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), UnsafeAlgebraInst(nullptr) {}
90 RecurrenceDescriptor(Value *Start, Instruction *Exit, RecurrenceKind K,
91 MinMaxRecurrenceKind MK,
92 Instruction *UAI /*Unsafe Algebra Inst*/)
93 : StartValue(Start), LoopExitInstr(Exit), Kind(K), MinMaxKind(MK),
94 UnsafeAlgebraInst(UAI) {}
96 /// This POD struct holds information about a potential recurrence operation.
100 InstDesc(bool IsRecur, Instruction *I, Instruction *UAI = nullptr)
101 : IsRecurrence(IsRecur), PatternLastInst(I), MinMaxKind(MRK_Invalid),
102 UnsafeAlgebraInst(UAI) {}
104 InstDesc(Instruction *I, MinMaxRecurrenceKind K, Instruction *UAI = nullptr)
105 : IsRecurrence(true), PatternLastInst(I), MinMaxKind(K),
106 UnsafeAlgebraInst(UAI) {}
108 bool isRecurrence() { return IsRecurrence; }
110 bool hasUnsafeAlgebra() { return UnsafeAlgebraInst != nullptr; }
112 Instruction *getUnsafeAlgebraInst() { return UnsafeAlgebraInst; }
114 MinMaxRecurrenceKind getMinMaxKind() { return MinMaxKind; }
116 Instruction *getPatternInst() { return PatternLastInst; }
119 // Is this instruction a recurrence candidate.
121 // The last instruction in a min/max pattern (select of the select(icmp())
122 // pattern), or the current recurrence instruction otherwise.
123 Instruction *PatternLastInst;
124 // If this is a min/max pattern the comparison predicate.
125 MinMaxRecurrenceKind MinMaxKind;
126 // Recurrence has unsafe algebra.
127 Instruction *UnsafeAlgebraInst;
130 /// Returns a struct describing if the instruction 'I' can be a recurrence
131 /// variable of type 'Kind'. If the recurrence is a min/max pattern of
132 /// select(icmp()) this function advances the instruction pointer 'I' from the
133 /// compare instruction to the select instruction and stores this pointer in
134 /// 'PatternLastInst' member of the returned struct.
135 static InstDesc isRecurrenceInstr(Instruction *I, RecurrenceKind Kind,
136 InstDesc &Prev, bool HasFunNoNaNAttr);
138 /// Returns true if instruction I has multiple uses in Insts
139 static bool hasMultipleUsesOf(Instruction *I,
140 SmallPtrSetImpl<Instruction *> &Insts);
142 /// Returns true if all uses of the instruction I is within the Set.
143 static bool areAllUsesIn(Instruction *I, SmallPtrSetImpl<Instruction *> &Set);
145 /// Returns a struct describing if the instruction if the instruction is a
146 /// Select(ICmp(X, Y), X, Y) instruction pattern corresponding to a min(X, Y)
148 static InstDesc isMinMaxSelectCmpPattern(Instruction *I, InstDesc &Prev);
150 /// Returns identity corresponding to the RecurrenceKind.
151 static Constant *getRecurrenceIdentity(RecurrenceKind K, Type *Tp);
153 /// Returns the opcode of binary operation corresponding to the
155 static unsigned getRecurrenceBinOp(RecurrenceKind Kind);
157 /// Returns a Min/Max operation corresponding to MinMaxRecurrenceKind.
158 static Value *createMinMaxOp(IRBuilder<> &Builder, MinMaxRecurrenceKind RK,
159 Value *Left, Value *Right);
161 /// Returns true if Phi is a reduction of type Kind and adds it to the
162 /// RecurrenceDescriptor.
163 static bool AddReductionVar(PHINode *Phi, RecurrenceKind Kind, Loop *TheLoop,
164 bool HasFunNoNaNAttr,
165 RecurrenceDescriptor &RedDes);
167 /// Returns true if Phi is a reduction in TheLoop. The RecurrenceDescriptor is
168 /// returned in RedDes.
169 static bool isReductionPHI(PHINode *Phi, Loop *TheLoop,
170 RecurrenceDescriptor &RedDes);
172 RecurrenceKind getRecurrenceKind() { return Kind; }
174 MinMaxRecurrenceKind getMinMaxRecurrenceKind() { return MinMaxKind; }
176 TrackingVH<Value> getRecurrenceStartValue() { return StartValue; }
178 Instruction *getLoopExitInstr() { return LoopExitInstr; }
180 /// Returns true if the recurrence has unsafe algebra which requires a relaxed
181 /// floating-point model.
182 bool hasUnsafeAlgebra() { return UnsafeAlgebraInst != nullptr; }
184 /// Returns first unsafe algebra instruction in the PHI node's use-chain.
185 Instruction *getUnsafeAlgebraInst() { return UnsafeAlgebraInst; }
188 // The starting value of the recurrence.
189 // It does not have to be zero!
190 TrackingVH<Value> StartValue;
191 // The instruction who's value is used outside the loop.
192 Instruction *LoopExitInstr;
193 // The kind of the recurrence.
195 // If this a min/max recurrence the kind of recurrence.
196 MinMaxRecurrenceKind MinMaxKind;
197 // First occurance of unasfe algebra in the PHI's use-chain.
198 Instruction *UnsafeAlgebraInst;
201 BasicBlock *InsertPreheaderForLoop(Loop *L, Pass *P);
203 /// \brief Simplify each loop in a loop nest recursively.
205 /// This takes a potentially un-simplified loop L (and its children) and turns
206 /// it into a simplified loop nest with preheaders and single backedges. It
207 /// will optionally update \c AliasAnalysis and \c ScalarEvolution analyses if
209 bool simplifyLoop(Loop *L, DominatorTree *DT, LoopInfo *LI, Pass *PP,
210 ScalarEvolution *SE = nullptr, AssumptionCache *AC = nullptr);
212 /// \brief Put loop into LCSSA form.
214 /// Looks at all instructions in the loop which have uses outside of the
215 /// current loop. For each, an LCSSA PHI node is inserted and the uses outside
216 /// the loop are rewritten to use this node.
218 /// LoopInfo and DominatorTree are required and preserved.
220 /// If ScalarEvolution is passed in, it will be preserved.
222 /// Returns true if any modifications are made to the loop.
223 bool formLCSSA(Loop &L, DominatorTree &DT, LoopInfo *LI,
224 ScalarEvolution *SE = nullptr);
226 /// \brief Put a loop nest into LCSSA form.
228 /// This recursively forms LCSSA for a loop nest.
230 /// LoopInfo and DominatorTree are required and preserved.
232 /// If ScalarEvolution is passed in, it will be preserved.
234 /// Returns true if any modifications are made to the loop.
235 bool formLCSSARecursively(Loop &L, DominatorTree &DT, LoopInfo *LI,
236 ScalarEvolution *SE = nullptr);
238 /// \brief Walk the specified region of the CFG (defined by all blocks
239 /// dominated by the specified block, and that are in the current loop) in
240 /// reverse depth first order w.r.t the DominatorTree. This allows us to visit
241 /// uses before definitions, allowing us to sink a loop body in one pass without
242 /// iteration. Takes DomTreeNode, AliasAnalysis, LoopInfo, DominatorTree,
243 /// DataLayout, TargetLibraryInfo, Loop, AliasSet information for all
244 /// instructions of the loop and loop safety information as arguments.
245 /// It returns changed status.
246 bool sinkRegion(DomTreeNode *, AliasAnalysis *, LoopInfo *, DominatorTree *,
247 TargetLibraryInfo *, Loop *, AliasSetTracker *,
250 /// \brief Walk the specified region of the CFG (defined by all blocks
251 /// dominated by the specified block, and that are in the current loop) in depth
252 /// first order w.r.t the DominatorTree. This allows us to visit definitions
253 /// before uses, allowing us to hoist a loop body in one pass without iteration.
254 /// Takes DomTreeNode, AliasAnalysis, LoopInfo, DominatorTree, DataLayout,
255 /// TargetLibraryInfo, Loop, AliasSet information for all instructions of the
256 /// loop and loop safety information as arguments. It returns changed status.
257 bool hoistRegion(DomTreeNode *, AliasAnalysis *, LoopInfo *, DominatorTree *,
258 TargetLibraryInfo *, Loop *, AliasSetTracker *,
261 /// \brief Try to promote memory values to scalars by sinking stores out of
262 /// the loop and moving loads to before the loop. We do this by looping over
263 /// the stores in the loop, looking for stores to Must pointers which are
264 /// loop invariant. It takes AliasSet, Loop exit blocks vector, loop exit blocks
265 /// insertion point vector, PredIteratorCache, LoopInfo, DominatorTree, Loop,
266 /// AliasSet information for all instructions of the loop and loop safety
267 /// information as arguments. It returns changed status.
268 bool promoteLoopAccessesToScalars(AliasSet &, SmallVectorImpl<BasicBlock*> &,
269 SmallVectorImpl<Instruction*> &,
270 PredIteratorCache &, LoopInfo *,
271 DominatorTree *, Loop *, AliasSetTracker *,
274 /// \brief Computes safety information for a loop
275 /// checks loop body & header for the possibility of may throw
276 /// exception, it takes LICMSafetyInfo and loop as argument.
277 /// Updates safety information in LICMSafetyInfo argument.
278 void computeLICMSafetyInfo(LICMSafetyInfo *, Loop *);
280 /// \brief Checks if the given PHINode in a loop header is an induction
281 /// variable. Returns true if this is an induction PHI along with the step
283 bool isInductionPHI(PHINode *, ScalarEvolution *, ConstantInt *&);