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Revert r354244 "[DAGCombiner] Eliminate dead stores to stack."
[llvm-complete.git] / lib / Target / X86 / X86AvoidStoreForwardingBlocks.cpp
blob3ac0b1ae5143d7aaaec5b7275698cd113b53ab4e
1 //===- X86AvoidStoreForwardingBlockis.cpp - Avoid HW Store Forward Block --===//
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 // If a load follows a store and reloads data that the store has written to
10 // memory, Intel microarchitectures can in many cases forward the data directly
11 // from the store to the load, This "store forwarding" saves cycles by enabling
12 // the load to directly obtain the data instead of accessing the data from
13 // cache or memory.
14 // A "store forward block" occurs in cases that a store cannot be forwarded to
15 // the load. The most typical case of store forward block on Intel Core
16 // microarchitecture that a small store cannot be forwarded to a large load.
17 // The estimated penalty for a store forward block is ~13 cycles.
18 //
19 // This pass tries to recognize and handle cases where "store forward block"
20 // is created by the compiler when lowering memcpy calls to a sequence
21 // of a load and a store.
22 //
23 // The pass currently only handles cases where memcpy is lowered to
24 // XMM/YMM registers, it tries to break the memcpy into smaller copies.
25 // breaking the memcpy should be possible since there is no atomicity
26 // guarantee for loads and stores to XMM/YMM.
27 //
28 // It could be better for performance to solve the problem by loading
29 // to XMM/YMM then inserting the partial store before storing back from XMM/YMM
30 // to memory, but this will result in a more conservative optimization since it
31 // requires we prove that all memory accesses between the blocking store and the
32 // load must alias/don't alias before we can move the store, whereas the
33 // transformation done here is correct regardless to other memory accesses.
34 //===----------------------------------------------------------------------===//
35
36 #include "X86InstrInfo.h"
37 #include "X86Subtarget.h"
38 #include "llvm/CodeGen/MachineBasicBlock.h"
39 #include "llvm/CodeGen/MachineFunction.h"
40 #include "llvm/CodeGen/MachineFunctionPass.h"
41 #include "llvm/CodeGen/MachineInstr.h"
42 #include "llvm/CodeGen/MachineInstrBuilder.h"
43 #include "llvm/CodeGen/MachineOperand.h"
44 #include "llvm/CodeGen/MachineRegisterInfo.h"
45 #include "llvm/IR/DebugInfoMetadata.h"
46 #include "llvm/IR/DebugLoc.h"
47 #include "llvm/IR/Function.h"
48 #include "llvm/MC/MCInstrDesc.h"
49
50 using namespace llvm;
51
52 #define DEBUG_TYPE "x86-avoid-SFB"
53
54 static cl::opt<bool> DisableX86AvoidStoreForwardBlocks(
55 "x86-disable-avoid-SFB", cl::Hidden,
56 cl::desc("X86: Disable Store Forwarding Blocks fixup."), cl::init(false));
57
58 static cl::opt<unsigned> X86AvoidSFBInspectionLimit(
59 "x86-sfb-inspection-limit",
60 cl::desc("X86: Number of instructions backward to "
61 "inspect for store forwarding blocks."),
62 cl::init(20), cl::Hidden);
63
64 namespace {
65
66 using DisplacementSizeMap = std::map<int64_t, unsigned>;
67
68 class X86AvoidSFBPass : public MachineFunctionPass {
69 public:
70 static char ID;
71 X86AvoidSFBPass() : MachineFunctionPass(ID) {
72 initializeX86AvoidSFBPassPass(*PassRegistry::getPassRegistry());
73 }
74
75 StringRef getPassName() const override {
76 return "X86 Avoid Store Forwarding Blocks";
77 }
78
79 bool runOnMachineFunction(MachineFunction &MF) override;
80
81 void getAnalysisUsage(AnalysisUsage &AU) const override {
82 MachineFunctionPass::getAnalysisUsage(AU);
83 AU.addRequired<AAResultsWrapperPass>();
84 }
85
86 private:
87 MachineRegisterInfo *MRI;
88 const X86InstrInfo *TII;
89 const X86RegisterInfo *TRI;
90 SmallVector<std::pair<MachineInstr *, MachineInstr *>, 2>
91 BlockedLoadsStoresPairs;
92 SmallVector<MachineInstr *, 2> ForRemoval;
93 AliasAnalysis *AA;
94
95 /// Returns couples of Load then Store to memory which look
96 /// like a memcpy.
97 void findPotentiallylBlockedCopies(MachineFunction &MF);
98 /// Break the memcpy's load and store into smaller copies
99 /// such that each memory load that was blocked by a smaller store
100 /// would now be copied separately.
101 void breakBlockedCopies(MachineInstr *LoadInst, MachineInstr *StoreInst,
102 const DisplacementSizeMap &BlockingStoresDispSizeMap);
103 /// Break a copy of size Size to smaller copies.
104 void buildCopies(int Size, MachineInstr *LoadInst, int64_t LdDispImm,
105 MachineInstr *StoreInst, int64_t StDispImm,
106 int64_t LMMOffset, int64_t SMMOffset);
107
108 void buildCopy(MachineInstr *LoadInst, unsigned NLoadOpcode, int64_t LoadDisp,
109 MachineInstr *StoreInst, unsigned NStoreOpcode,
110 int64_t StoreDisp, unsigned Size, int64_t LMMOffset,
111 int64_t SMMOffset);
112
113 bool alias(const MachineMemOperand &Op1, const MachineMemOperand &Op2) const;
114
115 unsigned getRegSizeInBytes(MachineInstr *Inst);
116 };
117
118 } // end anonymous namespace
119
120 char X86AvoidSFBPass::ID = 0;
121
122 INITIALIZE_PASS_BEGIN(X86AvoidSFBPass, DEBUG_TYPE, "Machine code sinking",
123 false, false)
124 INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass)
125 INITIALIZE_PASS_END(X86AvoidSFBPass, DEBUG_TYPE, "Machine code sinking", false,
126 false)
127
128 FunctionPass *llvm::createX86AvoidStoreForwardingBlocks() {
129 return new X86AvoidSFBPass();
130 }
131
132 static bool isXMMLoadOpcode(unsigned Opcode) {
133 return Opcode == X86::MOVUPSrm || Opcode == X86::MOVAPSrm ||
134 Opcode == X86::VMOVUPSrm || Opcode == X86::VMOVAPSrm ||
135 Opcode == X86::VMOVUPDrm || Opcode == X86::VMOVAPDrm ||
136 Opcode == X86::VMOVDQUrm || Opcode == X86::VMOVDQArm ||
137 Opcode == X86::VMOVUPSZ128rm || Opcode == X86::VMOVAPSZ128rm ||
138 Opcode == X86::VMOVUPDZ128rm || Opcode == X86::VMOVAPDZ128rm ||
139 Opcode == X86::VMOVDQU64Z128rm || Opcode == X86::VMOVDQA64Z128rm ||
140 Opcode == X86::VMOVDQU32Z128rm || Opcode == X86::VMOVDQA32Z128rm;
141 }
142 static bool isYMMLoadOpcode(unsigned Opcode) {
143 return Opcode == X86::VMOVUPSYrm || Opcode == X86::VMOVAPSYrm ||
144 Opcode == X86::VMOVUPDYrm || Opcode == X86::VMOVAPDYrm ||
145 Opcode == X86::VMOVDQUYrm || Opcode == X86::VMOVDQAYrm ||
146 Opcode == X86::VMOVUPSZ256rm || Opcode == X86::VMOVAPSZ256rm ||
147 Opcode == X86::VMOVUPDZ256rm || Opcode == X86::VMOVAPDZ256rm ||
148 Opcode == X86::VMOVDQU64Z256rm || Opcode == X86::VMOVDQA64Z256rm ||
149 Opcode == X86::VMOVDQU32Z256rm || Opcode == X86::VMOVDQA32Z256rm;
150 }
151
152 static bool isPotentialBlockedMemCpyLd(unsigned Opcode) {
153 return isXMMLoadOpcode(Opcode) || isYMMLoadOpcode(Opcode);
154 }
155
156 static bool isPotentialBlockedMemCpyPair(int LdOpcode, int StOpcode) {
157 switch (LdOpcode) {
158 case X86::MOVUPSrm:
159 case X86::MOVAPSrm:
160 return StOpcode == X86::MOVUPSmr || StOpcode == X86::MOVAPSmr;
161 case X86::VMOVUPSrm:
162 case X86::VMOVAPSrm:
163 return StOpcode == X86::VMOVUPSmr || StOpcode == X86::VMOVAPSmr;
164 case X86::VMOVUPDrm:
165 case X86::VMOVAPDrm:
166 return StOpcode == X86::VMOVUPDmr || StOpcode == X86::VMOVAPDmr;
167 case X86::VMOVDQUrm:
168 case X86::VMOVDQArm:
169 return StOpcode == X86::VMOVDQUmr || StOpcode == X86::VMOVDQAmr;
170 case X86::VMOVUPSZ128rm:
171 case X86::VMOVAPSZ128rm:
172 return StOpcode == X86::VMOVUPSZ128mr || StOpcode == X86::VMOVAPSZ128mr;
173 case X86::VMOVUPDZ128rm:
174 case X86::VMOVAPDZ128rm:
175 return StOpcode == X86::VMOVUPDZ128mr || StOpcode == X86::VMOVAPDZ128mr;
176 case X86::VMOVUPSYrm:
177 case X86::VMOVAPSYrm:
178 return StOpcode == X86::VMOVUPSYmr || StOpcode == X86::VMOVAPSYmr;
179 case X86::VMOVUPDYrm:
180 case X86::VMOVAPDYrm:
181 return StOpcode == X86::VMOVUPDYmr || StOpcode == X86::VMOVAPDYmr;
182 case X86::VMOVDQUYrm:
183 case X86::VMOVDQAYrm:
184 return StOpcode == X86::VMOVDQUYmr || StOpcode == X86::VMOVDQAYmr;
185 case X86::VMOVUPSZ256rm:
186 case X86::VMOVAPSZ256rm:
187 return StOpcode == X86::VMOVUPSZ256mr || StOpcode == X86::VMOVAPSZ256mr;
188 case X86::VMOVUPDZ256rm:
189 case X86::VMOVAPDZ256rm:
190 return StOpcode == X86::VMOVUPDZ256mr || StOpcode == X86::VMOVAPDZ256mr;
191 case X86::VMOVDQU64Z128rm:
192 case X86::VMOVDQA64Z128rm:
193 return StOpcode == X86::VMOVDQU64Z128mr || StOpcode == X86::VMOVDQA64Z128mr;
194 case X86::VMOVDQU32Z128rm:
195 case X86::VMOVDQA32Z128rm:
196 return StOpcode == X86::VMOVDQU32Z128mr || StOpcode == X86::VMOVDQA32Z128mr;
197 case X86::VMOVDQU64Z256rm:
198 case X86::VMOVDQA64Z256rm:
199 return StOpcode == X86::VMOVDQU64Z256mr || StOpcode == X86::VMOVDQA64Z256mr;
200 case X86::VMOVDQU32Z256rm:
201 case X86::VMOVDQA32Z256rm:
202 return StOpcode == X86::VMOVDQU32Z256mr || StOpcode == X86::VMOVDQA32Z256mr;
203 default:
204 return false;
205 }
206 }
207
208 static bool isPotentialBlockingStoreInst(int Opcode, int LoadOpcode) {
209 bool PBlock = false;
210 PBlock |= Opcode == X86::MOV64mr || Opcode == X86::MOV64mi32 ||
211 Opcode == X86::MOV32mr || Opcode == X86::MOV32mi ||
212 Opcode == X86::MOV16mr || Opcode == X86::MOV16mi ||
213 Opcode == X86::MOV8mr || Opcode == X86::MOV8mi;
214 if (isYMMLoadOpcode(LoadOpcode))
215 PBlock |= Opcode == X86::VMOVUPSmr || Opcode == X86::VMOVAPSmr ||
216 Opcode == X86::VMOVUPDmr || Opcode == X86::VMOVAPDmr ||
217 Opcode == X86::VMOVDQUmr || Opcode == X86::VMOVDQAmr ||
218 Opcode == X86::VMOVUPSZ128mr || Opcode == X86::VMOVAPSZ128mr ||
219 Opcode == X86::VMOVUPDZ128mr || Opcode == X86::VMOVAPDZ128mr ||
220 Opcode == X86::VMOVDQU64Z128mr ||
221 Opcode == X86::VMOVDQA64Z128mr ||
222 Opcode == X86::VMOVDQU32Z128mr || Opcode == X86::VMOVDQA32Z128mr;
223 return PBlock;
224 }
225
226 static const int MOV128SZ = 16;
227 static const int MOV64SZ = 8;
228 static const int MOV32SZ = 4;
229 static const int MOV16SZ = 2;
230 static const int MOV8SZ = 1;
231
232 static unsigned getYMMtoXMMLoadOpcode(unsigned LoadOpcode) {
233 switch (LoadOpcode) {
234 case X86::VMOVUPSYrm:
235 case X86::VMOVAPSYrm:
236 return X86::VMOVUPSrm;
237 case X86::VMOVUPDYrm:
238 case X86::VMOVAPDYrm:
239 return X86::VMOVUPDrm;
240 case X86::VMOVDQUYrm:
241 case X86::VMOVDQAYrm:
242 return X86::VMOVDQUrm;
243 case X86::VMOVUPSZ256rm:
244 case X86::VMOVAPSZ256rm:
245 return X86::VMOVUPSZ128rm;
246 case X86::VMOVUPDZ256rm:
247 case X86::VMOVAPDZ256rm:
248 return X86::VMOVUPDZ128rm;
249 case X86::VMOVDQU64Z256rm:
250 case X86::VMOVDQA64Z256rm:
251 return X86::VMOVDQU64Z128rm;
252 case X86::VMOVDQU32Z256rm:
253 case X86::VMOVDQA32Z256rm:
254 return X86::VMOVDQU32Z128rm;
255 default:
256 llvm_unreachable("Unexpected Load Instruction Opcode");
257 }
258 return 0;
259 }
260
261 static unsigned getYMMtoXMMStoreOpcode(unsigned StoreOpcode) {
262 switch (StoreOpcode) {
263 case X86::VMOVUPSYmr:
264 case X86::VMOVAPSYmr:
265 return X86::VMOVUPSmr;
266 case X86::VMOVUPDYmr:
267 case X86::VMOVAPDYmr:
268 return X86::VMOVUPDmr;
269 case X86::VMOVDQUYmr:
270 case X86::VMOVDQAYmr:
271 return X86::VMOVDQUmr;
272 case X86::VMOVUPSZ256mr:
273 case X86::VMOVAPSZ256mr:
274 return X86::VMOVUPSZ128mr;
275 case X86::VMOVUPDZ256mr:
276 case X86::VMOVAPDZ256mr:
277 return X86::VMOVUPDZ128mr;
278 case X86::VMOVDQU64Z256mr:
279 case X86::VMOVDQA64Z256mr:
280 return X86::VMOVDQU64Z128mr;
281 case X86::VMOVDQU32Z256mr:
282 case X86::VMOVDQA32Z256mr:
283 return X86::VMOVDQU32Z128mr;
284 default:
285 llvm_unreachable("Unexpected Load Instruction Opcode");
286 }
287 return 0;
288 }
289
290 static int getAddrOffset(MachineInstr *MI) {
291 const MCInstrDesc &Descl = MI->getDesc();
292 int AddrOffset = X86II::getMemoryOperandNo(Descl.TSFlags);
293 assert(AddrOffset != -1 && "Expected Memory Operand");
294 AddrOffset += X86II::getOperandBias(Descl);
295 return AddrOffset;
296 }
297
298 static MachineOperand &getBaseOperand(MachineInstr *MI) {
299 int AddrOffset = getAddrOffset(MI);
300 return MI->getOperand(AddrOffset + X86::AddrBaseReg);
301 }
302
303 static MachineOperand &getDispOperand(MachineInstr *MI) {
304 int AddrOffset = getAddrOffset(MI);
305 return MI->getOperand(AddrOffset + X86::AddrDisp);
306 }
307
308 // Relevant addressing modes contain only base register and immediate
309 // displacement or frameindex and immediate displacement.
310 // TODO: Consider expanding to other addressing modes in the future
311 static bool isRelevantAddressingMode(MachineInstr *MI) {
312 int AddrOffset = getAddrOffset(MI);
313 MachineOperand &Base = getBaseOperand(MI);
314 MachineOperand &Disp = getDispOperand(MI);
315 MachineOperand &Scale = MI->getOperand(AddrOffset + X86::AddrScaleAmt);
316 MachineOperand &Index = MI->getOperand(AddrOffset + X86::AddrIndexReg);
317 MachineOperand &Segment = MI->getOperand(AddrOffset + X86::AddrSegmentReg);
318
319 if (!((Base.isReg() && Base.getReg() != X86::NoRegister) || Base.isFI()))
320 return false;
321 if (!Disp.isImm())
322 return false;
323 if (Scale.getImm() != 1)
324 return false;
325 if (!(Index.isReg() && Index.getReg() == X86::NoRegister))
326 return false;
327 if (!(Segment.isReg() && Segment.getReg() == X86::NoRegister))
328 return false;
329 return true;
330 }
331
332 // Collect potentially blocking stores.
333 // Limit the number of instructions backwards we want to inspect
334 // since the effect of store block won't be visible if the store
335 // and load instructions have enough instructions in between to
336 // keep the core busy.
337 static SmallVector<MachineInstr *, 2>
338 findPotentialBlockers(MachineInstr *LoadInst) {
339 SmallVector<MachineInstr *, 2> PotentialBlockers;
340 unsigned BlockCount = 0;
341 const unsigned InspectionLimit = X86AvoidSFBInspectionLimit;
342 for (auto PBInst = std::next(MachineBasicBlock::reverse_iterator(LoadInst)),
343 E = LoadInst->getParent()->rend();
344 PBInst != E; ++PBInst) {
345 BlockCount++;
346 if (BlockCount >= InspectionLimit)
347 break;
348 MachineInstr &MI = *PBInst;
349 if (MI.getDesc().isCall())
350 return PotentialBlockers;
351 PotentialBlockers.push_back(&MI);
352 }
353 // If we didn't get to the instructions limit try predecessing blocks.
354 // Ideally we should traverse the predecessor blocks in depth with some
355 // coloring algorithm, but for now let's just look at the first order
356 // predecessors.
357 if (BlockCount < InspectionLimit) {
358 MachineBasicBlock *MBB = LoadInst->getParent();
359 int LimitLeft = InspectionLimit - BlockCount;
360 for (MachineBasicBlock::pred_iterator PB = MBB->pred_begin(),
361 PE = MBB->pred_end();
362 PB != PE; ++PB) {
363 MachineBasicBlock *PMBB = *PB;
364 int PredCount = 0;
365 for (MachineBasicBlock::reverse_iterator PBInst = PMBB->rbegin(),
366 PME = PMBB->rend();
367 PBInst != PME; ++PBInst) {
368 PredCount++;
369 if (PredCount >= LimitLeft)
370 break;
371 if (PBInst->getDesc().isCall())
372 break;
373 PotentialBlockers.push_back(&*PBInst);
374 }
375 }
376 }
377 return PotentialBlockers;
378 }
379
380 void X86AvoidSFBPass::buildCopy(MachineInstr *LoadInst, unsigned NLoadOpcode,
381 int64_t LoadDisp, MachineInstr *StoreInst,
382 unsigned NStoreOpcode, int64_t StoreDisp,
383 unsigned Size, int64_t LMMOffset,
384 int64_t SMMOffset) {
385 MachineOperand &LoadBase = getBaseOperand(LoadInst);
386 MachineOperand &StoreBase = getBaseOperand(StoreInst);
387 MachineBasicBlock *MBB = LoadInst->getParent();
388 MachineMemOperand *LMMO = *LoadInst->memoperands_begin();
389 MachineMemOperand *SMMO = *StoreInst->memoperands_begin();
390
391 unsigned Reg1 = MRI->createVirtualRegister(
392 TII->getRegClass(TII->get(NLoadOpcode), 0, TRI, *(MBB->getParent())));
393 MachineInstr *NewLoad =
394 BuildMI(*MBB, LoadInst, LoadInst->getDebugLoc(), TII->get(NLoadOpcode),
395 Reg1)
396 .add(LoadBase)
397 .addImm(1)
398 .addReg(X86::NoRegister)
399 .addImm(LoadDisp)
400 .addReg(X86::NoRegister)
401 .addMemOperand(
402 MBB->getParent()->getMachineMemOperand(LMMO, LMMOffset, Size));
403 if (LoadBase.isReg())
404 getBaseOperand(NewLoad).setIsKill(false);
405 LLVM_DEBUG(NewLoad->dump());
406 // If the load and store are consecutive, use the loadInst location to
407 // reduce register pressure.
408 MachineInstr *StInst = StoreInst;
409 if (StoreInst->getPrevNode() == LoadInst)
410 StInst = LoadInst;
411 MachineInstr *NewStore =
412 BuildMI(*MBB, StInst, StInst->getDebugLoc(), TII->get(NStoreOpcode))
413 .add(StoreBase)
414 .addImm(1)
415 .addReg(X86::NoRegister)
416 .addImm(StoreDisp)
417 .addReg(X86::NoRegister)
418 .addReg(Reg1)
419 .addMemOperand(
420 MBB->getParent()->getMachineMemOperand(SMMO, SMMOffset, Size));
421 if (StoreBase.isReg())
422 getBaseOperand(NewStore).setIsKill(false);
423 MachineOperand &StoreSrcVReg = StoreInst->getOperand(X86::AddrNumOperands);
424 assert(StoreSrcVReg.isReg() && "Expected virtual register");
425 NewStore->getOperand(X86::AddrNumOperands).setIsKill(StoreSrcVReg.isKill());
426 LLVM_DEBUG(NewStore->dump());
427 }
428
429 void X86AvoidSFBPass::buildCopies(int Size, MachineInstr *LoadInst,
430 int64_t LdDispImm, MachineInstr *StoreInst,
431 int64_t StDispImm, int64_t LMMOffset,
432 int64_t SMMOffset) {
433 int LdDisp = LdDispImm;
434 int StDisp = StDispImm;
435 while (Size > 0) {
436 if ((Size - MOV128SZ >= 0) && isYMMLoadOpcode(LoadInst->getOpcode())) {
437 Size = Size - MOV128SZ;
438 buildCopy(LoadInst, getYMMtoXMMLoadOpcode(LoadInst->getOpcode()), LdDisp,
439 StoreInst, getYMMtoXMMStoreOpcode(StoreInst->getOpcode()),
440 StDisp, MOV128SZ, LMMOffset, SMMOffset);
441 LdDisp += MOV128SZ;
442 StDisp += MOV128SZ;
443 LMMOffset += MOV128SZ;
444 SMMOffset += MOV128SZ;
445 continue;
446 }
447 if (Size - MOV64SZ >= 0) {
448 Size = Size - MOV64SZ;
449 buildCopy(LoadInst, X86::MOV64rm, LdDisp, StoreInst, X86::MOV64mr, StDisp,
450 MOV64SZ, LMMOffset, SMMOffset);
451 LdDisp += MOV64SZ;
452 StDisp += MOV64SZ;
453 LMMOffset += MOV64SZ;
454 SMMOffset += MOV64SZ;
455 continue;
456 }
457 if (Size - MOV32SZ >= 0) {
458 Size = Size - MOV32SZ;
459 buildCopy(LoadInst, X86::MOV32rm, LdDisp, StoreInst, X86::MOV32mr, StDisp,
460 MOV32SZ, LMMOffset, SMMOffset);
461 LdDisp += MOV32SZ;
462 StDisp += MOV32SZ;
463 LMMOffset += MOV32SZ;
464 SMMOffset += MOV32SZ;
465 continue;
466 }
467 if (Size - MOV16SZ >= 0) {
468 Size = Size - MOV16SZ;
469 buildCopy(LoadInst, X86::MOV16rm, LdDisp, StoreInst, X86::MOV16mr, StDisp,
470 MOV16SZ, LMMOffset, SMMOffset);
471 LdDisp += MOV16SZ;
472 StDisp += MOV16SZ;
473 LMMOffset += MOV16SZ;
474 SMMOffset += MOV16SZ;
475 continue;
476 }
477 if (Size - MOV8SZ >= 0) {
478 Size = Size - MOV8SZ;
479 buildCopy(LoadInst, X86::MOV8rm, LdDisp, StoreInst, X86::MOV8mr, StDisp,
480 MOV8SZ, LMMOffset, SMMOffset);
481 LdDisp += MOV8SZ;
482 StDisp += MOV8SZ;
483 LMMOffset += MOV8SZ;
484 SMMOffset += MOV8SZ;
485 continue;
486 }
487 }
488 assert(Size == 0 && "Wrong size division");
489 }
490
491 static void updateKillStatus(MachineInstr *LoadInst, MachineInstr *StoreInst) {
492 MachineOperand &LoadBase = getBaseOperand(LoadInst);
493 MachineOperand &StoreBase = getBaseOperand(StoreInst);
494 if (LoadBase.isReg()) {
495 MachineInstr *LastLoad = LoadInst->getPrevNode();
496 // If the original load and store to xmm/ymm were consecutive
497 // then the partial copies were also created in
498 // a consecutive order to reduce register pressure,
499 // and the location of the last load is before the last store.
500 if (StoreInst->getPrevNode() == LoadInst)
501 LastLoad = LoadInst->getPrevNode()->getPrevNode();
502 getBaseOperand(LastLoad).setIsKill(LoadBase.isKill());
503 }
504 if (StoreBase.isReg()) {
505 MachineInstr *StInst = StoreInst;
506 if (StoreInst->getPrevNode() == LoadInst)
507 StInst = LoadInst;
508 getBaseOperand(StInst->getPrevNode()).setIsKill(StoreBase.isKill());
509 }
510 }
511
512 bool X86AvoidSFBPass::alias(const MachineMemOperand &Op1,
513 const MachineMemOperand &Op2) const {
514 if (!Op1.getValue() || !Op2.getValue())
515 return true;
516
517 int64_t MinOffset = std::min(Op1.getOffset(), Op2.getOffset());
518 int64_t Overlapa = Op1.getSize() + Op1.getOffset() - MinOffset;
519 int64_t Overlapb = Op2.getSize() + Op2.getOffset() - MinOffset;
520
521 AliasResult AAResult =
522 AA->alias(MemoryLocation(Op1.getValue(), Overlapa, Op1.getAAInfo()),
523 MemoryLocation(Op2.getValue(), Overlapb, Op2.getAAInfo()));
524 return AAResult != NoAlias;
525 }
526
527 void X86AvoidSFBPass::findPotentiallylBlockedCopies(MachineFunction &MF) {
528 for (auto &MBB : MF)
529 for (auto &MI : MBB) {
530 if (!isPotentialBlockedMemCpyLd(MI.getOpcode()))
531 continue;
532 int DefVR = MI.getOperand(0).getReg();
533 if (!MRI->hasOneUse(DefVR))
534 continue;
535 for (auto UI = MRI->use_nodbg_begin(DefVR), UE = MRI->use_nodbg_end();
536 UI != UE;) {
537 MachineOperand &StoreMO = *UI++;
538 MachineInstr &StoreMI = *StoreMO.getParent();
539 // Skip cases where the memcpy may overlap.
540 if (StoreMI.getParent() == MI.getParent() &&
541 isPotentialBlockedMemCpyPair(MI.getOpcode(), StoreMI.getOpcode()) &&
542 isRelevantAddressingMode(&MI) &&
543 isRelevantAddressingMode(&StoreMI)) {
544 assert(MI.hasOneMemOperand() &&
545 "Expected one memory operand for load instruction");
546 assert(StoreMI.hasOneMemOperand() &&
547 "Expected one memory operand for store instruction");
548 if (!alias(**MI.memoperands_begin(), **StoreMI.memoperands_begin()))
549 BlockedLoadsStoresPairs.push_back(std::make_pair(&MI, &StoreMI));
550 }
551 }
552 }
553 }
554
555 unsigned X86AvoidSFBPass::getRegSizeInBytes(MachineInstr *LoadInst) {
556 auto TRC = TII->getRegClass(TII->get(LoadInst->getOpcode()), 0, TRI,
557 *LoadInst->getParent()->getParent());
558 return TRI->getRegSizeInBits(*TRC) / 8;
559 }
560
561 void X86AvoidSFBPass::breakBlockedCopies(
562 MachineInstr *LoadInst, MachineInstr *StoreInst,
563 const DisplacementSizeMap &BlockingStoresDispSizeMap) {
564 int64_t LdDispImm = getDispOperand(LoadInst).getImm();
565 int64_t StDispImm = getDispOperand(StoreInst).getImm();
566 int64_t LMMOffset = 0;
567 int64_t SMMOffset = 0;
568
569 int64_t LdDisp1 = LdDispImm;
570 int64_t LdDisp2 = 0;
571 int64_t StDisp1 = StDispImm;
572 int64_t StDisp2 = 0;
573 unsigned Size1 = 0;
574 unsigned Size2 = 0;
575 int64_t LdStDelta = StDispImm - LdDispImm;
576
577 for (auto DispSizePair : BlockingStoresDispSizeMap) {
578 LdDisp2 = DispSizePair.first;
579 StDisp2 = DispSizePair.first + LdStDelta;
580 Size2 = DispSizePair.second;
581 // Avoid copying overlapping areas.
582 if (LdDisp2 < LdDisp1) {
583 int OverlapDelta = LdDisp1 - LdDisp2;
584 LdDisp2 += OverlapDelta;
585 StDisp2 += OverlapDelta;
586 Size2 -= OverlapDelta;
587 }
588 Size1 = LdDisp2 - LdDisp1;
589
590 // Build a copy for the point until the current blocking store's
591 // displacement.
592 buildCopies(Size1, LoadInst, LdDisp1, StoreInst, StDisp1, LMMOffset,
593 SMMOffset);
594 // Build a copy for the current blocking store.
595 buildCopies(Size2, LoadInst, LdDisp2, StoreInst, StDisp2, LMMOffset + Size1,
596 SMMOffset + Size1);
597 LdDisp1 = LdDisp2 + Size2;
598 StDisp1 = StDisp2 + Size2;
599 LMMOffset += Size1 + Size2;
600 SMMOffset += Size1 + Size2;
601 }
602 unsigned Size3 = (LdDispImm + getRegSizeInBytes(LoadInst)) - LdDisp1;
603 buildCopies(Size3, LoadInst, LdDisp1, StoreInst, StDisp1, LMMOffset,
604 LMMOffset);
605 }
606
607 static bool hasSameBaseOpValue(MachineInstr *LoadInst,
608 MachineInstr *StoreInst) {
609 MachineOperand &LoadBase = getBaseOperand(LoadInst);
610 MachineOperand &StoreBase = getBaseOperand(StoreInst);
611 if (LoadBase.isReg() != StoreBase.isReg())
612 return false;
613 if (LoadBase.isReg())
614 return LoadBase.getReg() == StoreBase.getReg();
615 return LoadBase.getIndex() == StoreBase.getIndex();
616 }
617
618 static bool isBlockingStore(int64_t LoadDispImm, unsigned LoadSize,
619 int64_t StoreDispImm, unsigned StoreSize) {
620 return ((StoreDispImm >= LoadDispImm) &&
621 (StoreDispImm <= LoadDispImm + (LoadSize - StoreSize)));
622 }
623
624 // Keep track of all stores blocking a load
625 static void
626 updateBlockingStoresDispSizeMap(DisplacementSizeMap &BlockingStoresDispSizeMap,
627 int64_t DispImm, unsigned Size) {
628 if (BlockingStoresDispSizeMap.count(DispImm)) {
629 // Choose the smallest blocking store starting at this displacement.
630 if (BlockingStoresDispSizeMap[DispImm] > Size)
631 BlockingStoresDispSizeMap[DispImm] = Size;
632
633 } else
634 BlockingStoresDispSizeMap[DispImm] = Size;
635 }
636
637 // Remove blocking stores contained in each other.
638 static void
639 removeRedundantBlockingStores(DisplacementSizeMap &BlockingStoresDispSizeMap) {
640 if (BlockingStoresDispSizeMap.size() <= 1)
641 return;
642
643 SmallVector<std::pair<int64_t, unsigned>, 0> DispSizeStack;
644 for (auto DispSizePair : BlockingStoresDispSizeMap) {
645 int64_t CurrDisp = DispSizePair.first;
646 unsigned CurrSize = DispSizePair.second;
647 while (DispSizeStack.size()) {
648 int64_t PrevDisp = DispSizeStack.back().first;
649 unsigned PrevSize = DispSizeStack.back().second;
650 if (CurrDisp + CurrSize > PrevDisp + PrevSize)
651 break;
652 DispSizeStack.pop_back();
653 }
654 DispSizeStack.push_back(DispSizePair);
655 }
656 BlockingStoresDispSizeMap.clear();
657 for (auto Disp : DispSizeStack)
658 BlockingStoresDispSizeMap.insert(Disp);
659 }
660
661 bool X86AvoidSFBPass::runOnMachineFunction(MachineFunction &MF) {
662 bool Changed = false;
663
664 if (DisableX86AvoidStoreForwardBlocks || skipFunction(MF.getFunction()) ||
665 !MF.getSubtarget<X86Subtarget>().is64Bit())
666 return false;
667
668 MRI = &MF.getRegInfo();
669 assert(MRI->isSSA() && "Expected MIR to be in SSA form");
670 TII = MF.getSubtarget<X86Subtarget>().getInstrInfo();
671 TRI = MF.getSubtarget<X86Subtarget>().getRegisterInfo();
672 AA = &getAnalysis<AAResultsWrapperPass>().getAAResults();
673 LLVM_DEBUG(dbgs() << "Start X86AvoidStoreForwardBlocks\n";);
674 // Look for a load then a store to XMM/YMM which look like a memcpy
675 findPotentiallylBlockedCopies(MF);
676
677 for (auto LoadStoreInstPair : BlockedLoadsStoresPairs) {
678 MachineInstr *LoadInst = LoadStoreInstPair.first;
679 int64_t LdDispImm = getDispOperand(LoadInst).getImm();
680 DisplacementSizeMap BlockingStoresDispSizeMap;
681
682 SmallVector<MachineInstr *, 2> PotentialBlockers =
683 findPotentialBlockers(LoadInst);
684 for (auto PBInst : PotentialBlockers) {
685 if (!isPotentialBlockingStoreInst(PBInst->getOpcode(),
686 LoadInst->getOpcode()) ||
687 !isRelevantAddressingMode(PBInst))
688 continue;
689 int64_t PBstDispImm = getDispOperand(PBInst).getImm();
690 assert(PBInst->hasOneMemOperand() && "Expected One Memory Operand");
691 unsigned PBstSize = (*PBInst->memoperands_begin())->getSize();
692 // This check doesn't cover all cases, but it will suffice for now.
693 // TODO: take branch probability into consideration, if the blocking
694 // store is in an unreached block, breaking the memcopy could lose
695 // performance.
696 if (hasSameBaseOpValue(LoadInst, PBInst) &&
697 isBlockingStore(LdDispImm, getRegSizeInBytes(LoadInst), PBstDispImm,
698 PBstSize))
699 updateBlockingStoresDispSizeMap(BlockingStoresDispSizeMap, PBstDispImm,
700 PBstSize);
701 }
702
703 if (BlockingStoresDispSizeMap.empty())
704 continue;
705
706 // We found a store forward block, break the memcpy's load and store
707 // into smaller copies such that each smaller store that was causing
708 // a store block would now be copied separately.
709 MachineInstr *StoreInst = LoadStoreInstPair.second;
710 LLVM_DEBUG(dbgs() << "Blocked load and store instructions: \n");
711 LLVM_DEBUG(LoadInst->dump());
712 LLVM_DEBUG(StoreInst->dump());
713 LLVM_DEBUG(dbgs() << "Replaced with:\n");
714 removeRedundantBlockingStores(BlockingStoresDispSizeMap);
715 breakBlockedCopies(LoadInst, StoreInst, BlockingStoresDispSizeMap);
716 updateKillStatus(LoadInst, StoreInst);
717 ForRemoval.push_back(LoadInst);
718 ForRemoval.push_back(StoreInst);
719 }
720 for (auto RemovedInst : ForRemoval) {
721 RemovedInst->eraseFromParent();
722 }
723 ForRemoval.clear();
724 BlockedLoadsStoresPairs.clear();
725 LLVM_DEBUG(dbgs() << "End X86AvoidStoreForwardBlocks\n";);
726
727 return Changed;
728 }
The low level virtual machine