LLVM  9.0.0svn
IVDescriptors.h
Go to the documentation of this file.
1 //===- llvm/Analysis/IVDescriptors.h - IndVar Descriptors -------*- C++ -*-===//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This file "describes" induction and recurrence variables.
11 //
12 //===----------------------------------------------------------------------===//
13 
14 #ifndef LLVM_ANALYSIS_IVDESCRIPTORS_H
15 #define LLVM_ANALYSIS_IVDESCRIPTORS_H
16 
17 #include "llvm/ADT/DenseMap.h"
18 #include "llvm/ADT/Optional.h"
19 #include "llvm/ADT/SetVector.h"
20 #include "llvm/ADT/SmallPtrSet.h"
21 #include "llvm/ADT/SmallVector.h"
22 #include "llvm/ADT/StringRef.h"
28 #include "llvm/IR/Dominators.h"
29 #include "llvm/IR/IRBuilder.h"
30 #include "llvm/IR/InstrTypes.h"
31 #include "llvm/IR/Operator.h"
32 #include "llvm/IR/ValueHandle.h"
33 #include "llvm/Support/Casting.h"
34 
35 namespace llvm {
36 
37 class AliasSet;
38 class AliasSetTracker;
39 class BasicBlock;
40 class DataLayout;
41 class Loop;
42 class LoopInfo;
43 class OptimizationRemarkEmitter;
44 class PredicatedScalarEvolution;
45 class PredIteratorCache;
46 class ScalarEvolution;
47 class SCEV;
48 class TargetLibraryInfo;
49 class TargetTransformInfo;
50 
51 /// The RecurrenceDescriptor is used to identify recurrences variables in a
52 /// loop. Reduction is a special case of recurrence that has uses of the
53 /// recurrence variable outside the loop. The method isReductionPHI identifies
54 /// reductions that are basic recurrences.
55 ///
56 /// Basic recurrences are defined as the summation, product, OR, AND, XOR, min,
57 /// or max of a set of terms. For example: for(i=0; i<n; i++) { total +=
58 /// array[i]; } is a summation of array elements. Basic recurrences are a
59 /// special case of chains of recurrences (CR). See ScalarEvolution for CR
60 /// references.
61 
62 /// This struct holds information about recurrence variables.
64 public:
65  /// This enum represents the kinds of recurrences that we support.
67  RK_NoRecurrence, ///< Not a recurrence.
68  RK_IntegerAdd, ///< Sum of integers.
69  RK_IntegerMult, ///< Product of integers.
70  RK_IntegerOr, ///< Bitwise or logical OR of numbers.
71  RK_IntegerAnd, ///< Bitwise or logical AND of numbers.
72  RK_IntegerXor, ///< Bitwise or logical XOR of numbers.
73  RK_IntegerMinMax, ///< Min/max implemented in terms of select(cmp()).
74  RK_FloatAdd, ///< Sum of floats.
75  RK_FloatMult, ///< Product of floats.
76  RK_FloatMinMax ///< Min/max implemented in terms of select(cmp()).
77  };
78 
79  // This enum represents the kind of minmax recurrence.
88  };
89 
90  RecurrenceDescriptor() = default;
91 
95  : StartValue(Start), LoopExitInstr(Exit), Kind(K), MinMaxKind(MK),
96  UnsafeAlgebraInst(UAI), RecurrenceType(RT), IsSigned(Signed) {
97  CastInsts.insert(CI.begin(), CI.end());
98  }
99 
100  /// This POD struct holds information about a potential recurrence operation.
101  class InstDesc {
102  public:
103  InstDesc(bool IsRecur, Instruction *I, Instruction *UAI = nullptr)
104  : IsRecurrence(IsRecur), PatternLastInst(I), MinMaxKind(MRK_Invalid),
105  UnsafeAlgebraInst(UAI) {}
106 
108  : IsRecurrence(true), PatternLastInst(I), MinMaxKind(K),
109  UnsafeAlgebraInst(UAI) {}
110 
111  bool isRecurrence() { return IsRecurrence; }
112 
113  bool hasUnsafeAlgebra() { return UnsafeAlgebraInst != nullptr; }
114 
115  Instruction *getUnsafeAlgebraInst() { return UnsafeAlgebraInst; }
116 
117  MinMaxRecurrenceKind getMinMaxKind() { return MinMaxKind; }
118 
119  Instruction *getPatternInst() { return PatternLastInst; }
120 
121  private:
122  // Is this instruction a recurrence candidate.
123  bool IsRecurrence;
124  // The last instruction in a min/max pattern (select of the select(icmp())
125  // pattern), or the current recurrence instruction otherwise.
126  Instruction *PatternLastInst;
127  // If this is a min/max pattern the comparison predicate.
128  MinMaxRecurrenceKind MinMaxKind;
129  // Recurrence has unsafe algebra.
130  Instruction *UnsafeAlgebraInst;
131  };
132 
133  /// Returns a struct describing if the instruction 'I' can be a recurrence
134  /// variable of type 'Kind'. If the recurrence is a min/max pattern of
135  /// select(icmp()) this function advances the instruction pointer 'I' from the
136  /// compare instruction to the select instruction and stores this pointer in
137  /// 'PatternLastInst' member of the returned struct.
139  InstDesc &Prev, bool HasFunNoNaNAttr);
140 
141  /// Returns true if instruction I has multiple uses in Insts
142  static bool hasMultipleUsesOf(Instruction *I,
144  unsigned MaxNumUses);
145 
146  /// Returns true if all uses of the instruction I is within the Set.
148 
149  /// Returns a struct describing if the instruction if the instruction is a
150  /// Select(ICmp(X, Y), X, Y) instruction pattern corresponding to a min(X, Y)
151  /// or max(X, Y).
153 
154  /// Returns a struct describing if the instruction is a
155  /// Select(FCmp(X, Y), (Z = X op PHINode), PHINode) instruction pattern.
157 
158  /// Returns identity corresponding to the RecurrenceKind.
160 
161  /// Returns the opcode of binary operation corresponding to the
162  /// RecurrenceKind.
163  static unsigned getRecurrenceBinOp(RecurrenceKind Kind);
164 
165  /// Returns true if Phi is a reduction of type Kind and adds it to the
166  /// RecurrenceDescriptor. If either \p DB is non-null or \p AC and \p DT are
167  /// non-null, the minimal bit width needed to compute the reduction will be
168  /// computed.
169  static bool AddReductionVar(PHINode *Phi, RecurrenceKind Kind, Loop *TheLoop,
170  bool HasFunNoNaNAttr,
171  RecurrenceDescriptor &RedDes,
172  DemandedBits *DB = nullptr,
173  AssumptionCache *AC = nullptr,
174  DominatorTree *DT = nullptr);
175 
176  /// Returns true if Phi is a reduction in TheLoop. The RecurrenceDescriptor
177  /// is returned in RedDes. If either \p DB is non-null or \p AC and \p DT are
178  /// non-null, the minimal bit width needed to compute the reduction will be
179  /// computed.
180  static bool isReductionPHI(PHINode *Phi, Loop *TheLoop,
181  RecurrenceDescriptor &RedDes,
182  DemandedBits *DB = nullptr,
183  AssumptionCache *AC = nullptr,
184  DominatorTree *DT = nullptr);
185 
186  /// Returns true if Phi is a first-order recurrence. A first-order recurrence
187  /// is a non-reduction recurrence relation in which the value of the
188  /// recurrence in the current loop iteration equals a value defined in the
189  /// previous iteration. \p SinkAfter includes pairs of instructions where the
190  /// first will be rescheduled to appear after the second if/when the loop is
191  /// vectorized. It may be augmented with additional pairs if needed in order
192  /// to handle Phi as a first-order recurrence.
193  static bool
194  isFirstOrderRecurrence(PHINode *Phi, Loop *TheLoop,
196  DominatorTree *DT);
197 
199 
201 
203 
204  Instruction *getLoopExitInstr() { return LoopExitInstr; }
205 
206  /// Returns true if the recurrence has unsafe algebra which requires a relaxed
207  /// floating-point model.
208  bool hasUnsafeAlgebra() { return UnsafeAlgebraInst != nullptr; }
209 
210  /// Returns first unsafe algebra instruction in the PHI node's use-chain.
211  Instruction *getUnsafeAlgebraInst() { return UnsafeAlgebraInst; }
212 
213  /// Returns true if the recurrence kind is an integer kind.
214  static bool isIntegerRecurrenceKind(RecurrenceKind Kind);
215 
216  /// Returns true if the recurrence kind is a floating point kind.
218 
219  /// Returns true if the recurrence kind is an arithmetic kind.
220  static bool isArithmeticRecurrenceKind(RecurrenceKind Kind);
221 
222  /// Returns the type of the recurrence. This type can be narrower than the
223  /// actual type of the Phi if the recurrence has been type-promoted.
224  Type *getRecurrenceType() { return RecurrenceType; }
225 
226  /// Returns a reference to the instructions used for type-promoting the
227  /// recurrence.
229 
230  /// Returns true if all source operands of the recurrence are SExtInsts.
231  bool isSigned() { return IsSigned; }
232 
233 private:
234  // The starting value of the recurrence.
235  // It does not have to be zero!
236  TrackingVH<Value> StartValue;
237  // The instruction who's value is used outside the loop.
238  Instruction *LoopExitInstr = nullptr;
239  // The kind of the recurrence.
241  // If this a min/max recurrence the kind of recurrence.
242  MinMaxRecurrenceKind MinMaxKind = MRK_Invalid;
243  // First occurrence of unasfe algebra in the PHI's use-chain.
244  Instruction *UnsafeAlgebraInst = nullptr;
245  // The type of the recurrence.
246  Type *RecurrenceType = nullptr;
247  // True if all source operands of the recurrence are SExtInsts.
248  bool IsSigned = false;
249  // Instructions used for type-promoting the recurrence.
251 };
252 
253 /// A struct for saving information about induction variables.
255 public:
256  /// This enum represents the kinds of inductions that we support.
258  IK_NoInduction, ///< Not an induction variable.
259  IK_IntInduction, ///< Integer induction variable. Step = C.
260  IK_PtrInduction, ///< Pointer induction var. Step = C / sizeof(elem).
261  IK_FpInduction ///< Floating point induction variable.
262  };
263 
264 public:
265  /// Default constructor - creates an invalid induction.
266  InductionDescriptor() = default;
267 
268  /// Get the consecutive direction. Returns:
269  /// 0 - unknown or non-consecutive.
270  /// 1 - consecutive and increasing.
271  /// -1 - consecutive and decreasing.
272  int getConsecutiveDirection() const;
273 
274  Value *getStartValue() const { return StartValue; }
275  InductionKind getKind() const { return IK; }
276  const SCEV *getStep() const { return Step; }
277  BinaryOperator *getInductionBinOp() const { return InductionBinOp; }
278  ConstantInt *getConstIntStepValue() const;
279 
280  /// Returns true if \p Phi is an induction in the loop \p L. If \p Phi is an
281  /// induction, the induction descriptor \p D will contain the data describing
282  /// this induction. If by some other means the caller has a better SCEV
283  /// expression for \p Phi than the one returned by the ScalarEvolution
284  /// analysis, it can be passed through \p Expr. If the def-use chain
285  /// associated with the phi includes casts (that we know we can ignore
286  /// under proper runtime checks), they are passed through \p CastsToIgnore.
287  static bool
288  isInductionPHI(PHINode *Phi, const Loop *L, ScalarEvolution *SE,
289  InductionDescriptor &D, const SCEV *Expr = nullptr,
290  SmallVectorImpl<Instruction *> *CastsToIgnore = nullptr);
291 
292  /// Returns true if \p Phi is a floating point induction in the loop \p L.
293  /// If \p Phi is an induction, the induction descriptor \p D will contain
294  /// the data describing this induction.
295  static bool isFPInductionPHI(PHINode *Phi, const Loop *L, ScalarEvolution *SE,
297 
298  /// Returns true if \p Phi is a loop \p L induction, in the context associated
299  /// with the run-time predicate of PSE. If \p Assume is true, this can add
300  /// further SCEV predicates to \p PSE in order to prove that \p Phi is an
301  /// induction.
302  /// If \p Phi is an induction, \p D will contain the data describing this
303  /// induction.
304  static bool isInductionPHI(PHINode *Phi, const Loop *L,
306  InductionDescriptor &D, bool Assume = false);
307 
308  /// Returns true if the induction type is FP and the binary operator does
309  /// not have the "fast-math" property. Such operation requires a relaxed FP
310  /// mode.
312  return InductionBinOp && !cast<FPMathOperator>(InductionBinOp)->isFast();
313  }
314 
315  /// Returns induction operator that does not have "fast-math" property
316  /// and requires FP unsafe mode.
318  if (!InductionBinOp || cast<FPMathOperator>(InductionBinOp)->isFast())
319  return nullptr;
320  return InductionBinOp;
321  }
322 
323  /// Returns binary opcode of the induction operator.
325  return InductionBinOp ? InductionBinOp->getOpcode()
326  : Instruction::BinaryOpsEnd;
327  }
328 
329  /// Returns a reference to the type cast instructions in the induction
330  /// update chain, that are redundant when guarded with a runtime
331  /// SCEV overflow check.
333  return RedundantCasts;
334  }
335 
336 private:
337  /// Private constructor - used by \c isInductionPHI.
338  InductionDescriptor(Value *Start, InductionKind K, const SCEV *Step,
339  BinaryOperator *InductionBinOp = nullptr,
340  SmallVectorImpl<Instruction *> *Casts = nullptr);
341 
342  /// Start value.
343  TrackingVH<Value> StartValue;
344  /// Induction kind.
345  InductionKind IK = IK_NoInduction;
346  /// Step value.
347  const SCEV *Step = nullptr;
348  // Instruction that advances induction variable.
349  BinaryOperator *InductionBinOp = nullptr;
350  // Instructions used for type-casts of the induction variable,
351  // that are redundant when guarded with a runtime SCEV overflow check.
352  SmallVector<Instruction *, 2> RedundantCasts;
353 };
354 
355 } // end namespace llvm
356 
357 #endif // LLVM_ANALYSIS_IVDESCRIPTORS_H
Bitwise or logical XOR of numbers.
Definition: IVDescriptors.h:72
static bool isArithmeticRecurrenceKind(RecurrenceKind Kind)
Returns true if the recurrence kind is an arithmetic kind.
BinaryOperator * getInductionBinOp() const
This class represents lattice values for constants.
Definition: AllocatorList.h:24
Instruction * getUnsafeAlgebraInst()
Returns first unsafe algebra instruction in the PHI node&#39;s use-chain.
Various leaf nodes.
Definition: ISDOpcodes.h:60
Min/max implemented in terms of select(cmp()).
Definition: IVDescriptors.h:73
InstDesc(bool IsRecur, Instruction *I, Instruction *UAI=nullptr)
Instruction::BinaryOps getInductionOpcode() const
Returns binary opcode of the induction operator.
static bool AddReductionVar(PHINode *Phi, RecurrenceKind Kind, Loop *TheLoop, bool HasFunNoNaNAttr, RecurrenceDescriptor &RedDes, DemandedBits *DB=nullptr, AssumptionCache *AC=nullptr, DominatorTree *DT=nullptr)
Returns true if Phi is a reduction of type Kind and adds it to the RecurrenceDescriptor.
The main scalar evolution driver.
A cache of @llvm.assume calls within a function.
MinMaxRecurrenceKind getMinMaxRecurrenceKind()
InductionKind getKind() const
block Block Frequency true
Value * getStartValue() const
static InstDesc isRecurrenceInstr(Instruction *I, RecurrenceKind Kind, InstDesc &Prev, bool HasFunNoNaNAttr)
Returns a struct describing if the instruction &#39;I&#39; can be a recurrence variable of type &#39;Kind&#39;...
static bool hasMultipleUsesOf(Instruction *I, SmallPtrSetImpl< Instruction *> &Insts, unsigned MaxNumUses)
Returns true if instruction I has multiple uses in Insts.
bool isSigned()
Returns true if all source operands of the recurrence are SExtInsts.
bool hasUnsafeAlgebra()
Returns true if the recurrence has unsafe algebra which requires a relaxed floating-point model...
This class consists of common code factored out of the SmallVector class to reduce code duplication b...
Definition: APFloat.h:42
static bool areAllUsesIn(Instruction *I, SmallPtrSetImpl< Instruction *> &Set)
Returns true if all uses of the instruction I is within the Set.
static InstDesc isMinMaxSelectCmpPattern(Instruction *I, InstDesc &Prev)
Returns a struct describing if the instruction if the instruction is a Select(ICmp(X, Y), X, Y) instruction pattern corresponding to a min(X, Y) or max(X, Y).
Contains a collection of routines for determining if a given instruction is guaranteed to execute if ...
This POD struct holds information about a potential recurrence operation.
Concrete subclass of DominatorTreeBase that is used to compute a normal dominator tree...
Definition: Dominators.h:145
Bitwise or logical AND of numbers.
Definition: IVDescriptors.h:71
Pointer induction var. Step = C / sizeof(elem).
Integer induction variable. Step = C.
The instances of the Type class are immutable: once they are created, they are never changed...
Definition: Type.h:46
Min/max implemented in terms of select(cmp()).
Definition: IVDescriptors.h:76
Value handle that tracks a Value across RAUW.
Definition: ValueHandle.h:337
This is an important base class in LLVM.
Definition: Constant.h:42
Instruction * getUnsafeAlgebraInst()
Returns induction operator that does not have "fast-math" property and requires FP unsafe mode...
const SCEV * getStep() const
InstDesc(Instruction *I, MinMaxRecurrenceKind K, Instruction *UAI=nullptr)
static bool isReductionPHI(PHINode *Phi, Loop *TheLoop, RecurrenceDescriptor &RedDes, DemandedBits *DB=nullptr, AssumptionCache *AC=nullptr, DominatorTree *DT=nullptr)
Returns true if Phi is a reduction in TheLoop.
static InstDesc isConditionalRdxPattern(RecurrenceKind Kind, Instruction *I)
Returns a struct describing if the instruction is a Select(FCmp(X, Y), (Z = X op PHINode), PHINode) instruction pattern.
RecurrenceKind getRecurrenceKind()
static unsigned getRecurrenceBinOp(RecurrenceKind Kind)
Returns the opcode of binary operation corresponding to the RecurrenceKind.
static bool isFirstOrderRecurrence(PHINode *Phi, Loop *TheLoop, DenseMap< Instruction *, Instruction *> &SinkAfter, DominatorTree *DT)
Returns true if Phi is a first-order recurrence.
The RecurrenceDescriptor is used to identify recurrences variables in a loop.
Definition: IVDescriptors.h:63
MinMaxRecurrenceKind getMinMaxKind()
SmallPtrSet - This class implements a set which is optimized for holding SmallSize or less elements...
Definition: SmallPtrSet.h:418
This is the shared class of boolean and integer constants.
Definition: Constants.h:84
A struct for saving information about induction variables.
Bitwise or logical OR of numbers.
Definition: IVDescriptors.h:70
This is a &#39;vector&#39; (really, a variable-sized array), optimized for the case when the array is small...
Definition: SmallVector.h:847
RecurrenceDescriptor(Value *Start, Instruction *Exit, RecurrenceKind K, MinMaxRecurrenceKind MK, Instruction *UAI, Type *RT, bool Signed, SmallPtrSetImpl< Instruction *> &CI)
Definition: IVDescriptors.h:92
static bool isFloatingPointRecurrenceKind(RecurrenceKind Kind)
Returns true if the recurrence kind is a floating point kind.
An interface layer with SCEV used to manage how we see SCEV expressions for values in the context of ...
static GCRegistry::Add< StatepointGC > D("statepoint-example", "an example strategy for statepoint")
static Constant * getRecurrenceIdentity(RecurrenceKind K, Type *Tp)
Returns identity corresponding to the RecurrenceKind.
bool hasUnsafeAlgebra()
Returns true if the induction type is FP and the binary operator does not have the "fast-math" proper...
const SmallVectorImpl< Instruction * > & getCastInsts() const
Returns a reference to the type cast instructions in the induction update chain, that are redundant w...
iterator begin() const
Definition: SmallPtrSet.h:397
This class represents an analyzed expression in the program.
static bool isIntegerRecurrenceKind(RecurrenceKind Kind)
Returns true if the recurrence kind is an integer kind.
Instruction * getLoopExitInstr()
Represents a single loop in the control flow graph.
Definition: LoopInfo.h:465
#define I(x, y, z)
Definition: MD5.cpp:58
iterator end() const
Definition: SmallPtrSet.h:402
SmallPtrSet< Instruction *, 8 > & getCastInsts()
Returns a reference to the instructions used for type-promoting the recurrence.
LLVM Value Representation.
Definition: Value.h:73
TrackingVH< Value > getRecurrenceStartValue()
This pass exposes codegen information to IR-level passes.
InductionKind
This enum represents the kinds of inductions that we support.
RecurrenceKind
This enum represents the kinds of recurrences that we support.
Definition: IVDescriptors.h:66
Type * getRecurrenceType()
Returns the type of the recurrence.