LLVM  9.0.0svn
GVNHoist.cpp
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1 //===- GVNHoist.cpp - Hoist scalar and load expressions -------------------===//
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 // This pass hoists expressions from branches to a common dominator. It uses
10 // GVN (global value numbering) to discover expressions computing the same
11 // values. The primary goals of code-hoisting are:
12 // 1. To reduce the code size.
13 // 2. In some cases reduce critical path (by exposing more ILP).
14 //
15 // The algorithm factors out the reachability of values such that multiple
16 // queries to find reachability of values are fast. This is based on finding the
17 // ANTIC points in the CFG which do not change during hoisting. The ANTIC points
18 // are basically the dominance-frontiers in the inverse graph. So we introduce a
19 // data structure (CHI nodes) to keep track of values flowing out of a basic
20 // block. We only do this for values with multiple occurrences in the function
21 // as they are the potential hoistable candidates. This approach allows us to
22 // hoist instructions to a basic block with more than two successors, as well as
23 // deal with infinite loops in a trivial way.
24 //
25 // Limitations: This pass does not hoist fully redundant expressions because
26 // they are already handled by GVN-PRE. It is advisable to run gvn-hoist before
27 // and after gvn-pre because gvn-pre creates opportunities for more instructions
28 // to be hoisted.
29 //
30 // Hoisting may affect the performance in some cases. To mitigate that, hoisting
31 // is disabled in the following cases.
32 // 1. Scalars across calls.
33 // 2. geps when corresponding load/store cannot be hoisted.
34 //===----------------------------------------------------------------------===//
35 
36 #include "llvm/ADT/DenseMap.h"
37 #include "llvm/ADT/DenseSet.h"
38 #include "llvm/ADT/STLExtras.h"
39 #include "llvm/ADT/SmallPtrSet.h"
40 #include "llvm/ADT/SmallVector.h"
41 #include "llvm/ADT/Statistic.h"
52 #include "llvm/IR/Argument.h"
53 #include "llvm/IR/BasicBlock.h"
54 #include "llvm/IR/CFG.h"
55 #include "llvm/IR/Constants.h"
56 #include "llvm/IR/Dominators.h"
57 #include "llvm/IR/Function.h"
58 #include "llvm/IR/InstrTypes.h"
59 #include "llvm/IR/Instruction.h"
60 #include "llvm/IR/Instructions.h"
61 #include "llvm/IR/IntrinsicInst.h"
62 #include "llvm/IR/Intrinsics.h"
63 #include "llvm/IR/LLVMContext.h"
64 #include "llvm/IR/PassManager.h"
65 #include "llvm/IR/Use.h"
66 #include "llvm/IR/User.h"
67 #include "llvm/IR/Value.h"
68 #include "llvm/Pass.h"
69 #include "llvm/Support/Casting.h"
71 #include "llvm/Support/Debug.h"
73 #include "llvm/Transforms/Scalar.h"
75 #include <algorithm>
76 #include <cassert>
77 #include <iterator>
78 #include <memory>
79 #include <utility>
80 #include <vector>
81 
82 using namespace llvm;
83 
84 #define DEBUG_TYPE "gvn-hoist"
85 
86 STATISTIC(NumHoisted, "Number of instructions hoisted");
87 STATISTIC(NumRemoved, "Number of instructions removed");
88 STATISTIC(NumLoadsHoisted, "Number of loads hoisted");
89 STATISTIC(NumLoadsRemoved, "Number of loads removed");
90 STATISTIC(NumStoresHoisted, "Number of stores hoisted");
91 STATISTIC(NumStoresRemoved, "Number of stores removed");
92 STATISTIC(NumCallsHoisted, "Number of calls hoisted");
93 STATISTIC(NumCallsRemoved, "Number of calls removed");
94 
95 static cl::opt<int>
96  MaxHoistedThreshold("gvn-max-hoisted", cl::Hidden, cl::init(-1),
97  cl::desc("Max number of instructions to hoist "
98  "(default unlimited = -1)"));
99 
101  "gvn-hoist-max-bbs", cl::Hidden, cl::init(4),
102  cl::desc("Max number of basic blocks on the path between "
103  "hoisting locations (default = 4, unlimited = -1)"));
104 
106  "gvn-hoist-max-depth", cl::Hidden, cl::init(100),
107  cl::desc("Hoist instructions from the beginning of the BB up to the "
108  "maximum specified depth (default = 100, unlimited = -1)"));
109 
110 static cl::opt<int>
111  MaxChainLength("gvn-hoist-max-chain-length", cl::Hidden, cl::init(10),
112  cl::desc("Maximum length of dependent chains to hoist "
113  "(default = 10, unlimited = -1)"));
114 
115 namespace llvm {
116 
120 
121 // Each element of a hoisting list contains the basic block where to hoist and
122 // a list of instructions to be hoisted.
123 using HoistingPointInfo = std::pair<BasicBlock *, SmallVecInsn>;
124 
126 
127 // A map from a pair of VNs to all the instructions with those VNs.
128 using VNType = std::pair<unsigned, unsigned>;
129 
131 
132 // CHI keeps information about values flowing out of a basic block. It is
133 // similar to PHI but in the inverse graph, and used for outgoing values on each
134 // edge. For conciseness, it is computed only for instructions with multiple
135 // occurrences in the CFG because they are the only hoistable candidates.
136 // A (CHI[{V, B, I1}, {V, C, I2}]
137 // / \
138 // / \
139 // B(I1) C (I2)
140 // The Value number for both I1 and I2 is V, the CHI node will save the
141 // instruction as well as the edge where the value is flowing to.
142 struct CHIArg {
144 
145  // Edge destination (shows the direction of flow), may not be where the I is.
147 
148  // The instruction (VN) which uses the values flowing out of CHI.
150 
151  bool operator==(const CHIArg &A) { return VN == A.VN; }
152  bool operator!=(const CHIArg &A) { return !(*this == A); }
153 };
154 
158 using InValuesType =
160 
161 // An invalid value number Used when inserting a single value number into
162 // VNtoInsns.
163 enum : unsigned { InvalidVN = ~2U };
164 
165 // Records all scalar instructions candidate for code hoisting.
166 class InsnInfo {
167  VNtoInsns VNtoScalars;
168 
169 public:
170  // Inserts I and its value number in VNtoScalars.
172  // Scalar instruction.
173  unsigned V = VN.lookupOrAdd(I);
174  VNtoScalars[{V, InvalidVN}].push_back(I);
175  }
176 
177  const VNtoInsns &getVNTable() const { return VNtoScalars; }
178 };
179 
180 // Records all load instructions candidate for code hoisting.
181 class LoadInfo {
182  VNtoInsns VNtoLoads;
183 
184 public:
185  // Insert Load and the value number of its memory address in VNtoLoads.
187  if (Load->isSimple()) {
188  unsigned V = VN.lookupOrAdd(Load->getPointerOperand());
189  VNtoLoads[{V, InvalidVN}].push_back(Load);
190  }
191  }
192 
193  const VNtoInsns &getVNTable() const { return VNtoLoads; }
194 };
195 
196 // Records all store instructions candidate for code hoisting.
197 class StoreInfo {
198  VNtoInsns VNtoStores;
199 
200 public:
201  // Insert the Store and a hash number of the store address and the stored
202  // value in VNtoStores.
204  if (!Store->isSimple())
205  return;
206  // Hash the store address and the stored value.
207  Value *Ptr = Store->getPointerOperand();
208  Value *Val = Store->getValueOperand();
209  VNtoStores[{VN.lookupOrAdd(Ptr), VN.lookupOrAdd(Val)}].push_back(Store);
210  }
211 
212  const VNtoInsns &getVNTable() const { return VNtoStores; }
213 };
214 
215 // Records all call instructions candidate for code hoisting.
216 class CallInfo {
217  VNtoInsns VNtoCallsScalars;
218  VNtoInsns VNtoCallsLoads;
219  VNtoInsns VNtoCallsStores;
220 
221 public:
222  // Insert Call and its value numbering in one of the VNtoCalls* containers.
224  // A call that doesNotAccessMemory is handled as a Scalar,
225  // onlyReadsMemory will be handled as a Load instruction,
226  // all other calls will be handled as stores.
227  unsigned V = VN.lookupOrAdd(Call);
228  auto Entry = std::make_pair(V, InvalidVN);
229 
230  if (Call->doesNotAccessMemory())
231  VNtoCallsScalars[Entry].push_back(Call);
232  else if (Call->onlyReadsMemory())
233  VNtoCallsLoads[Entry].push_back(Call);
234  else
235  VNtoCallsStores[Entry].push_back(Call);
236  }
237 
238  const VNtoInsns &getScalarVNTable() const { return VNtoCallsScalars; }
239  const VNtoInsns &getLoadVNTable() const { return VNtoCallsLoads; }
240  const VNtoInsns &getStoreVNTable() const { return VNtoCallsStores; }
241 };
242 
243 static void combineKnownMetadata(Instruction *ReplInst, Instruction *I) {
244  static const unsigned KnownIDs[] = {
249  combineMetadata(ReplInst, I, KnownIDs, true);
250 }
251 
252 // This pass hoists common computations across branches sharing common
253 // dominator. The primary goal is to reduce the code size, and in some
254 // cases reduce critical path (by exposing more ILP).
255 class GVNHoist {
256 public:
259  : DT(DT), PDT(PDT), AA(AA), MD(MD), MSSA(MSSA),
260  MSSAUpdater(llvm::make_unique<MemorySSAUpdater>(MSSA)) {}
261 
262  bool run(Function &F) {
263  NumFuncArgs = F.arg_size();
264  VN.setDomTree(DT);
265  VN.setAliasAnalysis(AA);
266  VN.setMemDep(MD);
267  bool Res = false;
268  // Perform DFS Numbering of instructions.
269  unsigned BBI = 0;
270  for (const BasicBlock *BB : depth_first(&F.getEntryBlock())) {
271  DFSNumber[BB] = ++BBI;
272  unsigned I = 0;
273  for (auto &Inst : *BB)
274  DFSNumber[&Inst] = ++I;
275  }
276 
277  int ChainLength = 0;
278 
279  // FIXME: use lazy evaluation of VN to avoid the fix-point computation.
280  while (true) {
281  if (MaxChainLength != -1 && ++ChainLength >= MaxChainLength)
282  return Res;
283 
284  auto HoistStat = hoistExpressions(F);
285  if (HoistStat.first + HoistStat.second == 0)
286  return Res;
287 
288  if (HoistStat.second > 0)
289  // To address a limitation of the current GVN, we need to rerun the
290  // hoisting after we hoisted loads or stores in order to be able to
291  // hoist all scalars dependent on the hoisted ld/st.
292  VN.clear();
293 
294  Res = true;
295  }
296 
297  return Res;
298  }
299 
300  // Copied from NewGVN.cpp
301  // This function provides global ranking of operations so that we can place
302  // them in a canonical order. Note that rank alone is not necessarily enough
303  // for a complete ordering, as constants all have the same rank. However,
304  // generally, we will simplify an operation with all constants so that it
305  // doesn't matter what order they appear in.
306  unsigned int rank(const Value *V) const {
307  // Prefer constants to undef to anything else
308  // Undef is a constant, have to check it first.
309  // Prefer smaller constants to constantexprs
310  if (isa<ConstantExpr>(V))
311  return 2;
312  if (isa<UndefValue>(V))
313  return 1;
314  if (isa<Constant>(V))
315  return 0;
316  else if (auto *A = dyn_cast<Argument>(V))
317  return 3 + A->getArgNo();
318 
319  // Need to shift the instruction DFS by number of arguments + 3 to account
320  // for the constant and argument ranking above.
321  auto Result = DFSNumber.lookup(V);
322  if (Result > 0)
323  return 4 + NumFuncArgs + Result;
324  // Unreachable or something else, just return a really large number.
325  return ~0;
326  }
327 
328 private:
330  DominatorTree *DT;
331  PostDominatorTree *PDT;
332  AliasAnalysis *AA;
334  MemorySSA *MSSA;
335  std::unique_ptr<MemorySSAUpdater> MSSAUpdater;
337  BBSideEffectsSet BBSideEffects;
338  DenseSet<const BasicBlock *> HoistBarrier;
340  unsigned NumFuncArgs;
341  const bool HoistingGeps = false;
342 
343  enum InsKind { Unknown, Scalar, Load, Store };
344 
345  // Return true when there are exception handling in BB.
346  bool hasEH(const BasicBlock *BB) {
347  auto It = BBSideEffects.find(BB);
348  if (It != BBSideEffects.end())
349  return It->second;
350 
351  if (BB->isEHPad() || BB->hasAddressTaken()) {
352  BBSideEffects[BB] = true;
353  return true;
354  }
355 
356  if (BB->getTerminator()->mayThrow()) {
357  BBSideEffects[BB] = true;
358  return true;
359  }
360 
361  BBSideEffects[BB] = false;
362  return false;
363  }
364 
365  // Return true when a successor of BB dominates A.
366  bool successorDominate(const BasicBlock *BB, const BasicBlock *A) {
367  for (const BasicBlock *Succ : successors(BB))
368  if (DT->dominates(Succ, A))
369  return true;
370 
371  return false;
372  }
373 
374  // Return true when I1 appears before I2 in the instructions of BB.
375  bool firstInBB(const Instruction *I1, const Instruction *I2) {
376  assert(I1->getParent() == I2->getParent());
377  unsigned I1DFS = DFSNumber.lookup(I1);
378  unsigned I2DFS = DFSNumber.lookup(I2);
379  assert(I1DFS && I2DFS);
380  return I1DFS < I2DFS;
381  }
382 
383  // Return true when there are memory uses of Def in BB.
384  bool hasMemoryUse(const Instruction *NewPt, MemoryDef *Def,
385  const BasicBlock *BB) {
386  const MemorySSA::AccessList *Acc = MSSA->getBlockAccesses(BB);
387  if (!Acc)
388  return false;
389 
390  Instruction *OldPt = Def->getMemoryInst();
391  const BasicBlock *OldBB = OldPt->getParent();
392  const BasicBlock *NewBB = NewPt->getParent();
393  bool ReachedNewPt = false;
394 
395  for (const MemoryAccess &MA : *Acc)
396  if (const MemoryUse *MU = dyn_cast<MemoryUse>(&MA)) {
397  Instruction *Insn = MU->getMemoryInst();
398 
399  // Do not check whether MU aliases Def when MU occurs after OldPt.
400  if (BB == OldBB && firstInBB(OldPt, Insn))
401  break;
402 
403  // Do not check whether MU aliases Def when MU occurs before NewPt.
404  if (BB == NewBB) {
405  if (!ReachedNewPt) {
406  if (firstInBB(Insn, NewPt))
407  continue;
408  ReachedNewPt = true;
409  }
410  }
411  if (MemorySSAUtil::defClobbersUseOrDef(Def, MU, *AA))
412  return true;
413  }
414 
415  return false;
416  }
417 
418  bool hasEHhelper(const BasicBlock *BB, const BasicBlock *SrcBB,
419  int &NBBsOnAllPaths) {
420  // Stop walk once the limit is reached.
421  if (NBBsOnAllPaths == 0)
422  return true;
423 
424  // Impossible to hoist with exceptions on the path.
425  if (hasEH(BB))
426  return true;
427 
428  // No such instruction after HoistBarrier in a basic block was
429  // selected for hoisting so instructions selected within basic block with
430  // a hoist barrier can be hoisted.
431  if ((BB != SrcBB) && HoistBarrier.count(BB))
432  return true;
433 
434  return false;
435  }
436 
437  // Return true when there are exception handling or loads of memory Def
438  // between Def and NewPt. This function is only called for stores: Def is
439  // the MemoryDef of the store to be hoisted.
440 
441  // Decrement by 1 NBBsOnAllPaths for each block between HoistPt and BB, and
442  // return true when the counter NBBsOnAllPaths reaces 0, except when it is
443  // initialized to -1 which is unlimited.
444  bool hasEHOrLoadsOnPath(const Instruction *NewPt, MemoryDef *Def,
445  int &NBBsOnAllPaths) {
446  const BasicBlock *NewBB = NewPt->getParent();
447  const BasicBlock *OldBB = Def->getBlock();
448  assert(DT->dominates(NewBB, OldBB) && "invalid path");
449  assert(DT->dominates(Def->getDefiningAccess()->getBlock(), NewBB) &&
450  "def does not dominate new hoisting point");
451 
452  // Walk all basic blocks reachable in depth-first iteration on the inverse
453  // CFG from OldBB to NewBB. These blocks are all the blocks that may be
454  // executed between the execution of NewBB and OldBB. Hoisting an expression
455  // from OldBB into NewBB has to be safe on all execution paths.
456  for (auto I = idf_begin(OldBB), E = idf_end(OldBB); I != E;) {
457  const BasicBlock *BB = *I;
458  if (BB == NewBB) {
459  // Stop traversal when reaching HoistPt.
460  I.skipChildren();
461  continue;
462  }
463 
464  if (hasEHhelper(BB, OldBB, NBBsOnAllPaths))
465  return true;
466 
467  // Check that we do not move a store past loads.
468  if (hasMemoryUse(NewPt, Def, BB))
469  return true;
470 
471  // -1 is unlimited number of blocks on all paths.
472  if (NBBsOnAllPaths != -1)
473  --NBBsOnAllPaths;
474 
475  ++I;
476  }
477 
478  return false;
479  }
480 
481  // Return true when there are exception handling between HoistPt and BB.
482  // Decrement by 1 NBBsOnAllPaths for each block between HoistPt and BB, and
483  // return true when the counter NBBsOnAllPaths reaches 0, except when it is
484  // initialized to -1 which is unlimited.
485  bool hasEHOnPath(const BasicBlock *HoistPt, const BasicBlock *SrcBB,
486  int &NBBsOnAllPaths) {
487  assert(DT->dominates(HoistPt, SrcBB) && "Invalid path");
488 
489  // Walk all basic blocks reachable in depth-first iteration on
490  // the inverse CFG from BBInsn to NewHoistPt. These blocks are all the
491  // blocks that may be executed between the execution of NewHoistPt and
492  // BBInsn. Hoisting an expression from BBInsn into NewHoistPt has to be safe
493  // on all execution paths.
494  for (auto I = idf_begin(SrcBB), E = idf_end(SrcBB); I != E;) {
495  const BasicBlock *BB = *I;
496  if (BB == HoistPt) {
497  // Stop traversal when reaching NewHoistPt.
498  I.skipChildren();
499  continue;
500  }
501 
502  if (hasEHhelper(BB, SrcBB, NBBsOnAllPaths))
503  return true;
504 
505  // -1 is unlimited number of blocks on all paths.
506  if (NBBsOnAllPaths != -1)
507  --NBBsOnAllPaths;
508 
509  ++I;
510  }
511 
512  return false;
513  }
514 
515  // Return true when it is safe to hoist a memory load or store U from OldPt
516  // to NewPt.
517  bool safeToHoistLdSt(const Instruction *NewPt, const Instruction *OldPt,
518  MemoryUseOrDef *U, InsKind K, int &NBBsOnAllPaths) {
519  // In place hoisting is safe.
520  if (NewPt == OldPt)
521  return true;
522 
523  const BasicBlock *NewBB = NewPt->getParent();
524  const BasicBlock *OldBB = OldPt->getParent();
525  const BasicBlock *UBB = U->getBlock();
526 
527  // Check for dependences on the Memory SSA.
529  BasicBlock *DBB = D->getBlock();
530  if (DT->properlyDominates(NewBB, DBB))
531  // Cannot move the load or store to NewBB above its definition in DBB.
532  return false;
533 
534  if (NewBB == DBB && !MSSA->isLiveOnEntryDef(D))
535  if (auto *UD = dyn_cast<MemoryUseOrDef>(D))
536  if (!firstInBB(UD->getMemoryInst(), NewPt))
537  // Cannot move the load or store to NewPt above its definition in D.
538  return false;
539 
540  // Check for unsafe hoistings due to side effects.
541  if (K == InsKind::Store) {
542  if (hasEHOrLoadsOnPath(NewPt, dyn_cast<MemoryDef>(U), NBBsOnAllPaths))
543  return false;
544  } else if (hasEHOnPath(NewBB, OldBB, NBBsOnAllPaths))
545  return false;
546 
547  if (UBB == NewBB) {
548  if (DT->properlyDominates(DBB, NewBB))
549  return true;
550  assert(UBB == DBB);
551  assert(MSSA->locallyDominates(D, U));
552  }
553 
554  // No side effects: it is safe to hoist.
555  return true;
556  }
557 
558  // Return true when it is safe to hoist scalar instructions from all blocks in
559  // WL to HoistBB.
560  bool safeToHoistScalar(const BasicBlock *HoistBB, const BasicBlock *BB,
561  int &NBBsOnAllPaths) {
562  return !hasEHOnPath(HoistBB, BB, NBBsOnAllPaths);
563  }
564 
565  // In the inverse CFG, the dominance frontier of basic block (BB) is the
566  // point where ANTIC needs to be computed for instructions which are going
567  // to be hoisted. Since this point does not change during gvn-hoist,
568  // we compute it only once (on demand).
569  // The ides is inspired from:
570  // "Partial Redundancy Elimination in SSA Form"
571  // ROBERT KENNEDY, SUN CHAN, SHIN-MING LIU, RAYMOND LO, PENG TU and FRED CHOW
572  // They use similar idea in the forward graph to find fully redundant and
573  // partially redundant expressions, here it is used in the inverse graph to
574  // find fully anticipable instructions at merge point (post-dominator in
575  // the inverse CFG).
576  // Returns the edge via which an instruction in BB will get the values from.
577 
578  // Returns true when the values are flowing out to each edge.
579  bool valueAnticipable(CHIArgs C, Instruction *TI) const {
580  if (TI->getNumSuccessors() > (unsigned)size(C))
581  return false; // Not enough args in this CHI.
582 
583  for (auto CHI : C) {
584  BasicBlock *Dest = CHI.Dest;
585  // Find if all the edges have values flowing out of BB.
586  bool Found = llvm::any_of(
587  successors(TI), [Dest](const BasicBlock *BB) { return BB == Dest; });
588  if (!Found)
589  return false;
590  }
591  return true;
592  }
593 
594  // Check if it is safe to hoist values tracked by CHI in the range
595  // [Begin, End) and accumulate them in Safe.
596  void checkSafety(CHIArgs C, BasicBlock *BB, InsKind K,
597  SmallVectorImpl<CHIArg> &Safe) {
598  int NumBBsOnAllPaths = MaxNumberOfBBSInPath;
599  for (auto CHI : C) {
600  Instruction *Insn = CHI.I;
601  if (!Insn) // No instruction was inserted in this CHI.
602  continue;
603  if (K == InsKind::Scalar) {
604  if (safeToHoistScalar(BB, Insn->getParent(), NumBBsOnAllPaths))
605  Safe.push_back(CHI);
606  } else {
607  MemoryUseOrDef *UD = MSSA->getMemoryAccess(Insn);
608  if (safeToHoistLdSt(BB->getTerminator(), Insn, UD, K, NumBBsOnAllPaths))
609  Safe.push_back(CHI);
610  }
611  }
612  }
613 
615 
616  // Push all the VNs corresponding to BB into RenameStack.
617  void fillRenameStack(BasicBlock *BB, InValuesType &ValueBBs,
618  RenameStackType &RenameStack) {
619  auto it1 = ValueBBs.find(BB);
620  if (it1 != ValueBBs.end()) {
621  // Iterate in reverse order to keep lower ranked values on the top.
622  for (std::pair<VNType, Instruction *> &VI : reverse(it1->second)) {
623  // Get the value of instruction I
624  LLVM_DEBUG(dbgs() << "\nPushing on stack: " << *VI.second);
625  RenameStack[VI.first].push_back(VI.second);
626  }
627  }
628  }
629 
630  void fillChiArgs(BasicBlock *BB, OutValuesType &CHIBBs,
631  RenameStackType &RenameStack) {
632  // For each *predecessor* (because Post-DOM) of BB check if it has a CHI
633  for (auto Pred : predecessors(BB)) {
634  auto P = CHIBBs.find(Pred);
635  if (P == CHIBBs.end()) {
636  continue;
637  }
638  LLVM_DEBUG(dbgs() << "\nLooking at CHIs in: " << Pred->getName(););
639  // A CHI is found (BB -> Pred is an edge in the CFG)
640  // Pop the stack until Top(V) = Ve.
641  auto &VCHI = P->second;
642  for (auto It = VCHI.begin(), E = VCHI.end(); It != E;) {
643  CHIArg &C = *It;
644  if (!C.Dest) {
645  auto si = RenameStack.find(C.VN);
646  // The Basic Block where CHI is must dominate the value we want to
647  // track in a CHI. In the PDom walk, there can be values in the
648  // stack which are not control dependent e.g., nested loop.
649  if (si != RenameStack.end() && si->second.size() &&
650  DT->properlyDominates(Pred, si->second.back()->getParent())) {
651  C.Dest = BB; // Assign the edge
652  C.I = si->second.pop_back_val(); // Assign the argument
653  LLVM_DEBUG(dbgs()
654  << "\nCHI Inserted in BB: " << C.Dest->getName() << *C.I
655  << ", VN: " << C.VN.first << ", " << C.VN.second);
656  }
657  // Move to next CHI of a different value
658  It = std::find_if(It, VCHI.end(),
659  [It](CHIArg &A) { return A != *It; });
660  } else
661  ++It;
662  }
663  }
664  }
665 
666  // Walk the post-dominator tree top-down and use a stack for each value to
667  // store the last value you see. When you hit a CHI from a given edge, the
668  // value to use as the argument is at the top of the stack, add the value to
669  // CHI and pop.
670  void insertCHI(InValuesType &ValueBBs, OutValuesType &CHIBBs) {
671  auto Root = PDT->getNode(nullptr);
672  if (!Root)
673  return;
674  // Depth first walk on PDom tree to fill the CHIargs at each PDF.
675  RenameStackType RenameStack;
676  for (auto Node : depth_first(Root)) {
677  BasicBlock *BB = Node->getBlock();
678  if (!BB)
679  continue;
680 
681  // Collect all values in BB and push to stack.
682  fillRenameStack(BB, ValueBBs, RenameStack);
683 
684  // Fill outgoing values in each CHI corresponding to BB.
685  fillChiArgs(BB, CHIBBs, RenameStack);
686  }
687  }
688 
689  // Walk all the CHI-nodes to find ones which have a empty-entry and remove
690  // them Then collect all the instructions which are safe to hoist and see if
691  // they form a list of anticipable values. OutValues contains CHIs
692  // corresponding to each basic block.
693  void findHoistableCandidates(OutValuesType &CHIBBs, InsKind K,
694  HoistingPointList &HPL) {
695  auto cmpVN = [](const CHIArg &A, const CHIArg &B) { return A.VN < B.VN; };
696 
697  // CHIArgs now have the outgoing values, so check for anticipability and
698  // accumulate hoistable candidates in HPL.
699  for (std::pair<BasicBlock *, SmallVector<CHIArg, 2>> &A : CHIBBs) {
700  BasicBlock *BB = A.first;
701  SmallVectorImpl<CHIArg> &CHIs = A.second;
702  // Vector of PHIs contains PHIs for different instructions.
703  // Sort the args according to their VNs, such that identical
704  // instructions are together.
705  std::stable_sort(CHIs.begin(), CHIs.end(), cmpVN);
706  auto TI = BB->getTerminator();
707  auto B = CHIs.begin();
708  // [PreIt, PHIIt) form a range of CHIs which have identical VNs.
709  auto PHIIt = std::find_if(CHIs.begin(), CHIs.end(),
710  [B](CHIArg &A) { return A != *B; });
711  auto PrevIt = CHIs.begin();
712  while (PrevIt != PHIIt) {
713  // Collect values which satisfy safety checks.
715  // We check for safety first because there might be multiple values in
716  // the same path, some of which are not safe to be hoisted, but overall
717  // each edge has at least one value which can be hoisted, making the
718  // value anticipable along that path.
719  checkSafety(make_range(PrevIt, PHIIt), BB, K, Safe);
720 
721  // List of safe values should be anticipable at TI.
722  if (valueAnticipable(make_range(Safe.begin(), Safe.end()), TI)) {
723  HPL.push_back({BB, SmallVecInsn()});
724  SmallVecInsn &V = HPL.back().second;
725  for (auto B : Safe)
726  V.push_back(B.I);
727  }
728 
729  // Check other VNs
730  PrevIt = PHIIt;
731  PHIIt = std::find_if(PrevIt, CHIs.end(),
732  [PrevIt](CHIArg &A) { return A != *PrevIt; });
733  }
734  }
735  }
736 
737  // Compute insertion points for each values which can be fully anticipated at
738  // a dominator. HPL contains all such values.
739  void computeInsertionPoints(const VNtoInsns &Map, HoistingPointList &HPL,
740  InsKind K) {
741  // Sort VNs based on their rankings
742  std::vector<VNType> Ranks;
743  for (const auto &Entry : Map) {
744  Ranks.push_back(Entry.first);
745  }
746 
747  // TODO: Remove fully-redundant expressions.
748  // Get instruction from the Map, assume that all the Instructions
749  // with same VNs have same rank (this is an approximation).
750  llvm::sort(Ranks, [this, &Map](const VNType &r1, const VNType &r2) {
751  return (rank(*Map.lookup(r1).begin()) < rank(*Map.lookup(r2).begin()));
752  });
753 
754  // - Sort VNs according to their rank, and start with lowest ranked VN
755  // - Take a VN and for each instruction with same VN
756  // - Find the dominance frontier in the inverse graph (PDF)
757  // - Insert the chi-node at PDF
758  // - Remove the chi-nodes with missing entries
759  // - Remove values from CHI-nodes which do not truly flow out, e.g.,
760  // modified along the path.
761  // - Collect the remaining values that are still anticipable
763  ReverseIDFCalculator IDFs(*PDT);
764  OutValuesType OutValue;
765  InValuesType InValue;
766  for (const auto &R : Ranks) {
767  const SmallVecInsn &V = Map.lookup(R);
768  if (V.size() < 2)
769  continue;
770  const VNType &VN = R;
772  for (auto &I : V) {
773  BasicBlock *BBI = I->getParent();
774  if (!hasEH(BBI))
775  VNBlocks.insert(BBI);
776  }
777  // Compute the Post Dominance Frontiers of each basic block
778  // The dominance frontier of a live block X in the reverse
779  // control graph is the set of blocks upon which X is control
780  // dependent. The following sequence computes the set of blocks
781  // which currently have dead terminators that are control
782  // dependence sources of a block which is in NewLiveBlocks.
783  IDFs.setDefiningBlocks(VNBlocks);
784  IDFBlocks.clear();
785  IDFs.calculate(IDFBlocks);
786 
787  // Make a map of BB vs instructions to be hoisted.
788  for (unsigned i = 0; i < V.size(); ++i) {
789  InValue[V[i]->getParent()].push_back(std::make_pair(VN, V[i]));
790  }
791  // Insert empty CHI node for this VN. This is used to factor out
792  // basic blocks where the ANTIC can potentially change.
793  for (auto IDFB : IDFBlocks) {
794  for (unsigned i = 0; i < V.size(); ++i) {
795  CHIArg C = {VN, nullptr, nullptr};
796  // Ignore spurious PDFs.
797  if (DT->properlyDominates(IDFB, V[i]->getParent())) {
798  OutValue[IDFB].push_back(C);
799  LLVM_DEBUG(dbgs() << "\nInsertion a CHI for BB: " << IDFB->getName()
800  << ", for Insn: " << *V[i]);
801  }
802  }
803  }
804  }
805 
806  // Insert CHI args at each PDF to iterate on factored graph of
807  // control dependence.
808  insertCHI(InValue, OutValue);
809  // Using the CHI args inserted at each PDF, find fully anticipable values.
810  findHoistableCandidates(OutValue, K, HPL);
811  }
812 
813  // Return true when all operands of Instr are available at insertion point
814  // HoistPt. When limiting the number of hoisted expressions, one could hoist
815  // a load without hoisting its access function. So before hoisting any
816  // expression, make sure that all its operands are available at insert point.
817  bool allOperandsAvailable(const Instruction *I,
818  const BasicBlock *HoistPt) const {
819  for (const Use &Op : I->operands())
820  if (const auto *Inst = dyn_cast<Instruction>(&Op))
821  if (!DT->dominates(Inst->getParent(), HoistPt))
822  return false;
823 
824  return true;
825  }
826 
827  // Same as allOperandsAvailable with recursive check for GEP operands.
828  bool allGepOperandsAvailable(const Instruction *I,
829  const BasicBlock *HoistPt) const {
830  for (const Use &Op : I->operands())
831  if (const auto *Inst = dyn_cast<Instruction>(&Op))
832  if (!DT->dominates(Inst->getParent(), HoistPt)) {
833  if (const GetElementPtrInst *GepOp =
834  dyn_cast<GetElementPtrInst>(Inst)) {
835  if (!allGepOperandsAvailable(GepOp, HoistPt))
836  return false;
837  // Gep is available if all operands of GepOp are available.
838  } else {
839  // Gep is not available if it has operands other than GEPs that are
840  // defined in blocks not dominating HoistPt.
841  return false;
842  }
843  }
844  return true;
845  }
846 
847  // Make all operands of the GEP available.
848  void makeGepsAvailable(Instruction *Repl, BasicBlock *HoistPt,
849  const SmallVecInsn &InstructionsToHoist,
850  Instruction *Gep) const {
851  assert(allGepOperandsAvailable(Gep, HoistPt) &&
852  "GEP operands not available");
853 
854  Instruction *ClonedGep = Gep->clone();
855  for (unsigned i = 0, e = Gep->getNumOperands(); i != e; ++i)
856  if (Instruction *Op = dyn_cast<Instruction>(Gep->getOperand(i))) {
857  // Check whether the operand is already available.
858  if (DT->dominates(Op->getParent(), HoistPt))
859  continue;
860 
861  // As a GEP can refer to other GEPs, recursively make all the operands
862  // of this GEP available at HoistPt.
863  if (GetElementPtrInst *GepOp = dyn_cast<GetElementPtrInst>(Op))
864  makeGepsAvailable(ClonedGep, HoistPt, InstructionsToHoist, GepOp);
865  }
866 
867  // Copy Gep and replace its uses in Repl with ClonedGep.
868  ClonedGep->insertBefore(HoistPt->getTerminator());
869 
870  // Conservatively discard any optimization hints, they may differ on the
871  // other paths.
872  ClonedGep->dropUnknownNonDebugMetadata();
873 
874  // If we have optimization hints which agree with each other along different
875  // paths, preserve them.
876  for (const Instruction *OtherInst : InstructionsToHoist) {
877  const GetElementPtrInst *OtherGep;
878  if (auto *OtherLd = dyn_cast<LoadInst>(OtherInst))
879  OtherGep = cast<GetElementPtrInst>(OtherLd->getPointerOperand());
880  else
881  OtherGep = cast<GetElementPtrInst>(
882  cast<StoreInst>(OtherInst)->getPointerOperand());
883  ClonedGep->andIRFlags(OtherGep);
884  }
885 
886  // Replace uses of Gep with ClonedGep in Repl.
887  Repl->replaceUsesOfWith(Gep, ClonedGep);
888  }
889 
890  void updateAlignment(Instruction *I, Instruction *Repl) {
891  if (auto *ReplacementLoad = dyn_cast<LoadInst>(Repl)) {
892  ReplacementLoad->setAlignment(
893  std::min(ReplacementLoad->getAlignment(),
894  cast<LoadInst>(I)->getAlignment()));
895  ++NumLoadsRemoved;
896  } else if (auto *ReplacementStore = dyn_cast<StoreInst>(Repl)) {
897  ReplacementStore->setAlignment(
898  std::min(ReplacementStore->getAlignment(),
899  cast<StoreInst>(I)->getAlignment()));
900  ++NumStoresRemoved;
901  } else if (auto *ReplacementAlloca = dyn_cast<AllocaInst>(Repl)) {
902  ReplacementAlloca->setAlignment(
903  std::max(ReplacementAlloca->getAlignment(),
904  cast<AllocaInst>(I)->getAlignment()));
905  } else if (isa<CallInst>(Repl)) {
906  ++NumCallsRemoved;
907  }
908  }
909 
910  // Remove all the instructions in Candidates and replace their usage with Repl.
911  // Returns the number of instructions removed.
912  unsigned rauw(const SmallVecInsn &Candidates, Instruction *Repl,
913  MemoryUseOrDef *NewMemAcc) {
914  unsigned NR = 0;
915  for (Instruction *I : Candidates) {
916  if (I != Repl) {
917  ++NR;
918  updateAlignment(I, Repl);
919  if (NewMemAcc) {
920  // Update the uses of the old MSSA access with NewMemAcc.
921  MemoryAccess *OldMA = MSSA->getMemoryAccess(I);
922  OldMA->replaceAllUsesWith(NewMemAcc);
923  MSSAUpdater->removeMemoryAccess(OldMA);
924  }
925 
926  Repl->andIRFlags(I);
927  combineKnownMetadata(Repl, I);
928  I->replaceAllUsesWith(Repl);
929  // Also invalidate the Alias Analysis cache.
930  MD->removeInstruction(I);
931  I->eraseFromParent();
932  }
933  }
934  return NR;
935  }
936 
937  // Replace all Memory PHI usage with NewMemAcc.
938  void raMPHIuw(MemoryUseOrDef *NewMemAcc) {
940  for (User *U : NewMemAcc->users())
941  if (MemoryPhi *Phi = dyn_cast<MemoryPhi>(U))
942  UsePhis.insert(Phi);
943 
944  for (MemoryPhi *Phi : UsePhis) {
945  auto In = Phi->incoming_values();
946  if (llvm::all_of(In, [&](Use &U) { return U == NewMemAcc; })) {
947  Phi->replaceAllUsesWith(NewMemAcc);
948  MSSAUpdater->removeMemoryAccess(Phi);
949  }
950  }
951  }
952 
953  // Remove all other instructions and replace them with Repl.
954  unsigned removeAndReplace(const SmallVecInsn &Candidates, Instruction *Repl,
955  BasicBlock *DestBB, bool MoveAccess) {
956  MemoryUseOrDef *NewMemAcc = MSSA->getMemoryAccess(Repl);
957  if (MoveAccess && NewMemAcc) {
958  // The definition of this ld/st will not change: ld/st hoisting is
959  // legal when the ld/st is not moved past its current definition.
960  MSSAUpdater->moveToPlace(NewMemAcc, DestBB, MemorySSA::End);
961  }
962 
963  // Replace all other instructions with Repl with memory access NewMemAcc.
964  unsigned NR = rauw(Candidates, Repl, NewMemAcc);
965 
966  // Remove MemorySSA phi nodes with the same arguments.
967  if (NewMemAcc)
968  raMPHIuw(NewMemAcc);
969  return NR;
970  }
971 
972  // In the case Repl is a load or a store, we make all their GEPs
973  // available: GEPs are not hoisted by default to avoid the address
974  // computations to be hoisted without the associated load or store.
975  bool makeGepOperandsAvailable(Instruction *Repl, BasicBlock *HoistPt,
976  const SmallVecInsn &InstructionsToHoist) const {
977  // Check whether the GEP of a ld/st can be synthesized at HoistPt.
978  GetElementPtrInst *Gep = nullptr;
979  Instruction *Val = nullptr;
980  if (auto *Ld = dyn_cast<LoadInst>(Repl)) {
981  Gep = dyn_cast<GetElementPtrInst>(Ld->getPointerOperand());
982  } else if (auto *St = dyn_cast<StoreInst>(Repl)) {
983  Gep = dyn_cast<GetElementPtrInst>(St->getPointerOperand());
984  Val = dyn_cast<Instruction>(St->getValueOperand());
985  // Check that the stored value is available.
986  if (Val) {
987  if (isa<GetElementPtrInst>(Val)) {
988  // Check whether we can compute the GEP at HoistPt.
989  if (!allGepOperandsAvailable(Val, HoistPt))
990  return false;
991  } else if (!DT->dominates(Val->getParent(), HoistPt))
992  return false;
993  }
994  }
995 
996  // Check whether we can compute the Gep at HoistPt.
997  if (!Gep || !allGepOperandsAvailable(Gep, HoistPt))
998  return false;
999 
1000  makeGepsAvailable(Repl, HoistPt, InstructionsToHoist, Gep);
1001 
1002  if (Val && isa<GetElementPtrInst>(Val))
1003  makeGepsAvailable(Repl, HoistPt, InstructionsToHoist, Val);
1004 
1005  return true;
1006  }
1007 
1008  std::pair<unsigned, unsigned> hoist(HoistingPointList &HPL) {
1009  unsigned NI = 0, NL = 0, NS = 0, NC = 0, NR = 0;
1010  for (const HoistingPointInfo &HP : HPL) {
1011  // Find out whether we already have one of the instructions in HoistPt,
1012  // in which case we do not have to move it.
1013  BasicBlock *DestBB = HP.first;
1014  const SmallVecInsn &InstructionsToHoist = HP.second;
1015  Instruction *Repl = nullptr;
1016  for (Instruction *I : InstructionsToHoist)
1017  if (I->getParent() == DestBB)
1018  // If there are two instructions in HoistPt to be hoisted in place:
1019  // update Repl to be the first one, such that we can rename the uses
1020  // of the second based on the first.
1021  if (!Repl || firstInBB(I, Repl))
1022  Repl = I;
1023 
1024  // Keep track of whether we moved the instruction so we know whether we
1025  // should move the MemoryAccess.
1026  bool MoveAccess = true;
1027  if (Repl) {
1028  // Repl is already in HoistPt: it remains in place.
1029  assert(allOperandsAvailable(Repl, DestBB) &&
1030  "instruction depends on operands that are not available");
1031  MoveAccess = false;
1032  } else {
1033  // When we do not find Repl in HoistPt, select the first in the list
1034  // and move it to HoistPt.
1035  Repl = InstructionsToHoist.front();
1036 
1037  // We can move Repl in HoistPt only when all operands are available.
1038  // The order in which hoistings are done may influence the availability
1039  // of operands.
1040  if (!allOperandsAvailable(Repl, DestBB)) {
1041  // When HoistingGeps there is nothing more we can do to make the
1042  // operands available: just continue.
1043  if (HoistingGeps)
1044  continue;
1045 
1046  // When not HoistingGeps we need to copy the GEPs.
1047  if (!makeGepOperandsAvailable(Repl, DestBB, InstructionsToHoist))
1048  continue;
1049  }
1050 
1051  // Move the instruction at the end of HoistPt.
1052  Instruction *Last = DestBB->getTerminator();
1053  MD->removeInstruction(Repl);
1054  Repl->moveBefore(Last);
1055 
1056  DFSNumber[Repl] = DFSNumber[Last]++;
1057  }
1058 
1059  NR += removeAndReplace(InstructionsToHoist, Repl, DestBB, MoveAccess);
1060 
1061  if (isa<LoadInst>(Repl))
1062  ++NL;
1063  else if (isa<StoreInst>(Repl))
1064  ++NS;
1065  else if (isa<CallInst>(Repl))
1066  ++NC;
1067  else // Scalar
1068  ++NI;
1069  }
1070 
1071  NumHoisted += NL + NS + NC + NI;
1072  NumRemoved += NR;
1073  NumLoadsHoisted += NL;
1074  NumStoresHoisted += NS;
1075  NumCallsHoisted += NC;
1076  return {NI, NL + NC + NS};
1077  }
1078 
1079  // Hoist all expressions. Returns Number of scalars hoisted
1080  // and number of non-scalars hoisted.
1081  std::pair<unsigned, unsigned> hoistExpressions(Function &F) {
1082  InsnInfo II;
1083  LoadInfo LI;
1084  StoreInfo SI;
1085  CallInfo CI;
1086  for (BasicBlock *BB : depth_first(&F.getEntryBlock())) {
1087  int InstructionNb = 0;
1088  for (Instruction &I1 : *BB) {
1089  // If I1 cannot guarantee progress, subsequent instructions
1090  // in BB cannot be hoisted anyways.
1092  HoistBarrier.insert(BB);
1093  break;
1094  }
1095  // Only hoist the first instructions in BB up to MaxDepthInBB. Hoisting
1096  // deeper may increase the register pressure and compilation time.
1097  if (MaxDepthInBB != -1 && InstructionNb++ >= MaxDepthInBB)
1098  break;
1099 
1100  // Do not value number terminator instructions.
1101  if (I1.isTerminator())
1102  break;
1103 
1104  if (auto *Load = dyn_cast<LoadInst>(&I1))
1105  LI.insert(Load, VN);
1106  else if (auto *Store = dyn_cast<StoreInst>(&I1))
1107  SI.insert(Store, VN);
1108  else if (auto *Call = dyn_cast<CallInst>(&I1)) {
1109  if (auto *Intr = dyn_cast<IntrinsicInst>(Call)) {
1110  if (isa<DbgInfoIntrinsic>(Intr) ||
1111  Intr->getIntrinsicID() == Intrinsic::assume ||
1112  Intr->getIntrinsicID() == Intrinsic::sideeffect)
1113  continue;
1114  }
1115  if (Call->mayHaveSideEffects())
1116  break;
1117 
1118  if (Call->isConvergent())
1119  break;
1120 
1121  CI.insert(Call, VN);
1122  } else if (HoistingGeps || !isa<GetElementPtrInst>(&I1))
1123  // Do not hoist scalars past calls that may write to memory because
1124  // that could result in spills later. geps are handled separately.
1125  // TODO: We can relax this for targets like AArch64 as they have more
1126  // registers than X86.
1127  II.insert(&I1, VN);
1128  }
1129  }
1130 
1131  HoistingPointList HPL;
1132  computeInsertionPoints(II.getVNTable(), HPL, InsKind::Scalar);
1133  computeInsertionPoints(LI.getVNTable(), HPL, InsKind::Load);
1134  computeInsertionPoints(SI.getVNTable(), HPL, InsKind::Store);
1135  computeInsertionPoints(CI.getScalarVNTable(), HPL, InsKind::Scalar);
1136  computeInsertionPoints(CI.getLoadVNTable(), HPL, InsKind::Load);
1137  computeInsertionPoints(CI.getStoreVNTable(), HPL, InsKind::Store);
1138  return hoist(HPL);
1139  }
1140 };
1141 
1143 public:
1144  static char ID;
1145 
1148  }
1149 
1150  bool runOnFunction(Function &F) override {
1151  if (skipFunction(F))
1152  return false;
1153  auto &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree();
1154  auto &PDT = getAnalysis<PostDominatorTreeWrapperPass>().getPostDomTree();
1155  auto &AA = getAnalysis<AAResultsWrapperPass>().getAAResults();
1156  auto &MD = getAnalysis<MemoryDependenceWrapperPass>().getMemDep();
1157  auto &MSSA = getAnalysis<MemorySSAWrapperPass>().getMSSA();
1158 
1159  GVNHoist G(&DT, &PDT, &AA, &MD, &MSSA);
1160  return G.run(F);
1161  }
1162 
1163  void getAnalysisUsage(AnalysisUsage &AU) const override {
1172  }
1173 };
1174 
1175 } // end namespace llvm
1176 
1180  AliasAnalysis &AA = AM.getResult<AAManager>(F);
1182  MemorySSA &MSSA = AM.getResult<MemorySSAAnalysis>(F).getMSSA();
1183  GVNHoist G(&DT, &PDT, &AA, &MD, &MSSA);
1184  if (!G.run(F))
1185  return PreservedAnalyses::all();
1186 
1187  PreservedAnalyses PA;
1190  PA.preserve<GlobalsAA>();
1191  return PA;
1192 }
1193 
1194 char GVNHoistLegacyPass::ID = 0;
1195 
1197  "Early GVN Hoisting of Expressions", false, false)
1204  "Early GVN Hoisting of Expressions", false, false)
1205 
1206 FunctionPass *llvm::createGVNHoistPass() { return new GVNHoistLegacyPass(); }
Legacy wrapper pass to provide the GlobalsAAResult object.
uint64_t CallInst * C
Value * getValueOperand()
Definition: Instructions.h:409
SymbolTableList< Instruction >::iterator eraseFromParent()
This method unlinks &#39;this&#39; from the containing basic block and deletes it.
Definition: Instruction.cpp:67
static cl::opt< int > MaxDepthInBB("gvn-hoist-max-depth", cl::Hidden, cl::init(100), cl::desc("Hoist instructions from the beginning of the BB up to the " "maximum specified depth (default = 100, unlimited = -1)"))
static void r2(uint32_t &A, uint32_t &B, uint32_t &C, uint32_t &D, uint32_t &E, int I, uint32_t *Buf)
Definition: SHA1.cpp:54
bool isSimple() const
Definition: Instructions.h:276
gvn hoist
When an instruction is found to only use loop invariant operands that is safe to hoist, this instruction is called to do the dirty work.
Definition: GVNHoist.cpp:1203
AnalysisUsage & addPreserved()
Add the specified Pass class to the set of analyses preserved by this pass.
Provides a lazy, caching interface for making common memory aliasing information queries, backed by LLVM&#39;s alias analysis passes.
static PassRegistry * getPassRegistry()
getPassRegistry - Access the global registry object, which is automatically initialized at applicatio...
Value * getPointerOperand(Value *V)
A helper function that returns the pointer operand of a load, store or GEP instruction.
GCNRegPressure max(const GCNRegPressure &P1, const GCNRegPressure &P2)
bool doesNotAccessMemory(unsigned OpNo) const
Definition: InstrTypes.h:1465
PassT::Result & getResult(IRUnitT &IR, ExtraArgTs... ExtraArgs)
Get the result of an analysis pass for a given IR unit.
Definition: PassManager.h:769
This class represents lattice values for constants.
Definition: AllocatorList.h:23
MemoryAccess * getDefiningAccess() const
Get the access that produces the memory state used by this Use.
Definition: MemorySSA.h:254
This is the interface for a simple mod/ref and alias analysis over globals.
void dropUnknownNonDebugMetadata(ArrayRef< unsigned > KnownIDs)
Drop all unknown metadata except for debug locations.
Definition: Metadata.cpp:1198
PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM)
Run the pass over the function.
Definition: GVNHoist.cpp:1177
Implements a dense probed hash-table based set.
Definition: DenseSet.h:249
const AccessList * getBlockAccesses(const BasicBlock *BB) const
Return the list of MemoryAccess&#39;s for a given basic block.
Definition: MemorySSA.h:755
This provides a very simple, boring adaptor for a begin and end iterator into a range type...
This class represents a function call, abstracting a target machine&#39;s calling convention.
Represents a read-write access to memory, whether it is a must-alias, or a may-alias.
Definition: MemorySSA.h:372
bool isTerminator() const
Definition: Instruction.h:128
unsigned int rank(const Value *V) const
Definition: GVNHoist.cpp:306
bool all_of(R &&range, UnaryPredicate P)
Provide wrappers to std::all_of which take ranges instead of having to pass begin/end explicitly...
Definition: STLExtras.h:1185
bool properlyDominates(const DomTreeNodeBase< NodeT > *A, const DomTreeNodeBase< NodeT > *B) const
properlyDominates - Returns true iff A dominates B and A != B.
STATISTIC(NumFunctions, "Total number of functions")
Analysis pass which computes a DominatorTree.
Definition: Dominators.h:230
F(f)
FunctionPass * createGVNHoistPass()
Definition: GVNHoist.cpp:1206
An instruction for reading from memory.
Definition: Instructions.h:167
std::enable_if<!std::is_array< T >::value, std::unique_ptr< T > >::type make_unique(Args &&... args)
Constructs a new T() with the given args and returns a unique_ptr<T> which owns the object...
Definition: STLExtras.h:1393
const Instruction * getTerminator() const LLVM_READONLY
Returns the terminator instruction if the block is well formed or null if the block is not well forme...
Definition: BasicBlock.cpp:137
This defines the Use class.
static void combineKnownMetadata(Instruction *ReplInst, Instruction *I)
Definition: GVNHoist.cpp:243
gvn Early GVN Hoisting of Expressions
Definition: GVNHoist.cpp:1203
Represents read-only accesses to memory.
Definition: MemorySSA.h:316
AnalysisUsage & addRequired()
#define INITIALIZE_PASS_DEPENDENCY(depName)
Definition: PassSupport.h:50
static uint32_t getAlignment(const MCSectionCOFF &Sec)
Legacy analysis pass which computes MemorySSA.
Definition: MemorySSA.h:957
bool runOnFunction(Function &F) override
runOnFunction - Virtual method overriden by subclasses to do the per-function processing of the pass...
Definition: GVNHoist.cpp:1150
Constant Hoisting
A Use represents the edge between a Value definition and its users.
Definition: Use.h:55
void setDefiningBlocks(const SmallPtrSetImpl< BasicBlock *> &Blocks)
Give the IDF calculator the set of blocks in which the value is defined.
static bool defClobbersUseOrDef(MemoryDef *MD, const MemoryUseOrDef *MU, AliasAnalysis &AA)
Definition: MemorySSA.cpp:317
This class consists of common code factored out of the SmallVector class to reduce code duplication b...
Definition: APFloat.h:41
Encapsulates MemorySSA, including all data associated with memory accesses.
Definition: MemorySSA.h:700
void insert(Instruction *I, GVN::ValueTable &VN)
Definition: GVNHoist.cpp:171
An analysis that produces MemoryDependenceResults for a function.
unsigned Intr
static cl::opt< int > MaxChainLength("gvn-hoist-max-chain-length", cl::Hidden, cl::init(10), cl::desc("Maximum length of dependent chains to hoist " "(default = 10, unlimited = -1)"))
void getAnalysisUsage(AnalysisUsage &AU) const override
getAnalysisUsage - This function should be overriden by passes that need analysis information to do t...
Definition: GVNHoist.cpp:1163
auto reverse(ContainerTy &&C, typename std::enable_if< has_rbegin< ContainerTy >::value >::type *=nullptr) -> decltype(make_range(C.rbegin(), C.rend()))
Definition: STLExtras.h:266
INITIALIZE_PASS_BEGIN(GVNHoistLegacyPass, "gvn-hoist", "Early GVN Hoisting of Expressions", false, false) INITIALIZE_PASS_END(GVNHoistLegacyPass
Instruction * clone() const
Create a copy of &#39;this&#39; instruction that is identical in all ways except the following: ...
bool run(Function &F)
Definition: GVNHoist.cpp:262
MemoryUseOrDef * getMemoryAccess(const Instruction *I) const
Given a memory Mod/Ref&#39;ing instruction, get the MemorySSA access associated with it.
Definition: MemorySSA.h:717
void insert(LoadInst *Load, GVN::ValueTable &VN)
Definition: GVNHoist.cpp:186
The core GVN pass object.
Definition: GVN.h:68
void andIRFlags(const Value *V)
Logical &#39;and&#39; of any supported wrapping, exact, and fast-math flags of V and this instruction...
void combineMetadata(Instruction *K, const Instruction *J, ArrayRef< unsigned > KnownIDs, bool DoesKMove)
Combine the metadata of two instructions so that K can replace J.
Definition: Local.cpp:2276
const VNtoInsns & getVNTable() const
Definition: GVNHoist.cpp:177
An instruction for storing to memory.
Definition: Instructions.h:320
void replaceAllUsesWith(Value *V)
Change all uses of this to point to a new Value.
Definition: Value.cpp:429
const VNtoInsns & getLoadVNTable() const
Definition: GVNHoist.cpp:239
Concrete subclass of DominatorTreeBase that is used to compute a normal dominator tree...
Definition: Dominators.h:144
unsigned getNumSuccessors() const
Return the number of successors that this instruction has.
Value * getOperand(unsigned i) const
Definition: User.h:169
void replaceUsesOfWith(Value *From, Value *To)
Replace uses of one Value with another.
Definition: User.cpp:20
idf_iterator< T > idf_begin(const T &G)
iterator find(const_arg_type_t< KeyT > Val)
Definition: DenseMap.h:176
idf_iterator< T > idf_end(const T &G)
const BasicBlock & getEntryBlock() const
Definition: Function.h:642
an instruction for type-safe pointer arithmetic to access elements of arrays and structs ...
Definition: Instructions.h:873
void insert(CallInst *Call, GVN::ValueTable &VN)
Definition: GVNHoist.cpp:223
#define P(N)
initializer< Ty > init(const Ty &Val)
Definition: CommandLine.h:427
bool isGuaranteedToTransferExecutionToSuccessor(const Instruction *I)
Return true if this function can prove that the instruction I will always transfer execution to one o...
static GCRegistry::Add< OcamlGC > B("ocaml", "ocaml 3.10-compatible GC")
A set of analyses that are preserved following a run of a transformation pass.
Definition: PassManager.h:153
* if(!EatIfPresent(lltok::kw_thread_local)) return false
ParseOptionalThreadLocal := /*empty.
void insertBefore(Instruction *InsertPos)
Insert an unlinked instruction into a basic block immediately before the specified instruction...
Definition: Instruction.cpp:73
LLVM Basic Block Representation.
Definition: BasicBlock.h:57
const VNtoInsns & getScalarVNTable() const
Definition: GVNHoist.cpp:238
This class holds the mapping between values and value numbers.
Definition: GVN.h:89
This file provides the interface for LLVM&#39;s Global Value Numbering pass which eliminates fully redund...
SmallVector< Instruction *, 4 > SmallVecInsn
Definition: GVNHoist.cpp:118
static GCRegistry::Add< CoreCLRGC > E("coreclr", "CoreCLR-compatible GC")
This file contains the declarations for the subclasses of Constant, which represent the different fla...
A manager for alias analyses.
std::pair< iterator, bool > insert(PtrType Ptr)
Inserts Ptr if and only if there is no element in the container equal to Ptr.
Definition: SmallPtrSet.h:370
bool mayThrow() const
Return true if this instruction may throw an exception.
const VNtoInsns & getStoreVNTable() const
Definition: GVNHoist.cpp:240
Represent the analysis usage information of a pass.
bool any_of(R &&range, UnaryPredicate P)
Provide wrappers to std::any_of which take ranges instead of having to pass begin/end explicitly...
Definition: STLExtras.h:1192
Analysis pass providing a never-invalidated alias analysis result.
FunctionPass class - This class is used to implement most global optimizations.
Definition: Pass.h:284
size_t arg_size() const
Definition: Function.h:700
op_range operands()
Definition: User.h:237
Value * getPointerOperand()
Definition: Instructions.h:284
BasicBlock * Dest
Definition: GVNHoist.cpp:146
auto find_if(R &&Range, UnaryPredicate P) -> decltype(adl_begin(Range))
Provide wrappers to std::find_if which take ranges instead of having to pass begin/end explicitly...
Definition: STLExtras.h:1213
static void r1(uint32_t &A, uint32_t &B, uint32_t &C, uint32_t &D, uint32_t &E, int I, uint32_t *Buf)
Definition: SHA1.cpp:48
static PreservedAnalyses all()
Construct a special preserved set that preserves all passes.
Definition: PassManager.h:159
size_t size() const
Definition: SmallVector.h:52
Compute iterated dominance frontiers using a linear time algorithm.
DomTreeNodeBase< NodeT > * getNode(const NodeT *BB) const
getNode - return the (Post)DominatorTree node for the specified basic block.
A wrapper analysis pass for the legacy pass manager that exposes a MemoryDepnedenceResults instance...
An intrusive list with ownership and callbacks specified/controlled by ilist_traits, only with API safe for polymorphic types.
Definition: ilist.h:388
INITIALIZE_PASS_END(RegBankSelect, DEBUG_TYPE, "Assign register bank of generic virtual registers", false, false) RegBankSelect
static cl::opt< int > MaxNumberOfBBSInPath("gvn-hoist-max-bbs", cl::Hidden, cl::init(4), cl::desc("Max number of basic blocks on the path between " "hoisting locations (default = 4, unlimited = -1)"))
const VNtoInsns & getVNTable() const
Definition: GVNHoist.cpp:193
std::pair< unsigned, unsigned > VNType
Definition: GVNHoist.cpp:128
bool operator==(const CHIArg &A)
Definition: GVNHoist.cpp:151
void sort(IteratorTy Start, IteratorTy End)
Definition: STLExtras.h:1115
bool hasAddressTaken() const
Returns true if there are any uses of this basic block other than direct branches, switches, etc.
Definition: BasicBlock.h:391
iterator_range< T > make_range(T x, T y)
Convenience function for iterating over sub-ranges.
unsigned getNumOperands() const
Definition: User.h:191
SmallPtrSet - This class implements a set which is optimized for holding SmallSize or less elements...
Definition: SmallPtrSet.h:417
auto size(R &&Range, typename std::enable_if< std::is_same< typename std::iterator_traits< decltype(Range.begin())>::iterator_category, std::random_access_iterator_tag >::value, void >::type *=nullptr) -> decltype(std::distance(Range.begin(), Range.end()))
Get the size of a range.
Definition: STLExtras.h:1166
void calculate(SmallVectorImpl< BasicBlock *> &IDFBlocks)
Calculate iterated dominance frontiers.
bool locallyDominates(const MemoryAccess *A, const MemoryAccess *B) const
Given two memory accesses in the same basic block, determine whether MemoryAccess A dominates MemoryA...
Definition: MemorySSA.cpp:2044
This is a &#39;vector&#39; (really, a variable-sized array), optimized for the case when the array is small...
Definition: SmallVector.h:841
bool dominates(const Instruction *Def, const Use &U) const
Return true if Def dominates a use in User.
Definition: Dominators.cpp:248
Analysis pass which computes a PostDominatorTree.
const DataFlowGraph & G
Definition: RDFGraph.cpp:202
An analysis that produces MemorySSA for a function.
Definition: MemorySSA.h:921
BasicBlock * getBlock() const
Definition: MemorySSA.h:156
static GCRegistry::Add< StatepointGC > D("statepoint-example", "an example strategy for statepoint")
pred_range predecessors(BasicBlock *BB)
Definition: CFG.h:124
GVNHoist(DominatorTree *DT, PostDominatorTree *PDT, AliasAnalysis *AA, MemoryDependenceResults *MD, MemorySSA *MSSA)
Definition: GVNHoist.cpp:257
#define NC
Definition: regutils.h:42
raw_ostream & dbgs()
dbgs() - This returns a reference to a raw_ostream for debugging messages.
Definition: Debug.cpp:132
A range adaptor for a pair of iterators.
std::pair< BasicBlock *, SmallVecInsn > HoistingPointInfo
Definition: GVNHoist.cpp:123
Class that has the common methods + fields of memory uses/defs.
Definition: MemorySSA.h:244
typename SuperClass::iterator iterator
Definition: SmallVector.h:319
iterator_range< user_iterator > users()
Definition: Value.h:399
PostDominatorTree Class - Concrete subclass of DominatorTree that is used to compute the post-dominat...
Instruction * getMemoryInst() const
Get the instruction that this MemoryUse represents.
Definition: MemorySSA.h:251
void insert(StoreInst *Store, GVN::ValueTable &VN)
Definition: GVNHoist.cpp:203
This file provides various utilities for inspecting and working with the control flow graph in LLVM I...
void initializeGVNHoistLegacyPassPass(PassRegistry &)
StringRef getName() const
Return a constant reference to the value&#39;s name.
Definition: Value.cpp:214
bool onlyReadsMemory(unsigned OpNo) const
Definition: InstrTypes.h:1471
iterator end()
Definition: DenseMap.h:108
LLVM_NODISCARD std::enable_if<!is_simple_type< Y >::value, typename cast_retty< X, const Y >::ret_type >::type dyn_cast(const Y &Val)
Definition: Casting.h:332
void preserve()
Mark an analysis as preserved.
Definition: PassManager.h:174
bool isLiveOnEntryDef(const MemoryAccess *MA) const
Return true if MA represents the live on entry value.
Definition: MemorySSA.h:735
size_type count(const_arg_type_t< ValueT > V) const
Return 1 if the specified key is in the set, 0 otherwise.
Definition: DenseSet.h:91
uint32_t lookupOrAdd(Value *V)
lookup_or_add - Returns the value number for the specified value, assigning it a new number if it did...
Definition: GVN.cpp:480
const VNtoInsns & getVNTable() const
Definition: GVNHoist.cpp:212
ValueT lookup(const_arg_type_t< KeyT > Val) const
lookup - Return the entry for the specified key, or a default constructed value if no such entry exis...
Definition: DenseMap.h:211
static cl::opt< int > MaxHoistedThreshold("gvn-max-hoisted", cl::Hidden, cl::init(-1), cl::desc("Max number of instructions to hoist " "(default unlimited = -1)"))
iterator_range< df_iterator< T > > depth_first(const T &G)
Determine the iterated dominance frontier, given a set of defining blocks, and optionally, a set of live-in blocks.
assert(ImpDefSCC.getReg()==AMDGPU::SCC &&ImpDefSCC.isDef())
bool isEHPad() const
Return true if this basic block is an exception handling block.
Definition: BasicBlock.h:398
LLVM Value Representation.
Definition: Value.h:72
void removeInstruction(Instruction *InstToRemove)
Removes an instruction from the dependence analysis, updating the dependence of instructions that pre...
succ_range successors(Instruction *I)
Definition: CFG.h:259
SmallVectorImpl< CHIArg >::iterator CHIIt
Definition: GVNHoist.cpp:155
void moveBefore(Instruction *MovePos)
Unlink this instruction from its current basic block and insert it into the basic block that MovePos ...
Definition: Instruction.cpp:86
This file exposes an interface to building/using memory SSA to walk memory instructions using a use/d...
A container for analyses that lazily runs them and caches their results.
Legacy analysis pass which computes a DominatorTree.
Definition: Dominators.h:259
A wrapper pass to provide the legacy pass manager access to a suitably prepared AAResults object...
bool isSimple() const
Definition: Instructions.h:401
Represents phi nodes for memory accesses.
Definition: MemorySSA.h:478
Utility type to build an inheritance chain that makes it easy to rank overload candidates.
Definition: STLExtras.h:1010
This header defines various interfaces for pass management in LLVM.
bool operator!=(const CHIArg &A)
Definition: GVNHoist.cpp:152
#define LLVM_DEBUG(X)
Definition: Debug.h:122
Instruction * I
Definition: GVNHoist.cpp:149
Value * getPointerOperand()
Definition: Instructions.h:412
const BasicBlock * getParent() const
Definition: Instruction.h:66