Bug Summary

File:lib/Analysis/LoopInfo.cpp
Location:line 583, column 7
Description:Called C++ object pointer is null

Annotated Source Code

1//===- LoopInfo.cpp - Natural Loop Calculator -----------------------------===//
2//
3// The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// This file defines the LoopInfo class that is used to identify natural loops
11// and determine the loop depth of various nodes of the CFG. Note that the
12// loops identified may actually be several natural loops that share the same
13// header node... not just a single natural loop.
14//
15//===----------------------------------------------------------------------===//
16
17#include "llvm/Analysis/LoopInfo.h"
18#include "llvm/ADT/DepthFirstIterator.h"
19#include "llvm/ADT/SmallPtrSet.h"
20#include "llvm/Analysis/LoopInfoImpl.h"
21#include "llvm/Analysis/LoopIterator.h"
22#include "llvm/Analysis/ValueTracking.h"
23#include "llvm/IR/CFG.h"
24#include "llvm/IR/Constants.h"
25#include "llvm/IR/Dominators.h"
26#include "llvm/IR/Instructions.h"
27#include "llvm/IR/LLVMContext.h"
28#include "llvm/IR/Metadata.h"
29#include "llvm/IR/PassManager.h"
30#include "llvm/Support/CommandLine.h"
31#include "llvm/Support/Debug.h"
32#include "llvm/Support/raw_ostream.h"
33#include <algorithm>
34using namespace llvm;
35
36// Explicitly instantiate methods in LoopInfoImpl.h for IR-level Loops.
37template class llvm::LoopBase<BasicBlock, Loop>;
38template class llvm::LoopInfoBase<BasicBlock, Loop>;
39
40// Always verify loopinfo if expensive checking is enabled.
41#ifdef XDEBUG
42static bool VerifyLoopInfo = true;
43#else
44static bool VerifyLoopInfo = false;
45#endif
46static cl::opt<bool,true>
47VerifyLoopInfoX("verify-loop-info", cl::location(VerifyLoopInfo),
48 cl::desc("Verify loop info (time consuming)"));
49
50// Loop identifier metadata name.
51static const char *const LoopMDName = "llvm.loop";
52
53//===----------------------------------------------------------------------===//
54// Loop implementation
55//
56
57/// isLoopInvariant - Return true if the specified value is loop invariant
58///
59bool Loop::isLoopInvariant(const Value *V) const {
60 if (const Instruction *I = dyn_cast<Instruction>(V))
61 return !contains(I);
62 return true; // All non-instructions are loop invariant
63}
64
65/// hasLoopInvariantOperands - Return true if all the operands of the
66/// specified instruction are loop invariant.
67bool Loop::hasLoopInvariantOperands(const Instruction *I) const {
68 return all_of(I->operands(), [this](Value *V) { return isLoopInvariant(V); });
69}
70
71/// makeLoopInvariant - If the given value is an instruciton inside of the
72/// loop and it can be hoisted, do so to make it trivially loop-invariant.
73/// Return true if the value after any hoisting is loop invariant. This
74/// function can be used as a slightly more aggressive replacement for
75/// isLoopInvariant.
76///
77/// If InsertPt is specified, it is the point to hoist instructions to.
78/// If null, the terminator of the loop preheader is used.
79///
80bool Loop::makeLoopInvariant(Value *V, bool &Changed,
81 Instruction *InsertPt) const {
82 if (Instruction *I = dyn_cast<Instruction>(V))
83 return makeLoopInvariant(I, Changed, InsertPt);
84 return true; // All non-instructions are loop-invariant.
85}
86
87/// makeLoopInvariant - If the given instruction is inside of the
88/// loop and it can be hoisted, do so to make it trivially loop-invariant.
89/// Return true if the instruction after any hoisting is loop invariant. This
90/// function can be used as a slightly more aggressive replacement for
91/// isLoopInvariant.
92///
93/// If InsertPt is specified, it is the point to hoist instructions to.
94/// If null, the terminator of the loop preheader is used.
95///
96bool Loop::makeLoopInvariant(Instruction *I, bool &Changed,
97 Instruction *InsertPt) const {
98 // Test if the value is already loop-invariant.
99 if (isLoopInvariant(I))
100 return true;
101 if (!isSafeToSpeculativelyExecute(I))
102 return false;
103 if (I->mayReadFromMemory())
104 return false;
105 // EH block instructions are immobile.
106 if (I->isEHPad())
107 return false;
108 // Determine the insertion point, unless one was given.
109 if (!InsertPt) {
110 BasicBlock *Preheader = getLoopPreheader();
111 // Without a preheader, hoisting is not feasible.
112 if (!Preheader)
113 return false;
114 InsertPt = Preheader->getTerminator();
115 }
116 // Don't hoist instructions with loop-variant operands.
117 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
118 if (!makeLoopInvariant(I->getOperand(i), Changed, InsertPt))
119 return false;
120
121 // Hoist.
122 I->moveBefore(InsertPt);
123 Changed = true;
124 return true;
125}
126
127/// getCanonicalInductionVariable - Check to see if the loop has a canonical
128/// induction variable: an integer recurrence that starts at 0 and increments
129/// by one each time through the loop. If so, return the phi node that
130/// corresponds to it.
131///
132/// The IndVarSimplify pass transforms loops to have a canonical induction
133/// variable.
134///
135PHINode *Loop::getCanonicalInductionVariable() const {
136 BasicBlock *H = getHeader();
137
138 BasicBlock *Incoming = nullptr, *Backedge = nullptr;
139 pred_iterator PI = pred_begin(H);
140 assert(PI != pred_end(H) &&((PI != pred_end(H) && "Loop must have at least one backedge!"
) ? static_cast<void> (0) : __assert_fail ("PI != pred_end(H) && \"Loop must have at least one backedge!\""
, "/tmp/buildd/llvm-toolchain-snapshot-3.8~svn246424/lib/Analysis/LoopInfo.cpp"
, 141, __PRETTY_FUNCTION__))
141 "Loop must have at least one backedge!")((PI != pred_end(H) && "Loop must have at least one backedge!"
) ? static_cast<void> (0) : __assert_fail ("PI != pred_end(H) && \"Loop must have at least one backedge!\""
, "/tmp/buildd/llvm-toolchain-snapshot-3.8~svn246424/lib/Analysis/LoopInfo.cpp"
, 141, __PRETTY_FUNCTION__));
142 Backedge = *PI++;
143 if (PI == pred_end(H)) return nullptr; // dead loop
144 Incoming = *PI++;
145 if (PI != pred_end(H)) return nullptr; // multiple backedges?
146
147 if (contains(Incoming)) {
148 if (contains(Backedge))
149 return nullptr;
150 std::swap(Incoming, Backedge);
151 } else if (!contains(Backedge))
152 return nullptr;
153
154 // Loop over all of the PHI nodes, looking for a canonical indvar.
155 for (BasicBlock::iterator I = H->begin(); isa<PHINode>(I); ++I) {
156 PHINode *PN = cast<PHINode>(I);
157 if (ConstantInt *CI =
158 dyn_cast<ConstantInt>(PN->getIncomingValueForBlock(Incoming)))
159 if (CI->isNullValue())
160 if (Instruction *Inc =
161 dyn_cast<Instruction>(PN->getIncomingValueForBlock(Backedge)))
162 if (Inc->getOpcode() == Instruction::Add &&
163 Inc->getOperand(0) == PN)
164 if (ConstantInt *CI = dyn_cast<ConstantInt>(Inc->getOperand(1)))
165 if (CI->equalsInt(1))
166 return PN;
167 }
168 return nullptr;
169}
170
171/// isLCSSAForm - Return true if the Loop is in LCSSA form
172bool Loop::isLCSSAForm(DominatorTree &DT) const {
173 for (block_iterator BI = block_begin(), E = block_end(); BI != E; ++BI) {
174 BasicBlock *BB = *BI;
175 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E;++I)
176 for (Use &U : I->uses()) {
177 Instruction *UI = cast<Instruction>(U.getUser());
178 BasicBlock *UserBB = UI->getParent();
179 if (PHINode *P = dyn_cast<PHINode>(UI))
180 UserBB = P->getIncomingBlock(U);
181
182 // Check the current block, as a fast-path, before checking whether
183 // the use is anywhere in the loop. Most values are used in the same
184 // block they are defined in. Also, blocks not reachable from the
185 // entry are special; uses in them don't need to go through PHIs.
186 if (UserBB != BB &&
187 !contains(UserBB) &&
188 DT.isReachableFromEntry(UserBB))
189 return false;
190 }
191 }
192
193 return true;
194}
195
196/// isLoopSimplifyForm - Return true if the Loop is in the form that
197/// the LoopSimplify form transforms loops to, which is sometimes called
198/// normal form.
199bool Loop::isLoopSimplifyForm() const {
200 // Normal-form loops have a preheader, a single backedge, and all of their
201 // exits have all their predecessors inside the loop.
202 return getLoopPreheader() && getLoopLatch() && hasDedicatedExits();
203}
204
205/// isSafeToClone - Return true if the loop body is safe to clone in practice.
206/// Routines that reform the loop CFG and split edges often fail on indirectbr.
207bool Loop::isSafeToClone() const {
208 // Return false if any loop blocks contain indirectbrs, or there are any calls
209 // to noduplicate functions.
210 for (Loop::block_iterator I = block_begin(), E = block_end(); I != E; ++I) {
211 if (isa<IndirectBrInst>((*I)->getTerminator()))
212 return false;
213
214 if (const InvokeInst *II = dyn_cast<InvokeInst>((*I)->getTerminator()))
215 if (II->cannotDuplicate())
216 return false;
217
218 for (BasicBlock::iterator BI = (*I)->begin(), BE = (*I)->end(); BI != BE; ++BI) {
219 if (const CallInst *CI = dyn_cast<CallInst>(BI)) {
220 if (CI->cannotDuplicate())
221 return false;
222 }
223 if (BI->getType()->isTokenTy() && BI->isUsedOutsideOfBlock(*I))
224 return false;
225 }
226 }
227 return true;
228}
229
230MDNode *Loop::getLoopID() const {
231 MDNode *LoopID = nullptr;
232 if (isLoopSimplifyForm()) {
233 LoopID = getLoopLatch()->getTerminator()->getMetadata(LoopMDName);
234 } else {
235 // Go through each predecessor of the loop header and check the
236 // terminator for the metadata.
237 BasicBlock *H = getHeader();
238 for (block_iterator I = block_begin(), IE = block_end(); I != IE; ++I) {
239 TerminatorInst *TI = (*I)->getTerminator();
240 MDNode *MD = nullptr;
241
242 // Check if this terminator branches to the loop header.
243 for (unsigned i = 0, ie = TI->getNumSuccessors(); i != ie; ++i) {
244 if (TI->getSuccessor(i) == H) {
245 MD = TI->getMetadata(LoopMDName);
246 break;
247 }
248 }
249 if (!MD)
250 return nullptr;
251
252 if (!LoopID)
253 LoopID = MD;
254 else if (MD != LoopID)
255 return nullptr;
256 }
257 }
258 if (!LoopID || LoopID->getNumOperands() == 0 ||
259 LoopID->getOperand(0) != LoopID)
260 return nullptr;
261 return LoopID;
262}
263
264void Loop::setLoopID(MDNode *LoopID) const {
265 assert(LoopID && "Loop ID should not be null")((LoopID && "Loop ID should not be null") ? static_cast
<void> (0) : __assert_fail ("LoopID && \"Loop ID should not be null\""
, "/tmp/buildd/llvm-toolchain-snapshot-3.8~svn246424/lib/Analysis/LoopInfo.cpp"
, 265, __PRETTY_FUNCTION__));
266 assert(LoopID->getNumOperands() > 0 && "Loop ID needs at least one operand")((LoopID->getNumOperands() > 0 && "Loop ID needs at least one operand"
) ? static_cast<void> (0) : __assert_fail ("LoopID->getNumOperands() > 0 && \"Loop ID needs at least one operand\""
, "/tmp/buildd/llvm-toolchain-snapshot-3.8~svn246424/lib/Analysis/LoopInfo.cpp"
, 266, __PRETTY_FUNCTION__));
267 assert(LoopID->getOperand(0) == LoopID && "Loop ID should refer to itself")((LoopID->getOperand(0) == LoopID && "Loop ID should refer to itself"
) ? static_cast<void> (0) : __assert_fail ("LoopID->getOperand(0) == LoopID && \"Loop ID should refer to itself\""
, "/tmp/buildd/llvm-toolchain-snapshot-3.8~svn246424/lib/Analysis/LoopInfo.cpp"
, 267, __PRETTY_FUNCTION__));
268
269 if (isLoopSimplifyForm()) {
270 getLoopLatch()->getTerminator()->setMetadata(LoopMDName, LoopID);
271 return;
272 }
273
274 BasicBlock *H = getHeader();
275 for (block_iterator I = block_begin(), IE = block_end(); I != IE; ++I) {
276 TerminatorInst *TI = (*I)->getTerminator();
277 for (unsigned i = 0, ie = TI->getNumSuccessors(); i != ie; ++i) {
278 if (TI->getSuccessor(i) == H)
279 TI->setMetadata(LoopMDName, LoopID);
280 }
281 }
282}
283
284bool Loop::isAnnotatedParallel() const {
285 MDNode *desiredLoopIdMetadata = getLoopID();
286
287 if (!desiredLoopIdMetadata)
288 return false;
289
290 // The loop branch contains the parallel loop metadata. In order to ensure
291 // that any parallel-loop-unaware optimization pass hasn't added loop-carried
292 // dependencies (thus converted the loop back to a sequential loop), check
293 // that all the memory instructions in the loop contain parallelism metadata
294 // that point to the same unique "loop id metadata" the loop branch does.
295 for (block_iterator BB = block_begin(), BE = block_end(); BB != BE; ++BB) {
296 for (BasicBlock::iterator II = (*BB)->begin(), EE = (*BB)->end();
297 II != EE; II++) {
298
299 if (!II->mayReadOrWriteMemory())
300 continue;
301
302 // The memory instruction can refer to the loop identifier metadata
303 // directly or indirectly through another list metadata (in case of
304 // nested parallel loops). The loop identifier metadata refers to
305 // itself so we can check both cases with the same routine.
306 MDNode *loopIdMD =
307 II->getMetadata(LLVMContext::MD_mem_parallel_loop_access);
308
309 if (!loopIdMD)
310 return false;
311
312 bool loopIdMDFound = false;
313 for (unsigned i = 0, e = loopIdMD->getNumOperands(); i < e; ++i) {
314 if (loopIdMD->getOperand(i) == desiredLoopIdMetadata) {
315 loopIdMDFound = true;
316 break;
317 }
318 }
319
320 if (!loopIdMDFound)
321 return false;
322 }
323 }
324 return true;
325}
326
327
328/// hasDedicatedExits - Return true if no exit block for the loop
329/// has a predecessor that is outside the loop.
330bool Loop::hasDedicatedExits() const {
331 // Each predecessor of each exit block of a normal loop is contained
332 // within the loop.
333 SmallVector<BasicBlock *, 4> ExitBlocks;
334 getExitBlocks(ExitBlocks);
335 for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i)
336 for (pred_iterator PI = pred_begin(ExitBlocks[i]),
337 PE = pred_end(ExitBlocks[i]); PI != PE; ++PI)
338 if (!contains(*PI))
339 return false;
340 // All the requirements are met.
341 return true;
342}
343
344/// getUniqueExitBlocks - Return all unique successor blocks of this loop.
345/// These are the blocks _outside of the current loop_ which are branched to.
346/// This assumes that loop exits are in canonical form.
347///
348void
349Loop::getUniqueExitBlocks(SmallVectorImpl<BasicBlock *> &ExitBlocks) const {
350 assert(hasDedicatedExits() &&((hasDedicatedExits() && "getUniqueExitBlocks assumes the loop has canonical form exits!"
) ? static_cast<void> (0) : __assert_fail ("hasDedicatedExits() && \"getUniqueExitBlocks assumes the loop has canonical form exits!\""
, "/tmp/buildd/llvm-toolchain-snapshot-3.8~svn246424/lib/Analysis/LoopInfo.cpp"
, 351, __PRETTY_FUNCTION__))
351 "getUniqueExitBlocks assumes the loop has canonical form exits!")((hasDedicatedExits() && "getUniqueExitBlocks assumes the loop has canonical form exits!"
) ? static_cast<void> (0) : __assert_fail ("hasDedicatedExits() && \"getUniqueExitBlocks assumes the loop has canonical form exits!\""
, "/tmp/buildd/llvm-toolchain-snapshot-3.8~svn246424/lib/Analysis/LoopInfo.cpp"
, 351, __PRETTY_FUNCTION__));
352
353 SmallVector<BasicBlock *, 32> switchExitBlocks;
354
355 for (block_iterator BI = block_begin(), BE = block_end(); BI != BE; ++BI) {
356
357 BasicBlock *current = *BI;
358 switchExitBlocks.clear();
359
360 for (succ_iterator I = succ_begin(*BI), E = succ_end(*BI); I != E; ++I) {
361 // If block is inside the loop then it is not a exit block.
362 if (contains(*I))
363 continue;
364
365 pred_iterator PI = pred_begin(*I);
366 BasicBlock *firstPred = *PI;
367
368 // If current basic block is this exit block's first predecessor
369 // then only insert exit block in to the output ExitBlocks vector.
370 // This ensures that same exit block is not inserted twice into
371 // ExitBlocks vector.
372 if (current != firstPred)
373 continue;
374
375 // If a terminator has more then two successors, for example SwitchInst,
376 // then it is possible that there are multiple edges from current block
377 // to one exit block.
378 if (std::distance(succ_begin(current), succ_end(current)) <= 2) {
379 ExitBlocks.push_back(*I);
380 continue;
381 }
382
383 // In case of multiple edges from current block to exit block, collect
384 // only one edge in ExitBlocks. Use switchExitBlocks to keep track of
385 // duplicate edges.
386 if (std::find(switchExitBlocks.begin(), switchExitBlocks.end(), *I)
387 == switchExitBlocks.end()) {
388 switchExitBlocks.push_back(*I);
389 ExitBlocks.push_back(*I);
390 }
391 }
392 }
393}
394
395/// getUniqueExitBlock - If getUniqueExitBlocks would return exactly one
396/// block, return that block. Otherwise return null.
397BasicBlock *Loop::getUniqueExitBlock() const {
398 SmallVector<BasicBlock *, 8> UniqueExitBlocks;
399 getUniqueExitBlocks(UniqueExitBlocks);
400 if (UniqueExitBlocks.size() == 1)
401 return UniqueExitBlocks[0];
402 return nullptr;
403}
404
405#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
406void Loop::dump() const {
407 print(dbgs());
408}
409#endif
410
411//===----------------------------------------------------------------------===//
412// UnloopUpdater implementation
413//
414
415namespace {
416/// Find the new parent loop for all blocks within the "unloop" whose last
417/// backedges has just been removed.
418class UnloopUpdater {
419 Loop *Unloop;
420 LoopInfo *LI;
421
422 LoopBlocksDFS DFS;
423
424 // Map unloop's immediate subloops to their nearest reachable parents. Nested
425 // loops within these subloops will not change parents. However, an immediate
426 // subloop's new parent will be the nearest loop reachable from either its own
427 // exits *or* any of its nested loop's exits.
428 DenseMap<Loop*, Loop*> SubloopParents;
429
430 // Flag the presence of an irreducible backedge whose destination is a block
431 // directly contained by the original unloop.
432 bool FoundIB;
433
434public:
435 UnloopUpdater(Loop *UL, LoopInfo *LInfo) :
436 Unloop(UL), LI(LInfo), DFS(UL), FoundIB(false) {}
437
438 void updateBlockParents();
439
440 void removeBlocksFromAncestors();
441
442 void updateSubloopParents();
443
444protected:
445 Loop *getNearestLoop(BasicBlock *BB, Loop *BBLoop);
446};
447} // end anonymous namespace
448
449/// updateBlockParents - Update the parent loop for all blocks that are directly
450/// contained within the original "unloop".
451void UnloopUpdater::updateBlockParents() {
452 if (Unloop->getNumBlocks()) {
453 // Perform a post order CFG traversal of all blocks within this loop,
454 // propagating the nearest loop from sucessors to predecessors.
455 LoopBlocksTraversal Traversal(DFS, LI);
456 for (LoopBlocksTraversal::POTIterator POI = Traversal.begin(),
457 POE = Traversal.end(); POI != POE; ++POI) {
458
459 Loop *L = LI->getLoopFor(*POI);
460 Loop *NL = getNearestLoop(*POI, L);
461
462 if (NL != L) {
463 // For reducible loops, NL is now an ancestor of Unloop.
464 assert((NL != Unloop && (!NL || NL->contains(Unloop))) &&(((NL != Unloop && (!NL || NL->contains(Unloop))) &&
"uninitialized successor") ? static_cast<void> (0) : __assert_fail
("(NL != Unloop && (!NL || NL->contains(Unloop))) && \"uninitialized successor\""
, "/tmp/buildd/llvm-toolchain-snapshot-3.8~svn246424/lib/Analysis/LoopInfo.cpp"
, 465, __PRETTY_FUNCTION__))
465 "uninitialized successor")(((NL != Unloop && (!NL || NL->contains(Unloop))) &&
"uninitialized successor") ? static_cast<void> (0) : __assert_fail
("(NL != Unloop && (!NL || NL->contains(Unloop))) && \"uninitialized successor\""
, "/tmp/buildd/llvm-toolchain-snapshot-3.8~svn246424/lib/Analysis/LoopInfo.cpp"
, 465, __PRETTY_FUNCTION__));
466 LI->changeLoopFor(*POI, NL);
467 }
468 else {
469 // Or the current block is part of a subloop, in which case its parent
470 // is unchanged.
471 assert((FoundIB || Unloop->contains(L)) && "uninitialized successor")(((FoundIB || Unloop->contains(L)) && "uninitialized successor"
) ? static_cast<void> (0) : __assert_fail ("(FoundIB || Unloop->contains(L)) && \"uninitialized successor\""
, "/tmp/buildd/llvm-toolchain-snapshot-3.8~svn246424/lib/Analysis/LoopInfo.cpp"
, 471, __PRETTY_FUNCTION__));
472 }
473 }
474 }
475 // Each irreducible loop within the unloop induces a round of iteration using
476 // the DFS result cached by Traversal.
477 bool Changed = FoundIB;
478 for (unsigned NIters = 0; Changed; ++NIters) {
479 assert(NIters < Unloop->getNumBlocks() && "runaway iterative algorithm")((NIters < Unloop->getNumBlocks() && "runaway iterative algorithm"
) ? static_cast<void> (0) : __assert_fail ("NIters < Unloop->getNumBlocks() && \"runaway iterative algorithm\""
, "/tmp/buildd/llvm-toolchain-snapshot-3.8~svn246424/lib/Analysis/LoopInfo.cpp"
, 479, __PRETTY_FUNCTION__));
480
481 // Iterate over the postorder list of blocks, propagating the nearest loop
482 // from successors to predecessors as before.
483 Changed = false;
484 for (LoopBlocksDFS::POIterator POI = DFS.beginPostorder(),
485 POE = DFS.endPostorder(); POI != POE; ++POI) {
486
487 Loop *L = LI->getLoopFor(*POI);
488 Loop *NL = getNearestLoop(*POI, L);
489 if (NL != L) {
490 assert(NL != Unloop && (!NL || NL->contains(Unloop)) &&((NL != Unloop && (!NL || NL->contains(Unloop)) &&
"uninitialized successor") ? static_cast<void> (0) : __assert_fail
("NL != Unloop && (!NL || NL->contains(Unloop)) && \"uninitialized successor\""
, "/tmp/buildd/llvm-toolchain-snapshot-3.8~svn246424/lib/Analysis/LoopInfo.cpp"
, 491, __PRETTY_FUNCTION__))
491 "uninitialized successor")((NL != Unloop && (!NL || NL->contains(Unloop)) &&
"uninitialized successor") ? static_cast<void> (0) : __assert_fail
("NL != Unloop && (!NL || NL->contains(Unloop)) && \"uninitialized successor\""
, "/tmp/buildd/llvm-toolchain-snapshot-3.8~svn246424/lib/Analysis/LoopInfo.cpp"
, 491, __PRETTY_FUNCTION__));
492 LI->changeLoopFor(*POI, NL);
493 Changed = true;
494 }
495 }
496 }
497}
498
499/// removeBlocksFromAncestors - Remove unloop's blocks from all ancestors below
500/// their new parents.
501void UnloopUpdater::removeBlocksFromAncestors() {
502 // Remove all unloop's blocks (including those in nested subloops) from
503 // ancestors below the new parent loop.
504 for (Loop::block_iterator BI = Unloop->block_begin(),
505 BE = Unloop->block_end(); BI != BE; ++BI) {
506 Loop *OuterParent = LI->getLoopFor(*BI);
507 if (Unloop->contains(OuterParent)) {
508 while (OuterParent->getParentLoop() != Unloop)
509 OuterParent = OuterParent->getParentLoop();
510 OuterParent = SubloopParents[OuterParent];
511 }
512 // Remove blocks from former Ancestors except Unloop itself which will be
513 // deleted.
514 for (Loop *OldParent = Unloop->getParentLoop(); OldParent != OuterParent;
515 OldParent = OldParent->getParentLoop()) {
516 assert(OldParent && "new loop is not an ancestor of the original")((OldParent && "new loop is not an ancestor of the original"
) ? static_cast<void> (0) : __assert_fail ("OldParent && \"new loop is not an ancestor of the original\""
, "/tmp/buildd/llvm-toolchain-snapshot-3.8~svn246424/lib/Analysis/LoopInfo.cpp"
, 516, __PRETTY_FUNCTION__));
517 OldParent->removeBlockFromLoop(*BI);
518 }
519 }
520}
521
522/// updateSubloopParents - Update the parent loop for all subloops directly
523/// nested within unloop.
524void UnloopUpdater::updateSubloopParents() {
525 while (!Unloop->empty()) {
526 Loop *Subloop = *std::prev(Unloop->end());
527 Unloop->removeChildLoop(std::prev(Unloop->end()));
528
529 assert(SubloopParents.count(Subloop) && "DFS failed to visit subloop")((SubloopParents.count(Subloop) && "DFS failed to visit subloop"
) ? static_cast<void> (0) : __assert_fail ("SubloopParents.count(Subloop) && \"DFS failed to visit subloop\""
, "/tmp/buildd/llvm-toolchain-snapshot-3.8~svn246424/lib/Analysis/LoopInfo.cpp"
, 529, __PRETTY_FUNCTION__));
530 if (Loop *Parent = SubloopParents[Subloop])
531 Parent->addChildLoop(Subloop);
532 else
533 LI->addTopLevelLoop(Subloop);
534 }
535}
536
537/// getNearestLoop - Return the nearest parent loop among this block's
538/// successors. If a successor is a subloop header, consider its parent to be
539/// the nearest parent of the subloop's exits.
540///
541/// For subloop blocks, simply update SubloopParents and return NULL.
542Loop *UnloopUpdater::getNearestLoop(BasicBlock *BB, Loop *BBLoop) {
543
544 // Initially for blocks directly contained by Unloop, NearLoop == Unloop and
545 // is considered uninitialized.
546 Loop *NearLoop = BBLoop;
547
548 Loop *Subloop = nullptr;
549 if (NearLoop != Unloop && Unloop->contains(NearLoop)) {
550 Subloop = NearLoop;
551 // Find the subloop ancestor that is directly contained within Unloop.
552 while (Subloop->getParentLoop() != Unloop) {
553 Subloop = Subloop->getParentLoop();
554 assert(Subloop && "subloop is not an ancestor of the original loop")((Subloop && "subloop is not an ancestor of the original loop"
) ? static_cast<void> (0) : __assert_fail ("Subloop && \"subloop is not an ancestor of the original loop\""
, "/tmp/buildd/llvm-toolchain-snapshot-3.8~svn246424/lib/Analysis/LoopInfo.cpp"
, 554, __PRETTY_FUNCTION__));
555 }
556 // Get the current nearest parent of the Subloop exits, initially Unloop.
557 NearLoop =
558 SubloopParents.insert(std::make_pair(Subloop, Unloop)).first->second;
559 }
560
561 succ_iterator I = succ_begin(BB), E = succ_end(BB);
562 if (I == E) {
1
Taking false branch
→
563 assert(!Subloop && "subloop blocks must have a successor")((!Subloop && "subloop blocks must have a successor")
? static_cast<void> (0) : __assert_fail ("!Subloop && \"subloop blocks must have a successor\""
, "/tmp/buildd/llvm-toolchain-snapshot-3.8~svn246424/lib/Analysis/LoopInfo.cpp"
, 563, __PRETTY_FUNCTION__));
564 NearLoop = nullptr; // unloop blocks may now exit the function.
565 }
566 for (; I != E; ++I) {
2
←
Loop condition is true. Entering loop body
→
7
←
Loop condition is true. Entering loop body
→
13
←
Loop condition is true. Entering loop body
→
567 if (*I == BB)
3
←
Taking false branch
→
8
←
Taking false branch
→
14
←
Taking false branch
→
568 continue; // self loops are uninteresting
569
570 Loop *L = LI->getLoopFor(*I);
15
←
'L' initialized here
→
571 if (L == Unloop) {
4
←
Taking false branch
→
9
←
Taking false branch
→
16
←
Assuming pointer value is null
→
17
←
Taking true branch
→
572 // This successor has not been processed. This path must lead to an
573 // irreducible backedge.
574 assert((FoundIB || !DFS.hasPostorder(*I)) && "should have seen IB")(((FoundIB || !DFS.hasPostorder(*I)) && "should have seen IB"
) ? static_cast<void> (0) : __assert_fail ("(FoundIB || !DFS.hasPostorder(*I)) && \"should have seen IB\""
, "/tmp/buildd/llvm-toolchain-snapshot-3.8~svn246424/lib/Analysis/LoopInfo.cpp"
, 574, __PRETTY_FUNCTION__));
575 FoundIB = true;
576 }
577 if (L != Unloop && Unloop->contains(L)) {
5
←
Taking false branch
→
10
←
Taking true branch
→
18
←
Taking true branch
→
578 // Successor is in a subloop.
579 if (Subloop)
11
←
Taking false branch
→
19
←
Taking false branch
→
580 continue; // Branching within subloops. Ignore it.
581
582 // BB branches from the original into a subloop header.
583 assert(L->getParentLoop() == Unloop && "cannot skip into nested loops")((L->getParentLoop() == Unloop && "cannot skip into nested loops"
) ? static_cast<void> (0) : __assert_fail ("L->getParentLoop() == Unloop && \"cannot skip into nested loops\""
, "/tmp/buildd/llvm-toolchain-snapshot-3.8~svn246424/lib/Analysis/LoopInfo.cpp"
, 583, __PRETTY_FUNCTION__));
20
←
Within the expansion of the macro 'assert':
a
Called C++ object pointer is null
584
585 // Get the current nearest parent of the Subloop's exits.
586 L = SubloopParents[L];
587 // L could be Unloop if the only exit was an irreducible backedge.
588 }
589 if (L == Unloop) {
6
←
Taking false branch
→
12
←
Taking false branch
→
590 continue;
591 }
592 // Handle critical edges from Unloop into a sibling loop.
593 if (L && !L->contains(Unloop)) {
594 L = L->getParentLoop();
595 }
596 // Remember the nearest parent loop among successors or subloop exits.
597 if (NearLoop == Unloop || !NearLoop || NearLoop->contains(L))
598 NearLoop = L;
599 }
600 if (Subloop) {
601 SubloopParents[Subloop] = NearLoop;
602 return BBLoop;
603 }
604 return NearLoop;
605}
606
607LoopInfo::LoopInfo(const DominatorTreeBase<BasicBlock> &DomTree) {
608 analyze(DomTree);
609}
610
611/// updateUnloop - The last backedge has been removed from a loop--now the
612/// "unloop". Find a new parent for the blocks contained within unloop and
613/// update the loop tree. We don't necessarily have valid dominators at this
614/// point, but LoopInfo is still valid except for the removal of this loop.
615///
616/// Note that Unloop may now be an empty loop. Calling Loop::getHeader without
617/// checking first is illegal.
618void LoopInfo::updateUnloop(Loop *Unloop) {
619
620 // First handle the special case of no parent loop to simplify the algorithm.
621 if (!Unloop->getParentLoop()) {
622 // Since BBLoop had no parent, Unloop blocks are no longer in a loop.
623 for (Loop::block_iterator I = Unloop->block_begin(),
624 E = Unloop->block_end();
625 I != E; ++I) {
626
627 // Don't reparent blocks in subloops.
628 if (getLoopFor(*I) != Unloop)
629 continue;
630
631 // Blocks no longer have a parent but are still referenced by Unloop until
632 // the Unloop object is deleted.
633 changeLoopFor(*I, nullptr);
634 }
635
636 // Remove the loop from the top-level LoopInfo object.
637 for (iterator I = begin();; ++I) {
638 assert(I != end() && "Couldn't find loop")((I != end() && "Couldn't find loop") ? static_cast<
void> (0) : __assert_fail ("I != end() && \"Couldn't find loop\""
, "/tmp/buildd/llvm-toolchain-snapshot-3.8~svn246424/lib/Analysis/LoopInfo.cpp"
, 638, __PRETTY_FUNCTION__));
639 if (*I == Unloop) {
640 removeLoop(I);
641 break;
642 }
643 }
644
645 // Move all of the subloops to the top-level.
646 while (!Unloop->empty())
647 addTopLevelLoop(Unloop->removeChildLoop(std::prev(Unloop->end())));
648
649 return;
650 }
651
652 // Update the parent loop for all blocks within the loop. Blocks within
653 // subloops will not change parents.
654 UnloopUpdater Updater(Unloop, this);
655 Updater.updateBlockParents();
656
657 // Remove blocks from former ancestor loops.
658 Updater.removeBlocksFromAncestors();
659
660 // Add direct subloops as children in their new parent loop.
661 Updater.updateSubloopParents();
662
663 // Remove unloop from its parent loop.
664 Loop *ParentLoop = Unloop->getParentLoop();
665 for (Loop::iterator I = ParentLoop->begin();; ++I) {
666 assert(I != ParentLoop->end() && "Couldn't find loop")((I != ParentLoop->end() && "Couldn't find loop") ?
static_cast<void> (0) : __assert_fail ("I != ParentLoop->end() && \"Couldn't find loop\""
, "/tmp/buildd/llvm-toolchain-snapshot-3.8~svn246424/lib/Analysis/LoopInfo.cpp"
, 666, __PRETTY_FUNCTION__));
667 if (*I == Unloop) {
668 ParentLoop->removeChildLoop(I);
669 break;
670 }
671 }
672}
673
674char LoopAnalysis::PassID;
675
676LoopInfo LoopAnalysis::run(Function &F, AnalysisManager<Function> *AM) {
677 // FIXME: Currently we create a LoopInfo from scratch for every function.
678 // This may prove to be too wasteful due to deallocating and re-allocating
679 // memory each time for the underlying map and vector datastructures. At some
680 // point it may prove worthwhile to use a freelist and recycle LoopInfo
681 // objects. I don't want to add that kind of complexity until the scope of
682 // the problem is better understood.
683 LoopInfo LI;
684 LI.analyze(AM->getResult<DominatorTreeAnalysis>(F));
685 return LI;
686}
687
688PreservedAnalyses LoopPrinterPass::run(Function &F,
689 AnalysisManager<Function> *AM) {
690 AM->getResult<LoopAnalysis>(F).print(OS);
691 return PreservedAnalyses::all();
692}
693
694//===----------------------------------------------------------------------===//
695// LoopInfo implementation
696//
697
698char LoopInfoWrapperPass::ID = 0;
699INITIALIZE_PASS_BEGIN(LoopInfoWrapperPass, "loops", "Natural Loop Information",static void* initializeLoopInfoWrapperPassPassOnce(PassRegistry
&Registry) {
700 true, true)static void* initializeLoopInfoWrapperPassPassOnce(PassRegistry
&Registry) {
701INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)initializeDominatorTreeWrapperPassPass(Registry);
702INITIALIZE_PASS_END(LoopInfoWrapperPass, "loops", "Natural Loop Information",PassInfo *PI = new PassInfo("Natural Loop Information", "loops"
, & LoopInfoWrapperPass ::ID, PassInfo::NormalCtor_t(callDefaultCtor
< LoopInfoWrapperPass >), true, true); Registry.registerPass
(*PI, true); return PI; } void llvm::initializeLoopInfoWrapperPassPass
(PassRegistry &Registry) { static volatile sys::cas_flag initialized
= 0; sys::cas_flag old_val = sys::CompareAndSwap(&initialized
, 1, 0); if (old_val == 0) { initializeLoopInfoWrapperPassPassOnce
(Registry); sys::MemoryFence(); ; ; initialized = 2; ; } else
{ sys::cas_flag tmp = initialized; sys::MemoryFence(); while
(tmp != 2) { tmp = initialized; sys::MemoryFence(); } } ; }
703 true, true)PassInfo *PI = new PassInfo("Natural Loop Information", "loops"
, & LoopInfoWrapperPass ::ID, PassInfo::NormalCtor_t(callDefaultCtor
< LoopInfoWrapperPass >), true, true); Registry.registerPass
(*PI, true); return PI; } void llvm::initializeLoopInfoWrapperPassPass
(PassRegistry &Registry) { static volatile sys::cas_flag initialized
= 0; sys::cas_flag old_val = sys::CompareAndSwap(&initialized
, 1, 0); if (old_val == 0) { initializeLoopInfoWrapperPassPassOnce
(Registry); sys::MemoryFence(); ; ; initialized = 2; ; } else
{ sys::cas_flag tmp = initialized; sys::MemoryFence(); while
(tmp != 2) { tmp = initialized; sys::MemoryFence(); } } ; }
704
705bool LoopInfoWrapperPass::runOnFunction(Function &) {
706 releaseMemory();
707 LI.analyze(getAnalysis<DominatorTreeWrapperPass>().getDomTree());
708 return false;
709}
710
711void LoopInfoWrapperPass::verifyAnalysis() const {
712 // LoopInfoWrapperPass is a FunctionPass, but verifying every loop in the
713 // function each time verifyAnalysis is called is very expensive. The
714 // -verify-loop-info option can enable this. In order to perform some
715 // checking by default, LoopPass has been taught to call verifyLoop manually
716 // during loop pass sequences.
717 if (VerifyLoopInfo)
718 LI.verify();
719}
720
721void LoopInfoWrapperPass::getAnalysisUsage(AnalysisUsage &AU) const {
722 AU.setPreservesAll();
723 AU.addRequired<DominatorTreeWrapperPass>();
724}
725
726void LoopInfoWrapperPass::print(raw_ostream &OS, const Module *) const {
727 LI.print(OS);
728}
729
730//===----------------------------------------------------------------------===//
731// LoopBlocksDFS implementation
732//
733
734/// Traverse the loop blocks and store the DFS result.
735/// Useful for clients that just want the final DFS result and don't need to
736/// visit blocks during the initial traversal.
737void LoopBlocksDFS::perform(LoopInfo *LI) {
738 LoopBlocksTraversal Traversal(*this, LI);
739 for (LoopBlocksTraversal::POTIterator POI = Traversal.begin(),
740 POE = Traversal.end(); POI != POE; ++POI) ;
741}