LLVM  9.0.0svn
CorrelatedValuePropagation.cpp
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1 //===- CorrelatedValuePropagation.cpp - Propagate CFG-derived info --------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // This file implements the Correlated Value Propagation pass.
10 //
11 //===----------------------------------------------------------------------===//
12 
15 #include "llvm/ADT/Optional.h"
16 #include "llvm/ADT/SmallVector.h"
17 #include "llvm/ADT/Statistic.h"
22 #include "llvm/IR/Attributes.h"
23 #include "llvm/IR/BasicBlock.h"
24 #include "llvm/IR/CFG.h"
25 #include "llvm/IR/CallSite.h"
26 #include "llvm/IR/Constant.h"
27 #include "llvm/IR/ConstantRange.h"
28 #include "llvm/IR/Constants.h"
29 #include "llvm/IR/DerivedTypes.h"
30 #include "llvm/IR/Function.h"
31 #include "llvm/IR/IRBuilder.h"
32 #include "llvm/IR/InstrTypes.h"
33 #include "llvm/IR/Instruction.h"
34 #include "llvm/IR/Instructions.h"
35 #include "llvm/IR/IntrinsicInst.h"
36 #include "llvm/IR/Operator.h"
37 #include "llvm/IR/PassManager.h"
38 #include "llvm/IR/Type.h"
39 #include "llvm/IR/Value.h"
40 #include "llvm/Pass.h"
41 #include "llvm/Support/Casting.h"
43 #include "llvm/Support/Debug.h"
45 #include "llvm/Transforms/Scalar.h"
47 #include <cassert>
48 #include <utility>
49 
50 using namespace llvm;
51 
52 #define DEBUG_TYPE "correlated-value-propagation"
53 
54 STATISTIC(NumPhis, "Number of phis propagated");
55 STATISTIC(NumPhiCommon, "Number of phis deleted via common incoming value");
56 STATISTIC(NumSelects, "Number of selects propagated");
57 STATISTIC(NumMemAccess, "Number of memory access targets propagated");
58 STATISTIC(NumCmps, "Number of comparisons propagated");
59 STATISTIC(NumReturns, "Number of return values propagated");
60 STATISTIC(NumDeadCases, "Number of switch cases removed");
61 STATISTIC(NumSDivs, "Number of sdiv converted to udiv");
62 STATISTIC(NumUDivs, "Number of udivs whose width was decreased");
63 STATISTIC(NumAShrs, "Number of ashr converted to lshr");
64 STATISTIC(NumSRems, "Number of srem converted to urem");
65 STATISTIC(NumOverflows, "Number of overflow checks removed");
66 
67 static cl::opt<bool> DontAddNoWrapFlags("cvp-dont-add-nowrap-flags", cl::init(true));
68 
69 namespace {
70 
71  class CorrelatedValuePropagation : public FunctionPass {
72  public:
73  static char ID;
74 
75  CorrelatedValuePropagation(): FunctionPass(ID) {
77  }
78 
79  bool runOnFunction(Function &F) override;
80 
81  void getAnalysisUsage(AnalysisUsage &AU) const override {
86  }
87  };
88 
89 } // end anonymous namespace
90 
92 
93 INITIALIZE_PASS_BEGIN(CorrelatedValuePropagation, "correlated-propagation",
94  "Value Propagation", false, false)
97 INITIALIZE_PASS_END(CorrelatedValuePropagation, "correlated-propagation",
98  "Value Propagation", false, false)
99 
100 // Public interface to the Value Propagation pass
102  return new CorrelatedValuePropagation();
103 }
104 
105 static bool processSelect(SelectInst *S, LazyValueInfo *LVI) {
106  if (S->getType()->isVectorTy()) return false;
107  if (isa<Constant>(S->getOperand(0))) return false;
108 
109  Constant *C = LVI->getConstant(S->getCondition(), S->getParent(), S);
110  if (!C) return false;
111 
113  if (!CI) return false;
114 
115  Value *ReplaceWith = S->getTrueValue();
116  Value *Other = S->getFalseValue();
117  if (!CI->isOne()) std::swap(ReplaceWith, Other);
118  if (ReplaceWith == S) ReplaceWith = UndefValue::get(S->getType());
119 
120  S->replaceAllUsesWith(ReplaceWith);
121  S->eraseFromParent();
122 
123  ++NumSelects;
124 
125  return true;
126 }
127 
128 /// Try to simplify a phi with constant incoming values that match the edge
129 /// values of a non-constant value on all other edges:
130 /// bb0:
131 /// %isnull = icmp eq i8* %x, null
132 /// br i1 %isnull, label %bb2, label %bb1
133 /// bb1:
134 /// br label %bb2
135 /// bb2:
136 /// %r = phi i8* [ %x, %bb1 ], [ null, %bb0 ]
137 /// -->
138 /// %r = %x
140  DominatorTree *DT) {
141  // Collect incoming constants and initialize possible common value.
142  SmallVector<std::pair<Constant *, unsigned>, 4> IncomingConstants;
143  Value *CommonValue = nullptr;
144  for (unsigned i = 0, e = P->getNumIncomingValues(); i != e; ++i) {
145  Value *Incoming = P->getIncomingValue(i);
146  if (auto *IncomingConstant = dyn_cast<Constant>(Incoming)) {
147  IncomingConstants.push_back(std::make_pair(IncomingConstant, i));
148  } else if (!CommonValue) {
149  // The potential common value is initialized to the first non-constant.
150  CommonValue = Incoming;
151  } else if (Incoming != CommonValue) {
152  // There can be only one non-constant common value.
153  return false;
154  }
155  }
156 
157  if (!CommonValue || IncomingConstants.empty())
158  return false;
159 
160  // The common value must be valid in all incoming blocks.
161  BasicBlock *ToBB = P->getParent();
162  if (auto *CommonInst = dyn_cast<Instruction>(CommonValue))
163  if (!DT->dominates(CommonInst, ToBB))
164  return false;
165 
166  // We have a phi with exactly 1 variable incoming value and 1 or more constant
167  // incoming values. See if all constant incoming values can be mapped back to
168  // the same incoming variable value.
169  for (auto &IncomingConstant : IncomingConstants) {
170  Constant *C = IncomingConstant.first;
171  BasicBlock *IncomingBB = P->getIncomingBlock(IncomingConstant.second);
172  if (C != LVI->getConstantOnEdge(CommonValue, IncomingBB, ToBB, P))
173  return false;
174  }
175 
176  // All constant incoming values map to the same variable along the incoming
177  // edges of the phi. The phi is unnecessary.
178  P->replaceAllUsesWith(CommonValue);
179  P->eraseFromParent();
180  ++NumPhiCommon;
181  return true;
182 }
183 
185  const SimplifyQuery &SQ) {
186  bool Changed = false;
187 
188  BasicBlock *BB = P->getParent();
189  for (unsigned i = 0, e = P->getNumIncomingValues(); i < e; ++i) {
190  Value *Incoming = P->getIncomingValue(i);
191  if (isa<Constant>(Incoming)) continue;
192 
193  Value *V = LVI->getConstantOnEdge(Incoming, P->getIncomingBlock(i), BB, P);
194 
195  // Look if the incoming value is a select with a scalar condition for which
196  // LVI can tells us the value. In that case replace the incoming value with
197  // the appropriate value of the select. This often allows us to remove the
198  // select later.
199  if (!V) {
200  SelectInst *SI = dyn_cast<SelectInst>(Incoming);
201  if (!SI) continue;
202 
203  Value *Condition = SI->getCondition();
204  if (!Condition->getType()->isVectorTy()) {
205  if (Constant *C = LVI->getConstantOnEdge(
206  Condition, P->getIncomingBlock(i), BB, P)) {
207  if (C->isOneValue()) {
208  V = SI->getTrueValue();
209  } else if (C->isZeroValue()) {
210  V = SI->getFalseValue();
211  }
212  // Once LVI learns to handle vector types, we could also add support
213  // for vector type constants that are not all zeroes or all ones.
214  }
215  }
216 
217  // Look if the select has a constant but LVI tells us that the incoming
218  // value can never be that constant. In that case replace the incoming
219  // value with the other value of the select. This often allows us to
220  // remove the select later.
221  if (!V) {
223  if (!C) continue;
224 
225  if (LVI->getPredicateOnEdge(ICmpInst::ICMP_EQ, SI, C,
226  P->getIncomingBlock(i), BB, P) !=
228  continue;
229  V = SI->getTrueValue();
230  }
231 
232  LLVM_DEBUG(dbgs() << "CVP: Threading PHI over " << *SI << '\n');
233  }
234 
235  P->setIncomingValue(i, V);
236  Changed = true;
237  }
238 
239  if (Value *V = SimplifyInstruction(P, SQ)) {
240  P->replaceAllUsesWith(V);
241  P->eraseFromParent();
242  Changed = true;
243  }
244 
245  if (!Changed)
246  Changed = simplifyCommonValuePhi(P, LVI, DT);
247 
248  if (Changed)
249  ++NumPhis;
250 
251  return Changed;
252 }
253 
255  Value *Pointer = nullptr;
256  if (LoadInst *L = dyn_cast<LoadInst>(I))
257  Pointer = L->getPointerOperand();
258  else
259  Pointer = cast<StoreInst>(I)->getPointerOperand();
260 
261  if (isa<Constant>(Pointer)) return false;
262 
263  Constant *C = LVI->getConstant(Pointer, I->getParent(), I);
264  if (!C) return false;
265 
266  ++NumMemAccess;
267  I->replaceUsesOfWith(Pointer, C);
268  return true;
269 }
270 
271 /// See if LazyValueInfo's ability to exploit edge conditions or range
272 /// information is sufficient to prove this comparison. Even for local
273 /// conditions, this can sometimes prove conditions instcombine can't by
274 /// exploiting range information.
275 static bool processCmp(CmpInst *Cmp, LazyValueInfo *LVI) {
276  Value *Op0 = Cmp->getOperand(0);
277  auto *C = dyn_cast<Constant>(Cmp->getOperand(1));
278  if (!C)
279  return false;
280 
281  // As a policy choice, we choose not to waste compile time on anything where
282  // the comparison is testing local values. While LVI can sometimes reason
283  // about such cases, it's not its primary purpose. We do make sure to do
284  // the block local query for uses from terminator instructions, but that's
285  // handled in the code for each terminator.
286  auto *I = dyn_cast<Instruction>(Op0);
287  if (I && I->getParent() == Cmp->getParent())
288  return false;
289 
290  LazyValueInfo::Tristate Result =
291  LVI->getPredicateAt(Cmp->getPredicate(), Op0, C, Cmp);
292  if (Result == LazyValueInfo::Unknown)
293  return false;
294 
295  ++NumCmps;
296  Constant *TorF = ConstantInt::get(Type::getInt1Ty(Cmp->getContext()), Result);
297  Cmp->replaceAllUsesWith(TorF);
298  Cmp->eraseFromParent();
299  return true;
300 }
301 
302 /// Simplify a switch instruction by removing cases which can never fire. If the
303 /// uselessness of a case could be determined locally then constant propagation
304 /// would already have figured it out. Instead, walk the predecessors and
305 /// statically evaluate cases based on information available on that edge. Cases
306 /// that cannot fire no matter what the incoming edge can safely be removed. If
307 /// a case fires on every incoming edge then the entire switch can be removed
308 /// and replaced with a branch to the case destination.
310  DominatorTree *DT) {
312  Value *Cond = SI->getCondition();
313  BasicBlock *BB = SI->getParent();
314 
315  // If the condition was defined in same block as the switch then LazyValueInfo
316  // currently won't say anything useful about it, though in theory it could.
317  if (isa<Instruction>(Cond) && cast<Instruction>(Cond)->getParent() == BB)
318  return false;
319 
320  // If the switch is unreachable then trying to improve it is a waste of time.
321  pred_iterator PB = pred_begin(BB), PE = pred_end(BB);
322  if (PB == PE) return false;
323 
324  // Analyse each switch case in turn.
325  bool Changed = false;
326  DenseMap<BasicBlock*, int> SuccessorsCount;
327  for (auto *Succ : successors(BB))
328  SuccessorsCount[Succ]++;
329 
330  for (auto CI = SI->case_begin(), CE = SI->case_end(); CI != CE;) {
331  ConstantInt *Case = CI->getCaseValue();
332 
333  // Check to see if the switch condition is equal to/not equal to the case
334  // value on every incoming edge, equal/not equal being the same each time.
336  for (pred_iterator PI = PB; PI != PE; ++PI) {
337  // Is the switch condition equal to the case value?
339  Cond, Case, *PI,
340  BB, SI);
341  // Give up on this case if nothing is known.
342  if (Value == LazyValueInfo::Unknown) {
343  State = LazyValueInfo::Unknown;
344  break;
345  }
346 
347  // If this was the first edge to be visited, record that all other edges
348  // need to give the same result.
349  if (PI == PB) {
350  State = Value;
351  continue;
352  }
353 
354  // If this case is known to fire for some edges and known not to fire for
355  // others then there is nothing we can do - give up.
356  if (Value != State) {
357  State = LazyValueInfo::Unknown;
358  break;
359  }
360  }
361 
362  if (State == LazyValueInfo::False) {
363  // This case never fires - remove it.
364  BasicBlock *Succ = CI->getCaseSuccessor();
365  Succ->removePredecessor(BB);
366  CI = SI->removeCase(CI);
367  CE = SI->case_end();
368 
369  // The condition can be modified by removePredecessor's PHI simplification
370  // logic.
371  Cond = SI->getCondition();
372 
373  ++NumDeadCases;
374  Changed = true;
375  if (--SuccessorsCount[Succ] == 0)
377  continue;
378  }
379  if (State == LazyValueInfo::True) {
380  // This case always fires. Arrange for the switch to be turned into an
381  // unconditional branch by replacing the switch condition with the case
382  // value.
383  SI->setCondition(Case);
384  NumDeadCases += SI->getNumCases();
385  Changed = true;
386  break;
387  }
388 
389  // Increment the case iterator since we didn't delete it.
390  ++CI;
391  }
392 
393  if (Changed)
394  // If the switch has been simplified to the point where it can be replaced
395  // by a branch then do so now.
396  ConstantFoldTerminator(BB, /*DeleteDeadConditions = */ false,
397  /*TLI = */ nullptr, &DTU);
398  return Changed;
399 }
400 
401 // See if we can prove that the given overflow intrinsic will not overflow.
403  ConstantRange LRange = LVI->getConstantRange(
404  WO->getLHS(), WO->getParent(), WO);
405  ConstantRange RRange = LVI->getConstantRange(
406  WO->getRHS(), WO->getParent(), WO);
408  WO->getBinaryOp(), RRange, WO->getNoWrapKind());
409  return NWRegion.contains(LRange);
410 }
411 
413  IRBuilder<> B(WO);
414  Value *NewOp = B.CreateBinOp(
415  WO->getBinaryOp(), WO->getLHS(), WO->getRHS(), WO->getName());
416  // Constant-holing could have happened.
417  if (auto *Inst = dyn_cast<Instruction>(NewOp)) {
418  if (WO->isSigned())
419  Inst->setHasNoSignedWrap();
420  else
421  Inst->setHasNoUnsignedWrap();
422  }
423 
424  Value *NewI = B.CreateInsertValue(UndefValue::get(WO->getType()), NewOp, 0);
425  NewI = B.CreateInsertValue(NewI, ConstantInt::getFalse(WO->getContext()), 1);
426  WO->replaceAllUsesWith(NewI);
427  WO->eraseFromParent();
428  ++NumOverflows;
429 }
430 
431 /// Infer nonnull attributes for the arguments at the specified callsite.
432 static bool processCallSite(CallSite CS, LazyValueInfo *LVI) {
434  unsigned ArgNo = 0;
435 
436  if (auto *WO = dyn_cast<WithOverflowInst>(CS.getInstruction())) {
437  if (willNotOverflow(WO, LVI)) {
439  return true;
440  }
441  }
442 
443  // Deopt bundle operands are intended to capture state with minimal
444  // perturbance of the code otherwise. If we can find a constant value for
445  // any such operand and remove a use of the original value, that's
446  // desireable since it may allow further optimization of that value (e.g. via
447  // single use rules in instcombine). Since deopt uses tend to,
448  // idiomatically, appear along rare conditional paths, it's reasonable likely
449  // we may have a conditional fact with which LVI can fold.
450  if (auto DeoptBundle = CS.getOperandBundle(LLVMContext::OB_deopt)) {
451  bool Progress = false;
452  for (const Use &ConstU : DeoptBundle->Inputs) {
453  Use &U = const_cast<Use&>(ConstU);
454  Value *V = U.get();
455  if (V->getType()->isVectorTy()) continue;
456  if (isa<Constant>(V)) continue;
457 
458  Constant *C = LVI->getConstant(V, CS.getParent(), CS.getInstruction());
459  if (!C) continue;
460  U.set(C);
461  Progress = true;
462  }
463  if (Progress)
464  return true;
465  }
466 
467  for (Value *V : CS.args()) {
468  PointerType *Type = dyn_cast<PointerType>(V->getType());
469  // Try to mark pointer typed parameters as non-null. We skip the
470  // relatively expensive analysis for constants which are obviously either
471  // null or non-null to start with.
472  if (Type && !CS.paramHasAttr(ArgNo, Attribute::NonNull) &&
473  !isa<Constant>(V) &&
477  ArgNos.push_back(ArgNo);
478  ArgNo++;
479  }
480 
481  assert(ArgNo == CS.arg_size() && "sanity check");
482 
483  if (ArgNos.empty())
484  return false;
485 
486  AttributeList AS = CS.getAttributes();
487  LLVMContext &Ctx = CS.getInstruction()->getContext();
488  AS = AS.addParamAttribute(Ctx, ArgNos,
489  Attribute::get(Ctx, Attribute::NonNull));
490  CS.setAttributes(AS);
491 
492  return true;
493 }
494 
496  Constant *Zero = ConstantInt::get(SDI->getType(), 0);
497  for (Value *O : SDI->operands()) {
498  auto Result = LVI->getPredicateAt(ICmpInst::ICMP_SGE, O, Zero, SDI);
499  if (Result != LazyValueInfo::True)
500  return false;
501  }
502  return true;
503 }
504 
505 /// Try to shrink a udiv/urem's width down to the smallest power of two that's
506 /// sufficient to contain its operands.
507 static bool processUDivOrURem(BinaryOperator *Instr, LazyValueInfo *LVI) {
508  assert(Instr->getOpcode() == Instruction::UDiv ||
509  Instr->getOpcode() == Instruction::URem);
510  if (Instr->getType()->isVectorTy())
511  return false;
512 
513  // Find the smallest power of two bitwidth that's sufficient to hold Instr's
514  // operands.
515  auto OrigWidth = Instr->getType()->getIntegerBitWidth();
516  ConstantRange OperandRange(OrigWidth, /*isFullset=*/false);
517  for (Value *Operand : Instr->operands()) {
518  OperandRange = OperandRange.unionWith(
519  LVI->getConstantRange(Operand, Instr->getParent()));
520  }
521  // Don't shrink below 8 bits wide.
522  unsigned NewWidth = std::max<unsigned>(
523  PowerOf2Ceil(OperandRange.getUnsignedMax().getActiveBits()), 8);
524  // NewWidth might be greater than OrigWidth if OrigWidth is not a power of
525  // two.
526  if (NewWidth >= OrigWidth)
527  return false;
528 
529  ++NumUDivs;
530  IRBuilder<> B{Instr};
531  auto *TruncTy = Type::getIntNTy(Instr->getContext(), NewWidth);
532  auto *LHS = B.CreateTruncOrBitCast(Instr->getOperand(0), TruncTy,
533  Instr->getName() + ".lhs.trunc");
534  auto *RHS = B.CreateTruncOrBitCast(Instr->getOperand(1), TruncTy,
535  Instr->getName() + ".rhs.trunc");
536  auto *BO = B.CreateBinOp(Instr->getOpcode(), LHS, RHS, Instr->getName());
537  auto *Zext = B.CreateZExt(BO, Instr->getType(), Instr->getName() + ".zext");
538  if (auto *BinOp = dyn_cast<BinaryOperator>(BO))
539  if (BinOp->getOpcode() == Instruction::UDiv)
540  BinOp->setIsExact(Instr->isExact());
541 
542  Instr->replaceAllUsesWith(Zext);
543  Instr->eraseFromParent();
544  return true;
545 }
546 
547 static bool processSRem(BinaryOperator *SDI, LazyValueInfo *LVI) {
548  if (SDI->getType()->isVectorTy() || !hasPositiveOperands(SDI, LVI))
549  return false;
550 
551  ++NumSRems;
552  auto *BO = BinaryOperator::CreateURem(SDI->getOperand(0), SDI->getOperand(1),
553  SDI->getName(), SDI);
554  BO->setDebugLoc(SDI->getDebugLoc());
555  SDI->replaceAllUsesWith(BO);
556  SDI->eraseFromParent();
557 
558  // Try to process our new urem.
559  processUDivOrURem(BO, LVI);
560 
561  return true;
562 }
563 
564 /// See if LazyValueInfo's ability to exploit edge conditions or range
565 /// information is sufficient to prove the both operands of this SDiv are
566 /// positive. If this is the case, replace the SDiv with a UDiv. Even for local
567 /// conditions, this can sometimes prove conditions instcombine can't by
568 /// exploiting range information.
569 static bool processSDiv(BinaryOperator *SDI, LazyValueInfo *LVI) {
570  if (SDI->getType()->isVectorTy() || !hasPositiveOperands(SDI, LVI))
571  return false;
572 
573  ++NumSDivs;
574  auto *BO = BinaryOperator::CreateUDiv(SDI->getOperand(0), SDI->getOperand(1),
575  SDI->getName(), SDI);
576  BO->setDebugLoc(SDI->getDebugLoc());
577  BO->setIsExact(SDI->isExact());
578  SDI->replaceAllUsesWith(BO);
579  SDI->eraseFromParent();
580 
581  // Try to simplify our new udiv.
582  processUDivOrURem(BO, LVI);
583 
584  return true;
585 }
586 
587 static bool processAShr(BinaryOperator *SDI, LazyValueInfo *LVI) {
588  if (SDI->getType()->isVectorTy())
589  return false;
590 
591  Constant *Zero = ConstantInt::get(SDI->getType(), 0);
592  if (LVI->getPredicateAt(ICmpInst::ICMP_SGE, SDI->getOperand(0), Zero, SDI) !=
594  return false;
595 
596  ++NumAShrs;
597  auto *BO = BinaryOperator::CreateLShr(SDI->getOperand(0), SDI->getOperand(1),
598  SDI->getName(), SDI);
599  BO->setDebugLoc(SDI->getDebugLoc());
600  BO->setIsExact(SDI->isExact());
601  SDI->replaceAllUsesWith(BO);
602  SDI->eraseFromParent();
603 
604  return true;
605 }
606 
607 static bool processBinOp(BinaryOperator *BinOp, LazyValueInfo *LVI) {
608  using OBO = OverflowingBinaryOperator;
609 
610  if (DontAddNoWrapFlags)
611  return false;
612 
613  if (BinOp->getType()->isVectorTy())
614  return false;
615 
616  bool NSW = BinOp->hasNoSignedWrap();
617  bool NUW = BinOp->hasNoUnsignedWrap();
618  if (NSW && NUW)
619  return false;
620 
621  BasicBlock *BB = BinOp->getParent();
622 
623  Value *LHS = BinOp->getOperand(0);
624  Value *RHS = BinOp->getOperand(1);
625 
626  ConstantRange LRange = LVI->getConstantRange(LHS, BB, BinOp);
627  ConstantRange RRange = LVI->getConstantRange(RHS, BB, BinOp);
628 
629  bool Changed = false;
630  if (!NUW) {
632  BinOp->getOpcode(), RRange, OBO::NoUnsignedWrap);
633  bool NewNUW = NUWRange.contains(LRange);
634  BinOp->setHasNoUnsignedWrap(NewNUW);
635  Changed |= NewNUW;
636  }
637  if (!NSW) {
639  BinOp->getOpcode(), RRange, OBO::NoSignedWrap);
640  bool NewNSW = NSWRange.contains(LRange);
641  BinOp->setHasNoSignedWrap(NewNSW);
642  Changed |= NewNSW;
643  }
644 
645  return Changed;
646 }
647 
649  if (Constant *C = LVI->getConstant(V, At->getParent(), At))
650  return C;
651 
652  // TODO: The following really should be sunk inside LVI's core algorithm, or
653  // at least the outer shims around such.
654  auto *C = dyn_cast<CmpInst>(V);
655  if (!C) return nullptr;
656 
657  Value *Op0 = C->getOperand(0);
658  Constant *Op1 = dyn_cast<Constant>(C->getOperand(1));
659  if (!Op1) return nullptr;
660 
661  LazyValueInfo::Tristate Result =
662  LVI->getPredicateAt(C->getPredicate(), Op0, Op1, At);
663  if (Result == LazyValueInfo::Unknown)
664  return nullptr;
665 
666  return (Result == LazyValueInfo::True) ?
669 }
670 
671 static bool runImpl(Function &F, LazyValueInfo *LVI, DominatorTree *DT,
672  const SimplifyQuery &SQ) {
673  bool FnChanged = false;
674  // Visiting in a pre-order depth-first traversal causes us to simplify early
675  // blocks before querying later blocks (which require us to analyze early
676  // blocks). Eagerly simplifying shallow blocks means there is strictly less
677  // work to do for deep blocks. This also means we don't visit unreachable
678  // blocks.
679  for (BasicBlock *BB : depth_first(&F.getEntryBlock())) {
680  bool BBChanged = false;
681  for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); BI != BE;) {
682  Instruction *II = &*BI++;
683  switch (II->getOpcode()) {
684  case Instruction::Select:
685  BBChanged |= processSelect(cast<SelectInst>(II), LVI);
686  break;
687  case Instruction::PHI:
688  BBChanged |= processPHI(cast<PHINode>(II), LVI, DT, SQ);
689  break;
690  case Instruction::ICmp:
691  case Instruction::FCmp:
692  BBChanged |= processCmp(cast<CmpInst>(II), LVI);
693  break;
694  case Instruction::Load:
695  case Instruction::Store:
696  BBChanged |= processMemAccess(II, LVI);
697  break;
698  case Instruction::Call:
699  case Instruction::Invoke:
700  BBChanged |= processCallSite(CallSite(II), LVI);
701  break;
702  case Instruction::SRem:
703  BBChanged |= processSRem(cast<BinaryOperator>(II), LVI);
704  break;
705  case Instruction::SDiv:
706  BBChanged |= processSDiv(cast<BinaryOperator>(II), LVI);
707  break;
708  case Instruction::UDiv:
709  case Instruction::URem:
710  BBChanged |= processUDivOrURem(cast<BinaryOperator>(II), LVI);
711  break;
712  case Instruction::AShr:
713  BBChanged |= processAShr(cast<BinaryOperator>(II), LVI);
714  break;
715  case Instruction::Add:
716  case Instruction::Sub:
717  BBChanged |= processBinOp(cast<BinaryOperator>(II), LVI);
718  break;
719  }
720  }
721 
722  Instruction *Term = BB->getTerminator();
723  switch (Term->getOpcode()) {
724  case Instruction::Switch:
725  BBChanged |= processSwitch(cast<SwitchInst>(Term), LVI, DT);
726  break;
727  case Instruction::Ret: {
728  auto *RI = cast<ReturnInst>(Term);
729  // Try to determine the return value if we can. This is mainly here to
730  // simplify the writing of unit tests, but also helps to enable IPO by
731  // constant folding the return values of callees.
732  auto *RetVal = RI->getReturnValue();
733  if (!RetVal) break; // handle "ret void"
734  if (isa<Constant>(RetVal)) break; // nothing to do
735  if (auto *C = getConstantAt(RetVal, RI, LVI)) {
736  ++NumReturns;
737  RI->replaceUsesOfWith(RetVal, C);
738  BBChanged = true;
739  }
740  }
741  }
742 
743  FnChanged |= BBChanged;
744  }
745 
746  return FnChanged;
747 }
748 
750  if (skipFunction(F))
751  return false;
752 
753  LazyValueInfo *LVI = &getAnalysis<LazyValueInfoWrapperPass>().getLVI();
754  DominatorTree *DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
755 
756  return runImpl(F, LVI, DT, getBestSimplifyQuery(*this, F));
757 }
758 
763 
764  bool Changed = runImpl(F, LVI, DT, getBestSimplifyQuery(AM, F));
765 
766  if (!Changed)
767  return PreservedAnalyses::all();
769  PA.preserve<GlobalsAA>();
771  return PA;
772 }
Legacy wrapper pass to provide the GlobalsAAResult object.
Pass interface - Implemented by all &#39;passes&#39;.
Definition: Pass.h:80
uint64_t CallInst * C
unsigned getNumCases() const
Return the number of &#39;cases&#39; in this switch instruction, excluding the default case.
SymbolTableList< Instruction >::iterator eraseFromParent()
This method unlinks &#39;this&#39; from the containing basic block and deletes it.
Definition: Instruction.cpp:67
static ConstantInt * getFalse(LLVMContext &Context)
Definition: Constants.cpp:594
CaseIt case_end()
Returns a read/write iterator that points one past the last in the SwitchInst.
This class is the base class for the comparison instructions.
Definition: InstrTypes.h:699
AnalysisUsage & addPreserved()
Add the specified Pass class to the set of analyses preserved by this pass.
static IntegerType * getInt1Ty(LLVMContext &C)
Definition: Type.cpp:172
static PassRegistry * getPassRegistry()
getPassRegistry - Access the global registry object, which is automatically initialized at applicatio...
static bool processSwitch(SwitchInst *SI, LazyValueInfo *LVI, DominatorTree *DT)
Simplify a switch instruction by removing cases which can never fire.
Value * getPointerOperand(Value *V)
A helper function that returns the pointer operand of a load, store or GEP instruction.
Value * CreateBinOp(Instruction::BinaryOps Opc, Value *LHS, Value *RHS, const Twine &Name="", MDNode *FPMathTag=nullptr)
Definition: IRBuilder.h:1333
ConstantRange getConstantRange(Value *V, BasicBlock *BB, Instruction *CxtI=nullptr)
Return the ConstantRange constraint that is known to hold for the specified value at the end of the s...
static cl::opt< bool > DontAddNoWrapFlags("cvp-dont-add-nowrap-flags", cl::init(true))
Value * getRHS() const
PassT::Result & getResult(IRUnitT &IR, ExtraArgTs... ExtraArgs)
Get the result of an analysis pass for a given IR unit.
Definition: PassManager.h:776
static bool willNotOverflow(WithOverflowInst *WO, LazyValueInfo *LVI)
This class represents lattice values for constants.
Definition: AllocatorList.h:23
BinaryOps getOpcode() const
Definition: InstrTypes.h:379
static bool processPHI(PHINode *P, LazyValueInfo *LVI, DominatorTree *DT, const SimplifyQuery &SQ)
Wrapper around LazyValueInfo.
This is the interface for a simple mod/ref and alias analysis over globals.
bool ConstantFoldTerminator(BasicBlock *BB, bool DeleteDeadConditions=false, const TargetLibraryInfo *TLI=nullptr, DomTreeUpdater *DTU=nullptr)
If a terminator instruction is predicated on a constant value, convert it into an unconditional branc...
Definition: Local.cpp:109
void setAttributes(AttributeList PAL)
Set the parameter attributes of the call.
Definition: CallSite.h:341
This class represents a op.with.overflow intrinsic.
Instruction::BinaryOps getBinaryOp() const
Returns the binary operation underlying the intrinsic.
void removePredecessor(BasicBlock *Pred, bool KeepOneInputPHIs=false)
Notify the BasicBlock that the predecessor Pred is no longer able to reach it.
Definition: BasicBlock.cpp:301
static void processOverflowIntrinsic(WithOverflowInst *WO)
Value * getCondition() const
static bool processCmp(CmpInst *Cmp, LazyValueInfo *LVI)
See if LazyValueInfo&#39;s ability to exploit edge conditions or range information is sufficient to prove...
const Value * getTrueValue() const
CaseIt case_begin()
Returns a read/write iterator that points to the first case in the SwitchInst.
static bool processAShr(BinaryOperator *SDI, LazyValueInfo *LVI)
LLVMContext & getContext() const
All values hold a context through their type.
Definition: Value.cpp:709
STATISTIC(NumFunctions, "Total number of functions")
Analysis pass which computes a DominatorTree.
Definition: Dominators.h:230
F(f)
An instruction for reading from memory.
Definition: Instructions.h:167
Optional< OperandBundleUse > getOperandBundle(StringRef Name) const
Definition: CallSite.h:563
bool isVectorTy() const
True if this is an instance of VectorType.
Definition: Type.h:229
const SimplifyQuery getBestSimplifyQuery(Pass &, Function &)
bool hasNoSignedWrap() const
Determine whether the no signed wrap flag is set.
Value * get() const
Definition: Use.h:107
unsigned getNoWrapKind() const
Returns one of OBO::NoSignedWrap or OBO::NoUnsignedWrap.
AnalysisUsage & addRequired()
#define INITIALIZE_PASS_DEPENDENCY(depName)
Definition: PassSupport.h:50
Constant * getConstant(Value *V, BasicBlock *BB, Instruction *CxtI=nullptr)
Determine whether the specified value is known to be a constant at the end of the specified block...
This class represents the LLVM &#39;select&#39; instruction.
static bool hasPositiveOperands(BinaryOperator *SDI, LazyValueInfo *LVI)
A Use represents the edge between a Value definition and its users.
Definition: Use.h:55
This provides a uniform API for creating instructions and inserting them into a basic block: either a...
Definition: IRBuilder.h:742
This file contains the simple types necessary to represent the attributes associated with functions a...
static bool processSelect(SelectInst *S, LazyValueInfo *LVI)
bool contains(const APInt &Val) const
Return true if the specified value is in the set.
ELFYAML::ELF_STO Other
Definition: ELFYAML.cpp:851
static bool runImpl(Function &F, LazyValueInfo *LVI, DominatorTree *DT, const SimplifyQuery &SQ)
InstrTy * getInstruction() const
Definition: CallSite.h:96
unsigned getActiveBits() const
Compute the number of active bits in the value.
Definition: APInt.h:1532
bool isOne() const
This is just a convenience method to make client code smaller for a common case.
Definition: Constants.h:200
Type * getType() const
All values are typed, get the type of this value.
Definition: Value.h:244
unsigned getOpcode() const
Returns a member of one of the enums like Instruction::Add.
Definition: Instruction.h:125
bool paramHasAttr(unsigned ArgNo, Attribute::AttrKind Kind) const
Return true if the call or the callee has the given attribute.
Definition: CallSite.h:385
void replaceAllUsesWith(Value *V)
Change all uses of this to point to a new Value.
Definition: Value.cpp:429
Concrete subclass of DominatorTreeBase that is used to compute a normal dominator tree...
Definition: Dominators.h:144
Value * getOperand(unsigned i) const
Definition: User.h:169
Class to represent pointers.
Definition: DerivedTypes.h:498
void replaceUsesOfWith(Value *From, Value *To)
Replace uses of one Value with another.
Definition: User.cpp:20
static bool processUDivOrURem(BinaryOperator *Instr, LazyValueInfo *LVI)
Try to shrink a udiv/urem&#39;s width down to the smallest power of two that&#39;s sufficient to contain its ...
const BasicBlock & getEntryBlock() const
Definition: Function.h:645
Pass * createCorrelatedValuePropagationPass()
static bool runOnFunction(Function &F, bool PostInlining)
#define P(N)
initializer< Ty > init(const Ty &Val)
Definition: CommandLine.h:432
static GCRegistry::Add< OcamlGC > B("ocaml", "ocaml 3.10-compatible GC")
A set of analyses that are preserved following a run of a transformation pass.
Definition: PassManager.h:153
static ConstantPointerNull * get(PointerType *T)
Static factory methods - Return objects of the specified value.
Definition: Constants.cpp:1410
void set(Value *Val)
Definition: Value.h:670
Constant * getConstantOnEdge(Value *V, BasicBlock *FromBB, BasicBlock *ToBB, Instruction *CxtI=nullptr)
Determine whether the specified value is known to be a constant on the specified edge.
static bool processSDiv(BinaryOperator *SDI, LazyValueInfo *LVI)
See if LazyValueInfo&#39;s ability to exploit edge conditions or range information is sufficient to prove...
LLVM Basic Block Representation.
Definition: BasicBlock.h:57
LLVM_NODISCARD AttributeList addParamAttribute(LLVMContext &C, unsigned ArgNo, Attribute::AttrKind Kind) const
Add an argument attribute to the list.
Definition: Attributes.h:402
The instances of the Type class are immutable: once they are created, they are never changed...
Definition: Type.h:45
This is an important class for using LLVM in a threaded context.
Definition: LLVMContext.h:64
This is an important base class in LLVM.
Definition: Constant.h:41
This file contains the declarations for the subclasses of Constant, which represent the different fla...
AttributeList getAttributes() const
Get the parameter attributes of the call.
Definition: CallSite.h:337
Interval::pred_iterator pred_begin(Interval *I)
pred_begin/pred_end - define methods so that Intervals may be used just like BasicBlocks can with the...
Definition: Interval.h:112
correlated Value Propagation
APInt getUnsignedMax() const
Return the largest unsigned value contained in the ConstantRange.
Represent the analysis usage information of a pass.
Analysis pass providing a never-invalidated alias analysis result.
Utility class for integer operators which may exhibit overflow - Add, Sub, Mul, and Shl...
Definition: Operator.h:66
FunctionPass class - This class is used to implement most global optimizations.
Definition: Pass.h:284
Interval::pred_iterator pred_end(Interval *I)
Definition: Interval.h:115
op_range operands()
Definition: User.h:237
void applyUpdatesPermissive(ArrayRef< DominatorTree::UpdateType > Updates)
Submit updates to all available trees.
CaseIt removeCase(CaseIt I)
This method removes the specified case and its successor from the switch instruction.
const Value * getCondition() const
static UndefValue * get(Type *T)
Static factory methods - Return an &#39;undef&#39; object of the specified type.
Definition: Constants.cpp:1424
static PreservedAnalyses all()
Construct a special preserved set that preserves all passes.
Definition: PassManager.h:159
Value * getIncomingValue(unsigned i) const
Return incoming value number x.
bool isExact() const
Determine whether the exact flag is set.
INITIALIZE_PASS_END(RegBankSelect, DEBUG_TYPE, "Assign register bank of generic virtual registers", false, false) RegBankSelect
iterator_range< IterTy > args() const
Definition: CallSite.h:222
static bool processSRem(BinaryOperator *SDI, LazyValueInfo *LVI)
Tristate
This is used to return true/false/dunno results.
Definition: LazyValueInfo.h:62
Tristate getPredicateOnEdge(unsigned Pred, Value *V, Constant *C, BasicBlock *FromBB, BasicBlock *ToBB, Instruction *CxtI=nullptr)
Determine whether the specified value comparison with a constant is known to be true or false on the ...
Tristate getPredicateAt(unsigned Pred, Value *V, Constant *C, Instruction *CxtI)
Determine whether the specified value comparison with a constant is known to be true or false at the ...
void setHasNoSignedWrap(bool b=true)
Set or clear the nsw flag on this instruction, which must be an operator which supports this flag...
Iterator for intrusive lists based on ilist_node.
This is the shared class of boolean and integer constants.
Definition: Constants.h:83
void initializeCorrelatedValuePropagationPass(PassRegistry &)
This is a &#39;vector&#39; (really, a variable-sized array), optimized for the case when the array is small...
Definition: SmallVector.h:841
bool dominates(const Instruction *Def, const Use &U) const
Return true if Def dominates a use in User.
Definition: Dominators.cpp:248
unsigned arg_size() const
Definition: CallSite.h:226
This class represents a range of values.
Definition: ConstantRange.h:47
INITIALIZE_PASS_BEGIN(CorrelatedValuePropagation, "correlated-propagation", "Value Propagation", false, false) INITIALIZE_PASS_END(CorrelatedValuePropagation
static IntegerType * getIntNTy(LLVMContext &C, unsigned N)
Definition: Type.cpp:179
static Constant * get(Type *Ty, uint64_t V, bool isSigned=false)
If Ty is a vector type, return a Constant with a splat of the given value.
Definition: Constants.cpp:631
static bool processBinOp(BinaryOperator *BinOp, LazyValueInfo *LVI)
unsigned getNumIncomingValues() const
Return the number of incoming edges.
static ConstantInt * getTrue(LLVMContext &Context)
Definition: Constants.cpp:587
raw_ostream & dbgs()
dbgs() - This returns a reference to a raw_ostream for debugging messages.
Definition: Debug.cpp:132
void swap(llvm::BitVector &LHS, llvm::BitVector &RHS)
Implement std::swap in terms of BitVector swap.
Definition: BitVector.h:940
BBTy * getParent() const
Get the basic block containing the call site.
Definition: CallSite.h:101
const Value * getFalseValue() const
bool isSigned() const
Whether the intrinsic is signed or unsigned.
static bool processCallSite(CallSite CS, LazyValueInfo *LVI)
Infer nonnull attributes for the arguments at the specified callsite.
correlated propagation
Predicate getPredicate() const
Return the predicate for this instruction.
Definition: InstrTypes.h:784
This file provides various utilities for inspecting and working with the control flow graph in LLVM I...
const DebugLoc & getDebugLoc() const
Return the debug location for this node as a DebugLoc.
Definition: Instruction.h:321
void setCondition(Value *V)
unsigned getIntegerBitWidth() const
Definition: DerivedTypes.h:96
LLVM_NODISCARD bool empty() const
Definition: SmallVector.h:55
StringRef getName() const
Return a constant reference to the value&#39;s name.
Definition: Value.cpp:214
BasicBlock * getIncomingBlock(unsigned i) const
Return incoming basic block number i.
#define I(x, y, z)
Definition: MD5.cpp:58
LLVM_NODISCARD std::enable_if<!is_simple_type< Y >::value, typename cast_retty< X, const Y >::ret_type >::type dyn_cast(const Y &Val)
Definition: Casting.h:332
void preserve()
Mark an analysis as preserved.
Definition: PassManager.h:174
static bool processMemAccess(Instruction *I, LazyValueInfo *LVI)
static Attribute get(LLVMContext &Context, AttrKind Kind, uint64_t Val=0)
Return a uniquified Attribute object.
Definition: Attributes.cpp:80
bool hasNoUnsignedWrap() const
Determine whether the no unsigned wrap flag is set.
ConstantRange unionWith(const ConstantRange &CR, PreferredRangeType Type=Smallest) const
Return the range that results from the union of this range with another range.
iterator_range< df_iterator< T > > depth_first(const T &G)
void setHasNoUnsignedWrap(bool b=true)
Set or clear the nuw flag on this instruction, which must be an operator which supports this flag...
Multiway switch.
This pass computes, caches, and vends lazy value constraint information.
Definition: LazyValueInfo.h:31
static ConstantRange makeGuaranteedNoWrapRegion(Instruction::BinaryOps BinOp, const ConstantRange &Other, unsigned NoWrapKind)
Produce the largest range containing all X such that "X BinOp Y" is guaranteed not to wrap (overflow)...
assert(ImpDefSCC.getReg()==AMDGPU::SCC &&ImpDefSCC.isDef())
LLVM Value Representation.
Definition: Value.h:72
Value * getLHS() const
succ_range successors(Instruction *I)
Definition: CFG.h:259
static const Function * getParent(const Value *V)
static Constant * getConstantAt(Value *V, Instruction *At, LazyValueInfo *LVI)
A container for analyses that lazily runs them and caches their results.
Legacy analysis pass which computes a DominatorTree.
Definition: Dominators.h:259
Value * CreateInsertValue(Value *Agg, Value *Val, ArrayRef< unsigned > Idxs, const Twine &Name="")
Definition: IRBuilder.h:2129
This header defines various interfaces for pass management in LLVM.
void setIncomingValue(unsigned i, Value *V)
#define LLVM_DEBUG(X)
Definition: Debug.h:122
PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM)
static bool simplifyCommonValuePhi(PHINode *P, LazyValueInfo *LVI, DominatorTree *DT)
Try to simplify a phi with constant incoming values that match the edge values of a non-constant valu...
Value * SimplifyInstruction(Instruction *I, const SimplifyQuery &Q, OptimizationRemarkEmitter *ORE=nullptr)
See if we can compute a simplified version of this instruction.
signed greater or equal
Definition: InstrTypes.h:737
Analysis to compute lazy value information.
uint64_t PowerOf2Ceil(uint64_t A)
Returns the power of two which is greater than or equal to the given value.
Definition: MathExtras.h:658
const BasicBlock * getParent() const
Definition: Instruction.h:66