Bug Summary

File:lib/Transforms/Scalar/LoopUnswitch.cpp
Location:line 388, column 5
Description:Forming reference to null pointer

Annotated Source Code

1//===-- LoopUnswitch.cpp - Hoist loop-invariant conditionals in loop ------===//
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 pass transforms loops that contain branches on loop-invariant conditions
11// to have multiple loops. For example, it turns the left into the right code:
12//
13// for (...) if (lic)
14// A for (...)
15// if (lic) A; B; C
16// B else
17// C for (...)
18// A; C
19//
20// This can increase the size of the code exponentially (doubling it every time
21// a loop is unswitched) so we only unswitch if the resultant code will be
22// smaller than a threshold.
23//
24// This pass expects LICM to be run before it to hoist invariant conditions out
25// of the loop, to make the unswitching opportunity obvious.
26//
27//===----------------------------------------------------------------------===//
28
29#include "llvm/Transforms/Scalar.h"
30#include "llvm/ADT/STLExtras.h"
31#include "llvm/ADT/SmallPtrSet.h"
32#include "llvm/ADT/Statistic.h"
33#include "llvm/Analysis/CodeMetrics.h"
34#include "llvm/Analysis/InstructionSimplify.h"
35#include "llvm/Analysis/LoopInfo.h"
36#include "llvm/Analysis/LoopPass.h"
37#include "llvm/Analysis/ScalarEvolution.h"
38#include "llvm/Analysis/TargetTransformInfo.h"
39#include "llvm/IR/Constants.h"
40#include "llvm/IR/DerivedTypes.h"
41#include "llvm/IR/Dominators.h"
42#include "llvm/IR/Function.h"
43#include "llvm/IR/Instructions.h"
44#include "llvm/Support/CommandLine.h"
45#include "llvm/Support/Debug.h"
46#include "llvm/Support/raw_ostream.h"
47#include "llvm/Transforms/Utils/BasicBlockUtils.h"
48#include "llvm/Transforms/Utils/Cloning.h"
49#include "llvm/Transforms/Utils/Local.h"
50#include <algorithm>
51#include <map>
52#include <set>
53using namespace llvm;
54
55#define DEBUG_TYPE"loop-unswitch" "loop-unswitch"
56
57STATISTIC(NumBranches, "Number of branches unswitched")static llvm::Statistic NumBranches = { "loop-unswitch", "Number of branches unswitched"
, 0, 0 };
58STATISTIC(NumSwitches, "Number of switches unswitched")static llvm::Statistic NumSwitches = { "loop-unswitch", "Number of switches unswitched"
, 0, 0 };
59STATISTIC(NumSelects , "Number of selects unswitched")static llvm::Statistic NumSelects = { "loop-unswitch", "Number of selects unswitched"
, 0, 0 };
60STATISTIC(NumTrivial , "Number of unswitches that are trivial")static llvm::Statistic NumTrivial = { "loop-unswitch", "Number of unswitches that are trivial"
, 0, 0 };
61STATISTIC(NumSimplify, "Number of simplifications of unswitched code")static llvm::Statistic NumSimplify = { "loop-unswitch", "Number of simplifications of unswitched code"
, 0, 0 };
62STATISTIC(TotalInsts, "Total number of instructions analyzed")static llvm::Statistic TotalInsts = { "loop-unswitch", "Total number of instructions analyzed"
, 0, 0 };
63
64// The specific value of 100 here was chosen based only on intuition and a
65// few specific examples.
66static cl::opt<unsigned>
67Threshold("loop-unswitch-threshold", cl::desc("Max loop size to unswitch"),
68 cl::init(100), cl::Hidden);
69
70namespace {
71
72 class LUAnalysisCache {
73
74 typedef DenseMap<const SwitchInst*, SmallPtrSet<const Value *, 8> >
75 UnswitchedValsMap;
76
77 typedef UnswitchedValsMap::iterator UnswitchedValsIt;
78
79 struct LoopProperties {
80 unsigned CanBeUnswitchedCount;
81 unsigned SizeEstimation;
82 UnswitchedValsMap UnswitchedVals;
83 };
84
85 // Here we use std::map instead of DenseMap, since we need to keep valid
86 // LoopProperties pointer for current loop for better performance.
87 typedef std::map<const Loop*, LoopProperties> LoopPropsMap;
88 typedef LoopPropsMap::iterator LoopPropsMapIt;
89
90 LoopPropsMap LoopsProperties;
91 UnswitchedValsMap *CurLoopInstructions;
92 LoopProperties *CurrentLoopProperties;
93
94 // Max size of code we can produce on remained iterations.
95 unsigned MaxSize;
96
97 public:
98
99 LUAnalysisCache() :
100 CurLoopInstructions(nullptr), CurrentLoopProperties(nullptr),
101 MaxSize(Threshold)
102 {}
103
104 // Analyze loop. Check its size, calculate is it possible to unswitch
105 // it. Returns true if we can unswitch this loop.
106 bool countLoop(const Loop *L, const TargetTransformInfo &TTI);
107
108 // Clean all data related to given loop.
109 void forgetLoop(const Loop *L);
110
111 // Mark case value as unswitched.
112 // Since SI instruction can be partly unswitched, in order to avoid
113 // extra unswitching in cloned loops keep track all unswitched values.
114 void setUnswitched(const SwitchInst *SI, const Value *V);
115
116 // Check was this case value unswitched before or not.
117 bool isUnswitched(const SwitchInst *SI, const Value *V);
118
119 // Clone all loop-unswitch related loop properties.
120 // Redistribute unswitching quotas.
121 // Note, that new loop data is stored inside the VMap.
122 void cloneData(const Loop *NewLoop, const Loop *OldLoop,
123 const ValueToValueMapTy &VMap);
124 };
125
126 class LoopUnswitch : public LoopPass {
127 LoopInfo *LI; // Loop information
128 LPPassManager *LPM;
129
130 // LoopProcessWorklist - Used to check if second loop needs processing
131 // after RewriteLoopBodyWithConditionConstant rewrites first loop.
132 std::vector<Loop*> LoopProcessWorklist;
133
134 LUAnalysisCache BranchesInfo;
135
136 bool OptimizeForSize;
137 bool redoLoop;
138
139 Loop *currentLoop;
140 DominatorTree *DT;
141 BasicBlock *loopHeader;
142 BasicBlock *loopPreheader;
143
144 // LoopBlocks contains all of the basic blocks of the loop, including the
145 // preheader of the loop, the body of the loop, and the exit blocks of the
146 // loop, in that order.
147 std::vector<BasicBlock*> LoopBlocks;
148 // NewBlocks contained cloned copy of basic blocks from LoopBlocks.
149 std::vector<BasicBlock*> NewBlocks;
150
151 public:
152 static char ID; // Pass ID, replacement for typeid
153 explicit LoopUnswitch(bool Os = false) :
154 LoopPass(ID), OptimizeForSize(Os), redoLoop(false),
155 currentLoop(nullptr), DT(nullptr), loopHeader(nullptr),
156 loopPreheader(nullptr) {
157 initializeLoopUnswitchPass(*PassRegistry::getPassRegistry());
158 }
159
160 bool runOnLoop(Loop *L, LPPassManager &LPM) override;
161 bool processCurrentLoop();
162
163 /// This transformation requires natural loop information & requires that
164 /// loop preheaders be inserted into the CFG.
165 ///
166 void getAnalysisUsage(AnalysisUsage &AU) const override {
167 AU.addRequiredID(LoopSimplifyID);
168 AU.addPreservedID(LoopSimplifyID);
169 AU.addRequired<LoopInfo>();
170 AU.addPreserved<LoopInfo>();
171 AU.addRequiredID(LCSSAID);
172 AU.addPreservedID(LCSSAID);
173 AU.addPreserved<DominatorTreeWrapperPass>();
174 AU.addPreserved<ScalarEvolution>();
175 AU.addRequired<TargetTransformInfo>();
176 }
177
178 private:
179
180 void releaseMemory() override {
181 BranchesInfo.forgetLoop(currentLoop);
182 }
183
184 void initLoopData() {
185 loopHeader = currentLoop->getHeader();
186 loopPreheader = currentLoop->getLoopPreheader();
187 }
188
189 /// Split all of the edges from inside the loop to their exit blocks.
190 /// Update the appropriate Phi nodes as we do so.
191 void SplitExitEdges(Loop *L, const SmallVectorImpl<BasicBlock *> &ExitBlocks);
192
193 bool UnswitchIfProfitable(Value *LoopCond, Constant *Val);
194 void UnswitchTrivialCondition(Loop *L, Value *Cond, Constant *Val,
195 BasicBlock *ExitBlock);
196 void UnswitchNontrivialCondition(Value *LIC, Constant *OnVal, Loop *L);
197
198 void RewriteLoopBodyWithConditionConstant(Loop *L, Value *LIC,
199 Constant *Val, bool isEqual);
200
201 void EmitPreheaderBranchOnCondition(Value *LIC, Constant *Val,
202 BasicBlock *TrueDest,
203 BasicBlock *FalseDest,
204 Instruction *InsertPt);
205
206 void SimplifyCode(std::vector<Instruction*> &Worklist, Loop *L);
207 bool IsTrivialUnswitchCondition(Value *Cond, Constant **Val = nullptr,
208 BasicBlock **LoopExit = nullptr);
209
210 };
211}
212
213// Analyze loop. Check its size, calculate is it possible to unswitch
214// it. Returns true if we can unswitch this loop.
215bool LUAnalysisCache::countLoop(const Loop *L, const TargetTransformInfo &TTI) {
216
217 LoopPropsMapIt PropsIt;
218 bool Inserted;
219 std::tie(PropsIt, Inserted) =
220 LoopsProperties.insert(std::make_pair(L, LoopProperties()));
221
222 LoopProperties &Props = PropsIt->second;
223
224 if (Inserted) {
225 // New loop.
226
227 // Limit the number of instructions to avoid causing significant code
228 // expansion, and the number of basic blocks, to avoid loops with
229 // large numbers of branches which cause loop unswitching to go crazy.
230 // This is a very ad-hoc heuristic.
231
232 // FIXME: This is overly conservative because it does not take into
233 // consideration code simplification opportunities and code that can
234 // be shared by the resultant unswitched loops.
235 CodeMetrics Metrics;
236 for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
237 I != E; ++I)
238 Metrics.analyzeBasicBlock(*I, TTI);
239
240 Props.SizeEstimation = std::min(Metrics.NumInsts, Metrics.NumBlocks * 5);
241 Props.CanBeUnswitchedCount = MaxSize / (Props.SizeEstimation);
242 MaxSize -= Props.SizeEstimation * Props.CanBeUnswitchedCount;
243
244 if (Metrics.notDuplicatable) {
245 DEBUG(dbgs() << "NOT unswitching loop %"do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-unswitch")) { dbgs() << "NOT unswitching loop %"
<< L->getHeader()->getName() << ", contents cannot be "
<< "duplicated!\n"; } } while (0)
246 << L->getHeader()->getName() << ", contents cannot be "do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-unswitch")) { dbgs() << "NOT unswitching loop %"
<< L->getHeader()->getName() << ", contents cannot be "
<< "duplicated!\n"; } } while (0)
247 << "duplicated!\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-unswitch")) { dbgs() << "NOT unswitching loop %"
<< L->getHeader()->getName() << ", contents cannot be "
<< "duplicated!\n"; } } while (0);
248 return false;
249 }
250 }
251
252 if (!Props.CanBeUnswitchedCount) {
253 DEBUG(dbgs() << "NOT unswitching loop %"do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-unswitch")) { dbgs() << "NOT unswitching loop %"
<< L->getHeader()->getName() << ", cost too high: "
<< L->getBlocks().size() << "\n"; } } while (
0)
254 << L->getHeader()->getName() << ", cost too high: "do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-unswitch")) { dbgs() << "NOT unswitching loop %"
<< L->getHeader()->getName() << ", cost too high: "
<< L->getBlocks().size() << "\n"; } } while (
0)
255 << L->getBlocks().size() << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-unswitch")) { dbgs() << "NOT unswitching loop %"
<< L->getHeader()->getName() << ", cost too high: "
<< L->getBlocks().size() << "\n"; } } while (
0);
256 return false;
257 }
258
259 // Be careful. This links are good only before new loop addition.
260 CurrentLoopProperties = &Props;
261 CurLoopInstructions = &Props.UnswitchedVals;
262
263 return true;
264}
265
266// Clean all data related to given loop.
267void LUAnalysisCache::forgetLoop(const Loop *L) {
268
269 LoopPropsMapIt LIt = LoopsProperties.find(L);
270
271 if (LIt != LoopsProperties.end()) {
272 LoopProperties &Props = LIt->second;
273 MaxSize += Props.CanBeUnswitchedCount * Props.SizeEstimation;
274 LoopsProperties.erase(LIt);
275 }
276
277 CurrentLoopProperties = nullptr;
278 CurLoopInstructions = nullptr;
279}
280
281// Mark case value as unswitched.
282// Since SI instruction can be partly unswitched, in order to avoid
283// extra unswitching in cloned loops keep track all unswitched values.
284void LUAnalysisCache::setUnswitched(const SwitchInst *SI, const Value *V) {
285 (*CurLoopInstructions)[SI].insert(V);
286}
287
288// Check was this case value unswitched before or not.
289bool LUAnalysisCache::isUnswitched(const SwitchInst *SI, const Value *V) {
290 return (*CurLoopInstructions)[SI].count(V);
291}
292
293// Clone all loop-unswitch related loop properties.
294// Redistribute unswitching quotas.
295// Note, that new loop data is stored inside the VMap.
296void LUAnalysisCache::cloneData(const Loop *NewLoop, const Loop *OldLoop,
297 const ValueToValueMapTy &VMap) {
298
299 LoopProperties &NewLoopProps = LoopsProperties[NewLoop];
300 LoopProperties &OldLoopProps = *CurrentLoopProperties;
301 UnswitchedValsMap &Insts = OldLoopProps.UnswitchedVals;
302
303 // Reallocate "can-be-unswitched quota"
304
305 --OldLoopProps.CanBeUnswitchedCount;
306 unsigned Quota = OldLoopProps.CanBeUnswitchedCount;
307 NewLoopProps.CanBeUnswitchedCount = Quota / 2;
308 OldLoopProps.CanBeUnswitchedCount = Quota - Quota / 2;
309
310 NewLoopProps.SizeEstimation = OldLoopProps.SizeEstimation;
311
312 // Clone unswitched values info:
313 // for new loop switches we clone info about values that was
314 // already unswitched and has redundant successors.
315 for (UnswitchedValsIt I = Insts.begin(); I != Insts.end(); ++I) {
316 const SwitchInst *OldInst = I->first;
317 Value *NewI = VMap.lookup(OldInst);
318 const SwitchInst *NewInst = cast_or_null<SwitchInst>(NewI);
319 assert(NewInst && "All instructions that are in SrcBB must be in VMap.")((NewInst && "All instructions that are in SrcBB must be in VMap."
) ? static_cast<void> (0) : __assert_fail ("NewInst && \"All instructions that are in SrcBB must be in VMap.\""
, "/tmp/buildd/llvm-toolchain-snapshot-3.6~svn216889/lib/Transforms/Scalar/LoopUnswitch.cpp"
, 319, __PRETTY_FUNCTION__));
320
321 NewLoopProps.UnswitchedVals[NewInst] = OldLoopProps.UnswitchedVals[OldInst];
322 }
323}
324
325char LoopUnswitch::ID = 0;
326INITIALIZE_PASS_BEGIN(LoopUnswitch, "loop-unswitch", "Unswitch loops",static void* initializeLoopUnswitchPassOnce(PassRegistry &
Registry) {
327 false, false)static void* initializeLoopUnswitchPassOnce(PassRegistry &
Registry) {
328INITIALIZE_AG_DEPENDENCY(TargetTransformInfo)initializeTargetTransformInfoAnalysisGroup(Registry);
329INITIALIZE_PASS_DEPENDENCY(LoopSimplify)initializeLoopSimplifyPass(Registry);
330INITIALIZE_PASS_DEPENDENCY(LoopInfo)initializeLoopInfoPass(Registry);
331INITIALIZE_PASS_DEPENDENCY(LCSSA)initializeLCSSAPass(Registry);
332INITIALIZE_PASS_END(LoopUnswitch, "loop-unswitch", "Unswitch loops",PassInfo *PI = new PassInfo("Unswitch loops", "loop-unswitch"
, & LoopUnswitch ::ID, PassInfo::NormalCtor_t(callDefaultCtor
< LoopUnswitch >), false, false); Registry.registerPass
(*PI, true); return PI; } void llvm::initializeLoopUnswitchPass
(PassRegistry &Registry) { static volatile sys::cas_flag initialized
= 0; sys::cas_flag old_val = sys::CompareAndSwap(&initialized
, 1, 0); if (old_val == 0) { initializeLoopUnswitchPassOnce(Registry
); sys::MemoryFence(); AnnotateIgnoreWritesBegin("/tmp/buildd/llvm-toolchain-snapshot-3.6~svn216889/lib/Transforms/Scalar/LoopUnswitch.cpp"
, 333); AnnotateHappensBefore("/tmp/buildd/llvm-toolchain-snapshot-3.6~svn216889/lib/Transforms/Scalar/LoopUnswitch.cpp"
, 333, &initialized); initialized = 2; AnnotateIgnoreWritesEnd
("/tmp/buildd/llvm-toolchain-snapshot-3.6~svn216889/lib/Transforms/Scalar/LoopUnswitch.cpp"
, 333); } else { sys::cas_flag tmp = initialized; sys::MemoryFence
(); while (tmp != 2) { tmp = initialized; sys::MemoryFence();
} } AnnotateHappensAfter("/tmp/buildd/llvm-toolchain-snapshot-3.6~svn216889/lib/Transforms/Scalar/LoopUnswitch.cpp"
, 333, &initialized); }
333 false, false)PassInfo *PI = new PassInfo("Unswitch loops", "loop-unswitch"
, & LoopUnswitch ::ID, PassInfo::NormalCtor_t(callDefaultCtor
< LoopUnswitch >), false, false); Registry.registerPass
(*PI, true); return PI; } void llvm::initializeLoopUnswitchPass
(PassRegistry &Registry) { static volatile sys::cas_flag initialized
= 0; sys::cas_flag old_val = sys::CompareAndSwap(&initialized
, 1, 0); if (old_val == 0) { initializeLoopUnswitchPassOnce(Registry
); sys::MemoryFence(); AnnotateIgnoreWritesBegin("/tmp/buildd/llvm-toolchain-snapshot-3.6~svn216889/lib/Transforms/Scalar/LoopUnswitch.cpp"
, 333); AnnotateHappensBefore("/tmp/buildd/llvm-toolchain-snapshot-3.6~svn216889/lib/Transforms/Scalar/LoopUnswitch.cpp"
, 333, &initialized); initialized = 2; AnnotateIgnoreWritesEnd
("/tmp/buildd/llvm-toolchain-snapshot-3.6~svn216889/lib/Transforms/Scalar/LoopUnswitch.cpp"
, 333); } else { sys::cas_flag tmp = initialized; sys::MemoryFence
(); while (tmp != 2) { tmp = initialized; sys::MemoryFence();
} } AnnotateHappensAfter("/tmp/buildd/llvm-toolchain-snapshot-3.6~svn216889/lib/Transforms/Scalar/LoopUnswitch.cpp"
, 333, &initialized); }
334
335Pass *llvm::createLoopUnswitchPass(bool Os) {
336 return new LoopUnswitch(Os);
337}
338
339/// FindLIVLoopCondition - Cond is a condition that occurs in L. If it is
340/// invariant in the loop, or has an invariant piece, return the invariant.
341/// Otherwise, return null.
342static Value *FindLIVLoopCondition(Value *Cond, Loop *L, bool &Changed) {
343
344 // We started analyze new instruction, increment scanned instructions counter.
345 ++TotalInsts;
346
347 // We can never unswitch on vector conditions.
348 if (Cond->getType()->isVectorTy())
349 return nullptr;
350
351 // Constants should be folded, not unswitched on!
352 if (isa<Constant>(Cond)) return nullptr;
353
354 // TODO: Handle: br (VARIANT|INVARIANT).
355
356 // Hoist simple values out.
357 if (L->makeLoopInvariant(Cond, Changed))
358 return Cond;
359
360 if (BinaryOperator *BO = dyn_cast<BinaryOperator>(Cond))
361 if (BO->getOpcode() == Instruction::And ||
362 BO->getOpcode() == Instruction::Or) {
363 // If either the left or right side is invariant, we can unswitch on this,
364 // which will cause the branch to go away in one loop and the condition to
365 // simplify in the other one.
366 if (Value *LHS = FindLIVLoopCondition(BO->getOperand(0), L, Changed))
367 return LHS;
368 if (Value *RHS = FindLIVLoopCondition(BO->getOperand(1), L, Changed))
369 return RHS;
370 }
371
372 return nullptr;
373}
374
375bool LoopUnswitch::runOnLoop(Loop *L, LPPassManager &LPM_Ref) {
376 if (skipOptnoneFunction(L))
1
Taking false branch
→
377 return false;
378
379 LI = &getAnalysis<LoopInfo>();
380 LPM = &LPM_Ref;
381 DominatorTreeWrapperPass *DTWP =
382 getAnalysisIfAvailable<DominatorTreeWrapperPass>();
383 DT = DTWP ? &DTWP->getDomTree() : nullptr;
2
←
Assuming 'DTWP' is null
→
3
←
'?' condition is false
→
4
←
Null pointer value stored to field 'DT'
→
384 currentLoop = L;
385 Function *F = currentLoop->getHeader()->getParent();
386 bool Changed = false;
387 do {
388 assert(currentLoop->isLCSSAForm(*DT))((currentLoop->isLCSSAForm(*DT)) ? static_cast<void>
(0) : __assert_fail ("currentLoop->isLCSSAForm(*DT)", "/tmp/buildd/llvm-toolchain-snapshot-3.6~svn216889/lib/Transforms/Scalar/LoopUnswitch.cpp"
, 388, __PRETTY_FUNCTION__));
5
←
Within the expansion of the macro 'assert':
a
Forming reference to null pointer
389 redoLoop = false;
390 Changed |= processCurrentLoop();
391 } while(redoLoop);
392
393 if (Changed) {
394 // FIXME: Reconstruct dom info, because it is not preserved properly.
395 if (DT)
396 DT->recalculate(*F);
397 }
398 return Changed;
399}
400
401/// processCurrentLoop - Do actual work and unswitch loop if possible
402/// and profitable.
403bool LoopUnswitch::processCurrentLoop() {
404 bool Changed = false;
405
406 initLoopData();
407
408 // If LoopSimplify was unable to form a preheader, don't do any unswitching.
409 if (!loopPreheader)
410 return false;
411
412 // Loops with indirectbr cannot be cloned.
413 if (!currentLoop->isSafeToClone())
414 return false;
415
416 // Without dedicated exits, splitting the exit edge may fail.
417 if (!currentLoop->hasDedicatedExits())
418 return false;
419
420 LLVMContext &Context = loopHeader->getContext();
421
422 // Probably we reach the quota of branches for this loop. If so
423 // stop unswitching.
424 if (!BranchesInfo.countLoop(currentLoop, getAnalysis<TargetTransformInfo>()))
425 return false;
426
427 // Loop over all of the basic blocks in the loop. If we find an interior
428 // block that is branching on a loop-invariant condition, we can unswitch this
429 // loop.
430 for (Loop::block_iterator I = currentLoop->block_begin(),
431 E = currentLoop->block_end(); I != E; ++I) {
432 TerminatorInst *TI = (*I)->getTerminator();
433 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
434 // If this isn't branching on an invariant condition, we can't unswitch
435 // it.
436 if (BI->isConditional()) {
437 // See if this, or some part of it, is loop invariant. If so, we can
438 // unswitch on it if we desire.
439 Value *LoopCond = FindLIVLoopCondition(BI->getCondition(),
440 currentLoop, Changed);
441 if (LoopCond && UnswitchIfProfitable(LoopCond,
442 ConstantInt::getTrue(Context))) {
443 ++NumBranches;
444 return true;
445 }
446 }
447 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
448 Value *LoopCond = FindLIVLoopCondition(SI->getCondition(),
449 currentLoop, Changed);
450 unsigned NumCases = SI->getNumCases();
451 if (LoopCond && NumCases) {
452 // Find a value to unswitch on:
453 // FIXME: this should chose the most expensive case!
454 // FIXME: scan for a case with a non-critical edge?
455 Constant *UnswitchVal = nullptr;
456
457 // Do not process same value again and again.
458 // At this point we have some cases already unswitched and
459 // some not yet unswitched. Let's find the first not yet unswitched one.
460 for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end();
461 i != e; ++i) {
462 Constant *UnswitchValCandidate = i.getCaseValue();
463 if (!BranchesInfo.isUnswitched(SI, UnswitchValCandidate)) {
464 UnswitchVal = UnswitchValCandidate;
465 break;
466 }
467 }
468
469 if (!UnswitchVal)
470 continue;
471
472 if (UnswitchIfProfitable(LoopCond, UnswitchVal)) {
473 ++NumSwitches;
474 return true;
475 }
476 }
477 }
478
479 // Scan the instructions to check for unswitchable values.
480 for (BasicBlock::iterator BBI = (*I)->begin(), E = (*I)->end();
481 BBI != E; ++BBI)
482 if (SelectInst *SI = dyn_cast<SelectInst>(BBI)) {
483 Value *LoopCond = FindLIVLoopCondition(SI->getCondition(),
484 currentLoop, Changed);
485 if (LoopCond && UnswitchIfProfitable(LoopCond,
486 ConstantInt::getTrue(Context))) {
487 ++NumSelects;
488 return true;
489 }
490 }
491 }
492 return Changed;
493}
494
495/// isTrivialLoopExitBlock - Check to see if all paths from BB exit the
496/// loop with no side effects (including infinite loops).
497///
498/// If true, we return true and set ExitBB to the block we
499/// exit through.
500///
501static bool isTrivialLoopExitBlockHelper(Loop *L, BasicBlock *BB,
502 BasicBlock *&ExitBB,
503 std::set<BasicBlock*> &Visited) {
504 if (!Visited.insert(BB).second) {
505 // Already visited. Without more analysis, this could indicate an infinite
506 // loop.
507 return false;
508 }
509 if (!L->contains(BB)) {
510 // Otherwise, this is a loop exit, this is fine so long as this is the
511 // first exit.
512 if (ExitBB) return false;
513 ExitBB = BB;
514 return true;
515 }
516
517 // Otherwise, this is an unvisited intra-loop node. Check all successors.
518 for (succ_iterator SI = succ_begin(BB), E = succ_end(BB); SI != E; ++SI) {
519 // Check to see if the successor is a trivial loop exit.
520 if (!isTrivialLoopExitBlockHelper(L, *SI, ExitBB, Visited))
521 return false;
522 }
523
524 // Okay, everything after this looks good, check to make sure that this block
525 // doesn't include any side effects.
526 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
527 if (I->mayHaveSideEffects())
528 return false;
529
530 return true;
531}
532
533/// isTrivialLoopExitBlock - Return true if the specified block unconditionally
534/// leads to an exit from the specified loop, and has no side-effects in the
535/// process. If so, return the block that is exited to, otherwise return null.
536static BasicBlock *isTrivialLoopExitBlock(Loop *L, BasicBlock *BB) {
537 std::set<BasicBlock*> Visited;
538 Visited.insert(L->getHeader()); // Branches to header make infinite loops.
539 BasicBlock *ExitBB = nullptr;
540 if (isTrivialLoopExitBlockHelper(L, BB, ExitBB, Visited))
541 return ExitBB;
542 return nullptr;
543}
544
545/// IsTrivialUnswitchCondition - Check to see if this unswitch condition is
546/// trivial: that is, that the condition controls whether or not the loop does
547/// anything at all. If this is a trivial condition, unswitching produces no
548/// code duplications (equivalently, it produces a simpler loop and a new empty
549/// loop, which gets deleted).
550///
551/// If this is a trivial condition, return true, otherwise return false. When
552/// returning true, this sets Cond and Val to the condition that controls the
553/// trivial condition: when Cond dynamically equals Val, the loop is known to
554/// exit. Finally, this sets LoopExit to the BB that the loop exits to when
555/// Cond == Val.
556///
557bool LoopUnswitch::IsTrivialUnswitchCondition(Value *Cond, Constant **Val,
558 BasicBlock **LoopExit) {
559 BasicBlock *Header = currentLoop->getHeader();
560 TerminatorInst *HeaderTerm = Header->getTerminator();
561 LLVMContext &Context = Header->getContext();
562
563 BasicBlock *LoopExitBB = nullptr;
564 if (BranchInst *BI = dyn_cast<BranchInst>(HeaderTerm)) {
565 // If the header block doesn't end with a conditional branch on Cond, we
566 // can't handle it.
567 if (!BI->isConditional() || BI->getCondition() != Cond)
568 return false;
569
570 // Check to see if a successor of the branch is guaranteed to
571 // exit through a unique exit block without having any
572 // side-effects. If so, determine the value of Cond that causes it to do
573 // this.
574 if ((LoopExitBB = isTrivialLoopExitBlock(currentLoop,
575 BI->getSuccessor(0)))) {
576 if (Val) *Val = ConstantInt::getTrue(Context);
577 } else if ((LoopExitBB = isTrivialLoopExitBlock(currentLoop,
578 BI->getSuccessor(1)))) {
579 if (Val) *Val = ConstantInt::getFalse(Context);
580 }
581 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(HeaderTerm)) {
582 // If this isn't a switch on Cond, we can't handle it.
583 if (SI->getCondition() != Cond) return false;
584
585 // Check to see if a successor of the switch is guaranteed to go to the
586 // latch block or exit through a one exit block without having any
587 // side-effects. If so, determine the value of Cond that causes it to do
588 // this.
589 // Note that we can't trivially unswitch on the default case or
590 // on already unswitched cases.
591 for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end();
592 i != e; ++i) {
593 BasicBlock *LoopExitCandidate;
594 if ((LoopExitCandidate = isTrivialLoopExitBlock(currentLoop,
595 i.getCaseSuccessor()))) {
596 // Okay, we found a trivial case, remember the value that is trivial.
597 ConstantInt *CaseVal = i.getCaseValue();
598
599 // Check that it was not unswitched before, since already unswitched
600 // trivial vals are looks trivial too.
601 if (BranchesInfo.isUnswitched(SI, CaseVal))
602 continue;
603 LoopExitBB = LoopExitCandidate;
604 if (Val) *Val = CaseVal;
605 break;
606 }
607 }
608 }
609
610 // If we didn't find a single unique LoopExit block, or if the loop exit block
611 // contains phi nodes, this isn't trivial.
612 if (!LoopExitBB || isa<PHINode>(LoopExitBB->begin()))
613 return false; // Can't handle this.
614
615 if (LoopExit) *LoopExit = LoopExitBB;
616
617 // We already know that nothing uses any scalar values defined inside of this
618 // loop. As such, we just have to check to see if this loop will execute any
619 // side-effecting instructions (e.g. stores, calls, volatile loads) in the
620 // part of the loop that the code *would* execute. We already checked the
621 // tail, check the header now.
622 for (BasicBlock::iterator I = Header->begin(), E = Header->end(); I != E; ++I)
623 if (I->mayHaveSideEffects())
624 return false;
625 return true;
626}
627
628/// UnswitchIfProfitable - We have found that we can unswitch currentLoop when
629/// LoopCond == Val to simplify the loop. If we decide that this is profitable,
630/// unswitch the loop, reprocess the pieces, then return true.
631bool LoopUnswitch::UnswitchIfProfitable(Value *LoopCond, Constant *Val) {
632 Function *F = loopHeader->getParent();
633 Constant *CondVal = nullptr;
634 BasicBlock *ExitBlock = nullptr;
635
636 if (IsTrivialUnswitchCondition(LoopCond, &CondVal, &ExitBlock)) {
637 // If the condition is trivial, always unswitch. There is no code growth
638 // for this case.
639 UnswitchTrivialCondition(currentLoop, LoopCond, CondVal, ExitBlock);
640 return true;
641 }
642
643 // Check to see if it would be profitable to unswitch current loop.
644
645 // Do not do non-trivial unswitch while optimizing for size.
646 if (OptimizeForSize ||
647 F->getAttributes().hasAttribute(AttributeSet::FunctionIndex,
648 Attribute::OptimizeForSize))
649 return false;
650
651 UnswitchNontrivialCondition(LoopCond, Val, currentLoop);
652 return true;
653}
654
655/// CloneLoop - Recursively clone the specified loop and all of its children,
656/// mapping the blocks with the specified map.
657static Loop *CloneLoop(Loop *L, Loop *PL, ValueToValueMapTy &VM,
658 LoopInfo *LI, LPPassManager *LPM) {
659 Loop *New = new Loop();
660 LPM->insertLoop(New, PL);
661
662 // Add all of the blocks in L to the new loop.
663 for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
664 I != E; ++I)
665 if (LI->getLoopFor(*I) == L)
666 New->addBasicBlockToLoop(cast<BasicBlock>(VM[*I]), LI->getBase());
667
668 // Add all of the subloops to the new loop.
669 for (Loop::iterator I = L->begin(), E = L->end(); I != E; ++I)
670 CloneLoop(*I, New, VM, LI, LPM);
671
672 return New;
673}
674
675/// EmitPreheaderBranchOnCondition - Emit a conditional branch on two values
676/// if LIC == Val, branch to TrueDst, otherwise branch to FalseDest. Insert the
677/// code immediately before InsertPt.
678void LoopUnswitch::EmitPreheaderBranchOnCondition(Value *LIC, Constant *Val,
679 BasicBlock *TrueDest,
680 BasicBlock *FalseDest,
681 Instruction *InsertPt) {
682 // Insert a conditional branch on LIC to the two preheaders. The original
683 // code is the true version and the new code is the false version.
684 Value *BranchVal = LIC;
685 if (!isa<ConstantInt>(Val) ||
686 Val->getType() != Type::getInt1Ty(LIC->getContext()))
687 BranchVal = new ICmpInst(InsertPt, ICmpInst::ICMP_EQ, LIC, Val);
688 else if (Val != ConstantInt::getTrue(Val->getContext()))
689 // We want to enter the new loop when the condition is true.
690 std::swap(TrueDest, FalseDest);
691
692 // Insert the new branch.
693 BranchInst *BI = BranchInst::Create(TrueDest, FalseDest, BranchVal, InsertPt);
694
695 // If either edge is critical, split it. This helps preserve LoopSimplify
696 // form for enclosing loops.
697 SplitCriticalEdge(BI, 0, this, false, false, true);
698 SplitCriticalEdge(BI, 1, this, false, false, true);
699}
700
701/// UnswitchTrivialCondition - Given a loop that has a trivial unswitchable
702/// condition in it (a cond branch from its header block to its latch block,
703/// where the path through the loop that doesn't execute its body has no
704/// side-effects), unswitch it. This doesn't involve any code duplication, just
705/// moving the conditional branch outside of the loop and updating loop info.
706void LoopUnswitch::UnswitchTrivialCondition(Loop *L, Value *Cond,
707 Constant *Val,
708 BasicBlock *ExitBlock) {
709 DEBUG(dbgs() << "loop-unswitch: Trivial-Unswitch loop %"do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-unswitch")) { dbgs() << "loop-unswitch: Trivial-Unswitch loop %"
<< loopHeader->getName() << " [" << L->
getBlocks().size() << " blocks] in Function " << L
->getHeader()->getParent()->getName() << " on cond: "
<< *Val << " == " << *Cond << "\n"; }
} while (0)
710 << loopHeader->getName() << " [" << L->getBlocks().size()do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-unswitch")) { dbgs() << "loop-unswitch: Trivial-Unswitch loop %"
<< loopHeader->getName() << " [" << L->
getBlocks().size() << " blocks] in Function " << L
->getHeader()->getParent()->getName() << " on cond: "
<< *Val << " == " << *Cond << "\n"; }
} while (0)
711 << " blocks] in Function " << L->getHeader()->getParent()->getName()do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-unswitch")) { dbgs() << "loop-unswitch: Trivial-Unswitch loop %"
<< loopHeader->getName() << " [" << L->
getBlocks().size() << " blocks] in Function " << L
->getHeader()->getParent()->getName() << " on cond: "
<< *Val << " == " << *Cond << "\n"; }
} while (0)
712 << " on cond: " << *Val << " == " << *Cond << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-unswitch")) { dbgs() << "loop-unswitch: Trivial-Unswitch loop %"
<< loopHeader->getName() << " [" << L->
getBlocks().size() << " blocks] in Function " << L
->getHeader()->getParent()->getName() << " on cond: "
<< *Val << " == " << *Cond << "\n"; }
} while (0);
713
714 // First step, split the preheader, so that we know that there is a safe place
715 // to insert the conditional branch. We will change loopPreheader to have a
716 // conditional branch on Cond.
717 BasicBlock *NewPH = SplitEdge(loopPreheader, loopHeader, this);
718
719 // Now that we have a place to insert the conditional branch, create a place
720 // to branch to: this is the exit block out of the loop that we should
721 // short-circuit to.
722
723 // Split this block now, so that the loop maintains its exit block, and so
724 // that the jump from the preheader can execute the contents of the exit block
725 // without actually branching to it (the exit block should be dominated by the
726 // loop header, not the preheader).
727 assert(!L->contains(ExitBlock) && "Exit block is in the loop?")((!L->contains(ExitBlock) && "Exit block is in the loop?"
) ? static_cast<void> (0) : __assert_fail ("!L->contains(ExitBlock) && \"Exit block is in the loop?\""
, "/tmp/buildd/llvm-toolchain-snapshot-3.6~svn216889/lib/Transforms/Scalar/LoopUnswitch.cpp"
, 727, __PRETTY_FUNCTION__));
728 BasicBlock *NewExit = SplitBlock(ExitBlock, ExitBlock->begin(), this);
729
730 // Okay, now we have a position to branch from and a position to branch to,
731 // insert the new conditional branch.
732 EmitPreheaderBranchOnCondition(Cond, Val, NewExit, NewPH,
733 loopPreheader->getTerminator());
734 LPM->deleteSimpleAnalysisValue(loopPreheader->getTerminator(), L);
735 loopPreheader->getTerminator()->eraseFromParent();
736
737 // We need to reprocess this loop, it could be unswitched again.
738 redoLoop = true;
739
740 // Now that we know that the loop is never entered when this condition is a
741 // particular value, rewrite the loop with this info. We know that this will
742 // at least eliminate the old branch.
743 RewriteLoopBodyWithConditionConstant(L, Cond, Val, false);
744 ++NumTrivial;
745}
746
747/// SplitExitEdges - Split all of the edges from inside the loop to their exit
748/// blocks. Update the appropriate Phi nodes as we do so.
749void LoopUnswitch::SplitExitEdges(Loop *L,
750 const SmallVectorImpl<BasicBlock *> &ExitBlocks){
751
752 for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) {
753 BasicBlock *ExitBlock = ExitBlocks[i];
754 SmallVector<BasicBlock *, 4> Preds(pred_begin(ExitBlock),
755 pred_end(ExitBlock));
756
757 // Although SplitBlockPredecessors doesn't preserve loop-simplify in
758 // general, if we call it on all predecessors of all exits then it does.
759 if (!ExitBlock->isLandingPad()) {
760 SplitBlockPredecessors(ExitBlock, Preds, ".us-lcssa", this);
761 } else {
762 SmallVector<BasicBlock*, 2> NewBBs;
763 SplitLandingPadPredecessors(ExitBlock, Preds, ".us-lcssa", ".us-lcssa",
764 this, NewBBs);
765 }
766 }
767}
768
769/// UnswitchNontrivialCondition - We determined that the loop is profitable
770/// to unswitch when LIC equal Val. Split it into loop versions and test the
771/// condition outside of either loop. Return the loops created as Out1/Out2.
772void LoopUnswitch::UnswitchNontrivialCondition(Value *LIC, Constant *Val,
773 Loop *L) {
774 Function *F = loopHeader->getParent();
775 DEBUG(dbgs() << "loop-unswitch: Unswitching loop %"do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-unswitch")) { dbgs() << "loop-unswitch: Unswitching loop %"
<< loopHeader->getName() << " [" << L->
getBlocks().size() << " blocks] in Function " << F
->getName() << " when '" << *Val << "' == "
<< *LIC << "\n"; } } while (0)
776 << loopHeader->getName() << " [" << L->getBlocks().size()do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-unswitch")) { dbgs() << "loop-unswitch: Unswitching loop %"
<< loopHeader->getName() << " [" << L->
getBlocks().size() << " blocks] in Function " << F
->getName() << " when '" << *Val << "' == "
<< *LIC << "\n"; } } while (0)
777 << " blocks] in Function " << F->getName()do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-unswitch")) { dbgs() << "loop-unswitch: Unswitching loop %"
<< loopHeader->getName() << " [" << L->
getBlocks().size() << " blocks] in Function " << F
->getName() << " when '" << *Val << "' == "
<< *LIC << "\n"; } } while (0)
778 << " when '" << *Val << "' == " << *LIC << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-unswitch")) { dbgs() << "loop-unswitch: Unswitching loop %"
<< loopHeader->getName() << " [" << L->
getBlocks().size() << " blocks] in Function " << F
->getName() << " when '" << *Val << "' == "
<< *LIC << "\n"; } } while (0);
779
780 if (ScalarEvolution *SE = getAnalysisIfAvailable<ScalarEvolution>())
781 SE->forgetLoop(L);
782
783 LoopBlocks.clear();
784 NewBlocks.clear();
785
786 // First step, split the preheader and exit blocks, and add these blocks to
787 // the LoopBlocks list.
788 BasicBlock *NewPreheader = SplitEdge(loopPreheader, loopHeader, this);
789 LoopBlocks.push_back(NewPreheader);
790
791 // We want the loop to come after the preheader, but before the exit blocks.
792 LoopBlocks.insert(LoopBlocks.end(), L->block_begin(), L->block_end());
793
794 SmallVector<BasicBlock*, 8> ExitBlocks;
795 L->getUniqueExitBlocks(ExitBlocks);
796
797 // Split all of the edges from inside the loop to their exit blocks. Update
798 // the appropriate Phi nodes as we do so.
799 SplitExitEdges(L, ExitBlocks);
800
801 // The exit blocks may have been changed due to edge splitting, recompute.
802 ExitBlocks.clear();
803 L->getUniqueExitBlocks(ExitBlocks);
804
805 // Add exit blocks to the loop blocks.
806 LoopBlocks.insert(LoopBlocks.end(), ExitBlocks.begin(), ExitBlocks.end());
807
808 // Next step, clone all of the basic blocks that make up the loop (including
809 // the loop preheader and exit blocks), keeping track of the mapping between
810 // the instructions and blocks.
811 NewBlocks.reserve(LoopBlocks.size());
812 ValueToValueMapTy VMap;
813 for (unsigned i = 0, e = LoopBlocks.size(); i != e; ++i) {
814 BasicBlock *NewBB = CloneBasicBlock(LoopBlocks[i], VMap, ".us", F);
815
816 NewBlocks.push_back(NewBB);
817 VMap[LoopBlocks[i]] = NewBB; // Keep the BB mapping.
818 LPM->cloneBasicBlockSimpleAnalysis(LoopBlocks[i], NewBB, L);
819 }
820
821 // Splice the newly inserted blocks into the function right before the
822 // original preheader.
823 F->getBasicBlockList().splice(NewPreheader, F->getBasicBlockList(),
824 NewBlocks[0], F->end());
825
826 // Now we create the new Loop object for the versioned loop.
827 Loop *NewLoop = CloneLoop(L, L->getParentLoop(), VMap, LI, LPM);
828
829 // Recalculate unswitching quota, inherit simplified switches info for NewBB,
830 // Probably clone more loop-unswitch related loop properties.
831 BranchesInfo.cloneData(NewLoop, L, VMap);
832
833 Loop *ParentLoop = L->getParentLoop();
834 if (ParentLoop) {
835 // Make sure to add the cloned preheader and exit blocks to the parent loop
836 // as well.
837 ParentLoop->addBasicBlockToLoop(NewBlocks[0], LI->getBase());
838 }
839
840 for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) {
841 BasicBlock *NewExit = cast<BasicBlock>(VMap[ExitBlocks[i]]);
842 // The new exit block should be in the same loop as the old one.
843 if (Loop *ExitBBLoop = LI->getLoopFor(ExitBlocks[i]))
844 ExitBBLoop->addBasicBlockToLoop(NewExit, LI->getBase());
845
846 assert(NewExit->getTerminator()->getNumSuccessors() == 1 &&((NewExit->getTerminator()->getNumSuccessors() == 1 &&
"Exit block should have been split to have one successor!") ?
static_cast<void> (0) : __assert_fail ("NewExit->getTerminator()->getNumSuccessors() == 1 && \"Exit block should have been split to have one successor!\""
, "/tmp/buildd/llvm-toolchain-snapshot-3.6~svn216889/lib/Transforms/Scalar/LoopUnswitch.cpp"
, 847, __PRETTY_FUNCTION__))
847 "Exit block should have been split to have one successor!")((NewExit->getTerminator()->getNumSuccessors() == 1 &&
"Exit block should have been split to have one successor!") ?
static_cast<void> (0) : __assert_fail ("NewExit->getTerminator()->getNumSuccessors() == 1 && \"Exit block should have been split to have one successor!\""
, "/tmp/buildd/llvm-toolchain-snapshot-3.6~svn216889/lib/Transforms/Scalar/LoopUnswitch.cpp"
, 847, __PRETTY_FUNCTION__));
848 BasicBlock *ExitSucc = NewExit->getTerminator()->getSuccessor(0);
849
850 // If the successor of the exit block had PHI nodes, add an entry for
851 // NewExit.
852 for (BasicBlock::iterator I = ExitSucc->begin();
853 PHINode *PN = dyn_cast<PHINode>(I); ++I) {
854 Value *V = PN->getIncomingValueForBlock(ExitBlocks[i]);
855 ValueToValueMapTy::iterator It = VMap.find(V);
856 if (It != VMap.end()) V = It->second;
857 PN->addIncoming(V, NewExit);
858 }
859
860 if (LandingPadInst *LPad = NewExit->getLandingPadInst()) {
861 PHINode *PN = PHINode::Create(LPad->getType(), 0, "",
862 ExitSucc->getFirstInsertionPt());
863
864 for (pred_iterator I = pred_begin(ExitSucc), E = pred_end(ExitSucc);
865 I != E; ++I) {
866 BasicBlock *BB = *I;
867 LandingPadInst *LPI = BB->getLandingPadInst();
868 LPI->replaceAllUsesWith(PN);
869 PN->addIncoming(LPI, BB);
870 }
871 }
872 }
873
874 // Rewrite the code to refer to itself.
875 for (unsigned i = 0, e = NewBlocks.size(); i != e; ++i)
876 for (BasicBlock::iterator I = NewBlocks[i]->begin(),
877 E = NewBlocks[i]->end(); I != E; ++I)
878 RemapInstruction(I, VMap,RF_NoModuleLevelChanges|RF_IgnoreMissingEntries);
879
880 // Rewrite the original preheader to select between versions of the loop.
881 BranchInst *OldBR = cast<BranchInst>(loopPreheader->getTerminator());
882 assert(OldBR->isUnconditional() && OldBR->getSuccessor(0) == LoopBlocks[0] &&((OldBR->isUnconditional() && OldBR->getSuccessor
(0) == LoopBlocks[0] && "Preheader splitting did not work correctly!"
) ? static_cast<void> (0) : __assert_fail ("OldBR->isUnconditional() && OldBR->getSuccessor(0) == LoopBlocks[0] && \"Preheader splitting did not work correctly!\""
, "/tmp/buildd/llvm-toolchain-snapshot-3.6~svn216889/lib/Transforms/Scalar/LoopUnswitch.cpp"
, 883, __PRETTY_FUNCTION__))
883 "Preheader splitting did not work correctly!")((OldBR->isUnconditional() && OldBR->getSuccessor
(0) == LoopBlocks[0] && "Preheader splitting did not work correctly!"
) ? static_cast<void> (0) : __assert_fail ("OldBR->isUnconditional() && OldBR->getSuccessor(0) == LoopBlocks[0] && \"Preheader splitting did not work correctly!\""
, "/tmp/buildd/llvm-toolchain-snapshot-3.6~svn216889/lib/Transforms/Scalar/LoopUnswitch.cpp"
, 883, __PRETTY_FUNCTION__));
884
885 // Emit the new branch that selects between the two versions of this loop.
886 EmitPreheaderBranchOnCondition(LIC, Val, NewBlocks[0], LoopBlocks[0], OldBR);
887 LPM->deleteSimpleAnalysisValue(OldBR, L);
888 OldBR->eraseFromParent();
889
890 LoopProcessWorklist.push_back(NewLoop);
891 redoLoop = true;
892
893 // Keep a WeakVH holding onto LIC. If the first call to RewriteLoopBody
894 // deletes the instruction (for example by simplifying a PHI that feeds into
895 // the condition that we're unswitching on), we don't rewrite the second
896 // iteration.
897 WeakVH LICHandle(LIC);
898
899 // Now we rewrite the original code to know that the condition is true and the
900 // new code to know that the condition is false.
901 RewriteLoopBodyWithConditionConstant(L, LIC, Val, false);
902
903 // It's possible that simplifying one loop could cause the other to be
904 // changed to another value or a constant. If its a constant, don't simplify
905 // it.
906 if (!LoopProcessWorklist.empty() && LoopProcessWorklist.back() == NewLoop &&
907 LICHandle && !isa<Constant>(LICHandle))
908 RewriteLoopBodyWithConditionConstant(NewLoop, LICHandle, Val, true);
909}
910
911/// RemoveFromWorklist - Remove all instances of I from the worklist vector
912/// specified.
913static void RemoveFromWorklist(Instruction *I,
914 std::vector<Instruction*> &Worklist) {
915
916 Worklist.erase(std::remove(Worklist.begin(), Worklist.end(), I),
917 Worklist.end());
918}
919
920/// ReplaceUsesOfWith - When we find that I really equals V, remove I from the
921/// program, replacing all uses with V and update the worklist.
922static void ReplaceUsesOfWith(Instruction *I, Value *V,
923 std::vector<Instruction*> &Worklist,
924 Loop *L, LPPassManager *LPM) {
925 DEBUG(dbgs() << "Replace with '" << *V << "': " << *I)do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-unswitch")) { dbgs() << "Replace with '" <<
*V << "': " << *I; } } while (0);
926
927 // Add uses to the worklist, which may be dead now.
928 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
929 if (Instruction *Use = dyn_cast<Instruction>(I->getOperand(i)))
930 Worklist.push_back(Use);
931
932 // Add users to the worklist which may be simplified now.
933 for (User *U : I->users())
934 Worklist.push_back(cast<Instruction>(U));
935 LPM->deleteSimpleAnalysisValue(I, L);
936 RemoveFromWorklist(I, Worklist);
937 I->replaceAllUsesWith(V);
938 I->eraseFromParent();
939 ++NumSimplify;
940}
941
942// RewriteLoopBodyWithConditionConstant - We know either that the value LIC has
943// the value specified by Val in the specified loop, or we know it does NOT have
944// that value. Rewrite any uses of LIC or of properties correlated to it.
945void LoopUnswitch::RewriteLoopBodyWithConditionConstant(Loop *L, Value *LIC,
946 Constant *Val,
947 bool IsEqual) {
948 assert(!isa<Constant>(LIC) && "Why are we unswitching on a constant?")((!isa<Constant>(LIC) && "Why are we unswitching on a constant?"
) ? static_cast<void> (0) : __assert_fail ("!isa<Constant>(LIC) && \"Why are we unswitching on a constant?\""
, "/tmp/buildd/llvm-toolchain-snapshot-3.6~svn216889/lib/Transforms/Scalar/LoopUnswitch.cpp"
, 948, __PRETTY_FUNCTION__));
949
950 // FIXME: Support correlated properties, like:
951 // for (...)
952 // if (li1 < li2)
953 // ...
954 // if (li1 > li2)
955 // ...
956
957 // FOLD boolean conditions (X|LIC), (X&LIC). Fold conditional branches,
958 // selects, switches.
959 std::vector<Instruction*> Worklist;
960 LLVMContext &Context = Val->getContext();
961
962 // If we know that LIC == Val, or that LIC == NotVal, just replace uses of LIC
963 // in the loop with the appropriate one directly.
964 if (IsEqual || (isa<ConstantInt>(Val) &&
965 Val->getType()->isIntegerTy(1))) {
966 Value *Replacement;
967 if (IsEqual)
968 Replacement = Val;
969 else
970 Replacement = ConstantInt::get(Type::getInt1Ty(Val->getContext()),
971 !cast<ConstantInt>(Val)->getZExtValue());
972
973 for (User *U : LIC->users()) {
974 Instruction *UI = dyn_cast<Instruction>(U);
975 if (!UI || !L->contains(UI))
976 continue;
977 Worklist.push_back(UI);
978 }
979
980 for (std::vector<Instruction*>::iterator UI = Worklist.begin(),
981 UE = Worklist.end(); UI != UE; ++UI)
982 (*UI)->replaceUsesOfWith(LIC, Replacement);
983
984 SimplifyCode(Worklist, L);
985 return;
986 }
987
988 // Otherwise, we don't know the precise value of LIC, but we do know that it
989 // is certainly NOT "Val". As such, simplify any uses in the loop that we
990 // can. This case occurs when we unswitch switch statements.
991 for (User *U : LIC->users()) {
992 Instruction *UI = dyn_cast<Instruction>(U);
993 if (!UI || !L->contains(UI))
994 continue;
995
996 Worklist.push_back(UI);
997
998 // TODO: We could do other simplifications, for example, turning
999 // 'icmp eq LIC, Val' -> false.
1000
1001 // If we know that LIC is not Val, use this info to simplify code.
1002 SwitchInst *SI = dyn_cast<SwitchInst>(UI);
1003 if (!SI || !isa<ConstantInt>(Val)) continue;
1004
1005 SwitchInst::CaseIt DeadCase = SI->findCaseValue(cast<ConstantInt>(Val));
1006 // Default case is live for multiple values.
1007 if (DeadCase == SI->case_default()) continue;
1008
1009 // Found a dead case value. Don't remove PHI nodes in the
1010 // successor if they become single-entry, those PHI nodes may
1011 // be in the Users list.
1012
1013 BasicBlock *Switch = SI->getParent();
1014 BasicBlock *SISucc = DeadCase.getCaseSuccessor();
1015 BasicBlock *Latch = L->getLoopLatch();
1016
1017 BranchesInfo.setUnswitched(SI, Val);
1018
1019 if (!SI->findCaseDest(SISucc)) continue; // Edge is critical.
1020 // If the DeadCase successor dominates the loop latch, then the
1021 // transformation isn't safe since it will delete the sole predecessor edge
1022 // to the latch.
1023 if (Latch && DT->dominates(SISucc, Latch))
1024 continue;
1025
1026 // FIXME: This is a hack. We need to keep the successor around
1027 // and hooked up so as to preserve the loop structure, because
1028 // trying to update it is complicated. So instead we preserve the
1029 // loop structure and put the block on a dead code path.
1030 SplitEdge(Switch, SISucc, this);
1031 // Compute the successors instead of relying on the return value
1032 // of SplitEdge, since it may have split the switch successor
1033 // after PHI nodes.
1034 BasicBlock *NewSISucc = DeadCase.getCaseSuccessor();
1035 BasicBlock *OldSISucc = *succ_begin(NewSISucc);
1036 // Create an "unreachable" destination.
1037 BasicBlock *Abort = BasicBlock::Create(Context, "us-unreachable",
1038 Switch->getParent(),
1039 OldSISucc);
1040 new UnreachableInst(Context, Abort);
1041 // Force the new case destination to branch to the "unreachable"
1042 // block while maintaining a (dead) CFG edge to the old block.
1043 NewSISucc->getTerminator()->eraseFromParent();
1044 BranchInst::Create(Abort, OldSISucc,
1045 ConstantInt::getTrue(Context), NewSISucc);
1046 // Release the PHI operands for this edge.
1047 for (BasicBlock::iterator II = NewSISucc->begin();
1048 PHINode *PN = dyn_cast<PHINode>(II); ++II)
1049 PN->setIncomingValue(PN->getBasicBlockIndex(Switch),
1050 UndefValue::get(PN->getType()));
1051 // Tell the domtree about the new block. We don't fully update the
1052 // domtree here -- instead we force it to do a full recomputation
1053 // after the pass is complete -- but we do need to inform it of
1054 // new blocks.
1055 if (DT)
1056 DT->addNewBlock(Abort, NewSISucc);
1057 }
1058
1059 SimplifyCode(Worklist, L);
1060}
1061
1062/// SimplifyCode - Okay, now that we have simplified some instructions in the
1063/// loop, walk over it and constant prop, dce, and fold control flow where
1064/// possible. Note that this is effectively a very simple loop-structure-aware
1065/// optimizer. During processing of this loop, L could very well be deleted, so
1066/// it must not be used.
1067///
1068/// FIXME: When the loop optimizer is more mature, separate this out to a new
1069/// pass.
1070///
1071void LoopUnswitch::SimplifyCode(std::vector<Instruction*> &Worklist, Loop *L) {
1072 while (!Worklist.empty()) {
1073 Instruction *I = Worklist.back();
1074 Worklist.pop_back();
1075
1076 // Simple DCE.
1077 if (isInstructionTriviallyDead(I)) {
1078 DEBUG(dbgs() << "Remove dead instruction '" << *I)do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-unswitch")) { dbgs() << "Remove dead instruction '"
<< *I; } } while (0);
1079
1080 // Add uses to the worklist, which may be dead now.
1081 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
1082 if (Instruction *Use = dyn_cast<Instruction>(I->getOperand(i)))
1083 Worklist.push_back(Use);
1084 LPM->deleteSimpleAnalysisValue(I, L);
1085 RemoveFromWorklist(I, Worklist);
1086 I->eraseFromParent();
1087 ++NumSimplify;
1088 continue;
1089 }
1090
1091 // See if instruction simplification can hack this up. This is common for
1092 // things like "select false, X, Y" after unswitching made the condition be
1093 // 'false'. TODO: update the domtree properly so we can pass it here.
1094 if (Value *V = SimplifyInstruction(I))
1095 if (LI->replacementPreservesLCSSAForm(I, V)) {
1096 ReplaceUsesOfWith(I, V, Worklist, L, LPM);
1097 continue;
1098 }
1099
1100 // Special case hacks that appear commonly in unswitched code.
1101 if (BranchInst *BI = dyn_cast<BranchInst>(I)) {
1102 if (BI->isUnconditional()) {
1103 // If BI's parent is the only pred of the successor, fold the two blocks
1104 // together.
1105 BasicBlock *Pred = BI->getParent();
1106 BasicBlock *Succ = BI->getSuccessor(0);
1107 BasicBlock *SinglePred = Succ->getSinglePredecessor();
1108 if (!SinglePred) continue; // Nothing to do.
1109 assert(SinglePred == Pred && "CFG broken")((SinglePred == Pred && "CFG broken") ? static_cast<
void> (0) : __assert_fail ("SinglePred == Pred && \"CFG broken\""
, "/tmp/buildd/llvm-toolchain-snapshot-3.6~svn216889/lib/Transforms/Scalar/LoopUnswitch.cpp"
, 1109, __PRETTY_FUNCTION__));
1110
1111 DEBUG(dbgs() << "Merging blocks: " << Pred->getName() << " <- "do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-unswitch")) { dbgs() << "Merging blocks: " <<
Pred->getName() << " <- " << Succ->getName
() << "\n"; } } while (0)
1112 << Succ->getName() << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-unswitch")) { dbgs() << "Merging blocks: " <<
Pred->getName() << " <- " << Succ->getName
() << "\n"; } } while (0);
1113
1114 // Resolve any single entry PHI nodes in Succ.
1115 while (PHINode *PN = dyn_cast<PHINode>(Succ->begin()))
1116 ReplaceUsesOfWith(PN, PN->getIncomingValue(0), Worklist, L, LPM);
1117
1118 // If Succ has any successors with PHI nodes, update them to have
1119 // entries coming from Pred instead of Succ.
1120 Succ->replaceAllUsesWith(Pred);
1121
1122 // Move all of the successor contents from Succ to Pred.
1123 Pred->getInstList().splice(BI, Succ->getInstList(), Succ->begin(),
1124 Succ->end());
1125 LPM->deleteSimpleAnalysisValue(BI, L);
1126 BI->eraseFromParent();
1127 RemoveFromWorklist(BI, Worklist);
1128
1129 // Remove Succ from the loop tree.
1130 LI->removeBlock(Succ);
1131 LPM->deleteSimpleAnalysisValue(Succ, L);
1132 Succ->eraseFromParent();
1133 ++NumSimplify;
1134 continue;
1135 }
1136
1137 continue;
1138 }
1139 }
1140}