File: | lib/Target/AMDGPU/SIModeRegister.cpp |
Warning: | line 48, column 5 Value stored to 'Mode' is never read |
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1 | //===-- SIModeRegister.cpp - Mode Register --------------------------------===// |
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 | /// \file |
9 | /// This pass inserts changes to the Mode register settings as required. |
10 | /// Note that currently it only deals with the Double Precision Floating Point |
11 | /// rounding mode setting, but is intended to be generic enough to be easily |
12 | /// expanded. |
13 | /// |
14 | //===----------------------------------------------------------------------===// |
15 | // |
16 | #include "AMDGPU.h" |
17 | #include "AMDGPUInstrInfo.h" |
18 | #include "AMDGPUSubtarget.h" |
19 | #include "SIInstrInfo.h" |
20 | #include "SIMachineFunctionInfo.h" |
21 | #include "llvm/ADT/Statistic.h" |
22 | #include "llvm/CodeGen/MachineFunctionPass.h" |
23 | #include "llvm/CodeGen/MachineInstrBuilder.h" |
24 | #include "llvm/CodeGen/MachineRegisterInfo.h" |
25 | #include "llvm/IR/Constants.h" |
26 | #include "llvm/IR/Function.h" |
27 | #include "llvm/IR/LLVMContext.h" |
28 | #include "llvm/Support/Debug.h" |
29 | #include "llvm/Support/raw_ostream.h" |
30 | #include "llvm/Target/TargetMachine.h" |
31 | #include <queue> |
32 | |
33 | #define DEBUG_TYPE"si-mode-register" "si-mode-register" |
34 | |
35 | STATISTIC(NumSetregInserted, "Number of setreg of mode register inserted.")static llvm::Statistic NumSetregInserted = {"si-mode-register" , "NumSetregInserted", "Number of setreg of mode register inserted." , {0}, {false}}; |
36 | |
37 | using namespace llvm; |
38 | |
39 | struct Status { |
40 | // Mask is a bitmask where a '1' indicates the corresponding Mode bit has a |
41 | // known value |
42 | unsigned Mask; |
43 | unsigned Mode; |
44 | |
45 | Status() : Mask(0), Mode(0){}; |
46 | |
47 | Status(unsigned Mask, unsigned Mode) : Mask(Mask), Mode(Mode) { |
48 | Mode &= Mask; |
Value stored to 'Mode' is never read | |
49 | }; |
50 | |
51 | // merge two status values such that only values that don't conflict are |
52 | // preserved |
53 | Status merge(const Status &S) const { |
54 | return Status((Mask | S.Mask), ((Mode & ~S.Mask) | (S.Mode & S.Mask))); |
55 | } |
56 | |
57 | // merge an unknown value by using the unknown value's mask to remove bits |
58 | // from the result |
59 | Status mergeUnknown(unsigned newMask) { |
60 | return Status(Mask & ~newMask, Mode & ~newMask); |
61 | } |
62 | |
63 | // intersect two Status values to produce a mode and mask that is a subset |
64 | // of both values |
65 | Status intersect(const Status &S) const { |
66 | unsigned NewMask = (Mask & S.Mask) & (Mode ^ ~S.Mode); |
67 | unsigned NewMode = (Mode & NewMask); |
68 | return Status(NewMask, NewMode); |
69 | } |
70 | |
71 | // produce the delta required to change the Mode to the required Mode |
72 | Status delta(const Status &S) const { |
73 | return Status((S.Mask & (Mode ^ S.Mode)) | (~Mask & S.Mask), S.Mode); |
74 | } |
75 | |
76 | bool operator==(const Status &S) const { |
77 | return (Mask == S.Mask) && (Mode == S.Mode); |
78 | } |
79 | |
80 | bool operator!=(const Status &S) const { return !(*this == S); } |
81 | |
82 | bool isCompatible(Status &S) { |
83 | return ((Mask & S.Mask) == S.Mask) && ((Mode & S.Mask) == S.Mode); |
84 | } |
85 | |
86 | bool isCombinable(Status &S) { |
87 | return !(Mask & S.Mask) || isCompatible(S); |
88 | } |
89 | }; |
90 | |
91 | class BlockData { |
92 | public: |
93 | // The Status that represents the mode register settings required by the |
94 | // FirstInsertionPoint (if any) in this block. Calculated in Phase 1. |
95 | Status Require; |
96 | |
97 | // The Status that represents the net changes to the Mode register made by |
98 | // this block, Calculated in Phase 1. |
99 | Status Change; |
100 | |
101 | // The Status that represents the mode register settings on exit from this |
102 | // block. Calculated in Phase 2. |
103 | Status Exit; |
104 | |
105 | // The Status that represents the intersection of exit Mode register settings |
106 | // from all predecessor blocks. Calculated in Phase 2, and used by Phase 3. |
107 | Status Pred; |
108 | |
109 | // In Phase 1 we record the first instruction that has a mode requirement, |
110 | // which is used in Phase 3 if we need to insert a mode change. |
111 | MachineInstr *FirstInsertionPoint; |
112 | |
113 | BlockData() : FirstInsertionPoint(nullptr) {}; |
114 | }; |
115 | |
116 | namespace { |
117 | |
118 | class SIModeRegister : public MachineFunctionPass { |
119 | public: |
120 | static char ID; |
121 | |
122 | std::vector<std::unique_ptr<BlockData>> BlockInfo; |
123 | std::queue<MachineBasicBlock *> Phase2List; |
124 | |
125 | // The default mode register setting currently only caters for the floating |
126 | // point double precision rounding mode. |
127 | // We currently assume the default rounding mode is Round to Nearest |
128 | // NOTE: this should come from a per function rounding mode setting once such |
129 | // a setting exists. |
130 | unsigned DefaultMode = FP_ROUND_ROUND_TO_NEAREST0; |
131 | Status DefaultStatus = |
132 | Status(FP_ROUND_MODE_DP(0x3)(((0x3) & 0x3) << 2), FP_ROUND_MODE_DP(DefaultMode)(((DefaultMode) & 0x3) << 2)); |
133 | |
134 | public: |
135 | SIModeRegister() : MachineFunctionPass(ID) {} |
136 | |
137 | bool runOnMachineFunction(MachineFunction &MF) override; |
138 | |
139 | void getAnalysisUsage(AnalysisUsage &AU) const override { |
140 | AU.setPreservesCFG(); |
141 | MachineFunctionPass::getAnalysisUsage(AU); |
142 | } |
143 | |
144 | void processBlockPhase1(MachineBasicBlock &MBB, const SIInstrInfo *TII); |
145 | |
146 | void processBlockPhase2(MachineBasicBlock &MBB, const SIInstrInfo *TII); |
147 | |
148 | void processBlockPhase3(MachineBasicBlock &MBB, const SIInstrInfo *TII); |
149 | |
150 | Status getInstructionMode(MachineInstr &MI, const SIInstrInfo *TII); |
151 | |
152 | void insertSetreg(MachineBasicBlock &MBB, MachineInstr *I, |
153 | const SIInstrInfo *TII, Status InstrMode); |
154 | }; |
155 | } // End anonymous namespace. |
156 | |
157 | INITIALIZE_PASS(SIModeRegister, DEBUG_TYPE,static void *initializeSIModeRegisterPassOnce(PassRegistry & Registry) { PassInfo *PI = new PassInfo( "Insert required mode register values" , "si-mode-register", &SIModeRegister::ID, PassInfo::NormalCtor_t (callDefaultCtor<SIModeRegister>), false, false); Registry .registerPass(*PI, true); return PI; } static llvm::once_flag InitializeSIModeRegisterPassFlag; void llvm::initializeSIModeRegisterPass (PassRegistry &Registry) { llvm::call_once(InitializeSIModeRegisterPassFlag , initializeSIModeRegisterPassOnce, std::ref(Registry)); } |
158 | "Insert required mode register values", false, false)static void *initializeSIModeRegisterPassOnce(PassRegistry & Registry) { PassInfo *PI = new PassInfo( "Insert required mode register values" , "si-mode-register", &SIModeRegister::ID, PassInfo::NormalCtor_t (callDefaultCtor<SIModeRegister>), false, false); Registry .registerPass(*PI, true); return PI; } static llvm::once_flag InitializeSIModeRegisterPassFlag; void llvm::initializeSIModeRegisterPass (PassRegistry &Registry) { llvm::call_once(InitializeSIModeRegisterPassFlag , initializeSIModeRegisterPassOnce, std::ref(Registry)); } |
159 | |
160 | char SIModeRegister::ID = 0; |
161 | |
162 | char &llvm::SIModeRegisterID = SIModeRegister::ID; |
163 | |
164 | FunctionPass *llvm::createSIModeRegisterPass() { return new SIModeRegister(); } |
165 | |
166 | // Determine the Mode register setting required for this instruction. |
167 | // Instructions which don't use the Mode register return a null Status. |
168 | // Note this currently only deals with instructions that use the floating point |
169 | // double precision setting. |
170 | Status SIModeRegister::getInstructionMode(MachineInstr &MI, |
171 | const SIInstrInfo *TII) { |
172 | if (TII->usesFPDPRounding(MI)) { |
173 | switch (MI.getOpcode()) { |
174 | case AMDGPU::V_INTERP_P1LL_F16: |
175 | case AMDGPU::V_INTERP_P1LV_F16: |
176 | case AMDGPU::V_INTERP_P2_F16: |
177 | // f16 interpolation instructions need double precision round to zero |
178 | return Status(FP_ROUND_MODE_DP(3)(((3) & 0x3) << 2), |
179 | FP_ROUND_MODE_DP(FP_ROUND_ROUND_TO_ZERO)(((3) & 0x3) << 2)); |
180 | default: |
181 | return DefaultStatus; |
182 | } |
183 | } |
184 | return Status(); |
185 | } |
186 | |
187 | // Insert a setreg instruction to update the Mode register. |
188 | // It is possible (though unlikely) for an instruction to require a change to |
189 | // the value of disjoint parts of the Mode register when we don't know the |
190 | // value of the intervening bits. In that case we need to use more than one |
191 | // setreg instruction. |
192 | void SIModeRegister::insertSetreg(MachineBasicBlock &MBB, MachineInstr *MI, |
193 | const SIInstrInfo *TII, Status InstrMode) { |
194 | while (InstrMode.Mask) { |
195 | unsigned Offset = countTrailingZeros<unsigned>(InstrMode.Mask); |
196 | unsigned Width = countTrailingOnes<unsigned>(InstrMode.Mask >> Offset); |
197 | unsigned Value = (InstrMode.Mode >> Offset) & ((1 << Width) - 1); |
198 | BuildMI(MBB, MI, 0, TII->get(AMDGPU::S_SETREG_IMM32_B32)) |
199 | .addImm(Value) |
200 | .addImm(((Width - 1) << AMDGPU::Hwreg::WIDTH_M1_SHIFT_) | |
201 | (Offset << AMDGPU::Hwreg::OFFSET_SHIFT_) | |
202 | (AMDGPU::Hwreg::ID_MODE << AMDGPU::Hwreg::ID_SHIFT_)); |
203 | ++NumSetregInserted; |
204 | InstrMode.Mask &= ~(((1 << Width) - 1) << Offset); |
205 | } |
206 | } |
207 | |
208 | // In Phase 1 we iterate through the instructions of the block and for each |
209 | // instruction we get its mode usage. If the instruction uses the Mode register |
210 | // we: |
211 | // - update the Change status, which tracks the changes to the Mode register |
212 | // made by this block |
213 | // - if this instruction's requirements are compatible with the current setting |
214 | // of the Mode register we merge the modes |
215 | // - if it isn't compatible and an InsertionPoint isn't set, then we set the |
216 | // InsertionPoint to the current instruction, and we remember the current |
217 | // mode |
218 | // - if it isn't compatible and InsertionPoint is set we insert a seteg before |
219 | // that instruction (unless this instruction forms part of the block's |
220 | // entry requirements in which case the insertion is deferred until Phase 3 |
221 | // when predecessor exit values are known), and move the insertion point to |
222 | // this instruction |
223 | // - if this is a setreg instruction we treat it as an incompatible instruction. |
224 | // This is sub-optimal but avoids some nasty corner cases, and is expected to |
225 | // occur very rarely. |
226 | // - on exit we have set the Require, Change, and initial Exit modes. |
227 | void SIModeRegister::processBlockPhase1(MachineBasicBlock &MBB, |
228 | const SIInstrInfo *TII) { |
229 | auto NewInfo = llvm::make_unique<BlockData>(); |
230 | MachineInstr *InsertionPoint = nullptr; |
231 | // RequirePending is used to indicate whether we are collecting the initial |
232 | // requirements for the block, and need to defer the first InsertionPoint to |
233 | // Phase 3. It is set to false once we have set FirstInsertionPoint, or when |
234 | // we discover an explict setreg that means this block doesn't have any |
235 | // initial requirements. |
236 | bool RequirePending = true; |
237 | Status IPChange; |
238 | for (MachineInstr &MI : MBB) { |
239 | Status InstrMode = getInstructionMode(MI, TII); |
240 | if ((MI.getOpcode() == AMDGPU::S_SETREG_B32) || |
241 | (MI.getOpcode() == AMDGPU::S_SETREG_IMM32_B32)) { |
242 | // We preserve any explicit mode register setreg instruction we encounter, |
243 | // as we assume it has been inserted by a higher authority (this is |
244 | // likely to be a very rare occurrence). |
245 | unsigned Dst = TII->getNamedOperand(MI, AMDGPU::OpName::simm16)->getImm(); |
246 | if (((Dst & AMDGPU::Hwreg::ID_MASK_) >> AMDGPU::Hwreg::ID_SHIFT_) != |
247 | AMDGPU::Hwreg::ID_MODE) |
248 | continue; |
249 | |
250 | unsigned Width = ((Dst & AMDGPU::Hwreg::WIDTH_M1_MASK_) >> |
251 | AMDGPU::Hwreg::WIDTH_M1_SHIFT_) + |
252 | 1; |
253 | unsigned Offset = |
254 | (Dst & AMDGPU::Hwreg::OFFSET_MASK_) >> AMDGPU::Hwreg::OFFSET_SHIFT_; |
255 | unsigned Mask = ((1 << Width) - 1) << Offset; |
256 | |
257 | // If an InsertionPoint is set we will insert a setreg there. |
258 | if (InsertionPoint) { |
259 | insertSetreg(MBB, InsertionPoint, TII, IPChange.delta(NewInfo->Change)); |
260 | InsertionPoint = nullptr; |
261 | } |
262 | // If this is an immediate then we know the value being set, but if it is |
263 | // not an immediate then we treat the modified bits of the mode register |
264 | // as unknown. |
265 | if (MI.getOpcode() == AMDGPU::S_SETREG_IMM32_B32) { |
266 | unsigned Val = TII->getNamedOperand(MI, AMDGPU::OpName::imm)->getImm(); |
267 | unsigned Mode = (Val << Offset) & Mask; |
268 | Status Setreg = Status(Mask, Mode); |
269 | // If we haven't already set the initial requirements for the block we |
270 | // don't need to as the requirements start from this explicit setreg. |
271 | RequirePending = false; |
272 | NewInfo->Change = NewInfo->Change.merge(Setreg); |
273 | } else { |
274 | NewInfo->Change = NewInfo->Change.mergeUnknown(Mask); |
275 | } |
276 | } else if (!NewInfo->Change.isCompatible(InstrMode)) { |
277 | // This instruction uses the Mode register and its requirements aren't |
278 | // compatible with the current mode. |
279 | if (InsertionPoint) { |
280 | // If the required mode change cannot be included in the current |
281 | // InsertionPoint changes, we need a setreg and start a new |
282 | // InsertionPoint. |
283 | if (!IPChange.delta(NewInfo->Change).isCombinable(InstrMode)) { |
284 | if (RequirePending) { |
285 | // This is the first insertionPoint in the block so we will defer |
286 | // the insertion of the setreg to Phase 3 where we know whether or |
287 | // not it is actually needed. |
288 | NewInfo->FirstInsertionPoint = InsertionPoint; |
289 | NewInfo->Require = NewInfo->Change; |
290 | RequirePending = false; |
291 | } else { |
292 | insertSetreg(MBB, InsertionPoint, TII, |
293 | IPChange.delta(NewInfo->Change)); |
294 | IPChange = NewInfo->Change; |
295 | } |
296 | // Set the new InsertionPoint |
297 | InsertionPoint = &MI; |
298 | } |
299 | NewInfo->Change = NewInfo->Change.merge(InstrMode); |
300 | } else { |
301 | // No InsertionPoint is currently set - this is either the first in |
302 | // the block or we have previously seen an explicit setreg. |
303 | InsertionPoint = &MI; |
304 | IPChange = NewInfo->Change; |
305 | NewInfo->Change = NewInfo->Change.merge(InstrMode); |
306 | } |
307 | } |
308 | } |
309 | if (RequirePending) { |
310 | // If we haven't yet set the initial requirements for the block we set them |
311 | // now. |
312 | NewInfo->FirstInsertionPoint = InsertionPoint; |
313 | NewInfo->Require = NewInfo->Change; |
314 | } else if (InsertionPoint) { |
315 | // We need to insert a setreg at the InsertionPoint |
316 | insertSetreg(MBB, InsertionPoint, TII, IPChange.delta(NewInfo->Change)); |
317 | } |
318 | NewInfo->Exit = NewInfo->Change; |
319 | BlockInfo[MBB.getNumber()] = std::move(NewInfo); |
320 | } |
321 | |
322 | // In Phase 2 we revisit each block and calculate the common Mode register |
323 | // value provided by all predecessor blocks. If the Exit value for the block |
324 | // is changed, then we add the successor blocks to the worklist so that the |
325 | // exit value is propagated. |
326 | void SIModeRegister::processBlockPhase2(MachineBasicBlock &MBB, |
327 | const SIInstrInfo *TII) { |
328 | // BlockData *BI = BlockInfo[MBB.getNumber()]; |
329 | unsigned ThisBlock = MBB.getNumber(); |
330 | if (MBB.pred_empty()) { |
331 | // There are no predecessors, so use the default starting status. |
332 | BlockInfo[ThisBlock]->Pred = DefaultStatus; |
333 | } else { |
334 | // Build a status that is common to all the predecessors by intersecting |
335 | // all the predecessor exit status values. |
336 | MachineBasicBlock::pred_iterator P = MBB.pred_begin(), E = MBB.pred_end(); |
337 | MachineBasicBlock &PB = *(*P); |
338 | BlockInfo[ThisBlock]->Pred = BlockInfo[PB.getNumber()]->Exit; |
339 | |
340 | for (P = std::next(P); P != E; P = std::next(P)) { |
341 | MachineBasicBlock *Pred = *P; |
342 | BlockInfo[ThisBlock]->Pred = BlockInfo[ThisBlock]->Pred.intersect(BlockInfo[Pred->getNumber()]->Exit); |
343 | } |
344 | } |
345 | Status TmpStatus = BlockInfo[ThisBlock]->Pred.merge(BlockInfo[ThisBlock]->Change); |
346 | if (BlockInfo[ThisBlock]->Exit != TmpStatus) { |
347 | BlockInfo[ThisBlock]->Exit = TmpStatus; |
348 | // Add the successors to the work list so we can propagate the changed exit |
349 | // status. |
350 | for (MachineBasicBlock::succ_iterator S = MBB.succ_begin(), |
351 | E = MBB.succ_end(); |
352 | S != E; S = std::next(S)) { |
353 | MachineBasicBlock &B = *(*S); |
354 | Phase2List.push(&B); |
355 | } |
356 | } |
357 | } |
358 | |
359 | // In Phase 3 we revisit each block and if it has an insertion point defined we |
360 | // check whether the predecessor mode meets the block's entry requirements. If |
361 | // not we insert an appropriate setreg instruction to modify the Mode register. |
362 | void SIModeRegister::processBlockPhase3(MachineBasicBlock &MBB, |
363 | const SIInstrInfo *TII) { |
364 | // BlockData *BI = BlockInfo[MBB.getNumber()]; |
365 | unsigned ThisBlock = MBB.getNumber(); |
366 | if (!BlockInfo[ThisBlock]->Pred.isCompatible(BlockInfo[ThisBlock]->Require)) { |
367 | Status Delta = BlockInfo[ThisBlock]->Pred.delta(BlockInfo[ThisBlock]->Require); |
368 | if (BlockInfo[ThisBlock]->FirstInsertionPoint) |
369 | insertSetreg(MBB, BlockInfo[ThisBlock]->FirstInsertionPoint, TII, Delta); |
370 | else |
371 | insertSetreg(MBB, &MBB.instr_front(), TII, Delta); |
372 | } |
373 | } |
374 | |
375 | bool SIModeRegister::runOnMachineFunction(MachineFunction &MF) { |
376 | BlockInfo.resize(MF.getNumBlockIDs()); |
377 | const GCNSubtarget &ST = MF.getSubtarget<GCNSubtarget>(); |
378 | const SIInstrInfo *TII = ST.getInstrInfo(); |
379 | |
380 | // Processing is performed in a number of phases |
381 | |
382 | // Phase 1 - determine the initial mode required by each block, and add setreg |
383 | // instructions for intra block requirements. |
384 | for (MachineBasicBlock &BB : MF) |
385 | processBlockPhase1(BB, TII); |
386 | |
387 | // Phase 2 - determine the exit mode from each block. We add all blocks to the |
388 | // list here, but will also add any that need to be revisited during Phase 2 |
389 | // processing. |
390 | for (MachineBasicBlock &BB : MF) |
391 | Phase2List.push(&BB); |
392 | while (!Phase2List.empty()) { |
393 | processBlockPhase2(*Phase2List.front(), TII); |
394 | Phase2List.pop(); |
395 | } |
396 | |
397 | // Phase 3 - add an initial setreg to each block where the required entry mode |
398 | // is not satisfied by the exit mode of all its predecessors. |
399 | for (MachineBasicBlock &BB : MF) |
400 | processBlockPhase3(BB, TII); |
401 | |
402 | BlockInfo.clear(); |
403 | |
404 | return NumSetregInserted > 0; |
405 | } |