//
//===----------------------------------------------------------------------===//
-#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/AssumptionTracker.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/LoopSimplify.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());
+// 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;
+ }
+
+ // 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 = 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;
}
+ }
- // 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);
+ // 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);
+}
- virtual void getAnalysisUsage(AnalysisUsage &AU) const {
- // We need loop information to identify the loops...
- AU.addRequired<DominatorTree>();
- AU.addPreserved<DominatorTree>();
+/// 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.
+///
+BasicBlock *llvm::InsertPreheaderForLoop(Loop *L, Pass *PP) {
+ BasicBlock *Header = L->getHeader();
- AU.addRequired<LoopInfo>();
- AU.addPreserved<LoopInfo>();
+ // 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) {
+ BasicBlock *P = *PI;
+ if (!L->contains(P)) { // Coming in from outside the loop?
+ // 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 nullptr;
- AU.addPreserved<AliasAnalysis>();
- AU.addPreserved<ScalarEvolution>();
- AU.addPreserved<DependenceAnalysis>();
- AU.addPreservedID(BreakCriticalEdgesID); // No critical edges added.
+ // Keep track of it.
+ OutsideBlocks.push_back(P);
}
+ }
- /// 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);
- };
-}
+ // Split out the loop pre-header.
+ BasicBlock *PreheaderBB;
+ if (!Header->isLandingPad()) {
+ PreheaderBB = SplitBlockPredecessors(Header, OutsideBlocks, ".preheader",
+ PP);
+ } else {
+ SmallVector<BasicBlock*, 2> NewBBs;
+ SplitLandingPadPredecessors(Header, OutsideBlocks, ".preheader",
+ ".split-lp", PP, NewBBs);
+ PreheaderBB = NewBBs[0];
+ }
-static void PlaceSplitBlockCarefully(BasicBlock *NewBB,
- SmallVectorImpl<BasicBlock*> &SplitPreds,
- Loop *L);
+ PreheaderBB->getTerminator()->setDebugLoc(
+ Header->getFirstNonPHI()->getDebugLoc());
+ DEBUG(dbgs() << "LoopSimplify: Creating pre-header "
+ << PreheaderBB->getName() << "\n");
-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)
+ // Make sure that NewBB is put someplace intelligent, which doesn't mess up
+ // code layout too horribly.
+ placeSplitBlockCarefully(PreheaderBB, OutsideBlocks, L);
-// Publicly exposed interface to pass...
-char &llvm::LoopSimplifyID = LoopSimplify::ID;
-Pass *llvm::createLoopSimplifyPass() { return new LoopSimplify(); }
+ return PreheaderBB;
+}
-/// runOnLoop - Run down all loops in the CFG (recursively, but we could do
-/// it in any convenient order) inserting preheaders...
+/// \brief Ensure that the loop preheader dominates all exit blocks.
///
-bool LoopSimplify::runOnLoop(Loop *l, LPPassManager &LPM) {
- L = l;
- bool Changed = false;
- LI = &getAnalysis<LoopInfo>();
- AA = getAnalysisIfAvailable<AliasAnalysis>();
- DT = &getAnalysis<DominatorTree>();
- SE = getAnalysisIfAvailable<ScalarEvolution>();
+/// 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 nullptr;
- Changed |= ProcessLoop(L, LPM);
+ LoopBlocks.push_back(P);
+ }
+ }
- return Changed;
-}
+ assert(!LoopBlocks.empty() && "No edges coming in from outside the loop?");
+ BasicBlock *NewExitBB = nullptr;
-/// 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:
+ if (Exit->isLandingPad()) {
+ SmallVector<BasicBlock*, 2> NewBBs;
+ SplitLandingPadPredecessors(Exit, LoopBlocks,
+ ".loopexit", ".nonloopexit",
+ PP, NewBBs);
+ NewExitBB = NewBBs[0];
+ } else {
+ NewExitBB = SplitBlockPredecessors(Exit, LoopBlocks, ".loopexit", PP);
+ }
- // 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;
+ DEBUG(dbgs() << "LoopSimplify: Creating dedicated exit block "
+ << NewExitBB->getName() << "\n");
+ return NewExitBB;
+}
- 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);
+/// 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) {
+ SmallVector<BasicBlock *, 8> Worklist;
+ Worklist.push_back(InputBB);
+ do {
+ 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);
+ }
+ } while (!Worklist.empty());
+}
+
+/// \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,
+ AssumptionTracker *AT) {
+ for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ) {
+ PHINode *PN = cast<PHINode>(I);
+ ++I;
+ if (Value *V = SimplifyInstruction(PN, nullptr, nullptr, DT, AT)) {
+ // This is a degenerate PHI already, don't modify it!
+ PN->replaceAllUsesWith(V);
+ if (AA) AA->deleteValue(PN);
+ PN->eraseFromParent();
+ continue;
}
- // Delete each unique out-of-loop (and thus dead) predecessor.
- for (SmallPtrSet<BasicBlock*, 4>::iterator I = BadPreds.begin(),
- E = BadPreds.end(); I != E; ++I) {
+ // 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 nullptr;
+}
- DEBUG(dbgs() << "LoopSimplify: Deleting edge from dead predecessor "
- << (*I)->getName() << "\n");
+/// \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:
+/// ...
+/// 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.
+///
+static Loop *separateNestedLoop(Loop *L, BasicBlock *Preheader,
+ AliasAnalysis *AA, DominatorTree *DT,
+ LoopInfo *LI, ScalarEvolution *SE, Pass *PP,
+ AssumptionTracker *AT) {
+ // Don't try to separate loops without a preheader.
+ if (!Preheader)
+ return nullptr;
- // 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;
+ // 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, AA, DT, AT);
+ 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
+ // 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))) {
+ // We can't split indirectbr edges.
+ if (isa<IndirectBrInst>(PN->getIncomingBlock(i)->getTerminator()))
+ return nullptr;
+ OuterLoopPreds.push_back(PN->getIncomingBlock(i));
}
}
+ DEBUG(dbgs() << "LoopSimplify: Splitting out a new outer loop\n");
- // 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");
+ // If ScalarEvolution is around and knows anything about values in
+ // this loop, tell it to forget them, because we're about to
+ // substantially change it.
+ if (SE)
+ SE->forgetLoop(L);
- BI->setCondition(ConstantInt::get(Cond->getType(),
- !L->contains(BI->getSuccessor(0))));
+ BasicBlock *Header = L->getHeader();
+ BasicBlock *NewBB =
+ SplitBlockPredecessors(Header, OuterLoopPreds, ".outer", PP);
- // This may make the loop analyzable, force SCEV recomputation.
- if (SE)
- SE->forgetLoop(L);
+ // Make sure that NewBB is put someplace intelligent, which doesn't mess up
+ // code layout too horribly.
+ placeSplitBlockCarefully(NewBB, OuterLoopPreds, L);
- Changed = true;
- }
- }
+ // Create the new outer loop.
+ Loop *NewOuter = new Loop();
- // 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;
- }
- }
+ // 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);
- // 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);
+ // L is now a subloop of our outer loop.
+ NewOuter->addChildLoop(L);
- 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;
- }
- }
+ for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
+ I != E; ++I)
+ NewOuter->addBlockEntry(*I);
- // 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;
- }
- }
+ // Now reset the header in L, which had been moved by
+ // SplitBlockPredecessors for the outer loop.
+ L->moveToHeader(Header);
- // 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;
- }
+ // 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) {
+ BasicBlock *P = *PI;
+ if (DT->dominates(Header, P))
+ addBlockAndPredsToSet(P, Header, BlocksInL);
}
- // 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();
+ // 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;
}
+ }
- // 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;
+ return NewOuter;
+}
- // 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;
+/// \brief 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.
+static BasicBlock *insertUniqueBackedgeBlock(Loop *L, BasicBlock *Preheader,
+ AliasAnalysis *AA,
+ DominatorTree *DT, LoopInfo *LI) {
+ assert(L->getNumBackEdges() > 1 && "Must have > 1 backedge!");
- // 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;
+ // Get information about the loop
+ BasicBlock *Header = L->getHeader();
+ Function *F = Header->getParent();
- // 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");
+ // Unique backedge insertion currently depends on having a preheader.
+ if (!Preheader)
+ return nullptr;
- // 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);
+ // The header is not a landing pad; preheader insertion should ensure this.
+ assert(!Header->isLandingPad() && "Can't insert backedge to landing pad");
- assert(pred_begin(ExitingBlock) == pred_end(ExitingBlock));
- Changed = true;
- LI->removeBlock(ExitingBlock);
+ // 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){
+ BasicBlock *P = *I;
- 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);
+ // Indirectbr edges cannot be split, so we must fail if we find one.
+ if (isa<IndirectBrInst>(P->getTerminator()))
+ return nullptr;
- BI->getSuccessor(0)->removePredecessor(ExitingBlock);
- BI->getSuccessor(1)->removePredecessor(ExitingBlock);
- ExitingBlock->eraseFromParent();
- }
+ if (P != Preheader) BackedgeBlocks.push_back(P);
}
- 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.
-///
-BasicBlock *llvm::InsertPreheaderForLoop(Loop *L, Pass *PP) {
- 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) {
- BasicBlock *P = *PI;
- if (!L->contains(P)) { // Coming in from outside the loop?
- // 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;
+ // Create and insert the new backedge block...
+ BasicBlock *BEBlock = BasicBlock::Create(Header->getContext(),
+ Header->getName()+".backedge", F);
+ BranchInst *BETerminator = BranchInst::Create(Header, BEBlock);
- // Keep track of it.
- OutsideBlocks.push_back(P);
- }
- }
+ DEBUG(dbgs() << "LoopSimplify: Inserting unique backedge block "
+ << BEBlock->getName() << "\n");
- // Split out the loop pre-header.
- BasicBlock *PreheaderBB;
- if (!Header->isLandingPad()) {
- PreheaderBB = SplitBlockPredecessors(Header, OutsideBlocks, ".preheader",
- PP);
- } else {
- SmallVector<BasicBlock*, 2> NewBBs;
- SplitLandingPadPredecessors(Header, OutsideBlocks, ".preheader",
- ".split-lp", PP, NewBBs);
- PreheaderBB = NewBBs[0];
- }
+ // 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);
- PreheaderBB->getTerminator()->setDebugLoc(
- Header->getFirstNonPHI()->getDebugLoc());
- DEBUG(dbgs() << "LoopSimplify: Creating pre-header "
- << PreheaderBB->getName() << "\n");
+ // 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(), BackedgeBlocks.size(),
+ PN->getName()+".be", BETerminator);
+ if (AA) AA->copyValue(PN, NewPN);
- // Make sure that NewBB is put someplace intelligent, which doesn't mess up
- // code layout too horribly.
- PlaceSplitBlockCarefully(PreheaderBB, OutsideBlocks, L);
+ // 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 = nullptr;
+ 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)
+ UniqueValue = IV;
+ else if (UniqueValue != IV)
+ HasUniqueIncomingValue = false;
+ }
+ }
+ }
- return PreheaderBB;
-}
+ // 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);
-/// 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) {
- 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;
+ // Finally, add the newly constructed PHI node as the entry for the BEBlock.
+ PN->addIncoming(NewPN, BEBlock);
- LoopBlocks.push_back(P);
+ // 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);
}
}
- assert(!LoopBlocks.empty() && "No edges coming in from outside the loop?");
- BasicBlock *NewExitBB = 0;
-
- if (Exit->isLandingPad()) {
- SmallVector<BasicBlock*, 2> NewBBs;
- SplitLandingPadPredecessors(Exit, ArrayRef<BasicBlock*>(&LoopBlocks[0],
- LoopBlocks.size()),
- ".loopexit", ".nonloopexit",
- this, NewBBs);
- NewExitBB = NewBBs[0];
- } else {
- NewExitBB = SplitBlockPredecessors(Exit, LoopBlocks, ".loopexit", this);
+ // 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);
}
- DEBUG(dbgs() << "LoopSimplify: Creating dedicated exit block "
- << NewExitBB->getName() << "\n");
- return NewExitBB;
-}
+ //===--- Update all analyses which we must preserve now -----------------===//
-/// 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());
-}
+ // Update Loop Information - we know that this block is now in the current
+ // loop and all parent loops.
+ L->addBasicBlockToLoop(BEBlock, LI->getBase());
-/// 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) {
- for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ) {
- PHINode *PN = cast<PHINode>(I);
- ++I;
- if (Value *V = SimplifyInstruction(PN, 0, 0, DT)) {
- // This is a degenerate PHI already, don't modify it!
- PN->replaceAllUsesWith(V);
- if (AA) AA->deleteValue(PN);
- PN->eraseFromParent();
- continue;
- }
+ // Update dominator information
+ DT->splitBlock(BEBlock);
- // 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;
+ return BEBlock;
}
-// 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;
- }
+/// \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, AssumptionTracker *AT) {
+ bool Changed = false;
+ReprocessLoop:
- // 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.
+ // 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;
- // 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;
+ 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 (BasicBlock *P : BadPreds) {
+
+ DEBUG(dbgs() << "LoopSimplify: Deleting edge from dead predecessor "
+ << P->getName() << "\n");
+
+ // Inform each successor of each dead pred.
+ for (succ_iterator SI = succ_begin(P), SE = succ_end(P); SI != SE; ++SI)
+ (*SI)->removePredecessor(P);
+ // Zap the dead pred's terminator and replace it with unreachable.
+ TerminatorInst *TI = P->getTerminator();
+ TI->replaceAllUsesWith(UndefValue::get(TI->getType()));
+ P->getTerminator()->eraseFromParent();
+ new UnreachableInst(P->getContext(), P);
+ Changed = true;
}
}
- // 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);
-}
+ // 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");
-/// 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, LPPassManager &LPM,
- BasicBlock *Preheader) {
- // Don't try to separate loops without a preheader.
- if (!Preheader)
- return 0;
+ BI->setCondition(ConstantInt::get(Cond->getType(),
+ !L->contains(BI->getSuccessor(0))));
- // The header is not a landing pad; preheader insertion should ensure this.
- assert(!L->getHeader()->isLandingPad() &&
- "Can't insert backedge to landing pad");
+ // This may make the loop analyzable, force SCEV recomputation.
+ if (SE)
+ SE->forgetLoop(L);
- PHINode *PN = FindPHIToPartitionLoops(L, DT, AA, LI);
- if (PN == 0) return 0; // No known way to partition.
+ Changed = true;
+ }
+ }
- // 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))) {
- // We can't split indirectbr edges.
- if (isa<IndirectBrInst>(PN->getIncomingBlock(i)->getTerminator()))
- return 0;
- OuterLoopPreds.push_back(PN->getIncomingBlock(i));
+ // 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;
}
}
- DEBUG(dbgs() << "LoopSimplify: Splitting out a new outer loop\n");
- // If ScalarEvolution is around and knows anything about values in
- // this loop, tell it to forget them, because we're about to
- // substantially change it.
- if (SE)
- SE->forgetLoop(L);
+ // 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);
- BasicBlock *Header = L->getHeader();
- BasicBlock *NewBB =
- SplitBlockPredecessors(Header, OuterLoopPreds, ".outer", this);
+ 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;
+ }
+ }
- // Make sure that NewBB is put someplace intelligent, which doesn't mess up
- // code layout too horribly.
- PlaceSplitBlockCarefully(NewBB, OuterLoopPreds, L);
+ // 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, AT)) {
+ ++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;
+ }
+ }
- // Create the new outer loop.
- Loop *NewOuter = new Loop();
+ // 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, AT)) {
+ if (AA) AA->deleteValue(PN);
+ if (SE) SE->forgetValue(PN);
+ PN->replaceAllUsesWith(V);
+ PN->eraseFromParent();
+ }
- // 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);
+ // 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;
- // L is now a subloop of our outer loop.
- NewOuter->addChildLoop(L);
+ // 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;
- // Add the new loop to the pass manager queue.
- LPM.insertLoopIntoQueue(NewOuter);
+ // 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;
- for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
- I != E; ++I)
- NewOuter->addBlockEntry(*I);
+ // 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");
- // Now reset the header in L, which had been moved by
- // SplitBlockPredecessors for the outer loop.
- L->moveToHeader(Header);
+ // 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);
- // 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) {
- BasicBlock *P = *PI;
- if (DT->dominates(Header, P))
- AddBlockAndPredsToSet(P, Header, BlocksInL);
- }
+ assert(pred_begin(ExitingBlock) == pred_end(ExitingBlock));
+ Changed = true;
+ LI->removeBlock(ExitingBlock);
- // 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));
+ 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);
- // 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;
+ BI->getSuccessor(0)->removePredecessor(ExitingBlock);
+ BI->getSuccessor(1)->removePredecessor(ExitingBlock);
+ ExitingBlock->eraseFromParent();
}
}
- return NewOuter;
+ return Changed;
}
+bool llvm::simplifyLoop(Loop *L, DominatorTree *DT, LoopInfo *LI, Pass *PP,
+ AliasAnalysis *AA, ScalarEvolution *SE,
+ const DataLayout *DL, AssumptionTracker *AT) {
+ 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);
+ }
-/// 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.
-///
-BasicBlock *
-LoopSimplify::InsertUniqueBackedgeBlock(Loop *L, BasicBlock *Preheader) {
- assert(L->getNumBackEdges() > 1 && "Must have > 1 backedge!");
-
- // Get information about the loop
- BasicBlock *Header = L->getHeader();
- Function *F = Header->getParent();
-
- // Unique backedge insertion currently depends on having a preheader.
- if (!Preheader)
- return 0;
-
- // The header is not a landing pad; preheader insertion should ensure this.
- assert(!Header->isLandingPad() && "Can't insert backedge to landing pad");
-
- // 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){
- BasicBlock *P = *I;
+ while (!Worklist.empty())
+ Changed |= simplifyOneLoop(Worklist.pop_back_val(), Worklist, AA, DT, LI,
+ SE, PP, DL, AT);
- // Indirectbr edges cannot be split, so we must fail if we find one.
- if (isa<IndirectBrInst>(P->getTerminator()))
- return 0;
+ return Changed;
+}
- if (P != Preheader) BackedgeBlocks.push_back(P);
- }
+namespace {
+ struct LoopSimplify : public FunctionPass {
+ static char ID; // Pass identification, replacement for typeid
+ LoopSimplify() : FunctionPass(ID) {
+ initializeLoopSimplifyPass(*PassRegistry::getPassRegistry());
+ }
- // Create and insert the new backedge block...
- BasicBlock *BEBlock = BasicBlock::Create(Header->getContext(),
- Header->getName()+".backedge", F);
- BranchInst *BETerminator = BranchInst::Create(Header, BEBlock);
+ // 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;
+ AssumptionTracker *AT;
- DEBUG(dbgs() << "LoopSimplify: Inserting unique backedge block "
- << BEBlock->getName() << "\n");
+ bool runOnFunction(Function &F) override;
- // 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);
+ void getAnalysisUsage(AnalysisUsage &AU) const override {
+ AU.addRequired<AssumptionTracker>();
- // 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(), BackedgeBlocks.size(),
- PN->getName()+".be", BETerminator);
- if (AA) AA->copyValue(PN, NewPN);
+ // We need loop information to identify the loops...
+ AU.addRequired<DominatorTreeWrapperPass>();
+ AU.addPreserved<DominatorTreeWrapperPass>();
- // 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;
- }
- }
- }
+ AU.addRequired<LoopInfo>();
+ AU.addPreserved<LoopInfo>();
- // 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));
+ AU.addPreserved<AliasAnalysis>();
+ AU.addPreserved<ScalarEvolution>();
+ AU.addPreserved<DependenceAnalysis>();
+ AU.addPreservedID(BreakCriticalEdgesID); // No critical edges added.
}
- // 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);
- }
- }
+ /// verifyAnalysis() - Verify LoopSimplifyForm's guarantees.
+ void verifyAnalysis() const override;
+ };
+}
- // 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);
- }
+char LoopSimplify::ID = 0;
+INITIALIZE_PASS_BEGIN(LoopSimplify, "loop-simplify",
+ "Canonicalize natural loops", true, false)
+INITIALIZE_PASS_DEPENDENCY(AssumptionTracker)
+INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
+INITIALIZE_PASS_DEPENDENCY(LoopInfo)
+INITIALIZE_PASS_END(LoopSimplify, "loop-simplify",
+ "Canonicalize natural loops", true, false)
- //===--- Update all analyses which we must preserve now -----------------===//
+// Publicly exposed interface to pass...
+char &llvm::LoopSimplifyID = LoopSimplify::ID;
+Pass *llvm::createLoopSimplifyPass() { return new LoopSimplify(); }
- // Update Loop Information - we know that this block is now in the current
- // loop and all parent loops.
- L->addBasicBlockToLoop(BEBlock, LI->getBase());
+/// 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;
+ AT = &getAnalysis<AssumptionTracker>();
- // Update dominator information
- DT->splitBlock(BEBlock);
+ // 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, AT);
- return BEBlock;
+ return Changed;
}
-void LoopSimplify::verifyAnalysis() const {
+// 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
(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
+}
projects / oota-llvm.git / blobdiff