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
|
//===- LoopRotation.cpp - Loop Rotation Pass ------------------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements Loop Rotation Pass.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "loop-rotate"
#include "llvm/Transforms/Scalar.h"
#include "llvm/Function.h"
#include "llvm/IntrinsicInst.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/LoopPass.h"
#include "llvm/Analysis/Dominators.h"
#include "llvm/Analysis/ScalarEvolution.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/SmallVector.h"
using namespace llvm;
#define MAX_HEADER_SIZE 16
STATISTIC(NumRotated, "Number of loops rotated");
namespace {
class VISIBILITY_HIDDEN RenameData {
public:
RenameData(Instruction *O, Value *P, Instruction *H)
: Original(O), PreHeader(P), Header(H) { }
public:
Instruction *Original; // Original instruction
Value *PreHeader; // Original pre-header replacement
Instruction *Header; // New header replacement
};
class VISIBILITY_HIDDEN LoopRotate : public LoopPass {
public:
static char ID; // Pass ID, replacement for typeid
LoopRotate() : LoopPass(&ID) {}
// Rotate Loop L as many times as possible. Return true if
// loop is rotated at least once.
bool runOnLoop(Loop *L, LPPassManager &LPM);
// LCSSA form makes instruction renaming easier.
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequiredID(LoopSimplifyID);
AU.addPreservedID(LoopSimplifyID);
AU.addRequiredID(LCSSAID);
AU.addPreservedID(LCSSAID);
AU.addPreserved<ScalarEvolution>();
AU.addPreserved<LoopInfo>();
AU.addPreserved<DominatorTree>();
AU.addPreserved<DominanceFrontier>();
}
// Helper functions
/// Do actual work
bool rotateLoop(Loop *L, LPPassManager &LPM);
/// Initialize local data
void initialize();
/// Make sure all Exit block PHINodes have required incoming values.
/// If incoming value is constant or defined outside the loop then
/// PHINode may not have an entry for original pre-header.
void updateExitBlock();
/// Return true if this instruction is used outside original header.
bool usedOutsideOriginalHeader(Instruction *In);
/// Find Replacement information for instruction. Return NULL if it is
/// not available.
const RenameData *findReplacementData(Instruction *I);
/// After loop rotation, loop pre-header has multiple sucessors.
/// Insert one forwarding basic block to ensure that loop pre-header
/// has only one successor.
void preserveCanonicalLoopForm(LPPassManager &LPM);
private:
Loop *L;
BasicBlock *OrigHeader;
BasicBlock *OrigPreHeader;
BasicBlock *OrigLatch;
BasicBlock *NewHeader;
BasicBlock *Exit;
LPPassManager *LPM_Ptr;
SmallVector<RenameData, MAX_HEADER_SIZE> LoopHeaderInfo;
};
}
char LoopRotate::ID = 0;
static RegisterPass<LoopRotate> X("loop-rotate", "Rotate Loops");
Pass *llvm::createLoopRotatePass() { return new LoopRotate(); }
/// Rotate Loop L as many times as possible. Return true if
/// the loop is rotated at least once.
bool LoopRotate::runOnLoop(Loop *Lp, LPPassManager &LPM) {
bool RotatedOneLoop = false;
initialize();
LPM_Ptr = &LPM;
// One loop can be rotated multiple times.
while (rotateLoop(Lp,LPM)) {
RotatedOneLoop = true;
initialize();
}
return RotatedOneLoop;
}
/// Rotate loop LP. Return true if the loop is rotated.
bool LoopRotate::rotateLoop(Loop *Lp, LPPassManager &LPM) {
L = Lp;
OrigHeader = L->getHeader();
OrigPreHeader = L->getLoopPreheader();
OrigLatch = L->getLoopLatch();
// If the loop has only one block then there is not much to rotate.
if (L->getBlocks().size() == 1)
return false;
assert(OrigHeader && OrigLatch && OrigPreHeader &&
"Loop is not in canonical form");
// If the loop header is not one of the loop exiting blocks then
// either this loop is already rotated or it is not
// suitable for loop rotation transformations.
if (!L->isLoopExit(OrigHeader))
return false;
BranchInst *BI = dyn_cast<BranchInst>(OrigHeader->getTerminator());
if (!BI)
return false;
assert(BI->isConditional() && "Branch Instruction is not conditional");
// Updating PHInodes in loops with multiple exits adds complexity.
// Keep it simple, and restrict loop rotation to loops with one exit only.
// In future, lift this restriction and support for multiple exits if
// required.
SmallVector<BasicBlock*, 8> ExitBlocks;
L->getExitBlocks(ExitBlocks);
if (ExitBlocks.size() > 1)
return false;
// Check size of original header and reject
// loop if it is very big.
unsigned Size = 0;
// FIXME: Use common api to estimate size.
for (BasicBlock::const_iterator OI = OrigHeader->begin(),
OE = OrigHeader->end(); OI != OE; ++OI) {
if (isa<PHINode>(OI))
continue; // PHI nodes don't count.
if (isa<DbgInfoIntrinsic>(OI))
continue; // Debug intrinsics don't count as size.
Size++;
}
if (Size > MAX_HEADER_SIZE)
return false;
// Now, this loop is suitable for rotation.
// Find new Loop header. NewHeader is a Header's one and only successor
// that is inside loop. Header's other successor is outside the
// loop. Otherwise loop is not suitable for rotation.
Exit = BI->getSuccessor(0);
NewHeader = BI->getSuccessor(1);
if (L->contains(Exit))
std::swap(Exit, NewHeader);
assert(NewHeader && "Unable to determine new loop header");
assert(L->contains(NewHeader) && !L->contains(Exit) &&
"Unable to determine loop header and exit blocks");
// This code assumes that the new header has exactly one predecessor.
// Remove any single-entry PHI nodes in it.
assert(NewHeader->getSinglePredecessor() &&
"New header doesn't have one pred!");
FoldSingleEntryPHINodes(NewHeader);
// Copy PHI nodes and other instructions from the original header
// into the original pre-header. Unlike the original header, the original
// pre-header is not a member of the loop.
//
// The new loop header is the one and only successor of original header that
// is inside the loop. All other original header successors are outside
// the loop. Copy PHI Nodes from the original header into the new loop header.
// Add second incoming value, from original loop pre-header into these phi
// nodes. If a value defined in original header is used outside original
// header then new loop header will need new phi nodes with two incoming
// values, one definition from original header and second definition is
// from original loop pre-header.
// Remove terminator from Original pre-header. Original pre-header will
// receive a clone of original header terminator as a new terminator.
OrigPreHeader->getInstList().pop_back();
BasicBlock::iterator I = OrigHeader->begin(), E = OrigHeader->end();
PHINode *PN = 0;
for (; (PN = dyn_cast<PHINode>(I)); ++I) {
// PHI nodes are not copied into original pre-header. Instead their values
// are directly propagated.
Value *NPV = PN->getIncomingValueForBlock(OrigPreHeader);
// Create a new PHI node with two incoming values for NewHeader.
// One incoming value is from OrigLatch (through OrigHeader) and the
// second incoming value is from original pre-header.
PHINode *NH = PHINode::Create(PN->getType(), PN->getName(),
NewHeader->begin());
NH->addIncoming(PN->getIncomingValueForBlock(OrigLatch), OrigHeader);
NH->addIncoming(NPV, OrigPreHeader);
// "In" can be replaced by NH at various places.
LoopHeaderInfo.push_back(RenameData(PN, NPV, NH));
}
// Now, handle non-phi instructions.
for (; I != E; ++I) {
Instruction *In = I;
assert(!isa<PHINode>(In) && "PHINode is not expected here");
// This is not a PHI instruction. Insert its clone into original pre-header.
// If this instruction is using a value from same basic block then
// update it to use value from cloned instruction.
Instruction *C = In->clone();
C->setName(In->getName());
OrigPreHeader->getInstList().push_back(C);
for (unsigned opi = 0, e = In->getNumOperands(); opi != e; ++opi) {
Instruction *OpInsn = dyn_cast<Instruction>(In->getOperand(opi));
if (!OpInsn) continue; // Ignore non-instruction values.
if (const RenameData *D = findReplacementData(OpInsn))
C->setOperand(opi, D->PreHeader);
}
// If this instruction is used outside this basic block then
// create new PHINode for this instruction.
Instruction *NewHeaderReplacement = NULL;
if (usedOutsideOriginalHeader(In)) {
PHINode *PN = PHINode::Create(In->getType(), In->getName(),
NewHeader->begin());
PN->addIncoming(In, OrigHeader);
PN->addIncoming(C, OrigPreHeader);
NewHeaderReplacement = PN;
}
LoopHeaderInfo.push_back(RenameData(In, C, NewHeaderReplacement));
}
// Rename uses of original header instructions to reflect their new
// definitions (either from original pre-header node or from newly created
// new header PHINodes.
//
// Original header instructions are used in
// 1) Original header:
//
// If instruction is used in non-phi instructions then it is using
// defintion from original heder iteself. Do not replace this use
// with definition from new header or original pre-header.
//
// If instruction is used in phi node then it is an incoming
// value. Rename its use to reflect new definition from new-preheader
// or new header.
//
// 2) Inside loop but not in original header
//
// Replace this use to reflect definition from new header.
for (unsigned LHI = 0, LHI_E = LoopHeaderInfo.size(); LHI != LHI_E; ++LHI) {
const RenameData &ILoopHeaderInfo = LoopHeaderInfo[LHI];
if (!ILoopHeaderInfo.Header)
continue;
Instruction *OldPhi = ILoopHeaderInfo.Original;
Instruction *NewPhi = ILoopHeaderInfo.Header;
// Before replacing uses, collect them first, so that iterator is
// not invalidated.
SmallVector<Instruction *, 16> AllUses;
for (Value::use_iterator UI = OldPhi->use_begin(), UE = OldPhi->use_end();
UI != UE; ++UI)
AllUses.push_back(cast<Instruction>(UI));
for (SmallVector<Instruction *, 16>::iterator UI = AllUses.begin(),
UE = AllUses.end(); UI != UE; ++UI) {
Instruction *U = *UI;
BasicBlock *Parent = U->getParent();
// Used inside original header
if (Parent == OrigHeader) {
// Do not rename uses inside original header non-phi instructions.
PHINode *PU = dyn_cast<PHINode>(U);
if (!PU)
continue;
// Do not rename uses inside original header phi nodes, if the
// incoming value is for new header.
if (PU->getBasicBlockIndex(NewHeader) != -1
&& PU->getIncomingValueForBlock(NewHeader) == U)
continue;
U->replaceUsesOfWith(OldPhi, NewPhi);
continue;
}
// Used inside loop, but not in original header.
if (L->contains(U->getParent())) {
if (U != NewPhi)
U->replaceUsesOfWith(OldPhi, NewPhi);
continue;
}
// Used inside Exit Block. Since we are in LCSSA form, U must be PHINode.
if (U->getParent() == Exit) {
assert(isa<PHINode>(U) && "Use in Exit Block that is not PHINode");
PHINode *UPhi = cast<PHINode>(U);
// UPhi already has one incoming argument from original header.
// Add second incoming argument from new Pre header.
UPhi->addIncoming(ILoopHeaderInfo.PreHeader, OrigPreHeader);
} else {
// Used outside Exit block. Create a new PHI node in the exit block
// to receive the value from the new header and pre-header.
PHINode *PN = PHINode::Create(U->getType(), U->getName(),
Exit->begin());
PN->addIncoming(ILoopHeaderInfo.PreHeader, OrigPreHeader);
PN->addIncoming(OldPhi, OrigHeader);
U->replaceUsesOfWith(OldPhi, PN);
}
}
}
/// Make sure all Exit block PHINodes have required incoming values.
updateExitBlock();
// Update CFG
// Removing incoming branch from loop preheader to original header.
// Now original header is inside the loop.
for (BasicBlock::iterator I = OrigHeader->begin(), E = OrigHeader->end();
I != E; ++I)
if (PHINode *PN = dyn_cast<PHINode>(I))
PN->removeIncomingValue(OrigPreHeader);
// Make NewHeader as the new header for the loop.
L->moveToHeader(NewHeader);
preserveCanonicalLoopForm(LPM);
NumRotated++;
return true;
}
/// Make sure all Exit block PHINodes have required incoming values.
/// If an incoming value is constant or defined outside the loop then
/// PHINode may not have an entry for the original pre-header.
void LoopRotate::updateExitBlock() {
for (BasicBlock::iterator I = Exit->begin();
PHINode *PN = dyn_cast<PHINode>(I); ++I) {
// There is already one incoming value from original pre-header block.
if (PN->getBasicBlockIndex(OrigPreHeader) != -1)
continue;
const RenameData *ILoopHeaderInfo;
Value *V = PN->getIncomingValueForBlock(OrigHeader);
if (isa<Instruction>(V) &&
(ILoopHeaderInfo = findReplacementData(cast<Instruction>(V)))) {
assert(ILoopHeaderInfo->PreHeader && "Missing New Preheader Instruction");
PN->addIncoming(ILoopHeaderInfo->PreHeader, OrigPreHeader);
} else {
PN->addIncoming(V, OrigPreHeader);
}
}
}
/// Initialize local data
void LoopRotate::initialize() {
L = NULL;
OrigHeader = NULL;
OrigPreHeader = NULL;
NewHeader = NULL;
Exit = NULL;
LoopHeaderInfo.clear();
}
/// Return true if this instruction is used by any instructions in the loop that
/// aren't in original header.
bool LoopRotate::usedOutsideOriginalHeader(Instruction *In) {
for (Value::use_iterator UI = In->use_begin(), UE = In->use_end();
UI != UE; ++UI) {
BasicBlock *UserBB = cast<Instruction>(UI)->getParent();
if (UserBB != OrigHeader && L->contains(UserBB))
return true;
}
return false;
}
/// Find Replacement information for instruction. Return NULL if it is
/// not available.
const RenameData *LoopRotate::findReplacementData(Instruction *In) {
// Since LoopHeaderInfo is small, linear walk is OK.
for (unsigned LHI = 0, LHI_E = LoopHeaderInfo.size(); LHI != LHI_E; ++LHI) {
const RenameData &ILoopHeaderInfo = LoopHeaderInfo[LHI];
if (ILoopHeaderInfo.Original == In)
return &ILoopHeaderInfo;
}
return NULL;
}
/// After loop rotation, loop pre-header has multiple sucessors.
/// Insert one forwarding basic block to ensure that loop pre-header
/// has only one successor.
void LoopRotate::preserveCanonicalLoopForm(LPPassManager &LPM) {
// Right now original pre-header has two successors, new header and
// exit block. Insert new block between original pre-header and
// new header such that loop's new pre-header has only one successor.
BasicBlock *NewPreHeader = BasicBlock::Create("bb.nph",
OrigHeader->getParent(),
NewHeader);
LoopInfo &LI = LPM.getAnalysis<LoopInfo>();
if (Loop *PL = LI.getLoopFor(OrigPreHeader))
PL->addBasicBlockToLoop(NewPreHeader, LI.getBase());
BranchInst::Create(NewHeader, NewPreHeader);
BranchInst *OrigPH_BI = cast<BranchInst>(OrigPreHeader->getTerminator());
if (OrigPH_BI->getSuccessor(0) == NewHeader)
OrigPH_BI->setSuccessor(0, NewPreHeader);
else {
assert(OrigPH_BI->getSuccessor(1) == NewHeader &&
"Unexpected original pre-header terminator");
OrigPH_BI->setSuccessor(1, NewPreHeader);
}
for (BasicBlock::iterator I = NewHeader->begin(), E = NewHeader->end();
I != E; ++I) {
PHINode *PN = dyn_cast<PHINode>(I);
if (!PN)
break;
int index = PN->getBasicBlockIndex(OrigPreHeader);
assert(index != -1 && "Expected incoming value from Original PreHeader");
PN->setIncomingBlock(index, NewPreHeader);
assert(PN->getBasicBlockIndex(OrigPreHeader) == -1 &&
"Expected only one incoming value from Original PreHeader");
}
if (DominatorTree *DT = getAnalysisIfAvailable<DominatorTree>()) {
DT->addNewBlock(NewPreHeader, OrigPreHeader);
DT->changeImmediateDominator(L->getHeader(), NewPreHeader);
DT->changeImmediateDominator(Exit, OrigPreHeader);
for (Loop::block_iterator BI = L->block_begin(), BE = L->block_end();
BI != BE; ++BI) {
BasicBlock *B = *BI;
if (L->getHeader() != B) {
DomTreeNode *Node = DT->getNode(B);
if (Node && Node->getBlock() == OrigHeader)
DT->changeImmediateDominator(*BI, L->getHeader());
}
}
DT->changeImmediateDominator(OrigHeader, OrigLatch);
}
if (DominanceFrontier *DF = getAnalysisIfAvailable<DominanceFrontier>()) {
// New Preheader's dominance frontier is Exit block.
DominanceFrontier::DomSetType NewPHSet;
NewPHSet.insert(Exit);
DF->addBasicBlock(NewPreHeader, NewPHSet);
// New Header's dominance frontier now includes itself and Exit block
DominanceFrontier::iterator HeadI = DF->find(L->getHeader());
if (HeadI != DF->end()) {
DominanceFrontier::DomSetType & HeaderSet = HeadI->second;
HeaderSet.clear();
HeaderSet.insert(L->getHeader());
HeaderSet.insert(Exit);
} else {
DominanceFrontier::DomSetType HeaderSet;
HeaderSet.insert(L->getHeader());
HeaderSet.insert(Exit);
DF->addBasicBlock(L->getHeader(), HeaderSet);
}
// Original header (new Loop Latch)'s dominance frontier is Exit.
DominanceFrontier::iterator LatchI = DF->find(L->getLoopLatch());
if (LatchI != DF->end()) {
DominanceFrontier::DomSetType &LatchSet = LatchI->second;
LatchSet = LatchI->second;
LatchSet.clear();
LatchSet.insert(Exit);
} else {
DominanceFrontier::DomSetType LatchSet;
LatchSet.insert(Exit);
DF->addBasicBlock(L->getHeader(), LatchSet);
}
// If a loop block dominates new loop latch then its frontier is
// new header and Exit.
BasicBlock *NewLatch = L->getLoopLatch();
DominatorTree *DT = getAnalysisIfAvailable<DominatorTree>();
for (Loop::block_iterator BI = L->block_begin(), BE = L->block_end();
BI != BE; ++BI) {
BasicBlock *B = *BI;
if (DT->dominates(B, NewLatch)) {
DominanceFrontier::iterator BDFI = DF->find(B);
if (BDFI != DF->end()) {
DominanceFrontier::DomSetType &BSet = BDFI->second;
BSet = BDFI->second;
BSet.clear();
BSet.insert(L->getHeader());
BSet.insert(Exit);
} else {
DominanceFrontier::DomSetType BSet;
BSet.insert(L->getHeader());
BSet.insert(Exit);
DF->addBasicBlock(B, BSet);
}
}
}
}
// Preserve canonical loop form, which means Exit block should
// have only one predecessor.
BasicBlock *NExit = SplitEdge(L->getLoopLatch(), Exit, this);
// Preserve LCSSA.
BasicBlock::iterator I = Exit->begin(), E = Exit->end();
PHINode *PN = NULL;
for (; (PN = dyn_cast<PHINode>(I)); ++I) {
unsigned N = PN->getNumIncomingValues();
for (unsigned index = 0; index < N; ++index)
if (PN->getIncomingBlock(index) == NExit) {
PHINode *NewPN = PHINode::Create(PN->getType(), PN->getName(),
NExit->begin());
NewPN->addIncoming(PN->getIncomingValue(index), L->getLoopLatch());
PN->setIncomingValue(index, NewPN);
PN->setIncomingBlock(index, NExit);
break;
}
}
assert(NewHeader && L->getHeader() == NewHeader &&
"Invalid loop header after loop rotation");
assert(NewPreHeader && L->getLoopPreheader() == NewPreHeader &&
"Invalid loop preheader after loop rotation");
assert(L->getLoopLatch() &&
"Invalid loop latch after loop rotation");
}
|