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+//===- IVUsers.cpp - Induction Variable Users -------------------*- C++ -*-===//
+//
+// The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements bookkeeping for "interesting" users of expressions
+// computed from induction variables.
+//
+//===----------------------------------------------------------------------===//
+
+#define DEBUG_TYPE "iv-users"
+#include "llvm/Analysis/IVUsers.h"
+#include "llvm/Constants.h"
+#include "llvm/Instructions.h"
+#include "llvm/Type.h"
+#include "llvm/DerivedTypes.h"
+#include "llvm/Analysis/Dominators.h"
+#include "llvm/Analysis/LoopPass.h"
+#include "llvm/Analysis/ScalarEvolutionExpressions.h"
+#include "llvm/Target/TargetData.h"
+#include "llvm/Assembly/Writer.h"
+#include "llvm/ADT/STLExtras.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/raw_ostream.h"
+#include <algorithm>
+using namespace llvm;
+
+char IVUsers::ID = 0;
+INITIALIZE_PASS_BEGIN(IVUsers, "iv-users",
+ "Induction Variable Users", false, true)
+INITIALIZE_PASS_DEPENDENCY(LoopInfo)
+INITIALIZE_PASS_DEPENDENCY(DominatorTree)
+INITIALIZE_PASS_DEPENDENCY(ScalarEvolution)
+INITIALIZE_PASS_END(IVUsers, "iv-users",
+ "Induction Variable Users", false, true)
+
+Pass *llvm::createIVUsersPass() {
+ return new IVUsers();
+}
+
+/// isInteresting - Test whether the given expression is "interesting" when
+/// used by the given expression, within the context of analyzing the
+/// given loop.
+static bool isInteresting(const SCEV *S, const Instruction *I, const Loop *L,
+ ScalarEvolution *SE, LoopInfo *LI) {
+ // An addrec is interesting if it's affine or if it has an interesting start.
+ if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) {
+ // Keep things simple. Don't touch loop-variant strides unless they're
+ // only used outside the loop and we can simplify them.
+ if (AR->getLoop() == L)
+ return AR->isAffine() ||
+ (!L->contains(I) &&
+ SE->getSCEVAtScope(AR, LI->getLoopFor(I->getParent())) != AR);
+ // Otherwise recurse to see if the start value is interesting, and that
+ // the step value is not interesting, since we don't yet know how to
+ // do effective SCEV expansions for addrecs with interesting steps.
+ return isInteresting(AR->getStart(), I, L, SE, LI) &&
+ !isInteresting(AR->getStepRecurrence(*SE), I, L, SE, LI);
+ }
+
+ // An add is interesting if exactly one of its operands is interesting.
+ if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) {
+ bool AnyInterestingYet = false;
+ for (SCEVAddExpr::op_iterator OI = Add->op_begin(), OE = Add->op_end();
+ OI != OE; ++OI)
+ if (isInteresting(*OI, I, L, SE, LI)) {
+ if (AnyInterestingYet)
+ return false;
+ AnyInterestingYet = true;
+ }
+ return AnyInterestingYet;
+ }
+
+ // Nothing else is interesting here.
+ return false;
+}
+
+/// Return true if all loop headers that dominate this block are in simplified
+/// form.
+static bool isSimplifiedLoopNest(BasicBlock *BB, const DominatorTree *DT,
+ const LoopInfo *LI,
+ SmallPtrSet<Loop*,16> &SimpleLoopNests) {
+ Loop *NearestLoop = 0;
+ for (DomTreeNode *Rung = DT->getNode(BB);
+ Rung; Rung = Rung->getIDom()) {
+ BasicBlock *DomBB = Rung->getBlock();
+ Loop *DomLoop = LI->getLoopFor(DomBB);
+ if (DomLoop && DomLoop->getHeader() == DomBB) {
+ // If the domtree walk reaches a loop with no preheader, return false.
+ if (!DomLoop->isLoopSimplifyForm())
+ return false;
+ // If we have already checked this loop nest, stop checking.
+ if (SimpleLoopNests.count(DomLoop))
+ break;
+ // If we have not already checked this loop nest, remember the loop
+ // header nearest to BB. The nearest loop may not contain BB.
+ if (!NearestLoop)
+ NearestLoop = DomLoop;
+ }
+ }
+ if (NearestLoop)
+ SimpleLoopNests.insert(NearestLoop);
+ return true;
+}
+
+/// AddUsersImpl - Inspect the specified instruction. If it is a
+/// reducible SCEV, recursively add its users to the IVUsesByStride set and
+/// return true. Otherwise, return false.
+bool IVUsers::AddUsersImpl(Instruction *I,
+ SmallPtrSet<Loop*,16> &SimpleLoopNests) {
+ // Add this IV user to the Processed set before returning false to ensure that
+ // all IV users are members of the set. See IVUsers::isIVUserOrOperand.
+ if (!Processed.insert(I))
+ return true; // Instruction already handled.
+
+ if (!SE->isSCEVable(I->getType()))
+ return false; // Void and FP expressions cannot be reduced.
+
+ // LSR is not APInt clean, do not touch integers bigger than 64-bits.
+ // Also avoid creating IVs of non-native types. For example, we don't want a
+ // 64-bit IV in 32-bit code just because the loop has one 64-bit cast.
+ uint64_t Width = SE->getTypeSizeInBits(I->getType());
+ if (Width > 64 || (TD && !TD->isLegalInteger(Width)))
+ return false;
+
+ // Get the symbolic expression for this instruction.
+ const SCEV *ISE = SE->getSCEV(I);
+
+ // If we've come to an uninteresting expression, stop the traversal and
+ // call this a user.
+ if (!isInteresting(ISE, I, L, SE, LI))
+ return false;
+
+ SmallPtrSet<Instruction *, 4> UniqueUsers;
+ for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
+ UI != E; ++UI) {
+ Instruction *User = cast<Instruction>(*UI);
+ if (!UniqueUsers.insert(User))
+ continue;
+
+ // Do not infinitely recurse on PHI nodes.
+ if (isa<PHINode>(User) && Processed.count(User))
+ continue;
+
+ // Only consider IVUsers that are dominated by simplified loop
+ // headers. Otherwise, SCEVExpander will crash.
+ BasicBlock *UseBB = User->getParent();
+ // A phi's use is live out of its predecessor block.
+ if (PHINode *PHI = dyn_cast<PHINode>(User)) {
+ unsigned OperandNo = UI.getOperandNo();
+ unsigned ValNo = PHINode::getIncomingValueNumForOperand(OperandNo);
+ UseBB = PHI->getIncomingBlock(ValNo);
+ }
+ if (!isSimplifiedLoopNest(UseBB, DT, LI, SimpleLoopNests))
+ return false;
+
+ // Descend recursively, but not into PHI nodes outside the current loop.
+ // It's important to see the entire expression outside the loop to get
+ // choices that depend on addressing mode use right, although we won't
+ // consider references outside the loop in all cases.
+ // If User is already in Processed, we don't want to recurse into it again,
+ // but do want to record a second reference in the same instruction.
+ bool AddUserToIVUsers = false;
+ if (LI->getLoopFor(User->getParent()) != L) {
+ if (isa<PHINode>(User) || Processed.count(User) ||
+ !AddUsersImpl(User, SimpleLoopNests)) {
+ DEBUG(dbgs() << "FOUND USER in other loop: " << *User << '\n'
+ << " OF SCEV: " << *ISE << '\n');
+ AddUserToIVUsers = true;
+ }
+ } else if (Processed.count(User) || !AddUsersImpl(User, SimpleLoopNests)) {
+ DEBUG(dbgs() << "FOUND USER: " << *User << '\n'
+ << " OF SCEV: " << *ISE << '\n');
+ AddUserToIVUsers = true;
+ }
+
+ if (AddUserToIVUsers) {
+ // Okay, we found a user that we cannot reduce.
+ IVUses.push_back(new IVStrideUse(this, User, I));
+ IVStrideUse &NewUse = IVUses.back();
+ // Autodetect the post-inc loop set, populating NewUse.PostIncLoops.
+ // The regular return value here is discarded; instead of recording
+ // it, we just recompute it when we need it.
+ ISE = TransformForPostIncUse(NormalizeAutodetect,
+ ISE, User, I,
+ NewUse.PostIncLoops,
+ *SE, *DT);
+ DEBUG(if (SE->getSCEV(I) != ISE)
+ dbgs() << " NORMALIZED TO: " << *ISE << '\n');
+ }
+ }
+ return true;
+}
+
+bool IVUsers::AddUsersIfInteresting(Instruction *I) {
+ // SCEVExpander can only handle users that are dominated by simplified loop
+ // entries. Keep track of all loops that are only dominated by other simple
+ // loops so we don't traverse the domtree for each user.
+ SmallPtrSet<Loop*,16> SimpleLoopNests;
+
+ return AddUsersImpl(I, SimpleLoopNests);
+}
+
+IVStrideUse &IVUsers::AddUser(Instruction *User, Value *Operand) {
+ IVUses.push_back(new IVStrideUse(this, User, Operand));
+ return IVUses.back();
+}
+
+IVUsers::IVUsers()
+ : LoopPass(ID) {
+ initializeIVUsersPass(*PassRegistry::getPassRegistry());
+}
+
+void IVUsers::getAnalysisUsage(AnalysisUsage &AU) const {
+ AU.addRequired<LoopInfo>();
+ AU.addRequired<DominatorTree>();
+ AU.addRequired<ScalarEvolution>();
+ AU.setPreservesAll();
+}
+
+bool IVUsers::runOnLoop(Loop *l, LPPassManager &LPM) {
+
+ L = l;
+ LI = &getAnalysis<LoopInfo>();
+ DT = &getAnalysis<DominatorTree>();
+ SE = &getAnalysis<ScalarEvolution>();
+ TD = getAnalysisIfAvailable<TargetData>();
+
+ // Find all uses of induction variables in this loop, and categorize
+ // them by stride. Start by finding all of the PHI nodes in the header for
+ // this loop. If they are induction variables, inspect their uses.
+ for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ++I)
+ (void)AddUsersIfInteresting(I);
+
+ return false;
+}
+
+void IVUsers::print(raw_ostream &OS, const Module *M) const {
+ OS << "IV Users for loop ";
+ WriteAsOperand(OS, L->getHeader(), false);
+ if (SE->hasLoopInvariantBackedgeTakenCount(L)) {
+ OS << " with backedge-taken count "
+ << *SE->getBackedgeTakenCount(L);
+ }
+ OS << ":\n";
+
+ for (ilist<IVStrideUse>::const_iterator UI = IVUses.begin(),
+ E = IVUses.end(); UI != E; ++UI) {
+ OS << " ";
+ WriteAsOperand(OS, UI->getOperandValToReplace(), false);
+ OS << " = " << *getReplacementExpr(*UI);
+ for (PostIncLoopSet::const_iterator
+ I = UI->PostIncLoops.begin(),
+ E = UI->PostIncLoops.end(); I != E; ++I) {
+ OS << " (post-inc with loop ";
+ WriteAsOperand(OS, (*I)->getHeader(), false);
+ OS << ")";
+ }
+ OS << " in ";
+ UI->getUser()->print(OS);
+ OS << '\n';
+ }
+}
+
+void IVUsers::dump() const {
+ print(dbgs());
+}
+
+void IVUsers::releaseMemory() {
+ Processed.clear();
+ IVUses.clear();
+}
+
+/// getReplacementExpr - Return a SCEV expression which computes the
+/// value of the OperandValToReplace.
+const SCEV *IVUsers::getReplacementExpr(const IVStrideUse &IU) const {
+ return SE->getSCEV(IU.getOperandValToReplace());
+}
+
+/// getExpr - Return the expression for the use.
+const SCEV *IVUsers::getExpr(const IVStrideUse &IU) const {
+ return
+ TransformForPostIncUse(Normalize, getReplacementExpr(IU),
+ IU.getUser(), IU.getOperandValToReplace(),
+ const_cast<PostIncLoopSet &>(IU.getPostIncLoops()),
+ *SE, *DT);
+}
+
+static const SCEVAddRecExpr *findAddRecForLoop(const SCEV *S, const Loop *L) {
+ if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) {
+ if (AR->getLoop() == L)
+ return AR;
+ return findAddRecForLoop(AR->getStart(), L);
+ }
+
+ if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) {
+ for (SCEVAddExpr::op_iterator I = Add->op_begin(), E = Add->op_end();
+ I != E; ++I)
+ if (const SCEVAddRecExpr *AR = findAddRecForLoop(*I, L))
+ return AR;
+ return 0;
+ }
+
+ return 0;
+}
+
+const SCEV *IVUsers::getStride(const IVStrideUse &IU, const Loop *L) const {
+ if (const SCEVAddRecExpr *AR = findAddRecForLoop(getExpr(IU), L))
+ return AR->getStepRecurrence(*SE);
+ return 0;
+}
+
+void IVStrideUse::transformToPostInc(const Loop *L) {
+ PostIncLoops.insert(L);
+}
+
+void IVStrideUse::deleted() {
+ // Remove this user from the list.
+ Parent->Processed.erase(this->getUser());
+ Parent->IVUses.erase(this);
+ // this now dangles!
+}
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