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Diffstat (limited to 'release_23/lib/Transforms/Utils/LoopSimplify.cpp')
| -rw-r--r-- | release_23/lib/Transforms/Utils/LoopSimplify.cpp | 597 |
1 files changed, 0 insertions, 597 deletions
diff --git a/release_23/lib/Transforms/Utils/LoopSimplify.cpp b/release_23/lib/Transforms/Utils/LoopSimplify.cpp deleted file mode 100644 index 8e30e0428629..000000000000 --- a/release_23/lib/Transforms/Utils/LoopSimplify.cpp +++ /dev/null @@ -1,597 +0,0 @@ -//===- LoopSimplify.cpp - Loop Canonicalization Pass ----------------------===// -// -// The LLVM Compiler Infrastructure -// -// This file is distributed under the University of Illinois Open Source -// License. See LICENSE.TXT for details. -// -//===----------------------------------------------------------------------===// -// -// This pass performs several transformations to transform natural loops into a -// simpler form, which makes subsequent analyses and transformations simpler and -// more effective. -// -// Loop pre-header insertion guarantees that there is a single, non-critical -// entry edge from outside of the loop to the loop header. This simplifies a -// number of analyses and transformations, such as LICM. -// -// Loop exit-block insertion guarantees that all exit blocks from the loop -// (blocks which are outside of the loop that have predecessors inside of the -// loop) only have predecessors from inside of the loop (and are thus dominated -// by the loop header). This simplifies transformations such as store-sinking -// that are built into LICM. -// -// This pass also guarantees that loops will have exactly one backedge. -// -// Note that the simplifycfg pass will clean up blocks which are split out but -// end up being unnecessary, so usage of this pass should not pessimize -// generated code. -// -// This pass obviously modifies the CFG, but updates loop information and -// dominator information. -// -//===----------------------------------------------------------------------===// - -#define DEBUG_TYPE "loopsimplify" -#include "llvm/Transforms/Scalar.h" -#include "llvm/Constants.h" -#include "llvm/Instructions.h" -#include "llvm/Function.h" -#include "llvm/Type.h" -#include "llvm/Analysis/AliasAnalysis.h" -#include "llvm/Analysis/Dominators.h" -#include "llvm/Analysis/LoopInfo.h" -#include "llvm/Transforms/Utils/BasicBlockUtils.h" -#include "llvm/Support/CFG.h" -#include "llvm/Support/Compiler.h" -#include "llvm/ADT/SetOperations.h" -#include "llvm/ADT/SetVector.h" -#include "llvm/ADT/Statistic.h" -#include "llvm/ADT/DepthFirstIterator.h" -using namespace llvm; - -STATISTIC(NumInserted, "Number of pre-header or exit blocks inserted"); -STATISTIC(NumNested , "Number of nested loops split out"); - -namespace { - struct VISIBILITY_HIDDEN LoopSimplify : public FunctionPass { - static char ID; // Pass identification, replacement for typeid - LoopSimplify() : FunctionPass((intptr_t)&ID) {} - - // AA - If we have an alias analysis object to update, this is it, otherwise - // this is null. - AliasAnalysis *AA; - LoopInfo *LI; - DominatorTree *DT; - virtual bool runOnFunction(Function &F); - - virtual void getAnalysisUsage(AnalysisUsage &AU) const { - // We need loop information to identify the loops... - AU.addRequired<LoopInfo>(); - AU.addRequired<DominatorTree>(); - - AU.addPreserved<LoopInfo>(); - AU.addPreserved<DominatorTree>(); - AU.addPreserved<DominanceFrontier>(); - AU.addPreservedID(BreakCriticalEdgesID); // No critical edges added. - } - - /// verifyAnalysis() - Verify loop nest. - void verifyAnalysis() const { -#ifndef NDEBUG - LoopInfo *NLI = &getAnalysis<LoopInfo>(); - for (LoopInfo::iterator I = NLI->begin(), E = NLI->end(); I != E; ++I) - (*I)->verifyLoop(); -#endif - } - - private: - bool ProcessLoop(Loop *L); - BasicBlock *RewriteLoopExitBlock(Loop *L, BasicBlock *Exit); - void InsertPreheaderForLoop(Loop *L); - Loop *SeparateNestedLoop(Loop *L); - void InsertUniqueBackedgeBlock(Loop *L); - void PlaceSplitBlockCarefully(BasicBlock *NewBB, - SmallVectorImpl<BasicBlock*> &SplitPreds, - Loop *L); - }; - - char LoopSimplify::ID = 0; - RegisterPass<LoopSimplify> - X("loopsimplify", "Canonicalize natural loops", true); -} - -// Publically exposed interface to pass... -const PassInfo *llvm::LoopSimplifyID = X.getPassInfo(); -FunctionPass *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; - LI = &getAnalysis<LoopInfo>(); - AA = getAnalysisToUpdate<AliasAnalysis>(); - DT = &getAnalysis<DominatorTree>(); - - // Check to see that no blocks (other than the header) in loops have - // predecessors that are not in loops. This is not valid for natural loops, - // but can occur if the blocks are unreachable. Since they are unreachable we - // can just shamelessly destroy their terminators to make them not branch into - // the loop! - for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) { - // This case can only occur for unreachable blocks. Blocks that are - // unreachable can't be in loops, so filter those blocks out. - if (LI->getLoopFor(BB)) continue; - - bool BlockUnreachable = false; - TerminatorInst *TI = BB->getTerminator(); - - // Check to see if any successors of this block are non-loop-header loops - // that are not the header. - for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) { - // If this successor is not in a loop, BB is clearly ok. - Loop *L = LI->getLoopFor(TI->getSuccessor(i)); - if (!L) continue; - - // If the succ is the loop header, and if L is a top-level loop, then this - // is an entrance into a loop through the header, which is also ok. - if (L->getHeader() == TI->getSuccessor(i) && L->getParentLoop() == 0) - continue; - - // Otherwise, this is an entrance into a loop from some place invalid. - // Either the loop structure is invalid and this is not a natural loop (in - // which case the compiler is buggy somewhere else) or BB is unreachable. - BlockUnreachable = true; - break; - } - - // If this block is ok, check the next one. - if (!BlockUnreachable) continue; - - // Otherwise, this block is dead. To clean up the CFG and to allow later - // loop transformations to ignore this case, we delete the edges into the - // loop by replacing the terminator. - - // Remove PHI entries from the successors. - for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) - TI->getSuccessor(i)->removePredecessor(BB); - - // Add a new unreachable instruction before the old terminator. - new UnreachableInst(TI); - - // Delete the dead terminator. - if (AA) AA->deleteValue(TI); - if (!TI->use_empty()) - TI->replaceAllUsesWith(UndefValue::get(TI->getType())); - TI->eraseFromParent(); - Changed |= true; - } - - for (LoopInfo::iterator I = LI->begin(), E = LI->end(); I != E; ++I) - Changed |= ProcessLoop(*I); - - return Changed; -} - -/// ProcessLoop - Walk the loop structure in depth first order, ensuring that -/// all loops have preheaders. -/// -bool LoopSimplify::ProcessLoop(Loop *L) { - bool Changed = false; -ReprocessLoop: - - // Canonicalize inner loops before outer loops. Inner loop canonicalization - // can provide work for the outer loop to canonicalize. - for (Loop::iterator I = L->begin(), E = L->end(); I != E; ++I) - Changed |= ProcessLoop(*I); - - assert(L->getBlocks()[0] == L->getHeader() && - "Header isn't first block in loop?"); - - // Does the loop already have a preheader? If so, don't insert one. - if (L->getLoopPreheader() == 0) { - InsertPreheaderForLoop(L); - 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); - - SetVector<BasicBlock*> ExitBlockSet(ExitBlocks.begin(), ExitBlocks.end()); - for (SetVector<BasicBlock*>::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)) { - 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. - unsigned NumBackedges = L->getNumBackEdges(); - if (NumBackedges != 1) { - // 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 (NumBackedges < 8) { - if (Loop *NL = SeparateNestedLoop(L)) { - ++NumNested; - // This is a big restructuring change, reprocess the whole loop. - ProcessLoop(NL); - 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. - InsertUniqueBackedgeBlock(L); - 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 = PN->hasConstantValue()) { - PN->replaceAllUsesWith(V); - PN->eraseFromParent(); - } - - return Changed; -} - -/// InsertPreheaderForLoop - Once we discover that a loop doesn't have a -/// preheader, this method is called to insert one. This method has two phases: -/// preheader insertion and analysis updating. -/// -void LoopSimplify::InsertPreheaderForLoop(Loop *L) { - BasicBlock *Header = L->getHeader(); - - // Compute the set of predecessors of the loop that are not in the loop. - SmallVector<BasicBlock*, 8> OutsideBlocks; - for (pred_iterator PI = pred_begin(Header), PE = pred_end(Header); - PI != PE; ++PI) - if (!L->contains(*PI)) // Coming in from outside the loop? - OutsideBlocks.push_back(*PI); // Keep track of it... - - // Split out the loop pre-header. - BasicBlock *NewBB = - SplitBlockPredecessors(Header, &OutsideBlocks[0], OutsideBlocks.size(), - ".preheader", this); - - - //===--------------------------------------------------------------------===// - // Update analysis results now that we have performed the transformation - // - - // We know that we have loop information to update... update it now. - if (Loop *Parent = L->getParentLoop()) - Parent->addBasicBlockToLoop(NewBB, LI->getBase()); - - // Make sure that NewBB is put someplace intelligent, which doesn't mess up - // code layout too horribly. - PlaceSplitBlockCarefully(NewBB, OutsideBlocks, L); -} - -/// 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) { - SmallVector<BasicBlock*, 8> LoopBlocks; - for (pred_iterator I = pred_begin(Exit), E = pred_end(Exit); I != E; ++I) - if (L->contains(*I)) - LoopBlocks.push_back(*I); - - assert(!LoopBlocks.empty() && "No edges coming in from outside the loop?"); - BasicBlock *NewBB = SplitBlockPredecessors(Exit, &LoopBlocks[0], - LoopBlocks.size(), ".loopexit", - this); - - // Update Loop Information - we know that the new block will be in whichever - // loop the Exit block is in. Note that it may not be in that immediate loop, - // if the successor is some other loop header. In that case, we continue - // walking up the loop tree to find a loop that contains both the successor - // block and the predecessor block. - Loop *SuccLoop = LI->getLoopFor(Exit); - while (SuccLoop && !SuccLoop->contains(L->getHeader())) - SuccLoop = SuccLoop->getParentLoop(); - if (SuccLoop) - SuccLoop->addBasicBlockToLoop(NewBB, LI->getBase()); - - return NewBB; -} - -/// 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, - std::set<BasicBlock*> &Blocks) { - std::vector<BasicBlock *> WorkList; - WorkList.push_back(InputBB); - do { - BasicBlock *BB = WorkList.back(); WorkList.pop_back(); - 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); - } - } 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) { - for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ) { - PHINode *PN = cast<PHINode>(I); - ++I; - if (Value *V = PN->hasConstantValue()) - if (!isa<Instruction>(V) || DT->dominates(cast<Instruction>(V), PN)) { - // This is a degenerate PHI already, don't modify it! - PN->replaceAllUsesWith(V); - if (AA) AA->deleteValue(PN); - PN->eraseFromParent(); - continue; - } - - // Scan this PHI node looking for a use of the PHI node by itself. - for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) - if (PN->getIncomingValue(i) == PN && - L->contains(PN->getIncomingBlock(i))) - // We found something tasty to remove. - return PN; - } - return 0; -} - -// 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 LoopSimplify::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 -/// this: -/// -/// Loop: -/// ... -/// br cond, Loop, Next -/// ... -/// br cond2, Loop, Out -/// -/// To identify this common case, we look at the PHI nodes in the header of the -/// loop. PHI nodes with unchanging values on one backedge correspond to values -/// that change in the "outer" loop, but not in the "inner" loop. -/// -/// If we are able to separate out a loop, return the new outer loop that was -/// created. -/// -Loop *LoopSimplify::SeparateNestedLoop(Loop *L) { - PHINode *PN = FindPHIToPartitionLoops(L, DT, AA); - if (PN == 0) return 0; // 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 - // arguments. - SmallVector<BasicBlock*, 8> OuterLoopPreds; - for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) - if (PN->getIncomingValue(i) != PN || - !L->contains(PN->getIncomingBlock(i))) - OuterLoopPreds.push_back(PN->getIncomingBlock(i)); - - BasicBlock *Header = L->getHeader(); - BasicBlock *NewBB = SplitBlockPredecessors(Header, &OuterLoopPreds[0], - OuterLoopPreds.size(), - ".outer", this); - - // Make sure that NewBB is put someplace intelligent, which doesn't mess up - // code layout too horribly. - PlaceSplitBlockCarefully(NewBB, OuterLoopPreds, L); - - // Create the new outer loop. - Loop *NewOuter = new Loop(); - - // Change the parent loop to use the outer loop as its child now. - if (Loop *Parent = L->getParentLoop()) - Parent->replaceChildLoopWith(L, NewOuter); - else - LI->changeTopLevelLoop(L, NewOuter); - - // This block is going to be our new header block: add it to this loop and all - // parent loops. - NewOuter->addBasicBlockToLoop(NewBB, LI->getBase()); - - // L is now a subloop of our outer loop. - NewOuter->addChildLoop(L); - - for (unsigned i = 0, e = L->getBlocks().size(); i != e; ++i) - NewOuter->addBlockEntry(L->getBlocks()[i]); - - // Determine which blocks should stay in L and which should be moved out to - // the Outer loop now. - std::set<BasicBlock*> BlocksInL; - for (pred_iterator PI = pred_begin(Header), E = pred_end(Header); PI!=E; ++PI) - if (DT->dominates(Header, *PI)) - AddBlockAndPredsToSet(*PI, Header, BlocksInL); - - - // Scan all of the loop children of L, moving them to OuterLoop if they are - // not part of the inner loop. - const std::vector<Loop*> &SubLoops = L->getSubLoops(); - for (size_t I = 0; I != SubLoops.size(); ) - if (BlocksInL.count(SubLoops[I]->getHeader())) - ++I; // Loop remains in L - else - NewOuter->addChildLoop(L->removeChildLoop(SubLoops.begin() + I)); - - // Now that we know which blocks are in L and which need to be moved to - // OuterLoop, move any blocks that need it. - for (unsigned i = 0; i != L->getBlocks().size(); ++i) { - BasicBlock *BB = L->getBlocks()[i]; - if (!BlocksInL.count(BB)) { - // Move this block to the parent, updating the exit blocks sets - L->removeBlockFromLoop(BB); - if ((*LI)[BB] == L) - LI->changeLoopFor(BB, NewOuter); - --i; - } - } - - 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. -/// -void LoopSimplify::InsertUniqueBackedgeBlock(Loop *L) { - assert(L->getNumBackEdges() > 1 && "Must have > 1 backedge!"); - - // Get information about the loop - BasicBlock *Preheader = L->getLoopPreheader(); - BasicBlock *Header = L->getHeader(); - Function *F = Header->getParent(); - - // Figure out which basic blocks contain back-edges to the loop header. - std::vector<BasicBlock*> BackedgeBlocks; - for (pred_iterator I = pred_begin(Header), E = pred_end(Header); I != E; ++I) - if (*I != Preheader) BackedgeBlocks.push_back(*I); - - // Create and insert the new backedge block... - BasicBlock *BEBlock = BasicBlock::Create(Header->getName()+".backedge", F); - BranchInst *BETerminator = BranchInst::Create(Header, BEBlock); - - // Move the new backedge block to right after the last backedge block. - Function::iterator InsertPos = BackedgeBlocks.back(); ++InsertPos; - F->getBasicBlockList().splice(InsertPos, F->getBasicBlockList(), BEBlock); - - // Now that the block has been inserted into the function, create PHI nodes in - // the backedge block which correspond to any PHI nodes in the header block. - for (BasicBlock::iterator I = Header->begin(); isa<PHINode>(I); ++I) { - PHINode *PN = cast<PHINode>(I); - PHINode *NewPN = PHINode::Create(PN->getType(), PN->getName()+".be", - BETerminator); - NewPN->reserveOperandSpace(BackedgeBlocks.size()); - if (AA) AA->copyValue(PN, NewPN); - - // Loop over the PHI node, moving all entries except the one for the - // preheader over to the new PHI node. - unsigned PreheaderIdx = ~0U; - bool HasUniqueIncomingValue = true; - Value *UniqueValue = 0; - for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { - BasicBlock *IBB = PN->getIncomingBlock(i); - Value *IV = PN->getIncomingValue(i); - if (IBB == Preheader) { - PreheaderIdx = i; - } else { - NewPN->addIncoming(IV, IBB); - if (HasUniqueIncomingValue) { - if (UniqueValue == 0) - UniqueValue = IV; - else if (UniqueValue != IV) - HasUniqueIncomingValue = false; - } - } - } - - // Delete all of the incoming values from the old PN except the preheader's - assert(PreheaderIdx != ~0U && "PHI has no preheader entry??"); - if (PreheaderIdx != 0) { - PN->setIncomingValue(0, PN->getIncomingValue(PreheaderIdx)); - PN->setIncomingBlock(0, PN->getIncomingBlock(PreheaderIdx)); - } - // Nuke all entries except the zero'th. - for (unsigned i = 0, e = PN->getNumIncomingValues()-1; i != e; ++i) - PN->removeIncomingValue(e-i, false); - - // Finally, add the newly constructed PHI node as the entry for the BEBlock. - PN->addIncoming(NewPN, BEBlock); - - // As an optimization, if all incoming values in the new PhiNode (which is a - // subset of the incoming values of the old PHI node) have the same value, - // eliminate the PHI Node. - if (HasUniqueIncomingValue) { - NewPN->replaceAllUsesWith(UniqueValue); - if (AA) AA->deleteValue(NewPN); - BEBlock->getInstList().erase(NewPN); - } - } - - // Now that all of the PHI nodes have been inserted and adjusted, modify the - // backedge blocks to just to the BEBlock instead of the header. - for (unsigned i = 0, e = BackedgeBlocks.size(); i != e; ++i) { - TerminatorInst *TI = BackedgeBlocks[i]->getTerminator(); - for (unsigned Op = 0, e = TI->getNumSuccessors(); Op != e; ++Op) - if (TI->getSuccessor(Op) == Header) - TI->setSuccessor(Op, BEBlock); - } - - //===--- Update all analyses which we must preserve now -----------------===// - - // Update Loop Information - we know that this block is now in the current - // loop and all parent loops. - L->addBasicBlockToLoop(BEBlock, LI->getBase()); - - // Update dominator information - DT->splitBlock(BEBlock); - if (DominanceFrontier *DF = getAnalysisToUpdate<DominanceFrontier>()) - DF->splitBlock(BEBlock); -} |