1 //===- X86AvoidStoreForwardingBlocks.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 "X86.h"
37 #include "X86InstrInfo.h"
38 #include "X86Subtarget.h"
39 #include "llvm/Analysis/AliasAnalysis.h"
40 #include "llvm/CodeGen/MachineBasicBlock.h"
41 #include "llvm/CodeGen/MachineFunction.h"
42 #include "llvm/CodeGen/MachineFunctionPass.h"
43 #include "llvm/CodeGen/MachineInstr.h"
44 #include "llvm/CodeGen/MachineInstrBuilder.h"
45 #include "llvm/CodeGen/MachineOperand.h"
46 #include "llvm/CodeGen/MachineRegisterInfo.h"
47 #include "llvm/IR/DebugInfoMetadata.h"
48 #include "llvm/IR/DebugLoc.h"
49 #include "llvm/IR/Function.h"
50 #include "llvm/InitializePasses.h"
51 #include "llvm/MC/MCInstrDesc.h"
52 
53 using namespace llvm;
54 
55 #define DEBUG_TYPE "x86-avoid-SFB"
56 
57 static cl::opt<bool> DisableX86AvoidStoreForwardBlocks(
58     "x86-disable-avoid-SFB", cl::Hidden,
59     cl::desc("X86: Disable Store Forwarding Blocks fixup."), cl::init(false));
60 
61 static cl::opt<unsigned> X86AvoidSFBInspectionLimit(
62     "x86-sfb-inspection-limit",
63     cl::desc("X86: Number of instructions backward to "
64              "inspect for store forwarding blocks."),
65     cl::init(20), cl::Hidden);
66 
67 namespace {
68 
69 using DisplacementSizeMap = std::map<int64_t, unsigned>;
70 
71 class X86AvoidSFBPass : public MachineFunctionPass {
72 public:
73   static char ID;
X86AvoidSFBPass()74   X86AvoidSFBPass() : MachineFunctionPass(ID) { }
75 
getPassName() const76   StringRef getPassName() const override {
77     return "X86 Avoid Store Forwarding Blocks";
78   }
79 
80   bool runOnMachineFunction(MachineFunction &MF) override;
81 
getAnalysisUsage(AnalysisUsage & AU) const82   void getAnalysisUsage(AnalysisUsage &AU) const override {
83     MachineFunctionPass::getAnalysisUsage(AU);
84     AU.addRequired<AAResultsWrapperPass>();
85   }
86 
87 private:
88   MachineRegisterInfo *MRI = nullptr;
89   const X86InstrInfo *TII = nullptr;
90   const X86RegisterInfo *TRI = nullptr;
91   SmallVector<std::pair<MachineInstr *, MachineInstr *>, 2>
92       BlockedLoadsStoresPairs;
93   SmallVector<MachineInstr *, 2> ForRemoval;
94   AliasAnalysis *AA = nullptr;
95 
96   /// Returns couples of Load then Store to memory which look
97   ///  like a memcpy.
98   void findPotentiallylBlockedCopies(MachineFunction &MF);
99   /// Break the memcpy's load and store into smaller copies
100   /// such that each memory load that was blocked by a smaller store
101   /// would now be copied separately.
102   void breakBlockedCopies(MachineInstr *LoadInst, MachineInstr *StoreInst,
103                           const DisplacementSizeMap &BlockingStoresDispSizeMap);
104   /// Break a copy of size Size to smaller copies.
105   void buildCopies(int Size, MachineInstr *LoadInst, int64_t LdDispImm,
106                    MachineInstr *StoreInst, int64_t StDispImm,
107                    int64_t LMMOffset, int64_t SMMOffset);
108 
109   void buildCopy(MachineInstr *LoadInst, unsigned NLoadOpcode, int64_t LoadDisp,
110                  MachineInstr *StoreInst, unsigned NStoreOpcode,
111                  int64_t StoreDisp, unsigned Size, int64_t LMMOffset,
112                  int64_t SMMOffset);
113 
114   bool alias(const MachineMemOperand &Op1, const MachineMemOperand &Op2) const;
115 
116   unsigned getRegSizeInBytes(MachineInstr *Inst);
117 };
118 
119 } // end anonymous namespace
120 
121 char X86AvoidSFBPass::ID = 0;
122 
123 INITIALIZE_PASS_BEGIN(X86AvoidSFBPass, DEBUG_TYPE, "Machine code sinking",
124                       false, false)
INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass)125 INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass)
126 INITIALIZE_PASS_END(X86AvoidSFBPass, DEBUG_TYPE, "Machine code sinking", false,
127                     false)
128 
129 FunctionPass *llvm::createX86AvoidStoreForwardingBlocks() {
130   return new X86AvoidSFBPass();
131 }
132 
isXMMLoadOpcode(unsigned Opcode)133 static bool isXMMLoadOpcode(unsigned Opcode) {
134   return Opcode == X86::MOVUPSrm || Opcode == X86::MOVAPSrm ||
135          Opcode == X86::VMOVUPSrm || Opcode == X86::VMOVAPSrm ||
136          Opcode == X86::VMOVUPDrm || Opcode == X86::VMOVAPDrm ||
137          Opcode == X86::VMOVDQUrm || Opcode == X86::VMOVDQArm ||
138          Opcode == X86::VMOVUPSZ128rm || Opcode == X86::VMOVAPSZ128rm ||
139          Opcode == X86::VMOVUPDZ128rm || Opcode == X86::VMOVAPDZ128rm ||
140          Opcode == X86::VMOVDQU64Z128rm || Opcode == X86::VMOVDQA64Z128rm ||
141          Opcode == X86::VMOVDQU32Z128rm || Opcode == X86::VMOVDQA32Z128rm;
142 }
isYMMLoadOpcode(unsigned Opcode)143 static bool isYMMLoadOpcode(unsigned Opcode) {
144   return Opcode == X86::VMOVUPSYrm || Opcode == X86::VMOVAPSYrm ||
145          Opcode == X86::VMOVUPDYrm || Opcode == X86::VMOVAPDYrm ||
146          Opcode == X86::VMOVDQUYrm || Opcode == X86::VMOVDQAYrm ||
147          Opcode == X86::VMOVUPSZ256rm || Opcode == X86::VMOVAPSZ256rm ||
148          Opcode == X86::VMOVUPDZ256rm || Opcode == X86::VMOVAPDZ256rm ||
149          Opcode == X86::VMOVDQU64Z256rm || Opcode == X86::VMOVDQA64Z256rm ||
150          Opcode == X86::VMOVDQU32Z256rm || Opcode == X86::VMOVDQA32Z256rm;
151 }
152 
isPotentialBlockedMemCpyLd(unsigned Opcode)153 static bool isPotentialBlockedMemCpyLd(unsigned Opcode) {
154   return isXMMLoadOpcode(Opcode) || isYMMLoadOpcode(Opcode);
155 }
156 
isPotentialBlockedMemCpyPair(unsigned LdOpcode,unsigned StOpcode)157 static bool isPotentialBlockedMemCpyPair(unsigned LdOpcode, unsigned StOpcode) {
158   switch (LdOpcode) {
159   case X86::MOVUPSrm:
160   case X86::MOVAPSrm:
161     return StOpcode == X86::MOVUPSmr || StOpcode == X86::MOVAPSmr;
162   case X86::VMOVUPSrm:
163   case X86::VMOVAPSrm:
164     return StOpcode == X86::VMOVUPSmr || StOpcode == X86::VMOVAPSmr;
165   case X86::VMOVUPDrm:
166   case X86::VMOVAPDrm:
167     return StOpcode == X86::VMOVUPDmr || StOpcode == X86::VMOVAPDmr;
168   case X86::VMOVDQUrm:
169   case X86::VMOVDQArm:
170     return StOpcode == X86::VMOVDQUmr || StOpcode == X86::VMOVDQAmr;
171   case X86::VMOVUPSZ128rm:
172   case X86::VMOVAPSZ128rm:
173     return StOpcode == X86::VMOVUPSZ128mr || StOpcode == X86::VMOVAPSZ128mr;
174   case X86::VMOVUPDZ128rm:
175   case X86::VMOVAPDZ128rm:
176     return StOpcode == X86::VMOVUPDZ128mr || StOpcode == X86::VMOVAPDZ128mr;
177   case X86::VMOVUPSYrm:
178   case X86::VMOVAPSYrm:
179     return StOpcode == X86::VMOVUPSYmr || StOpcode == X86::VMOVAPSYmr;
180   case X86::VMOVUPDYrm:
181   case X86::VMOVAPDYrm:
182     return StOpcode == X86::VMOVUPDYmr || StOpcode == X86::VMOVAPDYmr;
183   case X86::VMOVDQUYrm:
184   case X86::VMOVDQAYrm:
185     return StOpcode == X86::VMOVDQUYmr || StOpcode == X86::VMOVDQAYmr;
186   case X86::VMOVUPSZ256rm:
187   case X86::VMOVAPSZ256rm:
188     return StOpcode == X86::VMOVUPSZ256mr || StOpcode == X86::VMOVAPSZ256mr;
189   case X86::VMOVUPDZ256rm:
190   case X86::VMOVAPDZ256rm:
191     return StOpcode == X86::VMOVUPDZ256mr || StOpcode == X86::VMOVAPDZ256mr;
192   case X86::VMOVDQU64Z128rm:
193   case X86::VMOVDQA64Z128rm:
194     return StOpcode == X86::VMOVDQU64Z128mr || StOpcode == X86::VMOVDQA64Z128mr;
195   case X86::VMOVDQU32Z128rm:
196   case X86::VMOVDQA32Z128rm:
197     return StOpcode == X86::VMOVDQU32Z128mr || StOpcode == X86::VMOVDQA32Z128mr;
198   case X86::VMOVDQU64Z256rm:
199   case X86::VMOVDQA64Z256rm:
200     return StOpcode == X86::VMOVDQU64Z256mr || StOpcode == X86::VMOVDQA64Z256mr;
201   case X86::VMOVDQU32Z256rm:
202   case X86::VMOVDQA32Z256rm:
203     return StOpcode == X86::VMOVDQU32Z256mr || StOpcode == X86::VMOVDQA32Z256mr;
204   default:
205     return false;
206   }
207 }
208 
isPotentialBlockingStoreInst(unsigned Opcode,unsigned LoadOpcode)209 static bool isPotentialBlockingStoreInst(unsigned Opcode, unsigned LoadOpcode) {
210   bool PBlock = false;
211   PBlock |= Opcode == X86::MOV64mr || Opcode == X86::MOV64mi32 ||
212             Opcode == X86::MOV32mr || Opcode == X86::MOV32mi ||
213             Opcode == X86::MOV16mr || Opcode == X86::MOV16mi ||
214             Opcode == X86::MOV8mr || Opcode == X86::MOV8mi;
215   if (isYMMLoadOpcode(LoadOpcode))
216     PBlock |= Opcode == X86::VMOVUPSmr || Opcode == X86::VMOVAPSmr ||
217               Opcode == X86::VMOVUPDmr || Opcode == X86::VMOVAPDmr ||
218               Opcode == X86::VMOVDQUmr || Opcode == X86::VMOVDQAmr ||
219               Opcode == X86::VMOVUPSZ128mr || Opcode == X86::VMOVAPSZ128mr ||
220               Opcode == X86::VMOVUPDZ128mr || Opcode == X86::VMOVAPDZ128mr ||
221               Opcode == X86::VMOVDQU64Z128mr ||
222               Opcode == X86::VMOVDQA64Z128mr ||
223               Opcode == X86::VMOVDQU32Z128mr || Opcode == X86::VMOVDQA32Z128mr;
224   return PBlock;
225 }
226 
227 static const int MOV128SZ = 16;
228 static const int MOV64SZ = 8;
229 static const int MOV32SZ = 4;
230 static const int MOV16SZ = 2;
231 static const int MOV8SZ = 1;
232 
getYMMtoXMMLoadOpcode(unsigned LoadOpcode)233 static unsigned getYMMtoXMMLoadOpcode(unsigned LoadOpcode) {
234   switch (LoadOpcode) {
235   case X86::VMOVUPSYrm:
236   case X86::VMOVAPSYrm:
237     return X86::VMOVUPSrm;
238   case X86::VMOVUPDYrm:
239   case X86::VMOVAPDYrm:
240     return X86::VMOVUPDrm;
241   case X86::VMOVDQUYrm:
242   case X86::VMOVDQAYrm:
243     return X86::VMOVDQUrm;
244   case X86::VMOVUPSZ256rm:
245   case X86::VMOVAPSZ256rm:
246     return X86::VMOVUPSZ128rm;
247   case X86::VMOVUPDZ256rm:
248   case X86::VMOVAPDZ256rm:
249     return X86::VMOVUPDZ128rm;
250   case X86::VMOVDQU64Z256rm:
251   case X86::VMOVDQA64Z256rm:
252     return X86::VMOVDQU64Z128rm;
253   case X86::VMOVDQU32Z256rm:
254   case X86::VMOVDQA32Z256rm:
255     return X86::VMOVDQU32Z128rm;
256   default:
257     llvm_unreachable("Unexpected Load Instruction Opcode");
258   }
259   return 0;
260 }
261 
getYMMtoXMMStoreOpcode(unsigned StoreOpcode)262 static unsigned getYMMtoXMMStoreOpcode(unsigned StoreOpcode) {
263   switch (StoreOpcode) {
264   case X86::VMOVUPSYmr:
265   case X86::VMOVAPSYmr:
266     return X86::VMOVUPSmr;
267   case X86::VMOVUPDYmr:
268   case X86::VMOVAPDYmr:
269     return X86::VMOVUPDmr;
270   case X86::VMOVDQUYmr:
271   case X86::VMOVDQAYmr:
272     return X86::VMOVDQUmr;
273   case X86::VMOVUPSZ256mr:
274   case X86::VMOVAPSZ256mr:
275     return X86::VMOVUPSZ128mr;
276   case X86::VMOVUPDZ256mr:
277   case X86::VMOVAPDZ256mr:
278     return X86::VMOVUPDZ128mr;
279   case X86::VMOVDQU64Z256mr:
280   case X86::VMOVDQA64Z256mr:
281     return X86::VMOVDQU64Z128mr;
282   case X86::VMOVDQU32Z256mr:
283   case X86::VMOVDQA32Z256mr:
284     return X86::VMOVDQU32Z128mr;
285   default:
286     llvm_unreachable("Unexpected Load Instruction Opcode");
287   }
288   return 0;
289 }
290 
getAddrOffset(const MachineInstr * MI)291 static int getAddrOffset(const MachineInstr *MI) {
292   const MCInstrDesc &Descl = MI->getDesc();
293   int AddrOffset = X86II::getMemoryOperandNo(Descl.TSFlags);
294   assert(AddrOffset != -1 && "Expected Memory Operand");
295   AddrOffset += X86II::getOperandBias(Descl);
296   return AddrOffset;
297 }
298 
getBaseOperand(MachineInstr * MI)299 static MachineOperand &getBaseOperand(MachineInstr *MI) {
300   int AddrOffset = getAddrOffset(MI);
301   return MI->getOperand(AddrOffset + X86::AddrBaseReg);
302 }
303 
getDispOperand(MachineInstr * MI)304 static MachineOperand &getDispOperand(MachineInstr *MI) {
305   int AddrOffset = getAddrOffset(MI);
306   return MI->getOperand(AddrOffset + X86::AddrDisp);
307 }
308 
309 // Relevant addressing modes contain only base register and immediate
310 // displacement or frameindex and immediate displacement.
311 // TODO: Consider expanding to other addressing modes in the future
isRelevantAddressingMode(MachineInstr * MI)312 static bool isRelevantAddressingMode(MachineInstr *MI) {
313   int AddrOffset = getAddrOffset(MI);
314   const MachineOperand &Base = getBaseOperand(MI);
315   const MachineOperand &Disp = getDispOperand(MI);
316   const MachineOperand &Scale = MI->getOperand(AddrOffset + X86::AddrScaleAmt);
317   const MachineOperand &Index = MI->getOperand(AddrOffset + X86::AddrIndexReg);
318   const MachineOperand &Segment = MI->getOperand(AddrOffset + X86::AddrSegmentReg);
319 
320   if (!((Base.isReg() && Base.getReg() != X86::NoRegister) || Base.isFI()))
321     return false;
322   if (!Disp.isImm())
323     return false;
324   if (Scale.getImm() != 1)
325     return false;
326   if (!(Index.isReg() && Index.getReg() == X86::NoRegister))
327     return false;
328   if (!(Segment.isReg() && Segment.getReg() == X86::NoRegister))
329     return false;
330   return true;
331 }
332 
333 // Collect potentially blocking stores.
334 // Limit the number of instructions backwards we want to inspect
335 // since the effect of store block won't be visible if the store
336 // and load instructions have enough instructions in between to
337 // keep the core busy.
338 static SmallVector<MachineInstr *, 2>
findPotentialBlockers(MachineInstr * LoadInst)339 findPotentialBlockers(MachineInstr *LoadInst) {
340   SmallVector<MachineInstr *, 2> PotentialBlockers;
341   unsigned BlockCount = 0;
342   const unsigned InspectionLimit = X86AvoidSFBInspectionLimit;
343   for (auto PBInst = std::next(MachineBasicBlock::reverse_iterator(LoadInst)),
344             E = LoadInst->getParent()->rend();
345        PBInst != E; ++PBInst) {
346     if (PBInst->isMetaInstruction())
347       continue;
348     BlockCount++;
349     if (BlockCount >= InspectionLimit)
350       break;
351     MachineInstr &MI = *PBInst;
352     if (MI.getDesc().isCall())
353       return PotentialBlockers;
354     PotentialBlockers.push_back(&MI);
355   }
356   // If we didn't get to the instructions limit try predecessing blocks.
357   // Ideally we should traverse the predecessor blocks in depth with some
358   // coloring algorithm, but for now let's just look at the first order
359   // predecessors.
360   if (BlockCount < InspectionLimit) {
361     MachineBasicBlock *MBB = LoadInst->getParent();
362     int LimitLeft = InspectionLimit - BlockCount;
363     for (MachineBasicBlock::pred_iterator PB = MBB->pred_begin(),
364                                           PE = MBB->pred_end();
365          PB != PE; ++PB) {
366       MachineBasicBlock *PMBB = *PB;
367       int PredCount = 0;
368       for (MachineBasicBlock::reverse_iterator PBInst = PMBB->rbegin(),
369                                                PME = PMBB->rend();
370            PBInst != PME; ++PBInst) {
371         if (PBInst->isMetaInstruction())
372           continue;
373         PredCount++;
374         if (PredCount >= LimitLeft)
375           break;
376         if (PBInst->getDesc().isCall())
377           break;
378         PotentialBlockers.push_back(&*PBInst);
379       }
380     }
381   }
382   return PotentialBlockers;
383 }
384 
buildCopy(MachineInstr * LoadInst,unsigned NLoadOpcode,int64_t LoadDisp,MachineInstr * StoreInst,unsigned NStoreOpcode,int64_t StoreDisp,unsigned Size,int64_t LMMOffset,int64_t SMMOffset)385 void X86AvoidSFBPass::buildCopy(MachineInstr *LoadInst, unsigned NLoadOpcode,
386                                 int64_t LoadDisp, MachineInstr *StoreInst,
387                                 unsigned NStoreOpcode, int64_t StoreDisp,
388                                 unsigned Size, int64_t LMMOffset,
389                                 int64_t SMMOffset) {
390   MachineOperand &LoadBase = getBaseOperand(LoadInst);
391   MachineOperand &StoreBase = getBaseOperand(StoreInst);
392   MachineBasicBlock *MBB = LoadInst->getParent();
393   MachineMemOperand *LMMO = *LoadInst->memoperands_begin();
394   MachineMemOperand *SMMO = *StoreInst->memoperands_begin();
395 
396   Register Reg1 = MRI->createVirtualRegister(
397       TII->getRegClass(TII->get(NLoadOpcode), 0, TRI, *(MBB->getParent())));
398   MachineInstr *NewLoad =
399       BuildMI(*MBB, LoadInst, LoadInst->getDebugLoc(), TII->get(NLoadOpcode),
400               Reg1)
401           .add(LoadBase)
402           .addImm(1)
403           .addReg(X86::NoRegister)
404           .addImm(LoadDisp)
405           .addReg(X86::NoRegister)
406           .addMemOperand(
407               MBB->getParent()->getMachineMemOperand(LMMO, LMMOffset, Size));
408   if (LoadBase.isReg())
409     getBaseOperand(NewLoad).setIsKill(false);
410   LLVM_DEBUG(NewLoad->dump());
411   // If the load and store are consecutive, use the loadInst location to
412   // reduce register pressure.
413   MachineInstr *StInst = StoreInst;
414   auto PrevInstrIt = prev_nodbg(MachineBasicBlock::instr_iterator(StoreInst),
415                                 MBB->instr_begin());
416   if (PrevInstrIt.getNodePtr() == LoadInst)
417     StInst = LoadInst;
418   MachineInstr *NewStore =
419       BuildMI(*MBB, StInst, StInst->getDebugLoc(), TII->get(NStoreOpcode))
420           .add(StoreBase)
421           .addImm(1)
422           .addReg(X86::NoRegister)
423           .addImm(StoreDisp)
424           .addReg(X86::NoRegister)
425           .addReg(Reg1)
426           .addMemOperand(
427               MBB->getParent()->getMachineMemOperand(SMMO, SMMOffset, Size));
428   if (StoreBase.isReg())
429     getBaseOperand(NewStore).setIsKill(false);
430   MachineOperand &StoreSrcVReg = StoreInst->getOperand(X86::AddrNumOperands);
431   assert(StoreSrcVReg.isReg() && "Expected virtual register");
432   NewStore->getOperand(X86::AddrNumOperands).setIsKill(StoreSrcVReg.isKill());
433   LLVM_DEBUG(NewStore->dump());
434 }
435 
buildCopies(int Size,MachineInstr * LoadInst,int64_t LdDispImm,MachineInstr * StoreInst,int64_t StDispImm,int64_t LMMOffset,int64_t SMMOffset)436 void X86AvoidSFBPass::buildCopies(int Size, MachineInstr *LoadInst,
437                                   int64_t LdDispImm, MachineInstr *StoreInst,
438                                   int64_t StDispImm, int64_t LMMOffset,
439                                   int64_t SMMOffset) {
440   int LdDisp = LdDispImm;
441   int StDisp = StDispImm;
442   while (Size > 0) {
443     if ((Size - MOV128SZ >= 0) && isYMMLoadOpcode(LoadInst->getOpcode())) {
444       Size = Size - MOV128SZ;
445       buildCopy(LoadInst, getYMMtoXMMLoadOpcode(LoadInst->getOpcode()), LdDisp,
446                 StoreInst, getYMMtoXMMStoreOpcode(StoreInst->getOpcode()),
447                 StDisp, MOV128SZ, LMMOffset, SMMOffset);
448       LdDisp += MOV128SZ;
449       StDisp += MOV128SZ;
450       LMMOffset += MOV128SZ;
451       SMMOffset += MOV128SZ;
452       continue;
453     }
454     if (Size - MOV64SZ >= 0) {
455       Size = Size - MOV64SZ;
456       buildCopy(LoadInst, X86::MOV64rm, LdDisp, StoreInst, X86::MOV64mr, StDisp,
457                 MOV64SZ, LMMOffset, SMMOffset);
458       LdDisp += MOV64SZ;
459       StDisp += MOV64SZ;
460       LMMOffset += MOV64SZ;
461       SMMOffset += MOV64SZ;
462       continue;
463     }
464     if (Size - MOV32SZ >= 0) {
465       Size = Size - MOV32SZ;
466       buildCopy(LoadInst, X86::MOV32rm, LdDisp, StoreInst, X86::MOV32mr, StDisp,
467                 MOV32SZ, LMMOffset, SMMOffset);
468       LdDisp += MOV32SZ;
469       StDisp += MOV32SZ;
470       LMMOffset += MOV32SZ;
471       SMMOffset += MOV32SZ;
472       continue;
473     }
474     if (Size - MOV16SZ >= 0) {
475       Size = Size - MOV16SZ;
476       buildCopy(LoadInst, X86::MOV16rm, LdDisp, StoreInst, X86::MOV16mr, StDisp,
477                 MOV16SZ, LMMOffset, SMMOffset);
478       LdDisp += MOV16SZ;
479       StDisp += MOV16SZ;
480       LMMOffset += MOV16SZ;
481       SMMOffset += MOV16SZ;
482       continue;
483     }
484     if (Size - MOV8SZ >= 0) {
485       Size = Size - MOV8SZ;
486       buildCopy(LoadInst, X86::MOV8rm, LdDisp, StoreInst, X86::MOV8mr, StDisp,
487                 MOV8SZ, LMMOffset, SMMOffset);
488       LdDisp += MOV8SZ;
489       StDisp += MOV8SZ;
490       LMMOffset += MOV8SZ;
491       SMMOffset += MOV8SZ;
492       continue;
493     }
494   }
495   assert(Size == 0 && "Wrong size division");
496 }
497 
updateKillStatus(MachineInstr * LoadInst,MachineInstr * StoreInst)498 static void updateKillStatus(MachineInstr *LoadInst, MachineInstr *StoreInst) {
499   MachineOperand &LoadBase = getBaseOperand(LoadInst);
500   MachineOperand &StoreBase = getBaseOperand(StoreInst);
501   auto *StorePrevNonDbgInstr =
502       prev_nodbg(MachineBasicBlock::instr_iterator(StoreInst),
503                  LoadInst->getParent()->instr_begin())
504           .getNodePtr();
505   if (LoadBase.isReg()) {
506     MachineInstr *LastLoad = LoadInst->getPrevNode();
507     // If the original load and store to xmm/ymm were consecutive
508     // then the partial copies were also created in
509     // a consecutive order to reduce register pressure,
510     // and the location of the last load is before the last store.
511     if (StorePrevNonDbgInstr == LoadInst)
512       LastLoad = LoadInst->getPrevNode()->getPrevNode();
513     getBaseOperand(LastLoad).setIsKill(LoadBase.isKill());
514   }
515   if (StoreBase.isReg()) {
516     MachineInstr *StInst = StoreInst;
517     if (StorePrevNonDbgInstr == LoadInst)
518       StInst = LoadInst;
519     getBaseOperand(StInst->getPrevNode()).setIsKill(StoreBase.isKill());
520   }
521 }
522 
alias(const MachineMemOperand & Op1,const MachineMemOperand & Op2) const523 bool X86AvoidSFBPass::alias(const MachineMemOperand &Op1,
524                             const MachineMemOperand &Op2) const {
525   if (!Op1.getValue() || !Op2.getValue())
526     return true;
527 
528   int64_t MinOffset = std::min(Op1.getOffset(), Op2.getOffset());
529   int64_t Overlapa = Op1.getSize() + Op1.getOffset() - MinOffset;
530   int64_t Overlapb = Op2.getSize() + Op2.getOffset() - MinOffset;
531 
532   AliasResult AAResult =
533       AA->alias(MemoryLocation(Op1.getValue(), Overlapa, Op1.getAAInfo()),
534                 MemoryLocation(Op2.getValue(), Overlapb, Op2.getAAInfo()));
535   return AAResult != NoAlias;
536 }
537 
findPotentiallylBlockedCopies(MachineFunction & MF)538 void X86AvoidSFBPass::findPotentiallylBlockedCopies(MachineFunction &MF) {
539   for (auto &MBB : MF)
540     for (auto &MI : MBB) {
541       if (!isPotentialBlockedMemCpyLd(MI.getOpcode()))
542         continue;
543       int DefVR = MI.getOperand(0).getReg();
544       if (!MRI->hasOneNonDBGUse(DefVR))
545         continue;
546       for (auto UI = MRI->use_nodbg_begin(DefVR), UE = MRI->use_nodbg_end();
547            UI != UE;) {
548         MachineOperand &StoreMO = *UI++;
549         MachineInstr &StoreMI = *StoreMO.getParent();
550         // Skip cases where the memcpy may overlap.
551         if (StoreMI.getParent() == MI.getParent() &&
552             isPotentialBlockedMemCpyPair(MI.getOpcode(), StoreMI.getOpcode()) &&
553             isRelevantAddressingMode(&MI) &&
554             isRelevantAddressingMode(&StoreMI) &&
555             MI.hasOneMemOperand() && StoreMI.hasOneMemOperand()) {
556           if (!alias(**MI.memoperands_begin(), **StoreMI.memoperands_begin()))
557             BlockedLoadsStoresPairs.push_back(std::make_pair(&MI, &StoreMI));
558         }
559       }
560     }
561 }
562 
getRegSizeInBytes(MachineInstr * LoadInst)563 unsigned X86AvoidSFBPass::getRegSizeInBytes(MachineInstr *LoadInst) {
564   const auto *TRC = TII->getRegClass(TII->get(LoadInst->getOpcode()), 0, TRI,
565                               *LoadInst->getParent()->getParent());
566   return TRI->getRegSizeInBits(*TRC) / 8;
567 }
568 
breakBlockedCopies(MachineInstr * LoadInst,MachineInstr * StoreInst,const DisplacementSizeMap & BlockingStoresDispSizeMap)569 void X86AvoidSFBPass::breakBlockedCopies(
570     MachineInstr *LoadInst, MachineInstr *StoreInst,
571     const DisplacementSizeMap &BlockingStoresDispSizeMap) {
572   int64_t LdDispImm = getDispOperand(LoadInst).getImm();
573   int64_t StDispImm = getDispOperand(StoreInst).getImm();
574   int64_t LMMOffset = 0;
575   int64_t SMMOffset = 0;
576 
577   int64_t LdDisp1 = LdDispImm;
578   int64_t LdDisp2 = 0;
579   int64_t StDisp1 = StDispImm;
580   int64_t StDisp2 = 0;
581   unsigned Size1 = 0;
582   unsigned Size2 = 0;
583   int64_t LdStDelta = StDispImm - LdDispImm;
584 
585   for (auto DispSizePair : BlockingStoresDispSizeMap) {
586     LdDisp2 = DispSizePair.first;
587     StDisp2 = DispSizePair.first + LdStDelta;
588     Size2 = DispSizePair.second;
589     // Avoid copying overlapping areas.
590     if (LdDisp2 < LdDisp1) {
591       int OverlapDelta = LdDisp1 - LdDisp2;
592       LdDisp2 += OverlapDelta;
593       StDisp2 += OverlapDelta;
594       Size2 -= OverlapDelta;
595     }
596     Size1 = LdDisp2 - LdDisp1;
597 
598     // Build a copy for the point until the current blocking store's
599     // displacement.
600     buildCopies(Size1, LoadInst, LdDisp1, StoreInst, StDisp1, LMMOffset,
601                 SMMOffset);
602     // Build a copy for the current blocking store.
603     buildCopies(Size2, LoadInst, LdDisp2, StoreInst, StDisp2, LMMOffset + Size1,
604                 SMMOffset + Size1);
605     LdDisp1 = LdDisp2 + Size2;
606     StDisp1 = StDisp2 + Size2;
607     LMMOffset += Size1 + Size2;
608     SMMOffset += Size1 + Size2;
609   }
610   unsigned Size3 = (LdDispImm + getRegSizeInBytes(LoadInst)) - LdDisp1;
611   buildCopies(Size3, LoadInst, LdDisp1, StoreInst, StDisp1, LMMOffset,
612               LMMOffset);
613 }
614 
hasSameBaseOpValue(MachineInstr * LoadInst,MachineInstr * StoreInst)615 static bool hasSameBaseOpValue(MachineInstr *LoadInst,
616                                MachineInstr *StoreInst) {
617   const MachineOperand &LoadBase = getBaseOperand(LoadInst);
618   const MachineOperand &StoreBase = getBaseOperand(StoreInst);
619   if (LoadBase.isReg() != StoreBase.isReg())
620     return false;
621   if (LoadBase.isReg())
622     return LoadBase.getReg() == StoreBase.getReg();
623   return LoadBase.getIndex() == StoreBase.getIndex();
624 }
625 
isBlockingStore(int64_t LoadDispImm,unsigned LoadSize,int64_t StoreDispImm,unsigned StoreSize)626 static bool isBlockingStore(int64_t LoadDispImm, unsigned LoadSize,
627                             int64_t StoreDispImm, unsigned StoreSize) {
628   return ((StoreDispImm >= LoadDispImm) &&
629           (StoreDispImm <= LoadDispImm + (LoadSize - StoreSize)));
630 }
631 
632 // Keep track of all stores blocking a load
633 static void
updateBlockingStoresDispSizeMap(DisplacementSizeMap & BlockingStoresDispSizeMap,int64_t DispImm,unsigned Size)634 updateBlockingStoresDispSizeMap(DisplacementSizeMap &BlockingStoresDispSizeMap,
635                                 int64_t DispImm, unsigned Size) {
636   if (BlockingStoresDispSizeMap.count(DispImm)) {
637     // Choose the smallest blocking store starting at this displacement.
638     if (BlockingStoresDispSizeMap[DispImm] > Size)
639       BlockingStoresDispSizeMap[DispImm] = Size;
640 
641   } else
642     BlockingStoresDispSizeMap[DispImm] = Size;
643 }
644 
645 // Remove blocking stores contained in each other.
646 static void
removeRedundantBlockingStores(DisplacementSizeMap & BlockingStoresDispSizeMap)647 removeRedundantBlockingStores(DisplacementSizeMap &BlockingStoresDispSizeMap) {
648   if (BlockingStoresDispSizeMap.size() <= 1)
649     return;
650 
651   SmallVector<std::pair<int64_t, unsigned>, 0> DispSizeStack;
652   for (auto DispSizePair : BlockingStoresDispSizeMap) {
653     int64_t CurrDisp = DispSizePair.first;
654     unsigned CurrSize = DispSizePair.second;
655     while (DispSizeStack.size()) {
656       int64_t PrevDisp = DispSizeStack.back().first;
657       unsigned PrevSize = DispSizeStack.back().second;
658       if (CurrDisp + CurrSize > PrevDisp + PrevSize)
659         break;
660       DispSizeStack.pop_back();
661     }
662     DispSizeStack.push_back(DispSizePair);
663   }
664   BlockingStoresDispSizeMap.clear();
665   for (auto Disp : DispSizeStack)
666     BlockingStoresDispSizeMap.insert(Disp);
667 }
668 
runOnMachineFunction(MachineFunction & MF)669 bool X86AvoidSFBPass::runOnMachineFunction(MachineFunction &MF) {
670   bool Changed = false;
671 
672   if (DisableX86AvoidStoreForwardBlocks || skipFunction(MF.getFunction()) ||
673       !MF.getSubtarget<X86Subtarget>().is64Bit())
674     return false;
675 
676   MRI = &MF.getRegInfo();
677   assert(MRI->isSSA() && "Expected MIR to be in SSA form");
678   TII = MF.getSubtarget<X86Subtarget>().getInstrInfo();
679   TRI = MF.getSubtarget<X86Subtarget>().getRegisterInfo();
680   AA = &getAnalysis<AAResultsWrapperPass>().getAAResults();
681   LLVM_DEBUG(dbgs() << "Start X86AvoidStoreForwardBlocks\n";);
682   // Look for a load then a store to XMM/YMM which look like a memcpy
683   findPotentiallylBlockedCopies(MF);
684 
685   for (auto LoadStoreInstPair : BlockedLoadsStoresPairs) {
686     MachineInstr *LoadInst = LoadStoreInstPair.first;
687     int64_t LdDispImm = getDispOperand(LoadInst).getImm();
688     DisplacementSizeMap BlockingStoresDispSizeMap;
689 
690     SmallVector<MachineInstr *, 2> PotentialBlockers =
691         findPotentialBlockers(LoadInst);
692     for (auto *PBInst : PotentialBlockers) {
693       if (!isPotentialBlockingStoreInst(PBInst->getOpcode(),
694                                         LoadInst->getOpcode()) ||
695           !isRelevantAddressingMode(PBInst) || !PBInst->hasOneMemOperand())
696         continue;
697       int64_t PBstDispImm = getDispOperand(PBInst).getImm();
698       unsigned PBstSize = (*PBInst->memoperands_begin())->getSize();
699       // This check doesn't cover all cases, but it will suffice for now.
700       // TODO: take branch probability into consideration, if the blocking
701       // store is in an unreached block, breaking the memcopy could lose
702       // performance.
703       if (hasSameBaseOpValue(LoadInst, PBInst) &&
704           isBlockingStore(LdDispImm, getRegSizeInBytes(LoadInst), PBstDispImm,
705                           PBstSize))
706         updateBlockingStoresDispSizeMap(BlockingStoresDispSizeMap, PBstDispImm,
707                                         PBstSize);
708     }
709 
710     if (BlockingStoresDispSizeMap.empty())
711       continue;
712 
713     // We found a store forward block, break the memcpy's load and store
714     // into smaller copies such that each smaller store that was causing
715     // a store block would now be copied separately.
716     MachineInstr *StoreInst = LoadStoreInstPair.second;
717     LLVM_DEBUG(dbgs() << "Blocked load and store instructions: \n");
718     LLVM_DEBUG(LoadInst->dump());
719     LLVM_DEBUG(StoreInst->dump());
720     LLVM_DEBUG(dbgs() << "Replaced with:\n");
721     removeRedundantBlockingStores(BlockingStoresDispSizeMap);
722     breakBlockedCopies(LoadInst, StoreInst, BlockingStoresDispSizeMap);
723     updateKillStatus(LoadInst, StoreInst);
724     ForRemoval.push_back(LoadInst);
725     ForRemoval.push_back(StoreInst);
726   }
727   for (auto *RemovedInst : ForRemoval) {
728     RemovedInst->eraseFromParent();
729   }
730   ForRemoval.clear();
731   BlockedLoadsStoresPairs.clear();
732   LLVM_DEBUG(dbgs() << "End X86AvoidStoreForwardBlocks\n";);
733 
734   return Changed;
735 }
736