aboutsummaryrefslogtreecommitdiffstats
path: root/lib/Analysis/CostModel.cpp
blob: b529c1a70aa3374ae0d40ff86f90c83872e2dc62 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
//===- CostModel.cpp ------ Cost Model Analysis ---------------------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file defines the cost model analysis. It provides a very basic cost
// estimation for LLVM-IR. This analysis uses the services of the codegen
// to approximate the cost of any IR instruction when lowered to machine
// instructions. The cost results are unit-less and the cost number represents
// the throughput of the machine assuming that all loads hit the cache, all
// branches are predicted, etc. The cost numbers can be added in order to
// compare two or more transformation alternatives.
//
//===----------------------------------------------------------------------===//

#include "llvm/ADT/STLExtras.h"
#include "llvm/Analysis/Passes.h"
#include "llvm/Analysis/TargetTransformInfo.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/Value.h"
#include "llvm/Pass.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
using namespace llvm;

#define CM_NAME "cost-model"
#define DEBUG_TYPE CM_NAME

static cl::opt<bool> EnableReduxCost("costmodel-reduxcost", cl::init(false),
                                     cl::Hidden,
                                     cl::desc("Recognize reduction patterns."));

namespace {
  class CostModelAnalysis : public FunctionPass {

  public:
    static char ID; // Class identification, replacement for typeinfo
    CostModelAnalysis() : FunctionPass(ID), F(nullptr), TTI(nullptr) {
      initializeCostModelAnalysisPass(
        *PassRegistry::getPassRegistry());
    }

    /// Returns the expected cost of the instruction.
    /// Returns -1 if the cost is unknown.
    /// Note, this method does not cache the cost calculation and it
    /// can be expensive in some cases.
    unsigned getInstructionCost(const Instruction *I) const;

  private:
    void getAnalysisUsage(AnalysisUsage &AU) const override;
    bool runOnFunction(Function &F) override;
    void print(raw_ostream &OS, const Module*) const override;

    /// The function that we analyze.
    Function *F;
    /// Target information.
    const TargetTransformInfo *TTI;
  };
}  // End of anonymous namespace

// Register this pass.
char CostModelAnalysis::ID = 0;
static const char cm_name[] = "Cost Model Analysis";
INITIALIZE_PASS_BEGIN(CostModelAnalysis, CM_NAME, cm_name, false, true)
INITIALIZE_PASS_END  (CostModelAnalysis, CM_NAME, cm_name, false, true)

FunctionPass *llvm::createCostModelAnalysisPass() {
  return new CostModelAnalysis();
}

void
CostModelAnalysis::getAnalysisUsage(AnalysisUsage &AU) const {
  AU.setPreservesAll();
}

bool
CostModelAnalysis::runOnFunction(Function &F) {
 this->F = &F;
 auto *TTIWP = getAnalysisIfAvailable<TargetTransformInfoWrapperPass>();
 TTI = TTIWP ? &TTIWP->getTTI(F) : nullptr;

 return false;
}

static bool isReverseVectorMask(SmallVectorImpl<int> &Mask) {
  for (unsigned i = 0, MaskSize = Mask.size(); i < MaskSize; ++i)
    if (Mask[i] > 0 && Mask[i] != (int)(MaskSize - 1 - i))
      return false;
  return true;
}

static bool isAlternateVectorMask(SmallVectorImpl<int> &Mask) {
  bool isAlternate = true;
  unsigned MaskSize = Mask.size();

  // Example: shufflevector A, B, <0,5,2,7>
  for (unsigned i = 0; i < MaskSize && isAlternate; ++i) {
    if (Mask[i] < 0)
      continue;
    isAlternate = Mask[i] == (int)((i & 1) ? MaskSize + i : i);
  }

  if (isAlternate)
    return true;

  isAlternate = true;
  // Example: shufflevector A, B, <4,1,6,3>
  for (unsigned i = 0; i < MaskSize && isAlternate; ++i) {
    if (Mask[i] < 0)
      continue;
    isAlternate = Mask[i] == (int)((i & 1) ? i : MaskSize + i);
  }

  return isAlternate;
}

static TargetTransformInfo::OperandValueKind getOperandInfo(Value *V) {
  TargetTransformInfo::OperandValueKind OpInfo =
    TargetTransformInfo::OK_AnyValue;

  // Check for a splat of a constant or for a non uniform vector of constants.
  if (isa<ConstantVector>(V) || isa<ConstantDataVector>(V)) {
    OpInfo = TargetTransformInfo::OK_NonUniformConstantValue;
    if (cast<Constant>(V)->getSplatValue() != nullptr)
      OpInfo = TargetTransformInfo::OK_UniformConstantValue;
  }

  return OpInfo;
}

static bool matchPairwiseShuffleMask(ShuffleVectorInst *SI, bool IsLeft,
                                     unsigned Level) {
  // We don't need a shuffle if we just want to have element 0 in position 0 of
  // the vector.
  if (!SI && Level == 0 && IsLeft)
    return true;
  else if (!SI)
    return false;

  SmallVector<int, 32> Mask(SI->getType()->getVectorNumElements(), -1);

  // Build a mask of 0, 2, ... (left) or 1, 3, ... (right) depending on whether
  // we look at the left or right side.
  for (unsigned i = 0, e = (1 << Level), val = !IsLeft; i != e; ++i, val += 2)
    Mask[i] = val;

  SmallVector<int, 16> ActualMask = SI->getShuffleMask();
  if (Mask != ActualMask)
    return false;

  return true;
}

static bool matchPairwiseReductionAtLevel(const BinaryOperator *BinOp,
                                          unsigned Level, unsigned NumLevels) {
  // Match one level of pairwise operations.
  // %rdx.shuf.0.0 = shufflevector <4 x float> %rdx, <4 x float> undef,
  //       <4 x i32> <i32 0, i32 2 , i32 undef, i32 undef>
  // %rdx.shuf.0.1 = shufflevector <4 x float> %rdx, <4 x float> undef,
  //       <4 x i32> <i32 1, i32 3, i32 undef, i32 undef>
  // %bin.rdx.0 = fadd <4 x float> %rdx.shuf.0.0, %rdx.shuf.0.1
  if (BinOp == nullptr)
    return false;

  assert(BinOp->getType()->isVectorTy() && "Expecting a vector type");

  unsigned Opcode = BinOp->getOpcode();
  Value *L = BinOp->getOperand(0);
  Value *R = BinOp->getOperand(1);

  ShuffleVectorInst *LS = dyn_cast<ShuffleVectorInst>(L);
  if (!LS && Level)
    return false;
  ShuffleVectorInst *RS = dyn_cast<ShuffleVectorInst>(R);
  if (!RS && Level)
    return false;

  // On level 0 we can omit one shufflevector instruction.
  if (!Level && !RS && !LS)
    return false;

  // Shuffle inputs must match.
  Value *NextLevelOpL = LS ? LS->getOperand(0) : nullptr;
  Value *NextLevelOpR = RS ? RS->getOperand(0) : nullptr;
  Value *NextLevelOp = nullptr;
  if (NextLevelOpR && NextLevelOpL) {
    // If we have two shuffles their operands must match.
    if (NextLevelOpL != NextLevelOpR)
      return false;

    NextLevelOp = NextLevelOpL;
  } else if (Level == 0 && (NextLevelOpR || NextLevelOpL)) {
    // On the first level we can omit the shufflevector <0, undef,...>. So the
    // input to the other shufflevector <1, undef> must match with one of the
    // inputs to the current binary operation.
    // Example:
    //  %NextLevelOpL = shufflevector %R, <1, undef ...>
    //  %BinOp        = fadd          %NextLevelOpL, %R
    if (NextLevelOpL && NextLevelOpL != R)
      return false;
    else if (NextLevelOpR && NextLevelOpR != L)
      return false;

    NextLevelOp = NextLevelOpL ? R : L;
  } else
    return false;

  // Check that the next levels binary operation exists and matches with the
  // current one.
  BinaryOperator *NextLevelBinOp = nullptr;
  if (Level + 1 != NumLevels) {
    if (!(NextLevelBinOp = dyn_cast<BinaryOperator>(NextLevelOp)))
      return false;
    else if (NextLevelBinOp->getOpcode() != Opcode)
      return false;
  }

  // Shuffle mask for pairwise operation must match.
  if (matchPairwiseShuffleMask(LS, true, Level)) {
    if (!matchPairwiseShuffleMask(RS, false, Level))
      return false;
  } else if (matchPairwiseShuffleMask(RS, true, Level)) {
    if (!matchPairwiseShuffleMask(LS, false, Level))
      return false;
  } else
    return false;

  if (++Level == NumLevels)
    return true;

  // Match next level.
  return matchPairwiseReductionAtLevel(NextLevelBinOp, Level, NumLevels);
}

static bool matchPairwiseReduction(const ExtractElementInst *ReduxRoot,
                                   unsigned &Opcode, Type *&Ty) {
  if (!EnableReduxCost)
    return false;

  // Need to extract the first element.
  ConstantInt *CI = dyn_cast<ConstantInt>(ReduxRoot->getOperand(1));
  unsigned Idx = ~0u;
  if (CI)
    Idx = CI->getZExtValue();
  if (Idx != 0)
    return false;

  BinaryOperator *RdxStart = dyn_cast<BinaryOperator>(ReduxRoot->getOperand(0));
  if (!RdxStart)
    return false;

  Type *VecTy = ReduxRoot->getOperand(0)->getType();
  unsigned NumVecElems = VecTy->getVectorNumElements();
  if (!isPowerOf2_32(NumVecElems))
    return false;

  // We look for a sequence of shuffle,shuffle,add triples like the following
  // that builds a pairwise reduction tree.
  //
  //  (X0, X1, X2, X3)
  //   (X0 + X1, X2 + X3, undef, undef)
  //    ((X0 + X1) + (X2 + X3), undef, undef, undef)
  //
  // %rdx.shuf.0.0 = shufflevector <4 x float> %rdx, <4 x float> undef,
  //       <4 x i32> <i32 0, i32 2 , i32 undef, i32 undef>
  // %rdx.shuf.0.1 = shufflevector <4 x float> %rdx, <4 x float> undef,
  //       <4 x i32> <i32 1, i32 3, i32 undef, i32 undef>
  // %bin.rdx.0 = fadd <4 x float> %rdx.shuf.0.0, %rdx.shuf.0.1
  // %rdx.shuf.1.0 = shufflevector <4 x float> %bin.rdx.0, <4 x float> undef,
  //       <4 x i32> <i32 0, i32 undef, i32 undef, i32 undef>
  // %rdx.shuf.1.1 = shufflevector <4 x float> %bin.rdx.0, <4 x float> undef,
  //       <4 x i32> <i32 1, i32 undef, i32 undef, i32 undef>
  // %bin.rdx8 = fadd <4 x float> %rdx.shuf.1.0, %rdx.shuf.1.1
  // %r = extractelement <4 x float> %bin.rdx8, i32 0
  if (!matchPairwiseReductionAtLevel(RdxStart, 0,  Log2_32(NumVecElems)))
    return false;

  Opcode = RdxStart->getOpcode();
  Ty = VecTy;

  return true;
}

static std::pair<Value *, ShuffleVectorInst *>
getShuffleAndOtherOprd(BinaryOperator *B) {

  Value *L = B->getOperand(0);
  Value *R = B->getOperand(1);
  ShuffleVectorInst *S = nullptr;

  if ((S = dyn_cast<ShuffleVectorInst>(L)))
    return std::make_pair(R, S);

  S = dyn_cast<ShuffleVectorInst>(R);
  return std::make_pair(L, S);
}

static bool matchVectorSplittingReduction(const ExtractElementInst *ReduxRoot,
                                          unsigned &Opcode, Type *&Ty) {
  if (!EnableReduxCost)
    return false;

  // Need to extract the first element.
  ConstantInt *CI = dyn_cast<ConstantInt>(ReduxRoot->getOperand(1));
  unsigned Idx = ~0u;
  if (CI)
    Idx = CI->getZExtValue();
  if (Idx != 0)
    return false;

  BinaryOperator *RdxStart = dyn_cast<BinaryOperator>(ReduxRoot->getOperand(0));
  if (!RdxStart)
    return false;
  unsigned RdxOpcode = RdxStart->getOpcode();

  Type *VecTy = ReduxRoot->getOperand(0)->getType();
  unsigned NumVecElems = VecTy->getVectorNumElements();
  if (!isPowerOf2_32(NumVecElems))
    return false;

  // We look for a sequence of shuffles and adds like the following matching one
  // fadd, shuffle vector pair at a time.
  //
  // %rdx.shuf = shufflevector <4 x float> %rdx, <4 x float> undef,
  //                           <4 x i32> <i32 2, i32 3, i32 undef, i32 undef>
  // %bin.rdx = fadd <4 x float> %rdx, %rdx.shuf
  // %rdx.shuf7 = shufflevector <4 x float> %bin.rdx, <4 x float> undef,
  //                          <4 x i32> <i32 1, i32 undef, i32 undef, i32 undef>
  // %bin.rdx8 = fadd <4 x float> %bin.rdx, %rdx.shuf7
  // %r = extractelement <4 x float> %bin.rdx8, i32 0

  unsigned MaskStart = 1;
  Value *RdxOp = RdxStart;
  SmallVector<int, 32> ShuffleMask(NumVecElems, 0);
  unsigned NumVecElemsRemain = NumVecElems;
  while (NumVecElemsRemain - 1) {
    // Check for the right reduction operation.
    BinaryOperator *BinOp;
    if (!(BinOp = dyn_cast<BinaryOperator>(RdxOp)))
      return false;
    if (BinOp->getOpcode() != RdxOpcode)
      return false;

    Value *NextRdxOp;
    ShuffleVectorInst *Shuffle;
    std::tie(NextRdxOp, Shuffle) = getShuffleAndOtherOprd(BinOp);

    // Check the current reduction operation and the shuffle use the same value.
    if (Shuffle == nullptr)
      return false;
    if (Shuffle->getOperand(0) != NextRdxOp)
      return false;

    // Check that shuffle masks matches.
    for (unsigned j = 0; j != MaskStart; ++j)
      ShuffleMask[j] = MaskStart + j;
    // Fill the rest of the mask with -1 for undef.
    std::fill(&ShuffleMask[MaskStart], ShuffleMask.end(), -1);

    SmallVector<int, 16> Mask = Shuffle->getShuffleMask();
    if (ShuffleMask != Mask)
      return false;

    RdxOp = NextRdxOp;
    NumVecElemsRemain /= 2;
    MaskStart *= 2;
  }

  Opcode = RdxOpcode;
  Ty = VecTy;
  return true;
}

unsigned CostModelAnalysis::getInstructionCost(const Instruction *I) const {
  if (!TTI)
    return -1;

  switch (I->getOpcode()) {
  case Instruction::GetElementPtr:{
    Type *ValTy = I->getOperand(0)->getType()->getPointerElementType();
    return TTI->getAddressComputationCost(ValTy);
  }

  case Instruction::Ret:
  case Instruction::PHI:
  case Instruction::Br: {
    return TTI->getCFInstrCost(I->getOpcode());
  }
  case Instruction::Add:
  case Instruction::FAdd:
  case Instruction::Sub:
  case Instruction::FSub:
  case Instruction::Mul:
  case Instruction::FMul:
  case Instruction::UDiv:
  case Instruction::SDiv:
  case Instruction::FDiv:
  case Instruction::URem:
  case Instruction::SRem:
  case Instruction::FRem:
  case Instruction::Shl:
  case Instruction::LShr:
  case Instruction::AShr:
  case Instruction::And:
  case Instruction::Or:
  case Instruction::Xor: {
    TargetTransformInfo::OperandValueKind Op1VK =
      getOperandInfo(I->getOperand(0));
    TargetTransformInfo::OperandValueKind Op2VK =
      getOperandInfo(I->getOperand(1));
    return TTI->getArithmeticInstrCost(I->getOpcode(), I->getType(), Op1VK,
                                       Op2VK);
  }
  case Instruction::Select: {
    const SelectInst *SI = cast<SelectInst>(I);
    Type *CondTy = SI->getCondition()->getType();
    return TTI->getCmpSelInstrCost(I->getOpcode(), I->getType(), CondTy);
  }
  case Instruction::ICmp:
  case Instruction::FCmp: {
    Type *ValTy = I->getOperand(0)->getType();
    return TTI->getCmpSelInstrCost(I->getOpcode(), ValTy);
  }
  case Instruction::Store: {
    const StoreInst *SI = cast<StoreInst>(I);
    Type *ValTy = SI->getValueOperand()->getType();
    return TTI->getMemoryOpCost(I->getOpcode(), ValTy,
                                 SI->getAlignment(),
                                 SI->getPointerAddressSpace());
  }
  case Instruction::Load: {
    const LoadInst *LI = cast<LoadInst>(I);
    return TTI->getMemoryOpCost(I->getOpcode(), I->getType(),
                                 LI->getAlignment(),
                                 LI->getPointerAddressSpace());
  }
  case Instruction::ZExt:
  case Instruction::SExt:
  case Instruction::FPToUI:
  case Instruction::FPToSI:
  case Instruction::FPExt:
  case Instruction::PtrToInt:
  case Instruction::IntToPtr:
  case Instruction::SIToFP:
  case Instruction::UIToFP:
  case Instruction::Trunc:
  case Instruction::FPTrunc:
  case Instruction::BitCast:
  case Instruction::AddrSpaceCast: {
    Type *SrcTy = I->getOperand(0)->getType();
    return TTI->getCastInstrCost(I->getOpcode(), I->getType(), SrcTy);
  }
  case Instruction::ExtractElement: {
    const ExtractElementInst * EEI = cast<ExtractElementInst>(I);
    ConstantInt *CI = dyn_cast<ConstantInt>(I->getOperand(1));
    unsigned Idx = -1;
    if (CI)
      Idx = CI->getZExtValue();

    // Try to match a reduction sequence (series of shufflevector and vector
    // adds followed by a extractelement).
    unsigned ReduxOpCode;
    Type *ReduxType;

    if (matchVectorSplittingReduction(EEI, ReduxOpCode, ReduxType))
      return TTI->getReductionCost(ReduxOpCode, ReduxType, false);
    else if (matchPairwiseReduction(EEI, ReduxOpCode, ReduxType))
      return TTI->getReductionCost(ReduxOpCode, ReduxType, true);

    return TTI->getVectorInstrCost(I->getOpcode(),
                                   EEI->getOperand(0)->getType(), Idx);
  }
  case Instruction::InsertElement: {
    const InsertElementInst * IE = cast<InsertElementInst>(I);
    ConstantInt *CI = dyn_cast<ConstantInt>(IE->getOperand(2));
    unsigned Idx = -1;
    if (CI)
      Idx = CI->getZExtValue();
    return TTI->getVectorInstrCost(I->getOpcode(),
                                   IE->getType(), Idx);
  }
  case Instruction::ShuffleVector: {
    const ShuffleVectorInst *Shuffle = cast<ShuffleVectorInst>(I);
    Type *VecTypOp0 = Shuffle->getOperand(0)->getType();
    unsigned NumVecElems = VecTypOp0->getVectorNumElements();
    SmallVector<int, 16> Mask = Shuffle->getShuffleMask();

    if (NumVecElems == Mask.size()) {
      if (isReverseVectorMask(Mask))
        return TTI->getShuffleCost(TargetTransformInfo::SK_Reverse, VecTypOp0,
                                   0, nullptr);
      if (isAlternateVectorMask(Mask))
        return TTI->getShuffleCost(TargetTransformInfo::SK_Alternate,
                                   VecTypOp0, 0, nullptr);
    }

    return -1;
  }
  case Instruction::Call:
    if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
      SmallVector<Type*, 4> Tys;
      for (unsigned J = 0, JE = II->getNumArgOperands(); J != JE; ++J)
        Tys.push_back(II->getArgOperand(J)->getType());

      return TTI->getIntrinsicInstrCost(II->getIntrinsicID(), II->getType(),
                                        Tys);
    }
    return -1;
  default:
    // We don't have any information on this instruction.
    return -1;
  }
}

void CostModelAnalysis::print(raw_ostream &OS, const Module*) const {
  if (!F)
    return;

  for (Function::iterator B = F->begin(), BE = F->end(); B != BE; ++B) {
    for (BasicBlock::iterator it = B->begin(), e = B->end(); it != e; ++it) {
      Instruction *Inst = it;
      unsigned Cost = getInstructionCost(Inst);
      if (Cost != (unsigned)-1)
        OS << "Cost Model: Found an estimated cost of " << Cost;
      else
        OS << "Cost Model: Unknown cost";

      OS << " for instruction: "<< *Inst << "\n";
    }
  }
}