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 NormalizePredTy Pred; 37 ScalarEvolution &SE; 38 39 DenseMap<const SCEV*, const SCEV*> Transformed; 40 41 public: 42 PostIncTransform(TransformKind kind, NormalizePredTy Pred, 43 ScalarEvolution &se) 44 : Kind(kind), Pred(Pred), SE(se) {} 45 46 const SCEV *TransformSubExpr(const SCEV *S); 47 48 protected: 49 const SCEV *TransformImpl(const SCEV *S); 50 }; 51 52 } // namespace 53 54 /// Implement post-inc transformation for all valid expression types. 55 const SCEV *PostIncTransform::TransformImpl(const SCEV *S) { 56 if (const SCEVCastExpr *X = dyn_cast<SCEVCastExpr>(S)) { 57 const SCEV *O = X->getOperand(); 58 const SCEV *N = TransformSubExpr(O); 59 if (O != N) 60 switch (S->getSCEVType()) { 61 case scZeroExtend: return SE.getZeroExtendExpr(N, S->getType()); 62 case scSignExtend: return SE.getSignExtendExpr(N, S->getType()); 63 case scTruncate: return SE.getTruncateExpr(N, S->getType()); 64 default: llvm_unreachable("Unexpected SCEVCastExpr kind!"); 65 } 66 return S; 67 } 68 69 if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) { 70 // An addrec. This is the interesting part. 71 SmallVector<const SCEV *, 8> Operands; 72 73 transform(AR->operands(), std::back_inserter(Operands), 74 [&](const SCEV *Op) { return TransformSubExpr(Op); }); 75 76 // Conservatively use AnyWrap until/unless we need FlagNW. 77 const SCEV *Result = 78 SE.getAddRecExpr(Operands, AR->getLoop(), SCEV::FlagAnyWrap); 79 switch (Kind) { 80 case Normalize: 81 // We want to normalize step expression, because otherwise we might not be 82 // able to denormalize to the original expression. 83 // 84 // Here is an example what will happen if we don't normalize step: 85 // ORIGINAL ISE: 86 // {(100 /u {1,+,1}<%bb16>),+,(100 /u {1,+,1}<%bb16>)}<%bb25> 87 // NORMALIZED ISE: 88 // {((-1 * (100 /u {1,+,1}<%bb16>)) + (100 /u {0,+,1}<%bb16>)),+, 89 // (100 /u {0,+,1}<%bb16>)}<%bb25> 90 // DENORMALIZED BACK ISE: 91 // {((2 * (100 /u {1,+,1}<%bb16>)) + (-1 * (100 /u {2,+,1}<%bb16>))),+, 92 // (100 /u {1,+,1}<%bb16>)}<%bb25> 93 // Note that the initial value changes after normalization + 94 // denormalization, which isn't correct. 95 if (Pred(AR)) { 96 const SCEV *TransformedStep = 97 TransformSubExpr(AR->getStepRecurrence(SE)); 98 Result = SE.getMinusSCEV(Result, TransformedStep); 99 } 100 #if 0 101 // See the comment on the assert above. 102 assert(S == TransformSubExpr(Result, User, OperandValToReplace) && 103 "SCEV normalization is not invertible!"); 104 #endif 105 break; 106 case Denormalize: 107 // Here we want to normalize step expressions for the same reasons, as 108 // stated above. 109 if (Pred(AR)) { 110 const SCEV *TransformedStep = 111 TransformSubExpr(AR->getStepRecurrence(SE)); 112 Result = SE.getAddExpr(Result, TransformedStep); 113 } 114 break; 115 } 116 return Result; 117 } 118 119 if (const SCEVNAryExpr *X = dyn_cast<SCEVNAryExpr>(S)) { 120 SmallVector<const SCEV *, 8> Operands; 121 bool Changed = false; 122 // Transform each operand. 123 for (auto *O : X->operands()) { 124 const SCEV *N = TransformSubExpr(O); 125 Changed |= N != O; 126 Operands.push_back(N); 127 } 128 // If any operand actually changed, return a transformed result. 129 if (Changed) 130 switch (S->getSCEVType()) { 131 case scAddExpr: return SE.getAddExpr(Operands); 132 case scMulExpr: return SE.getMulExpr(Operands); 133 case scSMaxExpr: return SE.getSMaxExpr(Operands); 134 case scUMaxExpr: return SE.getUMaxExpr(Operands); 135 default: llvm_unreachable("Unexpected SCEVNAryExpr kind!"); 136 } 137 return S; 138 } 139 140 if (const SCEVUDivExpr *X = dyn_cast<SCEVUDivExpr>(S)) { 141 const SCEV *LO = X->getLHS(); 142 const SCEV *RO = X->getRHS(); 143 const SCEV *LN = TransformSubExpr(LO); 144 const SCEV *RN = TransformSubExpr(RO); 145 if (LO != LN || RO != RN) 146 return SE.getUDivExpr(LN, RN); 147 return S; 148 } 149 150 llvm_unreachable("Unexpected SCEV kind!"); 151 } 152 153 /// Manage recursive transformation across an expression DAG. Revisiting 154 /// expressions would lead to exponential recursion. 155 const SCEV *PostIncTransform::TransformSubExpr(const SCEV *S) { 156 if (isa<SCEVConstant>(S) || isa<SCEVUnknown>(S)) 157 return S; 158 159 const SCEV *Result = Transformed.lookup(S); 160 if (Result) 161 return Result; 162 163 Result = TransformImpl(S); 164 Transformed[S] = Result; 165 return Result; 166 } 167 168 /// Top level driver for transforming an expression DAG into its requested 169 /// post-inc form (either "Normalized" or "Denormalized"). 170 static const SCEV *TransformForPostIncUse(TransformKind Kind, const SCEV *S, 171 NormalizePredTy Pred, 172 ScalarEvolution &SE) { 173 PostIncTransform Transform(Kind, Pred, SE); 174 return Transform.TransformSubExpr(S); 175 } 176 177 const SCEV *llvm::normalizeForPostIncUse(const SCEV *S, 178 const PostIncLoopSet &Loops, 179 ScalarEvolution &SE) { 180 auto Pred = [&](const SCEVAddRecExpr *AR) { 181 return Loops.count(AR->getLoop()); 182 }; 183 return TransformForPostIncUse(Normalize, S, Pred, SE); 184 } 185 186 const SCEV *llvm::normalizeForPostIncUseIf(const SCEV *S, NormalizePredTy Pred, 187 ScalarEvolution &SE) { 188 return TransformForPostIncUse(Normalize, S, Pred, SE); 189 } 190 191 const SCEV *llvm::denormalizeForPostIncUse(const SCEV *S, 192 const PostIncLoopSet &Loops, 193 ScalarEvolution &SE) { 194 auto Pred = [&](const SCEVAddRecExpr *AR) { 195 return Loops.count(AR->getLoop()); 196 }; 197 return TransformForPostIncUse(Denormalize, S, Pred, SE); 198 } 199