Bug Summary

File:lib/Transforms/Scalar/LoopUnswitch.cpp
Location:line 398, 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/AssumptionTracker.h"
34#include "llvm/Analysis/CodeMetrics.h"
35#include "llvm/Analysis/InstructionSimplify.h"
36#include "llvm/Analysis/LoopInfo.h"
37#include "llvm/Analysis/LoopPass.h"
38#include "llvm/Analysis/ScalarEvolution.h"
39#include "llvm/Analysis/TargetTransformInfo.h"
40#include "llvm/IR/Constants.h"
41#include "llvm/IR/DerivedTypes.h"
42#include "llvm/IR/Dominators.h"
43#include "llvm/IR/Function.h"
44#include "llvm/IR/Instructions.h"
45#include "llvm/Support/CommandLine.h"
46#include "llvm/Support/Debug.h"
47#include "llvm/Support/raw_ostream.h"
48#include "llvm/Transforms/Utils/BasicBlockUtils.h"
49#include "llvm/Transforms/Utils/Cloning.h"
50#include "llvm/Transforms/Utils/Local.h"
51#include <algorithm>
52#include <map>
53#include <set>
54using namespace llvm;
55
56#define DEBUG_TYPE"loop-unswitch" "loop-unswitch"
57
58STATISTIC(NumBranches, "Number of branches unswitched")static llvm::Statistic NumBranches = { "loop-unswitch", "Number of branches unswitched"
, 0, 0 };
59STATISTIC(NumSwitches, "Number of switches unswitched")static llvm::Statistic NumSwitches = { "loop-unswitch", "Number of switches unswitched"
, 0, 0 };
60STATISTIC(NumSelects , "Number of selects unswitched")static llvm::Statistic NumSelects = { "loop-unswitch", "Number of selects unswitched"
, 0, 0 };
61STATISTIC(NumTrivial , "Number of unswitches that are trivial")static llvm::Statistic NumTrivial = { "loop-unswitch", "Number of unswitches that are trivial"
, 0, 0 };
62STATISTIC(NumSimplify, "Number of simplifications of unswitched code")static llvm::Statistic NumSimplify = { "loop-unswitch", "Number of simplifications of unswitched code"
, 0, 0 };
63STATISTIC(TotalInsts, "Total number of instructions analyzed")static llvm::Statistic TotalInsts = { "loop-unswitch", "Total number of instructions analyzed"
, 0, 0 };
64
65// The specific value of 100 here was chosen based only on intuition and a
66// few specific examples.
67static cl::opt<unsigned>
68Threshold("loop-unswitch-threshold", cl::desc("Max loop size to unswitch"),
69 cl::init(100), cl::Hidden);
70
71namespace {
72
73 class LUAnalysisCache {
74
75 typedef DenseMap<const SwitchInst*, SmallPtrSet<const Value *, 8> >
76 UnswitchedValsMap;
77
78 typedef UnswitchedValsMap::iterator UnswitchedValsIt;
79
80 struct LoopProperties {
81 unsigned CanBeUnswitchedCount;
82 unsigned SizeEstimation;
83 UnswitchedValsMap UnswitchedVals;
84 };
85
86 // Here we use std::map instead of DenseMap, since we need to keep valid
87 // LoopProperties pointer for current loop for better performance.
88 typedef std::map<const Loop*, LoopProperties> LoopPropsMap;
89 typedef LoopPropsMap::iterator LoopPropsMapIt;
90
91 LoopPropsMap LoopsProperties;
92 UnswitchedValsMap *CurLoopInstructions;
93 LoopProperties *CurrentLoopProperties;
94
95 // Max size of code we can produce on remained iterations.
96 unsigned MaxSize;
97
98 public:
99
100 LUAnalysisCache() :
101 CurLoopInstructions(nullptr), CurrentLoopProperties(nullptr),
102 MaxSize(Threshold)
103 {}
104
105 // Analyze loop. Check its size, calculate is it possible to unswitch
106 // it. Returns true if we can unswitch this loop.
107 bool countLoop(const Loop *L, const TargetTransformInfo &TTI,
108 AssumptionTracker *AT);
109
110 // Clean all data related to given loop.
111 void forgetLoop(const Loop *L);
112
113 // Mark case value as unswitched.
114 // Since SI instruction can be partly unswitched, in order to avoid
115 // extra unswitching in cloned loops keep track all unswitched values.
116 void setUnswitched(const SwitchInst *SI, const Value *V);
117
118 // Check was this case value unswitched before or not.
119 bool isUnswitched(const SwitchInst *SI, const Value *V);
120
121 // Clone all loop-unswitch related loop properties.
122 // Redistribute unswitching quotas.
123 // Note, that new loop data is stored inside the VMap.
124 void cloneData(const Loop *NewLoop, const Loop *OldLoop,
125 const ValueToValueMapTy &VMap);
126 };
127
128 class LoopUnswitch : public LoopPass {
129 LoopInfo *LI; // Loop information
130 LPPassManager *LPM;
131 AssumptionTracker *AT;
132
133 // LoopProcessWorklist - Used to check if second loop needs processing
134 // after RewriteLoopBodyWithConditionConstant rewrites first loop.
135 std::vector<Loop*> LoopProcessWorklist;
136
137 LUAnalysisCache BranchesInfo;
138
139 bool OptimizeForSize;
140 bool redoLoop;
141
142 Loop *currentLoop;
143 DominatorTree *DT;
144 BasicBlock *loopHeader;
145 BasicBlock *loopPreheader;
146
147 // LoopBlocks contains all of the basic blocks of the loop, including the
148 // preheader of the loop, the body of the loop, and the exit blocks of the
149 // loop, in that order.
150 std::vector<BasicBlock*> LoopBlocks;
151 // NewBlocks contained cloned copy of basic blocks from LoopBlocks.
152 std::vector<BasicBlock*> NewBlocks;
153
154 public:
155 static char ID; // Pass ID, replacement for typeid
156 explicit LoopUnswitch(bool Os = false) :
157 LoopPass(ID), OptimizeForSize(Os), redoLoop(false),
158 currentLoop(nullptr), DT(nullptr), loopHeader(nullptr),
159 loopPreheader(nullptr) {
160 initializeLoopUnswitchPass(*PassRegistry::getPassRegistry());
161 }
162
163 bool runOnLoop(Loop *L, LPPassManager &LPM) override;
164 bool processCurrentLoop();
165
166 /// This transformation requires natural loop information & requires that
167 /// loop preheaders be inserted into the CFG.
168 ///
169 void getAnalysisUsage(AnalysisUsage &AU) const override {
170 AU.addRequired<AssumptionTracker>();
171 AU.addRequiredID(LoopSimplifyID);
172 AU.addPreservedID(LoopSimplifyID);
173 AU.addRequired<LoopInfo>();
174 AU.addPreserved<LoopInfo>();
175 AU.addRequiredID(LCSSAID);
176 AU.addPreservedID(LCSSAID);
177 AU.addPreserved<DominatorTreeWrapperPass>();
178 AU.addPreserved<ScalarEvolution>();
179 AU.addRequired<TargetTransformInfo>();
180 }
181
182 private:
183
184 void releaseMemory() override {
185 BranchesInfo.forgetLoop(currentLoop);
186 }
187
188 void initLoopData() {
189 loopHeader = currentLoop->getHeader();
190 loopPreheader = currentLoop->getLoopPreheader();
191 }
192
193 /// Split all of the edges from inside the loop to their exit blocks.
194 /// Update the appropriate Phi nodes as we do so.
195 void SplitExitEdges(Loop *L, const SmallVectorImpl<BasicBlock *> &ExitBlocks);
196
197 bool UnswitchIfProfitable(Value *LoopCond, Constant *Val);
198 void UnswitchTrivialCondition(Loop *L, Value *Cond, Constant *Val,
199 BasicBlock *ExitBlock);
200 void UnswitchNontrivialCondition(Value *LIC, Constant *OnVal, Loop *L);
201
202 void RewriteLoopBodyWithConditionConstant(Loop *L, Value *LIC,
203 Constant *Val, bool isEqual);
204
205 void EmitPreheaderBranchOnCondition(Value *LIC, Constant *Val,
206 BasicBlock *TrueDest,
207 BasicBlock *FalseDest,
208 Instruction *InsertPt);
209
210 void SimplifyCode(std::vector<Instruction*> &Worklist, Loop *L);
211 bool IsTrivialUnswitchCondition(Value *Cond, Constant **Val = nullptr,
212 BasicBlock **LoopExit = nullptr);
213
214 };
215}
216
217// Analyze loop. Check its size, calculate is it possible to unswitch
218// it. Returns true if we can unswitch this loop.
219bool LUAnalysisCache::countLoop(const Loop *L, const TargetTransformInfo &TTI,
220 AssumptionTracker *AT) {
221
222 LoopPropsMapIt PropsIt;
223 bool Inserted;
224 std::tie(PropsIt, Inserted) =
225 LoopsProperties.insert(std::make_pair(L, LoopProperties()));
226
227 LoopProperties &Props = PropsIt->second;
228
229 if (Inserted) {
230 // New loop.
231
232 // Limit the number of instructions to avoid causing significant code
233 // expansion, and the number of basic blocks, to avoid loops with
234 // large numbers of branches which cause loop unswitching to go crazy.
235 // This is a very ad-hoc heuristic.
236
237 SmallPtrSet<const Value *, 32> EphValues;
238 CodeMetrics::collectEphemeralValues(L, AT, EphValues);
239
240 // FIXME: This is overly conservative because it does not take into
241 // consideration code simplification opportunities and code that can
242 // be shared by the resultant unswitched loops.
243 CodeMetrics Metrics;
244 for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
245 I != E; ++I)
246 Metrics.analyzeBasicBlock(*I, TTI, EphValues);
247
248 Props.SizeEstimation = std::min(Metrics.NumInsts, Metrics.NumBlocks * 5);
249 Props.CanBeUnswitchedCount = MaxSize / (Props.SizeEstimation);
250 MaxSize -= Props.SizeEstimation * Props.CanBeUnswitchedCount;
251
252 if (Metrics.notDuplicatable) {
253 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)
254 << 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)
255 << "duplicated!\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-unswitch")) { dbgs() << "NOT unswitching loop %"
<< L->getHeader()->getName() << ", contents cannot be "
<< "duplicated!\n"; } } while (0);
256 return false;
257 }
258 }
259
260 if (!Props.CanBeUnswitchedCount) {
261 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)
262 << 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)
263 << 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);
264 return false;
265 }
266
267 // Be careful. This links are good only before new loop addition.
268 CurrentLoopProperties = &Props;
269 CurLoopInstructions = &Props.UnswitchedVals;
270
271 return true;
272}
273
274// Clean all data related to given loop.
275void LUAnalysisCache::forgetLoop(const Loop *L) {
276
277 LoopPropsMapIt LIt = LoopsProperties.find(L);
278
279 if (LIt != LoopsProperties.end()) {
280 LoopProperties &Props = LIt->second;
281 MaxSize += Props.CanBeUnswitchedCount * Props.SizeEstimation;
282 LoopsProperties.erase(LIt);
283 }
284
285 CurrentLoopProperties = nullptr;
286 CurLoopInstructions = nullptr;
287}
288
289// Mark case value as unswitched.
290// Since SI instruction can be partly unswitched, in order to avoid
291// extra unswitching in cloned loops keep track all unswitched values.
292void LUAnalysisCache::setUnswitched(const SwitchInst *SI, const Value *V) {
293 (*CurLoopInstructions)[SI].insert(V);
294}
295
296// Check was this case value unswitched before or not.
297bool LUAnalysisCache::isUnswitched(const SwitchInst *SI, const Value *V) {
298 return (*CurLoopInstructions)[SI].count(V);
299}
300
301// Clone all loop-unswitch related loop properties.
302// Redistribute unswitching quotas.
303// Note, that new loop data is stored inside the VMap.
304void LUAnalysisCache::cloneData(const Loop *NewLoop, const Loop *OldLoop,
305 const ValueToValueMapTy &VMap) {
306
307 LoopProperties &NewLoopProps = LoopsProperties[NewLoop];
308 LoopProperties &OldLoopProps = *CurrentLoopProperties;
309 UnswitchedValsMap &Insts = OldLoopProps.UnswitchedVals;
310
311 // Reallocate "can-be-unswitched quota"
312
313 --OldLoopProps.CanBeUnswitchedCount;
314 unsigned Quota = OldLoopProps.CanBeUnswitchedCount;
315 NewLoopProps.CanBeUnswitchedCount = Quota / 2;
316 OldLoopProps.CanBeUnswitchedCount = Quota - Quota / 2;
317
318 NewLoopProps.SizeEstimation = OldLoopProps.SizeEstimation;
319
320 // Clone unswitched values info:
321 // for new loop switches we clone info about values that was
322 // already unswitched and has redundant successors.
323 for (UnswitchedValsIt I = Insts.begin(); I != Insts.end(); ++I) {
324 const SwitchInst *OldInst = I->first;
325 Value *NewI = VMap.lookup(OldInst);
326 const SwitchInst *NewInst = cast_or_null<SwitchInst>(NewI);
327 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~svn225130/lib/Transforms/Scalar/LoopUnswitch.cpp"
, 327, __PRETTY_FUNCTION__));
328
329 NewLoopProps.UnswitchedVals[NewInst] = OldLoopProps.UnswitchedVals[OldInst];
330 }
331}
332
333char LoopUnswitch::ID = 0;
334INITIALIZE_PASS_BEGIN(LoopUnswitch, "loop-unswitch", "Unswitch loops",static void* initializeLoopUnswitchPassOnce(PassRegistry &
Registry) {
335 false, false)static void* initializeLoopUnswitchPassOnce(PassRegistry &
Registry) {
336INITIALIZE_AG_DEPENDENCY(TargetTransformInfo)initializeTargetTransformInfoAnalysisGroup(Registry);
337INITIALIZE_PASS_DEPENDENCY(AssumptionTracker)initializeAssumptionTrackerPass(Registry);
338INITIALIZE_PASS_DEPENDENCY(LoopSimplify)initializeLoopSimplifyPass(Registry);
339INITIALIZE_PASS_DEPENDENCY(LoopInfo)initializeLoopInfoPass(Registry);
340INITIALIZE_PASS_DEPENDENCY(LCSSA)initializeLCSSAPass(Registry);
341INITIALIZE_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~svn225130/lib/Transforms/Scalar/LoopUnswitch.cpp"
, 342); AnnotateHappensBefore("/tmp/buildd/llvm-toolchain-snapshot-3.6~svn225130/lib/Transforms/Scalar/LoopUnswitch.cpp"
, 342, &initialized); initialized = 2; AnnotateIgnoreWritesEnd
("/tmp/buildd/llvm-toolchain-snapshot-3.6~svn225130/lib/Transforms/Scalar/LoopUnswitch.cpp"
, 342); } else { sys::cas_flag tmp = initialized; sys::MemoryFence
(); while (tmp != 2) { tmp = initialized; sys::MemoryFence();
} } AnnotateHappensAfter("/tmp/buildd/llvm-toolchain-snapshot-3.6~svn225130/lib/Transforms/Scalar/LoopUnswitch.cpp"
, 342, &initialized); }
342 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~svn225130/lib/Transforms/Scalar/LoopUnswitch.cpp"
, 342); AnnotateHappensBefore("/tmp/buildd/llvm-toolchain-snapshot-3.6~svn225130/lib/Transforms/Scalar/LoopUnswitch.cpp"
, 342, &initialized); initialized = 2; AnnotateIgnoreWritesEnd
("/tmp/buildd/llvm-toolchain-snapshot-3.6~svn225130/lib/Transforms/Scalar/LoopUnswitch.cpp"
, 342); } else { sys::cas_flag tmp = initialized; sys::MemoryFence
(); while (tmp != 2) { tmp = initialized; sys::MemoryFence();
} } AnnotateHappensAfter("/tmp/buildd/llvm-toolchain-snapshot-3.6~svn225130/lib/Transforms/Scalar/LoopUnswitch.cpp"
, 342, &initialized); }
343
344Pass *llvm::createLoopUnswitchPass(bool Os) {
345 return new LoopUnswitch(Os);
346}
347
348/// FindLIVLoopCondition - Cond is a condition that occurs in L. If it is
349/// invariant in the loop, or has an invariant piece, return the invariant.
350/// Otherwise, return null.
351static Value *FindLIVLoopCondition(Value *Cond, Loop *L, bool &Changed) {
352
353 // We started analyze new instruction, increment scanned instructions counter.
354 ++TotalInsts;
355
356 // We can never unswitch on vector conditions.
357 if (Cond->getType()->isVectorTy())
358 return nullptr;
359
360 // Constants should be folded, not unswitched on!
361 if (isa<Constant>(Cond)) return nullptr;
362
363 // TODO: Handle: br (VARIANT|INVARIANT).
364
365 // Hoist simple values out.
366 if (L->makeLoopInvariant(Cond, Changed))
367 return Cond;
368
369 if (BinaryOperator *BO = dyn_cast<BinaryOperator>(Cond))
370 if (BO->getOpcode() == Instruction::And ||
371 BO->getOpcode() == Instruction::Or) {
372 // If either the left or right side is invariant, we can unswitch on this,
373 // which will cause the branch to go away in one loop and the condition to
374 // simplify in the other one.
375 if (Value *LHS = FindLIVLoopCondition(BO->getOperand(0), L, Changed))
376 return LHS;
377 if (Value *RHS = FindLIVLoopCondition(BO->getOperand(1), L, Changed))
378 return RHS;
379 }
380
381 return nullptr;
382}
383
384bool LoopUnswitch::runOnLoop(Loop *L, LPPassManager &LPM_Ref) {
385 if (skipOptnoneFunction(L))
1
Taking false branch
→
386 return false;
387
388 AT = &getAnalysis<AssumptionTracker>();
389 LI = &getAnalysis<LoopInfo>();
390 LPM = &LPM_Ref;
391 DominatorTreeWrapperPass *DTWP =
392 getAnalysisIfAvailable<DominatorTreeWrapperPass>();
393 DT = DTWP ? &DTWP->getDomTree() : nullptr;
2
←
Assuming 'DTWP' is null
→
3
←
'?' condition is false
→
4
←
Null pointer value stored to field 'DT'
→
394 currentLoop = L;
395 Function *F = currentLoop->getHeader()->getParent();
396 bool Changed = false;
397 do {
398 assert(currentLoop->isLCSSAForm(*DT))((currentLoop->isLCSSAForm(*DT)) ? static_cast<void>
(0) : __assert_fail ("currentLoop->isLCSSAForm(*DT)", "/tmp/buildd/llvm-toolchain-snapshot-3.6~svn225130/lib/Transforms/Scalar/LoopUnswitch.cpp"
, 398, __PRETTY_FUNCTION__));
5
←
Within the expansion of the macro 'assert':
a
Forming reference to null pointer
399 redoLoop = false;
400 Changed |= processCurrentLoop();
401 } while(redoLoop);
402
403 if (Changed) {
404 // FIXME: Reconstruct dom info, because it is not preserved properly.
405 if (DT)
406 DT->recalculate(*F);
407 }
408 return Changed;
409}
410
411/// processCurrentLoop - Do actual work and unswitch loop if possible
412/// and profitable.
413bool LoopUnswitch::processCurrentLoop() {
414 bool Changed = false;
415
416 initLoopData();
417
418 // If LoopSimplify was unable to form a preheader, don't do any unswitching.
419 if (!loopPreheader)
420 return false;
421
422 // Loops with indirectbr cannot be cloned.
423 if (!currentLoop->isSafeToClone())
424 return false;
425
426 // Without dedicated exits, splitting the exit edge may fail.
427 if (!currentLoop->hasDedicatedExits())
428 return false;
429
430 LLVMContext &Context = loopHeader->getContext();
431
432 // Probably we reach the quota of branches for this loop. If so
433 // stop unswitching.
434 if (!BranchesInfo.countLoop(currentLoop, getAnalysis<TargetTransformInfo>(),
435 AT))
436 return false;
437
438 // Loop over all of the basic blocks in the loop. If we find an interior
439 // block that is branching on a loop-invariant condition, we can unswitch this
440 // loop.
441 for (Loop::block_iterator I = currentLoop->block_begin(),
442 E = currentLoop->block_end(); I != E; ++I) {
443 TerminatorInst *TI = (*I)->getTerminator();
444 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
445 // If this isn't branching on an invariant condition, we can't unswitch
446 // it.
447 if (BI->isConditional()) {
448 // See if this, or some part of it, is loop invariant. If so, we can
449 // unswitch on it if we desire.
450 Value *LoopCond = FindLIVLoopCondition(BI->getCondition(),
451 currentLoop, Changed);
452 if (LoopCond && UnswitchIfProfitable(LoopCond,
453 ConstantInt::getTrue(Context))) {
454 ++NumBranches;
455 return true;
456 }
457 }
458 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
459 Value *LoopCond = FindLIVLoopCondition(SI->getCondition(),
460 currentLoop, Changed);
461 unsigned NumCases = SI->getNumCases();
462 if (LoopCond && NumCases) {
463 // Find a value to unswitch on:
464 // FIXME: this should chose the most expensive case!
465 // FIXME: scan for a case with a non-critical edge?
466 Constant *UnswitchVal = nullptr;
467
468 // Do not process same value again and again.
469 // At this point we have some cases already unswitched and
470 // some not yet unswitched. Let's find the first not yet unswitched one.
471 for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end();
472 i != e; ++i) {
473 Constant *UnswitchValCandidate = i.getCaseValue();
474 if (!BranchesInfo.isUnswitched(SI, UnswitchValCandidate)) {
475 UnswitchVal = UnswitchValCandidate;
476 break;
477 }
478 }
479
480 if (!UnswitchVal)
481 continue;
482
483 if (UnswitchIfProfitable(LoopCond, UnswitchVal)) {
484 ++NumSwitches;
485 return true;
486 }
487 }
488 }
489
490 // Scan the instructions to check for unswitchable values.
491 for (BasicBlock::iterator BBI = (*I)->begin(), E = (*I)->end();
492 BBI != E; ++BBI)
493 if (SelectInst *SI = dyn_cast<SelectInst>(BBI)) {
494 Value *LoopCond = FindLIVLoopCondition(SI->getCondition(),
495 currentLoop, Changed);
496 if (LoopCond && UnswitchIfProfitable(LoopCond,
497 ConstantInt::getTrue(Context))) {
498 ++NumSelects;
499 return true;
500 }
501 }
502 }
503 return Changed;
504}
505
506/// isTrivialLoopExitBlock - Check to see if all paths from BB exit the
507/// loop with no side effects (including infinite loops).
508///
509/// If true, we return true and set ExitBB to the block we
510/// exit through.
511///
512static bool isTrivialLoopExitBlockHelper(Loop *L, BasicBlock *BB,
513 BasicBlock *&ExitBB,
514 std::set<BasicBlock*> &Visited) {
515 if (!Visited.insert(BB).second) {
516 // Already visited. Without more analysis, this could indicate an infinite
517 // loop.
518 return false;
519 }
520 if (!L->contains(BB)) {
521 // Otherwise, this is a loop exit, this is fine so long as this is the
522 // first exit.
523 if (ExitBB) return false;
524 ExitBB = BB;
525 return true;
526 }
527
528 // Otherwise, this is an unvisited intra-loop node. Check all successors.
529 for (succ_iterator SI = succ_begin(BB), E = succ_end(BB); SI != E; ++SI) {
530 // Check to see if the successor is a trivial loop exit.
531 if (!isTrivialLoopExitBlockHelper(L, *SI, ExitBB, Visited))
532 return false;
533 }
534
535 // Okay, everything after this looks good, check to make sure that this block
536 // doesn't include any side effects.
537 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
538 if (I->mayHaveSideEffects())
539 return false;
540
541 return true;
542}
543
544/// isTrivialLoopExitBlock - Return true if the specified block unconditionally
545/// leads to an exit from the specified loop, and has no side-effects in the
546/// process. If so, return the block that is exited to, otherwise return null.
547static BasicBlock *isTrivialLoopExitBlock(Loop *L, BasicBlock *BB) {
548 std::set<BasicBlock*> Visited;
549 Visited.insert(L->getHeader()); // Branches to header make infinite loops.
550 BasicBlock *ExitBB = nullptr;
551 if (isTrivialLoopExitBlockHelper(L, BB, ExitBB, Visited))
552 return ExitBB;
553 return nullptr;
554}
555
556/// IsTrivialUnswitchCondition - Check to see if this unswitch condition is
557/// trivial: that is, that the condition controls whether or not the loop does
558/// anything at all. If this is a trivial condition, unswitching produces no
559/// code duplications (equivalently, it produces a simpler loop and a new empty
560/// loop, which gets deleted).
561///
562/// If this is a trivial condition, return true, otherwise return false. When
563/// returning true, this sets Cond and Val to the condition that controls the
564/// trivial condition: when Cond dynamically equals Val, the loop is known to
565/// exit. Finally, this sets LoopExit to the BB that the loop exits to when
566/// Cond == Val.
567///
568bool LoopUnswitch::IsTrivialUnswitchCondition(Value *Cond, Constant **Val,
569 BasicBlock **LoopExit) {
570 BasicBlock *Header = currentLoop->getHeader();
571 TerminatorInst *HeaderTerm = Header->getTerminator();
572 LLVMContext &Context = Header->getContext();
573
574 BasicBlock *LoopExitBB = nullptr;
575 if (BranchInst *BI = dyn_cast<BranchInst>(HeaderTerm)) {
576 // If the header block doesn't end with a conditional branch on Cond, we
577 // can't handle it.
578 if (!BI->isConditional() || BI->getCondition() != Cond)
579 return false;
580
581 // Check to see if a successor of the branch is guaranteed to
582 // exit through a unique exit block without having any
583 // side-effects. If so, determine the value of Cond that causes it to do
584 // this.
585 if ((LoopExitBB = isTrivialLoopExitBlock(currentLoop,
586 BI->getSuccessor(0)))) {
587 if (Val) *Val = ConstantInt::getTrue(Context);
588 } else if ((LoopExitBB = isTrivialLoopExitBlock(currentLoop,
589 BI->getSuccessor(1)))) {
590 if (Val) *Val = ConstantInt::getFalse(Context);
591 }
592 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(HeaderTerm)) {
593 // If this isn't a switch on Cond, we can't handle it.
594 if (SI->getCondition() != Cond) return false;
595
596 // Check to see if a successor of the switch is guaranteed to go to the
597 // latch block or exit through a one exit block without having any
598 // side-effects. If so, determine the value of Cond that causes it to do
599 // this.
600 // Note that we can't trivially unswitch on the default case or
601 // on already unswitched cases.
602 for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end();
603 i != e; ++i) {
604 BasicBlock *LoopExitCandidate;
605 if ((LoopExitCandidate = isTrivialLoopExitBlock(currentLoop,
606 i.getCaseSuccessor()))) {
607 // Okay, we found a trivial case, remember the value that is trivial.
608 ConstantInt *CaseVal = i.getCaseValue();
609
610 // Check that it was not unswitched before, since already unswitched
611 // trivial vals are looks trivial too.
612 if (BranchesInfo.isUnswitched(SI, CaseVal))
613 continue;
614 LoopExitBB = LoopExitCandidate;
615 if (Val) *Val = CaseVal;
616 break;
617 }
618 }
619 }
620
621 // If we didn't find a single unique LoopExit block, or if the loop exit block
622 // contains phi nodes, this isn't trivial.
623 if (!LoopExitBB || isa<PHINode>(LoopExitBB->begin()))
624 return false; // Can't handle this.
625
626 if (LoopExit) *LoopExit = LoopExitBB;
627
628 // We already know that nothing uses any scalar values defined inside of this
629 // loop. As such, we just have to check to see if this loop will execute any
630 // side-effecting instructions (e.g. stores, calls, volatile loads) in the
631 // part of the loop that the code *would* execute. We already checked the
632 // tail, check the header now.
633 for (BasicBlock::iterator I = Header->begin(), E = Header->end(); I != E; ++I)
634 if (I->mayHaveSideEffects())
635 return false;
636 return true;
637}
638
639/// UnswitchIfProfitable - We have found that we can unswitch currentLoop when
640/// LoopCond == Val to simplify the loop. If we decide that this is profitable,
641/// unswitch the loop, reprocess the pieces, then return true.
642bool LoopUnswitch::UnswitchIfProfitable(Value *LoopCond, Constant *Val) {
643 Function *F = loopHeader->getParent();
644 Constant *CondVal = nullptr;
645 BasicBlock *ExitBlock = nullptr;
646
647 if (IsTrivialUnswitchCondition(LoopCond, &CondVal, &ExitBlock)) {
648 // If the condition is trivial, always unswitch. There is no code growth
649 // for this case.
650 UnswitchTrivialCondition(currentLoop, LoopCond, CondVal, ExitBlock);
651 return true;
652 }
653
654 // Check to see if it would be profitable to unswitch current loop.
655
656 // Do not do non-trivial unswitch while optimizing for size.
657 if (OptimizeForSize ||
658 F->getAttributes().hasAttribute(AttributeSet::FunctionIndex,
659 Attribute::OptimizeForSize))
660 return false;
661
662 UnswitchNontrivialCondition(LoopCond, Val, currentLoop);
663 return true;
664}
665
666/// CloneLoop - Recursively clone the specified loop and all of its children,
667/// mapping the blocks with the specified map.
668static Loop *CloneLoop(Loop *L, Loop *PL, ValueToValueMapTy &VM,
669 LoopInfo *LI, LPPassManager *LPM) {
670 Loop *New = new Loop();
671 LPM->insertLoop(New, PL);
672
673 // Add all of the blocks in L to the new loop.
674 for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
675 I != E; ++I)
676 if (LI->getLoopFor(*I) == L)
677 New->addBasicBlockToLoop(cast<BasicBlock>(VM[*I]), LI->getBase());
678
679 // Add all of the subloops to the new loop.
680 for (Loop::iterator I = L->begin(), E = L->end(); I != E; ++I)
681 CloneLoop(*I, New, VM, LI, LPM);
682
683 return New;
684}
685
686/// EmitPreheaderBranchOnCondition - Emit a conditional branch on two values
687/// if LIC == Val, branch to TrueDst, otherwise branch to FalseDest. Insert the
688/// code immediately before InsertPt.
689void LoopUnswitch::EmitPreheaderBranchOnCondition(Value *LIC, Constant *Val,
690 BasicBlock *TrueDest,
691 BasicBlock *FalseDest,
692 Instruction *InsertPt) {
693 // Insert a conditional branch on LIC to the two preheaders. The original
694 // code is the true version and the new code is the false version.
695 Value *BranchVal = LIC;
696 if (!isa<ConstantInt>(Val) ||
697 Val->getType() != Type::getInt1Ty(LIC->getContext()))
698 BranchVal = new ICmpInst(InsertPt, ICmpInst::ICMP_EQ, LIC, Val);
699 else if (Val != ConstantInt::getTrue(Val->getContext()))
700 // We want to enter the new loop when the condition is true.
701 std::swap(TrueDest, FalseDest);
702
703 // Insert the new branch.
704 BranchInst *BI = BranchInst::Create(TrueDest, FalseDest, BranchVal, InsertPt);
705
706 // If either edge is critical, split it. This helps preserve LoopSimplify
707 // form for enclosing loops.
708 SplitCriticalEdge(BI, 0, this, false, false, true);
709 SplitCriticalEdge(BI, 1, this, false, false, true);
710}
711
712/// UnswitchTrivialCondition - Given a loop that has a trivial unswitchable
713/// condition in it (a cond branch from its header block to its latch block,
714/// where the path through the loop that doesn't execute its body has no
715/// side-effects), unswitch it. This doesn't involve any code duplication, just
716/// moving the conditional branch outside of the loop and updating loop info.
717void LoopUnswitch::UnswitchTrivialCondition(Loop *L, Value *Cond,
718 Constant *Val,
719 BasicBlock *ExitBlock) {
720 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)
721 << 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)
722 << " 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)
723 << " 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);
724
725 // First step, split the preheader, so that we know that there is a safe place
726 // to insert the conditional branch. We will change loopPreheader to have a
727 // conditional branch on Cond.
728 BasicBlock *NewPH = SplitEdge(loopPreheader, loopHeader, this);
729
730 // Now that we have a place to insert the conditional branch, create a place
731 // to branch to: this is the exit block out of the loop that we should
732 // short-circuit to.
733
734 // Split this block now, so that the loop maintains its exit block, and so
735 // that the jump from the preheader can execute the contents of the exit block
736 // without actually branching to it (the exit block should be dominated by the
737 // loop header, not the preheader).
738 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~svn225130/lib/Transforms/Scalar/LoopUnswitch.cpp"
, 738, __PRETTY_FUNCTION__));
739 BasicBlock *NewExit = SplitBlock(ExitBlock, ExitBlock->begin(), this);
740
741 // Okay, now we have a position to branch from and a position to branch to,
742 // insert the new conditional branch.
743 EmitPreheaderBranchOnCondition(Cond, Val, NewExit, NewPH,
744 loopPreheader->getTerminator());
745 LPM->deleteSimpleAnalysisValue(loopPreheader->getTerminator(), L);
746 loopPreheader->getTerminator()->eraseFromParent();
747
748 // We need to reprocess this loop, it could be unswitched again.
749 redoLoop = true;
750
751 // Now that we know that the loop is never entered when this condition is a
752 // particular value, rewrite the loop with this info. We know that this will
753 // at least eliminate the old branch.
754 RewriteLoopBodyWithConditionConstant(L, Cond, Val, false);
755 ++NumTrivial;
756}
757
758/// SplitExitEdges - Split all of the edges from inside the loop to their exit
759/// blocks. Update the appropriate Phi nodes as we do so.
760void LoopUnswitch::SplitExitEdges(Loop *L,
761 const SmallVectorImpl<BasicBlock *> &ExitBlocks){
762
763 for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) {
764 BasicBlock *ExitBlock = ExitBlocks[i];
765 SmallVector<BasicBlock *, 4> Preds(pred_begin(ExitBlock),
766 pred_end(ExitBlock));
767
768 // Although SplitBlockPredecessors doesn't preserve loop-simplify in
769 // general, if we call it on all predecessors of all exits then it does.
770 if (!ExitBlock->isLandingPad()) {
771 SplitBlockPredecessors(ExitBlock, Preds, ".us-lcssa", this);
772 } else {
773 SmallVector<BasicBlock*, 2> NewBBs;
774 SplitLandingPadPredecessors(ExitBlock, Preds, ".us-lcssa", ".us-lcssa",
775 this, NewBBs);
776 }
777 }
778}
779
780/// UnswitchNontrivialCondition - We determined that the loop is profitable
781/// to unswitch when LIC equal Val. Split it into loop versions and test the
782/// condition outside of either loop. Return the loops created as Out1/Out2.
783void LoopUnswitch::UnswitchNontrivialCondition(Value *LIC, Constant *Val,
784 Loop *L) {
785 Function *F = loopHeader->getParent();
786 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)
787 << 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)
788 << " 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)
789 << " 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);
790
791 if (ScalarEvolution *SE = getAnalysisIfAvailable<ScalarEvolution>())
792 SE->forgetLoop(L);
793
794 LoopBlocks.clear();
795 NewBlocks.clear();
796
797 // First step, split the preheader and exit blocks, and add these blocks to
798 // the LoopBlocks list.
799 BasicBlock *NewPreheader = SplitEdge(loopPreheader, loopHeader, this);
800 LoopBlocks.push_back(NewPreheader);
801
802 // We want the loop to come after the preheader, but before the exit blocks.
803 LoopBlocks.insert(LoopBlocks.end(), L->block_begin(), L->block_end());
804
805 SmallVector<BasicBlock*, 8> ExitBlocks;
806 L->getUniqueExitBlocks(ExitBlocks);
807
808 // Split all of the edges from inside the loop to their exit blocks. Update
809 // the appropriate Phi nodes as we do so.
810 SplitExitEdges(L, ExitBlocks);
811
812 // The exit blocks may have been changed due to edge splitting, recompute.
813 ExitBlocks.clear();
814 L->getUniqueExitBlocks(ExitBlocks);
815
816 // Add exit blocks to the loop blocks.
817 LoopBlocks.insert(LoopBlocks.end(), ExitBlocks.begin(), ExitBlocks.end());
818
819 // Next step, clone all of the basic blocks that make up the loop (including
820 // the loop preheader and exit blocks), keeping track of the mapping between
821 // the instructions and blocks.
822 NewBlocks.reserve(LoopBlocks.size());
823 ValueToValueMapTy VMap;
824 for (unsigned i = 0, e = LoopBlocks.size(); i != e; ++i) {
825 BasicBlock *NewBB = CloneBasicBlock(LoopBlocks[i], VMap, ".us", F);
826
827 NewBlocks.push_back(NewBB);
828 VMap[LoopBlocks[i]] = NewBB; // Keep the BB mapping.
829 LPM->cloneBasicBlockSimpleAnalysis(LoopBlocks[i], NewBB, L);
830 }
831
832 // Splice the newly inserted blocks into the function right before the
833 // original preheader.
834 F->getBasicBlockList().splice(NewPreheader, F->getBasicBlockList(),
835 NewBlocks[0], F->end());
836
837 // FIXME: We could register any cloned assumptions instead of clearing the
838 // whole function's cache.
839 AT->forgetCachedAssumptions(F);
840
841 // Now we create the new Loop object for the versioned loop.
842 Loop *NewLoop = CloneLoop(L, L->getParentLoop(), VMap, LI, LPM);
843
844 // Recalculate unswitching quota, inherit simplified switches info for NewBB,
845 // Probably clone more loop-unswitch related loop properties.
846 BranchesInfo.cloneData(NewLoop, L, VMap);
847
848 Loop *ParentLoop = L->getParentLoop();
849 if (ParentLoop) {
850 // Make sure to add the cloned preheader and exit blocks to the parent loop
851 // as well.
852 ParentLoop->addBasicBlockToLoop(NewBlocks[0], LI->getBase());
853 }
854
855 for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) {
856 BasicBlock *NewExit = cast<BasicBlock>(VMap[ExitBlocks[i]]);
857 // The new exit block should be in the same loop as the old one.
858 if (Loop *ExitBBLoop = LI->getLoopFor(ExitBlocks[i]))
859 ExitBBLoop->addBasicBlockToLoop(NewExit, LI->getBase());
860
861 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~svn225130/lib/Transforms/Scalar/LoopUnswitch.cpp"
, 862, __PRETTY_FUNCTION__))
862 "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~svn225130/lib/Transforms/Scalar/LoopUnswitch.cpp"
, 862, __PRETTY_FUNCTION__));
863 BasicBlock *ExitSucc = NewExit->getTerminator()->getSuccessor(0);
864
865 // If the successor of the exit block had PHI nodes, add an entry for
866 // NewExit.
867 for (BasicBlock::iterator I = ExitSucc->begin();
868 PHINode *PN = dyn_cast<PHINode>(I); ++I) {
869 Value *V = PN->getIncomingValueForBlock(ExitBlocks[i]);
870 ValueToValueMapTy::iterator It = VMap.find(V);
871 if (It != VMap.end()) V = It->second;
872 PN->addIncoming(V, NewExit);
873 }
874
875 if (LandingPadInst *LPad = NewExit->getLandingPadInst()) {
876 PHINode *PN = PHINode::Create(LPad->getType(), 0, "",
877 ExitSucc->getFirstInsertionPt());
878
879 for (pred_iterator I = pred_begin(ExitSucc), E = pred_end(ExitSucc);
880 I != E; ++I) {
881 BasicBlock *BB = *I;
882 LandingPadInst *LPI = BB->getLandingPadInst();
883 LPI->replaceAllUsesWith(PN);
884 PN->addIncoming(LPI, BB);
885 }
886 }
887 }
888
889 // Rewrite the code to refer to itself.
890 for (unsigned i = 0, e = NewBlocks.size(); i != e; ++i)
891 for (BasicBlock::iterator I = NewBlocks[i]->begin(),
892 E = NewBlocks[i]->end(); I != E; ++I)
893 RemapInstruction(I, VMap,RF_NoModuleLevelChanges|RF_IgnoreMissingEntries);
894
895 // Rewrite the original preheader to select between versions of the loop.
896 BranchInst *OldBR = cast<BranchInst>(loopPreheader->getTerminator());
897 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~svn225130/lib/Transforms/Scalar/LoopUnswitch.cpp"
, 898, __PRETTY_FUNCTION__))
898 "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~svn225130/lib/Transforms/Scalar/LoopUnswitch.cpp"
, 898, __PRETTY_FUNCTION__));
899
900 // Emit the new branch that selects between the two versions of this loop.
901 EmitPreheaderBranchOnCondition(LIC, Val, NewBlocks[0], LoopBlocks[0], OldBR);
902 LPM->deleteSimpleAnalysisValue(OldBR, L);
903 OldBR->eraseFromParent();
904
905 LoopProcessWorklist.push_back(NewLoop);
906 redoLoop = true;
907
908 // Keep a WeakVH holding onto LIC. If the first call to RewriteLoopBody
909 // deletes the instruction (for example by simplifying a PHI that feeds into
910 // the condition that we're unswitching on), we don't rewrite the second
911 // iteration.
912 WeakVH LICHandle(LIC);
913
914 // Now we rewrite the original code to know that the condition is true and the
915 // new code to know that the condition is false.
916 RewriteLoopBodyWithConditionConstant(L, LIC, Val, false);
917
918 // It's possible that simplifying one loop could cause the other to be
919 // changed to another value or a constant. If its a constant, don't simplify
920 // it.
921 if (!LoopProcessWorklist.empty() && LoopProcessWorklist.back() == NewLoop &&
922 LICHandle && !isa<Constant>(LICHandle))
923 RewriteLoopBodyWithConditionConstant(NewLoop, LICHandle, Val, true);
924}
925
926/// RemoveFromWorklist - Remove all instances of I from the worklist vector
927/// specified.
928static void RemoveFromWorklist(Instruction *I,
929 std::vector<Instruction*> &Worklist) {
930
931 Worklist.erase(std::remove(Worklist.begin(), Worklist.end(), I),
932 Worklist.end());
933}
934
935/// ReplaceUsesOfWith - When we find that I really equals V, remove I from the
936/// program, replacing all uses with V and update the worklist.
937static void ReplaceUsesOfWith(Instruction *I, Value *V,
938 std::vector<Instruction*> &Worklist,
939 Loop *L, LPPassManager *LPM) {
940 DEBUG(dbgs() << "Replace with '" << *V << "': " << *I)do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-unswitch")) { dbgs() << "Replace with '" <<
*V << "': " << *I; } } while (0);
941
942 // Add uses to the worklist, which may be dead now.
943 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
944 if (Instruction *Use = dyn_cast<Instruction>(I->getOperand(i)))
945 Worklist.push_back(Use);
946
947 // Add users to the worklist which may be simplified now.
948 for (User *U : I->users())
949 Worklist.push_back(cast<Instruction>(U));
950 LPM->deleteSimpleAnalysisValue(I, L);
951 RemoveFromWorklist(I, Worklist);
952 I->replaceAllUsesWith(V);
953 I->eraseFromParent();
954 ++NumSimplify;
955}
956
957// RewriteLoopBodyWithConditionConstant - We know either that the value LIC has
958// the value specified by Val in the specified loop, or we know it does NOT have
959// that value. Rewrite any uses of LIC or of properties correlated to it.
960void LoopUnswitch::RewriteLoopBodyWithConditionConstant(Loop *L, Value *LIC,
961 Constant *Val,
962 bool IsEqual) {
963 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~svn225130/lib/Transforms/Scalar/LoopUnswitch.cpp"
, 963, __PRETTY_FUNCTION__));
964
965 // FIXME: Support correlated properties, like:
966 // for (...)
967 // if (li1 < li2)
968 // ...
969 // if (li1 > li2)
970 // ...
971
972 // FOLD boolean conditions (X|LIC), (X&LIC). Fold conditional branches,
973 // selects, switches.
974 std::vector<Instruction*> Worklist;
975 LLVMContext &Context = Val->getContext();
976
977 // If we know that LIC == Val, or that LIC == NotVal, just replace uses of LIC
978 // in the loop with the appropriate one directly.
979 if (IsEqual || (isa<ConstantInt>(Val) &&
980 Val->getType()->isIntegerTy(1))) {
981 Value *Replacement;
982 if (IsEqual)
983 Replacement = Val;
984 else
985 Replacement = ConstantInt::get(Type::getInt1Ty(Val->getContext()),
986 !cast<ConstantInt>(Val)->getZExtValue());
987
988 for (User *U : LIC->users()) {
989 Instruction *UI = dyn_cast<Instruction>(U);
990 if (!UI || !L->contains(UI))
991 continue;
992 Worklist.push_back(UI);
993 }
994
995 for (std::vector<Instruction*>::iterator UI = Worklist.begin(),
996 UE = Worklist.end(); UI != UE; ++UI)
997 (*UI)->replaceUsesOfWith(LIC, Replacement);
998
999 SimplifyCode(Worklist, L);
1000 return;
1001 }
1002
1003 // Otherwise, we don't know the precise value of LIC, but we do know that it
1004 // is certainly NOT "Val". As such, simplify any uses in the loop that we
1005 // can. This case occurs when we unswitch switch statements.
1006 for (User *U : LIC->users()) {
1007 Instruction *UI = dyn_cast<Instruction>(U);
1008 if (!UI || !L->contains(UI))
1009 continue;
1010
1011 Worklist.push_back(UI);
1012
1013 // TODO: We could do other simplifications, for example, turning
1014 // 'icmp eq LIC, Val' -> false.
1015
1016 // If we know that LIC is not Val, use this info to simplify code.
1017 SwitchInst *SI = dyn_cast<SwitchInst>(UI);
1018 if (!SI || !isa<ConstantInt>(Val)) continue;
1019
1020 SwitchInst::CaseIt DeadCase = SI->findCaseValue(cast<ConstantInt>(Val));
1021 // Default case is live for multiple values.
1022 if (DeadCase == SI->case_default()) continue;
1023
1024 // Found a dead case value. Don't remove PHI nodes in the
1025 // successor if they become single-entry, those PHI nodes may
1026 // be in the Users list.
1027
1028 BasicBlock *Switch = SI->getParent();
1029 BasicBlock *SISucc = DeadCase.getCaseSuccessor();
1030 BasicBlock *Latch = L->getLoopLatch();
1031
1032 BranchesInfo.setUnswitched(SI, Val);
1033
1034 if (!SI->findCaseDest(SISucc)) continue; // Edge is critical.
1035 // If the DeadCase successor dominates the loop latch, then the
1036 // transformation isn't safe since it will delete the sole predecessor edge
1037 // to the latch.
1038 if (Latch && DT->dominates(SISucc, Latch))
1039 continue;
1040
1041 // FIXME: This is a hack. We need to keep the successor around
1042 // and hooked up so as to preserve the loop structure, because
1043 // trying to update it is complicated. So instead we preserve the
1044 // loop structure and put the block on a dead code path.
1045 SplitEdge(Switch, SISucc, this);
1046 // Compute the successors instead of relying on the return value
1047 // of SplitEdge, since it may have split the switch successor
1048 // after PHI nodes.
1049 BasicBlock *NewSISucc = DeadCase.getCaseSuccessor();
1050 BasicBlock *OldSISucc = *succ_begin(NewSISucc);
1051 // Create an "unreachable" destination.
1052 BasicBlock *Abort = BasicBlock::Create(Context, "us-unreachable",
1053 Switch->getParent(),
1054 OldSISucc);
1055 new UnreachableInst(Context, Abort);
1056 // Force the new case destination to branch to the "unreachable"
1057 // block while maintaining a (dead) CFG edge to the old block.
1058 NewSISucc->getTerminator()->eraseFromParent();
1059 BranchInst::Create(Abort, OldSISucc,
1060 ConstantInt::getTrue(Context), NewSISucc);
1061 // Release the PHI operands for this edge.
1062 for (BasicBlock::iterator II = NewSISucc->begin();
1063 PHINode *PN = dyn_cast<PHINode>(II); ++II)
1064 PN->setIncomingValue(PN->getBasicBlockIndex(Switch),
1065 UndefValue::get(PN->getType()));
1066 // Tell the domtree about the new block. We don't fully update the
1067 // domtree here -- instead we force it to do a full recomputation
1068 // after the pass is complete -- but we do need to inform it of
1069 // new blocks.
1070 if (DT)
1071 DT->addNewBlock(Abort, NewSISucc);
1072 }
1073
1074 SimplifyCode(Worklist, L);
1075}
1076
1077/// SimplifyCode - Okay, now that we have simplified some instructions in the
1078/// loop, walk over it and constant prop, dce, and fold control flow where
1079/// possible. Note that this is effectively a very simple loop-structure-aware
1080/// optimizer. During processing of this loop, L could very well be deleted, so
1081/// it must not be used.
1082///
1083/// FIXME: When the loop optimizer is more mature, separate this out to a new
1084/// pass.
1085///
1086void LoopUnswitch::SimplifyCode(std::vector<Instruction*> &Worklist, Loop *L) {
1087 while (!Worklist.empty()) {
1088 Instruction *I = Worklist.back();
1089 Worklist.pop_back();
1090
1091 // Simple DCE.
1092 if (isInstructionTriviallyDead(I)) {
1093 DEBUG(dbgs() << "Remove dead instruction '" << *I)do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-unswitch")) { dbgs() << "Remove dead instruction '"
<< *I; } } while (0);
1094
1095 // Add uses to the worklist, which may be dead now.
1096 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
1097 if (Instruction *Use = dyn_cast<Instruction>(I->getOperand(i)))
1098 Worklist.push_back(Use);
1099 LPM->deleteSimpleAnalysisValue(I, L);
1100 RemoveFromWorklist(I, Worklist);
1101 I->eraseFromParent();
1102 ++NumSimplify;
1103 continue;
1104 }
1105
1106 // See if instruction simplification can hack this up. This is common for
1107 // things like "select false, X, Y" after unswitching made the condition be
1108 // 'false'. TODO: update the domtree properly so we can pass it here.
1109 if (Value *V = SimplifyInstruction(I))
1110 if (LI->replacementPreservesLCSSAForm(I, V)) {
1111 ReplaceUsesOfWith(I, V, Worklist, L, LPM);
1112 continue;
1113 }
1114
1115 // Special case hacks that appear commonly in unswitched code.
1116 if (BranchInst *BI = dyn_cast<BranchInst>(I)) {
1117 if (BI->isUnconditional()) {
1118 // If BI's parent is the only pred of the successor, fold the two blocks
1119 // together.
1120 BasicBlock *Pred = BI->getParent();
1121 BasicBlock *Succ = BI->getSuccessor(0);
1122 BasicBlock *SinglePred = Succ->getSinglePredecessor();
1123 if (!SinglePred) continue; // Nothing to do.
1124 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~svn225130/lib/Transforms/Scalar/LoopUnswitch.cpp"
, 1124, __PRETTY_FUNCTION__));
1125
1126 DEBUG(dbgs() << "Merging blocks: " << Pred->getName() << " <- "do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-unswitch")) { dbgs() << "Merging blocks: " <<
Pred->getName() << " <- " << Succ->getName
() << "\n"; } } while (0)
1127 << Succ->getName() << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-unswitch")) { dbgs() << "Merging blocks: " <<
Pred->getName() << " <- " << Succ->getName
() << "\n"; } } while (0);
1128
1129 // Resolve any single entry PHI nodes in Succ.
1130 while (PHINode *PN = dyn_cast<PHINode>(Succ->begin()))
1131 ReplaceUsesOfWith(PN, PN->getIncomingValue(0), Worklist, L, LPM);
1132
1133 // If Succ has any successors with PHI nodes, update them to have
1134 // entries coming from Pred instead of Succ.
1135 Succ->replaceAllUsesWith(Pred);
1136
1137 // Move all of the successor contents from Succ to Pred.
1138 Pred->getInstList().splice(BI, Succ->getInstList(), Succ->begin(),
1139 Succ->end());
1140 LPM->deleteSimpleAnalysisValue(BI, L);
1141 BI->eraseFromParent();
1142 RemoveFromWorklist(BI, Worklist);
1143
1144 // Remove Succ from the loop tree.
1145 LI->removeBlock(Succ);
1146 LPM->deleteSimpleAnalysisValue(Succ, L);
1147 Succ->eraseFromParent();
1148 ++NumSimplify;
1149 continue;
1150 }
1151
1152 continue;
1153 }
1154 }
1155}