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//===- IVUsers.cpp - Induction Variable Users -------------------*- 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 bookkeeping for "interesting" users of expressions
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// computed from induction variables.
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//===----------------------------------------------------------------------===//
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#define DEBUG_TYPE "iv-users"
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#include "llvm/Analysis/IVUsers.h"
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#include "llvm/Constants.h"
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#include "llvm/Instructions.h"
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#include "llvm/Type.h"
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#include "llvm/DerivedTypes.h"
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#include "llvm/Analysis/Dominators.h"
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#include "llvm/Analysis/LoopPass.h"
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#include "llvm/Analysis/ScalarEvolutionExpressions.h"
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#include "llvm/ADT/STLExtras.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/raw_ostream.h"
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INITIALIZE_PASS(IVUsers, "iv-users", "Induction Variable Users", false, true);
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Pass *llvm::createIVUsersPass() {
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/// isInteresting - Test whether the given expression is "interesting" when
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/// used by the given expression, within the context of analyzing the
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static bool isInteresting(const SCEV *S, const Instruction *I, const Loop *L,
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ScalarEvolution *SE) {
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// An addrec is interesting if it's affine or if it has an interesting start.
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if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) {
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// Keep things simple. Don't touch loop-variant strides.
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if (AR->getLoop() == L)
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return AR->isAffine() || !L->contains(I);
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// Otherwise recurse to see if the start value is interesting, and that
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// the step value is not interesting, since we don't yet know how to
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// do effective SCEV expansions for addrecs with interesting steps.
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return isInteresting(AR->getStart(), I, L, SE) &&
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!isInteresting(AR->getStepRecurrence(*SE), I, L, SE);
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// An add is interesting if exactly one of its operands is interesting.
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if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) {
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bool AnyInterestingYet = false;
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for (SCEVAddExpr::op_iterator OI = Add->op_begin(), OE = Add->op_end();
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if (isInteresting(*OI, I, L, SE)) {
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if (AnyInterestingYet)
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AnyInterestingYet = true;
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return AnyInterestingYet;
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// Nothing else is interesting here.
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/// AddUsersIfInteresting - Inspect the specified instruction. If it is a
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/// reducible SCEV, recursively add its users to the IVUsesByStride set and
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/// return true. Otherwise, return false.
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bool IVUsers::AddUsersIfInteresting(Instruction *I) {
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if (!SE->isSCEVable(I->getType()))
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return false; // Void and FP expressions cannot be reduced.
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// LSR is not APInt clean, do not touch integers bigger than 64-bits.
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if (SE->getTypeSizeInBits(I->getType()) > 64)
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if (!Processed.insert(I))
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return true; // Instruction already handled.
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// Get the symbolic expression for this instruction.
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const SCEV *ISE = SE->getSCEV(I);
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// If we've come to an uninteresting expression, stop the traversal and
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if (!isInteresting(ISE, I, L, SE))
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SmallPtrSet<Instruction *, 4> UniqueUsers;
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for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
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Instruction *User = cast<Instruction>(*UI);
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if (!UniqueUsers.insert(User))
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// Do not infinitely recurse on PHI nodes.
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if (isa<PHINode>(User) && Processed.count(User))
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// Descend recursively, but not into PHI nodes outside the current loop.
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// It's important to see the entire expression outside the loop to get
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// choices that depend on addressing mode use right, although we won't
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// consider references outside the loop in all cases.
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// If User is already in Processed, we don't want to recurse into it again,
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// but do want to record a second reference in the same instruction.
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bool AddUserToIVUsers = false;
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if (LI->getLoopFor(User->getParent()) != L) {
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if (isa<PHINode>(User) || Processed.count(User) ||
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!AddUsersIfInteresting(User)) {
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DEBUG(dbgs() << "FOUND USER in other loop: " << *User << '\n'
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<< " OF SCEV: " << *ISE << '\n');
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AddUserToIVUsers = true;
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} else if (Processed.count(User) ||
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!AddUsersIfInteresting(User)) {
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DEBUG(dbgs() << "FOUND USER: " << *User << '\n'
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<< " OF SCEV: " << *ISE << '\n');
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AddUserToIVUsers = true;
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if (AddUserToIVUsers) {
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// Okay, we found a user that we cannot reduce.
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IVUses.push_back(new IVStrideUse(this, User, I));
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IVStrideUse &NewUse = IVUses.back();
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// Transform the expression into a normalized form.
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ISE = TransformForPostIncUse(NormalizeAutodetect,
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DEBUG(dbgs() << " NORMALIZED TO: " << *ISE << '\n');
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IVStrideUse &IVUsers::AddUser(Instruction *User, Value *Operand) {
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IVUses.push_back(new IVStrideUse(this, User, Operand));
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return IVUses.back();
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void IVUsers::getAnalysisUsage(AnalysisUsage &AU) const {
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AU.addRequired<LoopInfo>();
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AU.addRequired<DominatorTree>();
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AU.addRequired<ScalarEvolution>();
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AU.setPreservesAll();
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bool IVUsers::runOnLoop(Loop *l, LPPassManager &LPM) {
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LI = &getAnalysis<LoopInfo>();
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DT = &getAnalysis<DominatorTree>();
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SE = &getAnalysis<ScalarEvolution>();
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// Find all uses of induction variables in this loop, and categorize
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// them by stride. Start by finding all of the PHI nodes in the header for
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// this loop. If they are induction variables, inspect their uses.
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for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ++I)
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(void)AddUsersIfInteresting(I);
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void IVUsers::print(raw_ostream &OS, const Module *M) const {
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OS << "IV Users for loop ";
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WriteAsOperand(OS, L->getHeader(), false);
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if (SE->hasLoopInvariantBackedgeTakenCount(L)) {
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OS << " with backedge-taken count "
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<< *SE->getBackedgeTakenCount(L);
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for (ilist<IVStrideUse>::const_iterator UI = IVUses.begin(),
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E = IVUses.end(); UI != E; ++UI) {
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WriteAsOperand(OS, UI->getOperandValToReplace(), false);
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OS << " = " << *getReplacementExpr(*UI);
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for (PostIncLoopSet::const_iterator
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I = UI->PostIncLoops.begin(),
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E = UI->PostIncLoops.end(); I != E; ++I) {
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OS << " (post-inc with loop ";
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WriteAsOperand(OS, (*I)->getHeader(), false);
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UI->getUser()->print(OS);
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void IVUsers::dump() const {
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void IVUsers::releaseMemory() {
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/// getReplacementExpr - Return a SCEV expression which computes the
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/// value of the OperandValToReplace.
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const SCEV *IVUsers::getReplacementExpr(const IVStrideUse &IU) const {
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return SE->getSCEV(IU.getOperandValToReplace());
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/// getExpr - Return the expression for the use.
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const SCEV *IVUsers::getExpr(const IVStrideUse &IU) const {
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TransformForPostIncUse(Normalize, getReplacementExpr(IU),
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IU.getUser(), IU.getOperandValToReplace(),
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const_cast<PostIncLoopSet &>(IU.getPostIncLoops()),
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static const SCEVAddRecExpr *findAddRecForLoop(const SCEV *S, const Loop *L) {
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if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) {
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if (AR->getLoop() == L)
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return findAddRecForLoop(AR->getStart(), L);
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if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) {
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for (SCEVAddExpr::op_iterator I = Add->op_begin(), E = Add->op_end();
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if (const SCEVAddRecExpr *AR = findAddRecForLoop(*I, L))
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const SCEV *IVUsers::getStride(const IVStrideUse &IU, const Loop *L) const {
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if (const SCEVAddRecExpr *AR = findAddRecForLoop(getExpr(IU), L))
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return AR->getStepRecurrence(*SE);
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void IVStrideUse::transformToPostInc(const Loop *L) {
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PostIncLoops.insert(L);
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void IVStrideUse::deleted() {
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// Remove this user from the list.
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Parent->IVUses.erase(this);