1//===---- llvm/Analysis/ScalarEvolutionExpander.h - SCEV Exprs --*- C++ -*-===//
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 defines the classes used to generate code from scalar expressions.
10//
11//===----------------------------------------------------------------------===//
12
13#ifndef LLVM_TRANSFORMS_UTILS_SCALAREVOLUTIONEXPANDER_H
14#define LLVM_TRANSFORMS_UTILS_SCALAREVOLUTIONEXPANDER_H
15
16#include "llvm/ADT/DenseMap.h"
17#include "llvm/ADT/DenseSet.h"
18#include "llvm/ADT/SmallVector.h"
19#include "llvm/Analysis/InstSimplifyFolder.h"
20#include "llvm/Analysis/ScalarEvolutionExpressions.h"
21#include "llvm/Analysis/ScalarEvolutionNormalization.h"
22#include "llvm/Analysis/TargetTransformInfo.h"
23#include "llvm/IR/IRBuilder.h"
24#include "llvm/IR/ValueHandle.h"
25#include "llvm/Support/CommandLine.h"
26#include "llvm/Support/InstructionCost.h"
27
28namespace llvm {
29extern cl::opt<unsigned> SCEVCheapExpansionBudget;
30
31/// struct for holding enough information to help calculate the cost of the
32/// given SCEV when expanded into IR.
33struct SCEVOperand {
34 explicit SCEVOperand(unsigned Opc, int Idx, const SCEV *S) :
35 ParentOpcode(Opc), OperandIdx(Idx), S(S) { }
36 /// LLVM instruction opcode that uses the operand.
37 unsigned ParentOpcode;
38 /// The use index of an expanded instruction.
39 int OperandIdx;
40 /// The SCEV operand to be costed.
41 const SCEV* S;
42};
43
44/// This class uses information about analyze scalars to rewrite expressions
45/// in canonical form.
46///
47/// Clients should create an instance of this class when rewriting is needed,
48/// and destroy it when finished to allow the release of the associated
49/// memory.
50class SCEVExpander : public SCEVVisitor<SCEVExpander, Value *> {
51 ScalarEvolution &SE;
52 const DataLayout &DL;
53
54 // New instructions receive a name to identify them with the current pass.
55 const char *IVName;
56
57 /// Indicates whether LCSSA phis should be created for inserted values.
58 bool PreserveLCSSA;
59
60 // InsertedExpressions caches Values for reuse, so must track RAUW.
61 DenseMap<std::pair<const SCEV *, Instruction *>, TrackingVH<Value>>
62 InsertedExpressions;
63
64 // InsertedValues only flags inserted instructions so needs no RAUW.
65 DenseSet<AssertingVH<Value>> InsertedValues;
66 DenseSet<AssertingVH<Value>> InsertedPostIncValues;
67
68 /// Keep track of the existing IR values re-used during expansion.
69 /// FIXME: Ideally re-used instructions would not be added to
70 /// InsertedValues/InsertedPostIncValues.
71 SmallPtrSet<Value *, 16> ReusedValues;
72
73 // The induction variables generated.
74 SmallVector<WeakVH, 2> InsertedIVs;
75
76 /// A memoization of the "relevant" loop for a given SCEV.
77 DenseMap<const SCEV *, const Loop *> RelevantLoops;
78
79 /// Addrecs referring to any of the given loops are expanded in post-inc
80 /// mode. For example, expanding {1,+,1}<L> in post-inc mode returns the add
81 /// instruction that adds one to the phi for {0,+,1}<L>, as opposed to a new
82 /// phi starting at 1. This is only supported in non-canonical mode.
83 PostIncLoopSet PostIncLoops;
84
85 /// When this is non-null, addrecs expanded in the loop it indicates should
86 /// be inserted with increments at IVIncInsertPos.
87 const Loop *IVIncInsertLoop;
88
89 /// When expanding addrecs in the IVIncInsertLoop loop, insert the IV
90 /// increment at this position.
91 Instruction *IVIncInsertPos;
92
93 /// Phis that complete an IV chain. Reuse
94 DenseSet<AssertingVH<PHINode>> ChainedPhis;
95
96 /// When true, SCEVExpander tries to expand expressions in "canonical" form.
97 /// When false, expressions are expanded in a more literal form.
98 ///
99 /// In "canonical" form addrecs are expanded as arithmetic based on a
100 /// canonical induction variable. Note that CanonicalMode doesn't guarantee
101 /// that all expressions are expanded in "canonical" form. For some
102 /// expressions literal mode can be preferred.
103 bool CanonicalMode;
104
105 /// When invoked from LSR, the expander is in "strength reduction" mode. The
106 /// only difference is that phi's are only reused if they are already in
107 /// "expanded" form.
108 bool LSRMode;
109
110 typedef IRBuilder<InstSimplifyFolder, IRBuilderCallbackInserter> BuilderType;
111 BuilderType Builder;
112
113 // RAII object that stores the current insertion point and restores it when
114 // the object is destroyed. This includes the debug location. Duplicated
115 // from InsertPointGuard to add SetInsertPoint() which is used to updated
116 // InsertPointGuards stack when insert points are moved during SCEV
117 // expansion.
118 class SCEVInsertPointGuard {
119 IRBuilderBase &Builder;
120 AssertingVH<BasicBlock> Block;
121 BasicBlock::iterator Point;
122 DebugLoc DbgLoc;
123 SCEVExpander *SE;
124
125 SCEVInsertPointGuard(const SCEVInsertPointGuard &) = delete;
126 SCEVInsertPointGuard &operator=(const SCEVInsertPointGuard &) = delete;
127
128 public:
129 SCEVInsertPointGuard(IRBuilderBase &B, SCEVExpander *SE)
130 : Builder(B), Block(B.GetInsertBlock()), Point(B.GetInsertPoint()),
131 DbgLoc(B.getCurrentDebugLocation()), SE(SE) {
132 SE->InsertPointGuards.push_back(Elt: this);
133 }
134
135 ~SCEVInsertPointGuard() {
136 // These guards should always created/destroyed in FIFO order since they
137 // are used to guard lexically scoped blocks of code in
138 // ScalarEvolutionExpander.
139 assert(SE->InsertPointGuards.back() == this);
140 SE->InsertPointGuards.pop_back();
141 Builder.restoreIP(IP: IRBuilderBase::InsertPoint(Block, Point));
142 Builder.SetCurrentDebugLocation(DbgLoc);
143 }
144
145 BasicBlock::iterator GetInsertPoint() const { return Point; }
146 void SetInsertPoint(BasicBlock::iterator I) { Point = I; }
147 };
148
149 /// Stack of pointers to saved insert points, used to keep insert points
150 /// consistent when instructions are moved.
151 SmallVector<SCEVInsertPointGuard *, 8> InsertPointGuards;
152
153#ifdef LLVM_ENABLE_ABI_BREAKING_CHECKS
154 const char *DebugType;
155#endif
156
157 friend struct SCEVVisitor<SCEVExpander, Value *>;
158
159public:
160 /// Construct a SCEVExpander in "canonical" mode.
161 explicit SCEVExpander(ScalarEvolution &se, const DataLayout &DL,
162 const char *name, bool PreserveLCSSA = true)
163 : SE(se), DL(DL), IVName(name), PreserveLCSSA(PreserveLCSSA),
164 IVIncInsertLoop(nullptr), IVIncInsertPos(nullptr), CanonicalMode(true),
165 LSRMode(false),
166 Builder(se.getContext(), InstSimplifyFolder(DL),
167 IRBuilderCallbackInserter(
168 [this](Instruction *I) { rememberInstruction(I); })) {
169#ifdef LLVM_ENABLE_ABI_BREAKING_CHECKS
170 DebugType = "";
171#endif
172 }
173
174 ~SCEVExpander() {
175 // Make sure the insert point guard stack is consistent.
176 assert(InsertPointGuards.empty());
177 }
178
179#ifdef LLVM_ENABLE_ABI_BREAKING_CHECKS
180 void setDebugType(const char *s) { DebugType = s; }
181#endif
182
183 /// Erase the contents of the InsertedExpressions map so that users trying
184 /// to expand the same expression into multiple BasicBlocks or different
185 /// places within the same BasicBlock can do so.
186 void clear() {
187 InsertedExpressions.clear();
188 InsertedValues.clear();
189 InsertedPostIncValues.clear();
190 ReusedValues.clear();
191 ChainedPhis.clear();
192 InsertedIVs.clear();
193 }
194
195 ScalarEvolution *getSE() { return &SE; }
196 const SmallVectorImpl<WeakVH> &getInsertedIVs() const { return InsertedIVs; }
197
198 /// Return a vector containing all instructions inserted during expansion.
199 SmallVector<Instruction *, 32> getAllInsertedInstructions() const {
200 SmallVector<Instruction *, 32> Result;
201 for (const auto &VH : InsertedValues) {
202 Value *V = VH;
203 if (ReusedValues.contains(Ptr: V))
204 continue;
205 if (auto *Inst = dyn_cast<Instruction>(Val: V))
206 Result.push_back(Elt: Inst);
207 }
208 for (const auto &VH : InsertedPostIncValues) {
209 Value *V = VH;
210 if (ReusedValues.contains(Ptr: V))
211 continue;
212 if (auto *Inst = dyn_cast<Instruction>(Val: V))
213 Result.push_back(Elt: Inst);
214 }
215
216 return Result;
217 }
218
219 /// Return true for expressions that can't be evaluated at runtime
220 /// within given \b Budget.
221 ///
222 /// \p At is a parameter which specifies point in code where user is going to
223 /// expand these expressions. Sometimes this knowledge can lead to
224 /// a less pessimistic cost estimation.
225 bool isHighCostExpansion(ArrayRef<const SCEV *> Exprs, Loop *L,
226 unsigned Budget, const TargetTransformInfo *TTI,
227 const Instruction *At) {
228 assert(TTI && "This function requires TTI to be provided.");
229 assert(At && "This function requires At instruction to be provided.");
230 if (!TTI) // In assert-less builds, avoid crashing
231 return true; // by always claiming to be high-cost.
232 SmallVector<SCEVOperand, 8> Worklist;
233 SmallPtrSet<const SCEV *, 8> Processed;
234 InstructionCost Cost = 0;
235 unsigned ScaledBudget = Budget * TargetTransformInfo::TCC_Basic;
236 for (auto *Expr : Exprs)
237 Worklist.emplace_back(Args: -1, Args: -1, Args&: Expr);
238 while (!Worklist.empty()) {
239 const SCEVOperand WorkItem = Worklist.pop_back_val();
240 if (isHighCostExpansionHelper(WorkItem, L, At: *At, Cost, Budget: ScaledBudget, TTI: *TTI,
241 Processed, Worklist))
242 return true;
243 }
244 assert(Cost <= ScaledBudget && "Should have returned from inner loop.");
245 return false;
246 }
247
248 /// Return the induction variable increment's IV operand.
249 Instruction *getIVIncOperand(Instruction *IncV, Instruction *InsertPos,
250 bool allowScale);
251
252 /// Utility for hoisting \p IncV (with all subexpressions requried for its
253 /// computation) before \p InsertPos. If \p RecomputePoisonFlags is set, drops
254 /// all poison-generating flags from instructions being hoisted and tries to
255 /// re-infer them in the new location. It should be used when we are going to
256 /// introduce a new use in the new position that didn't exist before, and may
257 /// trigger new UB in case of poison.
258 bool hoistIVInc(Instruction *IncV, Instruction *InsertPos,
259 bool RecomputePoisonFlags = false);
260
261 /// replace congruent phis with their most canonical representative. Return
262 /// the number of phis eliminated.
263 unsigned replaceCongruentIVs(Loop *L, const DominatorTree *DT,
264 SmallVectorImpl<WeakTrackingVH> &DeadInsts,
265 const TargetTransformInfo *TTI = nullptr);
266
267 /// Return true if the given expression is safe to expand in the sense that
268 /// all materialized values are safe to speculate anywhere their operands are
269 /// defined, and the expander is capable of expanding the expression.
270 bool isSafeToExpand(const SCEV *S) const;
271
272 /// Return true if the given expression is safe to expand in the sense that
273 /// all materialized values are defined and safe to speculate at the specified
274 /// location and their operands are defined at this location.
275 bool isSafeToExpandAt(const SCEV *S, const Instruction *InsertionPoint) const;
276
277 /// Insert code to directly compute the specified SCEV expression into the
278 /// program. The code is inserted into the specified block.
279 Value *expandCodeFor(const SCEV *SH, Type *Ty, BasicBlock::iterator I);
280 Value *expandCodeFor(const SCEV *SH, Type *Ty, Instruction *I) {
281 return expandCodeFor(SH, Ty, I: I->getIterator());
282 }
283
284 /// Insert code to directly compute the specified SCEV expression into the
285 /// program. The code is inserted into the SCEVExpander's current
286 /// insertion point. If a type is specified, the result will be expanded to
287 /// have that type, with a cast if necessary.
288 Value *expandCodeFor(const SCEV *SH, Type *Ty = nullptr);
289
290 /// Generates a code sequence that evaluates this predicate. The inserted
291 /// instructions will be at position \p Loc. The result will be of type i1
292 /// and will have a value of 0 when the predicate is false and 1 otherwise.
293 Value *expandCodeForPredicate(const SCEVPredicate *Pred, Instruction *Loc);
294
295 /// A specialized variant of expandCodeForPredicate, handling the case when
296 /// we are expanding code for a SCEVComparePredicate.
297 Value *expandComparePredicate(const SCEVComparePredicate *Pred,
298 Instruction *Loc);
299
300 /// Generates code that evaluates if the \p AR expression will overflow.
301 Value *generateOverflowCheck(const SCEVAddRecExpr *AR, Instruction *Loc,
302 bool Signed);
303
304 /// A specialized variant of expandCodeForPredicate, handling the case when
305 /// we are expanding code for a SCEVWrapPredicate.
306 Value *expandWrapPredicate(const SCEVWrapPredicate *P, Instruction *Loc);
307
308 /// A specialized variant of expandCodeForPredicate, handling the case when
309 /// we are expanding code for a SCEVUnionPredicate.
310 Value *expandUnionPredicate(const SCEVUnionPredicate *Pred, Instruction *Loc);
311
312 /// Set the current IV increment loop and position.
313 void setIVIncInsertPos(const Loop *L, Instruction *Pos) {
314 assert(!CanonicalMode &&
315 "IV increment positions are not supported in CanonicalMode");
316 IVIncInsertLoop = L;
317 IVIncInsertPos = Pos;
318 }
319
320 /// Enable post-inc expansion for addrecs referring to the given
321 /// loops. Post-inc expansion is only supported in non-canonical mode.
322 void setPostInc(const PostIncLoopSet &L) {
323 assert(!CanonicalMode &&
324 "Post-inc expansion is not supported in CanonicalMode");
325 PostIncLoops = L;
326 }
327
328 /// Disable all post-inc expansion.
329 void clearPostInc() {
330 PostIncLoops.clear();
331
332 // When we change the post-inc loop set, cached expansions may no
333 // longer be valid.
334 InsertedPostIncValues.clear();
335 }
336
337 /// Disable the behavior of expanding expressions in canonical form rather
338 /// than in a more literal form. Non-canonical mode is useful for late
339 /// optimization passes.
340 void disableCanonicalMode() { CanonicalMode = false; }
341
342 void enableLSRMode() { LSRMode = true; }
343
344 /// Set the current insertion point. This is useful if multiple calls to
345 /// expandCodeFor() are going to be made with the same insert point and the
346 /// insert point may be moved during one of the expansions (e.g. if the
347 /// insert point is not a block terminator).
348 void setInsertPoint(Instruction *IP) {
349 assert(IP);
350 Builder.SetInsertPoint(IP);
351 }
352
353 void setInsertPoint(BasicBlock::iterator IP) {
354 Builder.SetInsertPoint(TheBB: IP->getParent(), IP);
355 }
356
357 /// Clear the current insertion point. This is useful if the instruction
358 /// that had been serving as the insertion point may have been deleted.
359 void clearInsertPoint() { Builder.ClearInsertionPoint(); }
360
361 /// Set location information used by debugging information.
362 void SetCurrentDebugLocation(DebugLoc L) {
363 Builder.SetCurrentDebugLocation(std::move(L));
364 }
365
366 /// Get location information used by debugging information.
367 DebugLoc getCurrentDebugLocation() const {
368 return Builder.getCurrentDebugLocation();
369 }
370
371 /// Return true if the specified instruction was inserted by the code
372 /// rewriter. If so, the client should not modify the instruction. Note that
373 /// this also includes instructions re-used during expansion.
374 bool isInsertedInstruction(Instruction *I) const {
375 return InsertedValues.count(V: I) || InsertedPostIncValues.count(V: I);
376 }
377
378 void setChainedPhi(PHINode *PN) { ChainedPhis.insert(V: PN); }
379
380 /// Determine whether there is an existing expansion of S that can be reused.
381 /// This is used to check whether S can be expanded cheaply.
382 ///
383 /// L is a hint which tells in which loop to look for the suitable value.
384 ///
385 /// Note that this function does not perform an exhaustive search. I.e if it
386 /// didn't find any value it does not mean that there is no such value.
387 bool hasRelatedExistingExpansion(const SCEV *S, const Instruction *At,
388 Loop *L);
389
390 /// Returns a suitable insert point after \p I, that dominates \p
391 /// MustDominate. Skips instructions inserted by the expander.
392 BasicBlock::iterator findInsertPointAfter(Instruction *I,
393 Instruction *MustDominate) const;
394
395private:
396 LLVMContext &getContext() const { return SE.getContext(); }
397
398 /// Recursive helper function for isHighCostExpansion.
399 bool isHighCostExpansionHelper(const SCEVOperand &WorkItem, Loop *L,
400 const Instruction &At, InstructionCost &Cost,
401 unsigned Budget,
402 const TargetTransformInfo &TTI,
403 SmallPtrSetImpl<const SCEV *> &Processed,
404 SmallVectorImpl<SCEVOperand> &Worklist);
405
406 /// Insert the specified binary operator, doing a small amount of work to
407 /// avoid inserting an obviously redundant operation, and hoisting to an
408 /// outer loop when the opportunity is there and it is safe.
409 Value *InsertBinop(Instruction::BinaryOps Opcode, Value *LHS, Value *RHS,
410 SCEV::NoWrapFlags Flags, bool IsSafeToHoist);
411
412 /// We want to cast \p V. What would be the best place for such a cast?
413 BasicBlock::iterator GetOptimalInsertionPointForCastOf(Value *V) const;
414
415 /// Arrange for there to be a cast of V to Ty at IP, reusing an existing
416 /// cast if a suitable one exists, moving an existing cast if a suitable one
417 /// exists but isn't in the right place, or creating a new one.
418 Value *ReuseOrCreateCast(Value *V, Type *Ty, Instruction::CastOps Op,
419 BasicBlock::iterator IP);
420
421 /// Insert a cast of V to the specified type, which must be possible with a
422 /// noop cast, doing what we can to share the casts.
423 Value *InsertNoopCastOfTo(Value *V, Type *Ty);
424
425 /// Expand a SCEVAddExpr with a pointer type into a GEP instead of using
426 /// ptrtoint+arithmetic+inttoptr.
427 Value *expandAddToGEP(const SCEV *Op, Value *V);
428
429 /// Find a previous Value in ExprValueMap for expand.
430 /// DropPoisonGeneratingInsts is populated with instructions for which
431 /// poison-generating flags must be dropped if the value is reused.
432 Value *FindValueInExprValueMap(
433 const SCEV *S, const Instruction *InsertPt,
434 SmallVectorImpl<Instruction *> &DropPoisonGeneratingInsts);
435
436 Value *expand(const SCEV *S);
437 Value *expand(const SCEV *S, BasicBlock::iterator I) {
438 setInsertPoint(I);
439 return expand(S);
440 }
441 Value *expand(const SCEV *S, Instruction *I) {
442 setInsertPoint(I);
443 return expand(S);
444 }
445
446 /// Determine the most "relevant" loop for the given SCEV.
447 const Loop *getRelevantLoop(const SCEV *);
448
449 Value *expandMinMaxExpr(const SCEVNAryExpr *S, Intrinsic::ID IntrinID,
450 Twine Name, bool IsSequential = false);
451
452 Value *visitConstant(const SCEVConstant *S) { return S->getValue(); }
453
454 Value *visitVScale(const SCEVVScale *S);
455
456 Value *visitPtrToIntExpr(const SCEVPtrToIntExpr *S);
457
458 Value *visitTruncateExpr(const SCEVTruncateExpr *S);
459
460 Value *visitZeroExtendExpr(const SCEVZeroExtendExpr *S);
461
462 Value *visitSignExtendExpr(const SCEVSignExtendExpr *S);
463
464 Value *visitAddExpr(const SCEVAddExpr *S);
465
466 Value *visitMulExpr(const SCEVMulExpr *S);
467
468 Value *visitUDivExpr(const SCEVUDivExpr *S);
469
470 Value *visitAddRecExpr(const SCEVAddRecExpr *S);
471
472 Value *visitSMaxExpr(const SCEVSMaxExpr *S);
473
474 Value *visitUMaxExpr(const SCEVUMaxExpr *S);
475
476 Value *visitSMinExpr(const SCEVSMinExpr *S);
477
478 Value *visitUMinExpr(const SCEVUMinExpr *S);
479
480 Value *visitSequentialUMinExpr(const SCEVSequentialUMinExpr *S);
481
482 Value *visitUnknown(const SCEVUnknown *S) { return S->getValue(); }
483
484 void rememberInstruction(Value *I);
485
486 bool isNormalAddRecExprPHI(PHINode *PN, Instruction *IncV, const Loop *L);
487
488 bool isExpandedAddRecExprPHI(PHINode *PN, Instruction *IncV, const Loop *L);
489
490 Value *expandAddRecExprLiterally(const SCEVAddRecExpr *);
491 PHINode *getAddRecExprPHILiterally(const SCEVAddRecExpr *Normalized,
492 const Loop *L, Type *&TruncTy,
493 bool &InvertStep);
494 Value *expandIVInc(PHINode *PN, Value *StepV, const Loop *L,
495 bool useSubtract);
496
497 void fixupInsertPoints(Instruction *I);
498
499 /// Create LCSSA PHIs for \p V, if it is required for uses at the Builder's
500 /// current insertion point.
501 Value *fixupLCSSAFormFor(Value *V);
502
503 /// Replace congruent phi increments with their most canonical representative.
504 /// May swap \p Phi and \p OrigPhi, if \p Phi is more canonical, due to its
505 /// increment.
506 void replaceCongruentIVInc(PHINode *&Phi, PHINode *&OrigPhi, Loop *L,
507 const DominatorTree *DT,
508 SmallVectorImpl<WeakTrackingVH> &DeadInsts);
509};
510
511/// Helper to remove instructions inserted during SCEV expansion, unless they
512/// are marked as used.
513class SCEVExpanderCleaner {
514 SCEVExpander &Expander;
515
516 /// Indicates whether the result of the expansion is used. If false, the
517 /// instructions added during expansion are removed.
518 bool ResultUsed;
519
520public:
521 SCEVExpanderCleaner(SCEVExpander &Expander)
522 : Expander(Expander), ResultUsed(false) {}
523
524 ~SCEVExpanderCleaner() { cleanup(); }
525
526 /// Indicate that the result of the expansion is used.
527 void markResultUsed() { ResultUsed = true; }
528
529 void cleanup();
530};
531} // namespace llvm
532
533#endif
534

source code of llvm/include/llvm/Transforms/Utils/ScalarEvolutionExpander.h