//
//===----------------------------------------------------------------------===//
-#define DEBUG_TYPE "loop-unroll"
#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/BasicBlock.h"
+#include "llvm/IR/BasicBlock.h"
+#include "llvm/IR/Dominators.h"
+#include "llvm/IR/Metadata.h"
+#include "llvm/IR/Module.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>
using namespace llvm;
+#define DEBUG_TYPE "loop-unroll"
+
STATISTIC(NumRuntimeUnrolled,
"Number of loops unrolled with run-time trip counts");
/// - Branch around the original loop if the trip count is less
/// than the unroll factor.
///
-static void ConnectProlog(Loop *L, Value *TripCount, unsigned Count,
+static void ConnectProlog(Loop *L, Value *BECount, 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 != 0 && "Loop must have a latch");
+ assert(Latch && "Loop must have a latch");
// Create a PHI node for each outgoing value from the original loop
// (which means it is an outgoing value from the prolog code too).
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
}
}
- // Create a branch around the orignal loop, which is taken if the
- // trip count is less than the unroll factor.
+ // Create a branch around the orignal loop, which is taken if there are no
+ // iterations remaining to be executed after running the prologue.
Instruction *InsertPt = PrologEnd->getTerminator();
- Instruction *BrLoopExit =
- new ICmpInst(InsertPt, ICmpInst::ICMP_ULT, TripCount,
- ConstantInt::get(TripCount->getType(), Count));
+ IRBuilder<> B(InsertPt);
+
+ assert(Count != 0 && "nonsensical Count!");
+
+ // If BECount <u (Count - 1) then (BECount + 1) & (Count - 1) == (BECount + 1)
+ // (since Count is a power of 2). This means %xtraiter is (BECount + 1) and
+ // and all of the iterations of this loop were executed by the prologue. Note
+ // that if BECount <u (Count - 1) then (BECount + 1) cannot unsigned-overflow.
+ Value *BrLoopExit =
+ B.CreateICmpULT(BECount, ConstantInt::get(BECount->getType(), Count - 1));
BasicBlock *Exit = L->getUniqueExitBlock();
- assert(Exit != 0 && "Loop must have a single exit block only");
+ assert(Exit && "Loop must have a single exit block only");
// 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);
- } else {
- SmallVector<BasicBlock*, 2> NewBBs;
- SplitLandingPadPredecessors(Exit, Preds, ".unr1-lcssa", ".unr2-lcssa",
- P, NewBBs);
- }
+ SplitBlockPredecessors(Exit, Preds, ".unr-lcssa", AA, DT, LI,
+ P->mustPreserveAnalysisID(LCSSAID));
// Add the branch to the exit block (around the unrolled loop)
- BranchInst::Create(Exit, NewPH, BrLoopExit, InsertPt);
+ B.CreateCondBr(BrLoopExit, Exit, NewPH);
InsertPt->eraseFromParent();
}
/// 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());
+ 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();
}
}
- // 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,
+bool llvm::UnrollRuntimeLoopProlog(Loop *L, unsigned Count,
+ bool AllowExpensiveTripCount, LoopInfo *LI,
LPPassManager *LPM) {
// for now, only unroll loops that contain a single exit
if (!L->getExitingBlock())
// Make sure the loop is in canonical form, and there is a single
// exit block only.
- if (!L->isLoopSimplifyForm() || L->getUniqueExitBlock() == 0)
+ if (!L->isLoopSimplifyForm() || !L->getUniqueExitBlock())
return false;
// Use Scalar Evolution to compute the trip count. This allows more
if (!LPM)
return false;
ScalarEvolution *SE = LPM->getAnalysisIfAvailable<ScalarEvolution>();
- if (SE == 0)
+ if (!SE)
return false;
// Only unroll loops with a computable trip count and the trip count needs
// to be an int value (allowing a pointer type is a TODO item)
- const SCEV *BECount = SE->getBackedgeTakenCount(L);
- if (isa<SCEVCouldNotCompute>(BECount) || !BECount->getType()->isIntegerTy())
+ const SCEV *BECountSC = SE->getBackedgeTakenCount(L);
+ if (isa<SCEVCouldNotCompute>(BECountSC) ||
+ !BECountSC->getType()->isIntegerTy())
return false;
+ unsigned BEWidth = cast<IntegerType>(BECountSC->getType())->getBitWidth();
+
// Add 1 since the backedge count doesn't include the first loop iteration
const SCEV *TripCountSC =
- SE->getAddExpr(BECount, SE->getConstant(BECount->getType(), 1));
+ SE->getAddExpr(BECountSC, SE->getConstant(BECountSC->getType(), 1));
if (isa<SCEVCouldNotCompute>(TripCountSC))
return false;
+ BasicBlock *Header = L->getHeader();
+ const DataLayout &DL = Header->getModule()->getDataLayout();
+ SCEVExpander Expander(*SE, DL, "loop-unroll");
+ if (!AllowExpensiveTripCount && Expander.isHighCostExpansion(TripCountSC, L))
+ return false;
+
// We only handle cases when the unroll factor is a power of 2.
// Count is the loop unroll factor, the number of extra copies added + 1.
- if ((Count & (Count-1)) != 0)
+ if (!isPowerOf2_32(Count))
+ return false;
+
+ // This constraint lets us deal with an overflowing trip count easily; see the
+ // comment on ModVal below.
+ if (Log2_32(Count) > BEWidth)
return false;
// If this loop is nested, then the loop unroller changes the code in
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:
// extra iterations = run-time trip count % (loop unroll factor + 1)
- SCEVExpander Expander(*SE, "loop-unroll");
Value *TripCount = Expander.expandCodeFor(TripCountSC, TripCountSC->getType(),
PreHeaderBR);
- Type *CountTy = TripCount->getType();
- BinaryOperator *ModVal =
- BinaryOperator::CreateURem(TripCount,
- ConstantInt::get(CountTy, Count),
- "xtraiter");
- ModVal->insertBefore(PreHeaderBR);
-
- // Check if for no extra iterations, then jump to unrolled loop
- Value *BranchVal = new ICmpInst(PreHeaderBR,
- ICmpInst::ICMP_NE, ModVal,
- ConstantInt::get(CountTy, 0), "lcmp");
- // Branch to either the extra iterations or the unrolled loop
+ Value *BECount = Expander.expandCodeFor(BECountSC, BECountSC->getType(),
+ PreHeaderBR);
+
+ IRBuilder<> B(PreHeaderBR);
+ Value *ModVal = B.CreateAnd(TripCount, Count - 1, "xtraiter");
+
+ // If ModVal is zero, we know that either
+ // 1. there are no iteration to be run in the prologue loop
+ // OR
+ // 2. the addition computing TripCount overflowed
+ //
+ // If (2) is true, we know that TripCount really is (1 << BEWidth) and so the
+ // number of iterations that remain to be run in the original loop is a
+ // multiple Count == (1 << Log2(Count)) because Log2(Count) <= BEWidth (we
+ // explicitly check this above).
+
+ Value *BranchVal = B.CreateIsNotNull(ModVal, "lcmp.mod");
+
+ // 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);
+ B.CreateCondBr(BranchVal, PEnd, PEnd);
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 = 0;
- 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
- 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;
+
+ bool UnrollPrologue = Count == 2;
+
+ // 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, BECount, Count, LastLoopBB, PEnd, PH, NewPH, VMap,
+ /*AliasAnalysis*/ nullptr, DT, LI, LPM->getAsPass());
NumRuntimeUnrolled++;
return true;
}
projects / oota-llvm.git / blobdiff