1 //===- llvm/Transforms/Utils/LoopUtils.h - Loop utilities -*- C++ -*-=========//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file defines some loop transformation utilities.
12 //===----------------------------------------------------------------------===//
14 #ifndef LLVM_TRANSFORMS_UTILS_LOOPUTILS_H
15 #define LLVM_TRANSFORMS_UTILS_LOOPUTILS_H
17 #include "llvm/ADT/SmallVector.h"
18 #include "llvm/IR/Dominators.h"
19 #include "llvm/IR/IRBuilder.h"
24 class AliasSetTracker;
25 class AssumptionCache;
32 class PredIteratorCache;
33 class ScalarEvolution;
34 class TargetLibraryInfo;
36 /// \brief Captures loop safety information.
37 /// It keep information for loop & its header may throw exception.
38 struct LICMSafetyInfo {
39 bool MayThrow; // The current loop contains an instruction which
41 bool HeaderMayThrow; // Same as previous, but specific to loop header
42 LICMSafetyInfo() : MayThrow(false), HeaderMayThrow(false)
46 /// The RecurrenceDescriptor is used to identify recurrences variables in a
47 /// loop. Reduction is a special case of recurrence that has uses of the
48 /// recurrence variable outside the loop. The method isReductionPHI identifies
49 /// reductions that are basic recurrences.
51 /// Basic recurrences are defined as the summation, product, OR, AND, XOR, min,
52 /// or max of a set of terms. For example: for(i=0; i<n; i++) { total +=
53 /// array[i]; } is a summation of array elements. Basic recurrences are a
54 /// special case of chains of recurrences (CR). See ScalarEvolution for CR
57 /// This struct holds information about recurrence variables.
58 class RecurrenceDescriptor {
61 /// This enum represents the kinds of recurrences that we support.
63 RK_NoRecurrence, ///< Not a recurrence.
64 RK_IntegerAdd, ///< Sum of integers.
65 RK_IntegerMult, ///< Product of integers.
66 RK_IntegerOr, ///< Bitwise or logical OR of numbers.
67 RK_IntegerAnd, ///< Bitwise or logical AND of numbers.
68 RK_IntegerXor, ///< Bitwise or logical XOR of numbers.
69 RK_IntegerMinMax, ///< Min/max implemented in terms of select(cmp()).
70 RK_FloatAdd, ///< Sum of floats.
71 RK_FloatMult, ///< Product of floats.
72 RK_FloatMinMax ///< Min/max implemented in terms of select(cmp()).
75 // This enum represents the kind of minmax recurrence.
76 enum MinMaxRecurrenceKind {
86 RecurrenceDescriptor()
87 : StartValue(nullptr), LoopExitInstr(nullptr), Kind(RK_NoRecurrence),
88 MinMaxKind(MRK_Invalid) {}
90 RecurrenceDescriptor(Value *Start, Instruction *Exit, RecurrenceKind K,
91 MinMaxRecurrenceKind MK)
92 : StartValue(Start), LoopExitInstr(Exit), Kind(K), MinMaxKind(MK) {}
94 /// This POD struct holds information about a potential recurrence operation.
98 InstDesc(bool IsRecur, Instruction *I)
99 : IsRecurrence(IsRecur), PatternLastInst(I), MinMaxKind(MRK_Invalid) {}
101 InstDesc(Instruction *I, MinMaxRecurrenceKind K)
102 : IsRecurrence(true), PatternLastInst(I), MinMaxKind(K) {}
104 bool isRecurrence() { return IsRecurrence; }
106 MinMaxRecurrenceKind getMinMaxKind() { return MinMaxKind; }
108 Instruction *getPatternInst() { return PatternLastInst; }
111 // Is this instruction a recurrence candidate.
113 // The last instruction in a min/max pattern (select of the select(icmp())
114 // pattern), or the current recurrence instruction otherwise.
115 Instruction *PatternLastInst;
116 // If this is a min/max pattern the comparison predicate.
117 MinMaxRecurrenceKind MinMaxKind;
120 /// Returns a struct describing if the instruction 'I' can be a recurrence
121 /// variable of type 'Kind'. If the recurrence is a min/max pattern of
122 /// select(icmp()) this function advances the instruction pointer 'I' from the
123 /// compare instruction to the select instruction and stores this pointer in
124 /// 'PatternLastInst' member of the returned struct.
125 static InstDesc isRecurrenceInstr(Instruction *I, RecurrenceKind Kind,
126 InstDesc &Prev, bool HasFunNoNaNAttr);
128 /// Returns true if instuction I has multiple uses in Insts
129 static bool hasMultipleUsesOf(Instruction *I,
130 SmallPtrSetImpl<Instruction *> &Insts);
132 /// Returns true if all uses of the instruction I is within the Set.
133 static bool areAllUsesIn(Instruction *I, SmallPtrSetImpl<Instruction *> &Set);
135 /// Returns a struct describing if the instruction if the instruction is a
136 /// Select(ICmp(X, Y), X, Y) instruction pattern corresponding to a min(X, Y)
138 static InstDesc isMinMaxSelectCmpPattern(Instruction *I, InstDesc &Prev);
140 /// Returns identity corresponding to the RecurrenceKind.
141 static Constant *getRecurrenceIdentity(RecurrenceKind K, Type *Tp);
143 /// Returns the opcode of binary operation corresponding to the
145 static unsigned getRecurrenceBinOp(RecurrenceKind Kind);
147 /// Returns a Min/Max operation corresponding to MinMaxRecurrenceKind.
148 static Value *createMinMaxOp(IRBuilder<> &Builder, MinMaxRecurrenceKind RK,
149 Value *Left, Value *Right);
151 /// Returns true if Phi is a reduction of type Kind and adds it to the
152 /// RecurrenceDescriptor.
153 static bool AddReductionVar(PHINode *Phi, RecurrenceKind Kind, Loop *TheLoop,
154 bool HasFunNoNaNAttr,
155 RecurrenceDescriptor &RedDes);
157 /// Returns true if Phi is a reduction in TheLoop. The RecurrenceDescriptor is
158 /// returned in RedDes.
159 static bool isReductionPHI(PHINode *Phi, Loop *TheLoop,
160 RecurrenceDescriptor &RedDes);
162 RecurrenceKind getRecurrenceKind() { return Kind; }
164 MinMaxRecurrenceKind getMinMaxRecurrenceKind() { return MinMaxKind; }
166 TrackingVH<Value> getRecurrenceStartValue() { return StartValue; }
168 Instruction *getLoopExitInstr() { return LoopExitInstr; }
171 // The starting value of the recurrence.
172 // It does not have to be zero!
173 TrackingVH<Value> StartValue;
174 // The instruction who's value is used outside the loop.
175 Instruction *LoopExitInstr;
176 // The kind of the recurrence.
178 // If this a min/max recurrence the kind of recurrence.
179 MinMaxRecurrenceKind MinMaxKind;
182 BasicBlock *InsertPreheaderForLoop(Loop *L, Pass *P);
184 /// \brief Simplify each loop in a loop nest recursively.
186 /// This takes a potentially un-simplified loop L (and its children) and turns
187 /// it into a simplified loop nest with preheaders and single backedges. It
188 /// will optionally update \c AliasAnalysis and \c ScalarEvolution analyses if
190 bool simplifyLoop(Loop *L, DominatorTree *DT, LoopInfo *LI, Pass *PP,
191 ScalarEvolution *SE = nullptr, AssumptionCache *AC = nullptr);
193 /// \brief Put loop into LCSSA form.
195 /// Looks at all instructions in the loop which have uses outside of the
196 /// current loop. For each, an LCSSA PHI node is inserted and the uses outside
197 /// the loop are rewritten to use this node.
199 /// LoopInfo and DominatorTree are required and preserved.
201 /// If ScalarEvolution is passed in, it will be preserved.
203 /// Returns true if any modifications are made to the loop.
204 bool formLCSSA(Loop &L, DominatorTree &DT, LoopInfo *LI,
205 ScalarEvolution *SE = nullptr);
207 /// \brief Put a loop nest into LCSSA form.
209 /// This recursively forms LCSSA for a loop nest.
211 /// LoopInfo and DominatorTree are required and preserved.
213 /// If ScalarEvolution is passed in, it will be preserved.
215 /// Returns true if any modifications are made to the loop.
216 bool formLCSSARecursively(Loop &L, DominatorTree &DT, LoopInfo *LI,
217 ScalarEvolution *SE = nullptr);
219 /// \brief Walk the specified region of the CFG (defined by all blocks
220 /// dominated by the specified block, and that are in the current loop) in
221 /// reverse depth first order w.r.t the DominatorTree. This allows us to visit
222 /// uses before definitions, allowing us to sink a loop body in one pass without
223 /// iteration. Takes DomTreeNode, AliasAnalysis, LoopInfo, DominatorTree,
224 /// DataLayout, TargetLibraryInfo, Loop, AliasSet information for all
225 /// instructions of the loop and loop safety information as arguments.
226 /// It returns changed status.
227 bool sinkRegion(DomTreeNode *, AliasAnalysis *, LoopInfo *, DominatorTree *,
228 TargetLibraryInfo *, Loop *, AliasSetTracker *,
231 /// \brief Walk the specified region of the CFG (defined by all blocks
232 /// dominated by the specified block, and that are in the current loop) in depth
233 /// first order w.r.t the DominatorTree. This allows us to visit definitions
234 /// before uses, allowing us to hoist a loop body in one pass without iteration.
235 /// Takes DomTreeNode, AliasAnalysis, LoopInfo, DominatorTree, DataLayout,
236 /// TargetLibraryInfo, Loop, AliasSet information for all instructions of the
237 /// loop and loop safety information as arguments. It returns changed status.
238 bool hoistRegion(DomTreeNode *, AliasAnalysis *, LoopInfo *, DominatorTree *,
239 TargetLibraryInfo *, Loop *, AliasSetTracker *,
242 /// \brief Try to promote memory values to scalars by sinking stores out of
243 /// the loop and moving loads to before the loop. We do this by looping over
244 /// the stores in the loop, looking for stores to Must pointers which are
245 /// loop invariant. It takes AliasSet, Loop exit blocks vector, loop exit blocks
246 /// insertion point vector, PredIteratorCache, LoopInfo, DominatorTree, Loop,
247 /// AliasSet information for all instructions of the loop and loop safety
248 /// information as arguments. It returns changed status.
249 bool promoteLoopAccessesToScalars(AliasSet &, SmallVectorImpl<BasicBlock*> &,
250 SmallVectorImpl<Instruction*> &,
251 PredIteratorCache &, LoopInfo *,
252 DominatorTree *, Loop *, AliasSetTracker *,
255 /// \brief Computes safety information for a loop
256 /// checks loop body & header for the possiblity of may throw
257 /// exception, it takes LICMSafetyInfo and loop as argument.
258 /// Updates safety information in LICMSafetyInfo argument.
259 void computeLICMSafetyInfo(LICMSafetyInfo *, Loop *);
261 /// \brief Checks if the given PHINode in a loop header is an induction
262 /// variable. Returns true if this is an induction PHI along with the step
264 bool isInductionPHI(PHINode *, ScalarEvolution *, ConstantInt *&);