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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/LoopInfo.h"
+#include "llvm/Analysis/LoopPass.h"
+#include "llvm/Analysis/ScalarEvolutionExpressions.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;
+static RegisterPass<IVUsers>
+X("iv-users", "Induction Variable Users", false, true);
+
+Pass *llvm::createIVUsersPass() {
+ return new IVUsers();
+}
+
+/// containsAddRecFromDifferentLoop - Determine whether expression S involves a
+/// subexpression that is an AddRec from a loop other than L. An outer loop
+/// of L is OK, but not an inner loop nor a disjoint loop.
+static bool containsAddRecFromDifferentLoop(SCEVHandle S, Loop *L) {
+ // This is very common, put it first.
+ if (isa<SCEVConstant>(S))
+ return false;
+ if (const SCEVCommutativeExpr *AE = dyn_cast<SCEVCommutativeExpr>(S)) {
+ for (unsigned int i=0; i< AE->getNumOperands(); i++)
+ if (containsAddRecFromDifferentLoop(AE->getOperand(i), L))
+ return true;
+ return false;
+ }
+ if (const SCEVAddRecExpr *AE = dyn_cast<SCEVAddRecExpr>(S)) {
+ if (const Loop *newLoop = AE->getLoop()) {
+ if (newLoop == L)
+ return false;
+ // if newLoop is an outer loop of L, this is OK.
+ if (!LoopInfoBase<BasicBlock>::isNotAlreadyContainedIn(L, newLoop))
+ return false;
+ }
+ return true;
+ }
+ if (const SCEVUDivExpr *DE = dyn_cast<SCEVUDivExpr>(S))
+ return containsAddRecFromDifferentLoop(DE->getLHS(), L) ||
+ containsAddRecFromDifferentLoop(DE->getRHS(), L);
+#if 0
+ // SCEVSDivExpr has been backed out temporarily, but will be back; we'll
+ // need this when it is.
+ if (const SCEVSDivExpr *DE = dyn_cast<SCEVSDivExpr>(S))
+ return containsAddRecFromDifferentLoop(DE->getLHS(), L) ||
+ containsAddRecFromDifferentLoop(DE->getRHS(), L);
+#endif
+ if (const SCEVCastExpr *CE = dyn_cast<SCEVCastExpr>(S))
+ return containsAddRecFromDifferentLoop(CE->getOperand(), L);
+ return false;
+}
+
+/// getSCEVStartAndStride - Compute the start and stride of this expression,
+/// returning false if the expression is not a start/stride pair, or true if it
+/// is. The stride must be a loop invariant expression, but the start may be
+/// a mix of loop invariant and loop variant expressions. The start cannot,
+/// however, contain an AddRec from a different loop, unless that loop is an
+/// outer loop of the current loop.
+static bool getSCEVStartAndStride(const SCEVHandle &SH, Loop *L, Loop *UseLoop,
+ SCEVHandle &Start, SCEVHandle &Stride,
+ bool &isSigned,
+ ScalarEvolution *SE, DominatorTree *DT) {
+ SCEVHandle TheAddRec = Start; // Initialize to zero.
+ bool isSExt = false;
+ bool isZExt = false;
+
+ // If the outer level is an AddExpr, the operands are all start values except
+ // for a nested AddRecExpr.
+ if (const SCEVAddExpr *AE = dyn_cast<SCEVAddExpr>(SH)) {
+ for (unsigned i = 0, e = AE->getNumOperands(); i != e; ++i)
+ if (const SCEVAddRecExpr *AddRec =
+ dyn_cast<SCEVAddRecExpr>(AE->getOperand(i))) {
+ if (AddRec->getLoop() == L)
+ TheAddRec = SE->getAddExpr(AddRec, TheAddRec);
+ else
+ return false; // Nested IV of some sort?
+ } else {
+ Start = SE->getAddExpr(Start, AE->getOperand(i));
+ }
+
+ } else if (const SCEVZeroExtendExpr *Z = dyn_cast<SCEVZeroExtendExpr>(SH)) {
+ TheAddRec = Z->getOperand();
+ isZExt = true;
+ } else if (const SCEVSignExtendExpr *S = dyn_cast<SCEVSignExtendExpr>(SH)) {
+ TheAddRec = S->getOperand();
+ isSExt = true;
+ } else if (isa<SCEVAddRecExpr>(SH)) {
+ TheAddRec = SH;
+ } else {
+ return false; // not analyzable.
+ }
+
+ const SCEVAddRecExpr *AddRec = dyn_cast<SCEVAddRecExpr>(TheAddRec);
+ if (!AddRec || AddRec->getLoop() != L) return false;
+
+ // Use getSCEVAtScope to attempt to simplify other loops out of
+ // the picture.
+ SCEVHandle AddRecStart = AddRec->getStart();
+ SCEVHandle BetterAddRecStart = SE->getSCEVAtScope(AddRecStart, UseLoop);
+ if (!isa<SCEVCouldNotCompute>(BetterAddRecStart))
+ AddRecStart = BetterAddRecStart;
+
+ // FIXME: If Start contains an SCEVAddRecExpr from a different loop, other
+ // than an outer loop of the current loop, reject it. LSR has no concept of
+ // operating on more than one loop at a time so don't confuse it with such
+ // expressions.
+ if (containsAddRecFromDifferentLoop(AddRecStart, L))
+ return false;
+
+ if (isSExt || isZExt)
+ Start = SE->getTruncateExpr(Start, AddRec->getType());
+
+ Start = SE->getAddExpr(Start, AddRecStart);
+
+ if (!isa<SCEVConstant>(AddRec->getStepRecurrence(*SE))) {
+ // If stride is an instruction, make sure it dominates the loop preheader.
+ // Otherwise we could end up with a use before def situation.
+ BasicBlock *Preheader = L->getLoopPreheader();
+ if (!AddRec->getStepRecurrence(*SE)->dominates(Preheader, DT))
+ return false;
+
+ DOUT << "[" << L->getHeader()->getName()
+ << "] Variable stride: " << *AddRec << "\n";
+ }
+
+ Stride = AddRec->getStepRecurrence(*SE);
+ isSigned = isSExt;
+ return true;
+}
+
+/// IVUseShouldUsePostIncValue - We have discovered a "User" of an IV expression
+/// and now we need to decide whether the user should use the preinc or post-inc
+/// value. If this user should use the post-inc version of the IV, return true.
+///
+/// Choosing wrong here can break dominance properties (if we choose to use the
+/// post-inc value when we cannot) or it can end up adding extra live-ranges to
+/// the loop, resulting in reg-reg copies (if we use the pre-inc value when we
+/// should use the post-inc value).
+static bool IVUseShouldUsePostIncValue(Instruction *User, Instruction *IV,
+ Loop *L, LoopInfo *LI, DominatorTree *DT,
+ Pass *P) {
+ // If the user is in the loop, use the preinc value.
+ if (L->contains(User->getParent())) return false;
+
+ BasicBlock *LatchBlock = L->getLoopLatch();
+
+ // Ok, the user is outside of the loop. If it is dominated by the latch
+ // block, use the post-inc value.
+ if (DT->dominates(LatchBlock, User->getParent()))
+ return true;
+
+ // There is one case we have to be careful of: PHI nodes. These little guys
+ // can live in blocks that are not dominated by the latch block, but (since
+ // their uses occur in the predecessor block, not the block the PHI lives in)
+ // should still use the post-inc value. Check for this case now.
+ PHINode *PN = dyn_cast<PHINode>(User);
+ if (!PN) return false; // not a phi, not dominated by latch block.
+
+ // Look at all of the uses of IV by the PHI node. If any use corresponds to
+ // a block that is not dominated by the latch block, give up and use the
+ // preincremented value.
+ unsigned NumUses = 0;
+ for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
+ if (PN->getIncomingValue(i) == IV) {
+ ++NumUses;
+ if (!DT->dominates(LatchBlock, PN->getIncomingBlock(i)))
+ return false;
+ }
+
+ // Okay, all uses of IV by PN are in predecessor blocks that really are
+ // dominated by the latch block. Use the post-incremented value.
+ return true;
+}
+
+/// AddUsersIfInteresting - 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::AddUsersIfInteresting(Instruction *I) {
+ 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.
+ if (SE->getTypeSizeInBits(I->getType()) > 64)
+ return false;
+
+ if (!Processed.insert(I))
+ return true; // Instruction already handled.
+
+ // Get the symbolic expression for this instruction.
+ SCEVHandle ISE = SE->getSCEV(I);
+ if (isa<SCEVCouldNotCompute>(ISE)) return false;
+
+ // Get the start and stride for this expression.
+ Loop *UseLoop = LI->getLoopFor(I->getParent());
+ SCEVHandle Start = SE->getIntegerSCEV(0, ISE->getType());
+ SCEVHandle Stride = Start;
+ bool isSigned = false; // Arbitrary initial value - pacifies compiler.
+
+ if (!getSCEVStartAndStride(ISE, L, UseLoop, Start, Stride, isSigned, SE, DT))
+ return false; // Non-reducible symbolic expression, bail out.
+
+ 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;
+
+ // 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 ouside 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) ||
+ !AddUsersIfInteresting(User)) {
+ DOUT << "FOUND USER in other loop: " << *User
+ << " OF SCEV: " << *ISE << "\n";
+ AddUserToIVUsers = true;
+ }
+ } else if (Processed.count(User) ||
+ !AddUsersIfInteresting(User)) {
+ DOUT << "FOUND USER: " << *User
+ << " OF SCEV: " << *ISE << "\n";
+ AddUserToIVUsers = true;
+ }
+
+ if (AddUserToIVUsers) {
+ IVUsersOfOneStride *StrideUses = IVUsesByStride[Stride];
+ if (!StrideUses) { // First occurrence of this stride?
+ StrideOrder.push_back(Stride);
+ StrideUses = new IVUsersOfOneStride(Stride);
+ IVUses.push_back(StrideUses);
+ IVUsesByStride[Stride] = StrideUses;
+ }
+
+ // Okay, we found a user that we cannot reduce. Analyze the instruction
+ // and decide what to do with it. If we are a use inside of the loop, use
+ // the value before incrementation, otherwise use it after incrementation.
+ if (IVUseShouldUsePostIncValue(User, I, L, LI, DT, this)) {
+ // The value used will be incremented by the stride more than we are
+ // expecting, so subtract this off.
+ SCEVHandle NewStart = SE->getMinusSCEV(Start, Stride);
+ StrideUses->addUser(NewStart, User, I, isSigned);
+ StrideUses->Users.back().setIsUseOfPostIncrementedValue(true);
+ DOUT << " USING POSTINC SCEV, START=" << *NewStart<< "\n";
+ } else {
+ StrideUses->addUser(Start, User, I, isSigned);
+ }
+ }
+ }
+ return true;
+}
+
+IVUsers::IVUsers()
+ : LoopPass(&ID) {
+}
+
+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>();
+
+ // 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)
+ AddUsersIfInteresting(I);
+
+ return false;
+}
+
+/// getReplacementExpr - Return a SCEV expression which computes the
+/// value of the OperandValToReplace of the given IVStrideUse.
+SCEVHandle IVUsers::getReplacementExpr(const IVStrideUse &U) const {
+ const Type *UseTy = U.getOperandValToReplace()->getType();
+ // Start with zero.
+ SCEVHandle RetVal = SE->getIntegerSCEV(0, U.getParent()->Stride->getType());
+ // Create the basic add recurrence.
+ RetVal = SE->getAddRecExpr(RetVal, U.getParent()->Stride, L);
+ // Add the offset in a separate step, because it may be loop-variant.
+ RetVal = SE->getAddExpr(RetVal, U.getOffset());
+ // For uses of post-incremented values, add an extra stride to compute
+ // the actual replacement value.
+ if (U.isUseOfPostIncrementedValue())
+ RetVal = SE->getAddExpr(RetVal, U.getParent()->Stride);
+ // Evaluate the expression out of the loop, if possible.
+ if (!L->contains(U.getUser()->getParent())) {
+ SCEVHandle ExitVal = SE->getSCEVAtScope(RetVal, L->getParentLoop());
+ if (!isa<SCEVCouldNotCompute>(ExitVal) && ExitVal->isLoopInvariant(L))
+ RetVal = ExitVal;
+ }
+ // Promote the result to the type of the use.
+ if (SE->getTypeSizeInBits(RetVal->getType()) !=
+ SE->getTypeSizeInBits(UseTy)) {
+ if (U.isSigned())
+ RetVal = SE->getSignExtendExpr(RetVal, UseTy);
+ else
+ RetVal = SE->getZeroExtendExpr(RetVal, UseTy);
+ }
+ return RetVal;
+}
+
+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 (unsigned Stride = 0, e = StrideOrder.size(); Stride != e; ++Stride) {
+ std::map<SCEVHandle, IVUsersOfOneStride*>::const_iterator SI =
+ IVUsesByStride.find(StrideOrder[Stride]);
+ assert(SI != IVUsesByStride.end() && "Stride doesn't exist!");
+ OS << " Stride " << *SI->first->getType() << " " << *SI->first << ":\n";
+
+ for (ilist<IVStrideUse>::const_iterator UI = SI->second->Users.begin(),
+ E = SI->second->Users.end(); UI != E; ++UI) {
+ OS << " ";
+ WriteAsOperand(OS, UI->getOperandValToReplace(), false);
+ OS << " = ";
+ OS << *getReplacementExpr(*UI);
+ if (UI->isUseOfPostIncrementedValue())
+ OS << " (post-inc)";
+ OS << " in ";
+ UI->getUser()->print(OS);
+ }
+ }
+}
+
+void IVUsers::print(std::ostream &o, const Module *M) const {
+ raw_os_ostream OS(o);
+ print(OS, M);
+}
+
+void IVUsers::dump() const {
+ print(errs());
+}
+
+void IVUsers::releaseMemory() {
+ IVUsesByStride.clear();
+ StrideOrder.clear();
+ Processed.clear();
+}
+
+void IVStrideUse::deleted() {
+ // Remove this user from the list.
+ Parent->Users.erase(this);
+ // this now dangles!
+}
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