X-Git-Url: http://demsky.eecs.uci.edu/git/?a=blobdiff_plain;f=lib%2FTransforms%2FScalar%2FLoopUnswitch.cpp;h=955622e0256c2274efb090c3a29dc113b950680a;hb=2a6a6457094e05e5f5ab34f90dbd25c13d61f8b5;hp=850be78f808be7c85b86b2ccc52f115904722c7f;hpb=e487abbfbf9fdef21e5216379b2e74436ef99c7b;p=oota-llvm.git diff --git a/lib/Transforms/Scalar/LoopUnswitch.cpp b/lib/Transforms/Scalar/LoopUnswitch.cpp index 850be78f808..955622e0256 100644 --- a/lib/Transforms/Scalar/LoopUnswitch.cpp +++ b/lib/Transforms/Scalar/LoopUnswitch.cpp @@ -2,8 +2,8 @@ // // The LLVM Compiler Infrastructure // -// This file was developed by the LLVM research group and is distributed under -// the University of Illinois Open Source License. See LICENSE.TXT for details. +// This file is distributed under the University of Illinois Open Source +// License. See LICENSE.TXT for details. // //===----------------------------------------------------------------------===// // @@ -29,102 +29,175 @@ #define DEBUG_TYPE "loop-unswitch" #include "llvm/Transforms/Scalar.h" #include "llvm/Constants.h" +#include "llvm/DerivedTypes.h" #include "llvm/Function.h" #include "llvm/Instructions.h" +#include "llvm/Analysis/ConstantFolding.h" #include "llvm/Analysis/LoopInfo.h" +#include "llvm/Analysis/LoopPass.h" +#include "llvm/Analysis/Dominators.h" #include "llvm/Transforms/Utils/Cloning.h" #include "llvm/Transforms/Utils/Local.h" +#include "llvm/Transforms/Utils/BasicBlockUtils.h" #include "llvm/ADT/Statistic.h" -#include "llvm/Support/Debug.h" +#include "llvm/ADT/SmallPtrSet.h" #include "llvm/Support/CommandLine.h" +#include "llvm/Support/Compiler.h" +#include "llvm/Support/Debug.h" #include -#include #include using namespace llvm; -namespace { - Statistic<> NumUnswitched("loop-unswitch", "Number of loops unswitched"); - cl::opt - Threshold("loop-unswitch-threshold", cl::desc("Max loop size to unswitch"), - cl::init(10), cl::Hidden); +STATISTIC(NumBranches, "Number of branches unswitched"); +STATISTIC(NumSwitches, "Number of switches unswitched"); +STATISTIC(NumSelects , "Number of selects unswitched"); +STATISTIC(NumTrivial , "Number of unswitches that are trivial"); +STATISTIC(NumSimplify, "Number of simplifications of unswitched code"); + +static cl::opt +Threshold("loop-unswitch-threshold", cl::desc("Max loop size to unswitch"), + cl::init(10), cl::Hidden); - class LoopUnswitch : public FunctionPass { +namespace { + class VISIBILITY_HIDDEN LoopUnswitch : public LoopPass { LoopInfo *LI; // Loop information + LPPassManager *LPM; + + // LoopProcessWorklist - Used to check if second loop needs processing + // after RewriteLoopBodyWithConditionConstant rewrites first loop. + std::vector LoopProcessWorklist; + SmallPtrSet UnswitchedVals; + + bool OptimizeForSize; + bool redoLoop; + + DominanceFrontier *DF; + DominatorTree *DT; + + /// LoopDF - Loop's dominance frontier. This set is a collection of + /// loop exiting blocks' DF member blocks. However this does set does not + /// includes basic blocks that are inside loop. + SmallPtrSet LoopDF; + + /// OrigLoopExitMap - This is used to map loop exiting block with + /// corresponding loop exit block, before updating CFG. + DenseMap OrigLoopExitMap; public: - virtual bool runOnFunction(Function &F); - bool visitLoop(Loop *L); + static char ID; // Pass ID, replacement for typeid + explicit LoopUnswitch(bool Os = false) : + LoopPass((intptr_t)&ID), OptimizeForSize(Os), redoLoop(false) {} + + bool runOnLoop(Loop *L, LPPassManager &LPM); + bool processLoop(Loop *L); /// This transformation requires natural loop information & requires that /// loop preheaders be inserted into the CFG... /// virtual void getAnalysisUsage(AnalysisUsage &AU) const { AU.addRequiredID(LoopSimplifyID); + AU.addPreservedID(LoopSimplifyID); AU.addRequired(); AU.addPreserved(); + AU.addRequiredID(LCSSAID); + AU.addPreservedID(LCSSAID); + AU.addPreserved(); + AU.addPreserved(); } private: - void VersionLoop(Value *LIC, Loop *L); - BasicBlock *SplitBlock(BasicBlock *BB, bool SplitAtTop); - void RewriteLoopBodyWithConditionConstant(Loop *L, Value *LIC, bool Val); - }; - RegisterOpt X("loop-unswitch", "Unswitch loops"); -} -FunctionPass *llvm::createLoopUnswitchPass() { return new LoopUnswitch(); } + /// RemoveLoopFromWorklist - If the specified loop is on the loop worklist, + /// remove it. + void RemoveLoopFromWorklist(Loop *L) { + std::vector::iterator I = std::find(LoopProcessWorklist.begin(), + LoopProcessWorklist.end(), L); + if (I != LoopProcessWorklist.end()) + LoopProcessWorklist.erase(I); + } -bool LoopUnswitch::runOnFunction(Function &F) { - bool Changed = false; - LI = &getAnalysis(); + /// Split all of the edges from inside the loop to their exit blocks. + /// Update the appropriate Phi nodes as we do so. + void SplitExitEdges(Loop *L, const SmallVector &ExitBlocks, + SmallVector &MiddleBlocks); - // Transform all the top-level loops. Copy the loop list so that the child - // can update the loop tree if it needs to delete the loop. - std::vector SubLoops(LI->begin(), LI->end()); - for (unsigned i = 0, e = SubLoops.size(); i != e; ++i) - Changed |= visitLoop(SubLoops[i]); + /// If BB's dominance frontier has a member that is not part of loop L then + /// remove it. Add NewDFMember in BB's dominance frontier. + void ReplaceLoopExternalDFMember(Loop *L, BasicBlock *BB, + BasicBlock *NewDFMember); + + bool UnswitchIfProfitable(Value *LoopCond, Constant *Val,Loop *L); + unsigned getLoopUnswitchCost(Loop *L, Value *LIC); + void UnswitchTrivialCondition(Loop *L, Value *Cond, Constant *Val, + BasicBlock *ExitBlock); + void UnswitchNontrivialCondition(Value *LIC, Constant *OnVal, Loop *L); - return Changed; + void RewriteLoopBodyWithConditionConstant(Loop *L, Value *LIC, + Constant *Val, bool isEqual); + + void EmitPreheaderBranchOnCondition(Value *LIC, Constant *Val, + BasicBlock *TrueDest, + BasicBlock *FalseDest, + Instruction *InsertPt); + + void SimplifyCode(std::vector &Worklist, Loop *L); + void RemoveBlockIfDead(BasicBlock *BB, + std::vector &Worklist, Loop *l); + void RemoveLoopFromHierarchy(Loop *L); + }; } +char LoopUnswitch::ID = 0; +static RegisterPass X("loop-unswitch", "Unswitch loops"); +LoopPass *llvm::createLoopUnswitchPass(bool Os) { + return new LoopUnswitch(Os); +} -/// InsertPHINodesForUsesOutsideLoop - If this instruction is used outside of -/// the specified loop, insert a PHI node in the appropriate exit block to merge -/// the values in the two different loop versions. -/// -/// Most values are not used outside of the loop they are defined in, so be -/// efficient for this case. -/// -static bool LoopValuesUsedOutsideLoop(Loop *L) { - // We will be doing lots of "loop contains block" queries. Loop::contains is - // linear time, use a set to speed this up. - std::set LoopBlocks; - - for (Loop::block_iterator BB = L->block_begin(), E = L->block_end(); - BB != E; ++BB) - LoopBlocks.insert(*BB); - - for (Loop::block_iterator BB = L->block_begin(), E = L->block_end(); - BB != E; ++BB) { - for (BasicBlock::iterator I = (*BB)->begin(), E = (*BB)->end(); I != E; ++I) - for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI != E; - ++UI) { - BasicBlock *UserBB = cast(*UI)->getParent(); - if (!LoopBlocks.count(UserBB)) - return true; - } - } - return false; +/// FindLIVLoopCondition - Cond is a condition that occurs in L. If it is +/// invariant in the loop, or has an invariant piece, return the invariant. +/// Otherwise, return null. +static Value *FindLIVLoopCondition(Value *Cond, Loop *L, bool &Changed) { + // Constants should be folded, not unswitched on! + if (isa(Cond)) return false; + + // TODO: Handle: br (VARIANT|INVARIANT). + // TODO: Hoist simple expressions out of loops. + if (L->isLoopInvariant(Cond)) return Cond; + + if (BinaryOperator *BO = dyn_cast(Cond)) + if (BO->getOpcode() == Instruction::And || + BO->getOpcode() == Instruction::Or) { + // If either the left or right side is invariant, we can unswitch on this, + // which will cause the branch to go away in one loop and the condition to + // simplify in the other one. + if (Value *LHS = FindLIVLoopCondition(BO->getOperand(0), L, Changed)) + return LHS; + if (Value *RHS = FindLIVLoopCondition(BO->getOperand(1), L, Changed)) + return RHS; + } + + return 0; } -bool LoopUnswitch::visitLoop(Loop *L) { +bool LoopUnswitch::runOnLoop(Loop *L, LPPassManager &LPM_Ref) { + LI = &getAnalysis(); + LPM = &LPM_Ref; + DF = getAnalysisToUpdate(); + DT = getAnalysisToUpdate(); + bool Changed = false; - // Recurse through all subloops before we process this loop. Copy the loop - // list so that the child can update the loop tree if it needs to delete the - // loop. - std::vector SubLoops(L->begin(), L->end()); - for (unsigned i = 0, e = SubLoops.size(); i != e; ++i) - Changed |= visitLoop(SubLoops[i]); + do { + redoLoop = false; + Changed |= processLoop(L); + } while(redoLoop); + + return Changed; +} + +/// processLoop - Do actual work and unswitch loop if possible and profitable. +bool LoopUnswitch::processLoop(Loop *L) { + assert(L->isLCSSAForm()); + bool Changed = false; // Loop over all of the basic blocks in the loop. If we find an interior // block that is branching on a loop-invariant condition, we can unswitch this @@ -132,157 +205,600 @@ bool LoopUnswitch::visitLoop(Loop *L) { for (Loop::block_iterator I = L->block_begin(), E = L->block_end(); I != E; ++I) { TerminatorInst *TI = (*I)->getTerminator(); - if (SwitchInst *SI = dyn_cast(TI)) { - if (!isa(SI) && L->isLoopInvariant(SI->getCondition())) - DEBUG(std::cerr << "TODO: Implement unswitching 'switch' loop %" - << L->getHeader()->getName() << ", cost = " - << L->getBlocks().size() << "\n" << **I); - continue; - } - - BranchInst *BI = dyn_cast(TI); - if (!BI) continue; - - // If this isn't branching on an invariant condition, we can't unswitch it. - if (!BI->isConditional() || isa(BI->getCondition()) || - !L->isLoopInvariant(BI->getCondition())) - continue; - - // Check to see if it would be profitable to unswitch this loop. - if (L->getBlocks().size() > Threshold) { - // FIXME: this should estimate growth by the amount of code shared by the - // resultant unswitched loops. This should have no code growth: - // for () { if (iv) {...} } - // as one copy of the loop will be empty. - // - DEBUG(std::cerr << "NOT unswitching loop %" - << L->getHeader()->getName() << ", cost too high: " - << L->getBlocks().size() << "\n"); - continue; + if (BranchInst *BI = dyn_cast(TI)) { + // If this isn't branching on an invariant condition, we can't unswitch + // it. + if (BI->isConditional()) { + // See if this, or some part of it, is loop invariant. If so, we can + // unswitch on it if we desire. + Value *LoopCond = FindLIVLoopCondition(BI->getCondition(), L, Changed); + if (LoopCond && UnswitchIfProfitable(LoopCond, ConstantInt::getTrue(), + L)) { + ++NumBranches; + return true; + } + } + } else if (SwitchInst *SI = dyn_cast(TI)) { + Value *LoopCond = FindLIVLoopCondition(SI->getCondition(), L, Changed); + if (LoopCond && SI->getNumCases() > 1) { + // Find a value to unswitch on: + // FIXME: this should chose the most expensive case! + Constant *UnswitchVal = SI->getCaseValue(1); + // Do not process same value again and again. + if (!UnswitchedVals.insert(UnswitchVal)) + continue; + + if (UnswitchIfProfitable(LoopCond, UnswitchVal, L)) { + ++NumSwitches; + return true; + } + } } - // If this loop has live-out values, we can't unswitch it. We need something - // like loop-closed SSA form in order to know how to insert PHI nodes for - // these values. - if (LoopValuesUsedOutsideLoop(L)) { - DEBUG(std::cerr << "NOT unswitching loop %" - << L->getHeader()->getName() - << ", a loop value is used outside loop!\n"); - continue; + // Scan the instructions to check for unswitchable values. + for (BasicBlock::iterator BBI = (*I)->begin(), E = (*I)->end(); + BBI != E; ++BBI) + if (SelectInst *SI = dyn_cast(BBI)) { + Value *LoopCond = FindLIVLoopCondition(SI->getCondition(), L, Changed); + if (LoopCond && UnswitchIfProfitable(LoopCond, ConstantInt::getTrue(), + L)) { + ++NumSelects; + return true; + } + } + } + + assert(L->isLCSSAForm()); + + return Changed; +} + +/// isTrivialLoopExitBlock - Check to see if all paths from BB either: +/// 1. Exit the loop with no side effects. +/// 2. Branch to the latch block with no side-effects. +/// +/// If these conditions are true, we return true and set ExitBB to the block we +/// exit through. +/// +static bool isTrivialLoopExitBlockHelper(Loop *L, BasicBlock *BB, + BasicBlock *&ExitBB, + std::set &Visited) { + if (!Visited.insert(BB).second) { + // Already visited and Ok, end of recursion. + return true; + } else if (!L->contains(BB)) { + // Otherwise, this is a loop exit, this is fine so long as this is the + // first exit. + if (ExitBB != 0) return false; + ExitBB = BB; + return true; + } + + // Otherwise, this is an unvisited intra-loop node. Check all successors. + for (succ_iterator SI = succ_begin(BB), E = succ_end(BB); SI != E; ++SI) { + // Check to see if the successor is a trivial loop exit. + if (!isTrivialLoopExitBlockHelper(L, *SI, ExitBB, Visited)) + return false; + } + + // Okay, everything after this looks good, check to make sure that this block + // doesn't include any side effects. + for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) + if (I->mayWriteToMemory()) + return false; + + return true; +} + +/// isTrivialLoopExitBlock - Return true if the specified block unconditionally +/// leads to an exit from the specified loop, and has no side-effects in the +/// process. If so, return the block that is exited to, otherwise return null. +static BasicBlock *isTrivialLoopExitBlock(Loop *L, BasicBlock *BB) { + std::set Visited; + Visited.insert(L->getHeader()); // Branches to header are ok. + BasicBlock *ExitBB = 0; + if (isTrivialLoopExitBlockHelper(L, BB, ExitBB, Visited)) + return ExitBB; + return 0; +} + +/// IsTrivialUnswitchCondition - Check to see if this unswitch condition is +/// trivial: that is, that the condition controls whether or not the loop does +/// anything at all. If this is a trivial condition, unswitching produces no +/// code duplications (equivalently, it produces a simpler loop and a new empty +/// loop, which gets deleted). +/// +/// If this is a trivial condition, return true, otherwise return false. When +/// returning true, this sets Cond and Val to the condition that controls the +/// trivial condition: when Cond dynamically equals Val, the loop is known to +/// exit. Finally, this sets LoopExit to the BB that the loop exits to when +/// Cond == Val. +/// +static bool IsTrivialUnswitchCondition(Loop *L, Value *Cond, Constant **Val = 0, + BasicBlock **LoopExit = 0) { + BasicBlock *Header = L->getHeader(); + TerminatorInst *HeaderTerm = Header->getTerminator(); + + BasicBlock *LoopExitBB = 0; + if (BranchInst *BI = dyn_cast(HeaderTerm)) { + // If the header block doesn't end with a conditional branch on Cond, we + // can't handle it. + if (!BI->isConditional() || BI->getCondition() != Cond) + return false; + + // Check to see if a successor of the branch is guaranteed to go to the + // latch block or exit through a one exit block without having any + // side-effects. If so, determine the value of Cond that causes it to do + // this. + if ((LoopExitBB = isTrivialLoopExitBlock(L, BI->getSuccessor(0)))) { + if (Val) *Val = ConstantInt::getTrue(); + } else if ((LoopExitBB = isTrivialLoopExitBlock(L, BI->getSuccessor(1)))) { + if (Val) *Val = ConstantInt::getFalse(); } - - //std::cerr << "BEFORE:\n"; LI->dump(); - VersionLoop(BI->getCondition(), L); - //std::cerr << "AFTER:\n"; LI->dump(); + } else if (SwitchInst *SI = dyn_cast(HeaderTerm)) { + // If this isn't a switch on Cond, we can't handle it. + if (SI->getCondition() != Cond) return false; - // FIXME: Why return here? What if we have: - // "for () { if (iv1) { if (iv2) { } } }" ? - return true; + // Check to see if a successor of the switch is guaranteed to go to the + // latch block or exit through a one exit block without having any + // side-effects. If so, determine the value of Cond that causes it to do + // this. Note that we can't trivially unswitch on the default case. + for (unsigned i = 1, e = SI->getNumSuccessors(); i != e; ++i) + if ((LoopExitBB = isTrivialLoopExitBlock(L, SI->getSuccessor(i)))) { + // Okay, we found a trivial case, remember the value that is trivial. + if (Val) *Val = SI->getCaseValue(i); + break; + } } - return Changed; + // If we didn't find a single unique LoopExit block, or if the loop exit block + // contains phi nodes, this isn't trivial. + if (!LoopExitBB || isa(LoopExitBB->begin())) + return false; // Can't handle this. + + if (LoopExit) *LoopExit = LoopExitBB; + + // We already know that nothing uses any scalar values defined inside of this + // loop. As such, we just have to check to see if this loop will execute any + // side-effecting instructions (e.g. stores, calls, volatile loads) in the + // part of the loop that the code *would* execute. We already checked the + // tail, check the header now. + for (BasicBlock::iterator I = Header->begin(), E = Header->end(); I != E; ++I) + if (I->mayWriteToMemory()) + return false; + return true; } -/// SplitBlock - Split the specified basic block into two pieces. If SplitAtTop -/// is false, this splits the block so the second half only has an unconditional -/// branch. If SplitAtTop is true, it makes it so the first half of the block -/// only has an unconditional branch in it. +/// getLoopUnswitchCost - Return the cost (code size growth) that will happen if +/// we choose to unswitch the specified loop on the specified value. /// -/// This method updates the LoopInfo for this function to correctly reflect the -/// CFG changes made. -BasicBlock *LoopUnswitch::SplitBlock(BasicBlock *BB, bool SplitAtTop) { - BasicBlock::iterator SplitPoint; - if (!SplitAtTop) - SplitPoint = BB->getTerminator(); - else { - SplitPoint = BB->begin(); - while (isa(SplitPoint)) ++SplitPoint; +unsigned LoopUnswitch::getLoopUnswitchCost(Loop *L, Value *LIC) { + // If the condition is trivial, always unswitch. There is no code growth for + // this case. + if (IsTrivialUnswitchCondition(L, LIC)) + return 0; + + // FIXME: This is really overly conservative. However, more liberal + // estimations have thus far resulted in excessive unswitching, which is bad + // both in compile time and in code size. This should be replaced once + // someone figures out how a good estimation. + return L->getBlocks().size(); + + unsigned Cost = 0; + // FIXME: this is brain dead. It should take into consideration code + // shrinkage. + for (Loop::block_iterator I = L->block_begin(), E = L->block_end(); + I != E; ++I) { + BasicBlock *BB = *I; + // Do not include empty blocks in the cost calculation. This happen due to + // loop canonicalization and will be removed. + if (BB->begin() == BasicBlock::iterator(BB->getTerminator())) + continue; + + // Count basic blocks. + ++Cost; } - BasicBlock *New = BB->splitBasicBlock(SplitPoint, BB->getName()+".tail"); - // New now lives in whichever loop that BB used to. - if (Loop *L = LI->getLoopFor(BB)) - L->addBasicBlockToLoop(New, *LI); - return SplitAtTop ? BB : New; + return Cost; } +/// UnswitchIfProfitable - We have found that we can unswitch L when +/// LoopCond == Val to simplify the loop. If we decide that this is profitable, +/// unswitch the loop, reprocess the pieces, then return true. +bool LoopUnswitch::UnswitchIfProfitable(Value *LoopCond, Constant *Val,Loop *L){ + // Check to see if it would be profitable to unswitch this loop. + unsigned Cost = getLoopUnswitchCost(L, LoopCond); + + // Do not do non-trivial unswitch while optimizing for size. + if (Cost && OptimizeForSize) + return false; + + if (Cost > Threshold) { + // FIXME: this should estimate growth by the amount of code shared by the + // resultant unswitched loops. + // + DOUT << "NOT unswitching loop %" + << L->getHeader()->getName() << ", cost too high: " + << L->getBlocks().size() << "\n"; + return false; + } + + // If this is a trivial condition to unswitch (which results in no code + // duplication), do it now. + Constant *CondVal; + BasicBlock *ExitBlock; + if (IsTrivialUnswitchCondition(L, LoopCond, &CondVal, &ExitBlock)) { + UnswitchTrivialCondition(L, LoopCond, CondVal, ExitBlock); + } else { + UnswitchNontrivialCondition(LoopCond, Val, L); + } + + return true; +} // RemapInstruction - Convert the instruction operands from referencing the // current values into those specified by ValueMap. // static inline void RemapInstruction(Instruction *I, - std::map &ValueMap) { + DenseMap &ValueMap) { for (unsigned op = 0, E = I->getNumOperands(); op != E; ++op) { Value *Op = I->getOperand(op); - std::map::iterator It = ValueMap.find(Op); + DenseMap::iterator It = ValueMap.find(Op); if (It != ValueMap.end()) Op = It->second; I->setOperand(op, Op); } } +// CloneDomInfo - NewBB is cloned from Orig basic block. Now clone Dominator +// Info. +// +// If Orig block's immediate dominator is mapped in VM then use corresponding +// immediate dominator from the map. Otherwise Orig block's dominator is also +// NewBB's dominator. +// +// OrigPreheader is loop pre-header before this pass started +// updating CFG. NewPrehader is loops new pre-header. However, after CFG +// manipulation, loop L may not exist. So rely on input parameter NewPreheader. +static void CloneDomInfo(BasicBlock *NewBB, BasicBlock *Orig, + BasicBlock *NewPreheader, BasicBlock *OrigPreheader, + BasicBlock *OrigHeader, + DominatorTree *DT, DominanceFrontier *DF, + DenseMap &VM) { + + // If NewBB alreay has found its place in domiantor tree then no need to do + // anything. + if (DT->getNode(NewBB)) + return; + + // If Orig does not have any immediate domiantor then its clone, NewBB, does + // not need any immediate dominator. + DomTreeNode *OrigNode = DT->getNode(Orig); + if (!OrigNode) + return; + DomTreeNode *OrigIDomNode = OrigNode->getIDom(); + if (!OrigIDomNode) + return; + + BasicBlock *OrigIDom = NULL; + + // If Orig is original loop header then its immediate dominator is + // NewPreheader. + if (Orig == OrigHeader) + OrigIDom = NewPreheader; + + // If Orig is new pre-header then its immediate dominator is + // original pre-header. + else if (Orig == NewPreheader) + OrigIDom = OrigPreheader; + + // Other as DT to find Orig's immediate dominator. + else + OrigIDom = OrigIDomNode->getBlock(); + + // Initially use Orig's immediate dominator as NewBB's immediate dominator. + BasicBlock *NewIDom = OrigIDom; + DenseMap::iterator I = VM.find(OrigIDom); + if (I != VM.end()) { + NewIDom = cast(I->second); + + // If NewIDom does not have corresponding dominatore tree node then + // get one. + if (!DT->getNode(NewIDom)) + CloneDomInfo(NewIDom, OrigIDom, NewPreheader, OrigPreheader, + OrigHeader, DT, DF, VM); + } + + DT->addNewBlock(NewBB, NewIDom); + + // Copy cloned dominance frontiner set + DominanceFrontier::DomSetType NewDFSet; + if (DF) { + DominanceFrontier::iterator DFI = DF->find(Orig); + if ( DFI != DF->end()) { + DominanceFrontier::DomSetType S = DFI->second; + for (DominanceFrontier::DomSetType::iterator I = S.begin(), E = S.end(); + I != E; ++I) { + BasicBlock *BB = *I; + DenseMap::iterator IDM = VM.find(BB); + if (IDM != VM.end()) + NewDFSet.insert(cast(IDM->second)); + else + NewDFSet.insert(BB); + } + } + DF->addBasicBlock(NewBB, NewDFSet); + } +} + /// CloneLoop - Recursively clone the specified loop and all of its children, /// mapping the blocks with the specified map. -static Loop *CloneLoop(Loop *L, Loop *PL, std::map &VM, - LoopInfo *LI) { +static Loop *CloneLoop(Loop *L, Loop *PL, DenseMap &VM, + LoopInfo *LI, LPPassManager *LPM) { Loop *New = new Loop(); - if (PL) - PL->addChildLoop(New); - else - LI->addTopLevelLoop(New); + LPM->insertLoop(New, PL); // Add all of the blocks in L to the new loop. for (Loop::block_iterator I = L->block_begin(), E = L->block_end(); I != E; ++I) if (LI->getLoopFor(*I) == L) - New->addBasicBlockToLoop(cast(VM[*I]), *LI); + New->addBasicBlockToLoop(cast(VM[*I]), LI->getBase()); // Add all of the subloops to the new loop. for (Loop::iterator I = L->begin(), E = L->end(); I != E; ++I) - CloneLoop(*I, New, VM, LI); + CloneLoop(*I, New, VM, LI, LPM); return New; } +/// EmitPreheaderBranchOnCondition - Emit a conditional branch on two values +/// if LIC == Val, branch to TrueDst, otherwise branch to FalseDest. Insert the +/// code immediately before InsertPt. +void LoopUnswitch::EmitPreheaderBranchOnCondition(Value *LIC, Constant *Val, + BasicBlock *TrueDest, + BasicBlock *FalseDest, + Instruction *InsertPt) { + // Insert a conditional branch on LIC to the two preheaders. The original + // code is the true version and the new code is the false version. + Value *BranchVal = LIC; + if (!isa(Val) || Val->getType() != Type::Int1Ty) + BranchVal = new ICmpInst(ICmpInst::ICMP_EQ, LIC, Val, "tmp", InsertPt); + else if (Val != ConstantInt::getTrue()) + // We want to enter the new loop when the condition is true. + std::swap(TrueDest, FalseDest); + + // Insert the new branch. + BranchInst::Create(TrueDest, FalseDest, BranchVal, InsertPt); +} -/// VersionLoop - We determined that the loop is profitable to unswitch and -/// contains a branch on a loop invariant condition. Split it into loop -/// versions and test the condition outside of either loop. -void LoopUnswitch::VersionLoop(Value *LIC, Loop *L) { - Function *F = L->getHeader()->getParent(); - DEBUG(std::cerr << "loop-unswitch: Unswitching loop %" - << L->getHeader()->getName() << " [" << L->getBlocks().size() - << " blocks] in Function " << F->getName() - << " on cond:" << *LIC << "\n"); +/// UnswitchTrivialCondition - Given a loop that has a trivial unswitchable +/// condition in it (a cond branch from its header block to its latch block, +/// where the path through the loop that doesn't execute its body has no +/// side-effects), unswitch it. This doesn't involve any code duplication, just +/// moving the conditional branch outside of the loop and updating loop info. +void LoopUnswitch::UnswitchTrivialCondition(Loop *L, Value *Cond, + Constant *Val, + BasicBlock *ExitBlock) { + DOUT << "loop-unswitch: Trivial-Unswitch loop %" + << L->getHeader()->getName() << " [" << L->getBlocks().size() + << " blocks] in Function " << L->getHeader()->getParent()->getName() + << " on cond: " << *Val << " == " << *Cond << "\n"; + + // First step, split the preheader, so that we know that there is a safe place + // to insert the conditional branch. We will change 'OrigPH' to have a + // conditional branch on Cond. + BasicBlock *OrigPH = L->getLoopPreheader(); + BasicBlock *NewPH = SplitEdge(OrigPH, L->getHeader(), this); + + // Now that we have a place to insert the conditional branch, create a place + // to branch to: this is the exit block out of the loop that we should + // short-circuit to. + + // Split this block now, so that the loop maintains its exit block, and so + // that the jump from the preheader can execute the contents of the exit block + // without actually branching to it (the exit block should be dominated by the + // loop header, not the preheader). + assert(!L->contains(ExitBlock) && "Exit block is in the loop?"); + BasicBlock *NewExit = SplitBlock(ExitBlock, ExitBlock->begin(), this); + + // Okay, now we have a position to branch from and a position to branch to, + // insert the new conditional branch. + EmitPreheaderBranchOnCondition(Cond, Val, NewExit, NewPH, + OrigPH->getTerminator()); + if (DT) { + DT->changeImmediateDominator(NewExit, OrigPH); + DT->changeImmediateDominator(NewPH, OrigPH); + } + + if (DF) { + // NewExit is now part of NewPH and Loop Header's dominance + // frontier. + DominanceFrontier::iterator DFI = DF->find(NewPH); + if (DFI != DF->end()) + DF->addToFrontier(DFI, NewExit); + DFI = DF->find(L->getHeader()); + DF->addToFrontier(DFI, NewExit); + + // ExitBlock does not have successors then NewExit is part of + // its dominance frontier. + if (succ_begin(ExitBlock) == succ_end(ExitBlock)) { + DFI = DF->find(ExitBlock); + DF->addToFrontier(DFI, NewExit); + } + } + LPM->deleteSimpleAnalysisValue(OrigPH->getTerminator(), L); + OrigPH->getTerminator()->eraseFromParent(); + + // We need to reprocess this loop, it could be unswitched again. + redoLoop = true; + + // Now that we know that the loop is never entered when this condition is a + // particular value, rewrite the loop with this info. We know that this will + // at least eliminate the old branch. + RewriteLoopBodyWithConditionConstant(L, Cond, Val, false); + ++NumTrivial; +} + +/// ReplaceLoopExternalDFMember - +/// If BB's dominance frontier has a member that is not part of loop L then +/// remove it. Add NewDFMember in BB's dominance frontier. +void LoopUnswitch::ReplaceLoopExternalDFMember(Loop *L, BasicBlock *BB, + BasicBlock *NewDFMember) { + + DominanceFrontier::iterator DFI = DF->find(BB); + if (DFI == DF->end()) + return; + + DominanceFrontier::DomSetType &DFSet = DFI->second; + for (DominanceFrontier::DomSetType::iterator DI = DFSet.begin(), + DE = DFSet.end(); DI != DE;) { + BasicBlock *B = *DI++; + if (L->contains(B)) + continue; + + DF->removeFromFrontier(DFI, B); + LoopDF.insert(B); + } + + DF->addToFrontier(DFI, NewDFMember); +} + +/// SplitExitEdges - Split all of the edges from inside the loop to their exit +/// blocks. Update the appropriate Phi nodes as we do so. +void LoopUnswitch::SplitExitEdges(Loop *L, + const SmallVector &ExitBlocks, + SmallVector &MiddleBlocks) { + + for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) { + BasicBlock *ExitBlock = ExitBlocks[i]; + std::vector Preds(pred_begin(ExitBlock), pred_end(ExitBlock)); + + for (unsigned j = 0, e = Preds.size(); j != e; ++j) { + BasicBlock* MiddleBlock = SplitEdge(Preds[j], ExitBlock, this); + MiddleBlocks.push_back(MiddleBlock); + BasicBlock* StartBlock = Preds[j]; + BasicBlock* EndBlock; + if (MiddleBlock->getSinglePredecessor() == ExitBlock) { + EndBlock = MiddleBlock; + MiddleBlock = EndBlock->getSinglePredecessor();; + } else { + EndBlock = ExitBlock; + } + + OrigLoopExitMap[StartBlock] = EndBlock; + + std::set InsertedPHIs; + PHINode* OldLCSSA = 0; + for (BasicBlock::iterator I = EndBlock->begin(); + (OldLCSSA = dyn_cast(I)); ++I) { + Value* OldValue = OldLCSSA->getIncomingValueForBlock(MiddleBlock); + PHINode* NewLCSSA = PHINode::Create(OldLCSSA->getType(), + OldLCSSA->getName() + ".us-lcssa", + MiddleBlock->getTerminator()); + NewLCSSA->addIncoming(OldValue, StartBlock); + OldLCSSA->setIncomingValue(OldLCSSA->getBasicBlockIndex(MiddleBlock), + NewLCSSA); + InsertedPHIs.insert(NewLCSSA); + } + + BasicBlock::iterator InsertPt = EndBlock->getFirstNonPHI(); + for (BasicBlock::iterator I = MiddleBlock->begin(); + (OldLCSSA = dyn_cast(I)) && InsertedPHIs.count(OldLCSSA) == 0; + ++I) { + PHINode *NewLCSSA = PHINode::Create(OldLCSSA->getType(), + OldLCSSA->getName() + ".us-lcssa", + InsertPt); + OldLCSSA->replaceAllUsesWith(NewLCSSA); + NewLCSSA->addIncoming(OldLCSSA, MiddleBlock); + } + + if (DF && DT) { + // StartBlock -- > MiddleBlock -- > EndBlock + // StartBlock is loop exiting block. EndBlock will become merge point + // of two loop exits after loop unswitch. + + // If StartBlock's DF member includes a block that is not loop member + // then replace that DF member with EndBlock. + + // If MiddleBlock's DF member includes a block that is not loop member + // tnen replace that DF member with EndBlock. + + ReplaceLoopExternalDFMember(L, StartBlock, EndBlock); + ReplaceLoopExternalDFMember(L, MiddleBlock, EndBlock); + } + } + } + +} +/// UnswitchNontrivialCondition - We determined that the loop is profitable +/// to unswitch when LIC equal Val. Split it into loop versions and test the +/// condition outside of either loop. Return the loops created as Out1/Out2. +void LoopUnswitch::UnswitchNontrivialCondition(Value *LIC, Constant *Val, + Loop *L) { + Function *F = L->getHeader()->getParent(); + DOUT << "loop-unswitch: Unswitching loop %" + << L->getHeader()->getName() << " [" << L->getBlocks().size() + << " blocks] in Function " << F->getName() + << " when '" << *Val << "' == " << *LIC << "\n"; + + // LoopBlocks contains all of the basic blocks of the loop, including the + // preheader of the loop, the body of the loop, and the exit blocks of the + // loop, in that order. std::vector LoopBlocks; // First step, split the preheader and exit blocks, and add these blocks to // the LoopBlocks list. + BasicBlock *OrigHeader = L->getHeader(); BasicBlock *OrigPreheader = L->getLoopPreheader(); - LoopBlocks.push_back(SplitBlock(OrigPreheader, false)); + BasicBlock *NewPreheader = SplitEdge(OrigPreheader, L->getHeader(), this); + LoopBlocks.push_back(NewPreheader); // We want the loop to come after the preheader, but before the exit blocks. LoopBlocks.insert(LoopBlocks.end(), L->block_begin(), L->block_end()); - std::vector ExitBlocks; - L->getExitBlocks(ExitBlocks); - std::sort(ExitBlocks.begin(), ExitBlocks.end()); - ExitBlocks.erase(std::unique(ExitBlocks.begin(), ExitBlocks.end()), - ExitBlocks.end()); - for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) - LoopBlocks.push_back(ExitBlocks[i] = SplitBlock(ExitBlocks[i], true)); + SmallVector ExitBlocks; + L->getUniqueExitBlocks(ExitBlocks); + + // Split all of the edges from inside the loop to their exit blocks. Update + // the appropriate Phi nodes as we do so. + SmallVector MiddleBlocks; + SplitExitEdges(L, ExitBlocks, MiddleBlocks); + + // The exit blocks may have been changed due to edge splitting, recompute. + ExitBlocks.clear(); + L->getUniqueExitBlocks(ExitBlocks); + + // Add exit blocks to the loop blocks. + LoopBlocks.insert(LoopBlocks.end(), ExitBlocks.begin(), ExitBlocks.end()); // Next step, clone all of the basic blocks that make up the loop (including // the loop preheader and exit blocks), keeping track of the mapping between // the instructions and blocks. std::vector NewBlocks; NewBlocks.reserve(LoopBlocks.size()); - std::map ValueMap; + DenseMap ValueMap; for (unsigned i = 0, e = LoopBlocks.size(); i != e; ++i) { - NewBlocks.push_back(CloneBasicBlock(LoopBlocks[i], ValueMap, ".us", F)); - ValueMap[LoopBlocks[i]] = NewBlocks.back(); // Keep the BB mapping. + BasicBlock *New = CloneBasicBlock(LoopBlocks[i], ValueMap, ".us", F); + NewBlocks.push_back(New); + ValueMap[LoopBlocks[i]] = New; // Keep the BB mapping. + LPM->cloneBasicBlockSimpleAnalysis(LoopBlocks[i], New, L); + } + + // OutSiders are basic block that are dominated by original header and + // at the same time they are not part of loop. + SmallPtrSet OutSiders; + if (DT) { + DomTreeNode *OrigHeaderNode = DT->getNode(OrigHeader); + for(std::vector::iterator DI = OrigHeaderNode->begin(), + DE = OrigHeaderNode->end(); DI != DE; ++DI) { + BasicBlock *B = (*DI)->getBlock(); + + DenseMap::iterator VI = ValueMap.find(B); + if (VI == ValueMap.end()) + OutSiders.insert(B); + } } // Splice the newly inserted blocks into the function right before the @@ -291,14 +807,34 @@ void LoopUnswitch::VersionLoop(Value *LIC, Loop *L) { NewBlocks[0], F->end()); // Now we create the new Loop object for the versioned loop. - Loop *NewLoop = CloneLoop(L, L->getParentLoop(), ValueMap, LI); - if (Loop *Parent = L->getParentLoop()) { + Loop *NewLoop = CloneLoop(L, L->getParentLoop(), ValueMap, LI, LPM); + Loop *ParentLoop = L->getParentLoop(); + if (ParentLoop) { // Make sure to add the cloned preheader and exit blocks to the parent loop // as well. - Parent->addBasicBlockToLoop(NewBlocks[0], *LI); - for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) - Parent->addBasicBlockToLoop(cast(ValueMap[ExitBlocks[i]]), - *LI); + ParentLoop->addBasicBlockToLoop(NewBlocks[0], LI->getBase()); + } + + for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) { + BasicBlock *NewExit = cast(ValueMap[ExitBlocks[i]]); + // The new exit block should be in the same loop as the old one. + if (Loop *ExitBBLoop = LI->getLoopFor(ExitBlocks[i])) + ExitBBLoop->addBasicBlockToLoop(NewExit, LI->getBase()); + + assert(NewExit->getTerminator()->getNumSuccessors() == 1 && + "Exit block should have been split to have one successor!"); + BasicBlock *ExitSucc = NewExit->getTerminator()->getSuccessor(0); + + // If the successor of the exit block had PHI nodes, add an entry for + // NewExit. + PHINode *PN; + for (BasicBlock::iterator I = ExitSucc->begin(); + (PN = dyn_cast(I)); ++I) { + Value *V = PN->getIncomingValueForBlock(ExitBlocks[i]); + DenseMap::iterator It = ValueMap.find(V); + if (It != ValueMap.end()) V = It->second; + PN->addIncoming(V, NewExit); + } } // Rewrite the code to refer to itself. @@ -308,44 +844,484 @@ void LoopUnswitch::VersionLoop(Value *LIC, Loop *L) { RemapInstruction(I, ValueMap); // Rewrite the original preheader to select between versions of the loop. - assert(isa(OrigPreheader->getTerminator()) && - cast(OrigPreheader->getTerminator())->isUnconditional() && - OrigPreheader->getTerminator()->getSuccessor(0) == LoopBlocks[0] && + BranchInst *OldBR = cast(OrigPreheader->getTerminator()); + assert(OldBR->isUnconditional() && OldBR->getSuccessor(0) == LoopBlocks[0] && "Preheader splitting did not work correctly!"); - // Remove the unconditional branch to LoopBlocks[0]. - OrigPreheader->getInstList().pop_back(); - // Insert a conditional branch on LIC to the two preheaders. The original - // code is the true version and the new code is the false version. - new BranchInst(LoopBlocks[0], NewBlocks[0], LIC, OrigPreheader); + // Emit the new branch that selects between the two versions of this loop. + EmitPreheaderBranchOnCondition(LIC, Val, NewBlocks[0], LoopBlocks[0], OldBR); + LPM->deleteSimpleAnalysisValue(OldBR, L); + OldBR->eraseFromParent(); + + // Update dominator info + if (DF && DT) { + + SmallVector ExitingBlocks; + L->getExitingBlocks(ExitingBlocks); + + // Clone dominator info for all cloned basic block. + for (unsigned i = 0, e = LoopBlocks.size(); i != e; ++i) { + BasicBlock *LBB = LoopBlocks[i]; + BasicBlock *NBB = NewBlocks[i]; + CloneDomInfo(NBB, LBB, NewPreheader, OrigPreheader, + OrigHeader, DT, DF, ValueMap); + + // If LBB's dominance frontier includes DFMember + // such that DFMember is also a member of LoopDF then + // - Remove DFMember from LBB's dominance frontier + // - Copy loop exiting blocks', that are dominated by BB, + // dominance frontier member in BB's dominance frontier + + DominanceFrontier::iterator LBBI = DF->find(LBB); + DominanceFrontier::iterator NBBI = DF->find(NBB); + if (LBBI == DF->end()) + continue; + + DominanceFrontier::DomSetType &LBSet = LBBI->second; + for (DominanceFrontier::DomSetType::iterator LI = LBSet.begin(), + LE = LBSet.end(); LI != LE; /* NULL */) { + BasicBlock *B = *LI++; + if (B == LBB && B == L->getHeader()) + continue; + bool removeB = false; + if (!LoopDF.count(B)) + continue; + + // If LBB dominates loop exits then insert loop exit block's DF + // into B's DF. + for(SmallVector::iterator + LExitI = ExitingBlocks.begin(), + LExitE = ExitingBlocks.end(); LExitI != LExitE; ++LExitI) { + BasicBlock *E = *LExitI; + + if (!DT->dominates(LBB,E)) + continue; + + DenseMap::iterator DFBI = + OrigLoopExitMap.find(E); + if (DFBI == OrigLoopExitMap.end()) + continue; + + BasicBlock *DFB = DFBI->second; + DF->addToFrontier(LBBI, DFB); + DF->addToFrontier(NBBI, DFB); + removeB = true; + } + + // If B's replacement is inserted in DF then now is the time to remove + // B. + if (removeB) { + DF->removeFromFrontier(LBBI, B); + if (L->contains(B)) + DF->removeFromFrontier(NBBI, cast(ValueMap[B])); + else + DF->removeFromFrontier(NBBI, B); + } + } + + } + + // MiddleBlocks are dominated by original pre header. SplitEdge updated + // MiddleBlocks' dominance frontier appropriately. + for (unsigned i = 0, e = MiddleBlocks.size(); i != e; ++i) { + BasicBlock *MBB = MiddleBlocks[i]; + if (!MBB->getSinglePredecessor()) + DT->changeImmediateDominator(MBB, OrigPreheader); + } + + // All Outsiders are now dominated by original pre header. + for (SmallPtrSet::iterator OI = OutSiders.begin(), + OE = OutSiders.end(); OI != OE; ++OI) { + BasicBlock *OB = *OI; + DT->changeImmediateDominator(OB, OrigPreheader); + } + + // New loop headers are dominated by original preheader + DT->changeImmediateDominator(NewBlocks[0], OrigPreheader); + DT->changeImmediateDominator(LoopBlocks[0], OrigPreheader); + } + + LoopProcessWorklist.push_back(NewLoop); + redoLoop = true; // Now we rewrite the original code to know that the condition is true and the // new code to know that the condition is false. - RewriteLoopBodyWithConditionConstant(L, LIC, true); - RewriteLoopBodyWithConditionConstant(NewLoop, LIC, false); - ++NumUnswitched; + RewriteLoopBodyWithConditionConstant(L , LIC, Val, false); + + // It's possible that simplifying one loop could cause the other to be + // deleted. If so, don't simplify it. + if (!LoopProcessWorklist.empty() && LoopProcessWorklist.back() == NewLoop) + RewriteLoopBodyWithConditionConstant(NewLoop, LIC, Val, true); +} + +/// RemoveFromWorklist - Remove all instances of I from the worklist vector +/// specified. +static void RemoveFromWorklist(Instruction *I, + std::vector &Worklist) { + std::vector::iterator WI = std::find(Worklist.begin(), + Worklist.end(), I); + while (WI != Worklist.end()) { + unsigned Offset = WI-Worklist.begin(); + Worklist.erase(WI); + WI = std::find(Worklist.begin()+Offset, Worklist.end(), I); + } +} + +/// ReplaceUsesOfWith - When we find that I really equals V, remove I from the +/// program, replacing all uses with V and update the worklist. +static void ReplaceUsesOfWith(Instruction *I, Value *V, + std::vector &Worklist, + Loop *L, LPPassManager *LPM) { + DOUT << "Replace with '" << *V << "': " << *I; + + // Add uses to the worklist, which may be dead now. + for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) + if (Instruction *Use = dyn_cast(I->getOperand(i))) + Worklist.push_back(Use); + + // Add users to the worklist which may be simplified now. + for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); + UI != E; ++UI) + Worklist.push_back(cast(*UI)); + LPM->deleteSimpleAnalysisValue(I, L); + RemoveFromWorklist(I, Worklist); + I->replaceAllUsesWith(V); + I->eraseFromParent(); + ++NumSimplify; +} + +/// RemoveBlockIfDead - If the specified block is dead, remove it, update loop +/// information, and remove any dead successors it has. +/// +void LoopUnswitch::RemoveBlockIfDead(BasicBlock *BB, + std::vector &Worklist, + Loop *L) { + if (pred_begin(BB) != pred_end(BB)) { + // This block isn't dead, since an edge to BB was just removed, see if there + // are any easy simplifications we can do now. + if (BasicBlock *Pred = BB->getSinglePredecessor()) { + // If it has one pred, fold phi nodes in BB. + while (isa(BB->begin())) + ReplaceUsesOfWith(BB->begin(), + cast(BB->begin())->getIncomingValue(0), + Worklist, L, LPM); + + // If this is the header of a loop and the only pred is the latch, we now + // have an unreachable loop. + if (Loop *L = LI->getLoopFor(BB)) + if (L->getHeader() == BB && L->contains(Pred)) { + // Remove the branch from the latch to the header block, this makes + // the header dead, which will make the latch dead (because the header + // dominates the latch). + LPM->deleteSimpleAnalysisValue(Pred->getTerminator(), L); + Pred->getTerminator()->eraseFromParent(); + new UnreachableInst(Pred); + + // The loop is now broken, remove it from LI. + RemoveLoopFromHierarchy(L); + + // Reprocess the header, which now IS dead. + RemoveBlockIfDead(BB, Worklist, L); + return; + } + + // If pred ends in a uncond branch, add uncond branch to worklist so that + // the two blocks will get merged. + if (BranchInst *BI = dyn_cast(Pred->getTerminator())) + if (BI->isUnconditional()) + Worklist.push_back(BI); + } + return; + } + + DOUT << "Nuking dead block: " << *BB; + + // Remove the instructions in the basic block from the worklist. + for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) { + RemoveFromWorklist(I, Worklist); + + // Anything that uses the instructions in this basic block should have their + // uses replaced with undefs. + if (!I->use_empty()) + I->replaceAllUsesWith(UndefValue::get(I->getType())); + } + + // If this is the edge to the header block for a loop, remove the loop and + // promote all subloops. + if (Loop *BBLoop = LI->getLoopFor(BB)) { + if (BBLoop->getLoopLatch() == BB) + RemoveLoopFromHierarchy(BBLoop); + } + + // Remove the block from the loop info, which removes it from any loops it + // was in. + LI->removeBlock(BB); + + + // Remove phi node entries in successors for this block. + TerminatorInst *TI = BB->getTerminator(); + std::vector Succs; + for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) { + Succs.push_back(TI->getSuccessor(i)); + TI->getSuccessor(i)->removePredecessor(BB); + } + + // Unique the successors, remove anything with multiple uses. + std::sort(Succs.begin(), Succs.end()); + Succs.erase(std::unique(Succs.begin(), Succs.end()), Succs.end()); + + // Remove the basic block, including all of the instructions contained in it. + LPM->deleteSimpleAnalysisValue(BB, L); + BB->eraseFromParent(); + // Remove successor blocks here that are not dead, so that we know we only + // have dead blocks in this list. Nondead blocks have a way of becoming dead, + // then getting removed before we revisit them, which is badness. + // + for (unsigned i = 0; i != Succs.size(); ++i) + if (pred_begin(Succs[i]) != pred_end(Succs[i])) { + // One exception is loop headers. If this block was the preheader for a + // loop, then we DO want to visit the loop so the loop gets deleted. + // We know that if the successor is a loop header, that this loop had to + // be the preheader: the case where this was the latch block was handled + // above and headers can only have two predecessors. + if (!LI->isLoopHeader(Succs[i])) { + Succs.erase(Succs.begin()+i); + --i; + } + } + + for (unsigned i = 0, e = Succs.size(); i != e; ++i) + RemoveBlockIfDead(Succs[i], Worklist, L); +} - // Try to unswitch each of our new loops now! - visitLoop(L); - visitLoop(NewLoop); +/// RemoveLoopFromHierarchy - We have discovered that the specified loop has +/// become unwrapped, either because the backedge was deleted, or because the +/// edge into the header was removed. If the edge into the header from the +/// latch block was removed, the loop is unwrapped but subloops are still alive, +/// so they just reparent loops. If the loops are actually dead, they will be +/// removed later. +void LoopUnswitch::RemoveLoopFromHierarchy(Loop *L) { + LPM->deleteLoopFromQueue(L); + RemoveLoopFromWorklist(L); } -// RewriteLoopBodyWithConditionConstant - We know that the boolean value LIC has -// the value specified by Val in the specified loop. Rewrite any uses of LIC or -// of properties correlated to it. + + +// RewriteLoopBodyWithConditionConstant - We know either that the value LIC has +// the value specified by Val in the specified loop, or we know it does NOT have +// that value. Rewrite any uses of LIC or of properties correlated to it. void LoopUnswitch::RewriteLoopBodyWithConditionConstant(Loop *L, Value *LIC, - bool Val) { + Constant *Val, + bool IsEqual) { + assert(!isa(LIC) && "Why are we unswitching on a constant?"); + // FIXME: Support correlated properties, like: // for (...) // if (li1 < li2) // ... // if (li1 > li2) // ... - ConstantBool *BoolVal = ConstantBool::get(Val); - + + // FOLD boolean conditions (X|LIC), (X&LIC). Fold conditional branches, + // selects, switches. std::vector Users(LIC->use_begin(), LIC->use_end()); - for (unsigned i = 0, e = Users.size(); i != e; ++i) - if (Instruction *U = dyn_cast(Users[i])) - if (L->contains(U->getParent())) - U->replaceUsesOfWith(LIC, BoolVal); + std::vector Worklist; + + // If we know that LIC == Val, or that LIC == NotVal, just replace uses of LIC + // in the loop with the appropriate one directly. + if (IsEqual || (isa(Val) && Val->getType() == Type::Int1Ty)) { + Value *Replacement; + if (IsEqual) + Replacement = Val; + else + Replacement = ConstantInt::get(Type::Int1Ty, + !cast(Val)->getZExtValue()); + + for (unsigned i = 0, e = Users.size(); i != e; ++i) + if (Instruction *U = cast(Users[i])) { + if (!L->contains(U->getParent())) + continue; + U->replaceUsesOfWith(LIC, Replacement); + Worklist.push_back(U); + } + } else { + // Otherwise, we don't know the precise value of LIC, but we do know that it + // is certainly NOT "Val". As such, simplify any uses in the loop that we + // can. This case occurs when we unswitch switch statements. + for (unsigned i = 0, e = Users.size(); i != e; ++i) + if (Instruction *U = cast(Users[i])) { + if (!L->contains(U->getParent())) + continue; + + Worklist.push_back(U); + + // If we know that LIC is not Val, use this info to simplify code. + if (SwitchInst *SI = dyn_cast(U)) { + for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i) { + if (SI->getCaseValue(i) == Val) { + // Found a dead case value. Don't remove PHI nodes in the + // successor if they become single-entry, those PHI nodes may + // be in the Users list. + + // FIXME: This is a hack. We need to keep the successor around + // and hooked up so as to preserve the loop structure, because + // trying to update it is complicated. So instead we preserve the + // loop structure and put the block on an dead code path. + + BasicBlock* Old = SI->getParent(); + BasicBlock* Split = SplitBlock(Old, SI, this); + + Instruction* OldTerm = Old->getTerminator(); + BranchInst::Create(Split, SI->getSuccessor(i), + ConstantInt::getTrue(), OldTerm); + + LPM->deleteSimpleAnalysisValue(Old->getTerminator(), L); + Old->getTerminator()->eraseFromParent(); + + PHINode *PN; + for (BasicBlock::iterator II = SI->getSuccessor(i)->begin(); + (PN = dyn_cast(II)); ++II) { + Value *InVal = PN->removeIncomingValue(Split, false); + PN->addIncoming(InVal, Old); + } + + SI->removeCase(i); + break; + } + } + } + + // TODO: We could do other simplifications, for example, turning + // LIC == Val -> false. + } + } + + SimplifyCode(Worklist, L); +} + +/// SimplifyCode - Okay, now that we have simplified some instructions in the +/// loop, walk over it and constant prop, dce, and fold control flow where +/// possible. Note that this is effectively a very simple loop-structure-aware +/// optimizer. During processing of this loop, L could very well be deleted, so +/// it must not be used. +/// +/// FIXME: When the loop optimizer is more mature, separate this out to a new +/// pass. +/// +void LoopUnswitch::SimplifyCode(std::vector &Worklist, Loop *L) { + while (!Worklist.empty()) { + Instruction *I = Worklist.back(); + Worklist.pop_back(); + + // Simple constant folding. + if (Constant *C = ConstantFoldInstruction(I)) { + ReplaceUsesOfWith(I, C, Worklist, L, LPM); + continue; + } + + // Simple DCE. + if (isInstructionTriviallyDead(I)) { + DOUT << "Remove dead instruction '" << *I; + + // Add uses to the worklist, which may be dead now. + for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) + if (Instruction *Use = dyn_cast(I->getOperand(i))) + Worklist.push_back(Use); + LPM->deleteSimpleAnalysisValue(I, L); + RemoveFromWorklist(I, Worklist); + I->eraseFromParent(); + ++NumSimplify; + continue; + } + + // Special case hacks that appear commonly in unswitched code. + switch (I->getOpcode()) { + case Instruction::Select: + if (ConstantInt *CB = dyn_cast(I->getOperand(0))) { + ReplaceUsesOfWith(I, I->getOperand(!CB->getZExtValue()+1), Worklist, L, + LPM); + continue; + } + break; + case Instruction::And: + if (isa(I->getOperand(0)) && + I->getOperand(0)->getType() == Type::Int1Ty) // constant -> RHS + cast(I)->swapOperands(); + if (ConstantInt *CB = dyn_cast(I->getOperand(1))) + if (CB->getType() == Type::Int1Ty) { + if (CB->isOne()) // X & 1 -> X + ReplaceUsesOfWith(I, I->getOperand(0), Worklist, L, LPM); + else // X & 0 -> 0 + ReplaceUsesOfWith(I, I->getOperand(1), Worklist, L, LPM); + continue; + } + break; + case Instruction::Or: + if (isa(I->getOperand(0)) && + I->getOperand(0)->getType() == Type::Int1Ty) // constant -> RHS + cast(I)->swapOperands(); + if (ConstantInt *CB = dyn_cast(I->getOperand(1))) + if (CB->getType() == Type::Int1Ty) { + if (CB->isOne()) // X | 1 -> 1 + ReplaceUsesOfWith(I, I->getOperand(1), Worklist, L, LPM); + else // X | 0 -> X + ReplaceUsesOfWith(I, I->getOperand(0), Worklist, L, LPM); + continue; + } + break; + case Instruction::Br: { + BranchInst *BI = cast(I); + if (BI->isUnconditional()) { + // If BI's parent is the only pred of the successor, fold the two blocks + // together. + BasicBlock *Pred = BI->getParent(); + BasicBlock *Succ = BI->getSuccessor(0); + BasicBlock *SinglePred = Succ->getSinglePredecessor(); + if (!SinglePred) continue; // Nothing to do. + assert(SinglePred == Pred && "CFG broken"); + + DOUT << "Merging blocks: " << Pred->getName() << " <- " + << Succ->getName() << "\n"; + + // Resolve any single entry PHI nodes in Succ. + while (PHINode *PN = dyn_cast(Succ->begin())) + ReplaceUsesOfWith(PN, PN->getIncomingValue(0), Worklist, L, LPM); + + // Move all of the successor contents from Succ to Pred. + Pred->getInstList().splice(BI, Succ->getInstList(), Succ->begin(), + Succ->end()); + LPM->deleteSimpleAnalysisValue(BI, L); + BI->eraseFromParent(); + RemoveFromWorklist(BI, Worklist); + + // If Succ has any successors with PHI nodes, update them to have + // entries coming from Pred instead of Succ. + Succ->replaceAllUsesWith(Pred); + + // Remove Succ from the loop tree. + LI->removeBlock(Succ); + LPM->deleteSimpleAnalysisValue(Succ, L); + Succ->eraseFromParent(); + ++NumSimplify; + } else if (ConstantInt *CB = dyn_cast(BI->getCondition())){ + // Conditional branch. Turn it into an unconditional branch, then + // remove dead blocks. + break; // FIXME: Enable. + + DOUT << "Folded branch: " << *BI; + BasicBlock *DeadSucc = BI->getSuccessor(CB->getZExtValue()); + BasicBlock *LiveSucc = BI->getSuccessor(!CB->getZExtValue()); + DeadSucc->removePredecessor(BI->getParent(), true); + Worklist.push_back(BranchInst::Create(LiveSucc, BI)); + LPM->deleteSimpleAnalysisValue(BI, L); + BI->eraseFromParent(); + RemoveFromWorklist(BI, Worklist); + ++NumSimplify; + + RemoveBlockIfDead(DeadSucc, Worklist, L); + } + break; + } + } + } }