| //===- 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/Assembly/AsmAnnotationWriter.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(); |
| } |
| |
| /// CollectSubexprs - Split S into subexpressions which can be pulled out into |
| /// separate registers. |
| static void CollectSubexprs(const SCEV *S, |
| SmallVectorImpl<const SCEV *> &Ops, |
| ScalarEvolution &SE) { |
| if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) { |
| // Break out add operands. |
| for (SCEVAddExpr::op_iterator I = Add->op_begin(), E = Add->op_end(); |
| I != E; ++I) |
| CollectSubexprs(*I, Ops, SE); |
| return; |
| } else if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) { |
| // Split a non-zero base out of an addrec. |
| if (!AR->getStart()->isZero()) { |
| CollectSubexprs(AR->getStart(), Ops, SE); |
| CollectSubexprs(SE.getAddRecExpr(SE.getIntegerSCEV(0, AR->getType()), |
| AR->getStepRecurrence(SE), |
| AR->getLoop()), Ops, SE); |
| return; |
| } |
| } |
| |
| // Otherwise use the value itself. |
| Ops.push_back(S); |
| } |
| |
| /// 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 SCEV *&SH, Loop *L, Loop *UseLoop, |
| const SCEV *&Start, const SCEV *&Stride, |
| ScalarEvolution *SE, DominatorTree *DT) { |
| const SCEV *TheAddRec = Start; // Initialize to zero. |
| |
| // 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))) |
| TheAddRec = SE->getAddExpr(AddRec, TheAddRec); |
| else |
| Start = SE->getAddExpr(Start, AE->getOperand(i)); |
| } else if (isa<SCEVAddRecExpr>(SH)) { |
| TheAddRec = SH; |
| } else { |
| return false; // not analyzable. |
| } |
| |
| // Break down TheAddRec into its component parts. |
| SmallVector<const SCEV *, 4> Subexprs; |
| CollectSubexprs(TheAddRec, Subexprs, *SE); |
| |
| // Look for an addrec on the current loop among the parts. |
| const SCEV *AddRecStride = 0; |
| for (SmallVectorImpl<const SCEV *>::iterator I = Subexprs.begin(), |
| E = Subexprs.end(); I != E; ++I) { |
| const SCEV *S = *I; |
| if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) |
| if (AR->getLoop() == L) { |
| *I = AR->getStart(); |
| AddRecStride = AR->getStepRecurrence(*SE); |
| break; |
| } |
| } |
| if (!AddRecStride) |
| return false; |
| |
| // Add up everything else into a start value (which may not be |
| // loop-invariant). |
| const SCEV *AddRecStart = SE->getAddExpr(Subexprs); |
| |
| // Use getSCEVAtScope to attempt to simplify other loops out of |
| // the picture. |
| AddRecStart = SE->getSCEVAtScope(AddRecStart, UseLoop); |
| |
| Start = SE->getAddExpr(Start, AddRecStart); |
| |
| // If stride is an instruction, make sure it properly dominates the header. |
| // Otherwise we could end up with a use before def situation. |
| if (!isa<SCEVConstant>(AddRecStride)) { |
| BasicBlock *Header = L->getHeader(); |
| if (!AddRecStride->properlyDominates(Header, DT)) |
| return false; |
| |
| DEBUG(dbgs() << "["; |
| WriteAsOperand(dbgs(), L->getHeader(), /*PrintType=*/false); |
| dbgs() << "] Variable stride: " << *AddRecStride << "\n"); |
| } |
| |
| Stride = AddRecStride; |
| 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, DominatorTree *DT) { |
| // If the user is in the loop, use the preinc value. |
| if (L->contains(User)) return false; |
| |
| BasicBlock *LatchBlock = L->getLoopLatch(); |
| if (!LatchBlock) |
| return false; |
| |
| // 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. |
| const SCEV *ISE = SE->getSCEV(I); |
| if (isa<SCEVCouldNotCompute>(ISE)) return false; |
| |
| // Get the start and stride for this expression. |
| Loop *UseLoop = LI->getLoopFor(I->getParent()); |
| const SCEV *Start = SE->getIntegerSCEV(0, ISE->getType()); |
| const SCEV *Stride = Start; |
| |
| if (!getSCEVStartAndStride(ISE, L, UseLoop, Start, Stride, SE, DT)) |
| return false; // Non-reducible symbolic expression, bail out. |
| |
| // Keep things simple. Don't touch loop-variant strides. |
| if (!Stride->isLoopInvariant(L) && L->contains(I)) |
| 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; |
| |
| // 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)) { |
| DEBUG(dbgs() << "FOUND USER in other loop: " << *User << '\n' |
| << " OF SCEV: " << *ISE << '\n'); |
| AddUserToIVUsers = true; |
| } |
| } else if (Processed.count(User) || |
| !AddUsersIfInteresting(User)) { |
| DEBUG(dbgs() << "FOUND USER: " << *User << '\n' |
| << " OF SCEV: " << *ISE << '\n'); |
| AddUserToIVUsers = true; |
| } |
| |
| if (AddUserToIVUsers) { |
| // 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, DT)) { |
| // The value used will be incremented by the stride more than we are |
| // expecting, so subtract this off. |
| const SCEV *NewStart = SE->getMinusSCEV(Start, Stride); |
| IVUses.push_back(new IVStrideUse(this, Stride, NewStart, User, I)); |
| IVUses.back().setIsUseOfPostIncrementedValue(true); |
| DEBUG(dbgs() << " USING POSTINC SCEV, START=" << *NewStart<< "\n"); |
| } else { |
| IVUses.push_back(new IVStrideUse(this, Stride, Start, User, I)); |
| } |
| } |
| } |
| return true; |
| } |
| |
| IVStrideUse &IVUsers::AddUser(const SCEV *Stride, const SCEV *Offset, |
| Instruction *User, Value *Operand) { |
| IVUses.push_back(new IVStrideUse(this, Stride, Offset, User, Operand)); |
| return IVUses.back(); |
| } |
| |
| 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. |
| const SCEV *IVUsers::getReplacementExpr(const IVStrideUse &U) const { |
| // Start with zero. |
| const SCEV *RetVal = SE->getIntegerSCEV(0, U.getStride()->getType()); |
| // Create the basic add recurrence. |
| RetVal = SE->getAddRecExpr(RetVal, U.getStride(), 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.getStride()); |
| return RetVal; |
| } |
| |
| /// getCanonicalExpr - Return a SCEV expression which computes the |
| /// value of the SCEV of the given IVStrideUse, ignoring the |
| /// isUseOfPostIncrementedValue flag. |
| const SCEV *IVUsers::getCanonicalExpr(const IVStrideUse &U) const { |
| // Start with zero. |
| const SCEV *RetVal = SE->getIntegerSCEV(0, U.getStride()->getType()); |
| // Create the basic add recurrence. |
| RetVal = SE->getAddRecExpr(RetVal, U.getStride(), L); |
| // Add the offset in a separate step, because it may be loop-variant. |
| RetVal = SE->getAddExpr(RetVal, U.getOffset()); |
| 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"; |
| |
| // Use a defualt AssemblyAnnotationWriter to suppress the default info |
| // comments, which aren't relevant here. |
| AssemblyAnnotationWriter Annotator; |
| for (ilist<IVStrideUse>::const_iterator UI = IVUses.begin(), |
| E = IVUses.end(); UI != E; ++UI) { |
| OS << " "; |
| WriteAsOperand(OS, UI->getOperandValToReplace(), false); |
| OS << " = " |
| << *getReplacementExpr(*UI); |
| if (UI->isUseOfPostIncrementedValue()) |
| OS << " (post-inc)"; |
| OS << " in "; |
| UI->getUser()->print(OS, &Annotator); |
| OS << '\n'; |
| } |
| } |
| |
| void IVUsers::dump() const { |
| print(dbgs()); |
| } |
| |
| void IVUsers::releaseMemory() { |
| Processed.clear(); |
| IVUses.clear(); |
| } |
| |
| void IVStrideUse::deleted() { |
| // Remove this user from the list. |
| Parent->IVUses.erase(this); |
| // this now dangles! |
| } |