1//===------- VectorCombine.cpp - Optimize partial vector operations -------===//
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 optimizes scalar/vector interactions using target cost models. The
10// transforms implemented here may not fit in traditional loop-based or SLP
11// vectorization passes.
12//
13//===----------------------------------------------------------------------===//
14
15#include "llvm/Transforms/Vectorize/VectorCombine.h"
16#include "llvm/ADT/Statistic.h"
17#include "llvm/Analysis/BasicAliasAnalysis.h"
18#include "llvm/Analysis/GlobalsModRef.h"
19#include "llvm/Analysis/TargetTransformInfo.h"
20#include "llvm/Analysis/ValueTracking.h"
21#include "llvm/Analysis/VectorUtils.h"
22#include "llvm/IR/Dominators.h"
23#include "llvm/IR/Function.h"
24#include "llvm/IR/IRBuilder.h"
25#include "llvm/IR/PatternMatch.h"
26#include "llvm/InitializePasses.h"
27#include "llvm/Pass.h"
28#include "llvm/Support/CommandLine.h"
29#include "llvm/Transforms/Utils/Local.h"
30#include "llvm/Transforms/Vectorize.h"
31
32using namespace llvm;
33using namespace llvm::PatternMatch;
34
35#define DEBUG_TYPE "vector-combine"
36STATISTIC(NumVecCmp, "Number of vector compares formed");
37STATISTIC(NumVecBO, "Number of vector binops formed");
38STATISTIC(NumVecCmpBO, "Number of vector compare + binop formed");
39STATISTIC(NumShufOfBitcast, "Number of shuffles moved after bitcast");
40STATISTIC(NumScalarBO, "Number of scalar binops formed");
41STATISTIC(NumScalarCmp, "Number of scalar compares formed");
42
43static cl::opt<bool> DisableVectorCombine(
44    "disable-vector-combine", cl::init(false), cl::Hidden,
45    cl::desc("Disable all vector combine transforms"));
46
47static cl::opt<bool> DisableBinopExtractShuffle(
48    "disable-binop-extract-shuffle", cl::init(false), cl::Hidden,
49    cl::desc("Disable binop extract to shuffle transforms"));
50
51static const unsigned InvalidIndex = std::numeric_limits<unsigned>::max();
52
53namespace {
54class VectorCombine {
55public:
56  VectorCombine(Function &F, const TargetTransformInfo &TTI,
57                const DominatorTree &DT)
58      : F(F), Builder(F.getContext()), TTI(TTI), DT(DT) {}
59
60  bool run();
61
62private:
63  Function &F;
64  IRBuilder<> Builder;
65  const TargetTransformInfo &TTI;
66  const DominatorTree &DT;
67
68  ExtractElementInst *getShuffleExtract(ExtractElementInst *Ext0,
69                                        ExtractElementInst *Ext1,
70                                        unsigned PreferredExtractIndex) const;
71  bool isExtractExtractCheap(ExtractElementInst *Ext0, ExtractElementInst *Ext1,
72                             unsigned Opcode,
73                             ExtractElementInst *&ConvertToShuffle,
74                             unsigned PreferredExtractIndex);
75  void foldExtExtCmp(ExtractElementInst *Ext0, ExtractElementInst *Ext1,
76                     Instruction &I);
77  void foldExtExtBinop(ExtractElementInst *Ext0, ExtractElementInst *Ext1,
78                       Instruction &I);
79  bool foldExtractExtract(Instruction &I);
80  bool foldBitcastShuf(Instruction &I);
81  bool scalarizeBinopOrCmp(Instruction &I);
82  bool foldExtractedCmps(Instruction &I);
83};
84} // namespace
85
86static void replaceValue(Value &Old, Value &New) {
87  Old.replaceAllUsesWith(&New);
88  New.takeName(&Old);
89}
90
91/// Determine which, if any, of the inputs should be replaced by a shuffle
92/// followed by extract from a different index.
93ExtractElementInst *VectorCombine::getShuffleExtract(
94    ExtractElementInst *Ext0, ExtractElementInst *Ext1,
95    unsigned PreferredExtractIndex = InvalidIndex) const {
96  assert(isa<ConstantInt>(Ext0->getIndexOperand()) &&
97         isa<ConstantInt>(Ext1->getIndexOperand()) &&
98         "Expected constant extract indexes");
99
100  unsigned Index0 = cast<ConstantInt>(Ext0->getIndexOperand())->getZExtValue();
101  unsigned Index1 = cast<ConstantInt>(Ext1->getIndexOperand())->getZExtValue();
102
103  // If the extract indexes are identical, no shuffle is needed.
104  if (Index0 == Index1)
105    return nullptr;
106
107  Type *VecTy = Ext0->getVectorOperand()->getType();
108  assert(VecTy == Ext1->getVectorOperand()->getType() && "Need matching types");
109  int Cost0 = TTI.getVectorInstrCost(Ext0->getOpcode(), VecTy, Index0);
110  int Cost1 = TTI.getVectorInstrCost(Ext1->getOpcode(), VecTy, Index1);
111
112  // We are extracting from 2 different indexes, so one operand must be shuffled
113  // before performing a vector operation and/or extract. The more expensive
114  // extract will be replaced by a shuffle.
115  if (Cost0 > Cost1)
116    return Ext0;
117  if (Cost1 > Cost0)
118    return Ext1;
119
120  // If the costs are equal and there is a preferred extract index, shuffle the
121  // opposite operand.
122  if (PreferredExtractIndex == Index0)
123    return Ext1;
124  if (PreferredExtractIndex == Index1)
125    return Ext0;
126
127  // Otherwise, replace the extract with the higher index.
128  return Index0 > Index1 ? Ext0 : Ext1;
129}
130
131/// Compare the relative costs of 2 extracts followed by scalar operation vs.
132/// vector operation(s) followed by extract. Return true if the existing
133/// instructions are cheaper than a vector alternative. Otherwise, return false
134/// and if one of the extracts should be transformed to a shufflevector, set
135/// \p ConvertToShuffle to that extract instruction.
136bool VectorCombine::isExtractExtractCheap(ExtractElementInst *Ext0,
137                                          ExtractElementInst *Ext1,
138                                          unsigned Opcode,
139                                          ExtractElementInst *&ConvertToShuffle,
140                                          unsigned PreferredExtractIndex) {
141  assert(isa<ConstantInt>(Ext0->getOperand(1)) &&
142         isa<ConstantInt>(Ext1->getOperand(1)) &&
143         "Expected constant extract indexes");
144  Type *ScalarTy = Ext0->getType();
145  auto *VecTy = cast<VectorType>(Ext0->getOperand(0)->getType());
146  int ScalarOpCost, VectorOpCost;
147
148  // Get cost estimates for scalar and vector versions of the operation.
149  bool IsBinOp = Instruction::isBinaryOp(Opcode);
150  if (IsBinOp) {
151    ScalarOpCost = TTI.getArithmeticInstrCost(Opcode, ScalarTy);
152    VectorOpCost = TTI.getArithmeticInstrCost(Opcode, VecTy);
153  } else {
154    assert((Opcode == Instruction::ICmp || Opcode == Instruction::FCmp) &&
155           "Expected a compare");
156    ScalarOpCost = TTI.getCmpSelInstrCost(Opcode, ScalarTy,
157                                          CmpInst::makeCmpResultType(ScalarTy));
158    VectorOpCost = TTI.getCmpSelInstrCost(Opcode, VecTy,
159                                          CmpInst::makeCmpResultType(VecTy));
160  }
161
162  // Get cost estimates for the extract elements. These costs will factor into
163  // both sequences.
164  unsigned Ext0Index = cast<ConstantInt>(Ext0->getOperand(1))->getZExtValue();
165  unsigned Ext1Index = cast<ConstantInt>(Ext1->getOperand(1))->getZExtValue();
166
167  int Extract0Cost =
168      TTI.getVectorInstrCost(Instruction::ExtractElement, VecTy, Ext0Index);
169  int Extract1Cost =
170      TTI.getVectorInstrCost(Instruction::ExtractElement, VecTy, Ext1Index);
171
172  // A more expensive extract will always be replaced by a splat shuffle.
173  // For example, if Ext0 is more expensive:
174  // opcode (extelt V0, Ext0), (ext V1, Ext1) -->
175  // extelt (opcode (splat V0, Ext0), V1), Ext1
176  // TODO: Evaluate whether that always results in lowest cost. Alternatively,
177  //       check the cost of creating a broadcast shuffle and shuffling both
178  //       operands to element 0.
179  int CheapExtractCost = std::min(Extract0Cost, Extract1Cost);
180
181  // Extra uses of the extracts mean that we include those costs in the
182  // vector total because those instructions will not be eliminated.
183  int OldCost, NewCost;
184  if (Ext0->getOperand(0) == Ext1->getOperand(0) && Ext0Index == Ext1Index) {
185    // Handle a special case. If the 2 extracts are identical, adjust the
186    // formulas to account for that. The extra use charge allows for either the
187    // CSE'd pattern or an unoptimized form with identical values:
188    // opcode (extelt V, C), (extelt V, C) --> extelt (opcode V, V), C
189    bool HasUseTax = Ext0 == Ext1 ? !Ext0->hasNUses(2)
190                                  : !Ext0->hasOneUse() || !Ext1->hasOneUse();
191    OldCost = CheapExtractCost + ScalarOpCost;
192    NewCost = VectorOpCost + CheapExtractCost + HasUseTax * CheapExtractCost;
193  } else {
194    // Handle the general case. Each extract is actually a different value:
195    // opcode (extelt V0, C0), (extelt V1, C1) --> extelt (opcode V0, V1), C
196    OldCost = Extract0Cost + Extract1Cost + ScalarOpCost;
197    NewCost = VectorOpCost + CheapExtractCost +
198              !Ext0->hasOneUse() * Extract0Cost +
199              !Ext1->hasOneUse() * Extract1Cost;
200  }
201
202  ConvertToShuffle = getShuffleExtract(Ext0, Ext1, PreferredExtractIndex);
203  if (ConvertToShuffle) {
204    if (IsBinOp && DisableBinopExtractShuffle)
205      return true;
206
207    // If we are extracting from 2 different indexes, then one operand must be
208    // shuffled before performing the vector operation. The shuffle mask is
209    // undefined except for 1 lane that is being translated to the remaining
210    // extraction lane. Therefore, it is a splat shuffle. Ex:
211    // ShufMask = { undef, undef, 0, undef }
212    // TODO: The cost model has an option for a "broadcast" shuffle
213    //       (splat-from-element-0), but no option for a more general splat.
214    NewCost +=
215        TTI.getShuffleCost(TargetTransformInfo::SK_PermuteSingleSrc, VecTy);
216  }
217
218  // Aggressively form a vector op if the cost is equal because the transform
219  // may enable further optimization.
220  // Codegen can reverse this transform (scalarize) if it was not profitable.
221  return OldCost < NewCost;
222}
223
224/// Create a shuffle that translates (shifts) 1 element from the input vector
225/// to a new element location.
226static Value *createShiftShuffle(Value *Vec, unsigned OldIndex,
227                                 unsigned NewIndex, IRBuilder<> &Builder) {
228  // The shuffle mask is undefined except for 1 lane that is being translated
229  // to the new element index. Example for OldIndex == 2 and NewIndex == 0:
230  // ShufMask = { 2, undef, undef, undef }
231  auto *VecTy = cast<FixedVectorType>(Vec->getType());
232  SmallVector<int, 32> ShufMask(VecTy->getNumElements(), UndefMaskElem);
233  ShufMask[NewIndex] = OldIndex;
234  Value *Undef = UndefValue::get(VecTy);
235  return Builder.CreateShuffleVector(Vec, Undef, ShufMask, "shift");
236}
237
238/// Given an extract element instruction with constant index operand, shuffle
239/// the source vector (shift the scalar element) to a NewIndex for extraction.
240/// Return null if the input can be constant folded, so that we are not creating
241/// unnecessary instructions.
242static ExtractElementInst *translateExtract(ExtractElementInst *ExtElt,
243                                            unsigned NewIndex,
244                                            IRBuilder<> &Builder) {
245  // If the extract can be constant-folded, this code is unsimplified. Defer
246  // to other passes to handle that.
247  Value *X = ExtElt->getVectorOperand();
248  Value *C = ExtElt->getIndexOperand();
249  assert(isa<ConstantInt>(C) && "Expected a constant index operand");
250  if (isa<Constant>(X))
251    return nullptr;
252
253  Value *Shuf = createShiftShuffle(X, cast<ConstantInt>(C)->getZExtValue(),
254                                   NewIndex, Builder);
255  return cast<ExtractElementInst>(Builder.CreateExtractElement(Shuf, NewIndex));
256}
257
258/// Try to reduce extract element costs by converting scalar compares to vector
259/// compares followed by extract.
260/// cmp (ext0 V0, C), (ext1 V1, C)
261void VectorCombine::foldExtExtCmp(ExtractElementInst *Ext0,
262                                  ExtractElementInst *Ext1, Instruction &I) {
263  assert(isa<CmpInst>(&I) && "Expected a compare");
264  assert(cast<ConstantInt>(Ext0->getIndexOperand())->getZExtValue() ==
265             cast<ConstantInt>(Ext1->getIndexOperand())->getZExtValue() &&
266         "Expected matching constant extract indexes");
267
268  // cmp Pred (extelt V0, C), (extelt V1, C) --> extelt (cmp Pred V0, V1), C
269  ++NumVecCmp;
270  CmpInst::Predicate Pred = cast<CmpInst>(&I)->getPredicate();
271  Value *V0 = Ext0->getVectorOperand(), *V1 = Ext1->getVectorOperand();
272  Value *VecCmp = Builder.CreateCmp(Pred, V0, V1);
273  Value *NewExt = Builder.CreateExtractElement(VecCmp, Ext0->getIndexOperand());
274  replaceValue(I, *NewExt);
275}
276
277/// Try to reduce extract element costs by converting scalar binops to vector
278/// binops followed by extract.
279/// bo (ext0 V0, C), (ext1 V1, C)
280void VectorCombine::foldExtExtBinop(ExtractElementInst *Ext0,
281                                    ExtractElementInst *Ext1, Instruction &I) {
282  assert(isa<BinaryOperator>(&I) && "Expected a binary operator");
283  assert(cast<ConstantInt>(Ext0->getIndexOperand())->getZExtValue() ==
284             cast<ConstantInt>(Ext1->getIndexOperand())->getZExtValue() &&
285         "Expected matching constant extract indexes");
286
287  // bo (extelt V0, C), (extelt V1, C) --> extelt (bo V0, V1), C
288  ++NumVecBO;
289  Value *V0 = Ext0->getVectorOperand(), *V1 = Ext1->getVectorOperand();
290  Value *VecBO =
291      Builder.CreateBinOp(cast<BinaryOperator>(&I)->getOpcode(), V0, V1);
292
293  // All IR flags are safe to back-propagate because any potential poison
294  // created in unused vector elements is discarded by the extract.
295  if (auto *VecBOInst = dyn_cast<Instruction>(VecBO))
296    VecBOInst->copyIRFlags(&I);
297
298  Value *NewExt = Builder.CreateExtractElement(VecBO, Ext0->getIndexOperand());
299  replaceValue(I, *NewExt);
300}
301
302/// Match an instruction with extracted vector operands.
303bool VectorCombine::foldExtractExtract(Instruction &I) {
304  // It is not safe to transform things like div, urem, etc. because we may
305  // create undefined behavior when executing those on unknown vector elements.
306  if (!isSafeToSpeculativelyExecute(&I))
307    return false;
308
309  Instruction *I0, *I1;
310  CmpInst::Predicate Pred = CmpInst::BAD_ICMP_PREDICATE;
311  if (!match(&I, m_Cmp(Pred, m_Instruction(I0), m_Instruction(I1))) &&
312      !match(&I, m_BinOp(m_Instruction(I0), m_Instruction(I1))))
313    return false;
314
315  Value *V0, *V1;
316  uint64_t C0, C1;
317  if (!match(I0, m_ExtractElt(m_Value(V0), m_ConstantInt(C0))) ||
318      !match(I1, m_ExtractElt(m_Value(V1), m_ConstantInt(C1))) ||
319      V0->getType() != V1->getType())
320    return false;
321
322  // If the scalar value 'I' is going to be re-inserted into a vector, then try
323  // to create an extract to that same element. The extract/insert can be
324  // reduced to a "select shuffle".
325  // TODO: If we add a larger pattern match that starts from an insert, this
326  //       probably becomes unnecessary.
327  auto *Ext0 = cast<ExtractElementInst>(I0);
328  auto *Ext1 = cast<ExtractElementInst>(I1);
329  uint64_t InsertIndex = InvalidIndex;
330  if (I.hasOneUse())
331    match(I.user_back(),
332          m_InsertElt(m_Value(), m_Value(), m_ConstantInt(InsertIndex)));
333
334  ExtractElementInst *ExtractToChange;
335  if (isExtractExtractCheap(Ext0, Ext1, I.getOpcode(), ExtractToChange,
336                            InsertIndex))
337    return false;
338
339  if (ExtractToChange) {
340    unsigned CheapExtractIdx = ExtractToChange == Ext0 ? C1 : C0;
341    ExtractElementInst *NewExtract =
342        translateExtract(ExtractToChange, CheapExtractIdx, Builder);
343    if (!NewExtract)
344      return false;
345    if (ExtractToChange == Ext0)
346      Ext0 = NewExtract;
347    else
348      Ext1 = NewExtract;
349  }
350
351  if (Pred != CmpInst::BAD_ICMP_PREDICATE)
352    foldExtExtCmp(Ext0, Ext1, I);
353  else
354    foldExtExtBinop(Ext0, Ext1, I);
355
356  return true;
357}
358
359/// If this is a bitcast of a shuffle, try to bitcast the source vector to the
360/// destination type followed by shuffle. This can enable further transforms by
361/// moving bitcasts or shuffles together.
362bool VectorCombine::foldBitcastShuf(Instruction &I) {
363  Value *V;
364  ArrayRef<int> Mask;
365  if (!match(&I, m_BitCast(
366                     m_OneUse(m_Shuffle(m_Value(V), m_Undef(), m_Mask(Mask))))))
367    return false;
368
369  // Disallow non-vector casts and length-changing shuffles.
370  // TODO: We could allow any shuffle.
371  auto *DestTy = dyn_cast<VectorType>(I.getType());
372  auto *SrcTy = cast<VectorType>(V->getType());
373  if (!DestTy || I.getOperand(0)->getType() != SrcTy)
374    return false;
375
376  // The new shuffle must not cost more than the old shuffle. The bitcast is
377  // moved ahead of the shuffle, so assume that it has the same cost as before.
378  if (TTI.getShuffleCost(TargetTransformInfo::SK_PermuteSingleSrc, DestTy) >
379      TTI.getShuffleCost(TargetTransformInfo::SK_PermuteSingleSrc, SrcTy))
380    return false;
381
382  unsigned DestNumElts = DestTy->getNumElements();
383  unsigned SrcNumElts = SrcTy->getNumElements();
384  SmallVector<int, 16> NewMask;
385  if (SrcNumElts <= DestNumElts) {
386    // The bitcast is from wide to narrow/equal elements. The shuffle mask can
387    // always be expanded to the equivalent form choosing narrower elements.
388    assert(DestNumElts % SrcNumElts == 0 && "Unexpected shuffle mask");
389    unsigned ScaleFactor = DestNumElts / SrcNumElts;
390    narrowShuffleMaskElts(ScaleFactor, Mask, NewMask);
391  } else {
392    // The bitcast is from narrow elements to wide elements. The shuffle mask
393    // must choose consecutive elements to allow casting first.
394    assert(SrcNumElts % DestNumElts == 0 && "Unexpected shuffle mask");
395    unsigned ScaleFactor = SrcNumElts / DestNumElts;
396    if (!widenShuffleMaskElts(ScaleFactor, Mask, NewMask))
397      return false;
398  }
399  // bitcast (shuf V, MaskC) --> shuf (bitcast V), MaskC'
400  ++NumShufOfBitcast;
401  Value *CastV = Builder.CreateBitCast(V, DestTy);
402  Value *Shuf =
403      Builder.CreateShuffleVector(CastV, UndefValue::get(DestTy), NewMask);
404  replaceValue(I, *Shuf);
405  return true;
406}
407
408/// Match a vector binop or compare instruction with at least one inserted
409/// scalar operand and convert to scalar binop/cmp followed by insertelement.
410bool VectorCombine::scalarizeBinopOrCmp(Instruction &I) {
411  CmpInst::Predicate Pred = CmpInst::BAD_ICMP_PREDICATE;
412  Value *Ins0, *Ins1;
413  if (!match(&I, m_BinOp(m_Value(Ins0), m_Value(Ins1))) &&
414      !match(&I, m_Cmp(Pred, m_Value(Ins0), m_Value(Ins1))))
415    return false;
416
417  // Do not convert the vector condition of a vector select into a scalar
418  // condition. That may cause problems for codegen because of differences in
419  // boolean formats and register-file transfers.
420  // TODO: Can we account for that in the cost model?
421  bool IsCmp = Pred != CmpInst::Predicate::BAD_ICMP_PREDICATE;
422  if (IsCmp)
423    for (User *U : I.users())
424      if (match(U, m_Select(m_Specific(&I), m_Value(), m_Value())))
425        return false;
426
427  // Match against one or both scalar values being inserted into constant
428  // vectors:
429  // vec_op VecC0, (inselt VecC1, V1, Index)
430  // vec_op (inselt VecC0, V0, Index), VecC1
431  // vec_op (inselt VecC0, V0, Index), (inselt VecC1, V1, Index)
432  // TODO: Deal with mismatched index constants and variable indexes?
433  Constant *VecC0 = nullptr, *VecC1 = nullptr;
434  Value *V0 = nullptr, *V1 = nullptr;
435  uint64_t Index0 = 0, Index1 = 0;
436  if (!match(Ins0, m_InsertElt(m_Constant(VecC0), m_Value(V0),
437                               m_ConstantInt(Index0))) &&
438      !match(Ins0, m_Constant(VecC0)))
439    return false;
440  if (!match(Ins1, m_InsertElt(m_Constant(VecC1), m_Value(V1),
441                               m_ConstantInt(Index1))) &&
442      !match(Ins1, m_Constant(VecC1)))
443    return false;
444
445  bool IsConst0 = !V0;
446  bool IsConst1 = !V1;
447  if (IsConst0 && IsConst1)
448    return false;
449  if (!IsConst0 && !IsConst1 && Index0 != Index1)
450    return false;
451
452  // Bail for single insertion if it is a load.
453  // TODO: Handle this once getVectorInstrCost can cost for load/stores.
454  auto *I0 = dyn_cast_or_null<Instruction>(V0);
455  auto *I1 = dyn_cast_or_null<Instruction>(V1);
456  if ((IsConst0 && I1 && I1->mayReadFromMemory()) ||
457      (IsConst1 && I0 && I0->mayReadFromMemory()))
458    return false;
459
460  uint64_t Index = IsConst0 ? Index1 : Index0;
461  Type *ScalarTy = IsConst0 ? V1->getType() : V0->getType();
462  Type *VecTy = I.getType();
463  assert(VecTy->isVectorTy() &&
464         (IsConst0 || IsConst1 || V0->getType() == V1->getType()) &&
465         (ScalarTy->isIntegerTy() || ScalarTy->isFloatingPointTy() ||
466          ScalarTy->isPointerTy()) &&
467         "Unexpected types for insert element into binop or cmp");
468
469  unsigned Opcode = I.getOpcode();
470  int ScalarOpCost, VectorOpCost;
471  if (IsCmp) {
472    ScalarOpCost = TTI.getCmpSelInstrCost(Opcode, ScalarTy);
473    VectorOpCost = TTI.getCmpSelInstrCost(Opcode, VecTy);
474  } else {
475    ScalarOpCost = TTI.getArithmeticInstrCost(Opcode, ScalarTy);
476    VectorOpCost = TTI.getArithmeticInstrCost(Opcode, VecTy);
477  }
478
479  // Get cost estimate for the insert element. This cost will factor into
480  // both sequences.
481  int InsertCost =
482      TTI.getVectorInstrCost(Instruction::InsertElement, VecTy, Index);
483  int OldCost = (IsConst0 ? 0 : InsertCost) + (IsConst1 ? 0 : InsertCost) +
484                VectorOpCost;
485  int NewCost = ScalarOpCost + InsertCost +
486                (IsConst0 ? 0 : !Ins0->hasOneUse() * InsertCost) +
487                (IsConst1 ? 0 : !Ins1->hasOneUse() * InsertCost);
488
489  // We want to scalarize unless the vector variant actually has lower cost.
490  if (OldCost < NewCost)
491    return false;
492
493  // vec_op (inselt VecC0, V0, Index), (inselt VecC1, V1, Index) -->
494  // inselt NewVecC, (scalar_op V0, V1), Index
495  if (IsCmp)
496    ++NumScalarCmp;
497  else
498    ++NumScalarBO;
499
500  // For constant cases, extract the scalar element, this should constant fold.
501  if (IsConst0)
502    V0 = ConstantExpr::getExtractElement(VecC0, Builder.getInt64(Index));
503  if (IsConst1)
504    V1 = ConstantExpr::getExtractElement(VecC1, Builder.getInt64(Index));
505
506  Value *Scalar =
507      IsCmp ? Builder.CreateCmp(Pred, V0, V1)
508            : Builder.CreateBinOp((Instruction::BinaryOps)Opcode, V0, V1);
509
510  Scalar->setName(I.getName() + ".scalar");
511
512  // All IR flags are safe to back-propagate. There is no potential for extra
513  // poison to be created by the scalar instruction.
514  if (auto *ScalarInst = dyn_cast<Instruction>(Scalar))
515    ScalarInst->copyIRFlags(&I);
516
517  // Fold the vector constants in the original vectors into a new base vector.
518  Constant *NewVecC = IsCmp ? ConstantExpr::getCompare(Pred, VecC0, VecC1)
519                            : ConstantExpr::get(Opcode, VecC0, VecC1);
520  Value *Insert = Builder.CreateInsertElement(NewVecC, Scalar, Index);
521  replaceValue(I, *Insert);
522  return true;
523}
524
525/// Try to combine a scalar binop + 2 scalar compares of extracted elements of
526/// a vector into vector operations followed by extract. Note: The SLP pass
527/// may miss this pattern because of implementation problems.
528bool VectorCombine::foldExtractedCmps(Instruction &I) {
529  // We are looking for a scalar binop of booleans.
530  // binop i1 (cmp Pred I0, C0), (cmp Pred I1, C1)
531  if (!I.isBinaryOp() || !I.getType()->isIntegerTy(1))
532    return false;
533
534  // The compare predicates should match, and each compare should have a
535  // constant operand.
536  // TODO: Relax the one-use constraints.
537  Value *B0 = I.getOperand(0), *B1 = I.getOperand(1);
538  Instruction *I0, *I1;
539  Constant *C0, *C1;
540  CmpInst::Predicate P0, P1;
541  if (!match(B0, m_OneUse(m_Cmp(P0, m_Instruction(I0), m_Constant(C0)))) ||
542      !match(B1, m_OneUse(m_Cmp(P1, m_Instruction(I1), m_Constant(C1)))) ||
543      P0 != P1)
544    return false;
545
546  // The compare operands must be extracts of the same vector with constant
547  // extract indexes.
548  // TODO: Relax the one-use constraints.
549  Value *X;
550  uint64_t Index0, Index1;
551  if (!match(I0, m_OneUse(m_ExtractElt(m_Value(X), m_ConstantInt(Index0)))) ||
552      !match(I1, m_OneUse(m_ExtractElt(m_Specific(X), m_ConstantInt(Index1)))))
553    return false;
554
555  auto *Ext0 = cast<ExtractElementInst>(I0);
556  auto *Ext1 = cast<ExtractElementInst>(I1);
557  ExtractElementInst *ConvertToShuf = getShuffleExtract(Ext0, Ext1);
558  if (!ConvertToShuf)
559    return false;
560
561  // The original scalar pattern is:
562  // binop i1 (cmp Pred (ext X, Index0), C0), (cmp Pred (ext X, Index1), C1)
563  CmpInst::Predicate Pred = P0;
564  unsigned CmpOpcode = CmpInst::isFPPredicate(Pred) ? Instruction::FCmp
565                                                    : Instruction::ICmp;
566  auto *VecTy = dyn_cast<FixedVectorType>(X->getType());
567  if (!VecTy)
568    return false;
569
570  int OldCost = TTI.getVectorInstrCost(Ext0->getOpcode(), VecTy, Index0);
571  OldCost += TTI.getVectorInstrCost(Ext1->getOpcode(), VecTy, Index1);
572  OldCost += TTI.getCmpSelInstrCost(CmpOpcode, I0->getType()) * 2;
573  OldCost += TTI.getArithmeticInstrCost(I.getOpcode(), I.getType());
574
575  // The proposed vector pattern is:
576  // vcmp = cmp Pred X, VecC
577  // ext (binop vNi1 vcmp, (shuffle vcmp, Index1)), Index0
578  int CheapIndex = ConvertToShuf == Ext0 ? Index1 : Index0;
579  int ExpensiveIndex = ConvertToShuf == Ext0 ? Index0 : Index1;
580  auto *CmpTy = cast<FixedVectorType>(CmpInst::makeCmpResultType(X->getType()));
581  int NewCost = TTI.getCmpSelInstrCost(CmpOpcode, X->getType());
582  NewCost +=
583      TTI.getShuffleCost(TargetTransformInfo::SK_PermuteSingleSrc, CmpTy);
584  NewCost += TTI.getArithmeticInstrCost(I.getOpcode(), CmpTy);
585  NewCost += TTI.getVectorInstrCost(Ext0->getOpcode(), CmpTy, CheapIndex);
586
587  // Aggressively form vector ops if the cost is equal because the transform
588  // may enable further optimization.
589  // Codegen can reverse this transform (scalarize) if it was not profitable.
590  if (OldCost < NewCost)
591    return false;
592
593  // Create a vector constant from the 2 scalar constants.
594  SmallVector<Constant *, 32> CmpC(VecTy->getNumElements(),
595                                   UndefValue::get(VecTy->getElementType()));
596  CmpC[Index0] = C0;
597  CmpC[Index1] = C1;
598  Value *VCmp = Builder.CreateCmp(Pred, X, ConstantVector::get(CmpC));
599
600  Value *Shuf = createShiftShuffle(VCmp, ExpensiveIndex, CheapIndex, Builder);
601  Value *VecLogic = Builder.CreateBinOp(cast<BinaryOperator>(I).getOpcode(),
602                                        VCmp, Shuf);
603  Value *NewExt = Builder.CreateExtractElement(VecLogic, CheapIndex);
604  replaceValue(I, *NewExt);
605  ++NumVecCmpBO;
606  return true;
607}
608
609/// This is the entry point for all transforms. Pass manager differences are
610/// handled in the callers of this function.
611bool VectorCombine::run() {
612  if (DisableVectorCombine)
613    return false;
614
615  bool MadeChange = false;
616  for (BasicBlock &BB : F) {
617    // Ignore unreachable basic blocks.
618    if (!DT.isReachableFromEntry(&BB))
619      continue;
620    // Do not delete instructions under here and invalidate the iterator.
621    // Walk the block forwards to enable simple iterative chains of transforms.
622    // TODO: It could be more efficient to remove dead instructions
623    //       iteratively in this loop rather than waiting until the end.
624    for (Instruction &I : BB) {
625      if (isa<DbgInfoIntrinsic>(I))
626        continue;
627      Builder.SetInsertPoint(&I);
628      MadeChange |= foldExtractExtract(I);
629      MadeChange |= foldBitcastShuf(I);
630      MadeChange |= scalarizeBinopOrCmp(I);
631      MadeChange |= foldExtractedCmps(I);
632    }
633  }
634
635  // We're done with transforms, so remove dead instructions.
636  if (MadeChange)
637    for (BasicBlock &BB : F)
638      SimplifyInstructionsInBlock(&BB);
639
640  return MadeChange;
641}
642
643// Pass manager boilerplate below here.
644
645namespace {
646class VectorCombineLegacyPass : public FunctionPass {
647public:
648  static char ID;
649  VectorCombineLegacyPass() : FunctionPass(ID) {
650    initializeVectorCombineLegacyPassPass(*PassRegistry::getPassRegistry());
651  }
652
653  void getAnalysisUsage(AnalysisUsage &AU) const override {
654    AU.addRequired<DominatorTreeWrapperPass>();
655    AU.addRequired<TargetTransformInfoWrapperPass>();
656    AU.setPreservesCFG();
657    AU.addPreserved<DominatorTreeWrapperPass>();
658    AU.addPreserved<GlobalsAAWrapperPass>();
659    AU.addPreserved<AAResultsWrapperPass>();
660    AU.addPreserved<BasicAAWrapperPass>();
661    FunctionPass::getAnalysisUsage(AU);
662  }
663
664  bool runOnFunction(Function &F) override {
665    if (skipFunction(F))
666      return false;
667    auto &TTI = getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F);
668    auto &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree();
669    VectorCombine Combiner(F, TTI, DT);
670    return Combiner.run();
671  }
672};
673} // namespace
674
675char VectorCombineLegacyPass::ID = 0;
676INITIALIZE_PASS_BEGIN(VectorCombineLegacyPass, "vector-combine",
677                      "Optimize scalar/vector ops", false,
678                      false)
679INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
680INITIALIZE_PASS_END(VectorCombineLegacyPass, "vector-combine",
681                    "Optimize scalar/vector ops", false, false)
682Pass *llvm::createVectorCombinePass() {
683  return new VectorCombineLegacyPass();
684}
685
686PreservedAnalyses VectorCombinePass::run(Function &F,
687                                         FunctionAnalysisManager &FAM) {
688  TargetTransformInfo &TTI = FAM.getResult<TargetIRAnalysis>(F);
689  DominatorTree &DT = FAM.getResult<DominatorTreeAnalysis>(F);
690  VectorCombine Combiner(F, TTI, DT);
691  if (!Combiner.run())
692    return PreservedAnalyses::all();
693  PreservedAnalyses PA;
694  PA.preserveSet<CFGAnalyses>();
695  PA.preserve<GlobalsAA>();
696  PA.preserve<AAManager>();
697  PA.preserve<BasicAA>();
698  return PA;
699}
700