineFunction(MachineFunction & MF)215 bool GCNPreRAOptimizations::runOnMachineFunction(MachineFunction &MF) {
216 if (skipFunction(MF.getFunction()))
217 return false;
218
219 const GCNSubtarget &ST = MF.getSubtarget<GCNSubtarget>();
220 TII = ST.getInstrInfo();
221 MRI = &MF.getRegInfo();
222 LIS = &getAnalysis<LiveIntervalsWrapperPass>().getLIS();
223 TRI = ST.getRegisterInfo();
224
225 bool Changed = false;
226
227 for (unsigned I = 0, E = MRI->getNumVirtRegs(); I != E; ++I) {
228 Register Reg = Register::index2VirtReg(I);
229 if (!LIS->hasInterval(Reg))
230 continue;
231 const TargetRegisterClass *RC = MRI->getRegClass(Reg);
232 if ((RC->MC->getSizeInBits() != 64 || !TRI->isSGPRClass(RC)) &&
233 (ST.hasGFX90AInsts() || !TRI->isAGPRClass(RC)))
234 continue;
235
236 Changed |= processReg(Reg);
237 }
238
239 return Changed;
240 }
241