1 //===- ScalarEvolutionNormalization.cpp - See below -------------*- 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 implements utilities for working with "normalized" expressions.
11 // See the comments at the top of ScalarEvolutionNormalization.h for details.
13 //===----------------------------------------------------------------------===//
15 #include "llvm/Analysis/Dominators.h"
16 #include "llvm/Analysis/LoopInfo.h"
17 #include "llvm/Analysis/ScalarEvolutionExpressions.h"
18 #include "llvm/Analysis/ScalarEvolutionNormalization.h"
21 /// IVUseShouldUsePostIncValue - We have discovered a "User" of an IV expression
22 /// and now we need to decide whether the user should use the preinc or post-inc
23 /// value. If this user should use the post-inc version of the IV, return true.
25 /// Choosing wrong here can break dominance properties (if we choose to use the
26 /// post-inc value when we cannot) or it can end up adding extra live-ranges to
27 /// the loop, resulting in reg-reg copies (if we use the pre-inc value when we
28 /// should use the post-inc value).
29 static bool IVUseShouldUsePostIncValue(Instruction *User, Value *Operand,
30 const Loop *L, DominatorTree *DT) {
31 // If the user is in the loop, use the preinc value.
32 if (L->contains(User)) return false;
34 BasicBlock *LatchBlock = L->getLoopLatch();
38 // Ok, the user is outside of the loop. If it is dominated by the latch
39 // block, use the post-inc value.
40 if (DT->dominates(LatchBlock, User->getParent()))
43 // There is one case we have to be careful of: PHI nodes. These little guys
44 // can live in blocks that are not dominated by the latch block, but (since
45 // their uses occur in the predecessor block, not the block the PHI lives in)
46 // should still use the post-inc value. Check for this case now.
47 PHINode *PN = dyn_cast<PHINode>(User);
48 if (!PN || !Operand) return false; // not a phi, not dominated by latch block.
50 // Look at all of the uses of Operand by the PHI node. If any use corresponds
51 // to a block that is not dominated by the latch block, give up and use the
52 // preincremented value.
53 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
54 if (PN->getIncomingValue(i) == Operand &&
55 !DT->dominates(LatchBlock, PN->getIncomingBlock(i)))
58 // Okay, all uses of Operand by PN are in predecessor blocks that really are
59 // dominated by the latch block. Use the post-incremented value.
63 const SCEV *llvm::TransformForPostIncUse(TransformKind Kind,
66 Value *OperandValToReplace,
67 PostIncLoopSet &Loops,
70 if (isa<SCEVConstant>(S) || isa<SCEVUnknown>(S))
73 if (const SCEVCastExpr *X = dyn_cast<SCEVCastExpr>(S)) {
74 const SCEV *O = X->getOperand();
75 const SCEV *N = TransformForPostIncUse(Kind, O, User, OperandValToReplace,
78 switch (S->getSCEVType()) {
79 case scZeroExtend: return SE.getZeroExtendExpr(N, S->getType());
80 case scSignExtend: return SE.getSignExtendExpr(N, S->getType());
81 case scTruncate: return SE.getTruncateExpr(N, S->getType());
82 default: llvm_unreachable("Unexpected SCEVCastExpr kind!");
87 if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) {
88 // An addrec. This is the interesting part.
89 SmallVector<const SCEV *, 8> Operands;
90 const Loop *L = AR->getLoop();
91 // The addrec conceptually uses its operands at loop entry.
92 Instruction *LUser = L->getHeader()->begin();
93 // Transform each operand.
94 for (SCEVNAryExpr::op_iterator I = AR->op_begin(), E = AR->op_end();
97 const SCEV *N = TransformForPostIncUse(Kind, O, LUser, 0, Loops, SE, DT);
98 Operands.push_back(N);
100 const SCEV *Result = SE.getAddRecExpr(Operands, L);
102 default: llvm_unreachable("Unexpected transform name!");
103 case NormalizeAutodetect:
104 if (IVUseShouldUsePostIncValue(User, OperandValToReplace, L, &DT)) {
105 const SCEV *TransformedStep =
106 TransformForPostIncUse(Kind, AR->getStepRecurrence(SE),
107 User, OperandValToReplace, Loops, SE, DT);
108 Result = SE.getMinusSCEV(Result, TransformedStep);
112 assert(S == TransformForPostIncUse(Denormalize, Result,
113 User, OperandValToReplace,
115 "SCEV normalization is not invertible!");
119 if (Loops.count(L)) {
120 const SCEV *TransformedStep =
121 TransformForPostIncUse(Kind, AR->getStepRecurrence(SE),
122 User, OperandValToReplace, Loops, SE, DT);
123 Result = SE.getMinusSCEV(Result, TransformedStep);
126 assert(S == TransformForPostIncUse(Denormalize, Result,
127 User, OperandValToReplace,
129 "SCEV normalization is not invertible!");
134 Result = cast<SCEVAddRecExpr>(Result)->getPostIncExpr(SE);
140 if (const SCEVNAryExpr *X = dyn_cast<SCEVNAryExpr>(S)) {
141 SmallVector<const SCEV *, 8> Operands;
142 bool Changed = false;
143 // Transform each operand.
144 for (SCEVNAryExpr::op_iterator I = X->op_begin(), E = X->op_end();
147 const SCEV *N = TransformForPostIncUse(Kind, O, User, OperandValToReplace,
150 Operands.push_back(N);
152 // If any operand actually changed, return a transformed result.
154 switch (S->getSCEVType()) {
155 case scAddExpr: return SE.getAddExpr(Operands);
156 case scMulExpr: return SE.getMulExpr(Operands);
157 case scSMaxExpr: return SE.getSMaxExpr(Operands);
158 case scUMaxExpr: return SE.getUMaxExpr(Operands);
159 default: llvm_unreachable("Unexpected SCEVNAryExpr kind!");
164 if (const SCEVUDivExpr *X = dyn_cast<SCEVUDivExpr>(S)) {
165 const SCEV *LO = X->getLHS();
166 const SCEV *RO = X->getRHS();
167 const SCEV *LN = TransformForPostIncUse(Kind, LO, User, OperandValToReplace,
169 const SCEV *RN = TransformForPostIncUse(Kind, RO, User, OperandValToReplace,
171 if (LO != LN || RO != RN)
172 return SE.getUDivExpr(LN, RN);
176 llvm_unreachable("Unexpected SCEV kind!");