//
// This pass also guarantees that loops will have exactly one backedge.
//
+// Indirectbr instructions introduce several complications. If the loop
+// contains or is entered by an indirectbr instruction, it may not be possible
+// to transform the loop and make these guarantees. Client code should check
+// that these conditions are true before relying on them.
+//
// 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.
#include "llvm/Type.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/Dominators.h"
-#include "llvm/Analysis/LoopInfo.h"
+#include "llvm/Analysis/LoopPass.h"
+#include "llvm/Analysis/ScalarEvolution.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#include "llvm/Transforms/Utils/Local.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"
STATISTIC(NumNested , "Number of nested loops split out");
namespace {
- struct VISIBILITY_HIDDEN LoopSimplify : public FunctionPass {
+ struct LoopSimplify : public LoopPass {
static char ID; // Pass identification, replacement for typeid
- LoopSimplify() : FunctionPass(&ID) {}
+ LoopSimplify() : LoopPass(&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);
+ 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<LoopInfo>();
- AU.addRequired<DominatorTree>();
+ AU.addRequiredTransitive<LoopInfo>();
+ AU.addRequiredTransitive<DominatorTree>();
AU.addPreserved<LoopInfo>();
AU.addPreserved<DominatorTree>();
AU.addPreserved<DominanceFrontier>();
AU.addPreserved<AliasAnalysis>();
+ AU.addPreserved<ScalarEvolution>();
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
- }
+ /// verifyAnalysis() - Verify LoopSimplifyForm's guarantees.
+ void verifyAnalysis() const;
private:
- bool ProcessLoop(Loop *L);
+ bool ProcessLoop(Loop *L, LPPassManager &LPM);
BasicBlock *RewriteLoopExitBlock(Loop *L, BasicBlock *Exit);
BasicBlock *InsertPreheaderForLoop(Loop *L);
- Loop *SeparateNestedLoop(Loop *L);
- void InsertUniqueBackedgeBlock(Loop *L, BasicBlock *Preheader);
+ Loop *SeparateNestedLoop(Loop *L, LPPassManager &LPM);
+ BasicBlock *InsertUniqueBackedgeBlock(Loop *L, BasicBlock *Preheader);
void PlaceSplitBlockCarefully(BasicBlock *NewBB,
SmallVectorImpl<BasicBlock*> &SplitPreds,
Loop *L);
// Publically exposed interface to pass...
const PassInfo *const llvm::LoopSimplifyID = &X;
-FunctionPass *llvm::createLoopSimplifyPass() { return new LoopSimplify(); }
+Pass *llvm::createLoopSimplifyPass() { return new LoopSimplify(); }
-/// runOnFunction - Run down all loops in the CFG (recursively, but we could do
+/// runOnLoop - 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 LoopSimplify::runOnLoop(Loop *l, LPPassManager &LPM) {
+ L = l;
bool Changed = false;
LI = &getAnalysis<LoopInfo>();
AA = getAnalysisIfAvailable<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->getContext(), 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);
+ 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) {
+bool LoopSimplify::ProcessLoop(Loop *L, LPPassManager &LPM) {
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?");
+
+ // Check to see that no blocks (other than the header) in this loop that has
+ // 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)
+ if (!L->contains(*PI))
+ BadPreds.insert(*PI);
+
+ // Delete each unique out-of-loop (and thus dead) predecessor.
+ for (SmallPtrSet<BasicBlock *, 4>::iterator I = BadPreds.begin(),
+ E = BadPreds.end(); I != E; ++I) {
+ // 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;
+ }
+ }
// Does the loop already have a preheader? If so, don't insert one.
BasicBlock *Preheader = L->getLoopPreheader();
if (!Preheader) {
Preheader = InsertPreheaderForLoop(L);
- NumInserted++;
- Changed = true;
+ if (Preheader) {
+ NumInserted++;
+ Changed = true;
+ }
}
// Next, check to make sure that all exit nodes of the loop only have
// Must be exactly this loop: no subloops, parent loops, or non-loop preds
// allowed.
if (!L->contains(*PI)) {
- RewriteLoopExitBlock(L, ExitBlock);
- NumInserted++;
- Changed = true;
+ 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.
- unsigned NumBackedges = L->getNumBackEdges();
- if (NumBackedges != 1) {
+ 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 (NumBackedges < 8) {
- if (Loop *NL = SeparateNestedLoop(L)) {
+ if (L->getNumBackEdges() < 8) {
+ if (SeparateNestedLoop(L, LPM)) {
++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, Preheader);
- NumInserted++;
- Changed = true;
+ LoopLatch = InsertUniqueBackedgeBlock(L, Preheader);
+ if (LoopLatch) {
+ NumInserted++;
+ Changed = true;
+ }
}
// Scan over the PHI nodes in the loop header. Since they now have only two
// loop-invariant instructions out of the way to open up more
// opportunities, and the disadvantage of having the responsibility
// to preserve dominator information.
- if (ExitBlocks.size() > 1 && L->getUniqueExitBlock()) {
+ 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) {
SmallVector<BasicBlock*, 8> ExitingBlocks;
L->getExitingBlocks(ExitingBlocks);
for (unsigned i = 0, e = ExitingBlocks.size(); i != e; ++i) {
Instruction *Inst = I++;
if (Inst == CI)
continue;
- if (!L->makeLoopInvariant(Inst, Changed, Preheader->getTerminator())) {
+ if (!L->makeLoopInvariant(Inst, Changed,
+ Preheader ? Preheader->getTerminator() : 0)) {
AllInvariant = false;
break;
}
DomTreeNode *Node = DT->getNode(ExitingBlock);
const std::vector<DomTreeNodeBase<BasicBlock> *> &Children =
Node->getChildren();
- for (unsigned k = 0, g = Children.size(); k != g; ++k) {
- DT->changeImmediateDominator(Children[k], Node->getIDom());
- if (DF) DF->changeImmediateDominator(Children[k]->getBlock(),
+ while (!Children.empty()) {
+ DomTreeNode *Child = Children.front();
+ DT->changeImmediateDominator(Child, Node->getIDom());
+ if (DF) DF->changeImmediateDominator(Child->getBlock(),
Node->getIDom()->getBlock(),
DT);
}
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...
+ if (!L->contains(*PI)) { // 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>((*PI)->getTerminator())) return 0;
+
+ // Keep track of it.
+ OutsideBlocks.push_back(*PI);
+ }
// 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.
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))
+ if (L->contains(*I)) {
+ // Don't do this if the loop is exited via an indirect branch.
+ if (isa<IndirectBrInst>((*I)->getTerminator())) return 0;
+
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;
}
/// If we are able to separate out a loop, return the new outer loop that was
/// created.
///
-Loop *LoopSimplify::SeparateNestedLoop(Loop *L) {
+Loop *LoopSimplify::SeparateNestedLoop(Loop *L, LPPassManager &LPM) {
PHINode *PN = FindPHIToPartitionLoops(L, DT, AA);
if (PN == 0) return 0; // No known way to partition.
SmallVector<BasicBlock*, 8> OuterLoopPreds;
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
if (PN->getIncomingValue(i) != PN ||
- !L->contains(PN->getIncomingBlock(i)))
+ !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));
+ }
BasicBlock *Header = L->getHeader();
BasicBlock *NewBB = SplitBlockPredecessors(Header, &OuterLoopPreds[0],
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);
+ // 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);
+ // Now reset the header in L, which had been moved by
+ // SplitBlockPredecessors for the outer loop.
+ L->moveToHeader(Header);
+
// Determine which blocks should stay in L and which should be moved out to
// the Outer loop now.
std::set<BasicBlock*> BlocksInL;
/// 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, BasicBlock *Preheader) {
+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;
+
// 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)
DT->splitBlock(BEBlock);
if (DominanceFrontier *DF = getAnalysisIfAvailable<DominanceFrontier>())
DF->splitBlock(BEBlock);
+
+ return BEBlock;
+}
+
+void LoopSimplify::verifyAnalysis() const {
+ // 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
+ // that there is an indirectbr near any time there's trouble.
+
+ // Indirectbr can interfere with preheader and unique backedge insertion.
+ if (!L->getLoopPreheader() || !L->getLoopLatch()) {
+ bool HasIndBrPred = false;
+ for (pred_iterator PI = pred_begin(L->getHeader()),
+ PE = pred_end(L->getHeader()); PI != PE; ++PI)
+ if (isa<IndirectBrInst>((*PI)->getTerminator())) {
+ HasIndBrPred = true;
+ break;
+ }
+ assert(HasIndBrPred &&
+ "LoopSimplify has no excuse for missing loop header info!");
+ }
+
+ // Indirectbr can interfere with exit block canonicalization.
+ if (!L->hasDedicatedExits()) {
+ bool HasIndBrExiting = false;
+ SmallVector<BasicBlock*, 8> ExitingBlocks;
+ L->getExitingBlocks(ExitingBlocks);
+ for (unsigned i = 0, e = ExitingBlocks.size(); i != e; ++i)
+ if (isa<IndirectBrInst>((ExitingBlocks[i])->getTerminator())) {
+ HasIndBrExiting = true;
+ break;
+ }
+ assert(HasIndBrExiting &&
+ "LoopSimplify has no excuse for missing exit block info!");
+ }
}
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