/// Adds ClonedBB to LoopInfo, creates a new loop for ClonedBB if necessary
/// and adds a mapping from the original loop to the new loop to NewLoops.
/// Returns nullptr if no new loop was created and a pointer to the
/// original loop OriginalBB was part of otherwise.
const Loop* llvm::addClonedBlockToLoopInfo(BasicBlock *OriginalBB,
BasicBlock *ClonedBB, LoopInfo *LI,
NewLoopsMap &NewLoops) {
// Figure out which loop New is in.
const Loop *OldLoop = LI->getLoopFor(OriginalBB);
assert(OldLoop && "Should (at least) be in the loop being unrolled!");
Loop *&NewLoop = NewLoops[OldLoop];
if (!NewLoop) {
// Found a new sub-loop.
assert(OriginalBB == OldLoop->getHeader() &&
"Header should be first in RPO");
NewLoop = new Loop();
Loop *NewLoopParent = NewLoops.lookup(OldLoop->getParentLoop());
if (NewLoopParent)
NewLoopParent->addChildLoop(NewLoop);
else
LI->addTopLevelLoop(NewLoop);
NewLoop->addBasicBlockToLoop(ClonedBB, *LI);
return OldLoop;
} else {
NewLoop->addBasicBlockToLoop(ClonedBB, *LI);
return nullptr;
}
}
/// \brief Clones a loop \p OrigLoop. Returns the loop and the blocks in \p
/// Blocks.
///
/// Updates LoopInfo and DominatorTree assuming the loop is dominated by block
/// \p LoopDomBB. Insert the new blocks before block specified in \p Before.
Loop *llvm::cloneLoopWithPreheader(BasicBlock *Before, BasicBlock *LoopDomBB,
Loop *OrigLoop, ValueToValueMapTy &VMap,
const Twine &NameSuffix, LoopInfo *LI,
DominatorTree *DT,
SmallVectorImpl<BasicBlock *> &Blocks) {
assert(OrigLoop->getSubLoops().empty() &&
"Loop to be cloned cannot have inner loop");
Function *F = OrigLoop->getHeader()->getParent();
Loop *ParentLoop = OrigLoop->getParentLoop();
Loop *NewLoop = new Loop();
if (ParentLoop)
ParentLoop->addChildLoop(NewLoop);
else
LI->addTopLevelLoop(NewLoop);
BasicBlock *OrigPH = OrigLoop->getLoopPreheader();
assert(OrigPH && "No preheader");
BasicBlock *NewPH = CloneBasicBlock(OrigPH, VMap, NameSuffix, F);
// To rename the loop PHIs.
VMap[OrigPH] = NewPH;
Blocks.push_back(NewPH);
// Update LoopInfo.
if (ParentLoop)
ParentLoop->addBasicBlockToLoop(NewPH, *LI);
// Update DominatorTree.
DT->addNewBlock(NewPH, LoopDomBB);
for (BasicBlock *BB : OrigLoop->getBlocks()) {
BasicBlock *NewBB = CloneBasicBlock(BB, VMap, NameSuffix, F);
VMap[BB] = NewBB;
// Update LoopInfo.
NewLoop->addBasicBlockToLoop(NewBB, *LI);
// Add DominatorTree node. After seeing all blocks, update to correct IDom.
DT->addNewBlock(NewBB, NewPH);
Blocks.push_back(NewBB);
}
for (BasicBlock *BB : OrigLoop->getBlocks()) {
// Update DominatorTree.
BasicBlock *IDomBB = DT->getNode(BB)->getIDom()->getBlock();
DT->changeImmediateDominator(cast<BasicBlock>(VMap[BB]),
cast<BasicBlock>(VMap[IDomBB]));
}
// Move them physically from the end of the block list.
F->getBasicBlockList().splice(Before->getIterator(), F->getBasicBlockList(),
NewPH);
F->getBasicBlockList().splice(Before->getIterator(), F->getBasicBlockList(),
NewLoop->getHeader()->getIterator(), F->end());
return NewLoop;
}
void LoopInterchangeTransform::restructureLoops(Loop *InnerLoop,
Loop *OuterLoop) {
Loop *OuterLoopParent = OuterLoop->getParentLoop();
if (OuterLoopParent) {
// Remove the loop from its parent loop.
removeChildLoop(OuterLoopParent, OuterLoop);
removeChildLoop(OuterLoop, InnerLoop);
OuterLoopParent->addChildLoop(InnerLoop);
} else {
removeChildLoop(OuterLoop, InnerLoop);
LI->changeTopLevelLoop(OuterLoop, InnerLoop);
}
while (!InnerLoop->empty())
OuterLoop->addChildLoop(InnerLoop->removeChildLoop(InnerLoop->begin()));
InnerLoop->addChildLoop(OuterLoop);
}
void LoopInterchangeTransform::restructureLoops(Loop *InnerLoop,
Loop *OuterLoop) {
Loop *OuterLoopParent = OuterLoop->getParentLoop();
if (OuterLoopParent) {
// Remove the loop from its parent loop.
removeChildLoop(OuterLoopParent, OuterLoop);
removeChildLoop(OuterLoop, InnerLoop);
OuterLoopParent->addChildLoop(InnerLoop);
} else {
removeChildLoop(OuterLoop, InnerLoop);
LI->changeTopLevelLoop(OuterLoop, InnerLoop);
}
for (Loop::iterator I = InnerLoop->begin(), E = InnerLoop->end(); I != E; ++I)
OuterLoop->addChildLoop(InnerLoop->removeChildLoop(I));
InnerLoop->addChildLoop(OuterLoop);
}
/// \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,
DominatorTree *DT, LoopInfo *LI,
ScalarEvolution *SE, Pass *PP,
AssumptionCache *AC) {
// Don't try to separate loops without a preheader.
if (!Preheader)
return nullptr;
// The header is not a landing pad; preheader insertion should ensure this.
BasicBlock *Header = L->getHeader();
assert(!Header->isLandingPad() && "Can't insert backedge to landing pad");
if (!Header->canSplitPredecessors())
return nullptr;
PHINode *PN = findPHIToPartitionLoops(L, DT, AC);
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 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);
bool PreserveLCSSA = PP->mustPreserveAnalysisID(LCSSAID);
BasicBlock *NewBB = SplitBlockPredecessors(Header, OuterLoopPreds, ".outer",
DT, LI, PreserveLCSSA);
// 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);
// L is now a subloop of our outer loop.
NewOuter->addChildLoop(L);
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;
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 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;
}
// We generate a loop of either of the following structures:
//
// BeforeBB BeforeBB
// | |
// v v
// GuardBB PreHeaderBB
// / | | _____
// __ PreHeaderBB | v \/ |
// / \ / | HeaderBB latch
// latch HeaderBB | |\ |
// \ / \ / | \------/
// < \ / |
// \ / v
// ExitBB ExitBB
//
// depending on whether or not we know that it is executed at least once. If
// not, GuardBB checks if the loop is executed at least once. If this is the
// case we branch to PreHeaderBB and subsequently to the HeaderBB, which
// contains the loop iv 'polly.indvar', the incremented loop iv
// 'polly.indvar_next' as well as the condition to check if we execute another
// iteration of the loop. After the loop has finished, we branch to ExitBB.
Value *polly::createLoop(Value *LB, Value *UB, Value *Stride,
PollyIRBuilder &Builder, Pass *P, LoopInfo &LI,
DominatorTree &DT, BasicBlock *&ExitBB,
ICmpInst::Predicate Predicate,
ScopAnnotator *Annotator, bool Parallel,
bool UseGuard) {
Function *F = Builder.GetInsertBlock()->getParent();
LLVMContext &Context = F->getContext();
assert(LB->getType() == UB->getType() && "Types of loop bounds do not match");
IntegerType *LoopIVType = dyn_cast<IntegerType>(UB->getType());
assert(LoopIVType && "UB is not integer?");
BasicBlock *BeforeBB = Builder.GetInsertBlock();
BasicBlock *GuardBB =
UseGuard ? BasicBlock::Create(Context, "polly.loop_if", F) : nullptr;
BasicBlock *HeaderBB = BasicBlock::Create(Context, "polly.loop_header", F);
BasicBlock *PreHeaderBB =
BasicBlock::Create(Context, "polly.loop_preheader", F);
// Update LoopInfo
Loop *OuterLoop = LI.getLoopFor(BeforeBB);
Loop *NewLoop = new Loop();
if (OuterLoop)
OuterLoop->addChildLoop(NewLoop);
else
LI.addTopLevelLoop(NewLoop);
if (OuterLoop) {
if (GuardBB)
OuterLoop->addBasicBlockToLoop(GuardBB, LI);
OuterLoop->addBasicBlockToLoop(PreHeaderBB, LI);
}
NewLoop->addBasicBlockToLoop(HeaderBB, LI);
// Notify the annotator (if present) that we have a new loop, but only
// after the header block is set.
if (Annotator)
Annotator->pushLoop(NewLoop, Parallel);
// ExitBB
ExitBB = SplitBlock(BeforeBB, &*Builder.GetInsertPoint(), &DT, &LI);
ExitBB->setName("polly.loop_exit");
// BeforeBB
if (GuardBB) {
BeforeBB->getTerminator()->setSuccessor(0, GuardBB);
DT.addNewBlock(GuardBB, BeforeBB);
// GuardBB
Builder.SetInsertPoint(GuardBB);
Value *LoopGuard;
LoopGuard = Builder.CreateICmp(Predicate, LB, UB);
LoopGuard->setName("polly.loop_guard");
Builder.CreateCondBr(LoopGuard, PreHeaderBB, ExitBB);
DT.addNewBlock(PreHeaderBB, GuardBB);
} else {
BeforeBB->getTerminator()->setSuccessor(0, PreHeaderBB);
DT.addNewBlock(PreHeaderBB, BeforeBB);
}
// PreHeaderBB
Builder.SetInsertPoint(PreHeaderBB);
Builder.CreateBr(HeaderBB);
// HeaderBB
DT.addNewBlock(HeaderBB, PreHeaderBB);
Builder.SetInsertPoint(HeaderBB);
PHINode *IV = Builder.CreatePHI(LoopIVType, 2, "polly.indvar");
IV->addIncoming(LB, PreHeaderBB);
Stride = Builder.CreateZExtOrBitCast(Stride, LoopIVType);
Value *IncrementedIV = Builder.CreateNSWAdd(IV, Stride, "polly.indvar_next");
Value *LoopCondition;
UB = Builder.CreateSub(UB, Stride, "polly.adjust_ub");
LoopCondition = Builder.CreateICmp(Predicate, IV, UB);
LoopCondition->setName("polly.loop_cond");
// Create the loop latch and annotate it as such.
BranchInst *B = Builder.CreateCondBr(LoopCondition, HeaderBB, ExitBB);
if (Annotator)
Annotator->annotateLoopLatch(B, NewLoop, Parallel);
IV->addIncoming(IncrementedIV, HeaderBB);
if (GuardBB)
DT.changeImmediateDominator(ExitBB, GuardBB);
else
DT.changeImmediateDominator(ExitBB, HeaderBB);
// The loop body should be added here.
Builder.SetInsertPoint(HeaderBB->getFirstNonPHI());
return IV;
}
/// Unroll the given loop by Count. The loop must be in LCSSA form. Returns true
/// if unrolling was successful, or false if the loop was unmodified. Unrolling
/// can only fail when the loop's latch block is not terminated by a conditional
/// branch instruction. However, if the trip count (and multiple) are not known,
/// loop unrolling will mostly produce more code that is no faster.
///
/// TripCount is generally defined as the number of times the loop header
/// executes. UnrollLoop relaxes the definition to permit early exits: here
/// TripCount is the iteration on which control exits LatchBlock if no early
/// exits were taken. Note that UnrollLoop assumes that the loop counter test
/// terminates LatchBlock in order to remove unnecesssary instances of the
/// test. In other words, control may exit the loop prior to TripCount
/// iterations via an early branch, but control may not exit the loop from the
/// LatchBlock's terminator prior to TripCount iterations.
///
/// Similarly, TripMultiple divides the number of times that the LatchBlock may
/// execute without exiting the loop.
///
/// The LoopInfo Analysis that is passed will be kept consistent.
///
/// If a LoopPassManager is passed in, and the loop is fully removed, it will be
/// removed from the LoopPassManager as well. LPM can also be NULL.
///
/// This utility preserves LoopInfo. If DominatorTree or ScalarEvolution are
/// available from the Pass it must also preserve those analyses.
bool llvm::UnrollLoop(Loop *L, unsigned Count, unsigned TripCount,
bool AllowRuntime, unsigned TripMultiple, LoopInfo *LI,
Pass *PP, LPPassManager *LPM, AssumptionCache *AC) {
BasicBlock *Preheader = L->getLoopPreheader();
if (!Preheader) {
DEBUG(dbgs() << " Can't unroll; loop preheader-insertion failed.\n");
return false;
}
BasicBlock *LatchBlock = L->getLoopLatch();
if (!LatchBlock) {
DEBUG(dbgs() << " Can't unroll; loop exit-block-insertion failed.\n");
return false;
}
// Loops with indirectbr cannot be cloned.
if (!L->isSafeToClone()) {
DEBUG(dbgs() << " Can't unroll; Loop body cannot be cloned.\n");
return false;
}
BasicBlock *Header = L->getHeader();
BranchInst *BI = dyn_cast<BranchInst>(LatchBlock->getTerminator());
if (!BI || BI->isUnconditional()) {
// The loop-rotate pass can be helpful to avoid this in many cases.
DEBUG(dbgs() <<
" Can't unroll; loop not terminated by a conditional branch.\n");
return false;
}
if (Header->hasAddressTaken()) {
// The loop-rotate pass can be helpful to avoid this in many cases.
DEBUG(dbgs() <<
" Won't unroll loop: address of header block is taken.\n");
return false;
}
if (TripCount != 0)
DEBUG(dbgs() << " Trip Count = " << TripCount << "\n");
if (TripMultiple != 1)
DEBUG(dbgs() << " Trip Multiple = " << TripMultiple << "\n");
// Effectively "DCE" unrolled iterations that are beyond the tripcount
// and will never be executed.
if (TripCount != 0 && Count > TripCount)
Count = TripCount;
// Don't enter the unroll code if there is nothing to do. This way we don't
// need to support "partial unrolling by 1".
if (TripCount == 0 && Count < 2)
return false;
assert(Count > 0);
assert(TripMultiple > 0);
assert(TripCount == 0 || TripCount % TripMultiple == 0);
// Are we eliminating the loop control altogether?
bool CompletelyUnroll = Count == TripCount;
// We assume a run-time trip count if the compiler cannot
// figure out the loop trip count and the unroll-runtime
// flag is specified.
bool RuntimeTripCount = (TripCount == 0 && Count > 0 && AllowRuntime);
if (RuntimeTripCount && !UnrollRuntimeLoopProlog(L, Count, LI, LPM))
return false;
// Notify ScalarEvolution that the loop will be substantially changed,
// if not outright eliminated.
ScalarEvolution *SE =
PP ? PP->getAnalysisIfAvailable<ScalarEvolution>() : nullptr;
if (SE)
SE->forgetLoop(L);
// If we know the trip count, we know the multiple...
unsigned BreakoutTrip = 0;
if (TripCount != 0) {
BreakoutTrip = TripCount % Count;
TripMultiple = 0;
} else {
// Figure out what multiple to use.
BreakoutTrip = TripMultiple =
(unsigned)GreatestCommonDivisor64(Count, TripMultiple);
}
// Report the unrolling decision.
DebugLoc LoopLoc = L->getStartLoc();
Function *F = Header->getParent();
LLVMContext &Ctx = F->getContext();
if (CompletelyUnroll) {
DEBUG(dbgs() << "COMPLETELY UNROLLING loop %" << Header->getName()
<< " with trip count " << TripCount << "!\n");
emitOptimizationRemark(Ctx, DEBUG_TYPE, *F, LoopLoc,
Twine("completely unrolled loop with ") +
Twine(TripCount) + " iterations");
} else {
auto EmitDiag = [&](const Twine &T) {
emitOptimizationRemark(Ctx, DEBUG_TYPE, *F, LoopLoc,
"unrolled loop by a factor of " + Twine(Count) +
T);
};
DEBUG(dbgs() << "UNROLLING loop %" << Header->getName()
<< " by " << Count);
if (TripMultiple == 0 || BreakoutTrip != TripMultiple) {
DEBUG(dbgs() << " with a breakout at trip " << BreakoutTrip);
EmitDiag(" with a breakout at trip " + Twine(BreakoutTrip));
} else if (TripMultiple != 1) {
DEBUG(dbgs() << " with " << TripMultiple << " trips per branch");
EmitDiag(" with " + Twine(TripMultiple) + " trips per branch");
} else if (RuntimeTripCount) {
DEBUG(dbgs() << " with run-time trip count");
EmitDiag(" with run-time trip count");
}
DEBUG(dbgs() << "!\n");
}
bool ContinueOnTrue = L->contains(BI->getSuccessor(0));
BasicBlock *LoopExit = BI->getSuccessor(ContinueOnTrue);
// For the first iteration of the loop, we should use the precloned values for
// PHI nodes. Insert associations now.
ValueToValueMapTy LastValueMap;
std::vector<PHINode*> OrigPHINode;
for (BasicBlock::iterator I = Header->begin(); isa<PHINode>(I); ++I) {
OrigPHINode.push_back(cast<PHINode>(I));
}
std::vector<BasicBlock*> Headers;
std::vector<BasicBlock*> Latches;
Headers.push_back(Header);
Latches.push_back(LatchBlock);
// The current on-the-fly SSA update requires blocks to be processed in
// reverse postorder so that LastValueMap contains the correct value at each
// exit.
LoopBlocksDFS DFS(L);
DFS.perform(LI);
// Stash the DFS iterators before adding blocks to the loop.
LoopBlocksDFS::RPOIterator BlockBegin = DFS.beginRPO();
LoopBlocksDFS::RPOIterator BlockEnd = DFS.endRPO();
for (unsigned It = 1; It != Count; ++It) {
std::vector<BasicBlock*> NewBlocks;
SmallDenseMap<const Loop *, Loop *, 4> NewLoops;
NewLoops[L] = L;
for (LoopBlocksDFS::RPOIterator BB = BlockBegin; BB != BlockEnd; ++BB) {
ValueToValueMapTy VMap;
BasicBlock *New = CloneBasicBlock(*BB, VMap, "." + Twine(It));
Header->getParent()->getBasicBlockList().push_back(New);
// Tell LI about New.
if (*BB == Header) {
assert(LI->getLoopFor(*BB) == L && "Header should not be in a sub-loop");
L->addBasicBlockToLoop(New, *LI);
} else {
// Figure out which loop New is in.
const Loop *OldLoop = LI->getLoopFor(*BB);
assert(OldLoop && "Should (at least) be in the loop being unrolled!");
Loop *&NewLoop = NewLoops[OldLoop];
if (!NewLoop) {
// Found a new sub-loop.
assert(*BB == OldLoop->getHeader() &&
"Header should be first in RPO");
Loop *NewLoopParent = NewLoops.lookup(OldLoop->getParentLoop());
assert(NewLoopParent &&
"Expected parent loop before sub-loop in RPO");
NewLoop = new Loop;
NewLoopParent->addChildLoop(NewLoop);
// Forget the old loop, since its inputs may have changed.
if (SE)
SE->forgetLoop(OldLoop);
}
NewLoop->addBasicBlockToLoop(New, *LI);
}
if (*BB == Header)
// Loop over all of the PHI nodes in the block, changing them to use
// the incoming values from the previous block.
for (unsigned i = 0, e = OrigPHINode.size(); i != e; ++i) {
PHINode *NewPHI = cast<PHINode>(VMap[OrigPHINode[i]]);
Value *InVal = NewPHI->getIncomingValueForBlock(LatchBlock);
if (Instruction *InValI = dyn_cast<Instruction>(InVal))
if (It > 1 && L->contains(InValI))
InVal = LastValueMap[InValI];
VMap[OrigPHINode[i]] = InVal;
New->getInstList().erase(NewPHI);
}
// Update our running map of newest clones
LastValueMap[*BB] = New;
for (ValueToValueMapTy::iterator VI = VMap.begin(), VE = VMap.end();
VI != VE; ++VI)
LastValueMap[VI->first] = VI->second;
// Add phi entries for newly created values to all exit blocks.
for (succ_iterator SI = succ_begin(*BB), SE = succ_end(*BB);
SI != SE; ++SI) {
if (L->contains(*SI))
continue;
for (BasicBlock::iterator BBI = (*SI)->begin();
PHINode *phi = dyn_cast<PHINode>(BBI); ++BBI) {
Value *Incoming = phi->getIncomingValueForBlock(*BB);
ValueToValueMapTy::iterator It = LastValueMap.find(Incoming);
if (It != LastValueMap.end())
Incoming = It->second;
phi->addIncoming(Incoming, New);
}
}
// Keep track of new headers and latches as we create them, so that
// we can insert the proper branches later.
if (*BB == Header)
Headers.push_back(New);
if (*BB == LatchBlock)
Latches.push_back(New);
NewBlocks.push_back(New);
}
// Remap all instructions in the most recent iteration
for (unsigned i = 0; i < NewBlocks.size(); ++i)
for (BasicBlock::iterator I = NewBlocks[i]->begin(),
E = NewBlocks[i]->end(); I != E; ++I)
::RemapInstruction(I, LastValueMap);
}
// Loop over the PHI nodes in the original block, setting incoming values.
for (unsigned i = 0, e = OrigPHINode.size(); i != e; ++i) {
PHINode *PN = OrigPHINode[i];
if (CompletelyUnroll) {
PN->replaceAllUsesWith(PN->getIncomingValueForBlock(Preheader));
Header->getInstList().erase(PN);
}
else if (Count > 1) {
Value *InVal = PN->removeIncomingValue(LatchBlock, false);
// If this value was defined in the loop, take the value defined by the
// last iteration of the loop.
if (Instruction *InValI = dyn_cast<Instruction>(InVal)) {
if (L->contains(InValI))
InVal = LastValueMap[InVal];
}
assert(Latches.back() == LastValueMap[LatchBlock] && "bad last latch");
PN->addIncoming(InVal, Latches.back());
}
}
// Now that all the basic blocks for the unrolled iterations are in place,
// set up the branches to connect them.
for (unsigned i = 0, e = Latches.size(); i != e; ++i) {
// The original branch was replicated in each unrolled iteration.
BranchInst *Term = cast<BranchInst>(Latches[i]->getTerminator());
// The branch destination.
unsigned j = (i + 1) % e;
BasicBlock *Dest = Headers[j];
bool NeedConditional = true;
if (RuntimeTripCount && j != 0) {
NeedConditional = false;
}
// For a complete unroll, make the last iteration end with a branch
// to the exit block.
if (CompletelyUnroll && j == 0) {
Dest = LoopExit;
NeedConditional = false;
}
// If we know the trip count or a multiple of it, we can safely use an
// unconditional branch for some iterations.
if (j != BreakoutTrip && (TripMultiple == 0 || j % TripMultiple != 0)) {
NeedConditional = false;
}
if (NeedConditional) {
// Update the conditional branch's successor for the following
// iteration.
Term->setSuccessor(!ContinueOnTrue, Dest);
} else {
// Remove phi operands at this loop exit
if (Dest != LoopExit) {
BasicBlock *BB = Latches[i];
for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB);
SI != SE; ++SI) {
if (*SI == Headers[i])
continue;
for (BasicBlock::iterator BBI = (*SI)->begin();
PHINode *Phi = dyn_cast<PHINode>(BBI); ++BBI) {
Phi->removeIncomingValue(BB, false);
}
}
}
// Replace the conditional branch with an unconditional one.
BranchInst::Create(Dest, Term);
Term->eraseFromParent();
}
}
// Merge adjacent basic blocks, if possible.
SmallPtrSet<Loop *, 4> ForgottenLoops;
for (unsigned i = 0, e = Latches.size(); i != e; ++i) {
BranchInst *Term = cast<BranchInst>(Latches[i]->getTerminator());
if (Term->isUnconditional()) {
BasicBlock *Dest = Term->getSuccessor(0);
if (BasicBlock *Fold = FoldBlockIntoPredecessor(Dest, LI, LPM,
ForgottenLoops))
std::replace(Latches.begin(), Latches.end(), Dest, Fold);
}
}
// FIXME: We could register any cloned assumptions instead of clearing the
// whole function's cache.
AC->clear();
DominatorTree *DT = nullptr;
if (PP) {
// FIXME: Reconstruct dom info, because it is not preserved properly.
// Incrementally updating domtree after loop unrolling would be easy.
if (DominatorTreeWrapperPass *DTWP =
PP->getAnalysisIfAvailable<DominatorTreeWrapperPass>()) {
DT = &DTWP->getDomTree();
DT->recalculate(*L->getHeader()->getParent());
}
// Simplify any new induction variables in the partially unrolled loop.
if (SE && !CompletelyUnroll) {
SmallVector<WeakVH, 16> DeadInsts;
simplifyLoopIVs(L, SE, LPM, DeadInsts);
// Aggressively clean up dead instructions that simplifyLoopIVs already
// identified. Any remaining should be cleaned up below.
while (!DeadInsts.empty())
if (Instruction *Inst =
dyn_cast_or_null<Instruction>(&*DeadInsts.pop_back_val()))
RecursivelyDeleteTriviallyDeadInstructions(Inst);
}
}
// At this point, the code is well formed. We now do a quick sweep over the
// inserted code, doing constant propagation and dead code elimination as we
// go.
const std::vector<BasicBlock*> &NewLoopBlocks = L->getBlocks();
for (std::vector<BasicBlock*>::const_iterator BB = NewLoopBlocks.begin(),
BBE = NewLoopBlocks.end(); BB != BBE; ++BB)
for (BasicBlock::iterator I = (*BB)->begin(), E = (*BB)->end(); I != E; ) {
Instruction *Inst = I++;
if (isInstructionTriviallyDead(Inst))
(*BB)->getInstList().erase(Inst);
else if (Value *V = SimplifyInstruction(Inst))
if (LI->replacementPreservesLCSSAForm(Inst, V)) {
Inst->replaceAllUsesWith(V);
(*BB)->getInstList().erase(Inst);
}
}
NumCompletelyUnrolled += CompletelyUnroll;
++NumUnrolled;
Loop *OuterL = L->getParentLoop();
// Remove the loop from the LoopPassManager if it's completely removed.
if (CompletelyUnroll && LPM != nullptr)
LPM->deleteLoopFromQueue(L);
// If we have a pass and a DominatorTree we should re-simplify impacted loops
// to ensure subsequent analyses can rely on this form. We want to simplify
// at least one layer outside of the loop that was unrolled so that any
// changes to the parent loop exposed by the unrolling are considered.
if (PP && DT) {
if (!OuterL && !CompletelyUnroll)
OuterL = L;
if (OuterL) {
DataLayoutPass *DLP = PP->getAnalysisIfAvailable<DataLayoutPass>();
const DataLayout *DL = DLP ? &DLP->getDataLayout() : nullptr;
simplifyLoop(OuterL, DT, LI, PP, /*AliasAnalysis*/ nullptr, SE, DL, AC);
// LCSSA must be performed on the outermost affected loop. The unrolled
// loop's last loop latch is guaranteed to be in the outermost loop after
// deleteLoopFromQueue updates LoopInfo.
Loop *LatchLoop = LI->getLoopFor(Latches.back());
if (!OuterL->contains(LatchLoop))
while (OuterL->getParentLoop() != LatchLoop)
OuterL = OuterL->getParentLoop();
formLCSSARecursively(*OuterL, *DT, LI, SE);
}
}
return true;
}
/// Create a clone of the blocks in a loop and connect them together.
/// If UnrollProlog is true, loop structure will not be cloned, otherwise a new
/// loop will be created including all cloned blocks, and the iterator of it
/// switches to count NewIter down to 0.
///
static void CloneLoopBlocks(Loop *L, Value *NewIter, const bool UnrollProlog,
BasicBlock *InsertTop, BasicBlock *InsertBot,
std::vector<BasicBlock *> &NewBlocks,
LoopBlocksDFS &LoopBlocks, ValueToValueMapTy &VMap,
LoopInfo *LI) {
BasicBlock *Preheader = L->getLoopPreheader();
BasicBlock *Header = L->getHeader();
BasicBlock *Latch = L->getLoopLatch();
Function *F = Header->getParent();
LoopBlocksDFS::RPOIterator BlockBegin = LoopBlocks.beginRPO();
LoopBlocksDFS::RPOIterator BlockEnd = LoopBlocks.endRPO();
Loop *NewLoop = 0;
Loop *ParentLoop = L->getParentLoop();
if (!UnrollProlog) {
NewLoop = new Loop();
if (ParentLoop)
ParentLoop->addChildLoop(NewLoop);
else
LI->addTopLevelLoop(NewLoop);
}
// For each block in the original loop, create a new copy,
// and update the value map with the newly created values.
for (LoopBlocksDFS::RPOIterator BB = BlockBegin; BB != BlockEnd; ++BB) {
BasicBlock *NewBB = CloneBasicBlock(*BB, VMap, ".prol", F);
NewBlocks.push_back(NewBB);
if (NewLoop)
NewLoop->addBasicBlockToLoop(NewBB, *LI);
else if (ParentLoop)
ParentLoop->addBasicBlockToLoop(NewBB, *LI);
VMap[*BB] = NewBB;
if (Header == *BB) {
// For the first block, add a CFG connection to this newly
// created block.
InsertTop->getTerminator()->setSuccessor(0, NewBB);
}
if (Latch == *BB) {
// For the last block, if UnrollProlog is true, create a direct jump to
// InsertBot. If not, create a loop back to cloned head.
VMap.erase((*BB)->getTerminator());
BasicBlock *FirstLoopBB = cast<BasicBlock>(VMap[Header]);
BranchInst *LatchBR = cast<BranchInst>(NewBB->getTerminator());
IRBuilder<> Builder(LatchBR);
if (UnrollProlog) {
Builder.CreateBr(InsertBot);
} else {
PHINode *NewIdx = PHINode::Create(NewIter->getType(), 2, "prol.iter",
FirstLoopBB->getFirstNonPHI());
Value *IdxSub =
Builder.CreateSub(NewIdx, ConstantInt::get(NewIdx->getType(), 1),
NewIdx->getName() + ".sub");
Value *IdxCmp =
Builder.CreateIsNotNull(IdxSub, NewIdx->getName() + ".cmp");
Builder.CreateCondBr(IdxCmp, FirstLoopBB, InsertBot);
NewIdx->addIncoming(NewIter, InsertTop);
NewIdx->addIncoming(IdxSub, NewBB);
}
LatchBR->eraseFromParent();
}
}
// Change the incoming values to the ones defined in the preheader or
// cloned loop.
for (BasicBlock::iterator I = Header->begin(); isa<PHINode>(I); ++I) {
PHINode *NewPHI = cast<PHINode>(VMap[I]);
if (UnrollProlog) {
VMap[I] = NewPHI->getIncomingValueForBlock(Preheader);
cast<BasicBlock>(VMap[Header])->getInstList().erase(NewPHI);
} else {
unsigned idx = NewPHI->getBasicBlockIndex(Preheader);
NewPHI->setIncomingBlock(idx, InsertTop);
BasicBlock *NewLatch = cast<BasicBlock>(VMap[Latch]);
idx = NewPHI->getBasicBlockIndex(Latch);
Value *InVal = NewPHI->getIncomingValue(idx);
NewPHI->setIncomingBlock(idx, NewLatch);
if (VMap[InVal])
NewPHI->setIncomingValue(idx, VMap[InVal]);
}
}
if (NewLoop) {
// Add unroll disable metadata to disable future unrolling for this loop.
SmallVector<Metadata *, 4> MDs;
// Reserve first location for self reference to the LoopID metadata node.
MDs.push_back(nullptr);
MDNode *LoopID = NewLoop->getLoopID();
if (LoopID) {
// First remove any existing loop unrolling metadata.
for (unsigned i = 1, ie = LoopID->getNumOperands(); i < ie; ++i) {
bool IsUnrollMetadata = false;
MDNode *MD = dyn_cast<MDNode>(LoopID->getOperand(i));
if (MD) {
const MDString *S = dyn_cast<MDString>(MD->getOperand(0));
IsUnrollMetadata = S && S->getString().startswith("llvm.loop.unroll.");
}
if (!IsUnrollMetadata)
MDs.push_back(LoopID->getOperand(i));
}
}
LLVMContext &Context = NewLoop->getHeader()->getContext();
SmallVector<Metadata *, 1> DisableOperands;
DisableOperands.push_back(MDString::get(Context, "llvm.loop.unroll.disable"));
MDNode *DisableNode = MDNode::get(Context, DisableOperands);
MDs.push_back(DisableNode);
MDNode *NewLoopID = MDNode::get(Context, MDs);
// Set operand 0 to refer to the loop id itself.
NewLoopID->replaceOperandWith(0, NewLoopID);
NewLoop->setLoopID(NewLoopID);
}
}
