diff options
Diffstat (limited to 'contrib/llvm/lib/Transforms/Utils/LoopSimplify.cpp')
| -rw-r--r-- | contrib/llvm/lib/Transforms/Utils/LoopSimplify.cpp | 829 |
1 files changed, 444 insertions, 385 deletions
diff --git a/contrib/llvm/lib/Transforms/Utils/LoopSimplify.cpp b/contrib/llvm/lib/Transforms/Utils/LoopSimplify.cpp index 6d5f16c..ef42291 100644 --- a/contrib/llvm/lib/Transforms/Utils/LoopSimplify.cpp +++ b/contrib/llvm/lib/Transforms/Utils/LoopSimplify.cpp @@ -37,331 +37,72 @@ // //===----------------------------------------------------------------------===// -#define DEBUG_TYPE "loop-simplify" #include "llvm/Transforms/Scalar.h" #include "llvm/ADT/DepthFirstIterator.h" #include "llvm/ADT/SetOperations.h" #include "llvm/ADT/SetVector.h" +#include "llvm/ADT/SmallVector.h" #include "llvm/ADT/Statistic.h" #include "llvm/Analysis/AliasAnalysis.h" #include "llvm/Analysis/DependenceAnalysis.h" -#include "llvm/Analysis/Dominators.h" #include "llvm/Analysis/InstructionSimplify.h" -#include "llvm/Analysis/LoopPass.h" +#include "llvm/Analysis/LoopInfo.h" #include "llvm/Analysis/ScalarEvolution.h" +#include "llvm/IR/CFG.h" #include "llvm/IR/Constants.h" +#include "llvm/IR/DataLayout.h" +#include "llvm/IR/Dominators.h" #include "llvm/IR/Function.h" #include "llvm/IR/Instructions.h" #include "llvm/IR/IntrinsicInst.h" #include "llvm/IR/LLVMContext.h" #include "llvm/IR/Type.h" -#include "llvm/Support/CFG.h" #include "llvm/Support/Debug.h" #include "llvm/Transforms/Utils/BasicBlockUtils.h" #include "llvm/Transforms/Utils/Local.h" #include "llvm/Transforms/Utils/LoopUtils.h" using namespace llvm; +#define DEBUG_TYPE "loop-simplify" + STATISTIC(NumInserted, "Number of pre-header or exit blocks inserted"); STATISTIC(NumNested , "Number of nested loops split out"); -namespace { - struct LoopSimplify : public LoopPass { - static char ID; // Pass identification, replacement for typeid - LoopSimplify() : LoopPass(ID) { - initializeLoopSimplifyPass(*PassRegistry::getPassRegistry()); - } - - // AA - If we have an alias analysis object to update, this is it, otherwise - // this is null. - AliasAnalysis *AA; - LoopInfo *LI; - DominatorTree *DT; - ScalarEvolution *SE; - Loop *L; - virtual bool runOnLoop(Loop *L, LPPassManager &LPM); - - virtual void getAnalysisUsage(AnalysisUsage &AU) const { - // We need loop information to identify the loops... - AU.addRequired<DominatorTree>(); - AU.addPreserved<DominatorTree>(); - - AU.addRequired<LoopInfo>(); - AU.addPreserved<LoopInfo>(); - - AU.addPreserved<AliasAnalysis>(); - AU.addPreserved<ScalarEvolution>(); - AU.addPreserved<DependenceAnalysis>(); - AU.addPreservedID(BreakCriticalEdgesID); // No critical edges added. - } - - /// verifyAnalysis() - Verify LoopSimplifyForm's guarantees. - void verifyAnalysis() const; - - private: - bool ProcessLoop(Loop *L, LPPassManager &LPM); - BasicBlock *RewriteLoopExitBlock(Loop *L, BasicBlock *Exit); - Loop *SeparateNestedLoop(Loop *L, LPPassManager &LPM, - BasicBlock *Preheader); - BasicBlock *InsertUniqueBackedgeBlock(Loop *L, BasicBlock *Preheader); - }; -} - -static void PlaceSplitBlockCarefully(BasicBlock *NewBB, - SmallVectorImpl<BasicBlock*> &SplitPreds, - Loop *L); - -char LoopSimplify::ID = 0; -INITIALIZE_PASS_BEGIN(LoopSimplify, "loop-simplify", - "Canonicalize natural loops", true, false) -INITIALIZE_PASS_DEPENDENCY(DominatorTree) -INITIALIZE_PASS_DEPENDENCY(LoopInfo) -INITIALIZE_PASS_END(LoopSimplify, "loop-simplify", - "Canonicalize natural loops", true, false) - -// Publicly exposed interface to pass... -char &llvm::LoopSimplifyID = LoopSimplify::ID; -Pass *llvm::createLoopSimplifyPass() { return new LoopSimplify(); } - -/// runOnLoop - Run down all loops in the CFG (recursively, but we could do -/// it in any convenient order) inserting preheaders... -/// -bool LoopSimplify::runOnLoop(Loop *l, LPPassManager &LPM) { - L = l; - bool Changed = false; - LI = &getAnalysis<LoopInfo>(); - AA = getAnalysisIfAvailable<AliasAnalysis>(); - DT = &getAnalysis<DominatorTree>(); - SE = getAnalysisIfAvailable<ScalarEvolution>(); - - Changed |= ProcessLoop(L, LPM); - - return Changed; -} - -/// ProcessLoop - Walk the loop structure in depth first order, ensuring that -/// all loops have preheaders. -/// -bool LoopSimplify::ProcessLoop(Loop *L, LPPassManager &LPM) { - bool Changed = false; -ReprocessLoop: - - // Check to see that no blocks (other than the header) in this loop have - // predecessors that are not in the loop. This is not valid for natural - // loops, but can occur if the blocks are unreachable. Since they are - // unreachable we can just shamelessly delete those CFG edges! - for (Loop::block_iterator BB = L->block_begin(), E = L->block_end(); - BB != E; ++BB) { - if (*BB == L->getHeader()) continue; - - SmallPtrSet<BasicBlock*, 4> BadPreds; - for (pred_iterator PI = pred_begin(*BB), - PE = pred_end(*BB); PI != PE; ++PI) { - BasicBlock *P = *PI; - if (!L->contains(P)) - BadPreds.insert(P); - } - - // Delete each unique out-of-loop (and thus dead) predecessor. - for (SmallPtrSet<BasicBlock*, 4>::iterator I = BadPreds.begin(), - E = BadPreds.end(); I != E; ++I) { - - DEBUG(dbgs() << "LoopSimplify: Deleting edge from dead predecessor " - << (*I)->getName() << "\n"); - - // Inform each successor of each dead pred. - for (succ_iterator SI = succ_begin(*I), SE = succ_end(*I); SI != SE; ++SI) - (*SI)->removePredecessor(*I); - // Zap the dead pred's terminator and replace it with unreachable. - TerminatorInst *TI = (*I)->getTerminator(); - TI->replaceAllUsesWith(UndefValue::get(TI->getType())); - (*I)->getTerminator()->eraseFromParent(); - new UnreachableInst((*I)->getContext(), *I); - Changed = true; - } - } - - // If there are exiting blocks with branches on undef, resolve the undef in - // the direction which will exit the loop. This will help simplify loop - // trip count computations. - SmallVector<BasicBlock*, 8> ExitingBlocks; - L->getExitingBlocks(ExitingBlocks); - for (SmallVectorImpl<BasicBlock *>::iterator I = ExitingBlocks.begin(), - E = ExitingBlocks.end(); I != E; ++I) - if (BranchInst *BI = dyn_cast<BranchInst>((*I)->getTerminator())) - if (BI->isConditional()) { - if (UndefValue *Cond = dyn_cast<UndefValue>(BI->getCondition())) { - - DEBUG(dbgs() << "LoopSimplify: Resolving \"br i1 undef\" to exit in " - << (*I)->getName() << "\n"); - - BI->setCondition(ConstantInt::get(Cond->getType(), - !L->contains(BI->getSuccessor(0)))); - - // This may make the loop analyzable, force SCEV recomputation. - if (SE) - SE->forgetLoop(L); - - Changed = true; - } - } - - // Does the loop already have a preheader? If so, don't insert one. - BasicBlock *Preheader = L->getLoopPreheader(); - if (!Preheader) { - Preheader = InsertPreheaderForLoop(L, this); - if (Preheader) { - ++NumInserted; - Changed = true; - } - } - - // Next, check to make sure that all exit nodes of the loop only have - // predecessors that are inside of the loop. This check guarantees that the - // loop preheader/header will dominate the exit blocks. If the exit block has - // predecessors from outside of the loop, split the edge now. - SmallVector<BasicBlock*, 8> ExitBlocks; - L->getExitBlocks(ExitBlocks); - - SmallSetVector<BasicBlock *, 8> ExitBlockSet(ExitBlocks.begin(), - ExitBlocks.end()); - for (SmallSetVector<BasicBlock *, 8>::iterator I = ExitBlockSet.begin(), - E = ExitBlockSet.end(); I != E; ++I) { - BasicBlock *ExitBlock = *I; - for (pred_iterator PI = pred_begin(ExitBlock), PE = pred_end(ExitBlock); - PI != PE; ++PI) - // Must be exactly this loop: no subloops, parent loops, or non-loop preds - // allowed. - if (!L->contains(*PI)) { - if (RewriteLoopExitBlock(L, ExitBlock)) { - ++NumInserted; - Changed = true; - } - break; - } - } - - // If the header has more than two predecessors at this point (from the - // preheader and from multiple backedges), we must adjust the loop. - BasicBlock *LoopLatch = L->getLoopLatch(); - if (!LoopLatch) { - // If this is really a nested loop, rip it out into a child loop. Don't do - // this for loops with a giant number of backedges, just factor them into a - // common backedge instead. - if (L->getNumBackEdges() < 8) { - if (SeparateNestedLoop(L, LPM, Preheader)) { - ++NumNested; - // This is a big restructuring change, reprocess the whole loop. - Changed = true; - // GCC doesn't tail recursion eliminate this. - goto ReprocessLoop; - } - } - - // If we either couldn't, or didn't want to, identify nesting of the loops, - // insert a new block that all backedges target, then make it jump to the - // loop header. - LoopLatch = InsertUniqueBackedgeBlock(L, Preheader); - if (LoopLatch) { - ++NumInserted; - Changed = true; - } +// If the block isn't already, move the new block to right after some 'outside +// block' block. This prevents the preheader from being placed inside the loop +// body, e.g. when the loop hasn't been rotated. +static void placeSplitBlockCarefully(BasicBlock *NewBB, + SmallVectorImpl<BasicBlock *> &SplitPreds, + Loop *L) { + // Check to see if NewBB is already well placed. + Function::iterator BBI = NewBB; --BBI; + for (unsigned i = 0, e = SplitPreds.size(); i != e; ++i) { + if (&*BBI == SplitPreds[i]) + return; } - // Scan over the PHI nodes in the loop header. Since they now have only two - // incoming values (the loop is canonicalized), we may have simplified the PHI - // down to 'X = phi [X, Y]', which should be replaced with 'Y'. - PHINode *PN; - for (BasicBlock::iterator I = L->getHeader()->begin(); - (PN = dyn_cast<PHINode>(I++)); ) - if (Value *V = SimplifyInstruction(PN, 0, 0, DT)) { - if (AA) AA->deleteValue(PN); - if (SE) SE->forgetValue(PN); - PN->replaceAllUsesWith(V); - PN->eraseFromParent(); - } - - // If this loop has multiple exits and the exits all go to the same - // block, attempt to merge the exits. This helps several passes, such - // as LoopRotation, which do not support loops with multiple exits. - // SimplifyCFG also does this (and this code uses the same utility - // function), however this code is loop-aware, where SimplifyCFG is - // not. That gives it the advantage of being able to hoist - // loop-invariant instructions out of the way to open up more - // opportunities, and the disadvantage of having the responsibility - // to preserve dominator information. - bool UniqueExit = true; - if (!ExitBlocks.empty()) - for (unsigned i = 1, e = ExitBlocks.size(); i != e; ++i) - if (ExitBlocks[i] != ExitBlocks[0]) { - UniqueExit = false; - break; - } - if (UniqueExit) { - for (unsigned i = 0, e = ExitingBlocks.size(); i != e; ++i) { - BasicBlock *ExitingBlock = ExitingBlocks[i]; - if (!ExitingBlock->getSinglePredecessor()) continue; - BranchInst *BI = dyn_cast<BranchInst>(ExitingBlock->getTerminator()); - if (!BI || !BI->isConditional()) continue; - CmpInst *CI = dyn_cast<CmpInst>(BI->getCondition()); - if (!CI || CI->getParent() != ExitingBlock) continue; - - // Attempt to hoist out all instructions except for the - // comparison and the branch. - bool AllInvariant = true; - for (BasicBlock::iterator I = ExitingBlock->begin(); &*I != BI; ) { - Instruction *Inst = I++; - // Skip debug info intrinsics. - if (isa<DbgInfoIntrinsic>(Inst)) - continue; - if (Inst == CI) - continue; - if (!L->makeLoopInvariant(Inst, Changed, - Preheader ? Preheader->getTerminator() : 0)) { - AllInvariant = false; - break; - } - } - if (!AllInvariant) continue; - - // The block has now been cleared of all instructions except for - // a comparison and a conditional branch. SimplifyCFG may be able - // to fold it now. - if (!FoldBranchToCommonDest(BI)) continue; - - // Success. The block is now dead, so remove it from the loop, - // update the dominator tree and delete it. - DEBUG(dbgs() << "LoopSimplify: Eliminating exiting block " - << ExitingBlock->getName() << "\n"); - - // If any reachable control flow within this loop has changed, notify - // ScalarEvolution. Currently assume the parent loop doesn't change - // (spliting edges doesn't count). If blocks, CFG edges, or other values - // in the parent loop change, then we need call to forgetLoop() for the - // parent instead. - if (SE) - SE->forgetLoop(L); - - assert(pred_begin(ExitingBlock) == pred_end(ExitingBlock)); - Changed = true; - LI->removeBlock(ExitingBlock); - - DomTreeNode *Node = DT->getNode(ExitingBlock); - const std::vector<DomTreeNodeBase<BasicBlock> *> &Children = - Node->getChildren(); - while (!Children.empty()) { - DomTreeNode *Child = Children.front(); - DT->changeImmediateDominator(Child, Node->getIDom()); - } - DT->eraseNode(ExitingBlock); + // If it isn't already after an outside block, move it after one. This is + // always good as it makes the uncond branch from the outside block into a + // fall-through. - BI->getSuccessor(0)->removePredecessor(ExitingBlock); - BI->getSuccessor(1)->removePredecessor(ExitingBlock); - ExitingBlock->eraseFromParent(); + // Figure out *which* outside block to put this after. Prefer an outside + // block that neighbors a BB actually in the loop. + BasicBlock *FoundBB = nullptr; + for (unsigned i = 0, e = SplitPreds.size(); i != e; ++i) { + Function::iterator BBI = SplitPreds[i]; + if (++BBI != NewBB->getParent()->end() && + L->contains(BBI)) { + FoundBB = SplitPreds[i]; + break; } } - return Changed; + // If our heuristic for a *good* bb to place this after doesn't find + // anything, just pick something. It's likely better than leaving it within + // the loop. + if (!FoundBB) + FoundBB = SplitPreds[0]; + NewBB->moveAfter(FoundBB); } /// InsertPreheaderForLoop - Once we discover that a loop doesn't have a @@ -380,7 +121,7 @@ BasicBlock *llvm::InsertPreheaderForLoop(Loop *L, Pass *PP) { // If the loop is branched to from an indirect branch, we won't // be able to fully transform the loop, because it prohibits // edge splitting. - if (isa<IndirectBrInst>(P->getTerminator())) return 0; + if (isa<IndirectBrInst>(P->getTerminator())) return nullptr; // Keep track of it. OutsideBlocks.push_back(P); @@ -406,38 +147,39 @@ BasicBlock *llvm::InsertPreheaderForLoop(Loop *L, Pass *PP) { // Make sure that NewBB is put someplace intelligent, which doesn't mess up // code layout too horribly. - PlaceSplitBlockCarefully(PreheaderBB, OutsideBlocks, L); + placeSplitBlockCarefully(PreheaderBB, OutsideBlocks, L); return PreheaderBB; } -/// RewriteLoopExitBlock - Ensure that the loop preheader dominates all exit -/// blocks. This method is used to split exit blocks that have predecessors -/// outside of the loop. -BasicBlock *LoopSimplify::RewriteLoopExitBlock(Loop *L, BasicBlock *Exit) { +/// \brief Ensure that the loop preheader dominates all exit blocks. +/// +/// This method is used to split exit blocks that have predecessors outside of +/// the loop. +static BasicBlock *rewriteLoopExitBlock(Loop *L, BasicBlock *Exit, Pass *PP) { SmallVector<BasicBlock*, 8> LoopBlocks; for (pred_iterator I = pred_begin(Exit), E = pred_end(Exit); I != E; ++I) { BasicBlock *P = *I; if (L->contains(P)) { // Don't do this if the loop is exited via an indirect branch. - if (isa<IndirectBrInst>(P->getTerminator())) return 0; + if (isa<IndirectBrInst>(P->getTerminator())) return nullptr; LoopBlocks.push_back(P); } } assert(!LoopBlocks.empty() && "No edges coming in from outside the loop?"); - BasicBlock *NewExitBB = 0; + BasicBlock *NewExitBB = nullptr; if (Exit->isLandingPad()) { SmallVector<BasicBlock*, 2> NewBBs; SplitLandingPadPredecessors(Exit, ArrayRef<BasicBlock*>(&LoopBlocks[0], LoopBlocks.size()), ".loopexit", ".nonloopexit", - this, NewBBs); + PP, NewBBs); NewExitBB = NewBBs[0]; } else { - NewExitBB = SplitBlockPredecessors(Exit, LoopBlocks, ".loopexit", this); + NewExitBB = SplitBlockPredecessors(Exit, LoopBlocks, ".loopexit", PP); } DEBUG(dbgs() << "LoopSimplify: Creating dedicated exit block " @@ -445,33 +187,33 @@ BasicBlock *LoopSimplify::RewriteLoopExitBlock(Loop *L, BasicBlock *Exit) { return NewExitBB; } -/// AddBlockAndPredsToSet - Add the specified block, and all of its -/// predecessors, to the specified set, if it's not already in there. Stop -/// predecessor traversal when we reach StopBlock. -static void AddBlockAndPredsToSet(BasicBlock *InputBB, BasicBlock *StopBlock, +/// Add the specified block, and all of its predecessors, to the specified set, +/// if it's not already in there. Stop predecessor traversal when we reach +/// StopBlock. +static void addBlockAndPredsToSet(BasicBlock *InputBB, BasicBlock *StopBlock, std::set<BasicBlock*> &Blocks) { - std::vector<BasicBlock *> WorkList; - WorkList.push_back(InputBB); + SmallVector<BasicBlock *, 8> Worklist; + Worklist.push_back(InputBB); do { - BasicBlock *BB = WorkList.back(); WorkList.pop_back(); + BasicBlock *BB = Worklist.pop_back_val(); if (Blocks.insert(BB).second && BB != StopBlock) // If BB is not already processed and it is not a stop block then // insert its predecessor in the work list for (pred_iterator I = pred_begin(BB), E = pred_end(BB); I != E; ++I) { BasicBlock *WBB = *I; - WorkList.push_back(WBB); + Worklist.push_back(WBB); } - } while(!WorkList.empty()); + } while (!Worklist.empty()); } -/// FindPHIToPartitionLoops - The first part of loop-nestification is to find a -/// PHI node that tells us how to partition the loops. -static PHINode *FindPHIToPartitionLoops(Loop *L, DominatorTree *DT, - AliasAnalysis *AA, LoopInfo *LI) { +/// \brief The first part of loop-nestification is to find a PHI node that tells +/// us how to partition the loops. +static PHINode *findPHIToPartitionLoops(Loop *L, AliasAnalysis *AA, + DominatorTree *DT) { for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ) { PHINode *PN = cast<PHINode>(I); ++I; - if (Value *V = SimplifyInstruction(PN, 0, 0, DT)) { + if (Value *V = SimplifyInstruction(PN, nullptr, nullptr, DT)) { // This is a degenerate PHI already, don't modify it! PN->replaceAllUsesWith(V); if (AA) AA->deleteValue(PN); @@ -486,49 +228,13 @@ static PHINode *FindPHIToPartitionLoops(Loop *L, DominatorTree *DT, // We found something tasty to remove. return PN; } - return 0; + return nullptr; } -// PlaceSplitBlockCarefully - If the block isn't already, move the new block to -// right after some 'outside block' block. This prevents the preheader from -// being placed inside the loop body, e.g. when the loop hasn't been rotated. -void PlaceSplitBlockCarefully(BasicBlock *NewBB, - SmallVectorImpl<BasicBlock*> &SplitPreds, - Loop *L) { - // Check to see if NewBB is already well placed. - Function::iterator BBI = NewBB; --BBI; - for (unsigned i = 0, e = SplitPreds.size(); i != e; ++i) { - if (&*BBI == SplitPreds[i]) - return; - } - - // If it isn't already after an outside block, move it after one. This is - // always good as it makes the uncond branch from the outside block into a - // fall-through. - - // Figure out *which* outside block to put this after. Prefer an outside - // block that neighbors a BB actually in the loop. - BasicBlock *FoundBB = 0; - for (unsigned i = 0, e = SplitPreds.size(); i != e; ++i) { - Function::iterator BBI = SplitPreds[i]; - if (++BBI != NewBB->getParent()->end() && - L->contains(BBI)) { - FoundBB = SplitPreds[i]; - break; - } - } - - // If our heuristic for a *good* bb to place this after doesn't find - // anything, just pick something. It's likely better than leaving it within - // the loop. - if (!FoundBB) - FoundBB = SplitPreds[0]; - NewBB->moveAfter(FoundBB); -} - - -/// SeparateNestedLoop - If this loop has multiple backedges, try to pull one of -/// them out into a nested loop. This is important for code that looks like +/// \brief If this loop has multiple backedges, try to pull one of them out into +/// a nested loop. +/// +/// This is important for code that looks like /// this: /// /// Loop: @@ -544,18 +250,19 @@ void PlaceSplitBlockCarefully(BasicBlock *NewBB, /// If we are able to separate out a loop, return the new outer loop that was /// created. /// -Loop *LoopSimplify::SeparateNestedLoop(Loop *L, LPPassManager &LPM, - BasicBlock *Preheader) { +static Loop *separateNestedLoop(Loop *L, BasicBlock *Preheader, + AliasAnalysis *AA, DominatorTree *DT, + LoopInfo *LI, ScalarEvolution *SE, Pass *PP) { // Don't try to separate loops without a preheader. if (!Preheader) - return 0; + return nullptr; // The header is not a landing pad; preheader insertion should ensure this. assert(!L->getHeader()->isLandingPad() && "Can't insert backedge to landing pad"); - PHINode *PN = FindPHIToPartitionLoops(L, DT, AA, LI); - if (PN == 0) return 0; // No known way to partition. + PHINode *PN = findPHIToPartitionLoops(L, AA, DT); + if (!PN) return nullptr; // No known way to partition. // Pull out all predecessors that have varying values in the loop. This // handles the case when a PHI node has multiple instances of itself as @@ -566,7 +273,7 @@ Loop *LoopSimplify::SeparateNestedLoop(Loop *L, LPPassManager &LPM, !L->contains(PN->getIncomingBlock(i))) { // We can't split indirectbr edges. if (isa<IndirectBrInst>(PN->getIncomingBlock(i)->getTerminator())) - return 0; + return nullptr; OuterLoopPreds.push_back(PN->getIncomingBlock(i)); } } @@ -580,11 +287,11 @@ Loop *LoopSimplify::SeparateNestedLoop(Loop *L, LPPassManager &LPM, BasicBlock *Header = L->getHeader(); BasicBlock *NewBB = - SplitBlockPredecessors(Header, OuterLoopPreds, ".outer", this); + SplitBlockPredecessors(Header, OuterLoopPreds, ".outer", PP); // Make sure that NewBB is put someplace intelligent, which doesn't mess up // code layout too horribly. - PlaceSplitBlockCarefully(NewBB, OuterLoopPreds, L); + placeSplitBlockCarefully(NewBB, OuterLoopPreds, L); // Create the new outer loop. Loop *NewOuter = new Loop(); @@ -598,9 +305,6 @@ Loop *LoopSimplify::SeparateNestedLoop(Loop *L, LPPassManager &LPM, // L is now a subloop of our outer loop. NewOuter->addChildLoop(L); - // Add the new loop to the pass manager queue. - LPM.insertLoopIntoQueue(NewOuter); - for (Loop::block_iterator I = L->block_begin(), E = L->block_end(); I != E; ++I) NewOuter->addBlockEntry(*I); @@ -615,7 +319,7 @@ Loop *LoopSimplify::SeparateNestedLoop(Loop *L, LPPassManager &LPM, for (pred_iterator PI=pred_begin(Header), E = pred_end(Header); PI!=E; ++PI) { BasicBlock *P = *PI; if (DT->dominates(Header, P)) - AddBlockAndPredsToSet(P, Header, BlocksInL); + addBlockAndPredsToSet(P, Header, BlocksInL); } // Scan all of the loop children of L, moving them to OuterLoop if they are @@ -643,15 +347,15 @@ Loop *LoopSimplify::SeparateNestedLoop(Loop *L, LPPassManager &LPM, return NewOuter; } - - -/// InsertUniqueBackedgeBlock - This method is called when the specified loop -/// has more than one backedge in it. If this occurs, revector all of these -/// backedges to target a new basic block and have that block branch to the loop -/// header. This ensures that loops have exactly one backedge. +/// \brief This method is called when the specified loop has more than one +/// backedge in it. /// -BasicBlock * -LoopSimplify::InsertUniqueBackedgeBlock(Loop *L, BasicBlock *Preheader) { +/// If this occurs, revector all of these backedges to target a new basic block +/// and have that block branch to the loop header. This ensures that loops +/// have exactly one backedge. +static BasicBlock *insertUniqueBackedgeBlock(Loop *L, BasicBlock *Preheader, + AliasAnalysis *AA, + DominatorTree *DT, LoopInfo *LI) { assert(L->getNumBackEdges() > 1 && "Must have > 1 backedge!"); // Get information about the loop @@ -660,7 +364,7 @@ LoopSimplify::InsertUniqueBackedgeBlock(Loop *L, BasicBlock *Preheader) { // Unique backedge insertion currently depends on having a preheader. if (!Preheader) - return 0; + return nullptr; // The header is not a landing pad; preheader insertion should ensure this. assert(!Header->isLandingPad() && "Can't insert backedge to landing pad"); @@ -672,7 +376,7 @@ LoopSimplify::InsertUniqueBackedgeBlock(Loop *L, BasicBlock *Preheader) { // Indirectbr edges cannot be split, so we must fail if we find one. if (isa<IndirectBrInst>(P->getTerminator())) - return 0; + return nullptr; if (P != Preheader) BackedgeBlocks.push_back(P); } @@ -701,7 +405,7 @@ LoopSimplify::InsertUniqueBackedgeBlock(Loop *L, BasicBlock *Preheader) { // preheader over to the new PHI node. unsigned PreheaderIdx = ~0U; bool HasUniqueIncomingValue = true; - Value *UniqueValue = 0; + Value *UniqueValue = nullptr; for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { BasicBlock *IBB = PN->getIncomingBlock(i); Value *IV = PN->getIncomingValue(i); @@ -710,7 +414,7 @@ LoopSimplify::InsertUniqueBackedgeBlock(Loop *L, BasicBlock *Preheader) { } else { NewPN->addIncoming(IV, IBB); if (HasUniqueIncomingValue) { - if (UniqueValue == 0) + if (!UniqueValue) UniqueValue = IV; else if (UniqueValue != IV) HasUniqueIncomingValue = false; @@ -762,7 +466,350 @@ LoopSimplify::InsertUniqueBackedgeBlock(Loop *L, BasicBlock *Preheader) { return BEBlock; } -void LoopSimplify::verifyAnalysis() const { +/// \brief Simplify one loop and queue further loops for simplification. +/// +/// FIXME: Currently this accepts both lots of analyses that it uses and a raw +/// Pass pointer. The Pass pointer is used by numerous utilities to update +/// specific analyses. Rather than a pass it would be much cleaner and more +/// explicit if they accepted the analysis directly and then updated it. +static bool simplifyOneLoop(Loop *L, SmallVectorImpl<Loop *> &Worklist, + AliasAnalysis *AA, DominatorTree *DT, LoopInfo *LI, + ScalarEvolution *SE, Pass *PP, + const DataLayout *DL) { + bool Changed = false; +ReprocessLoop: + + // Check to see that no blocks (other than the header) in this loop have + // predecessors that are not in the loop. This is not valid for natural + // loops, but can occur if the blocks are unreachable. Since they are + // unreachable we can just shamelessly delete those CFG edges! + for (Loop::block_iterator BB = L->block_begin(), E = L->block_end(); + BB != E; ++BB) { + if (*BB == L->getHeader()) continue; + + SmallPtrSet<BasicBlock*, 4> BadPreds; + for (pred_iterator PI = pred_begin(*BB), + PE = pred_end(*BB); PI != PE; ++PI) { + BasicBlock *P = *PI; + if (!L->contains(P)) + BadPreds.insert(P); + } + + // Delete each unique out-of-loop (and thus dead) predecessor. + for (SmallPtrSet<BasicBlock*, 4>::iterator I = BadPreds.begin(), + E = BadPreds.end(); I != E; ++I) { + + DEBUG(dbgs() << "LoopSimplify: Deleting edge from dead predecessor " + << (*I)->getName() << "\n"); + + // Inform each successor of each dead pred. + for (succ_iterator SI = succ_begin(*I), SE = succ_end(*I); SI != SE; ++SI) + (*SI)->removePredecessor(*I); + // Zap the dead pred's terminator and replace it with unreachable. + TerminatorInst *TI = (*I)->getTerminator(); + TI->replaceAllUsesWith(UndefValue::get(TI->getType())); + (*I)->getTerminator()->eraseFromParent(); + new UnreachableInst((*I)->getContext(), *I); + Changed = true; + } + } + + // If there are exiting blocks with branches on undef, resolve the undef in + // the direction which will exit the loop. This will help simplify loop + // trip count computations. + SmallVector<BasicBlock*, 8> ExitingBlocks; + L->getExitingBlocks(ExitingBlocks); + for (SmallVectorImpl<BasicBlock *>::iterator I = ExitingBlocks.begin(), + E = ExitingBlocks.end(); I != E; ++I) + if (BranchInst *BI = dyn_cast<BranchInst>((*I)->getTerminator())) + if (BI->isConditional()) { + if (UndefValue *Cond = dyn_cast<UndefValue>(BI->getCondition())) { + + DEBUG(dbgs() << "LoopSimplify: Resolving \"br i1 undef\" to exit in " + << (*I)->getName() << "\n"); + + BI->setCondition(ConstantInt::get(Cond->getType(), + !L->contains(BI->getSuccessor(0)))); + + // This may make the loop analyzable, force SCEV recomputation. + if (SE) + SE->forgetLoop(L); + + Changed = true; + } + } + + // Does the loop already have a preheader? If so, don't insert one. + BasicBlock *Preheader = L->getLoopPreheader(); + if (!Preheader) { + Preheader = InsertPreheaderForLoop(L, PP); + if (Preheader) { + ++NumInserted; + Changed = true; + } + } + + // Next, check to make sure that all exit nodes of the loop only have + // predecessors that are inside of the loop. This check guarantees that the + // loop preheader/header will dominate the exit blocks. If the exit block has + // predecessors from outside of the loop, split the edge now. + SmallVector<BasicBlock*, 8> ExitBlocks; + L->getExitBlocks(ExitBlocks); + + SmallSetVector<BasicBlock *, 8> ExitBlockSet(ExitBlocks.begin(), + ExitBlocks.end()); + for (SmallSetVector<BasicBlock *, 8>::iterator I = ExitBlockSet.begin(), + E = ExitBlockSet.end(); I != E; ++I) { + BasicBlock *ExitBlock = *I; + for (pred_iterator PI = pred_begin(ExitBlock), PE = pred_end(ExitBlock); + PI != PE; ++PI) + // Must be exactly this loop: no subloops, parent loops, or non-loop preds + // allowed. + if (!L->contains(*PI)) { + if (rewriteLoopExitBlock(L, ExitBlock, PP)) { + ++NumInserted; + Changed = true; + } + break; + } + } + + // If the header has more than two predecessors at this point (from the + // preheader and from multiple backedges), we must adjust the loop. + BasicBlock *LoopLatch = L->getLoopLatch(); + if (!LoopLatch) { + // If this is really a nested loop, rip it out into a child loop. Don't do + // this for loops with a giant number of backedges, just factor them into a + // common backedge instead. + if (L->getNumBackEdges() < 8) { + if (Loop *OuterL = separateNestedLoop(L, Preheader, AA, DT, LI, SE, PP)) { + ++NumNested; + // Enqueue the outer loop as it should be processed next in our + // depth-first nest walk. + Worklist.push_back(OuterL); + + // This is a big restructuring change, reprocess the whole loop. + Changed = true; + // GCC doesn't tail recursion eliminate this. + // FIXME: It isn't clear we can't rely on LLVM to TRE this. + goto ReprocessLoop; + } + } + + // If we either couldn't, or didn't want to, identify nesting of the loops, + // insert a new block that all backedges target, then make it jump to the + // loop header. + LoopLatch = insertUniqueBackedgeBlock(L, Preheader, AA, DT, LI); + if (LoopLatch) { + ++NumInserted; + Changed = true; + } + } + + // Scan over the PHI nodes in the loop header. Since they now have only two + // incoming values (the loop is canonicalized), we may have simplified the PHI + // down to 'X = phi [X, Y]', which should be replaced with 'Y'. + PHINode *PN; + for (BasicBlock::iterator I = L->getHeader()->begin(); + (PN = dyn_cast<PHINode>(I++)); ) + if (Value *V = SimplifyInstruction(PN, nullptr, nullptr, DT)) { + if (AA) AA->deleteValue(PN); + if (SE) SE->forgetValue(PN); + PN->replaceAllUsesWith(V); + PN->eraseFromParent(); + } + + // If this loop has multiple exits and the exits all go to the same + // block, attempt to merge the exits. This helps several passes, such + // as LoopRotation, which do not support loops with multiple exits. + // SimplifyCFG also does this (and this code uses the same utility + // function), however this code is loop-aware, where SimplifyCFG is + // not. That gives it the advantage of being able to hoist + // loop-invariant instructions out of the way to open up more + // opportunities, and the disadvantage of having the responsibility + // to preserve dominator information. + bool UniqueExit = true; + if (!ExitBlocks.empty()) + for (unsigned i = 1, e = ExitBlocks.size(); i != e; ++i) + if (ExitBlocks[i] != ExitBlocks[0]) { + UniqueExit = false; + break; + } + if (UniqueExit) { + for (unsigned i = 0, e = ExitingBlocks.size(); i != e; ++i) { + BasicBlock *ExitingBlock = ExitingBlocks[i]; + if (!ExitingBlock->getSinglePredecessor()) continue; + BranchInst *BI = dyn_cast<BranchInst>(ExitingBlock->getTerminator()); + if (!BI || !BI->isConditional()) continue; + CmpInst *CI = dyn_cast<CmpInst>(BI->getCondition()); + if (!CI || CI->getParent() != ExitingBlock) continue; + + // Attempt to hoist out all instructions except for the + // comparison and the branch. + bool AllInvariant = true; + bool AnyInvariant = false; + for (BasicBlock::iterator I = ExitingBlock->begin(); &*I != BI; ) { + Instruction *Inst = I++; + // Skip debug info intrinsics. + if (isa<DbgInfoIntrinsic>(Inst)) + continue; + if (Inst == CI) + continue; + if (!L->makeLoopInvariant(Inst, AnyInvariant, + Preheader ? Preheader->getTerminator() + : nullptr)) { + AllInvariant = false; + break; + } + } + if (AnyInvariant) { + Changed = true; + // The loop disposition of all SCEV expressions that depend on any + // hoisted values have also changed. + if (SE) + SE->forgetLoopDispositions(L); + } + if (!AllInvariant) continue; + + // The block has now been cleared of all instructions except for + // a comparison and a conditional branch. SimplifyCFG may be able + // to fold it now. + if (!FoldBranchToCommonDest(BI, DL)) continue; + + // Success. The block is now dead, so remove it from the loop, + // update the dominator tree and delete it. + DEBUG(dbgs() << "LoopSimplify: Eliminating exiting block " + << ExitingBlock->getName() << "\n"); + + // Notify ScalarEvolution before deleting this block. Currently assume the + // parent loop doesn't change (spliting edges doesn't count). If blocks, + // CFG edges, or other values in the parent loop change, then we need call + // to forgetLoop() for the parent instead. + if (SE) + SE->forgetLoop(L); + + assert(pred_begin(ExitingBlock) == pred_end(ExitingBlock)); + Changed = true; + LI->removeBlock(ExitingBlock); + + DomTreeNode *Node = DT->getNode(ExitingBlock); + const std::vector<DomTreeNodeBase<BasicBlock> *> &Children = + Node->getChildren(); + while (!Children.empty()) { + DomTreeNode *Child = Children.front(); + DT->changeImmediateDominator(Child, Node->getIDom()); + } + DT->eraseNode(ExitingBlock); + + BI->getSuccessor(0)->removePredecessor(ExitingBlock); + BI->getSuccessor(1)->removePredecessor(ExitingBlock); + ExitingBlock->eraseFromParent(); + } + } + + return Changed; +} + +bool llvm::simplifyLoop(Loop *L, DominatorTree *DT, LoopInfo *LI, Pass *PP, + AliasAnalysis *AA, ScalarEvolution *SE, + const DataLayout *DL) { + bool Changed = false; + + // Worklist maintains our depth-first queue of loops in this nest to process. + SmallVector<Loop *, 4> Worklist; + Worklist.push_back(L); + + // Walk the worklist from front to back, pushing newly found sub loops onto + // the back. This will let us process loops from back to front in depth-first + // order. We can use this simple process because loops form a tree. + for (unsigned Idx = 0; Idx != Worklist.size(); ++Idx) { + Loop *L2 = Worklist[Idx]; + for (Loop::iterator I = L2->begin(), E = L2->end(); I != E; ++I) + Worklist.push_back(*I); + } + + while (!Worklist.empty()) + Changed |= simplifyOneLoop(Worklist.pop_back_val(), Worklist, AA, DT, LI, + SE, PP, DL); + + return Changed; +} + +namespace { + struct LoopSimplify : public FunctionPass { + static char ID; // Pass identification, replacement for typeid + LoopSimplify() : FunctionPass(ID) { + initializeLoopSimplifyPass(*PassRegistry::getPassRegistry()); + } + + // AA - If we have an alias analysis object to update, this is it, otherwise + // this is null. + AliasAnalysis *AA; + DominatorTree *DT; + LoopInfo *LI; + ScalarEvolution *SE; + const DataLayout *DL; + + bool runOnFunction(Function &F) override; + + void getAnalysisUsage(AnalysisUsage &AU) const override { + // We need loop information to identify the loops... + AU.addRequired<DominatorTreeWrapperPass>(); + AU.addPreserved<DominatorTreeWrapperPass>(); + + AU.addRequired<LoopInfo>(); + AU.addPreserved<LoopInfo>(); + + AU.addPreserved<AliasAnalysis>(); + AU.addPreserved<ScalarEvolution>(); + AU.addPreserved<DependenceAnalysis>(); + AU.addPreservedID(BreakCriticalEdgesID); // No critical edges added. + } + + /// verifyAnalysis() - Verify LoopSimplifyForm's guarantees. + void verifyAnalysis() const override; + }; +} + +char LoopSimplify::ID = 0; +INITIALIZE_PASS_BEGIN(LoopSimplify, "loop-simplify", + "Canonicalize natural loops", true, false) +INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass) +INITIALIZE_PASS_DEPENDENCY(LoopInfo) +INITIALIZE_PASS_END(LoopSimplify, "loop-simplify", + "Canonicalize natural loops", true, false) + +// Publicly exposed interface to pass... +char &llvm::LoopSimplifyID = LoopSimplify::ID; +Pass *llvm::createLoopSimplifyPass() { return new LoopSimplify(); } + +/// runOnFunction - Run down all loops in the CFG (recursively, but we could do +/// it in any convenient order) inserting preheaders... +/// +bool LoopSimplify::runOnFunction(Function &F) { + bool Changed = false; + AA = getAnalysisIfAvailable<AliasAnalysis>(); + LI = &getAnalysis<LoopInfo>(); + DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree(); + SE = getAnalysisIfAvailable<ScalarEvolution>(); + DataLayoutPass *DLP = getAnalysisIfAvailable<DataLayoutPass>(); + DL = DLP ? &DLP->getDataLayout() : nullptr; + + // Simplify each loop nest in the function. + for (LoopInfo::iterator I = LI->begin(), E = LI->end(); I != E; ++I) + Changed |= simplifyLoop(*I, DT, LI, this, AA, SE, DL); + + return Changed; +} + +// FIXME: Restore this code when we re-enable verification in verifyAnalysis +// below. +#if 0 +static void verifyLoop(Loop *L) { + // Verify subloops. + for (Loop::iterator I = L->begin(), E = L->end(); I != E; ++I) + verifyLoop(*I); + // It used to be possible to just assert L->isLoopSimplifyForm(), however // with the introduction of indirectbr, there are now cases where it's // not possible to transform a loop as necessary. We can at least check @@ -799,3 +846,15 @@ void LoopSimplify::verifyAnalysis() const { (void)HasIndBrExiting; } } +#endif + +void LoopSimplify::verifyAnalysis() const { + // FIXME: This routine is being called mid-way through the loop pass manager + // as loop passes destroy this analysis. That's actually fine, but we have no + // way of expressing that here. Once all of the passes that destroy this are + // hoisted out of the loop pass manager we can add back verification here. +#if 0 + for (LoopInfo::iterator I = LI->begin(), E = LI->end(); I != E; ++I) + verifyLoop(*I); +#endif +} |
