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//===- ScalarEvolutionNormalization.cpp - See below -------------*- C++ -*-===//
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// The LLVM Compiler Infrastructure
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//===----------------------------------------------------------------------===//
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// This file implements utilities for working with "normalized" expressions.
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// See the comments at the top of ScalarEvolutionNormalization.h for details.
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//===----------------------------------------------------------------------===//
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#include "llvm/Analysis/Dominators.h"
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#include "llvm/Analysis/LoopInfo.h"
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#include "llvm/Analysis/ScalarEvolutionExpressions.h"
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#include "llvm/Analysis/ScalarEvolutionNormalization.h"
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/// IVUseShouldUsePostIncValue - We have discovered a "User" of an IV expression
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/// and now we need to decide whether the user should use the preinc or post-inc
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/// value. If this user should use the post-inc version of the IV, return true.
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/// Choosing wrong here can break dominance properties (if we choose to use the
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/// post-inc value when we cannot) or it can end up adding extra live-ranges to
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/// the loop, resulting in reg-reg copies (if we use the pre-inc value when we
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/// should use the post-inc value).
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static bool IVUseShouldUsePostIncValue(Instruction *User, Value *Operand,
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const Loop *L, DominatorTree *DT) {
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// If the user is in the loop, use the preinc value.
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if (L->contains(User)) return false;
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BasicBlock *LatchBlock = L->getLoopLatch();
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// Ok, the user is outside of the loop. If it is dominated by the latch
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// block, use the post-inc value.
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if (DT->dominates(LatchBlock, User->getParent()))
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// There is one case we have to be careful of: PHI nodes. These little guys
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// can live in blocks that are not dominated by the latch block, but (since
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// their uses occur in the predecessor block, not the block the PHI lives in)
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// should still use the post-inc value. Check for this case now.
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PHINode *PN = dyn_cast<PHINode>(User);
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if (!PN || !Operand) return false; // not a phi, not dominated by latch block.
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// Look at all of the uses of Operand by the PHI node. If any use corresponds
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// to a block that is not dominated by the latch block, give up and use the
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// preincremented value.
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for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
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if (PN->getIncomingValue(i) == Operand &&
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!DT->dominates(LatchBlock, PN->getIncomingBlock(i)))
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// Okay, all uses of Operand by PN are in predecessor blocks that really are
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// dominated by the latch block. Use the post-incremented value.
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const SCEV *llvm::TransformForPostIncUse(TransformKind Kind,
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Value *OperandValToReplace,
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PostIncLoopSet &Loops,
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if (isa<SCEVConstant>(S) || isa<SCEVUnknown>(S))
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if (const SCEVCastExpr *X = dyn_cast<SCEVCastExpr>(S)) {
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const SCEV *O = X->getOperand();
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const SCEV *N = TransformForPostIncUse(Kind, O, User, OperandValToReplace,
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switch (S->getSCEVType()) {
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case scZeroExtend: return SE.getZeroExtendExpr(N, S->getType());
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case scSignExtend: return SE.getSignExtendExpr(N, S->getType());
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case scTruncate: return SE.getTruncateExpr(N, S->getType());
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default: llvm_unreachable("Unexpected SCEVCastExpr kind!");
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if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) {
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// An addrec. This is the interesting part.
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SmallVector<const SCEV *, 8> Operands;
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const Loop *L = AR->getLoop();
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// The addrec conceptually uses its operands at loop entry.
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Instruction *LUser = L->getHeader()->begin();
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// Transform each operand.
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for (SCEVNAryExpr::op_iterator I = AR->op_begin(), E = AR->op_end();
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const SCEV *N = TransformForPostIncUse(Kind, O, LUser, 0, Loops, SE, DT);
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Operands.push_back(N);
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const SCEV *Result = SE.getAddRecExpr(Operands, L);
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default: llvm_unreachable("Unexpected transform name!");
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case NormalizeAutodetect:
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if (IVUseShouldUsePostIncValue(User, OperandValToReplace, L, &DT)) {
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const SCEV *TransformedStep =
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TransformForPostIncUse(Kind, AR->getStepRecurrence(SE),
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User, OperandValToReplace, Loops, SE, DT);
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Result = SE.getMinusSCEV(Result, TransformedStep);
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// This assert is conceptually correct, but ScalarEvolution currently
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// sometimes fails to canonicalize two equal SCEVs to exactly the same
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// form. It's possibly a pessimization when this happens, but it isn't a
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// correctness problem, so disable this assert for now.
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assert(S == TransformForPostIncUse(Denormalize, Result,
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User, OperandValToReplace,
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"SCEV normalization is not invertible!");
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if (Loops.count(L)) {
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const SCEV *TransformedStep =
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TransformForPostIncUse(Kind, AR->getStepRecurrence(SE),
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User, OperandValToReplace, Loops, SE, DT);
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Result = SE.getMinusSCEV(Result, TransformedStep);
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// See the comment on the assert above.
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assert(S == TransformForPostIncUse(Denormalize, Result,
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User, OperandValToReplace,
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"SCEV normalization is not invertible!");
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Result = cast<SCEVAddRecExpr>(Result)->getPostIncExpr(SE);
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if (const SCEVNAryExpr *X = dyn_cast<SCEVNAryExpr>(S)) {
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SmallVector<const SCEV *, 8> Operands;
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bool Changed = false;
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// Transform each operand.
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for (SCEVNAryExpr::op_iterator I = X->op_begin(), E = X->op_end();
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const SCEV *N = TransformForPostIncUse(Kind, O, User, OperandValToReplace,
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Operands.push_back(N);
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// If any operand actually changed, return a transformed result.
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switch (S->getSCEVType()) {
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case scAddExpr: return SE.getAddExpr(Operands);
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case scMulExpr: return SE.getMulExpr(Operands);
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case scSMaxExpr: return SE.getSMaxExpr(Operands);
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case scUMaxExpr: return SE.getUMaxExpr(Operands);
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default: llvm_unreachable("Unexpected SCEVNAryExpr kind!");
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if (const SCEVUDivExpr *X = dyn_cast<SCEVUDivExpr>(S)) {
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const SCEV *LO = X->getLHS();
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const SCEV *RO = X->getRHS();
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const SCEV *LN = TransformForPostIncUse(Kind, LO, User, OperandValToReplace,
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const SCEV *RN = TransformForPostIncUse(Kind, RO, User, OperandValToReplace,
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if (LO != LN || RO != RN)
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return SE.getUDivExpr(LN, RN);
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llvm_unreachable("Unexpected SCEV kind!");