1 //===- ScalarEvolutionNormalization.cpp - See below -----------------------===// 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 implements utilities for working with "normalized" expressions. 11 // See the comments at the top of ScalarEvolutionNormalization.h for details. 12 // 13 //===----------------------------------------------------------------------===// 14 15 #include "llvm/Analysis/LoopInfo.h" 16 #include "llvm/Analysis/ScalarEvolutionExpressions.h" 17 #include "llvm/Analysis/ScalarEvolutionNormalization.h" 18 using namespace llvm; 19 20 namespace { 21 22 /// TransformKind - Different types of transformations that 23 /// TransformForPostIncUse can do. 24 enum TransformKind { 25 /// Normalize - Normalize according to the given loops. 26 Normalize, 27 /// Denormalize - Perform the inverse transform on the expression with the 28 /// given loop set. 29 Denormalize 30 }; 31 32 /// Hold the state used during post-inc expression transformation, including a 33 /// map of transformed expressions. 34 class PostIncTransform { 35 TransformKind Kind; 36 Optional<NormalizePredTy> Pred; 37 const PostIncLoopSet &Loops; 38 ScalarEvolution &SE; 39 40 DenseMap<const SCEV*, const SCEV*> Transformed; 41 42 public: 43 PostIncTransform(TransformKind kind, Optional<NormalizePredTy> Pred, 44 const PostIncLoopSet &loops, ScalarEvolution &se) 45 : Kind(kind), Pred(Pred), Loops(loops), SE(se) {} 46 47 const SCEV *TransformSubExpr(const SCEV *S); 48 49 protected: 50 const SCEV *TransformImpl(const SCEV *S); 51 }; 52 53 } // namespace 54 55 /// Implement post-inc transformation for all valid expression types. 56 const SCEV *PostIncTransform::TransformImpl(const SCEV *S) { 57 if (const SCEVCastExpr *X = dyn_cast<SCEVCastExpr>(S)) { 58 const SCEV *O = X->getOperand(); 59 const SCEV *N = TransformSubExpr(O); 60 if (O != N) 61 switch (S->getSCEVType()) { 62 case scZeroExtend: return SE.getZeroExtendExpr(N, S->getType()); 63 case scSignExtend: return SE.getSignExtendExpr(N, S->getType()); 64 case scTruncate: return SE.getTruncateExpr(N, S->getType()); 65 default: llvm_unreachable("Unexpected SCEVCastExpr kind!"); 66 } 67 return S; 68 } 69 70 if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) { 71 // An addrec. This is the interesting part. 72 SmallVector<const SCEV *, 8> Operands; 73 const Loop *L = AR->getLoop(); 74 75 transform(AR->operands(), std::back_inserter(Operands), 76 [&](const SCEV *Op) { return TransformSubExpr(Op); }); 77 78 // Conservatively use AnyWrap until/unless we need FlagNW. 79 const SCEV *Result = SE.getAddRecExpr(Operands, L, SCEV::FlagAnyWrap); 80 switch (Kind) { 81 case Normalize: 82 // We want to normalize step expression, because otherwise we might not be 83 // able to denormalize to the original expression. 84 // 85 // Here is an example what will happen if we don't normalize step: 86 // ORIGINAL ISE: 87 // {(100 /u {1,+,1}<%bb16>),+,(100 /u {1,+,1}<%bb16>)}<%bb25> 88 // NORMALIZED ISE: 89 // {((-1 * (100 /u {1,+,1}<%bb16>)) + (100 /u {0,+,1}<%bb16>)),+, 90 // (100 /u {0,+,1}<%bb16>)}<%bb25> 91 // DENORMALIZED BACK ISE: 92 // {((2 * (100 /u {1,+,1}<%bb16>)) + (-1 * (100 /u {2,+,1}<%bb16>))),+, 93 // (100 /u {1,+,1}<%bb16>)}<%bb25> 94 // Note that the initial value changes after normalization + 95 // denormalization, which isn't correct. 96 if ((Pred && (*Pred)(AR)) || (!Pred && Loops.count(L))) { 97 const SCEV *TransformedStep = 98 TransformSubExpr(AR->getStepRecurrence(SE)); 99 Result = SE.getMinusSCEV(Result, TransformedStep); 100 } 101 #if 0 102 // See the comment on the assert above. 103 assert(S == TransformSubExpr(Result, User, OperandValToReplace) && 104 "SCEV normalization is not invertible!"); 105 #endif 106 break; 107 case Denormalize: 108 // Here we want to normalize step expressions for the same reasons, as 109 // stated above. 110 if (Loops.count(L)) { 111 const SCEV *TransformedStep = 112 TransformSubExpr(AR->getStepRecurrence(SE)); 113 Result = SE.getAddExpr(Result, TransformedStep); 114 } 115 break; 116 } 117 return Result; 118 } 119 120 if (const SCEVNAryExpr *X = dyn_cast<SCEVNAryExpr>(S)) { 121 SmallVector<const SCEV *, 8> Operands; 122 bool Changed = false; 123 // Transform each operand. 124 for (SCEVNAryExpr::op_iterator I = X->op_begin(), E = X->op_end(); 125 I != E; ++I) { 126 const SCEV *O = *I; 127 const SCEV *N = TransformSubExpr(O); 128 Changed |= N != O; 129 Operands.push_back(N); 130 } 131 // If any operand actually changed, return a transformed result. 132 if (Changed) 133 switch (S->getSCEVType()) { 134 case scAddExpr: return SE.getAddExpr(Operands); 135 case scMulExpr: return SE.getMulExpr(Operands); 136 case scSMaxExpr: return SE.getSMaxExpr(Operands); 137 case scUMaxExpr: return SE.getUMaxExpr(Operands); 138 default: llvm_unreachable("Unexpected SCEVNAryExpr kind!"); 139 } 140 return S; 141 } 142 143 if (const SCEVUDivExpr *X = dyn_cast<SCEVUDivExpr>(S)) { 144 const SCEV *LO = X->getLHS(); 145 const SCEV *RO = X->getRHS(); 146 const SCEV *LN = TransformSubExpr(LO); 147 const SCEV *RN = TransformSubExpr(RO); 148 if (LO != LN || RO != RN) 149 return SE.getUDivExpr(LN, RN); 150 return S; 151 } 152 153 llvm_unreachable("Unexpected SCEV kind!"); 154 } 155 156 /// Manage recursive transformation across an expression DAG. Revisiting 157 /// expressions would lead to exponential recursion. 158 const SCEV *PostIncTransform::TransformSubExpr(const SCEV *S) { 159 if (isa<SCEVConstant>(S) || isa<SCEVUnknown>(S)) 160 return S; 161 162 const SCEV *Result = Transformed.lookup(S); 163 if (Result) 164 return Result; 165 166 Result = TransformImpl(S); 167 Transformed[S] = Result; 168 return Result; 169 } 170 171 /// Top level driver for transforming an expression DAG into its requested 172 /// post-inc form (either "Normalized" or "Denormalized"). 173 static const SCEV *TransformForPostIncUse(TransformKind Kind, const SCEV *S, 174 Optional<NormalizePredTy> Pred, 175 const PostIncLoopSet &Loops, 176 ScalarEvolution &SE) { 177 PostIncTransform Transform(Kind, Pred, Loops, SE); 178 return Transform.TransformSubExpr(S); 179 } 180 181 const SCEV *llvm::normalizeForPostIncUse(const SCEV *S, 182 const PostIncLoopSet &Loops, 183 ScalarEvolution &SE) { 184 return TransformForPostIncUse(Normalize, S, None, Loops, SE); 185 } 186 187 const SCEV *llvm::normalizeForPostIncUseIf(const SCEV *S, NormalizePredTy Pred, 188 ScalarEvolution &SE) { 189 PostIncLoopSet Empty; 190 return TransformForPostIncUse(Normalize, S, Pred, Empty, SE); 191 } 192 193 const SCEV *llvm::denormalizeForPostIncUse(const SCEV *S, 194 const PostIncLoopSet &Loops, 195 ScalarEvolution &SE) { 196 return TransformForPostIncUse(Denormalize, S, None, Loops, SE); 197 } 198