| //===-- LoopUnswitch.cpp - Hoist loop-invariant conditionals in loop ------===// |
| // |
| // 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 pass transforms loops that contain branches on loop-invariant conditions |
| // to have multiple loops. For example, it turns the left into the right code: |
| // |
| // for (...) if (lic) |
| // A for (...) |
| // if (lic) A; B; C |
| // B else |
| // C for (...) |
| // A; C |
| // |
| // This can increase the size of the code exponentially (doubling it every time |
| // a loop is unswitched) so we only unswitch if the resultant code will be |
| // smaller than a threshold. |
| // |
| // This pass expects LICM to be run before it to hoist invariant conditions out |
| // of the loop, to make the unswitching opportunity obvious. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #define DEBUG_TYPE "loop-unswitch" |
| #include "llvm/Transforms/Scalar.h" |
| #include "llvm/Constants.h" |
| #include "llvm/Function.h" |
| #include "llvm/Instructions.h" |
| #include "llvm/Analysis/LoopInfo.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/Support/CommandLine.h" |
| #include <algorithm> |
| #include <iostream> |
| #include <set> |
| using namespace llvm; |
| |
| namespace { |
| Statistic<> NumBranches("loop-unswitch", "Number of branches unswitched"); |
| Statistic<> NumSwitches("loop-unswitch", "Number of switches unswitched"); |
| Statistic<> NumSelects ("loop-unswitch", "Number of selects unswitched"); |
| Statistic<> NumTrivial ("loop-unswitch", |
| "Number of unswitches that are trivial"); |
| cl::opt<unsigned> |
| Threshold("loop-unswitch-threshold", cl::desc("Max loop size to unswitch"), |
| cl::init(10), cl::Hidden); |
| |
| class LoopUnswitch : public FunctionPass { |
| LoopInfo *LI; // Loop information |
| public: |
| virtual bool runOnFunction(Function &F); |
| bool visitLoop(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<LoopInfo>(); |
| AU.addPreserved<LoopInfo>(); |
| } |
| |
| private: |
| bool UnswitchIfProfitable(Value *LoopCond, Constant *Val,Loop *L); |
| unsigned getLoopUnswitchCost(Loop *L, Value *LIC); |
| void VersionLoop(Value *LIC, Constant *OnVal, |
| Loop *L, Loop *&Out1, Loop *&Out2); |
| BasicBlock *SplitEdge(BasicBlock *From, BasicBlock *To); |
| void RewriteLoopBodyWithConditionConstant(Loop *L, Value *LIC,Constant *Val, |
| bool isEqual); |
| void UnswitchTrivialCondition(Loop *L, Value *Cond, Constant *Val, |
| BasicBlock *ExitBlock); |
| }; |
| RegisterOpt<LoopUnswitch> X("loop-unswitch", "Unswitch loops"); |
| } |
| |
| FunctionPass *llvm::createLoopUnswitchPass() { return new LoopUnswitch(); } |
| |
| bool LoopUnswitch::runOnFunction(Function &F) { |
| bool Changed = false; |
| LI = &getAnalysis<LoopInfo>(); |
| |
| // 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<Loop*> SubLoops(LI->begin(), LI->end()); |
| for (unsigned i = 0, e = SubLoops.size(); i != e; ++i) |
| Changed |= visitLoop(SubLoops[i]); |
| |
| return Changed; |
| } |
| |
| |
| /// LoopValuesUsedOutsideLoop - Return true if there are any values defined in |
| /// the loop that are used by instructions outside of it. |
| 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<BasicBlock*> 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<Instruction>(*UI)->getParent(); |
| if (!LoopBlocks.count(UserBB)) |
| return true; |
| } |
| } |
| return false; |
| } |
| |
| /// FindTrivialLoopExitBlock - We know that we have a branch from the loop |
| /// header to the specified latch block. See if one of the successors of the |
| /// latch block is an exit, and if so what block it is. |
| static BasicBlock *FindTrivialLoopExitBlock(Loop *L, BasicBlock *Latch) { |
| BasicBlock *Header = L->getHeader(); |
| BranchInst *LatchBranch = dyn_cast<BranchInst>(Latch->getTerminator()); |
| if (!LatchBranch || !LatchBranch->isConditional()) return 0; |
| |
| // Simple case, the latch block is a conditional branch. The target that |
| // doesn't go to the loop header is our block if it is not in the loop. |
| if (LatchBranch->getSuccessor(0) == Header) { |
| if (L->contains(LatchBranch->getSuccessor(1))) return false; |
| return LatchBranch->getSuccessor(1); |
| } else { |
| assert(LatchBranch->getSuccessor(1) == Header); |
| if (L->contains(LatchBranch->getSuccessor(0))) return false; |
| return LatchBranch->getSuccessor(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 ConstantBool::True if the loop body |
| /// runs when the condition is true, False if the loop body executes when the |
| /// condition is false. Otherwise, return null to indicate a complex condition. |
| static bool IsTrivialUnswitchCondition(Loop *L, Value *Cond, |
| Constant **Val = 0, |
| BasicBlock **LoopExit = 0) { |
| BasicBlock *Header = L->getHeader(); |
| BranchInst *HeaderTerm = dyn_cast<BranchInst>(Header->getTerminator()); |
| |
| // If the header block doesn't end with a conditional branch on Cond, we can't |
| // handle it. |
| if (!HeaderTerm || !HeaderTerm->isConditional() || |
| HeaderTerm->getCondition() != Cond) |
| return false; |
| |
| // Check to see if the conditional branch goes to the latch block. If not, |
| // it's not trivial. This also determines the value of Cond that will execute |
| // the loop. |
| BasicBlock *Latch = L->getLoopLatch(); |
| if (HeaderTerm->getSuccessor(1) == Latch) { |
| if (Val) *Val = ConstantBool::True; |
| } else if (HeaderTerm->getSuccessor(0) == Latch) |
| if (Val) *Val = ConstantBool::False; |
| else |
| return false; // Doesn't branch to latch block. |
| |
| // The latch block must end with a conditional branch where one edge goes to |
| // the header (this much we know) and one edge goes OUT of the loop. |
| BasicBlock *LoopExitBlock = FindTrivialLoopExitBlock(L, Latch); |
| if (!LoopExitBlock) return 0; |
| if (LoopExit) *LoopExit = LoopExitBlock; |
| |
| // 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. |
| for (BasicBlock::iterator I = Header->begin(), E = Header->end(); I != E; ++I) |
| if (I->mayWriteToMemory()) |
| return false; |
| for (BasicBlock::iterator I = Latch->begin(), E = Latch->end(); I != E; ++I) |
| if (I->mayWriteToMemory()) |
| return false; |
| return true; |
| } |
| |
| /// getLoopUnswitchCost - Return the cost (code size growth) that will happen if |
| /// we choose to unswitch the specified loop on the specified value. |
| /// |
| 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; |
| |
| 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; |
| } |
| |
| return Cost; |
| } |
| |
| /// 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<Constant>(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<BinaryOperator>(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 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<Loop*> SubLoops(L->begin(), L->end()); |
| for (unsigned i = 0, e = SubLoops.size(); i != e; ++i) |
| Changed |= visitLoop(SubLoops[i]); |
| |
| // 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 |
| // loop. |
| for (Loop::block_iterator I = L->block_begin(), E = L->block_end(); |
| I != E; ++I) { |
| TerminatorInst *TI = (*I)->getTerminator(); |
| if (BranchInst *BI = dyn_cast<BranchInst>(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, ConstantBool::True, L)) { |
| ++NumBranches; |
| return true; |
| } |
| } |
| } else if (SwitchInst *SI = dyn_cast<SwitchInst>(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); |
| if (UnswitchIfProfitable(LoopCond, UnswitchVal, L)) { |
| ++NumSwitches; |
| return true; |
| } |
| } |
| } |
| |
| // 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<SelectInst>(BBI)) { |
| Value *LoopCond = FindLIVLoopCondition(SI->getCondition(), L, Changed); |
| if (LoopCond && UnswitchIfProfitable(LoopCond, ConstantBool::True, L)) { |
| ++NumSelects; |
| return true; |
| } |
| } |
| } |
| |
| return Changed; |
| } |
| |
| /// 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. |
| if (getLoopUnswitchCost(L, LoopCond) > Threshold) { |
| // FIXME: this should estimate growth by the amount of code shared by the |
| // resultant unswitched loops. |
| // |
| DEBUG(std::cerr << "NOT unswitching loop %" |
| << L->getHeader()->getName() << ", cost too high: " |
| << L->getBlocks().size() << "\n"); |
| return false; |
| } |
| |
| // 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"); |
| return false; |
| } |
| |
| //std::cerr << "BEFORE:\n"; LI->dump(); |
| Loop *NewLoop1 = 0, *NewLoop2 = 0; |
| |
| // 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); |
| NewLoop1 = L; |
| } else { |
| VersionLoop(LoopCond, Val, L, NewLoop1, NewLoop2); |
| } |
| |
| //std::cerr << "AFTER:\n"; LI->dump(); |
| |
| // Try to unswitch each of our new loops now! |
| if (NewLoop1) visitLoop(NewLoop1); |
| if (NewLoop2) visitLoop(NewLoop2); |
| return true; |
| } |
| |
| BasicBlock *LoopUnswitch::SplitEdge(BasicBlock *BB, BasicBlock *Succ) { |
| TerminatorInst *LatchTerm = BB->getTerminator(); |
| unsigned SuccNum = 0; |
| for (unsigned i = 0, e = LatchTerm->getNumSuccessors(); ; ++i) { |
| assert(i != e && "Didn't find edge?"); |
| if (LatchTerm->getSuccessor(i) == Succ) { |
| SuccNum = i; |
| break; |
| } |
| } |
| |
| // If this is a critical edge, let SplitCriticalEdge do it. |
| if (SplitCriticalEdge(BB->getTerminator(), SuccNum, this)) |
| return LatchTerm->getSuccessor(SuccNum); |
| |
| // If the edge isn't critical, then BB has a single successor or Succ has a |
| // single pred. Split the block. |
| BasicBlock *BlockToSplit; |
| BasicBlock::iterator SplitPoint; |
| if (BasicBlock *SP = Succ->getSinglePredecessor()) { |
| // If the successor only has a single pred, split the top of the successor |
| // block. |
| assert(SP == BB && "CFG broken"); |
| BlockToSplit = Succ; |
| SplitPoint = Succ->begin(); |
| } else { |
| // Otherwise, if BB has a single successor, split it at the bottom of the |
| // block. |
| assert(BB->getTerminator()->getNumSuccessors() == 1 && |
| "Should have a single succ!"); |
| BlockToSplit = BB; |
| SplitPoint = BB->getTerminator(); |
| } |
| |
| BasicBlock *New = |
| BlockToSplit->splitBasicBlock(SplitPoint, |
| BlockToSplit->getName()+".tail"); |
| // New now lives in whichever loop that BB used to. |
| if (Loop *L = LI->getLoopFor(BlockToSplit)) |
| L->addBasicBlockToLoop(New, *LI); |
| return New; |
| } |
| |
| |
| |
| // RemapInstruction - Convert the instruction operands from referencing the |
| // current values into those specified by ValueMap. |
| // |
| static inline void RemapInstruction(Instruction *I, |
| std::map<const Value *, Value*> &ValueMap) { |
| for (unsigned op = 0, E = I->getNumOperands(); op != E; ++op) { |
| Value *Op = I->getOperand(op); |
| std::map<const Value *, Value*>::iterator It = ValueMap.find(Op); |
| if (It != ValueMap.end()) Op = It->second; |
| I->setOperand(op, Op); |
| } |
| } |
| |
| /// 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<const Value*, Value*> &VM, |
| LoopInfo *LI) { |
| Loop *New = new Loop(); |
| |
| if (PL) |
| PL->addChildLoop(New); |
| else |
| LI->addTopLevelLoop(New); |
| |
| // 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<BasicBlock>(VM[*I]), *LI); |
| |
| // 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); |
| |
| 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. |
| static void 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<ConstantBool>(Val)) { |
| BranchVal = BinaryOperator::createSetEQ(LIC, Val, "tmp", InsertPt); |
| } else if (Val != ConstantBool::True) { |
| // We want to enter the new loop when the condition is true. |
| std::swap(TrueDest, FalseDest); |
| } |
| |
| // Insert the new branch. |
| new BranchInst(TrueDest, FalseDest, BranchVal, InsertPt); |
| } |
| |
| |
| /// 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) { |
| DEBUG(std::cerr << "loop-unswitch: Trivial-Unswitch loop %" |
| << L->getHeader()->getName() << " [" << L->getBlocks().size() |
| << " blocks] in Function " << L->getHeader()->getParent()->getName() |
| << " on cond:" << *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()); |
| |
| // 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 edge now, so that the loop maintains its exit block. |
| assert(!L->contains(ExitBlock) && "Exit block is in the loop?"); |
| BasicBlock *NewExit = SplitEdge(L->getLoopLatch(), ExitBlock); |
| assert(NewExit != ExitBlock && "Edge not split!"); |
| |
| // Okay, now we have a position to branch from and a position to branch to, |
| // insert the new conditional branch. |
| EmitPreheaderBranchOnCondition(Cond, Val, NewPH, NewExit, |
| OrigPH->getTerminator()); |
| OrigPH->getTerminator()->eraseFromParent(); |
| |
| // 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, true); |
| ++NumTrivial; |
| } |
| |
| |
| /// VersionLoop - 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::VersionLoop(Value *LIC, Constant *Val, Loop *L, |
| Loop *&Out1, Loop *&Out2) { |
| Function *F = L->getHeader()->getParent(); |
| |
| DEBUG(std::cerr << "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<BasicBlock*> LoopBlocks; |
| |
| // First step, split the preheader and exit blocks, and add these blocks to |
| // the LoopBlocks list. |
| BasicBlock *OrigPreheader = L->getLoopPreheader(); |
| LoopBlocks.push_back(SplitEdge(OrigPreheader, L->getHeader())); |
| |
| // 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<BasicBlock*> ExitBlocks; |
| L->getExitBlocks(ExitBlocks); |
| std::sort(ExitBlocks.begin(), ExitBlocks.end()); |
| ExitBlocks.erase(std::unique(ExitBlocks.begin(), ExitBlocks.end()), |
| ExitBlocks.end()); |
| |
| // Split all of the edges from inside the loop to their exit blocks. This |
| // unswitching trivial: no phi nodes to update. |
| unsigned NumBlocks = L->getBlocks().size(); |
| for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) { |
| BasicBlock *ExitBlock = ExitBlocks[i]; |
| std::vector<BasicBlock*> Preds(pred_begin(ExitBlock), pred_end(ExitBlock)); |
| |
| for (unsigned j = 0, e = Preds.size(); j != e; ++j) { |
| assert(L->contains(Preds[j]) && |
| "All preds of loop exit blocks must be the same loop!"); |
| SplitEdge(Preds[j], ExitBlock); |
| } |
| } |
| |
| // The exit blocks may have been changed due to edge splitting, recompute. |
| ExitBlocks.clear(); |
| L->getExitBlocks(ExitBlocks); |
| std::sort(ExitBlocks.begin(), ExitBlocks.end()); |
| ExitBlocks.erase(std::unique(ExitBlocks.begin(), ExitBlocks.end()), |
| ExitBlocks.end()); |
| |
| // 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<BasicBlock*> NewBlocks; |
| NewBlocks.reserve(LoopBlocks.size()); |
| std::map<const Value*, Value*> ValueMap; |
| for (unsigned i = 0, e = LoopBlocks.size(); i != e; ++i) { |
| BasicBlock *New = CloneBasicBlock(LoopBlocks[i], ValueMap, ".us", F); |
| NewBlocks.push_back(New); |
| ValueMap[LoopBlocks[i]] = New; // Keep the BB mapping. |
| } |
| |
| // Splice the newly inserted blocks into the function right before the |
| // original preheader. |
| F->getBasicBlockList().splice(LoopBlocks[0], F->getBasicBlockList(), |
| NewBlocks[0], F->end()); |
| |
| // Now we create the new Loop object for the versioned loop. |
| Loop *NewLoop = CloneLoop(L, L->getParentLoop(), ValueMap, LI); |
| Loop *ParentLoop = L->getParentLoop(); |
| if (ParentLoop) { |
| // Make sure to add the cloned preheader and exit blocks to the parent loop |
| // as well. |
| ParentLoop->addBasicBlockToLoop(NewBlocks[0], *LI); |
| } |
| |
| for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) { |
| BasicBlock *NewExit = cast<BasicBlock>(ValueMap[ExitBlocks[i]]); |
| if (ParentLoop) |
| ParentLoop->addBasicBlockToLoop(cast<BasicBlock>(NewExit), *LI); |
| |
| 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<PHINode>(I)); ++I) { |
| Value *V = PN->getIncomingValueForBlock(ExitBlocks[i]); |
| std::map<const Value *, Value*>::iterator It = ValueMap.find(V); |
| if (It != ValueMap.end()) V = It->second; |
| PN->addIncoming(V, NewExit); |
| } |
| } |
| |
| // Rewrite the code to refer to itself. |
| for (unsigned i = 0, e = NewBlocks.size(); i != e; ++i) |
| for (BasicBlock::iterator I = NewBlocks[i]->begin(), |
| E = NewBlocks[i]->end(); I != E; ++I) |
| RemapInstruction(I, ValueMap); |
| |
| // Rewrite the original preheader to select between versions of the loop. |
| BranchInst *OldBR = cast<BranchInst>(OrigPreheader->getTerminator()); |
| assert(OldBR->isUnconditional() && OldBR->getSuccessor(0) == LoopBlocks[0] && |
| "Preheader splitting did not work correctly!"); |
| |
| // Emit the new branch that selects between the two versions of this loop. |
| EmitPreheaderBranchOnCondition(LIC, Val, NewBlocks[0], LoopBlocks[0], OldBR); |
| OldBR->eraseFromParent(); |
| |
| // 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, Val, false); |
| RewriteLoopBodyWithConditionConstant(NewLoop, LIC, Val, true); |
| Out1 = L; |
| Out2 = NewLoop; |
| } |
| |
| // 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, |
| Constant *Val, |
| bool IsEqual) { |
| assert(!isa<Constant>(LIC) && "Why are we unswitching on a constant?"); |
| |
| // FIXME: Support correlated properties, like: |
| // for (...) |
| // if (li1 < li2) |
| // ... |
| // if (li1 > li2) |
| // ... |
| |
| // NotVal - If Val is a bool, this contains its inverse. |
| Constant *NotVal = 0; |
| if (ConstantBool *CB = dyn_cast<ConstantBool>(Val)) |
| NotVal = ConstantBool::get(!CB->getValue()); |
| |
| // FOLD boolean conditions (X|LIC), (X&LIC). Fold conditional branches, |
| // selects, switches. |
| std::vector<User*> Users(LIC->use_begin(), LIC->use_end()); |
| |
| // Haha, this loop could be unswitched. Get it? The unswitch pass could |
| // unswitch itself. Amazing. |
| for (unsigned i = 0, e = Users.size(); i != e; ++i) |
| if (Instruction *U = cast<Instruction>(Users[i])) |
| if (L->contains(U->getParent())) |
| if (IsEqual) { |
| U->replaceUsesOfWith(LIC, Val); |
| } else if (NotVal) { |
| U->replaceUsesOfWith(LIC, NotVal); |
| } else { |
| // If we know that LIC is not Val, use this info to simplify code. |
| if (SwitchInst *SI = dyn_cast<SwitchInst>(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. |
| SI->getSuccessor(i)->removePredecessor(SI->getParent(), true); |
| SI->removeCase(i); |
| break; |
| } |
| } |
| } |
| |
| // TODO: We could simplify stuff like X == C. |
| } |
| } |