#include "llvm/Transforms/Utils/UnrollLoop.h"
#include "llvm/ADT/Statistic.h"
+#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/LoopIterator.h"
#include "llvm/Analysis/LoopPass.h"
#include "llvm/Analysis/ScalarEvolution.h"
#include "llvm/Analysis/ScalarEvolutionExpander.h"
#include "llvm/IR/BasicBlock.h"
+#include "llvm/IR/Dominators.h"
+#include "llvm/IR/Metadata.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
+#include "llvm/Transforms/Scalar.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#include "llvm/Transforms/Utils/Cloning.h"
#include <algorithm>
static void ConnectProlog(Loop *L, Value *TripCount, unsigned Count,
BasicBlock *LastPrologBB, BasicBlock *PrologEnd,
BasicBlock *OrigPH, BasicBlock *NewPH,
- ValueToValueMapTy &LVMap, Pass *P) {
+ ValueToValueMapTy &VMap, AliasAnalysis *AA,
+ DominatorTree *DT, LoopInfo *LI, Pass *P) {
BasicBlock *Latch = L->getLoopLatch();
assert(Latch && "Loop must have a latch");
// The new PHI node is inserted in the prolog end basic block.
// The new PHI name is added as an operand of a PHI node in either
// the loop header or the loop exit block.
- for (BasicBlock *Succ : successors(Latch)) {
- for (BasicBlock::iterator BBI = Succ->begin();
+ for (succ_iterator SBI = succ_begin(Latch), SBE = succ_end(Latch);
+ SBI != SBE; ++SBI) {
+ for (BasicBlock::iterator BBI = (*SBI)->begin();
PHINode *PN = dyn_cast<PHINode>(BBI); ++BBI) {
// Add a new PHI node to the prolog end block and add the
Value *V = PN->getIncomingValueForBlock(Latch);
if (Instruction *I = dyn_cast<Instruction>(V)) {
if (L->contains(I)) {
- V = LVMap[I];
+ V = VMap[I];
}
}
// Adding a value to the new PHI node from the last prolog block
// Split the exit to maintain loop canonicalization guarantees
SmallVector<BasicBlock*, 4> Preds(pred_begin(Exit), pred_end(Exit));
if (!Exit->isLandingPad()) {
- SplitBlockPredecessors(Exit, Preds, ".unr-lcssa", P);
+ SplitBlockPredecessors(Exit, Preds, ".unr-lcssa", AA, DT, LI,
+ P->mustPreserveAnalysisID(LCSSAID));
} else {
SmallVector<BasicBlock*, 2> NewBBs;
SplitLandingPadPredecessors(Exit, Preds, ".unr1-lcssa", ".unr2-lcssa",
- P, NewBBs);
+ NewBBs, AA, DT, LI,
+ P->mustPreserveAnalysisID(LCSSAID));
}
// Add the branch to the exit block (around the unrolled loop)
BranchInst::Create(Exit, NewPH, BrLoopExit, InsertPt);
}
/// Create a clone of the blocks in a loop and connect them together.
-/// This function doesn't create a clone of the loop structure.
+/// 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.
///
-/// There are two value maps that are defined and used. VMap is
-/// for the values in the current loop instance. LVMap contains
-/// the values from the last loop instance. We need the LVMap values
-/// to update the initial values for the current loop instance.
-///
-static void CloneLoopBlocks(Loop *L,
- bool FirstCopy,
- BasicBlock *InsertTop,
- BasicBlock *InsertBot,
+static void CloneLoopBlocks(Loop *L, Value *NewIter, const bool UnrollProlog,
+ BasicBlock *InsertTop, BasicBlock *InsertBot,
std::vector<BasicBlock *> &NewBlocks,
- LoopBlocksDFS &LoopBlocks,
- ValueToValueMapTy &VMap,
- ValueToValueMapTy &LVMap,
+ 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, ".unr", F);
+ BasicBlock *NewBB = CloneBasicBlock(*BB, VMap, ".prol", F);
NewBlocks.push_back(NewBB);
- if (Loop *ParentLoop = L->getParentLoop())
- ParentLoop->addBasicBlockToLoop(NewBB, LI->getBase());
+ 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
+ // created block.
InsertTop->getTerminator()->setSuccessor(0, NewBB);
- // Change the incoming values to the ones defined in the
- // previously cloned loop.
- for (BasicBlock::iterator I = Header->begin(); isa<PHINode>(I); ++I) {
- PHINode *NewPHI = cast<PHINode>(VMap[I]);
- if (FirstCopy) {
- // We replace the first phi node with the value from the preheader
- VMap[I] = NewPHI->getIncomingValueForBlock(Preheader);
- NewBB->getInstList().erase(NewPHI);
- } else {
- // Update VMap with values from the previous block
- unsigned idx = NewPHI->getBasicBlockIndex(Latch);
- Value *InVal = NewPHI->getIncomingValue(idx);
- if (Instruction *I = dyn_cast<Instruction>(InVal))
- if (L->contains(I))
- InVal = LVMap[InVal];
- NewPHI->setIncomingValue(idx, InVal);
- NewPHI->setIncomingBlock(idx, InsertTop);
- }
- }
}
-
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());
- NewBB->getTerminator()->eraseFromParent();
- BranchInst::Create(InsertBot, NewBB);
+ BasicBlock *FirstLoopBB = cast<BasicBlock>(VMap[Header]);
+ BranchInst *LatchBR = cast<BranchInst>(NewBB->getTerminator());
+ if (UnrollProlog) {
+ LatchBR->eraseFromParent();
+ BranchInst::Create(InsertBot, NewBB);
+ } else {
+ PHINode *NewIdx = PHINode::Create(NewIter->getType(), 2, "prol.iter",
+ FirstLoopBB->getFirstNonPHI());
+ IRBuilder<> Builder(LatchBR);
+ Value *IdxSub =
+ Builder.CreateSub(NewIdx, ConstantInt::get(NewIdx->getType(), 1),
+ NewIdx->getName() + ".sub");
+ Value *IdxCmp =
+ Builder.CreateIsNotNull(IdxSub, NewIdx->getName() + ".cmp");
+ BranchInst::Create(FirstLoopBB, InsertBot, IdxCmp, NewBB);
+ NewIdx->addIncoming(NewIter, InsertTop);
+ NewIdx->addIncoming(IdxSub, NewBB);
+ LatchBR->eraseFromParent();
+ }
}
}
- // LastValueMap is updated with the values for the current loop
- // which are used the next time this function is called.
- for (ValueToValueMapTy::iterator VI = VMap.begin(), VE = VMap.end();
- VI != VE; ++VI) {
- LVMap[VI->first] = VI->second;
+
+ // 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);
}
}
/// instruction in SimplifyCFG.cpp. Then, the backend decides how code for
/// the switch instruction is generated.
///
-/// extraiters = tripcount % loopfactor
-/// if (extraiters == 0) jump Loop:
-/// if (extraiters == loopfactor) jump L1
-/// if (extraiters == loopfactor-1) jump L2
-/// ...
-/// L1: LoopBody;
-/// L2: LoopBody;
-/// ...
-/// if tripcount < loopfactor jump End
-/// Loop:
-/// ...
-/// End:
+/// extraiters = tripcount % loopfactor
+/// if (extraiters == 0) jump Loop:
+/// else jump Prol
+/// Prol: LoopBody;
+/// extraiters -= 1 // Omitted if unroll factor is 2.
+/// if (extraiters != 0) jump Prol: // Omitted if unroll factor is 2.
+/// if (tripcount < loopfactor) jump End
+/// Loop:
+/// ...
+/// End:
///
bool llvm::UnrollRuntimeLoopProlog(Loop *L, unsigned Count, LoopInfo *LI,
LPPassManager *LPM) {
if (isa<SCEVCouldNotCompute>(BECount) || !BECount->getType()->isIntegerTy())
return false;
+ // If BECount is INT_MAX, we can't compute trip-count without overflow.
+ if (BECount->isAllOnesValue())
+ return false;
+
// Add 1 since the backedge count doesn't include the first loop iteration
const SCEV *TripCountSC =
SE->getAddExpr(BECount, SE->getConstant(BECount->getType(), 1));
if (Loop *ParentLoop = L->getParentLoop())
SE->forgetLoop(ParentLoop);
+ // Grab analyses that we preserve.
+ auto *DTWP = LPM->getAnalysisIfAvailable<DominatorTreeWrapperPass>();
+ auto *DT = DTWP ? &DTWP->getDomTree() : nullptr;
+
BasicBlock *PH = L->getLoopPreheader();
BasicBlock *Header = L->getHeader();
BasicBlock *Latch = L->getLoopLatch();
// It helps to splits the original preheader twice, one for the end of the
// prolog code and one for a new loop preheader
- BasicBlock *PEnd = SplitEdge(PH, Header, LPM->getAsPass());
- BasicBlock *NewPH = SplitBlock(PEnd, PEnd->getTerminator(), LPM->getAsPass());
+ BasicBlock *PEnd = SplitEdge(PH, Header, DT, LI);
+ BasicBlock *NewPH = SplitBlock(PEnd, PEnd->getTerminator(), DT, LI);
BranchInst *PreHeaderBR = cast<BranchInst>(PH->getTerminator());
// Compute the number of extra iterations required, which is:
IRBuilder<> B(PreHeaderBR);
Value *ModVal = B.CreateAnd(TripCount, Count - 1, "xtraiter");
- // Check if for no extra iterations, then jump to unrolled loop. We have to
- // check that the trip count computation didn't overflow when adding one to
- // the backedge taken count.
+ // Check if for no extra iterations, then jump to cloned/unrolled loop.
+ // We have to check that the trip count computation didn't overflow when
+ // adding one to the backedge taken count.
Value *LCmp = B.CreateIsNotNull(ModVal, "lcmp.mod");
Value *OverflowCheck = B.CreateIsNull(TripCount, "lcmp.overflow");
Value *BranchVal = B.CreateOr(OverflowCheck, LCmp, "lcmp.or");
- // Branch to either the extra iterations or the unrolled loop
+ // Branch to either the extra iterations or the cloned/unrolled loop
// We will fix up the true branch label when adding loop body copies
BranchInst::Create(PEnd, PEnd, BranchVal, PreHeaderBR);
assert(PreHeaderBR->isUnconditional() &&
PreHeaderBR->getSuccessor(0) == PEnd &&
"CFG edges in Preheader are not correct");
PreHeaderBR->eraseFromParent();
-
- ValueToValueMapTy LVMap;
Function *F = Header->getParent();
- // These variables are used to update the CFG links in each iteration
- BasicBlock *CompareBB = nullptr;
- BasicBlock *LastLoopBB = PH;
// Get an ordered list of blocks in the loop to help with the ordering of the
// cloned blocks in the prolog code
LoopBlocksDFS LoopBlocks(L);
// and generate a condition that branches to the copy depending on the
// number of 'left over' iterations.
//
- for (unsigned leftOverIters = Count-1; leftOverIters > 0; --leftOverIters) {
- std::vector<BasicBlock*> NewBlocks;
- ValueToValueMapTy VMap;
-
- // Clone all the basic blocks in the loop, but we don't clone the loop
- // This function adds the appropriate CFG connections.
- CloneLoopBlocks(L, (leftOverIters == Count-1), LastLoopBB, PEnd, NewBlocks,
- LoopBlocks, VMap, LVMap, LI);
- LastLoopBB = cast<BasicBlock>(VMap[Latch]);
-
- // Insert the cloned blocks into function just before the original loop
- F->getBasicBlockList().splice(PEnd, F->getBasicBlockList(),
- NewBlocks[0], F->end());
-
- // Generate the code for the comparison which determines if the loop
- // prolog code needs to be executed.
- if (leftOverIters == Count-1) {
- // There is no compare block for the fall-thru case when for the last
- // left over iteration
- CompareBB = NewBlocks[0];
- } else {
- // Create a new block for the comparison
- BasicBlock *NewBB = BasicBlock::Create(CompareBB->getContext(), "unr.cmp",
- F, CompareBB);
- if (Loop *ParentLoop = L->getParentLoop()) {
- // Add the new block to the parent loop, if needed
- ParentLoop->addBasicBlockToLoop(NewBB, LI->getBase());
- }
-
- // The comparison w/ the extra iteration value and branch
- Type *CountTy = TripCount->getType();
- Value *BranchVal = new ICmpInst(*NewBB, ICmpInst::ICMP_EQ, ModVal,
- ConstantInt::get(CountTy, leftOverIters),
- "un.tmp");
- // Branch to either the extra iterations or the unrolled loop
- BranchInst::Create(NewBlocks[0], CompareBB,
- BranchVal, NewBB);
- CompareBB = NewBB;
- PH->getTerminator()->setSuccessor(0, NewBB);
- VMap[NewPH] = CompareBB;
- }
-
- // Rewrite the cloned instruction operands to use the values
- // created when the clone is created.
- for (unsigned i = 0, e = NewBlocks.size(); i != e; ++i) {
- for (BasicBlock::iterator I = NewBlocks[i]->begin(),
- E = NewBlocks[i]->end(); I != E; ++I) {
- RemapInstruction(I, VMap,
- RF_NoModuleLevelChanges|RF_IgnoreMissingEntries);
- }
+ std::vector<BasicBlock *> NewBlocks;
+ ValueToValueMapTy VMap;
+
+ // If unroll count is 2 and we can't overflow in tripcount computation (which
+ // is BECount + 1), then we don't need a loop for prologue, and we can unroll
+ // it. We can be sure that we don't overflow only if tripcount is a constant.
+ bool UnrollPrologue = (Count == 2 && isa<ConstantInt>(TripCount));
+
+ // Clone all the basic blocks in the loop. If Count is 2, we don't clone
+ // the loop, otherwise we create a cloned loop to execute the extra
+ // iterations. This function adds the appropriate CFG connections.
+ CloneLoopBlocks(L, ModVal, UnrollPrologue, PH, PEnd, NewBlocks, LoopBlocks,
+ VMap, LI);
+
+ // Insert the cloned blocks into function just before the original loop
+ F->getBasicBlockList().splice(PEnd, F->getBasicBlockList(), NewBlocks[0],
+ F->end());
+
+ // Rewrite the cloned instruction operands to use the values
+ // created when the clone is created.
+ for (unsigned i = 0, e = NewBlocks.size(); i != e; ++i) {
+ for (BasicBlock::iterator I = NewBlocks[i]->begin(),
+ E = NewBlocks[i]->end();
+ I != E; ++I) {
+ RemapInstruction(I, VMap,
+ RF_NoModuleLevelChanges | RF_IgnoreMissingEntries);
}
}
// Connect the prolog code to the original loop and update the
// PHI functions.
- ConnectProlog(L, TripCount, Count, LastLoopBB, PEnd, PH, NewPH, LVMap,
- LPM->getAsPass());
+ BasicBlock *LastLoopBB = cast<BasicBlock>(VMap[Latch]);
+ ConnectProlog(L, TripCount, Count, LastLoopBB, PEnd, PH, NewPH, VMap,
+ /*AliasAnalysis*/ nullptr, DT, LI, LPM->getAsPass());
NumRuntimeUnrolled++;
return true;
}
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