1 //===---- llvm/Analysis/ScalarEvolutionExpander.h - SCEV Exprs --*- 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 the classes used to generate code from scalar expressions.
12 //===----------------------------------------------------------------------===//
14 #ifndef LLVM_ANALYSIS_SCALAREVOLUTIONEXPANDER_H
15 #define LLVM_ANALYSIS_SCALAREVOLUTIONEXPANDER_H
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"
27 class TargetTransformInfo;
29 /// Return true if the given expression is safe to expand in the sense that
30 /// all materialized values are safe to speculate.
31 bool isSafeToExpand(const SCEV *S, ScalarEvolution &SE);
33 /// This class uses information about analyze scalars to rewrite expressions
34 /// in canonical form.
36 /// Clients should create an instance of this class when rewriting is needed,
37 /// and destroy it when finished to allow the release of the associated
39 class SCEVExpander : public SCEVVisitor<SCEVExpander, Value*> {
43 // New instructions receive a name to identifies them with the current pass.
46 // InsertedExpressions caches Values for reuse, so must track RAUW.
47 DenseMap<std::pair<const SCEV *, Instruction *>, TrackingVH<Value>>
50 // InsertedValues only flags inserted instructions so needs no RAUW.
51 DenseSet<AssertingVH<Value>> InsertedValues;
52 DenseSet<AssertingVH<Value>> InsertedPostIncValues;
54 /// A memoization of the "relevant" loop for a given SCEV.
55 DenseMap<const SCEV *, const Loop *> RelevantLoops;
57 /// Addrecs referring to any of the given loops are expanded in post-inc
58 /// mode. For example, expanding {1,+,1}<L> in post-inc mode returns the add
59 /// instruction that adds one to the phi for {0,+,1}<L>, as opposed to a new
60 /// phi starting at 1. This is only supported in non-canonical mode.
61 PostIncLoopSet PostIncLoops;
63 /// When this is non-null, addrecs expanded in the loop it indicates should
64 /// be inserted with increments at IVIncInsertPos.
65 const Loop *IVIncInsertLoop;
67 /// When expanding addrecs in the IVIncInsertLoop loop, insert the IV
68 /// increment at this position.
69 Instruction *IVIncInsertPos;
71 /// Phis that complete an IV chain. Reuse
72 DenseSet<AssertingVH<PHINode>> ChainedPhis;
74 /// When true, expressions are expanded in "canonical" form. In particular,
75 /// addrecs are expanded as arithmetic based on a canonical induction
76 /// variable. When false, expression are expanded in a more literal form.
79 /// When invoked from LSR, the expander is in "strength reduction" mode. The
80 /// only difference is that phi's are only reused if they are already in
84 typedef IRBuilder<TargetFolder> BuilderType;
87 // RAII object that stores the current insertion point and restores it when
88 // the object is destroyed. This includes the debug location. Duplicated
89 // from InsertPointGuard to add SetInsertPoint() which is used to updated
90 // InsertPointGuards stack when insert points are moved during SCEV
92 class SCEVInsertPointGuard {
93 IRBuilderBase &Builder;
94 AssertingVH<BasicBlock> Block;
95 BasicBlock::iterator Point;
99 SCEVInsertPointGuard(const SCEVInsertPointGuard &) = delete;
100 SCEVInsertPointGuard &operator=(const SCEVInsertPointGuard &) = delete;
103 SCEVInsertPointGuard(IRBuilderBase &B, SCEVExpander *SE)
104 : Builder(B), Block(B.GetInsertBlock()), Point(B.GetInsertPoint()),
105 DbgLoc(B.getCurrentDebugLocation()), SE(SE) {
106 SE->InsertPointGuards.push_back(this);
109 ~SCEVInsertPointGuard() {
110 // These guards should always created/destroyed in FIFO order since they
111 // are used to guard lexically scoped blocks of code in
112 // ScalarEvolutionExpander.
113 assert(SE->InsertPointGuards.back() == this);
114 SE->InsertPointGuards.pop_back();
115 Builder.restoreIP(IRBuilderBase::InsertPoint(Block, Point));
116 Builder.SetCurrentDebugLocation(DbgLoc);
119 BasicBlock::iterator GetInsertPoint() const { return Point; }
120 void SetInsertPoint(BasicBlock::iterator I) { Point = I; }
123 /// Stack of pointers to saved insert points, used to keep insert points
124 /// consistent when instructions are moved.
125 SmallVector<SCEVInsertPointGuard *, 8> InsertPointGuards;
128 const char *DebugType;
131 friend struct SCEVVisitor<SCEVExpander, Value*>;
134 /// Construct a SCEVExpander in "canonical" mode.
135 explicit SCEVExpander(ScalarEvolution &se, const DataLayout &DL,
137 : SE(se), DL(DL), IVName(name), IVIncInsertLoop(nullptr),
138 IVIncInsertPos(nullptr), CanonicalMode(true), LSRMode(false),
139 Builder(se.getContext(), TargetFolder(DL)) {
146 // Make sure the insert point guard stack is consistent.
147 assert(InsertPointGuards.empty());
151 void setDebugType(const char* s) { DebugType = s; }
154 /// Erase the contents of the InsertedExpressions map so that users trying
155 /// to expand the same expression into multiple BasicBlocks or different
156 /// places within the same BasicBlock can do so.
158 InsertedExpressions.clear();
159 InsertedValues.clear();
160 InsertedPostIncValues.clear();
164 /// Return true for expressions that may incur non-trivial cost to evaluate
167 /// At is an optional parameter which specifies point in code where user is
168 /// going to expand this expression. Sometimes this knowledge can lead to a
169 /// more accurate cost estimation.
170 bool isHighCostExpansion(const SCEV *Expr, Loop *L,
171 const Instruction *At = nullptr) {
172 SmallPtrSet<const SCEV *, 8> Processed;
173 return isHighCostExpansionHelper(Expr, L, At, Processed);
176 /// This method returns the canonical induction variable of the specified
177 /// type for the specified loop (inserting one if there is none). A
178 /// canonical induction variable starts at zero and steps by one on each
180 PHINode *getOrInsertCanonicalInductionVariable(const Loop *L, Type *Ty);
182 /// Return the induction variable increment's IV operand.
183 Instruction *getIVIncOperand(Instruction *IncV, Instruction *InsertPos,
186 /// Utility for hoisting an IV increment.
187 bool hoistIVInc(Instruction *IncV, Instruction *InsertPos);
189 /// replace congruent phis with their most canonical representative. Return
190 /// the number of phis eliminated.
191 unsigned replaceCongruentIVs(Loop *L, const DominatorTree *DT,
192 SmallVectorImpl<WeakTrackingVH> &DeadInsts,
193 const TargetTransformInfo *TTI = nullptr);
195 /// Insert code to directly compute the specified SCEV expression into the
196 /// program. The inserted code is inserted into the specified block.
197 Value *expandCodeFor(const SCEV *SH, Type *Ty, Instruction *I);
199 /// Insert code to directly compute the specified SCEV expression into the
200 /// program. The inserted code is inserted into the SCEVExpander's current
201 /// insertion point. If a type is specified, the result will be expanded to
202 /// have that type, with a cast if necessary.
203 Value *expandCodeFor(const SCEV *SH, Type *Ty = nullptr);
206 /// Generates a code sequence that evaluates this predicate. The inserted
207 /// instructions will be at position \p Loc. The result will be of type i1
208 /// and will have a value of 0 when the predicate is false and 1 otherwise.
209 Value *expandCodeForPredicate(const SCEVPredicate *Pred, Instruction *Loc);
211 /// A specialized variant of expandCodeForPredicate, handling the case when
212 /// we are expanding code for a SCEVEqualPredicate.
213 Value *expandEqualPredicate(const SCEVEqualPredicate *Pred,
216 /// Generates code that evaluates if the \p AR expression will overflow.
217 Value *generateOverflowCheck(const SCEVAddRecExpr *AR, Instruction *Loc,
220 /// A specialized variant of expandCodeForPredicate, handling the case when
221 /// we are expanding code for a SCEVWrapPredicate.
222 Value *expandWrapPredicate(const SCEVWrapPredicate *P, Instruction *Loc);
224 /// A specialized variant of expandCodeForPredicate, handling the case when
225 /// we are expanding code for a SCEVUnionPredicate.
226 Value *expandUnionPredicate(const SCEVUnionPredicate *Pred,
229 /// Set the current IV increment loop and position.
230 void setIVIncInsertPos(const Loop *L, Instruction *Pos) {
231 assert(!CanonicalMode &&
232 "IV increment positions are not supported in CanonicalMode");
234 IVIncInsertPos = Pos;
237 /// Enable post-inc expansion for addrecs referring to the given
238 /// loops. Post-inc expansion is only supported in non-canonical mode.
239 void setPostInc(const PostIncLoopSet &L) {
240 assert(!CanonicalMode &&
241 "Post-inc expansion is not supported in CanonicalMode");
245 /// Disable all post-inc expansion.
246 void clearPostInc() {
247 PostIncLoops.clear();
249 // When we change the post-inc loop set, cached expansions may no
251 InsertedPostIncValues.clear();
254 /// Disable the behavior of expanding expressions in canonical form rather
255 /// than in a more literal form. Non-canonical mode is useful for late
256 /// optimization passes.
257 void disableCanonicalMode() { CanonicalMode = false; }
259 void enableLSRMode() { LSRMode = true; }
261 /// Set the current insertion point. This is useful if multiple calls to
262 /// expandCodeFor() are going to be made with the same insert point and the
263 /// insert point may be moved during one of the expansions (e.g. if the
264 /// insert point is not a block terminator).
265 void setInsertPoint(Instruction *IP) {
267 Builder.SetInsertPoint(IP);
270 /// Clear the current insertion point. This is useful if the instruction
271 /// that had been serving as the insertion point may have been deleted.
272 void clearInsertPoint() {
273 Builder.ClearInsertionPoint();
276 /// Return true if the specified instruction was inserted by the code
277 /// rewriter. If so, the client should not modify the instruction.
278 bool isInsertedInstruction(Instruction *I) const {
279 return InsertedValues.count(I) || InsertedPostIncValues.count(I);
282 void setChainedPhi(PHINode *PN) { ChainedPhis.insert(PN); }
284 /// Try to find existing LLVM IR value for S available at the point At.
285 Value *getExactExistingExpansion(const SCEV *S, const Instruction *At,
288 /// Try to find the ValueOffsetPair for S. The function is mainly used to
289 /// check whether S can be expanded cheaply. If this returns a non-None
290 /// value, we know we can codegen the `ValueOffsetPair` into a suitable
291 /// expansion identical with S so that S can be expanded cheaply.
293 /// L is a hint which tells in which loop to look for the suitable value.
294 /// On success return value which is equivalent to the expanded S at point
295 /// At. Return nullptr if value was not found.
297 /// Note that this function does not perform an exhaustive search. I.e if it
298 /// didn't find any value it does not mean that there is no such value.
300 Optional<ScalarEvolution::ValueOffsetPair>
301 getRelatedExistingExpansion(const SCEV *S, const Instruction *At, Loop *L);
304 LLVMContext &getContext() const { return SE.getContext(); }
306 /// Recursive helper function for isHighCostExpansion.
307 bool isHighCostExpansionHelper(const SCEV *S, Loop *L,
308 const Instruction *At,
309 SmallPtrSetImpl<const SCEV *> &Processed);
311 /// Insert the specified binary operator, doing a small amount of work to
312 /// avoid inserting an obviously redundant operation.
313 Value *InsertBinop(Instruction::BinaryOps Opcode, Value *LHS, Value *RHS);
315 /// Arrange for there to be a cast of V to Ty at IP, reusing an existing
316 /// cast if a suitable one exists, moving an existing cast if a suitable one
317 /// exists but isn't in the right place, or or creating a new one.
318 Value *ReuseOrCreateCast(Value *V, Type *Ty,
319 Instruction::CastOps Op,
320 BasicBlock::iterator IP);
322 /// Insert a cast of V to the specified type, which must be possible with a
323 /// noop cast, doing what we can to share the casts.
324 Value *InsertNoopCastOfTo(Value *V, Type *Ty);
326 /// Expand a SCEVAddExpr with a pointer type into a GEP instead of using
327 /// ptrtoint+arithmetic+inttoptr.
328 Value *expandAddToGEP(const SCEV *const *op_begin,
329 const SCEV *const *op_end,
330 PointerType *PTy, Type *Ty, Value *V);
332 /// Find a previous Value in ExprValueMap for expand.
333 ScalarEvolution::ValueOffsetPair
334 FindValueInExprValueMap(const SCEV *S, const Instruction *InsertPt);
336 Value *expand(const SCEV *S);
338 /// Determine the most "relevant" loop for the given SCEV.
339 const Loop *getRelevantLoop(const SCEV *);
341 Value *visitConstant(const SCEVConstant *S) {
342 return S->getValue();
345 Value *visitTruncateExpr(const SCEVTruncateExpr *S);
347 Value *visitZeroExtendExpr(const SCEVZeroExtendExpr *S);
349 Value *visitSignExtendExpr(const SCEVSignExtendExpr *S);
351 Value *visitAddExpr(const SCEVAddExpr *S);
353 Value *visitMulExpr(const SCEVMulExpr *S);
355 Value *visitUDivExpr(const SCEVUDivExpr *S);
357 Value *visitAddRecExpr(const SCEVAddRecExpr *S);
359 Value *visitSMaxExpr(const SCEVSMaxExpr *S);
361 Value *visitUMaxExpr(const SCEVUMaxExpr *S);
363 Value *visitUnknown(const SCEVUnknown *S) {
364 return S->getValue();
367 void rememberInstruction(Value *I);
369 bool isNormalAddRecExprPHI(PHINode *PN, Instruction *IncV, const Loop *L);
371 bool isExpandedAddRecExprPHI(PHINode *PN, Instruction *IncV, const Loop *L);
373 Value *expandAddRecExprLiterally(const SCEVAddRecExpr *);
374 PHINode *getAddRecExprPHILiterally(const SCEVAddRecExpr *Normalized,
380 Value *expandIVInc(PHINode *PN, Value *StepV, const Loop *L,
381 Type *ExpandTy, Type *IntTy, bool useSubtract);
383 void hoistBeforePos(DominatorTree *DT, Instruction *InstToHoist,
384 Instruction *Pos, PHINode *LoopPhi);
386 void fixupInsertPoints(Instruction *I);