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1 : //===---- llvm/Analysis/ScalarEvolutionExpander.h - SCEV Exprs --*- 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 defines the classes used to generate code from scalar expressions.
11 : //
12 : //===----------------------------------------------------------------------===//
13 :
14 : #ifndef LLVM_ANALYSIS_SCALAREVOLUTIONEXPANDER_H
15 : #define LLVM_ANALYSIS_SCALAREVOLUTIONEXPANDER_H
16 :
17 : #include "llvm/ADT/DenseMap.h"
18 : #include "llvm/ADT/DenseSet.h"
19 : #include "llvm/ADT/Optional.h"
20 : #include "llvm/Analysis/ScalarEvolutionExpressions.h"
21 : #include "llvm/Analysis/ScalarEvolutionNormalization.h"
22 : #include "llvm/Analysis/TargetFolder.h"
23 : #include "llvm/IR/IRBuilder.h"
24 : #include "llvm/IR/ValueHandle.h"
25 :
26 : namespace llvm {
27 : class TargetTransformInfo;
28 :
29 : /// Return true if the given expression is safe to expand in the sense that
30 : /// all materialized values are safe to speculate anywhere their operands are
31 : /// defined.
32 : bool isSafeToExpand(const SCEV *S, ScalarEvolution &SE);
33 :
34 : /// Return true if the given expression is safe to expand in the sense that
35 : /// all materialized values are defined and safe to speculate at the specified
36 : /// location and their operands are defined at this location.
37 : bool isSafeToExpandAt(const SCEV *S, const Instruction *InsertionPoint,
38 : ScalarEvolution &SE);
39 :
40 : /// This class uses information about analyze scalars to rewrite expressions
41 : /// in canonical form.
42 : ///
43 : /// Clients should create an instance of this class when rewriting is needed,
44 : /// and destroy it when finished to allow the release of the associated
45 : /// memory.
46 : class SCEVExpander : public SCEVVisitor<SCEVExpander, Value*> {
47 : ScalarEvolution &SE;
48 : const DataLayout &DL;
49 :
50 : // New instructions receive a name to identify them with the current pass.
51 : const char* IVName;
52 :
53 : // InsertedExpressions caches Values for reuse, so must track RAUW.
54 : DenseMap<std::pair<const SCEV *, Instruction *>, TrackingVH<Value>>
55 : InsertedExpressions;
56 :
57 : // InsertedValues only flags inserted instructions so needs no RAUW.
58 : DenseSet<AssertingVH<Value>> InsertedValues;
59 : DenseSet<AssertingVH<Value>> InsertedPostIncValues;
60 :
61 : /// A memoization of the "relevant" loop for a given SCEV.
62 : DenseMap<const SCEV *, const Loop *> RelevantLoops;
63 :
64 : /// Addrecs referring to any of the given loops are expanded in post-inc
65 : /// mode. For example, expanding {1,+,1}<L> in post-inc mode returns the add
66 : /// instruction that adds one to the phi for {0,+,1}<L>, as opposed to a new
67 : /// phi starting at 1. This is only supported in non-canonical mode.
68 : PostIncLoopSet PostIncLoops;
69 :
70 : /// When this is non-null, addrecs expanded in the loop it indicates should
71 : /// be inserted with increments at IVIncInsertPos.
72 : const Loop *IVIncInsertLoop;
73 :
74 : /// When expanding addrecs in the IVIncInsertLoop loop, insert the IV
75 : /// increment at this position.
76 : Instruction *IVIncInsertPos;
77 :
78 : /// Phis that complete an IV chain. Reuse
79 : DenseSet<AssertingVH<PHINode>> ChainedPhis;
80 :
81 : /// When true, expressions are expanded in "canonical" form. In particular,
82 : /// addrecs are expanded as arithmetic based on a canonical induction
83 : /// variable. When false, expression are expanded in a more literal form.
84 : bool CanonicalMode;
85 :
86 : /// When invoked from LSR, the expander is in "strength reduction" mode. The
87 : /// only difference is that phi's are only reused if they are already in
88 : /// "expanded" form.
89 : bool LSRMode;
90 :
91 : typedef IRBuilder<TargetFolder> BuilderType;
92 : BuilderType Builder;
93 :
94 : // RAII object that stores the current insertion point and restores it when
95 : // the object is destroyed. This includes the debug location. Duplicated
96 : // from InsertPointGuard to add SetInsertPoint() which is used to updated
97 : // InsertPointGuards stack when insert points are moved during SCEV
98 : // expansion.
99 : class SCEVInsertPointGuard {
100 : IRBuilderBase &Builder;
101 : AssertingVH<BasicBlock> Block;
102 : BasicBlock::iterator Point;
103 : DebugLoc DbgLoc;
104 : SCEVExpander *SE;
105 :
106 : SCEVInsertPointGuard(const SCEVInsertPointGuard &) = delete;
107 : SCEVInsertPointGuard &operator=(const SCEVInsertPointGuard &) = delete;
108 :
109 : public:
110 123469 : SCEVInsertPointGuard(IRBuilderBase &B, SCEVExpander *SE)
111 123469 : : Builder(B), Block(B.GetInsertBlock()), Point(B.GetInsertPoint()),
112 123469 : DbgLoc(B.getCurrentDebugLocation()), SE(SE) {
113 123469 : SE->InsertPointGuards.push_back(this);
114 123469 : }
115 :
116 246938 : ~SCEVInsertPointGuard() {
117 : // These guards should always created/destroyed in FIFO order since they
118 : // are used to guard lexically scoped blocks of code in
119 : // ScalarEvolutionExpander.
120 : assert(SE->InsertPointGuards.back() == this);
121 123469 : SE->InsertPointGuards.pop_back();
122 123469 : Builder.restoreIP(IRBuilderBase::InsertPoint(Block, Point));
123 246938 : Builder.SetCurrentDebugLocation(DbgLoc);
124 123469 : }
125 :
126 0 : BasicBlock::iterator GetInsertPoint() const { return Point; }
127 1 : void SetInsertPoint(BasicBlock::iterator I) { Point = I; }
128 : };
129 :
130 : /// Stack of pointers to saved insert points, used to keep insert points
131 : /// consistent when instructions are moved.
132 : SmallVector<SCEVInsertPointGuard *, 8> InsertPointGuards;
133 :
134 : #ifndef NDEBUG
135 : const char *DebugType;
136 : #endif
137 :
138 : friend struct SCEVVisitor<SCEVExpander, Value*>;
139 :
140 : public:
141 : /// Construct a SCEVExpander in "canonical" mode.
142 26223 : explicit SCEVExpander(ScalarEvolution &se, const DataLayout &DL,
143 : const char *name)
144 26223 : : SE(se), DL(DL), IVName(name), IVIncInsertLoop(nullptr),
145 : IVIncInsertPos(nullptr), CanonicalMode(true), LSRMode(false),
146 52446 : Builder(se.getContext(), TargetFolder(DL)) {
147 : #ifndef NDEBUG
148 : DebugType = "";
149 : #endif
150 26223 : }
151 :
152 52446 : ~SCEVExpander() {
153 : // Make sure the insert point guard stack is consistent.
154 : assert(InsertPointGuards.empty());
155 26223 : }
156 :
157 : #ifndef NDEBUG
158 : void setDebugType(const char* s) { DebugType = s; }
159 : #endif
160 :
161 : /// Erase the contents of the InsertedExpressions map so that users trying
162 : /// to expand the same expression into multiple BasicBlocks or different
163 : /// places within the same BasicBlock can do so.
164 10008 : void clear() {
165 10008 : InsertedExpressions.clear();
166 : InsertedValues.clear();
167 : InsertedPostIncValues.clear();
168 : ChainedPhis.clear();
169 10008 : }
170 :
171 : /// Return true for expressions that may incur non-trivial cost to evaluate
172 : /// at runtime.
173 : ///
174 : /// At is an optional parameter which specifies point in code where user is
175 : /// going to expand this expression. Sometimes this knowledge can lead to a
176 : /// more accurate cost estimation.
177 2657 : bool isHighCostExpansion(const SCEV *Expr, Loop *L,
178 : const Instruction *At = nullptr) {
179 : SmallPtrSet<const SCEV *, 8> Processed;
180 2657 : return isHighCostExpansionHelper(Expr, L, At, Processed);
181 : }
182 :
183 : /// This method returns the canonical induction variable of the specified
184 : /// type for the specified loop (inserting one if there is none). A
185 : /// canonical induction variable starts at zero and steps by one on each
186 : /// iteration.
187 : PHINode *getOrInsertCanonicalInductionVariable(const Loop *L, Type *Ty);
188 :
189 : /// Return the induction variable increment's IV operand.
190 : Instruction *getIVIncOperand(Instruction *IncV, Instruction *InsertPos,
191 : bool allowScale);
192 :
193 : /// Utility for hoisting an IV increment.
194 : bool hoistIVInc(Instruction *IncV, Instruction *InsertPos);
195 :
196 : /// replace congruent phis with their most canonical representative. Return
197 : /// the number of phis eliminated.
198 : unsigned replaceCongruentIVs(Loop *L, const DominatorTree *DT,
199 : SmallVectorImpl<WeakTrackingVH> &DeadInsts,
200 : const TargetTransformInfo *TTI = nullptr);
201 :
202 : /// Insert code to directly compute the specified SCEV expression into the
203 : /// program. The inserted code is inserted into the specified block.
204 : Value *expandCodeFor(const SCEV *SH, Type *Ty, Instruction *I);
205 :
206 : /// Insert code to directly compute the specified SCEV expression into the
207 : /// program. The inserted code is inserted into the SCEVExpander's current
208 : /// insertion point. If a type is specified, the result will be expanded to
209 : /// have that type, with a cast if necessary.
210 : Value *expandCodeFor(const SCEV *SH, Type *Ty = nullptr);
211 :
212 :
213 : /// Generates a code sequence that evaluates this predicate. The inserted
214 : /// instructions will be at position \p Loc. The result will be of type i1
215 : /// and will have a value of 0 when the predicate is false and 1 otherwise.
216 : Value *expandCodeForPredicate(const SCEVPredicate *Pred, Instruction *Loc);
217 :
218 : /// A specialized variant of expandCodeForPredicate, handling the case when
219 : /// we are expanding code for a SCEVEqualPredicate.
220 : Value *expandEqualPredicate(const SCEVEqualPredicate *Pred,
221 : Instruction *Loc);
222 :
223 : /// Generates code that evaluates if the \p AR expression will overflow.
224 : Value *generateOverflowCheck(const SCEVAddRecExpr *AR, Instruction *Loc,
225 : bool Signed);
226 :
227 : /// A specialized variant of expandCodeForPredicate, handling the case when
228 : /// we are expanding code for a SCEVWrapPredicate.
229 : Value *expandWrapPredicate(const SCEVWrapPredicate *P, Instruction *Loc);
230 :
231 : /// A specialized variant of expandCodeForPredicate, handling the case when
232 : /// we are expanding code for a SCEVUnionPredicate.
233 : Value *expandUnionPredicate(const SCEVUnionPredicate *Pred,
234 : Instruction *Loc);
235 :
236 : /// Set the current IV increment loop and position.
237 0 : void setIVIncInsertPos(const Loop *L, Instruction *Pos) {
238 : assert(!CanonicalMode &&
239 : "IV increment positions are not supported in CanonicalMode");
240 4030 : IVIncInsertLoop = L;
241 4030 : IVIncInsertPos = Pos;
242 0 : }
243 :
244 : /// Enable post-inc expansion for addrecs referring to the given
245 : /// loops. Post-inc expansion is only supported in non-canonical mode.
246 : void setPostInc(const PostIncLoopSet &L) {
247 : assert(!CanonicalMode &&
248 : "Post-inc expansion is not supported in CanonicalMode");
249 15981 : PostIncLoops = L;
250 : }
251 :
252 : /// Disable all post-inc expansion.
253 : void clearPostInc() {
254 17642 : PostIncLoops.clear();
255 :
256 : // When we change the post-inc loop set, cached expansions may no
257 : // longer be valid.
258 : InsertedPostIncValues.clear();
259 : }
260 :
261 : /// Disable the behavior of expanding expressions in canonical form rather
262 : /// than in a more literal form. Non-canonical mode is useful for late
263 : /// optimization passes.
264 9681 : void disableCanonicalMode() { CanonicalMode = false; }
265 :
266 4030 : void enableLSRMode() { LSRMode = true; }
267 :
268 : /// Set the current insertion point. This is useful if multiple calls to
269 : /// expandCodeFor() are going to be made with the same insert point and the
270 : /// insert point may be moved during one of the expansions (e.g. if the
271 : /// insert point is not a block terminator).
272 : void setInsertPoint(Instruction *IP) {
273 : assert(IP);
274 37265 : Builder.SetInsertPoint(IP);
275 : }
276 :
277 : /// Clear the current insertion point. This is useful if the instruction
278 : /// that had been serving as the insertion point may have been deleted.
279 : void clearInsertPoint() {
280 : Builder.ClearInsertionPoint();
281 : }
282 :
283 : /// Return true if the specified instruction was inserted by the code
284 : /// rewriter. If so, the client should not modify the instruction.
285 56919 : bool isInsertedInstruction(Instruction *I) const {
286 56919 : return InsertedValues.count(I) || InsertedPostIncValues.count(I);
287 : }
288 :
289 318 : void setChainedPhi(PHINode *PN) { ChainedPhis.insert(PN); }
290 :
291 : /// Try to find existing LLVM IR value for S available at the point At.
292 : Value *getExactExistingExpansion(const SCEV *S, const Instruction *At,
293 : Loop *L);
294 :
295 : /// Try to find the ValueOffsetPair for S. The function is mainly used to
296 : /// check whether S can be expanded cheaply. If this returns a non-None
297 : /// value, we know we can codegen the `ValueOffsetPair` into a suitable
298 : /// expansion identical with S so that S can be expanded cheaply.
299 : ///
300 : /// L is a hint which tells in which loop to look for the suitable value.
301 : /// On success return value which is equivalent to the expanded S at point
302 : /// At. Return nullptr if value was not found.
303 : ///
304 : /// Note that this function does not perform an exhaustive search. I.e if it
305 : /// didn't find any value it does not mean that there is no such value.
306 : ///
307 : Optional<ScalarEvolution::ValueOffsetPair>
308 : getRelatedExistingExpansion(const SCEV *S, const Instruction *At, Loop *L);
309 :
310 : private:
311 : LLVMContext &getContext() const { return SE.getContext(); }
312 :
313 : /// Recursive helper function for isHighCostExpansion.
314 : bool isHighCostExpansionHelper(const SCEV *S, Loop *L,
315 : const Instruction *At,
316 : SmallPtrSetImpl<const SCEV *> &Processed);
317 :
318 : /// Insert the specified binary operator, doing a small amount of work to
319 : /// avoid inserting an obviously redundant operation.
320 : Value *InsertBinop(Instruction::BinaryOps Opcode, Value *LHS, Value *RHS);
321 :
322 : /// Arrange for there to be a cast of V to Ty at IP, reusing an existing
323 : /// cast if a suitable one exists, moving an existing cast if a suitable one
324 : /// exists but isn't in the right place, or creating a new one.
325 : Value *ReuseOrCreateCast(Value *V, Type *Ty,
326 : Instruction::CastOps Op,
327 : BasicBlock::iterator IP);
328 :
329 : /// Insert a cast of V to the specified type, which must be possible with a
330 : /// noop cast, doing what we can to share the casts.
331 : Value *InsertNoopCastOfTo(Value *V, Type *Ty);
332 :
333 : /// Expand a SCEVAddExpr with a pointer type into a GEP instead of using
334 : /// ptrtoint+arithmetic+inttoptr.
335 : Value *expandAddToGEP(const SCEV *const *op_begin,
336 : const SCEV *const *op_end,
337 : PointerType *PTy, Type *Ty, Value *V);
338 : Value *expandAddToGEP(const SCEV *Op, PointerType *PTy, Type *Ty, Value *V);
339 :
340 : /// Find a previous Value in ExprValueMap for expand.
341 : ScalarEvolution::ValueOffsetPair
342 : FindValueInExprValueMap(const SCEV *S, const Instruction *InsertPt);
343 :
344 : Value *expand(const SCEV *S);
345 :
346 : /// Determine the most "relevant" loop for the given SCEV.
347 : const Loop *getRelevantLoop(const SCEV *);
348 :
349 0 : Value *visitConstant(const SCEVConstant *S) {
350 17493 : return S->getValue();
351 : }
352 :
353 : Value *visitTruncateExpr(const SCEVTruncateExpr *S);
354 :
355 : Value *visitZeroExtendExpr(const SCEVZeroExtendExpr *S);
356 :
357 : Value *visitSignExtendExpr(const SCEVSignExtendExpr *S);
358 :
359 : Value *visitAddExpr(const SCEVAddExpr *S);
360 :
361 : Value *visitMulExpr(const SCEVMulExpr *S);
362 :
363 : Value *visitUDivExpr(const SCEVUDivExpr *S);
364 :
365 : Value *visitAddRecExpr(const SCEVAddRecExpr *S);
366 :
367 : Value *visitSMaxExpr(const SCEVSMaxExpr *S);
368 :
369 : Value *visitUMaxExpr(const SCEVUMaxExpr *S);
370 :
371 0 : Value *visitUnknown(const SCEVUnknown *S) {
372 0 : return S->getValue();
373 : }
374 :
375 : void rememberInstruction(Value *I);
376 :
377 : bool isNormalAddRecExprPHI(PHINode *PN, Instruction *IncV, const Loop *L);
378 :
379 : bool isExpandedAddRecExprPHI(PHINode *PN, Instruction *IncV, const Loop *L);
380 :
381 : Value *expandAddRecExprLiterally(const SCEVAddRecExpr *);
382 : PHINode *getAddRecExprPHILiterally(const SCEVAddRecExpr *Normalized,
383 : const Loop *L,
384 : Type *ExpandTy,
385 : Type *IntTy,
386 : Type *&TruncTy,
387 : bool &InvertStep);
388 : Value *expandIVInc(PHINode *PN, Value *StepV, const Loop *L,
389 : Type *ExpandTy, Type *IntTy, bool useSubtract);
390 :
391 : void hoistBeforePos(DominatorTree *DT, Instruction *InstToHoist,
392 : Instruction *Pos, PHINode *LoopPhi);
393 :
394 : void fixupInsertPoints(Instruction *I);
395 : };
396 : }
397 :
398 : #endif
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