Diff 139316

include/llvm/Transforms/Utils/LoopRotationUtils.h

This file was added.

				//===-------------------- LoopRotationUtils.h --------------------------*- C++
				//-*-===//
				lebedev.riUnsubmitted Not Done Reply Inline Actions Please fix the first line lebedev.ri: Please fix the first line
				jinlinAuthorUnsubmitted Not Done Reply Inline Actions Done. jinlin: Done.
				//
				// The LLVM Compiler Infrastructure
				//
				// This file is distributed under the University of Illinois Open Source
				// License. See LICENSE.TXT for details.
				//
				//===----------------------------------------------------------------------===//
				//
				// This file exposes an interface to transform the loop into the do-while loop.
				//
				//===----------------------------------------------------------------------===//

				#ifndef LLVM_TRANSFORMS_UTILS_LOOPROTATIONUTIL_H
				#define LLVM_TRANSFORMS_UTILS_LOOPROTATIONUTIL_H

				namespace llvm {

				class AssumptionCache;
				class DominatorTree;
				class Loop;
				class LoopInfo;
				class ScalarEvolution;
				struct SimplifyQuery;
				class TargetTransformInfo;

				bool LoopRotation(Loop L, unsigned MaxHeaderSize, LoopInfo LI,
				const TargetTransformInfo TTI, AssumptionCache AC,
				DominatorTree DT, ScalarEvolution SE,
				const SimplifyQuery &SQ);

				} // namespace llvm

				#endif

lib/Transforms/Scalar/LoopRotation.cpp

Show All 31 Lines
#include "llvm/IR/Module.h"		#include "llvm/IR/Module.h"
#include "llvm/Support/CommandLine.h"		#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"		#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"		#include "llvm/Support/raw_ostream.h"
#include "llvm/Transforms/Scalar.h"		#include "llvm/Transforms/Scalar.h"
#include "llvm/Transforms/Scalar/LoopPassManager.h"		#include "llvm/Transforms/Scalar/LoopPassManager.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"		#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#include "llvm/Transforms/Utils/Local.h"		#include "llvm/Transforms/Utils/Local.h"
		#include "llvm/Transforms/Utils/LoopRotationUtils.h"
#include "llvm/Transforms/Utils/LoopUtils.h"		#include "llvm/Transforms/Utils/LoopUtils.h"
#include "llvm/Transforms/Utils/SSAUpdater.h"		#include "llvm/Transforms/Utils/SSAUpdater.h"
		dmgreenUnsubmitted Done Reply Inline Actions Can some of these headers now be removed? dmgreen: Can some of these headers now be removed?
#include "llvm/Transforms/Utils/ValueMapper.h"		#include "llvm/Transforms/Utils/ValueMapper.h"
using namespace llvm;		using namespace llvm;

#define DEBUG_TYPE "loop-rotate"		#define DEBUG_TYPE "loop-rotate"

static cl::opt<unsigned> DefaultRotationThreshold(		static cl::opt<unsigned> DefaultRotationThreshold(
"rotation-max-header-size", cl::init(16), cl::Hidden,		"rotation-max-header-size", cl::init(16), cl::Hidden,
cl::desc("The default maximum header size for automatic loop rotation"));		cl::desc("The default maximum header size for automatic loop rotation"));

STATISTIC(NumRotated, "Number of loops rotated");

namespace {
/// A simple loop rotation transformation.
class LoopRotate {
const unsigned MaxHeaderSize;
LoopInfo *LI;
const TargetTransformInfo *TTI;
AssumptionCache *AC;
DominatorTree *DT;
ScalarEvolution *SE;
const SimplifyQuery &SQ;

public:
LoopRotate(unsigned MaxHeaderSize, LoopInfo *LI,
const TargetTransformInfo TTI, AssumptionCache AC,
DominatorTree DT, ScalarEvolution SE, const SimplifyQuery &SQ)
: MaxHeaderSize(MaxHeaderSize), LI(LI), TTI(TTI), AC(AC), DT(DT), SE(SE),
SQ(SQ) {}
bool processLoop(Loop *L);

private:
bool rotateLoop(Loop *L, bool SimplifiedLatch);
bool simplifyLoopLatch(Loop *L);
};
} // end anonymous namespace

/// RewriteUsesOfClonedInstructions - We just cloned the instructions from the
/// old header into the preheader. If there were uses of the values produced by
/// these instruction that were outside of the loop, we have to insert PHI nodes
/// to merge the two values. Do this now.
static void RewriteUsesOfClonedInstructions(BasicBlock *OrigHeader,
BasicBlock *OrigPreheader,
ValueToValueMapTy &ValueMap,
SmallVectorImpl<PHINode> InsertedPHIs) {
// Remove PHI node entries that are no longer live.
BasicBlock::iterator I, E = OrigHeader->end();
for (I = OrigHeader->begin(); PHINode *PN = dyn_cast<PHINode>(I); ++I)
PN->removeIncomingValue(PN->getBasicBlockIndex(OrigPreheader));

// Now fix up users of the instructions in OrigHeader, inserting PHI nodes
// as necessary.
SSAUpdater SSA(InsertedPHIs);
for (I = OrigHeader->begin(); I != E; ++I) {
Value OrigHeaderVal = &I;

// If there are no uses of the value (e.g. because it returns void), there
// is nothing to rewrite.
if (OrigHeaderVal->use_empty())
continue;

Value *OrigPreHeaderVal = ValueMap.lookup(OrigHeaderVal);

// The value now exits in two versions: the initial value in the preheader
// and the loop "next" value in the original header.
SSA.Initialize(OrigHeaderVal->getType(), OrigHeaderVal->getName());
SSA.AddAvailableValue(OrigHeader, OrigHeaderVal);
SSA.AddAvailableValue(OrigPreheader, OrigPreHeaderVal);

// Visit each use of the OrigHeader instruction.
for (Value::use_iterator UI = OrigHeaderVal->use_begin(),
UE = OrigHeaderVal->use_end();
UI != UE;) {
// Grab the use before incrementing the iterator.
Use &U = *UI;

// Increment the iterator before removing the use from the list.
++UI;

// SSAUpdater can't handle a non-PHI use in the same block as an
// earlier def. We can easily handle those cases manually.
Instruction *UserInst = cast<Instruction>(U.getUser());
if (!isa<PHINode>(UserInst)) {
BasicBlock *UserBB = UserInst->getParent();

// The original users in the OrigHeader are already using the
// original definitions.
if (UserBB == OrigHeader)
continue;

// Users in the OrigPreHeader need to use the value to which the
// original definitions are mapped.
if (UserBB == OrigPreheader) {
U = OrigPreHeaderVal;
continue;
}
}

// Anything else can be handled by SSAUpdater.
SSA.RewriteUse(U);
}

// Replace MetadataAsValue(ValueAsMetadata(OrigHeaderVal)) uses in debug
// intrinsics.
SmallVector<DbgValueInst *, 1> DbgValues;
llvm::findDbgValues(DbgValues, OrigHeaderVal);
for (auto &DbgValue : DbgValues) {
// The original users in the OrigHeader are already using the original
// definitions.
BasicBlock *UserBB = DbgValue->getParent();
if (UserBB == OrigHeader)
continue;

// Users in the OrigPreHeader need to use the value to which the
// original definitions are mapped and anything else can be handled by
// the SSAUpdater. To avoid adding PHINodes, check if the value is
// available in UserBB, if not substitute undef.
Value *NewVal;
if (UserBB == OrigPreheader)
NewVal = OrigPreHeaderVal;
else if (SSA.HasValueForBlock(UserBB))
NewVal = SSA.GetValueInMiddleOfBlock(UserBB);
else
NewVal = UndefValue::get(OrigHeaderVal->getType());
DbgValue->setOperand(0,
MetadataAsValue::get(OrigHeaderVal->getContext(),
ValueAsMetadata::get(NewVal)));
}
}
}

/// Rotate loop LP. Return true if the loop is rotated.
///
/// \param SimplifiedLatch is true if the latch was just folded into the final
/// loop exit. In this case we may want to rotate even though the new latch is
/// now an exiting branch. This rotation would have happened had the latch not
/// been simplified. However, if SimplifiedLatch is false, then we avoid
/// rotating loops in which the latch exits to avoid excessive or endless
/// rotation. LoopRotate should be repeatable and converge to a canonical
/// form. This property is satisfied because simplifying the loop latch can only
/// happen once across multiple invocations of the LoopRotate pass.
bool LoopRotate::rotateLoop(Loop *L, bool SimplifiedLatch) {
// If the loop has only one block then there is not much to rotate.
if (L->getBlocks().size() == 1)
return false;

BasicBlock *OrigHeader = L->getHeader();
BasicBlock *OrigLatch = L->getLoopLatch();

BranchInst *BI = dyn_cast<BranchInst>(OrigHeader->getTerminator());
if (!BI \|\| BI->isUnconditional())
return false;

// If the loop header is not one of the loop exiting blocks then
// either this loop is already rotated or it is not
// suitable for loop rotation transformations.
if (!L->isLoopExiting(OrigHeader))
return false;

// If the loop latch already contains a branch that leaves the loop then the
// loop is already rotated.
if (!OrigLatch)
return false;

// Rotate if either the loop latch does not exit the loop, or if the loop
// latch was just simplified.
if (L->isLoopExiting(OrigLatch) && !SimplifiedLatch)
return false;

// Check size of original header and reject loop if it is very big or we can't
// duplicate blocks inside it.
{
SmallPtrSet<const Value *, 32> EphValues;
CodeMetrics::collectEphemeralValues(L, AC, EphValues);

CodeMetrics Metrics;
Metrics.analyzeBasicBlock(OrigHeader, *TTI, EphValues);
if (Metrics.notDuplicatable) {
DEBUG(dbgs() << "LoopRotation: NOT rotating - contains non-duplicatable"
<< " instructions: ";
L->dump());
return false;
}
if (Metrics.convergent) {
DEBUG(dbgs() << "LoopRotation: NOT rotating - contains convergent "
"instructions: ";
L->dump());
return false;
}
if (Metrics.NumInsts > MaxHeaderSize)
return false;
}

// Now, this loop is suitable for rotation.
BasicBlock *OrigPreheader = L->getLoopPreheader();

// If the loop could not be converted to canonical form, it must have an
// indirectbr in it, just give up.
if (!OrigPreheader \|\| !L->hasDedicatedExits())
return false;

// Anything ScalarEvolution may know about this loop or the PHI nodes
// in its header will soon be invalidated.
if (SE)
SE->forgetLoop(L);

DEBUG(dbgs() << "LoopRotation: rotating "; L->dump());

// Find new Loop header. NewHeader is a Header's one and only successor
// that is inside loop. Header's other successor is outside the
// loop. Otherwise loop is not suitable for rotation.
BasicBlock *Exit = BI->getSuccessor(0);
BasicBlock *NewHeader = BI->getSuccessor(1);
if (L->contains(Exit))
std::swap(Exit, NewHeader);
assert(NewHeader && "Unable to determine new loop header");
assert(L->contains(NewHeader) && !L->contains(Exit) &&
"Unable to determine loop header and exit blocks");

// This code assumes that the new header has exactly one predecessor.
// Remove any single-entry PHI nodes in it.
assert(NewHeader->getSinglePredecessor() &&
"New header doesn't have one pred!");
FoldSingleEntryPHINodes(NewHeader);

// Begin by walking OrigHeader and populating ValueMap with an entry for
// each Instruction.
BasicBlock::iterator I = OrigHeader->begin(), E = OrigHeader->end();
ValueToValueMapTy ValueMap;

// For PHI nodes, the value available in OldPreHeader is just the
// incoming value from OldPreHeader.
for (; PHINode *PN = dyn_cast<PHINode>(I); ++I)
ValueMap[PN] = PN->getIncomingValueForBlock(OrigPreheader);

// For the rest of the instructions, either hoist to the OrigPreheader if
// possible or create a clone in the OldPreHeader if not.
TerminatorInst *LoopEntryBranch = OrigPreheader->getTerminator();

// Record all debug intrinsics preceding LoopEntryBranch to avoid duplication.
using DbgIntrinsicHash =
std::pair<std::pair<Value , DILocalVariable >, DIExpression *>;
auto makeHash = [](DbgInfoIntrinsic *D) -> DbgIntrinsicHash {
return {{D->getVariableLocation(), D->getVariable()}, D->getExpression()};
};
SmallDenseSet<DbgIntrinsicHash, 8> DbgIntrinsics;
for (auto I = std::next(OrigPreheader->rbegin()), E = OrigPreheader->rend();
I != E; ++I) {
if (auto DII = dyn_cast<DbgInfoIntrinsic>(&I))
DbgIntrinsics.insert(makeHash(DII));
else
break;
}

while (I != E) {
Instruction Inst = &I++;

// If the instruction's operands are invariant and it doesn't read or write
// memory, then it is safe to hoist. Doing this doesn't change the order of
// execution in the preheader, but does prevent the instruction from
// executing in each iteration of the loop. This means it is safe to hoist
// something that might trap, but isn't safe to hoist something that reads
// memory (without proving that the loop doesn't write).
if (L->hasLoopInvariantOperands(Inst) && !Inst->mayReadFromMemory() &&
!Inst->mayWriteToMemory() && !isa<TerminatorInst>(Inst) &&
!isa<DbgInfoIntrinsic>(Inst) && !isa<AllocaInst>(Inst)) {
Inst->moveBefore(LoopEntryBranch);
continue;
}

// Otherwise, create a duplicate of the instruction.
Instruction *C = Inst->clone();

// Eagerly remap the operands of the instruction.
RemapInstruction(C, ValueMap,
RF_NoModuleLevelChanges \| RF_IgnoreMissingLocals);

// Avoid inserting the same intrinsic twice.
if (auto *DII = dyn_cast<DbgInfoIntrinsic>(C))
if (DbgIntrinsics.count(makeHash(DII))) {
C->deleteValue();
continue;
}

// With the operands remapped, see if the instruction constant folds or is
// otherwise simplifyable. This commonly occurs because the entry from PHI
// nodes allows icmps and other instructions to fold.
Value *V = SimplifyInstruction(C, SQ);
if (V && LI->replacementPreservesLCSSAForm(C, V)) {
// If so, then delete the temporary instruction and stick the folded value
// in the map.
ValueMap[Inst] = V;
if (!C->mayHaveSideEffects()) {
C->deleteValue();
C = nullptr;
}
} else {
ValueMap[Inst] = C;
}
if (C) {
// Otherwise, stick the new instruction into the new block!
C->setName(Inst->getName());
C->insertBefore(LoopEntryBranch);

if (auto *II = dyn_cast<IntrinsicInst>(C))
if (II->getIntrinsicID() == Intrinsic::assume)
AC->registerAssumption(II);
}
}

// Along with all the other instructions, we just cloned OrigHeader's
// terminator into OrigPreHeader. Fix up the PHI nodes in each of OrigHeader's
// successors by duplicating their incoming values for OrigHeader.
TerminatorInst *TI = OrigHeader->getTerminator();
for (BasicBlock *SuccBB : TI->successors())
for (BasicBlock::iterator BI = SuccBB->begin();
PHINode *PN = dyn_cast<PHINode>(BI); ++BI)
PN->addIncoming(PN->getIncomingValueForBlock(OrigHeader), OrigPreheader);

// Now that OrigPreHeader has a clone of OrigHeader's terminator, remove
// OrigPreHeader's old terminator (the original branch into the loop), and
// remove the corresponding incoming values from the PHI nodes in OrigHeader.
LoopEntryBranch->eraseFromParent();


SmallVector<PHINode*, 2> InsertedPHIs;
// If there were any uses of instructions in the duplicated block outside the
// loop, update them, inserting PHI nodes as required
RewriteUsesOfClonedInstructions(OrigHeader, OrigPreheader, ValueMap,
&InsertedPHIs);

// Attach dbg.value intrinsics to the new phis if that phi uses a value that
// previously had debug metadata attached. This keeps the debug info
// up-to-date in the loop body.
if (!InsertedPHIs.empty())
insertDebugValuesForPHIs(OrigHeader, InsertedPHIs);

// NewHeader is now the header of the loop.
L->moveToHeader(NewHeader);
assert(L->getHeader() == NewHeader && "Latch block is our new header");

// Inform DT about changes to the CFG.
if (DT) {
// The OrigPreheader branches to the NewHeader and Exit now. Then, inform
// the DT about the removed edge to the OrigHeader (that got removed).
SmallVector<DominatorTree::UpdateType, 3> Updates;
Updates.push_back({DominatorTree::Insert, OrigPreheader, Exit});
Updates.push_back({DominatorTree::Insert, OrigPreheader, NewHeader});
Updates.push_back({DominatorTree::Delete, OrigPreheader, OrigHeader});
DT->applyUpdates(Updates);
}

// At this point, we've finished our major CFG changes. As part of cloning
// the loop into the preheader we've simplified instructions and the
// duplicated conditional branch may now be branching on a constant. If it is
// branching on a constant and if that constant means that we enter the loop,
// then we fold away the cond branch to an uncond branch. This simplifies the
// loop in cases important for nested loops, and it also means we don't have
// to split as many edges.
BranchInst *PHBI = cast<BranchInst>(OrigPreheader->getTerminator());
assert(PHBI->isConditional() && "Should be clone of BI condbr!");
if (!isa<ConstantInt>(PHBI->getCondition()) \|\|
PHBI->getSuccessor(cast<ConstantInt>(PHBI->getCondition())->isZero()) !=
NewHeader) {
// The conditional branch can't be folded, handle the general case.
// Split edges as necessary to preserve LoopSimplify form.

// Right now OrigPreHeader has two successors, NewHeader and ExitBlock, and
// thus is not a preheader anymore.
// Split the edge to form a real preheader.
BasicBlock *NewPH = SplitCriticalEdge(
OrigPreheader, NewHeader,
CriticalEdgeSplittingOptions(DT, LI).setPreserveLCSSA());
NewPH->setName(NewHeader->getName() + ".lr.ph");

// Preserve canonical loop form, which means that 'Exit' should have only
// one predecessor. Note that Exit could be an exit block for multiple
// nested loops, causing both of the edges to now be critical and need to
// be split.
SmallVector<BasicBlock *, 4> ExitPreds(pred_begin(Exit), pred_end(Exit));
bool SplitLatchEdge = false;
for (BasicBlock *ExitPred : ExitPreds) {
// We only need to split loop exit edges.
Loop *PredLoop = LI->getLoopFor(ExitPred);
if (!PredLoop \|\| PredLoop->contains(Exit))
continue;
if (isa<IndirectBrInst>(ExitPred->getTerminator()))
continue;
SplitLatchEdge \|= L->getLoopLatch() == ExitPred;
BasicBlock *ExitSplit = SplitCriticalEdge(
ExitPred, Exit,
CriticalEdgeSplittingOptions(DT, LI).setPreserveLCSSA());
ExitSplit->moveBefore(Exit);
}
assert(SplitLatchEdge &&
"Despite splitting all preds, failed to split latch exit?");
} else {
// We can fold the conditional branch in the preheader, this makes things
// simpler. The first step is to remove the extra edge to the Exit block.
Exit->removePredecessor(OrigPreheader, true /preserve LCSSA/);
BranchInst *NewBI = BranchInst::Create(NewHeader, PHBI);
NewBI->setDebugLoc(PHBI->getDebugLoc());
PHBI->eraseFromParent();

// With our CFG finalized, update DomTree if it is available.
if (DT) DT->deleteEdge(OrigPreheader, Exit);
}

assert(L->getLoopPreheader() && "Invalid loop preheader after loop rotation");
assert(L->getLoopLatch() && "Invalid loop latch after loop rotation");

// Now that the CFG and DomTree are in a consistent state again, try to merge
// the OrigHeader block into OrigLatch. This will succeed if they are
// connected by an unconditional branch. This is just a cleanup so the
// emitted code isn't too gross in this common case.
MergeBlockIntoPredecessor(OrigHeader, DT, LI);

DEBUG(dbgs() << "LoopRotation: into "; L->dump());

++NumRotated;
return true;
}

/// Determine whether the instructions in this range may be safely and cheaply
/// speculated. This is not an important enough situation to develop complex
/// heuristics. We handle a single arithmetic instruction along with any type
/// conversions.
static bool shouldSpeculateInstrs(BasicBlock::iterator Begin,
BasicBlock::iterator End, Loop *L) {
bool seenIncrement = false;
bool MultiExitLoop = false;

if (!L->getExitingBlock())
MultiExitLoop = true;

for (BasicBlock::iterator I = Begin; I != End; ++I) {

if (!isSafeToSpeculativelyExecute(&*I))
return false;

if (isa<DbgInfoIntrinsic>(I))
continue;

switch (I->getOpcode()) {
default:
return false;
case Instruction::GetElementPtr:
// GEPs are cheap if all indices are constant.
if (!cast<GEPOperator>(I)->hasAllConstantIndices())
return false;
// fall-thru to increment case
LLVM_FALLTHROUGH;
case Instruction::Add:
case Instruction::Sub:
case Instruction::And:
case Instruction::Or:
case Instruction::Xor:
case Instruction::Shl:
case Instruction::LShr:
case Instruction::AShr: {
Value *IVOpnd =
!isa<Constant>(I->getOperand(0))
? I->getOperand(0)
: !isa<Constant>(I->getOperand(1)) ? I->getOperand(1) : nullptr;
if (!IVOpnd)
return false;

// If increment operand is used outside of the loop, this speculation
// could cause extra live range interference.
if (MultiExitLoop) {
for (User *UseI : IVOpnd->users()) {
auto *UserInst = cast<Instruction>(UseI);
if (!L->contains(UserInst))
return false;
}
}

if (seenIncrement)
return false;
seenIncrement = true;
break;
}
case Instruction::Trunc:
case Instruction::ZExt:
case Instruction::SExt:
// ignore type conversions
break;
}
}
return true;
}

/// Fold the loop tail into the loop exit by speculating the loop tail
/// instructions. Typically, this is a single post-increment. In the case of a
/// simple 2-block loop, hoisting the increment can be much better than
/// duplicating the entire loop header. In the case of loops with early exits,
/// rotation will not work anyway, but simplifyLoopLatch will put the loop in
/// canonical form so downstream passes can handle it.
///
/// I don't believe this invalidates SCEV.
bool LoopRotate::simplifyLoopLatch(Loop *L) {
BasicBlock *Latch = L->getLoopLatch();
if (!Latch \|\| Latch->hasAddressTaken())
return false;

BranchInst *Jmp = dyn_cast<BranchInst>(Latch->getTerminator());
if (!Jmp \|\| !Jmp->isUnconditional())
return false;

BasicBlock *LastExit = Latch->getSinglePredecessor();
if (!LastExit \|\| !L->isLoopExiting(LastExit))
return false;

BranchInst *BI = dyn_cast<BranchInst>(LastExit->getTerminator());
if (!BI)
return false;

if (!shouldSpeculateInstrs(Latch->begin(), Jmp->getIterator(), L))
return false;

DEBUG(dbgs() << "Folding loop latch " << Latch->getName() << " into "
<< LastExit->getName() << "\n");

// Hoist the instructions from Latch into LastExit.
LastExit->getInstList().splice(BI->getIterator(), Latch->getInstList(),
Latch->begin(), Jmp->getIterator());

unsigned FallThruPath = BI->getSuccessor(0) == Latch ? 0 : 1;
BasicBlock *Header = Jmp->getSuccessor(0);
assert(Header == L->getHeader() && "expected a backward branch");

// Remove Latch from the CFG so that LastExit becomes the new Latch.
BI->setSuccessor(FallThruPath, Header);
Latch->replaceSuccessorsPhiUsesWith(LastExit);
Jmp->eraseFromParent();

// Nuke the Latch block.
assert(Latch->empty() && "unable to evacuate Latch");
LI->removeBlock(Latch);
if (DT)
DT->eraseNode(Latch);
Latch->eraseFromParent();
return true;
}

/// Rotate \c L, and return true if any modification was made.
bool LoopRotate::processLoop(Loop *L) {
// Save the loop metadata.
MDNode *LoopMD = L->getLoopID();

// Simplify the loop latch before attempting to rotate the header
// upward. Rotation may not be needed if the loop tail can be folded into the
// loop exit.
bool SimplifiedLatch = simplifyLoopLatch(L);

bool MadeChange = rotateLoop(L, SimplifiedLatch);
assert((!MadeChange \|\| L->isLoopExiting(L->getLoopLatch())) &&
"Loop latch should be exiting after loop-rotate.");

// Restore the loop metadata.
// NB! We presume LoopRotation DOESN'T ADD its own metadata.
if ((MadeChange \|\| SimplifiedLatch) && LoopMD)
L->setLoopID(LoopMD);

return MadeChange \|\| SimplifiedLatch;
}

LoopRotatePass::LoopRotatePass(bool EnableHeaderDuplication)		LoopRotatePass::LoopRotatePass(bool EnableHeaderDuplication)
: EnableHeaderDuplication(EnableHeaderDuplication) {}		: EnableHeaderDuplication(EnableHeaderDuplication) {}

PreservedAnalyses LoopRotatePass::run(Loop &L, LoopAnalysisManager &AM,		PreservedAnalyses LoopRotatePass::run(Loop &L, LoopAnalysisManager &AM,
LoopStandardAnalysisResults &AR,		LoopStandardAnalysisResults &AR,
LPMUpdater &) {		LPMUpdater &) {
int Threshold = EnableHeaderDuplication ? DefaultRotationThreshold : 0;		int Threshold = EnableHeaderDuplication ? DefaultRotationThreshold : 0;
const DataLayout &DL = L.getHeader()->getModule()->getDataLayout();		const DataLayout &DL = L.getHeader()->getModule()->getDataLayout();
const SimplifyQuery SQ = getBestSimplifyQuery(AR, DL);		const SimplifyQuery SQ = getBestSimplifyQuery(AR, DL);
LoopRotate LR(Threshold, &AR.LI, &AR.TTI, &AR.AC, &AR.DT, &AR.SE,
SQ);

bool Changed = LR.processLoop(&L);		bool Changed =
		LoopRotation(&L, Threshold, &AR.LI, &AR.TTI, &AR.AC, &AR.DT, &AR.SE, SQ);

if (!Changed)		if (!Changed)
return PreservedAnalyses::all();		return PreservedAnalyses::all();

return getLoopPassPreservedAnalyses();		return getLoopPassPreservedAnalyses();
}		}

namespace {		namespace {

Show All 25 Lines	bool runOnLoop(Loop *L, LPPassManager &LPM) override {
auto *LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();		auto *LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
const auto *TTI = &getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F);		const auto *TTI = &getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F);
auto *AC = &getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);		auto *AC = &getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
auto *DTWP = getAnalysisIfAvailable<DominatorTreeWrapperPass>();		auto *DTWP = getAnalysisIfAvailable<DominatorTreeWrapperPass>();
auto *DT = DTWP ? &DTWP->getDomTree() : nullptr;		auto *DT = DTWP ? &DTWP->getDomTree() : nullptr;
auto *SEWP = getAnalysisIfAvailable<ScalarEvolutionWrapperPass>();		auto *SEWP = getAnalysisIfAvailable<ScalarEvolutionWrapperPass>();
auto *SE = SEWP ? &SEWP->getSE() : nullptr;		auto *SE = SEWP ? &SEWP->getSE() : nullptr;
const SimplifyQuery SQ = getBestSimplifyQuery(*this, F);		const SimplifyQuery SQ = getBestSimplifyQuery(*this, F);
LoopRotate LR(MaxHeaderSize, LI, TTI, AC, DT, SE, SQ);		return LoopRotation(L, MaxHeaderSize, LI, TTI, AC, DT, SE, SQ);
return LR.processLoop(L);
}		}
};		};
}		}

char LoopRotateLegacyPass::ID = 0;		char LoopRotateLegacyPass::ID = 0;
INITIALIZE_PASS_BEGIN(LoopRotateLegacyPass, "loop-rotate", "Rotate Loops",		INITIALIZE_PASS_BEGIN(LoopRotateLegacyPass, "loop-rotate", "Rotate Loops",
false, false)		false, false)
INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)		INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
INITIALIZE_PASS_DEPENDENCY(LoopPass)		INITIALIZE_PASS_DEPENDENCY(LoopPass)
INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)		INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)
INITIALIZE_PASS_END(LoopRotateLegacyPass, "loop-rotate", "Rotate Loops", false,		INITIALIZE_PASS_END(LoopRotateLegacyPass, "loop-rotate", "Rotate Loops", false,
false)		false)

Pass *llvm::createLoopRotatePass(int MaxHeaderSize) {		Pass *llvm::createLoopRotatePass(int MaxHeaderSize) {
return new LoopRotateLegacyPass(MaxHeaderSize);		return new LoopRotateLegacyPass(MaxHeaderSize);
}		}

lib/Transforms/Utils/CMakeLists.txt

Show All 19 Lines	add_llvm_library(LLVMTransformUtils
GlobalStatus.cpp		GlobalStatus.cpp
InlineFunction.cpp		InlineFunction.cpp
ImportedFunctionsInliningStatistics.cpp		ImportedFunctionsInliningStatistics.cpp
InstructionNamer.cpp		InstructionNamer.cpp
IntegerDivision.cpp		IntegerDivision.cpp
LCSSA.cpp		LCSSA.cpp
LibCallsShrinkWrap.cpp		LibCallsShrinkWrap.cpp
Local.cpp		Local.cpp
		LoopRotationUtils.cpp
LoopSimplify.cpp		LoopSimplify.cpp
LoopUnroll.cpp		LoopUnroll.cpp
LoopUnrollPeel.cpp		LoopUnrollPeel.cpp
LoopUnrollRuntime.cpp		LoopUnrollRuntime.cpp
LoopUtils.cpp		LoopUtils.cpp
LoopVersioning.cpp		LoopVersioning.cpp
LowerInvoke.cpp		LowerInvoke.cpp
LowerMemIntrinsics.cpp		LowerMemIntrinsics.cpp
Show All 30 Lines

lib/Transforms/Utils/LoopRotationUtils.cpp

This file was added.

				//===----------------- LoopRotationUtils.cpp -----------------------------===//
				//
				// The LLVM Compiler Infrastructure
				//
				// This file is distributed under the University of Illinois Open Source
				// License. See LICENSE.TXT for details.
				//
				//===----------------------------------------------------------------------===//
				//
				// The existing LoopRotation.cpp is implemented as one of loop passes instead of
				// being a utility. The user cannot easily perform the loop rotation selectively
				// (or on demand) under different optimization level. For example, the loop
				// rotation is needed as part of the logic to convert a loop into a loop with
				// bottom test for a transformation. If the loop rotation is simply added as a
				// loop pass before the transformation, the pass is skipped if it is compiled at
				// -O0 or if it is explicitly disabled by the user, causing the compiler to
				// generate incorrect code. Furthermore, as a loop pass it will rotate all loops
				// instead of just the relevant loops.
				//
				// We provide a utility interface for the loop rotation so that the loop
				// rotation can be called on demand. The changeset is as follows:
				lebedev.riUnsubmitted Not Done Reply Inline Actions This should probably be in the differential's description, not as comment in the source code. lebedev.ri: This should probably be in the differential's description, not as comment in the source code.
				// 1) Create a new file lib/Transforms/Utils/LoopRotationUtils.cpp and move
				// the main implementation of class LoopRotate into this file.
				// 2) Create a new file llvm/include/Transform/Utils/LoopRotationUtils.h with
				// the interface LoopRotation(...).
				// 3) Original LoopRotation.cpp is changed to use the utility function
				// LoopRotation in LoopRotationUtils.cpp. This is done in the same way community
				// did for mem-to-reg implementation.
				//
				//===----------------------------------------------------------------------===//

				#include "llvm/Transforms/Utils/LoopRotationUtils.h"
				#include "llvm/ADT/Statistic.h"
				#include "llvm/Analysis/AliasAnalysis.h"
				#include "llvm/Analysis/AssumptionCache.h"
				#include "llvm/Analysis/BasicAliasAnalysis.h"
				#include "llvm/Analysis/CodeMetrics.h"
				#include "llvm/Analysis/GlobalsModRef.h"
				#include "llvm/Analysis/InstructionSimplify.h"
				#include "llvm/Analysis/LoopPass.h"
				dmgreenUnsubmitted Not Done Reply Inline Actions I believe this header has moved to Analysis/Utils/Local.h dmgreen: I believe this header has moved to Analysis/Utils/Local.h
				jinlinAuthorUnsubmitted Not Done Reply Inline Actions The header file path is correct. /export/iusers/XXX/v15/llvm/include/llvm=>find . -name "Local.h" ./Transforms/Utils/Local.h jinlin: The header file path is correct. /export/iusers/XXX/v15/llvm/include/llvm=>find . -name…
				dmgreenUnsubmitted Not Done Reply Inline Actions https://reviews.llvm.org/rL328165 is the commit I was thinking about. It only went in a couple of days ago. dmgreen: https://reviews.llvm.org/rL328165 is the commit I was thinking about. It only went in a couple…
				jinlinAuthorUnsubmitted Not Done Reply Inline Actions Hi Dave. Thanks so much for your update. I will update the header file on it. Thanks, Jin jinlin: Hi Dave. Thanks so much for your update. I will update the header file on it. Thanks, Jin
				jinlinAuthorUnsubmitted Not Done Reply Inline Actions Hi Dave, The changes have passed with the tests. However, I don't have privilege to check in the changes. Would you please do me a favor to check in the changes? Thanks, Jin jinlin: Hi Dave, The changes have passed with the tests. However, I don't have privilege to check in…
				#include "llvm/Analysis/ScalarEvolution.h"
				#include "llvm/Analysis/ScalarEvolutionAliasAnalysis.h"
				#include "llvm/Analysis/TargetTransformInfo.h"
				#include "llvm/Analysis/ValueTracking.h"
				#include "llvm/IR/CFG.h"
				#include "llvm/IR/DebugInfoMetadata.h"
				#include "llvm/IR/Dominators.h"
				#include "llvm/IR/Function.h"
				#include "llvm/IR/IntrinsicInst.h"
				#include "llvm/IR/Module.h"
				#include "llvm/Support/CommandLine.h"
				#include "llvm/Support/Debug.h"
				#include "llvm/Support/raw_ostream.h"
				#include "llvm/Transforms/Scalar.h"
				#include "llvm/Transforms/Scalar/LoopPassManager.h"
				#include "llvm/Transforms/Utils/BasicBlockUtils.h"
				#include "llvm/Transforms/Utils/Local.h"
				#include "llvm/Transforms/Utils/LoopUtils.h"
				#include "llvm/Transforms/Utils/SSAUpdater.h"
				#include "llvm/Transforms/Utils/ValueMapper.h"
				using namespace llvm;

				#define DEBUG_TYPE "loop-rotate"

				STATISTIC(NumRotated, "Number of loops rotated");

				namespace {
				/// A simple loop rotation transformation.
				class LoopRotate {
				const unsigned MaxHeaderSize;
				LoopInfo *LI;
				const TargetTransformInfo *TTI;
				AssumptionCache *AC;
				DominatorTree *DT;
				ScalarEvolution *SE;
				const SimplifyQuery &SQ;

				public:
				LoopRotate(unsigned MaxHeaderSize, LoopInfo *LI,
				const TargetTransformInfo TTI, AssumptionCache AC,
				DominatorTree DT, ScalarEvolution SE, const SimplifyQuery &SQ)
				: MaxHeaderSize(MaxHeaderSize), LI(LI), TTI(TTI), AC(AC), DT(DT), SE(SE),
				SQ(SQ) {}
				bool processLoop(Loop *L);

				private:
				bool rotateLoop(Loop *L, bool SimplifiedLatch);
				bool simplifyLoopLatch(Loop *L);
				};
				} // end anonymous namespace

				/// RewriteUsesOfClonedInstructions - We just cloned the instructions from the
				/// old header into the preheader. If there were uses of the values produced by
				/// these instruction that were outside of the loop, we have to insert PHI nodes
				/// to merge the two values. Do this now.
				static void RewriteUsesOfClonedInstructions(
				BasicBlock OrigHeader, BasicBlock OrigPreheader,
				ValueToValueMapTy &ValueMap, SmallVectorImpl<PHINode > InsertedPHIs) {
				// Remove PHI node entries that are no longer live.
				BasicBlock::iterator I, E = OrigHeader->end();
				for (I = OrigHeader->begin(); PHINode *PN = dyn_cast<PHINode>(I); ++I)
				PN->removeIncomingValue(PN->getBasicBlockIndex(OrigPreheader));

				// Now fix up users of the instructions in OrigHeader, inserting PHI nodes
				// as necessary.
				SSAUpdater SSA(InsertedPHIs);
				for (I = OrigHeader->begin(); I != E; ++I) {
				Value OrigHeaderVal = &I;

				// If there are no uses of the value (e.g. because it returns void), there
				// is nothing to rewrite.
				if (OrigHeaderVal->use_empty())
				continue;

				Value *OrigPreHeaderVal = ValueMap.lookup(OrigHeaderVal);

				// The value now exits in two versions: the initial value in the preheader
				// and the loop "next" value in the original header.
				SSA.Initialize(OrigHeaderVal->getType(), OrigHeaderVal->getName());
				SSA.AddAvailableValue(OrigHeader, OrigHeaderVal);
				SSA.AddAvailableValue(OrigPreheader, OrigPreHeaderVal);

				// Visit each use of the OrigHeader instruction.
				for (Value::use_iterator UI = OrigHeaderVal->use_begin(),
				UE = OrigHeaderVal->use_end();
				UI != UE;) {
				// Grab the use before incrementing the iterator.
				Use &U = *UI;

				// Increment the iterator before removing the use from the list.
				++UI;

				// SSAUpdater can't handle a non-PHI use in the same block as an
				// earlier def. We can easily handle those cases manually.
				Instruction *UserInst = cast<Instruction>(U.getUser());
				if (!isa<PHINode>(UserInst)) {
				BasicBlock *UserBB = UserInst->getParent();

				// The original users in the OrigHeader are already using the
				// original definitions.
				if (UserBB == OrigHeader)
				continue;

				// Users in the OrigPreHeader need to use the value to which the
				// original definitions are mapped.
				if (UserBB == OrigPreheader) {
				U = OrigPreHeaderVal;
				continue;
				}
				}

				// Anything else can be handled by SSAUpdater.
				SSA.RewriteUse(U);
				}

				// Replace MetadataAsValue(ValueAsMetadata(OrigHeaderVal)) uses in debug
				// intrinsics.
				SmallVector<DbgValueInst *, 1> DbgValues;
				llvm::findDbgValues(DbgValues, OrigHeaderVal);
				for (auto &DbgValue : DbgValues) {
				// The original users in the OrigHeader are already using the original
				// definitions.
				BasicBlock *UserBB = DbgValue->getParent();
				if (UserBB == OrigHeader)
				continue;

				// Users in the OrigPreHeader need to use the value to which the
				// original definitions are mapped and anything else can be handled by
				// the SSAUpdater. To avoid adding PHINodes, check if the value is
				// available in UserBB, if not substitute undef.
				Value *NewVal;
				if (UserBB == OrigPreheader)
				NewVal = OrigPreHeaderVal;
				else if (SSA.HasValueForBlock(UserBB))
				NewVal = SSA.GetValueInMiddleOfBlock(UserBB);
				else
				NewVal = UndefValue::get(OrigHeaderVal->getType());
				DbgValue->setOperand(0,
				MetadataAsValue::get(OrigHeaderVal->getContext(),
				ValueAsMetadata::get(NewVal)));
				}
				}
				}

				/// Rotate loop LP. Return true if the loop is rotated.
				///
				/// \param SimplifiedLatch is true if the latch was just folded into the final
				/// loop exit. In this case we may want to rotate even though the new latch is
				/// now an exiting branch. This rotation would have happened had the latch not
				/// been simplified. However, if SimplifiedLatch is false, then we avoid
				/// rotating loops in which the latch exits to avoid excessive or endless
				/// rotation. LoopRotate should be repeatable and converge to a canonical
				/// form. This property is satisfied because simplifying the loop latch can only
				/// happen once across multiple invocations of the LoopRotate pass.
				bool LoopRotate::rotateLoop(Loop *L, bool SimplifiedLatch) {
				// If the loop has only one block then there is not much to rotate.
				if (L->getBlocks().size() == 1)
				return false;

				BasicBlock *OrigHeader = L->getHeader();
				BasicBlock *OrigLatch = L->getLoopLatch();

				BranchInst *BI = dyn_cast<BranchInst>(OrigHeader->getTerminator());
				if (!BI \|\| BI->isUnconditional())
				return false;

				// If the loop header is not one of the loop exiting blocks then
				// either this loop is already rotated or it is not
				// suitable for loop rotation transformations.
				if (!L->isLoopExiting(OrigHeader))
				return false;

				// If the loop latch already contains a branch that leaves the loop then the
				// loop is already rotated.
				if (!OrigLatch)
				return false;

				// Rotate if either the loop latch does not exit the loop, or if the loop
				// latch was just simplified.
				if (L->isLoopExiting(OrigLatch) && !SimplifiedLatch)
				return false;

				// Check size of original header and reject loop if it is very big or we can't
				// duplicate blocks inside it.
				{
				SmallPtrSet<const Value *, 32> EphValues;
				CodeMetrics::collectEphemeralValues(L, AC, EphValues);

				CodeMetrics Metrics;
				Metrics.analyzeBasicBlock(OrigHeader, *TTI, EphValues);
				if (Metrics.notDuplicatable) {
				DEBUG(dbgs() << "LoopRotation: NOT rotating - contains non-duplicatable"
				<< " instructions: ";
				L->dump());
				return false;
				}
				if (Metrics.convergent) {
				DEBUG(dbgs() << "LoopRotation: NOT rotating - contains convergent "
				"instructions: ";
				L->dump());
				return false;
				}
				if (Metrics.NumInsts > MaxHeaderSize)
				return false;
				}

				// Now, this loop is suitable for rotation.
				BasicBlock *OrigPreheader = L->getLoopPreheader();

				// If the loop could not be converted to canonical form, it must have an
				// indirectbr in it, just give up.
				if (!OrigPreheader \|\| !L->hasDedicatedExits())
				return false;

				// Anything ScalarEvolution may know about this loop or the PHI nodes
				// in its header will soon be invalidated.
				if (SE)
				SE->forgetLoop(L);

				DEBUG(dbgs() << "LoopRotation: rotating "; L->dump());

				// Find new Loop header. NewHeader is a Header's one and only successor
				// that is inside loop. Header's other successor is outside the
				// loop. Otherwise loop is not suitable for rotation.
				BasicBlock *Exit = BI->getSuccessor(0);
				BasicBlock *NewHeader = BI->getSuccessor(1);
				if (L->contains(Exit))
				std::swap(Exit, NewHeader);
				assert(NewHeader && "Unable to determine new loop header");
				assert(L->contains(NewHeader) && !L->contains(Exit) &&
				"Unable to determine loop header and exit blocks");

				// This code assumes that the new header has exactly one predecessor.
				// Remove any single-entry PHI nodes in it.
				assert(NewHeader->getSinglePredecessor() &&
				"New header doesn't have one pred!");
				FoldSingleEntryPHINodes(NewHeader);

				// Begin by walking OrigHeader and populating ValueMap with an entry for
				// each Instruction.
				BasicBlock::iterator I = OrigHeader->begin(), E = OrigHeader->end();
				ValueToValueMapTy ValueMap;

				// For PHI nodes, the value available in OldPreHeader is just the
				// incoming value from OldPreHeader.
				for (; PHINode *PN = dyn_cast<PHINode>(I); ++I)
				ValueMap[PN] = PN->getIncomingValueForBlock(OrigPreheader);

				// For the rest of the instructions, either hoist to the OrigPreheader if
				// possible or create a clone in the OldPreHeader if not.
				TerminatorInst *LoopEntryBranch = OrigPreheader->getTerminator();

				// Record all debug intrinsics preceding LoopEntryBranch to avoid duplication.
				using DbgIntrinsicHash =
				std::pair<std::pair<Value , DILocalVariable >, DIExpression *>;
				auto makeHash = [](DbgInfoIntrinsic *D) -> DbgIntrinsicHash {
				return {{D->getVariableLocation(), D->getVariable()}, D->getExpression()};
				};
				SmallDenseSet<DbgIntrinsicHash, 8> DbgIntrinsics;
				for (auto I = std::next(OrigPreheader->rbegin()), E = OrigPreheader->rend();
				I != E; ++I) {
				if (auto DII = dyn_cast<DbgInfoIntrinsic>(&I))
				DbgIntrinsics.insert(makeHash(DII));
				else
				break;
				}

				while (I != E) {
				Instruction Inst = &I++;

				// If the instruction's operands are invariant and it doesn't read or write
				// memory, then it is safe to hoist. Doing this doesn't change the order of
				// execution in the preheader, but does prevent the instruction from
				// executing in each iteration of the loop. This means it is safe to hoist
				// something that might trap, but isn't safe to hoist something that reads
				// memory (without proving that the loop doesn't write).
				if (L->hasLoopInvariantOperands(Inst) && !Inst->mayReadFromMemory() &&
				!Inst->mayWriteToMemory() && !isa<TerminatorInst>(Inst) &&
				!isa<DbgInfoIntrinsic>(Inst) && !isa<AllocaInst>(Inst)) {
				Inst->moveBefore(LoopEntryBranch);
				continue;
				}

				// Otherwise, create a duplicate of the instruction.
				Instruction *C = Inst->clone();

				// Eagerly remap the operands of the instruction.
				RemapInstruction(C, ValueMap,
				RF_NoModuleLevelChanges \| RF_IgnoreMissingLocals);

				// Avoid inserting the same intrinsic twice.
				if (auto *DII = dyn_cast<DbgInfoIntrinsic>(C))
				if (DbgIntrinsics.count(makeHash(DII))) {
				C->deleteValue();
				continue;
				}

				// With the operands remapped, see if the instruction constant folds or is
				// otherwise simplifyable. This commonly occurs because the entry from PHI
				// nodes allows icmps and other instructions to fold.
				Value *V = SimplifyInstruction(C, SQ);
				if (V && LI->replacementPreservesLCSSAForm(C, V)) {
				// If so, then delete the temporary instruction and stick the folded value
				// in the map.
				ValueMap[Inst] = V;
				if (!C->mayHaveSideEffects()) {
				C->deleteValue();
				C = nullptr;
				}
				} else {
				ValueMap[Inst] = C;
				}
				if (C) {
				// Otherwise, stick the new instruction into the new block!
				C->setName(Inst->getName());
				C->insertBefore(LoopEntryBranch);

				if (auto *II = dyn_cast<IntrinsicInst>(C))
				if (II->getIntrinsicID() == Intrinsic::assume)
				AC->registerAssumption(II);
				}
				}

				// Along with all the other instructions, we just cloned OrigHeader's
				// terminator into OrigPreHeader. Fix up the PHI nodes in each of OrigHeader's
				// successors by duplicating their incoming values for OrigHeader.
				TerminatorInst *TI = OrigHeader->getTerminator();
				for (BasicBlock *SuccBB : TI->successors())
				for (BasicBlock::iterator BI = SuccBB->begin();
				PHINode *PN = dyn_cast<PHINode>(BI); ++BI)
				PN->addIncoming(PN->getIncomingValueForBlock(OrigHeader), OrigPreheader);

				// Now that OrigPreHeader has a clone of OrigHeader's terminator, remove
				// OrigPreHeader's old terminator (the original branch into the loop), and
				// remove the corresponding incoming values from the PHI nodes in OrigHeader.
				LoopEntryBranch->eraseFromParent();

				SmallVector<PHINode *, 2> InsertedPHIs;
				// If there were any uses of instructions in the duplicated block outside the
				// loop, update them, inserting PHI nodes as required
				RewriteUsesOfClonedInstructions(OrigHeader, OrigPreheader, ValueMap,
				&InsertedPHIs);

				// Attach dbg.value intrinsics to the new phis if that phi uses a value that
				// previously had debug metadata attached. This keeps the debug info
				// up-to-date in the loop body.
				if (!InsertedPHIs.empty())
				insertDebugValuesForPHIs(OrigHeader, InsertedPHIs);

				// NewHeader is now the header of the loop.
				L->moveToHeader(NewHeader);
				assert(L->getHeader() == NewHeader && "Latch block is our new header");

				// Inform DT about changes to the CFG.
				if (DT) {
				// The OrigPreheader branches to the NewHeader and Exit now. Then, inform
				// the DT about the removed edge to the OrigHeader (that got removed).
				SmallVector<DominatorTree::UpdateType, 3> Updates;
				Updates.push_back({DominatorTree::Insert, OrigPreheader, Exit});
				Updates.push_back({DominatorTree::Insert, OrigPreheader, NewHeader});
				Updates.push_back({DominatorTree::Delete, OrigPreheader, OrigHeader});
				DT->applyUpdates(Updates);
				}

				// At this point, we've finished our major CFG changes. As part of cloning
				// the loop into the preheader we've simplified instructions and the
				// duplicated conditional branch may now be branching on a constant. If it is
				// branching on a constant and if that constant means that we enter the loop,
				// then we fold away the cond branch to an uncond branch. This simplifies the
				// loop in cases important for nested loops, and it also means we don't have
				// to split as many edges.
				BranchInst *PHBI = cast<BranchInst>(OrigPreheader->getTerminator());
				assert(PHBI->isConditional() && "Should be clone of BI condbr!");
				if (!isa<ConstantInt>(PHBI->getCondition()) \|\|
				PHBI->getSuccessor(cast<ConstantInt>(PHBI->getCondition())->isZero()) !=
				NewHeader) {
				// The conditional branch can't be folded, handle the general case.
				// Split edges as necessary to preserve LoopSimplify form.

				// Right now OrigPreHeader has two successors, NewHeader and ExitBlock, and
				// thus is not a preheader anymore.
				// Split the edge to form a real preheader.
				BasicBlock *NewPH = SplitCriticalEdge(
				OrigPreheader, NewHeader,
				CriticalEdgeSplittingOptions(DT, LI).setPreserveLCSSA());
				NewPH->setName(NewHeader->getName() + ".lr.ph");

				// Preserve canonical loop form, which means that 'Exit' should have only
				// one predecessor. Note that Exit could be an exit block for multiple
				// nested loops, causing both of the edges to now be critical and need to
				// be split.
				SmallVector<BasicBlock *, 4> ExitPreds(pred_begin(Exit), pred_end(Exit));
				bool SplitLatchEdge = false;
				for (BasicBlock *ExitPred : ExitPreds) {
				// We only need to split loop exit edges.
				Loop *PredLoop = LI->getLoopFor(ExitPred);
				if (!PredLoop \|\| PredLoop->contains(Exit))
				continue;
				if (isa<IndirectBrInst>(ExitPred->getTerminator()))
				continue;
				SplitLatchEdge \|= L->getLoopLatch() == ExitPred;
				BasicBlock *ExitSplit = SplitCriticalEdge(
				ExitPred, Exit,
				CriticalEdgeSplittingOptions(DT, LI).setPreserveLCSSA());
				ExitSplit->moveBefore(Exit);
				}
				assert(SplitLatchEdge &&
				"Despite splitting all preds, failed to split latch exit?");
				} else {
				// We can fold the conditional branch in the preheader, this makes things
				// simpler. The first step is to remove the extra edge to the Exit block.
				Exit->removePredecessor(OrigPreheader, true /preserve LCSSA/);
				BranchInst *NewBI = BranchInst::Create(NewHeader, PHBI);
				NewBI->setDebugLoc(PHBI->getDebugLoc());
				PHBI->eraseFromParent();

				// With our CFG finalized, update DomTree if it is available.
				if (DT)
				DT->deleteEdge(OrigPreheader, Exit);
				}

				assert(L->getLoopPreheader() && "Invalid loop preheader after loop rotation");
				assert(L->getLoopLatch() && "Invalid loop latch after loop rotation");

				// Now that the CFG and DomTree are in a consistent state again, try to merge
				// the OrigHeader block into OrigLatch. This will succeed if they are
				// connected by an unconditional branch. This is just a cleanup so the
				// emitted code isn't too gross in this common case.
				MergeBlockIntoPredecessor(OrigHeader, DT, LI);

				DEBUG(dbgs() << "LoopRotation: into "; L->dump());

				++NumRotated;
				return true;
				}

				/// Determine whether the instructions in this range may be safely and cheaply
				/// speculated. This is not an important enough situation to develop complex
				/// heuristics. We handle a single arithmetic instruction along with any type
				/// conversions.
				static bool shouldSpeculateInstrs(BasicBlock::iterator Begin,
				BasicBlock::iterator End, Loop *L) {
				bool seenIncrement = false;
				bool MultiExitLoop = false;

				if (!L->getExitingBlock())
				MultiExitLoop = true;

				for (BasicBlock::iterator I = Begin; I != End; ++I) {

				if (!isSafeToSpeculativelyExecute(&*I))
				return false;

				if (isa<DbgInfoIntrinsic>(I))
				continue;

				switch (I->getOpcode()) {
				default:
				return false;
				case Instruction::GetElementPtr:
				// GEPs are cheap if all indices are constant.
				if (!cast<GEPOperator>(I)->hasAllConstantIndices())
				return false;
				// fall-thru to increment case
				LLVM_FALLTHROUGH;
				case Instruction::Add:
				case Instruction::Sub:
				case Instruction::And:
				case Instruction::Or:
				case Instruction::Xor:
				case Instruction::Shl:
				case Instruction::LShr:
				case Instruction::AShr: {
				Value *IVOpnd =
				!isa<Constant>(I->getOperand(0))
				? I->getOperand(0)
				: !isa<Constant>(I->getOperand(1)) ? I->getOperand(1) : nullptr;
				if (!IVOpnd)
				return false;

				// If increment operand is used outside of the loop, this speculation
				// could cause extra live range interference.
				if (MultiExitLoop) {
				for (User *UseI : IVOpnd->users()) {
				auto *UserInst = cast<Instruction>(UseI);
				if (!L->contains(UserInst))
				return false;
				}
				}

				if (seenIncrement)
				return false;
				seenIncrement = true;
				break;
				}
				case Instruction::Trunc:
				case Instruction::ZExt:
				case Instruction::SExt:
				// ignore type conversions
				break;
				}
				}
				return true;
				}

				/// Fold the loop tail into the loop exit by speculating the loop tail
				/// instructions. Typically, this is a single post-increment. In the case of a
				/// simple 2-block loop, hoisting the increment can be much better than
				/// duplicating the entire loop header. In the case of loops with early exits,
				/// rotation will not work anyway, but simplifyLoopLatch will put the loop in
				/// canonical form so downstream passes can handle it.
				///
				/// I don't believe this invalidates SCEV.
				bool LoopRotate::simplifyLoopLatch(Loop *L) {
				BasicBlock *Latch = L->getLoopLatch();
				if (!Latch \|\| Latch->hasAddressTaken())
				return false;

				BranchInst *Jmp = dyn_cast<BranchInst>(Latch->getTerminator());
				if (!Jmp \|\| !Jmp->isUnconditional())
				return false;

				BasicBlock *LastExit = Latch->getSinglePredecessor();
				if (!LastExit \|\| !L->isLoopExiting(LastExit))
				return false;

				BranchInst *BI = dyn_cast<BranchInst>(LastExit->getTerminator());
				if (!BI)
				return false;

				if (!shouldSpeculateInstrs(Latch->begin(), Jmp->getIterator(), L))
				return false;

				DEBUG(dbgs() << "Folding loop latch " << Latch->getName() << " into "
				<< LastExit->getName() << "\n");

				// Hoist the instructions from Latch into LastExit.
				LastExit->getInstList().splice(BI->getIterator(), Latch->getInstList(),
				Latch->begin(), Jmp->getIterator());

				unsigned FallThruPath = BI->getSuccessor(0) == Latch ? 0 : 1;
				BasicBlock *Header = Jmp->getSuccessor(0);
				assert(Header == L->getHeader() && "expected a backward branch");

				// Remove Latch from the CFG so that LastExit becomes the new Latch.
				BI->setSuccessor(FallThruPath, Header);
				Latch->replaceSuccessorsPhiUsesWith(LastExit);
				Jmp->eraseFromParent();

				// Nuke the Latch block.
				assert(Latch->empty() && "unable to evacuate Latch");
				LI->removeBlock(Latch);
				if (DT)
				DT->eraseNode(Latch);
				Latch->eraseFromParent();
				return true;
				}

				/// Rotate \c L, and return true if any modification was made.
				bool LoopRotate::processLoop(Loop *L) {
				// Save the loop metadata.
				MDNode *LoopMD = L->getLoopID();

				// Simplify the loop latch before attempting to rotate the header
				// upward. Rotation may not be needed if the loop tail can be folded into the
				// loop exit.
				bool SimplifiedLatch = simplifyLoopLatch(L);

				bool MadeChange = rotateLoop(L, SimplifiedLatch);
				assert((!MadeChange \|\| L->isLoopExiting(L->getLoopLatch())) &&
				"Loop latch should be exiting after loop-rotate.");

				// Restore the loop metadata.
				// NB! We presume LoopRotation DOESN'T ADD its own metadata.
				if ((MadeChange \|\| SimplifiedLatch) && LoopMD)
				L->setLoopID(LoopMD);

				return MadeChange \|\| SimplifiedLatch;
				}

				bool llvm::LoopRotation(Loop L, unsigned MaxHeaderSize, LoopInfo LI,
				const TargetTransformInfo TTI, AssumptionCache AC,
				DominatorTree DT, ScalarEvolution SE,
				const SimplifyQuery &SQ) {
				LoopRotate LR(MaxHeaderSize, LI, TTI, AC, DT, SE, SQ);

				return LR.processLoop(L);
				}

This is an archive of the discontinued LLVM Phabricator instance.

Restructuring LoopRotation.cpp to create Loop Rotation Pass with Loop Rotation Utility Interface
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Diff 139316

include/llvm/Transforms/Utils/LoopRotationUtils.h

lib/Transforms/Scalar/LoopRotation.cpp

lib/Transforms/Utils/CMakeLists.txt

lib/Transforms/Utils/LoopRotationUtils.cpp

This is an archive of the discontinued LLVM Phabricator instance.

Restructuring LoopRotation.cpp to create Loop Rotation Pass with Loop Rotation Utility InterfaceClosedPublic

Details

Diff Detail

Event Timeline

Revision Contents

Diff 139316

include/llvm/Transforms/Utils/LoopRotationUtils.h

lib/Transforms/Scalar/LoopRotation.cpp

lib/Transforms/Utils/CMakeLists.txt

lib/Transforms/Utils/LoopRotationUtils.cpp

Restructuring LoopRotation.cpp to create Loop Rotation Pass with Loop Rotation Utility Interface
ClosedPublic