llvm.org GIT mirror llvm / dbe266b lib / Transforms / Scalar / LoopIdiomRecognize.cpp
dbe266b

Tree @dbe266b (Download .tar.gz)

LoopIdiomRecognize.cpp @dbe266braw · history · blame

  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
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
//===-- LoopIdiomRecognize.cpp - Loop idiom recognition -------------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This pass implements an idiom recognizer that transforms simple loops into a
// non-loop form.  In cases that this kicks in, it can be a significant
// performance win.
//
//===----------------------------------------------------------------------===//
//
// TODO List:
//
// Future loop memory idioms to recognize:
//   memcmp, memmove, strlen, etc.
// Future floating point idioms to recognize in -ffast-math mode:
//   fpowi
// Future integer operation idioms to recognize:
//   ctpop, ctlz, cttz
//
// Beware that isel's default lowering for ctpop is highly inefficient for
// i64 and larger types when i64 is legal and the value has few bits set.  It
// would be good to enhance isel to emit a loop for ctpop in this case.
//
// We should enhance the memset/memcpy recognition to handle multiple stores in
// the loop.  This would handle things like:
//   void foo(_Complex float *P)
//     for (i) { __real__(*P) = 0;  __imag__(*P) = 0; }
//
// We should enhance this to handle negative strides through memory.
// Alternatively (and perhaps better) we could rely on an earlier pass to force
// forward iteration through memory, which is generally better for cache
// behavior.  Negative strides *do* happen for memset/memcpy loops.
//
// This could recognize common matrix multiplies and dot product idioms and
// replace them with calls to BLAS (if linked in??).
//
//===----------------------------------------------------------------------===//

#define DEBUG_TYPE "loop-idiom"
#include "llvm/Transforms/Scalar.h"
#include "llvm/IntrinsicInst.h"
#include "llvm/Module.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/LoopPass.h"
#include "llvm/Analysis/ScalarEvolutionExpressions.h"
#include "llvm/Analysis/ScalarEvolutionExpander.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/Target/TargetData.h"
#include "llvm/Target/TargetLibraryInfo.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/IRBuilder.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/ADT/Statistic.h"
using namespace llvm;

STATISTIC(NumMemSet, "Number of memset's formed from loop stores");
STATISTIC(NumMemCpy, "Number of memcpy's formed from loop load+stores");

namespace {
  class LoopIdiomRecognize : public LoopPass {
    Loop *CurLoop;
    const TargetData *TD;
    DominatorTree *DT;
    ScalarEvolution *SE;
    TargetLibraryInfo *TLI;
  public:
    static char ID;
    explicit LoopIdiomRecognize() : LoopPass(ID) {
      initializeLoopIdiomRecognizePass(*PassRegistry::getPassRegistry());
    }

    bool runOnLoop(Loop *L, LPPassManager &LPM);
    bool runOnLoopBlock(BasicBlock *BB, const SCEV *BECount,
                        SmallVectorImpl<BasicBlock*> &ExitBlocks);

    bool processLoopStore(StoreInst *SI, const SCEV *BECount);
    bool processLoopMemSet(MemSetInst *MSI, const SCEV *BECount);

    bool processLoopStridedStore(Value *DestPtr, unsigned StoreSize,
                                 unsigned StoreAlignment,
                                 Value *SplatValue, Instruction *TheStore,
                                 const SCEVAddRecExpr *Ev,
                                 const SCEV *BECount);
    bool processLoopStoreOfLoopLoad(StoreInst *SI, unsigned StoreSize,
                                    const SCEVAddRecExpr *StoreEv,
                                    const SCEVAddRecExpr *LoadEv,
                                    const SCEV *BECount);

    /// This transformation requires natural loop information & requires that
    /// loop preheaders be inserted into the CFG.
    ///
    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
      AU.addRequired<LoopInfo>();
      AU.addPreserved<LoopInfo>();
      AU.addRequiredID(LoopSimplifyID);
      AU.addPreservedID(LoopSimplifyID);
      AU.addRequiredID(LCSSAID);
      AU.addPreservedID(LCSSAID);
      AU.addRequired<AliasAnalysis>();
      AU.addPreserved<AliasAnalysis>();
      AU.addRequired<ScalarEvolution>();
      AU.addPreserved<ScalarEvolution>();
      AU.addPreserved<DominatorTree>();
      AU.addRequired<DominatorTree>();
      AU.addRequired<TargetLibraryInfo>();
    }
  };
}

char LoopIdiomRecognize::ID = 0;
INITIALIZE_PASS_BEGIN(LoopIdiomRecognize, "loop-idiom", "Recognize loop idioms",
                      false, false)
INITIALIZE_PASS_DEPENDENCY(LoopInfo)
INITIALIZE_PASS_DEPENDENCY(DominatorTree)
INITIALIZE_PASS_DEPENDENCY(LoopSimplify)
INITIALIZE_PASS_DEPENDENCY(LCSSA)
INITIALIZE_PASS_DEPENDENCY(ScalarEvolution)
INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfo)
INITIALIZE_AG_DEPENDENCY(AliasAnalysis)
INITIALIZE_PASS_END(LoopIdiomRecognize, "loop-idiom", "Recognize loop idioms",
                    false, false)

Pass *llvm::createLoopIdiomPass() { return new LoopIdiomRecognize(); }

/// deleteDeadInstruction - Delete this instruction.  Before we do, go through
/// and zero out all the operands of this instruction.  If any of them become
/// dead, delete them and the computation tree that feeds them.
///
static void deleteDeadInstruction(Instruction *I, ScalarEvolution &SE) {
  SmallVector<Instruction*, 32> NowDeadInsts;

  NowDeadInsts.push_back(I);

  // Before we touch this instruction, remove it from SE!
  do {
    Instruction *DeadInst = NowDeadInsts.pop_back_val();

    // This instruction is dead, zap it, in stages.  Start by removing it from
    // SCEV.
    SE.forgetValue(DeadInst);

    for (unsigned op = 0, e = DeadInst->getNumOperands(); op != e; ++op) {
      Value *Op = DeadInst->getOperand(op);
      DeadInst->setOperand(op, 0);

      // If this operand just became dead, add it to the NowDeadInsts list.
      if (!Op->use_empty()) continue;

      if (Instruction *OpI = dyn_cast<Instruction>(Op))
        if (isInstructionTriviallyDead(OpI))
          NowDeadInsts.push_back(OpI);
    }

    DeadInst->eraseFromParent();

  } while (!NowDeadInsts.empty());
}

/// deleteIfDeadInstruction - If the specified value is a dead instruction,
/// delete it and any recursively used instructions.
static void deleteIfDeadInstruction(Value *V, ScalarEvolution &SE) {
  if (Instruction *I = dyn_cast<Instruction>(V))
    if (isInstructionTriviallyDead(I))
      deleteDeadInstruction(I, SE);
}

bool LoopIdiomRecognize::runOnLoop(Loop *L, LPPassManager &LPM) {
  CurLoop = L;

  // Disable loop idiom recognition if the function's name is a common idiom. 
  StringRef Name = L->getHeader()->getParent()->getName();
  if (Name == "memset" || Name == "memcpy")
    return false;

  // The trip count of the loop must be analyzable.
  SE = &getAnalysis<ScalarEvolution>();
  if (!SE->hasLoopInvariantBackedgeTakenCount(L))
    return false;
  const SCEV *BECount = SE->getBackedgeTakenCount(L);
  if (isa<SCEVCouldNotCompute>(BECount)) return false;

  // If this loop executes exactly one time, then it should be peeled, not
  // optimized by this pass.
  if (const SCEVConstant *BECst = dyn_cast<SCEVConstant>(BECount))
    if (BECst->getValue()->getValue() == 0)
      return false;

  // We require target data for now.
  TD = getAnalysisIfAvailable<TargetData>();
  if (TD == 0) return false;

  DT = &getAnalysis<DominatorTree>();
  LoopInfo &LI = getAnalysis<LoopInfo>();
  TLI = &getAnalysis<TargetLibraryInfo>();

  SmallVector<BasicBlock*, 8> ExitBlocks;
  CurLoop->getUniqueExitBlocks(ExitBlocks);

  DEBUG(dbgs() << "loop-idiom Scanning: F["
               << L->getHeader()->getParent()->getName()
               << "] Loop %" << L->getHeader()->getName() << "\n");

  bool MadeChange = false;
  // Scan all the blocks in the loop that are not in subloops.
  for (Loop::block_iterator BI = L->block_begin(), E = L->block_end(); BI != E;
       ++BI) {
    // Ignore blocks in subloops.
    if (LI.getLoopFor(*BI) != CurLoop)
      continue;

    MadeChange |= runOnLoopBlock(*BI, BECount, ExitBlocks);
  }
  return MadeChange;
}

/// runOnLoopBlock - Process the specified block, which lives in a counted loop
/// with the specified backedge count.  This block is known to be in the current
/// loop and not in any subloops.
bool LoopIdiomRecognize::runOnLoopBlock(BasicBlock *BB, const SCEV *BECount,
                                     SmallVectorImpl<BasicBlock*> &ExitBlocks) {
  // We can only promote stores in this block if they are unconditionally
  // executed in the loop.  For a block to be unconditionally executed, it has
  // to dominate all the exit blocks of the loop.  Verify this now.
  for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i)
    if (!DT->dominates(BB, ExitBlocks[i]))
      return false;

  bool MadeChange = false;
  for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ) {
    Instruction *Inst = I++;
    // Look for store instructions, which may be optimized to memset/memcpy.
    if (StoreInst *SI = dyn_cast<StoreInst>(Inst))  {
      WeakVH InstPtr(I);
      if (!processLoopStore(SI, BECount)) continue;
      MadeChange = true;

      // If processing the store invalidated our iterator, start over from the
      // top of the block.
      if (InstPtr == 0)
        I = BB->begin();
      continue;
    }

    // Look for memset instructions, which may be optimized to a larger memset.
    if (MemSetInst *MSI = dyn_cast<MemSetInst>(Inst))  {
      WeakVH InstPtr(I);
      if (!processLoopMemSet(MSI, BECount)) continue;
      MadeChange = true;

      // If processing the memset invalidated our iterator, start over from the
      // top of the block.
      if (InstPtr == 0)
        I = BB->begin();
      continue;
    }
  }

  return MadeChange;
}


/// processLoopStore - See if this store can be promoted to a memset or memcpy.
bool LoopIdiomRecognize::processLoopStore(StoreInst *SI, const SCEV *BECount) {
  if (!SI->isSimple()) return false;

  Value *StoredVal = SI->getValueOperand();
  Value *StorePtr = SI->getPointerOperand();

  // Reject stores that are so large that they overflow an unsigned.
  uint64_t SizeInBits = TD->getTypeSizeInBits(StoredVal->getType());
  if ((SizeInBits & 7) || (SizeInBits >> 32) != 0)
    return false;

  // See if the pointer expression is an AddRec like {base,+,1} on the current
  // loop, which indicates a strided store.  If we have something else, it's a
  // random store we can't handle.
  const SCEVAddRecExpr *StoreEv =
    dyn_cast<SCEVAddRecExpr>(SE->getSCEV(StorePtr));
  if (StoreEv == 0 || StoreEv->getLoop() != CurLoop || !StoreEv->isAffine())
    return false;

  // Check to see if the stride matches the size of the store.  If so, then we
  // know that every byte is touched in the loop.
  unsigned StoreSize = (unsigned)SizeInBits >> 3;
  const SCEVConstant *Stride = dyn_cast<SCEVConstant>(StoreEv->getOperand(1));

  if (Stride == 0 || StoreSize != Stride->getValue()->getValue()) {
    // TODO: Could also handle negative stride here someday, that will require
    // the validity check in mayLoopAccessLocation to be updated though.
    // Enable this to print exact negative strides.
    if (0 && Stride && StoreSize == -Stride->getValue()->getValue()) {
      dbgs() << "NEGATIVE STRIDE: " << *SI << "\n";
      dbgs() << "BB: " << *SI->getParent();
    }

    return false;
  }

  // See if we can optimize just this store in isolation.
  if (processLoopStridedStore(StorePtr, StoreSize, SI->getAlignment(),
                              StoredVal, SI, StoreEv, BECount))
    return true;

  // If the stored value is a strided load in the same loop with the same stride
  // this this may be transformable into a memcpy.  This kicks in for stuff like
  //   for (i) A[i] = B[i];
  if (LoadInst *LI = dyn_cast<LoadInst>(StoredVal)) {
    const SCEVAddRecExpr *LoadEv =
      dyn_cast<SCEVAddRecExpr>(SE->getSCEV(LI->getOperand(0)));
    if (LoadEv && LoadEv->getLoop() == CurLoop && LoadEv->isAffine() &&
        StoreEv->getOperand(1) == LoadEv->getOperand(1) && LI->isSimple())
      if (processLoopStoreOfLoopLoad(SI, StoreSize, StoreEv, LoadEv, BECount))
        return true;
  }
  //errs() << "UNHANDLED strided store: " << *StoreEv << " - " << *SI << "\n";

  return false;
}

/// processLoopMemSet - See if this memset can be promoted to a large memset.
bool LoopIdiomRecognize::
processLoopMemSet(MemSetInst *MSI, const SCEV *BECount) {
  // We can only handle non-volatile memsets with a constant size.
  if (MSI->isVolatile() || !isa<ConstantInt>(MSI->getLength())) return false;

  // If we're not allowed to hack on memset, we fail.
  if (!TLI->has(LibFunc::memset))
    return false;

  Value *Pointer = MSI->getDest();

  // See if the pointer expression is an AddRec like {base,+,1} on the current
  // loop, which indicates a strided store.  If we have something else, it's a
  // random store we can't handle.
  const SCEVAddRecExpr *Ev = dyn_cast<SCEVAddRecExpr>(SE->getSCEV(Pointer));
  if (Ev == 0 || Ev->getLoop() != CurLoop || !Ev->isAffine())
    return false;

  // Reject memsets that are so large that they overflow an unsigned.
  uint64_t SizeInBytes = cast<ConstantInt>(MSI->getLength())->getZExtValue();
  if ((SizeInBytes >> 32) != 0)
    return false;

  // Check to see if the stride matches the size of the memset.  If so, then we
  // know that every byte is touched in the loop.
  const SCEVConstant *Stride = dyn_cast<SCEVConstant>(Ev->getOperand(1));

  // TODO: Could also handle negative stride here someday, that will require the
  // validity check in mayLoopAccessLocation to be updated though.
  if (Stride == 0 || MSI->getLength() != Stride->getValue())
    return false;

  return processLoopStridedStore(Pointer, (unsigned)SizeInBytes,
                                 MSI->getAlignment(), MSI->getValue(),
                                 MSI, Ev, BECount);
}


/// mayLoopAccessLocation - Return true if the specified loop might access the
/// specified pointer location, which is a loop-strided access.  The 'Access'
/// argument specifies what the verboten forms of access are (read or write).
static bool mayLoopAccessLocation(Value *Ptr,AliasAnalysis::ModRefResult Access,
                                  Loop *L, const SCEV *BECount,
                                  unsigned StoreSize, AliasAnalysis &AA,
                                  Instruction *IgnoredStore) {
  // Get the location that may be stored across the loop.  Since the access is
  // strided positively through memory, we say that the modified location starts
  // at the pointer and has infinite size.
  uint64_t AccessSize = AliasAnalysis::UnknownSize;

  // If the loop iterates a fixed number of times, we can refine the access size
  // to be exactly the size of the memset, which is (BECount+1)*StoreSize
  if (const SCEVConstant *BECst = dyn_cast<SCEVConstant>(BECount))
    AccessSize = (BECst->getValue()->getZExtValue()+1)*StoreSize;

  // TODO: For this to be really effective, we have to dive into the pointer
  // operand in the store.  Store to &A[i] of 100 will always return may alias
  // with store of &A[100], we need to StoreLoc to be "A" with size of 100,
  // which will then no-alias a store to &A[100].
  AliasAnalysis::Location StoreLoc(Ptr, AccessSize);

  for (Loop::block_iterator BI = L->block_begin(), E = L->block_end(); BI != E;
       ++BI)
    for (BasicBlock::iterator I = (*BI)->begin(), E = (*BI)->end(); I != E; ++I)
      if (&*I != IgnoredStore &&
          (AA.getModRefInfo(I, StoreLoc) & Access))
        return true;

  return false;
}

/// getMemSetPatternValue - If a strided store of the specified value is safe to
/// turn into a memset_pattern16, return a ConstantArray of 16 bytes that should
/// be passed in.  Otherwise, return null.
///
/// Note that we don't ever attempt to use memset_pattern8 or 4, because these
/// just replicate their input array and then pass on to memset_pattern16.
static Constant *getMemSetPatternValue(Value *V, const TargetData &TD) {
  // If the value isn't a constant, we can't promote it to being in a constant
  // array.  We could theoretically do a store to an alloca or something, but
  // that doesn't seem worthwhile.
  Constant *C = dyn_cast<Constant>(V);
  if (C == 0) return 0;

  // Only handle simple values that are a power of two bytes in size.
  uint64_t Size = TD.getTypeSizeInBits(V->getType());
  if (Size == 0 || (Size & 7) || (Size & (Size-1)))
    return 0;

  // Don't care enough about darwin/ppc to implement this.
  if (TD.isBigEndian())
    return 0;

  // Convert to size in bytes.
  Size /= 8;

  // TODO: If CI is larger than 16-bytes, we can try slicing it in half to see
  // if the top and bottom are the same (e.g. for vectors and large integers).
  if (Size > 16) return 0;

  // If the constant is exactly 16 bytes, just use it.
  if (Size == 16) return C;

  // Otherwise, we'll use an array of the constants.
  unsigned ArraySize = 16/Size;
  ArrayType *AT = ArrayType::get(V->getType(), ArraySize);
  return ConstantArray::get(AT, std::vector<Constant*>(ArraySize, C));
}


/// processLoopStridedStore - We see a strided store of some value.  If we can
/// transform this into a memset or memset_pattern in the loop preheader, do so.
bool LoopIdiomRecognize::
processLoopStridedStore(Value *DestPtr, unsigned StoreSize,
                        unsigned StoreAlignment, Value *StoredVal,
                        Instruction *TheStore, const SCEVAddRecExpr *Ev,
                        const SCEV *BECount) {

  // If the stored value is a byte-wise value (like i32 -1), then it may be
  // turned into a memset of i8 -1, assuming that all the consecutive bytes
  // are stored.  A store of i32 0x01020304 can never be turned into a memset,
  // but it can be turned into memset_pattern if the target supports it.
  Value *SplatValue = isBytewiseValue(StoredVal);
  Constant *PatternValue = 0;

  // If we're allowed to form a memset, and the stored value would be acceptable
  // for memset, use it.
  if (SplatValue && TLI->has(LibFunc::memset) &&
      // Verify that the stored value is loop invariant.  If not, we can't
      // promote the memset.
      CurLoop->isLoopInvariant(SplatValue)) {
    // Keep and use SplatValue.
    PatternValue = 0;
  } else if (TLI->has(LibFunc::memset_pattern16) &&
             (PatternValue = getMemSetPatternValue(StoredVal, *TD))) {
    // It looks like we can use PatternValue!
    SplatValue = 0;
  } else {
    // Otherwise, this isn't an idiom we can transform.  For example, we can't
    // do anything with a 3-byte store.
    return false;
  }

  // The trip count of the loop and the base pointer of the addrec SCEV is
  // guaranteed to be loop invariant, which means that it should dominate the
  // header.  This allows us to insert code for it in the preheader.
  BasicBlock *Preheader = CurLoop->getLoopPreheader();
  IRBuilder<> Builder(Preheader->getTerminator());
  SCEVExpander Expander(*SE, "loop-idiom");

  // Okay, we have a strided store "p[i]" of a splattable value.  We can turn
  // this into a memset in the loop preheader now if we want.  However, this
  // would be unsafe to do if there is anything else in the loop that may read
  // or write to the aliased location.  Check for any overlap by generating the
  // base pointer and checking the region.
  unsigned AddrSpace = cast<PointerType>(DestPtr->getType())->getAddressSpace();
  Value *BasePtr =
    Expander.expandCodeFor(Ev->getStart(), Builder.getInt8PtrTy(AddrSpace),
                           Preheader->getTerminator());


  if (mayLoopAccessLocation(BasePtr, AliasAnalysis::ModRef,
                            CurLoop, BECount,
                            StoreSize, getAnalysis<AliasAnalysis>(), TheStore)){
    Expander.clear();
    // If we generated new code for the base pointer, clean up.
    deleteIfDeadInstruction(BasePtr, *SE);
    return false;
  }

  // Okay, everything looks good, insert the memset.

  // The # stored bytes is (BECount+1)*Size.  Expand the trip count out to
  // pointer size if it isn't already.
  Type *IntPtr = TD->getIntPtrType(DestPtr->getContext());
  BECount = SE->getTruncateOrZeroExtend(BECount, IntPtr);

  const SCEV *NumBytesS = SE->getAddExpr(BECount, SE->getConstant(IntPtr, 1),
                                         SCEV::FlagNUW);
  if (StoreSize != 1)
    NumBytesS = SE->getMulExpr(NumBytesS, SE->getConstant(IntPtr, StoreSize),
                               SCEV::FlagNUW);

  Value *NumBytes =
    Expander.expandCodeFor(NumBytesS, IntPtr, Preheader->getTerminator());

  CallInst *NewCall;
  if (SplatValue)
    NewCall = Builder.CreateMemSet(BasePtr, SplatValue,NumBytes,StoreAlignment);
  else {
    Module *M = TheStore->getParent()->getParent()->getParent();
    Value *MSP = M->getOrInsertFunction("memset_pattern16",
                                        Builder.getVoidTy(),
                                        Builder.getInt8PtrTy(),
                                        Builder.getInt8PtrTy(), IntPtr,
                                        (void*)0);

    // Otherwise we should form a memset_pattern16.  PatternValue is known to be
    // an constant array of 16-bytes.  Plop the value into a mergable global.
    GlobalVariable *GV = new GlobalVariable(*M, PatternValue->getType(), true,
                                            GlobalValue::InternalLinkage,
                                            PatternValue, ".memset_pattern");
    GV->setUnnamedAddr(true); // Ok to merge these.
    GV->setAlignment(16);
    Value *PatternPtr = ConstantExpr::getBitCast(GV, Builder.getInt8PtrTy());
    NewCall = Builder.CreateCall3(MSP, BasePtr, PatternPtr, NumBytes);
  }

  DEBUG(dbgs() << "  Formed memset: " << *NewCall << "\n"
               << "    from store to: " << *Ev << " at: " << *TheStore << "\n");
  NewCall->setDebugLoc(TheStore->getDebugLoc());

  // Okay, the memset has been formed.  Zap the original store and anything that
  // feeds into it.
  deleteDeadInstruction(TheStore, *SE);
  ++NumMemSet;
  return true;
}

/// processLoopStoreOfLoopLoad - We see a strided store whose value is a
/// same-strided load.
bool LoopIdiomRecognize::
processLoopStoreOfLoopLoad(StoreInst *SI, unsigned StoreSize,
                           const SCEVAddRecExpr *StoreEv,
                           const SCEVAddRecExpr *LoadEv,
                           const SCEV *BECount) {
  // If we're not allowed to form memcpy, we fail.
  if (!TLI->has(LibFunc::memcpy))
    return false;

  LoadInst *LI = cast<LoadInst>(SI->getValueOperand());

  // The trip count of the loop and the base pointer of the addrec SCEV is
  // guaranteed to be loop invariant, which means that it should dominate the
  // header.  This allows us to insert code for it in the preheader.
  BasicBlock *Preheader = CurLoop->getLoopPreheader();
  IRBuilder<> Builder(Preheader->getTerminator());
  SCEVExpander Expander(*SE, "loop-idiom");

  // Okay, we have a strided store "p[i]" of a loaded value.  We can turn
  // this into a memcpy in the loop preheader now if we want.  However, this
  // would be unsafe to do if there is anything else in the loop that may read
  // or write the memory region we're storing to.  This includes the load that
  // feeds the stores.  Check for an alias by generating the base address and
  // checking everything.
  Value *StoreBasePtr =
    Expander.expandCodeFor(StoreEv->getStart(),
                           Builder.getInt8PtrTy(SI->getPointerAddressSpace()),
                           Preheader->getTerminator());

  if (mayLoopAccessLocation(StoreBasePtr, AliasAnalysis::ModRef,
                            CurLoop, BECount, StoreSize,
                            getAnalysis<AliasAnalysis>(), SI)) {
    Expander.clear();
    // If we generated new code for the base pointer, clean up.
    deleteIfDeadInstruction(StoreBasePtr, *SE);
    return false;
  }

  // For a memcpy, we have to make sure that the input array is not being
  // mutated by the loop.
  Value *LoadBasePtr =
    Expander.expandCodeFor(LoadEv->getStart(),
                           Builder.getInt8PtrTy(LI->getPointerAddressSpace()),
                           Preheader->getTerminator());

  if (mayLoopAccessLocation(LoadBasePtr, AliasAnalysis::Mod, CurLoop, BECount,
                            StoreSize, getAnalysis<AliasAnalysis>(), SI)) {
    Expander.clear();
    // If we generated new code for the base pointer, clean up.
    deleteIfDeadInstruction(LoadBasePtr, *SE);
    deleteIfDeadInstruction(StoreBasePtr, *SE);
    return false;
  }

  // Okay, everything is safe, we can transform this!


  // The # stored bytes is (BECount+1)*Size.  Expand the trip count out to
  // pointer size if it isn't already.
  Type *IntPtr = TD->getIntPtrType(SI->getContext());
  BECount = SE->getTruncateOrZeroExtend(BECount, IntPtr);

  const SCEV *NumBytesS = SE->getAddExpr(BECount, SE->getConstant(IntPtr, 1),
                                         SCEV::FlagNUW);
  if (StoreSize != 1)
    NumBytesS = SE->getMulExpr(NumBytesS, SE->getConstant(IntPtr, StoreSize),
                               SCEV::FlagNUW);

  Value *NumBytes =
    Expander.expandCodeFor(NumBytesS, IntPtr, Preheader->getTerminator());

  CallInst *NewCall =
    Builder.CreateMemCpy(StoreBasePtr, LoadBasePtr, NumBytes,
                         std::min(SI->getAlignment(), LI->getAlignment()));
  NewCall->setDebugLoc(SI->getDebugLoc());

  DEBUG(dbgs() << "  Formed memcpy: " << *NewCall << "\n"
               << "    from load ptr=" << *LoadEv << " at: " << *LI << "\n"
               << "    from store ptr=" << *StoreEv << " at: " << *SI << "\n");


  // Okay, the memset has been formed.  Zap the original store and anything that
  // feeds into it.
  deleteDeadInstruction(SI, *SE);
  ++NumMemCpy;
  return true;
}