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llvm-project/llvm/lib/Transforms/Scalar/LoopInterchange.cpp

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//===- LoopInterchange.cpp - Loop interchange pass------------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This Pass handles loop interchange transform.
// This pass interchanges loops to provide a more cache-friendly memory access
// patterns.
//
//===----------------------------------------------------------------------===//
#include "llvm/ADT/SmallVector.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/AssumptionCache.h"
#include "llvm/Analysis/BlockFrequencyInfo.h"
#include "llvm/Analysis/CodeMetrics.h"
#include "llvm/Analysis/DependenceAnalysis.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/LoopIterator.h"
#include "llvm/Analysis/LoopPass.h"
#include "llvm/Analysis/OptimizationDiagnosticInfo.h"
#include "llvm/Analysis/ScalarEvolution.h"
#include "llvm/Analysis/ScalarEvolutionExpander.h"
#include "llvm/Analysis/ScalarEvolutionExpressions.h"
#include "llvm/Analysis/TargetTransformInfo.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/InstIterator.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/Module.h"
#include "llvm/Pass.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/LoopUtils.h"
using namespace llvm;
#define DEBUG_TYPE "loop-interchange"
static cl::opt<int> LoopInterchangeCostThreshold(
"loop-interchange-threshold", cl::init(0), cl::Hidden,
cl::desc("Interchange if you gain more than this number"));
namespace {
typedef SmallVector<Loop *, 8> LoopVector;
// TODO: Check if we can use a sparse matrix here.
typedef std::vector<std::vector<char>> CharMatrix;
// Maximum number of dependencies that can be handled in the dependency matrix.
static const unsigned MaxMemInstrCount = 100;
// Maximum loop depth supported.
static const unsigned MaxLoopNestDepth = 10;
struct LoopInterchange;
#ifdef DUMP_DEP_MATRICIES
void printDepMatrix(CharMatrix &DepMatrix) {
for (auto &Row : DepMatrix) {
for (auto D : Row)
DEBUG(dbgs() << D << " ");
DEBUG(dbgs() << "\n");
}
}
#endif
static bool populateDependencyMatrix(CharMatrix &DepMatrix, unsigned Level,
Loop *L, DependenceInfo *DI) {
typedef SmallVector<Value *, 16> ValueVector;
ValueVector MemInstr;
// For each block.
for (BasicBlock *BB : L->blocks()) {
// Scan the BB and collect legal loads and stores.
for (Instruction &I : *BB) {
if (!isa<Instruction>(I))
return false;
if (auto *Ld = dyn_cast<LoadInst>(&I)) {
if (!Ld->isSimple())
return false;
MemInstr.push_back(&I);
} else if (auto *St = dyn_cast<StoreInst>(&I)) {
if (!St->isSimple())
return false;
MemInstr.push_back(&I);
}
}
}
DEBUG(dbgs() << "Found " << MemInstr.size()
<< " Loads and Stores to analyze\n");
ValueVector::iterator I, IE, J, JE;
for (I = MemInstr.begin(), IE = MemInstr.end(); I != IE; ++I) {
for (J = I, JE = MemInstr.end(); J != JE; ++J) {
std::vector<char> Dep;
Instruction *Src = cast<Instruction>(*I);
Instruction *Dst = cast<Instruction>(*J);
if (Src == Dst)
continue;
// Ignore Input dependencies.
if (isa<LoadInst>(Src) && isa<LoadInst>(Dst))
continue;
// Track Output, Flow, and Anti dependencies.
if (auto D = DI->depends(Src, Dst, true)) {
assert(D->isOrdered() && "Expected an output, flow or anti dep.");
DEBUG(StringRef DepType =
D->isFlow() ? "flow" : D->isAnti() ? "anti" : "output";
dbgs() << "Found " << DepType
<< " dependency between Src and Dst\n"
<< " Src:" << *Src << "\n Dst:" << *Dst << '\n');
unsigned Levels = D->getLevels();
char Direction;
for (unsigned II = 1; II <= Levels; ++II) {
const SCEV *Distance = D->getDistance(II);
const SCEVConstant *SCEVConst =
dyn_cast_or_null<SCEVConstant>(Distance);
if (SCEVConst) {
const ConstantInt *CI = SCEVConst->getValue();
if (CI->isNegative())
Direction = '<';
else if (CI->isZero())
Direction = '=';
else
Direction = '>';
Dep.push_back(Direction);
} else if (D->isScalar(II)) {
Direction = 'S';
Dep.push_back(Direction);
} else {
unsigned Dir = D->getDirection(II);
if (Dir == Dependence::DVEntry::LT ||
Dir == Dependence::DVEntry::LE)
Direction = '<';
else if (Dir == Dependence::DVEntry::GT ||
Dir == Dependence::DVEntry::GE)
Direction = '>';
else if (Dir == Dependence::DVEntry::EQ)
Direction = '=';
else
Direction = '*';
Dep.push_back(Direction);
}
}
while (Dep.size() != Level) {
Dep.push_back('I');
}
DepMatrix.push_back(Dep);
if (DepMatrix.size() > MaxMemInstrCount) {
DEBUG(dbgs() << "Cannot handle more than " << MaxMemInstrCount
<< " dependencies inside loop\n");
return false;
}
}
}
}
// We don't have a DepMatrix to check legality return false.
if (DepMatrix.size() == 0)
return false;
return true;
}
// A loop is moved from index 'from' to an index 'to'. Update the Dependence
// matrix by exchanging the two columns.
static void interChangeDependencies(CharMatrix &DepMatrix, unsigned FromIndx,
unsigned ToIndx) {
unsigned numRows = DepMatrix.size();
for (unsigned i = 0; i < numRows; ++i) {
char TmpVal = DepMatrix[i][ToIndx];
DepMatrix[i][ToIndx] = DepMatrix[i][FromIndx];
DepMatrix[i][FromIndx] = TmpVal;
}
}
// Checks if outermost non '=','S'or'I' dependence in the dependence matrix is
// '>'
static bool isOuterMostDepPositive(CharMatrix &DepMatrix, unsigned Row,
unsigned Column) {
for (unsigned i = 0; i <= Column; ++i) {
if (DepMatrix[Row][i] == '<')
return false;
if (DepMatrix[Row][i] == '>')
return true;
}
// All dependencies were '=','S' or 'I'
return false;
}
// Checks if no dependence exist in the dependency matrix in Row before Column.
static bool containsNoDependence(CharMatrix &DepMatrix, unsigned Row,
unsigned Column) {
for (unsigned i = 0; i < Column; ++i) {
if (DepMatrix[Row][i] != '=' && DepMatrix[Row][i] != 'S' &&
DepMatrix[Row][i] != 'I')
return false;
}
return true;
}
static bool validDepInterchange(CharMatrix &DepMatrix, unsigned Row,
unsigned OuterLoopId, char InnerDep,
char OuterDep) {
if (isOuterMostDepPositive(DepMatrix, Row, OuterLoopId))
return false;
if (InnerDep == OuterDep)
return true;
// It is legal to interchange if and only if after interchange no row has a
// '>' direction as the leftmost non-'='.
if (InnerDep == '=' || InnerDep == 'S' || InnerDep == 'I')
return true;
if (InnerDep == '<')
return true;
if (InnerDep == '>') {
// If OuterLoopId represents outermost loop then interchanging will make the
// 1st dependency as '>'
if (OuterLoopId == 0)
return false;
// If all dependencies before OuterloopId are '=','S'or 'I'. Then
// interchanging will result in this row having an outermost non '='
// dependency of '>'
if (!containsNoDependence(DepMatrix, Row, OuterLoopId))
return true;
}
return false;
}
// Checks if it is legal to interchange 2 loops.
// [Theorem] A permutation of the loops in a perfect nest is legal if and only
// if the direction matrix, after the same permutation is applied to its
// columns, has no ">" direction as the leftmost non-"=" direction in any row.
static bool isLegalToInterChangeLoops(CharMatrix &DepMatrix,
unsigned InnerLoopId,
unsigned OuterLoopId) {
unsigned NumRows = DepMatrix.size();
// For each row check if it is valid to interchange.
for (unsigned Row = 0; Row < NumRows; ++Row) {
char InnerDep = DepMatrix[Row][InnerLoopId];
char OuterDep = DepMatrix[Row][OuterLoopId];
if (InnerDep == '*' || OuterDep == '*')
return false;
if (!validDepInterchange(DepMatrix, Row, OuterLoopId, InnerDep, OuterDep))
return false;
}
return true;
}
static void populateWorklist(Loop &L, SmallVector<LoopVector, 8> &V) {
DEBUG(dbgs() << "Calling populateWorklist on Func: "
<< L.getHeader()->getParent()->getName() << " Loop: %"
<< L.getHeader()->getName() << '\n');
LoopVector LoopList;
Loop *CurrentLoop = &L;
const std::vector<Loop *> *Vec = &CurrentLoop->getSubLoops();
while (!Vec->empty()) {
// The current loop has multiple subloops in it hence it is not tightly
// nested.
// Discard all loops above it added into Worklist.
if (Vec->size() != 1) {
LoopList.clear();
return;
}
LoopList.push_back(CurrentLoop);
CurrentLoop = Vec->front();
Vec = &CurrentLoop->getSubLoops();
}
LoopList.push_back(CurrentLoop);
V.push_back(std::move(LoopList));
}
static PHINode *getInductionVariable(Loop *L, ScalarEvolution *SE) {
PHINode *InnerIndexVar = L->getCanonicalInductionVariable();
if (InnerIndexVar)
return InnerIndexVar;
if (L->getLoopLatch() == nullptr || L->getLoopPredecessor() == nullptr)
return nullptr;
for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ++I) {
PHINode *PhiVar = cast<PHINode>(I);
Type *PhiTy = PhiVar->getType();
if (!PhiTy->isIntegerTy() && !PhiTy->isFloatingPointTy() &&
!PhiTy->isPointerTy())
return nullptr;
const SCEVAddRecExpr *AddRec =
dyn_cast<SCEVAddRecExpr>(SE->getSCEV(PhiVar));
if (!AddRec || !AddRec->isAffine())
continue;
const SCEV *Step = AddRec->getStepRecurrence(*SE);
if (!isa<SCEVConstant>(Step))
continue;
// Found the induction variable.
// FIXME: Handle loops with more than one induction variable. Note that,
// currently, legality makes sure we have only one induction variable.
return PhiVar;
}
return nullptr;
}
/// LoopInterchangeLegality checks if it is legal to interchange the loop.
class LoopInterchangeLegality {
public:
LoopInterchangeLegality(Loop *Outer, Loop *Inner, ScalarEvolution *SE,
LoopInfo *LI, DominatorTree *DT, bool PreserveLCSSA,
OptimizationRemarkEmitter *ORE)
: OuterLoop(Outer), InnerLoop(Inner), SE(SE), LI(LI), DT(DT),
PreserveLCSSA(PreserveLCSSA), ORE(ORE), InnerLoopHasReduction(false) {}
/// Check if the loops can be interchanged.
bool canInterchangeLoops(unsigned InnerLoopId, unsigned OuterLoopId,
CharMatrix &DepMatrix);
/// Check if the loop structure is understood. We do not handle triangular
/// loops for now.
bool isLoopStructureUnderstood(PHINode *InnerInductionVar);
bool currentLimitations();
bool hasInnerLoopReduction() { return InnerLoopHasReduction; }
private:
bool tightlyNested(Loop *Outer, Loop *Inner);
bool containsUnsafeInstructionsInHeader(BasicBlock *BB);
bool areAllUsesReductions(Instruction *Ins, Loop *L);
bool containsUnsafeInstructionsInLatch(BasicBlock *BB);
bool findInductionAndReductions(Loop *L,
SmallVector<PHINode *, 8> &Inductions,
SmallVector<PHINode *, 8> &Reductions);
Loop *OuterLoop;
Loop *InnerLoop;
ScalarEvolution *SE;
LoopInfo *LI;
DominatorTree *DT;
bool PreserveLCSSA;
/// Interface to emit optimization remarks.
OptimizationRemarkEmitter *ORE;
bool InnerLoopHasReduction;
};
/// LoopInterchangeProfitability checks if it is profitable to interchange the
/// loop.
class LoopInterchangeProfitability {
public:
LoopInterchangeProfitability(Loop *Outer, Loop *Inner, ScalarEvolution *SE,
OptimizationRemarkEmitter *ORE)
: OuterLoop(Outer), InnerLoop(Inner), SE(SE), ORE(ORE) {}
/// Check if the loop interchange is profitable.
bool isProfitable(unsigned InnerLoopId, unsigned OuterLoopId,
CharMatrix &DepMatrix);
private:
int getInstrOrderCost();
Loop *OuterLoop;
Loop *InnerLoop;
/// Scev analysis.
ScalarEvolution *SE;
/// Interface to emit optimization remarks.
OptimizationRemarkEmitter *ORE;
};
/// LoopInterchangeTransform interchanges the loop.
class LoopInterchangeTransform {
public:
LoopInterchangeTransform(Loop *Outer, Loop *Inner, ScalarEvolution *SE,
LoopInfo *LI, DominatorTree *DT,
BasicBlock *LoopNestExit,
bool InnerLoopContainsReductions)
: OuterLoop(Outer), InnerLoop(Inner), SE(SE), LI(LI), DT(DT),
LoopExit(LoopNestExit),
InnerLoopHasReduction(InnerLoopContainsReductions) {}
/// Interchange OuterLoop and InnerLoop.
bool transform();
void restructureLoops(Loop *InnerLoop, Loop *OuterLoop);
void removeChildLoop(Loop *OuterLoop, Loop *InnerLoop);
private:
void splitInnerLoopLatch(Instruction *);
void splitInnerLoopHeader();
bool adjustLoopLinks();
void adjustLoopPreheaders();
bool adjustLoopBranches();
void updateIncomingBlock(BasicBlock *CurrBlock, BasicBlock *OldPred,
BasicBlock *NewPred);
Loop *OuterLoop;
Loop *InnerLoop;
/// Scev analysis.
ScalarEvolution *SE;
LoopInfo *LI;
DominatorTree *DT;
BasicBlock *LoopExit;
bool InnerLoopHasReduction;
};
// Main LoopInterchange Pass.
struct LoopInterchange : public FunctionPass {
static char ID;
ScalarEvolution *SE;
LoopInfo *LI;
DependenceInfo *DI;
DominatorTree *DT;
bool PreserveLCSSA;
/// Interface to emit optimization remarks.
OptimizationRemarkEmitter *ORE;
LoopInterchange()
: FunctionPass(ID), SE(nullptr), LI(nullptr), DI(nullptr), DT(nullptr) {
initializeLoopInterchangePass(*PassRegistry::getPassRegistry());
}
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.addRequired<ScalarEvolutionWrapperPass>();
AU.addRequired<AAResultsWrapperPass>();
AU.addRequired<DominatorTreeWrapperPass>();
AU.addRequired<LoopInfoWrapperPass>();
AU.addRequired<DependenceAnalysisWrapperPass>();
AU.addRequiredID(LoopSimplifyID);
AU.addRequiredID(LCSSAID);
AU.addRequired<OptimizationRemarkEmitterWrapperPass>();
}
bool runOnFunction(Function &F) override {
if (skipFunction(F))
return false;
SE = &getAnalysis<ScalarEvolutionWrapperPass>().getSE();
LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
DI = &getAnalysis<DependenceAnalysisWrapperPass>().getDI();
auto *DTWP = getAnalysisIfAvailable<DominatorTreeWrapperPass>();
DT = DTWP ? &DTWP->getDomTree() : nullptr;
ORE = &getAnalysis<OptimizationRemarkEmitterWrapperPass>().getORE();
PreserveLCSSA = mustPreserveAnalysisID(LCSSAID);
// Build up a worklist of loop pairs to analyze.
SmallVector<LoopVector, 8> Worklist;
for (Loop *L : *LI)
populateWorklist(*L, Worklist);
DEBUG(dbgs() << "Worklist size = " << Worklist.size() << "\n");
bool Changed = true;
while (!Worklist.empty()) {
LoopVector LoopList = Worklist.pop_back_val();
Changed = processLoopList(LoopList, F);
}
return Changed;
}
bool isComputableLoopNest(LoopVector LoopList) {
for (Loop *L : LoopList) {
const SCEV *ExitCountOuter = SE->getBackedgeTakenCount(L);
if (ExitCountOuter == SE->getCouldNotCompute()) {
DEBUG(dbgs() << "Couldn't compute backedge count\n");
return false;
}
if (L->getNumBackEdges() != 1) {
DEBUG(dbgs() << "NumBackEdges is not equal to 1\n");
return false;
}
if (!L->getExitingBlock()) {
DEBUG(dbgs() << "Loop doesn't have unique exit block\n");
return false;
}
}
return true;
}
unsigned selectLoopForInterchange(const LoopVector &LoopList) {
// TODO: Add a better heuristic to select the loop to be interchanged based
// on the dependence matrix. Currently we select the innermost loop.
return LoopList.size() - 1;
}
bool processLoopList(LoopVector LoopList, Function &F) {
bool Changed = false;
unsigned LoopNestDepth = LoopList.size();
if (LoopNestDepth < 2) {
DEBUG(dbgs() << "Loop doesn't contain minimum nesting level.\n");
return false;
}
if (LoopNestDepth > MaxLoopNestDepth) {
DEBUG(dbgs() << "Cannot handle loops of depth greater than "
<< MaxLoopNestDepth << "\n");
return false;
}
if (!isComputableLoopNest(LoopList)) {
DEBUG(dbgs() << "Not valid loop candidate for interchange\n");
return false;
}
DEBUG(dbgs() << "Processing LoopList of size = " << LoopNestDepth << "\n");
CharMatrix DependencyMatrix;
Loop *OuterMostLoop = *(LoopList.begin());
if (!populateDependencyMatrix(DependencyMatrix, LoopNestDepth,
OuterMostLoop, DI)) {
DEBUG(dbgs() << "Populating dependency matrix failed\n");
return false;
}
#ifdef DUMP_DEP_MATRICIES
DEBUG(dbgs() << "Dependence before interchange\n");
printDepMatrix(DependencyMatrix);
#endif
BasicBlock *OuterMostLoopLatch = OuterMostLoop->getLoopLatch();
BranchInst *OuterMostLoopLatchBI =
dyn_cast<BranchInst>(OuterMostLoopLatch->getTerminator());
if (!OuterMostLoopLatchBI)
return false;
// Since we currently do not handle LCSSA PHI's any failure in loop
// condition will now branch to LoopNestExit.
// TODO: This should be removed once we handle LCSSA PHI nodes.
// Get the Outermost loop exit.
BasicBlock *LoopNestExit;
if (OuterMostLoopLatchBI->getSuccessor(0) == OuterMostLoop->getHeader())
LoopNestExit = OuterMostLoopLatchBI->getSuccessor(1);
else
LoopNestExit = OuterMostLoopLatchBI->getSuccessor(0);
if (isa<PHINode>(LoopNestExit->begin())) {
DEBUG(dbgs() << "PHI Nodes in loop nest exit is not handled for now "
"since on failure all loops branch to loop nest exit.\n");
return false;
}
unsigned SelecLoopId = selectLoopForInterchange(LoopList);
// Move the selected loop outwards to the best possible position.
for (unsigned i = SelecLoopId; i > 0; i--) {
bool Interchanged =
processLoop(LoopList, i, i - 1, LoopNestExit, DependencyMatrix);
if (!Interchanged)
return Changed;
// Loops interchanged reflect the same in LoopList
std::swap(LoopList[i - 1], LoopList[i]);
// Update the DependencyMatrix
interChangeDependencies(DependencyMatrix, i, i - 1);
DT->recalculate(F);
#ifdef DUMP_DEP_MATRICIES
DEBUG(dbgs() << "Dependence after interchange\n");
printDepMatrix(DependencyMatrix);
#endif
Changed |= Interchanged;
}
return Changed;
}
bool processLoop(LoopVector LoopList, unsigned InnerLoopId,
unsigned OuterLoopId, BasicBlock *LoopNestExit,
std::vector<std::vector<char>> &DependencyMatrix) {
DEBUG(dbgs() << "Processing Inner Loop Id = " << InnerLoopId
<< " and OuterLoopId = " << OuterLoopId << "\n");
Loop *InnerLoop = LoopList[InnerLoopId];
Loop *OuterLoop = LoopList[OuterLoopId];
LoopInterchangeLegality LIL(OuterLoop, InnerLoop, SE, LI, DT,
PreserveLCSSA, ORE);
if (!LIL.canInterchangeLoops(InnerLoopId, OuterLoopId, DependencyMatrix)) {
DEBUG(dbgs() << "Not interchanging Loops. Cannot prove legality\n");
return false;
}
DEBUG(dbgs() << "Loops are legal to interchange\n");
LoopInterchangeProfitability LIP(OuterLoop, InnerLoop, SE, ORE);
if (!LIP.isProfitable(InnerLoopId, OuterLoopId, DependencyMatrix)) {
DEBUG(dbgs() << "Interchanging loops not profitable\n");
return false;
}
ORE->emit(OptimizationRemark(DEBUG_TYPE, "Interchanged",
InnerLoop->getStartLoc(),
InnerLoop->getHeader())
<< "Loop interchanged with enclosing loop.");
LoopInterchangeTransform LIT(OuterLoop, InnerLoop, SE, LI, DT,
LoopNestExit, LIL.hasInnerLoopReduction());
LIT.transform();
DEBUG(dbgs() << "Loops interchanged\n");
return true;
}
};
} // end of namespace
bool LoopInterchangeLegality::areAllUsesReductions(Instruction *Ins, Loop *L) {
return none_of(Ins->users(), [=](User *U) -> bool {
auto *UserIns = dyn_cast<PHINode>(U);
RecurrenceDescriptor RD;
return !UserIns || !RecurrenceDescriptor::isReductionPHI(UserIns, L, RD);
});
}
bool LoopInterchangeLegality::containsUnsafeInstructionsInHeader(
BasicBlock *BB) {
for (auto I = BB->begin(), E = BB->end(); I != E; ++I) {
// Load corresponding to reduction PHI's are safe while concluding if
// tightly nested.
if (LoadInst *L = dyn_cast<LoadInst>(I)) {
if (!areAllUsesReductions(L, InnerLoop))
return true;
} else if (I->mayHaveSideEffects() || I->mayReadFromMemory())
return true;
}
return false;
}
bool LoopInterchangeLegality::containsUnsafeInstructionsInLatch(
BasicBlock *BB) {
for (auto I = BB->begin(), E = BB->end(); I != E; ++I) {
// Stores corresponding to reductions are safe while concluding if tightly
// nested.
if (StoreInst *L = dyn_cast<StoreInst>(I)) {
if (!isa<PHINode>(L->getOperand(0)))
return true;
} else if (I->mayHaveSideEffects() || I->mayReadFromMemory())
return true;
}
return false;
}
bool LoopInterchangeLegality::tightlyNested(Loop *OuterLoop, Loop *InnerLoop) {
BasicBlock *OuterLoopHeader = OuterLoop->getHeader();
BasicBlock *InnerLoopPreHeader = InnerLoop->getLoopPreheader();
BasicBlock *OuterLoopLatch = OuterLoop->getLoopLatch();
DEBUG(dbgs() << "Checking if loops are tightly nested\n");
// A perfectly nested loop will not have any branch in between the outer and
// inner block i.e. outer header will branch to either inner preheader and
// outerloop latch.
BranchInst *OuterLoopHeaderBI =
dyn_cast<BranchInst>(OuterLoopHeader->getTerminator());
if (!OuterLoopHeaderBI)
return false;
for (BasicBlock *Succ : OuterLoopHeaderBI->successors())
if (Succ != InnerLoopPreHeader && Succ != OuterLoopLatch)
return false;
DEBUG(dbgs() << "Checking instructions in Loop header and Loop latch\n");
// We do not have any basic block in between now make sure the outer header
// and outer loop latch doesn't contain any unsafe instructions.
if (containsUnsafeInstructionsInHeader(OuterLoopHeader) ||
containsUnsafeInstructionsInLatch(OuterLoopLatch))
return false;
DEBUG(dbgs() << "Loops are perfectly nested\n");
// We have a perfect loop nest.
return true;
}
bool LoopInterchangeLegality::isLoopStructureUnderstood(
PHINode *InnerInduction) {
unsigned Num = InnerInduction->getNumOperands();
BasicBlock *InnerLoopPreheader = InnerLoop->getLoopPreheader();
for (unsigned i = 0; i < Num; ++i) {
Value *Val = InnerInduction->getOperand(i);
if (isa<Constant>(Val))
continue;
Instruction *I = dyn_cast<Instruction>(Val);
if (!I)
return false;
// TODO: Handle triangular loops.
// e.g. for(int i=0;i<N;i++)
// for(int j=i;j<N;j++)
unsigned IncomBlockIndx = PHINode::getIncomingValueNumForOperand(i);
if (InnerInduction->getIncomingBlock(IncomBlockIndx) ==
InnerLoopPreheader &&
!OuterLoop->isLoopInvariant(I)) {
return false;
}
}
return true;
}
bool LoopInterchangeLegality::findInductionAndReductions(
Loop *L, SmallVector<PHINode *, 8> &Inductions,
SmallVector<PHINode *, 8> &Reductions) {
if (!L->getLoopLatch() || !L->getLoopPredecessor())
return false;
for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ++I) {
RecurrenceDescriptor RD;
InductionDescriptor ID;
PHINode *PHI = cast<PHINode>(I);
if (InductionDescriptor::isInductionPHI(PHI, L, SE, ID))
Inductions.push_back(PHI);
else if (RecurrenceDescriptor::isReductionPHI(PHI, L, RD))
Reductions.push_back(PHI);
else {
DEBUG(
dbgs() << "Failed to recognize PHI as an induction or reduction.\n");
return false;
}
}
return true;
}
static bool containsSafePHI(BasicBlock *Block, bool isOuterLoopExitBlock) {
for (auto I = Block->begin(); isa<PHINode>(I); ++I) {
PHINode *PHI = cast<PHINode>(I);
// Reduction lcssa phi will have only 1 incoming block that from loop latch.
if (PHI->getNumIncomingValues() > 1)
return false;
Instruction *Ins = dyn_cast<Instruction>(PHI->getIncomingValue(0));
if (!Ins)
return false;
// Incoming value for lcssa phi's in outer loop exit can only be inner loop
// exits lcssa phi else it would not be tightly nested.
if (!isa<PHINode>(Ins) && isOuterLoopExitBlock)
return false;
}
return true;
}
static BasicBlock *getLoopLatchExitBlock(BasicBlock *LatchBlock,
BasicBlock *LoopHeader) {
if (BranchInst *BI = dyn_cast<BranchInst>(LatchBlock->getTerminator())) {
assert(BI->getNumSuccessors() == 2 &&
"Branch leaving loop latch must have 2 successors");
for (BasicBlock *Succ : BI->successors()) {
if (Succ == LoopHeader)
continue;
return Succ;
}
}
return nullptr;
}
// This function indicates the current limitations in the transform as a result
// of which we do not proceed.
bool LoopInterchangeLegality::currentLimitations() {
BasicBlock *InnerLoopPreHeader = InnerLoop->getLoopPreheader();
BasicBlock *InnerLoopHeader = InnerLoop->getHeader();
BasicBlock *InnerLoopLatch = InnerLoop->getLoopLatch();
BasicBlock *OuterLoopLatch = OuterLoop->getLoopLatch();
BasicBlock *OuterLoopHeader = OuterLoop->getHeader();
PHINode *InnerInductionVar;
SmallVector<PHINode *, 8> Inductions;
SmallVector<PHINode *, 8> Reductions;
if (!findInductionAndReductions(InnerLoop, Inductions, Reductions)) {
DEBUG(dbgs() << "Only inner loops with induction or reduction PHI nodes "
<< "are supported currently.\n");
ORE->emit(OptimizationRemarkMissed(DEBUG_TYPE,
"UnsupportedPHIInner",
InnerLoop->getStartLoc(),
InnerLoop->getHeader())
<< "Only inner loops with induction or reduction PHI nodes can be"
" interchange currently.");
return true;
}
// TODO: Currently we handle only loops with 1 induction variable.
if (Inductions.size() != 1) {
DEBUG(dbgs() << "We currently only support loops with 1 induction variable."
<< "Failed to interchange due to current limitation\n");
ORE->emit(OptimizationRemarkMissed(DEBUG_TYPE,
"MultiInductionInner",
InnerLoop->getStartLoc(),
InnerLoop->getHeader())
<< "Only inner loops with 1 induction variable can be "
"interchanged currently.");
return true;
}
if (Reductions.size() > 0)
InnerLoopHasReduction = true;
InnerInductionVar = Inductions.pop_back_val();
Reductions.clear();
if (!findInductionAndReductions(OuterLoop, Inductions, Reductions)) {
DEBUG(dbgs() << "Only outer loops with induction or reduction PHI nodes "
<< "are supported currently.\n");
ORE->emit(OptimizationRemarkMissed(DEBUG_TYPE,
"UnsupportedPHIOuter",
OuterLoop->getStartLoc(),
OuterLoop->getHeader())
<< "Only outer loops with induction or reduction PHI nodes can be"
" interchanged currently.");
return true;
}
// Outer loop cannot have reduction because then loops will not be tightly
// nested.
if (!Reductions.empty()) {
DEBUG(dbgs() << "Outer loops with reductions are not supported "
<< "currently.\n");
ORE->emit(OptimizationRemarkMissed(DEBUG_TYPE,
"ReductionsOuter",
OuterLoop->getStartLoc(),
OuterLoop->getHeader())
<< "Outer loops with reductions cannot be interchangeed "
"currently.");
return true;
}
// TODO: Currently we handle only loops with 1 induction variable.
if (Inductions.size() != 1) {
DEBUG(dbgs() << "Loops with more than 1 induction variables are not "
<< "supported currently.\n");
ORE->emit(OptimizationRemarkMissed(DEBUG_TYPE,
"MultiIndutionOuter",
OuterLoop->getStartLoc(),
OuterLoop->getHeader())
<< "Only outer loops with 1 induction variable can be "
"interchanged currently.");
return true;
}
// TODO: Triangular loops are not handled for now.
if (!isLoopStructureUnderstood(InnerInductionVar)) {
DEBUG(dbgs() << "Loop structure not understood by pass\n");
ORE->emit(OptimizationRemarkMissed(DEBUG_TYPE,
"UnsupportedStructureInner",
InnerLoop->getStartLoc(),
InnerLoop->getHeader())
<< "Inner loop structure not understood currently.");
return true;
}
// TODO: We only handle LCSSA PHI's corresponding to reduction for now.
BasicBlock *LoopExitBlock =
getLoopLatchExitBlock(OuterLoopLatch, OuterLoopHeader);
if (!LoopExitBlock || !containsSafePHI(LoopExitBlock, true)) {
DEBUG(dbgs() << "Can only handle LCSSA PHIs in outer loops currently.\n");
ORE->emit(OptimizationRemarkMissed(DEBUG_TYPE,
"NoLCSSAPHIOuter",
OuterLoop->getStartLoc(),
OuterLoop->getHeader())
<< "Only outer loops with LCSSA PHIs can be interchange "
"currently.");
return true;
}
LoopExitBlock = getLoopLatchExitBlock(InnerLoopLatch, InnerLoopHeader);
if (!LoopExitBlock || !containsSafePHI(LoopExitBlock, false)) {
DEBUG(dbgs() << "Can only handle LCSSA PHIs in inner loops currently.\n");
ORE->emit(OptimizationRemarkMissed(DEBUG_TYPE,
"NoLCSSAPHIOuterInner",
InnerLoop->getStartLoc(),
InnerLoop->getHeader())
<< "Only inner loops with LCSSA PHIs can be interchange "
"currently.");
return true;
}
// TODO: Current limitation: Since we split the inner loop latch at the point
// were induction variable is incremented (induction.next); We cannot have
// more than 1 user of induction.next since it would result in broken code
// after split.
// e.g.
// for(i=0;i<N;i++) {
// for(j = 0;j<M;j++) {
// A[j+1][i+2] = A[j][i]+k;
// }
// }
Instruction *InnerIndexVarInc = nullptr;
if (InnerInductionVar->getIncomingBlock(0) == InnerLoopPreHeader)
InnerIndexVarInc =
dyn_cast<Instruction>(InnerInductionVar->getIncomingValue(1));
else
InnerIndexVarInc =
dyn_cast<Instruction>(InnerInductionVar->getIncomingValue(0));
if (!InnerIndexVarInc) {
DEBUG(dbgs() << "Did not find an instruction to increment the induction "
<< "variable.\n");
ORE->emit(OptimizationRemarkMissed(DEBUG_TYPE,
"NoIncrementInInner",
InnerLoop->getStartLoc(),
InnerLoop->getHeader())
<< "The inner loop does not increment the induction variable.");
return true;
}
// Since we split the inner loop latch on this induction variable. Make sure
// we do not have any instruction between the induction variable and branch
// instruction.
bool FoundInduction = false;
for (const Instruction &I : reverse(*InnerLoopLatch)) {
if (isa<BranchInst>(I) || isa<CmpInst>(I) || isa<TruncInst>(I))
continue;
// We found an instruction. If this is not induction variable then it is not
// safe to split this loop latch.
if (!I.isIdenticalTo(InnerIndexVarInc)) {
DEBUG(dbgs() << "Found unsupported instructions between induction "
<< "variable increment and branch.\n");
ORE->emit(OptimizationRemarkMissed(DEBUG_TYPE,
"UnsupportedInsBetweenInduction",
InnerLoop->getStartLoc(),
InnerLoop->getHeader())
<< "Found unsupported instruction between induction variable "
"increment and branch.");
return true;
}
FoundInduction = true;
break;
}
// The loop latch ended and we didn't find the induction variable return as
// current limitation.
if (!FoundInduction) {
DEBUG(dbgs() << "Did not find the induction variable.\n");
ORE->emit(OptimizationRemarkMissed(DEBUG_TYPE,
"NoIndutionVariable",
InnerLoop->getStartLoc(),
InnerLoop->getHeader())
<< "Did not find the induction variable.");
return true;
}
return false;
}
bool LoopInterchangeLegality::canInterchangeLoops(unsigned InnerLoopId,
unsigned OuterLoopId,
CharMatrix &DepMatrix) {
if (!isLegalToInterChangeLoops(DepMatrix, InnerLoopId, OuterLoopId)) {
DEBUG(dbgs() << "Failed interchange InnerLoopId = " << InnerLoopId
<< " and OuterLoopId = " << OuterLoopId
<< " due to dependence\n");
ORE->emit(OptimizationRemarkMissed(DEBUG_TYPE,
"Dependence",
InnerLoop->getStartLoc(),
InnerLoop->getHeader())
<< "Cannot interchange loops due to dependences.");
return false;
}
// Check if outer and inner loop contain legal instructions only.
for (auto *BB : OuterLoop->blocks())
for (Instruction &I : *BB)
if (CallInst *CI = dyn_cast<CallInst>(&I)) {
// readnone functions do not prevent interchanging.
if (CI->doesNotReadMemory())
continue;
DEBUG(dbgs() << "Loops with call instructions cannot be interchanged "
<< "safely.");
return false;
}
// Create unique Preheaders if we already do not have one.
BasicBlock *OuterLoopPreHeader = OuterLoop->getLoopPreheader();
BasicBlock *InnerLoopPreHeader = InnerLoop->getLoopPreheader();
// Create a unique outer preheader -
// 1) If OuterLoop preheader is not present.
// 2) If OuterLoop Preheader is same as OuterLoop Header
// 3) If OuterLoop Preheader is same as Header of the previous loop.
// 4) If OuterLoop Preheader is Entry node.
if (!OuterLoopPreHeader || OuterLoopPreHeader == OuterLoop->getHeader() ||
isa<PHINode>(OuterLoopPreHeader->begin()) ||
!OuterLoopPreHeader->getUniquePredecessor()) {
OuterLoopPreHeader =
InsertPreheaderForLoop(OuterLoop, DT, LI, PreserveLCSSA);
}
if (!InnerLoopPreHeader || InnerLoopPreHeader == InnerLoop->getHeader() ||
InnerLoopPreHeader == OuterLoop->getHeader()) {
InnerLoopPreHeader =
InsertPreheaderForLoop(InnerLoop, DT, LI, PreserveLCSSA);
}
// TODO: The loops could not be interchanged due to current limitations in the
// transform module.
if (currentLimitations()) {
DEBUG(dbgs() << "Not legal because of current transform limitation\n");
return false;
}
// Check if the loops are tightly nested.
if (!tightlyNested(OuterLoop, InnerLoop)) {
DEBUG(dbgs() << "Loops not tightly nested\n");
ORE->emit(OptimizationRemarkMissed(DEBUG_TYPE,
"NotTightlyNested",
InnerLoop->getStartLoc(),
InnerLoop->getHeader())
<< "Cannot interchange loops because they are not tightly "
"nested.");
return false;
}
return true;
}
int LoopInterchangeProfitability::getInstrOrderCost() {
unsigned GoodOrder, BadOrder;
BadOrder = GoodOrder = 0;
for (BasicBlock *BB : InnerLoop->blocks()) {
for (Instruction &Ins : *BB) {
if (const GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(&Ins)) {
unsigned NumOp = GEP->getNumOperands();
bool FoundInnerInduction = false;
bool FoundOuterInduction = false;
for (unsigned i = 0; i < NumOp; ++i) {
const SCEV *OperandVal = SE->getSCEV(GEP->getOperand(i));
const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(OperandVal);
if (!AR)
continue;
// If we find the inner induction after an outer induction e.g.
// for(int i=0;i<N;i++)
// for(int j=0;j<N;j++)
// A[i][j] = A[i-1][j-1]+k;
// then it is a good order.
if (AR->getLoop() == InnerLoop) {
// We found an InnerLoop induction after OuterLoop induction. It is
// a good order.
FoundInnerInduction = true;
if (FoundOuterInduction) {
GoodOrder++;
break;
}
}
// If we find the outer induction after an inner induction e.g.
// for(int i=0;i<N;i++)
// for(int j=0;j<N;j++)
// A[j][i] = A[j-1][i-1]+k;
// then it is a bad order.
if (AR->getLoop() == OuterLoop) {
// We found an OuterLoop induction after InnerLoop induction. It is
// a bad order.
FoundOuterInduction = true;
if (FoundInnerInduction) {
BadOrder++;
break;
}
}
}
}
}
}
return GoodOrder - BadOrder;
}
static bool isProfitableForVectorization(unsigned InnerLoopId,
unsigned OuterLoopId,
CharMatrix &DepMatrix) {
// TODO: Improve this heuristic to catch more cases.
// If the inner loop is loop independent or doesn't carry any dependency it is
// profitable to move this to outer position.
for (auto &Row : DepMatrix) {
if (Row[InnerLoopId] != 'S' && Row[InnerLoopId] != 'I')
return false;
// TODO: We need to improve this heuristic.
if (Row[OuterLoopId] != '=')
return false;
}
// If outer loop has dependence and inner loop is loop independent then it is
// profitable to interchange to enable parallelism.
return true;
}
bool LoopInterchangeProfitability::isProfitable(unsigned InnerLoopId,
unsigned OuterLoopId,
CharMatrix &DepMatrix) {
// TODO: Add better profitability checks.
// e.g
// 1) Construct dependency matrix and move the one with no loop carried dep
// inside to enable vectorization.
// This is rough cost estimation algorithm. It counts the good and bad order
// of induction variables in the instruction and allows reordering if number
// of bad orders is more than good.
int Cost = getInstrOrderCost();
DEBUG(dbgs() << "Cost = " << Cost << "\n");
if (Cost < -LoopInterchangeCostThreshold)
return true;
// It is not profitable as per current cache profitability model. But check if
// we can move this loop outside to improve parallelism.
if (isProfitableForVectorization(InnerLoopId, OuterLoopId, DepMatrix))
return true;
ORE->emit(OptimizationRemarkMissed(DEBUG_TYPE,
"InterchangeNotProfitable",
InnerLoop->getStartLoc(),
InnerLoop->getHeader())
<< "Interchanging loops is too costly (cost="
<< ore::NV("Cost", Cost) << ", threshold="
<< ore::NV("Threshold", LoopInterchangeCostThreshold) <<
") and it does not improve parallelism.");
return false;
}
void LoopInterchangeTransform::removeChildLoop(Loop *OuterLoop,
Loop *InnerLoop) {
for (Loop::iterator I = OuterLoop->begin(), E = OuterLoop->end(); I != E;
++I) {
if (*I == InnerLoop) {
OuterLoop->removeChildLoop(I);
return;
}
}
llvm_unreachable("Couldn't find loop");
}
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);
}
bool LoopInterchangeTransform::transform() {
bool Transformed = false;
Instruction *InnerIndexVar;
if (InnerLoop->getSubLoops().size() == 0) {
BasicBlock *InnerLoopPreHeader = InnerLoop->getLoopPreheader();
DEBUG(dbgs() << "Calling Split Inner Loop\n");
PHINode *InductionPHI = getInductionVariable(InnerLoop, SE);
if (!InductionPHI) {
DEBUG(dbgs() << "Failed to find the point to split loop latch \n");
return false;
}
if (InductionPHI->getIncomingBlock(0) == InnerLoopPreHeader)
InnerIndexVar = dyn_cast<Instruction>(InductionPHI->getIncomingValue(1));
else
InnerIndexVar = dyn_cast<Instruction>(InductionPHI->getIncomingValue(0));
//
// Split at the place were the induction variable is
// incremented/decremented.
// TODO: This splitting logic may not work always. Fix this.
splitInnerLoopLatch(InnerIndexVar);
DEBUG(dbgs() << "splitInnerLoopLatch done\n");
// Splits the inner loops phi nodes out into a separate basic block.
splitInnerLoopHeader();
DEBUG(dbgs() << "splitInnerLoopHeader done\n");
}
Transformed |= adjustLoopLinks();
if (!Transformed) {
DEBUG(dbgs() << "adjustLoopLinks failed\n");
return false;
}
restructureLoops(InnerLoop, OuterLoop);
return true;
}
void LoopInterchangeTransform::splitInnerLoopLatch(Instruction *Inc) {
BasicBlock *InnerLoopLatch = InnerLoop->getLoopLatch();
BasicBlock *InnerLoopLatchPred = InnerLoopLatch;
InnerLoopLatch = SplitBlock(InnerLoopLatchPred, Inc, DT, LI);
}
void LoopInterchangeTransform::splitInnerLoopHeader() {
// Split the inner loop header out. Here make sure that the reduction PHI's
// stay in the innerloop body.
BasicBlock *InnerLoopHeader = InnerLoop->getHeader();
BasicBlock *InnerLoopPreHeader = InnerLoop->getLoopPreheader();
if (InnerLoopHasReduction) {
// FIXME: Check if the induction PHI will always be the first PHI.
BasicBlock *New = InnerLoopHeader->splitBasicBlock(
++(InnerLoopHeader->begin()), InnerLoopHeader->getName() + ".split");
if (LI)
if (Loop *L = LI->getLoopFor(InnerLoopHeader))
L->addBasicBlockToLoop(New, *LI);
// Adjust Reduction PHI's in the block.
SmallVector<PHINode *, 8> PHIVec;
for (auto I = New->begin(); isa<PHINode>(I); ++I) {
PHINode *PHI = dyn_cast<PHINode>(I);
Value *V = PHI->getIncomingValueForBlock(InnerLoopPreHeader);
PHI->replaceAllUsesWith(V);
PHIVec.push_back((PHI));
}
for (PHINode *P : PHIVec) {
P->eraseFromParent();
}
} else {
SplitBlock(InnerLoopHeader, InnerLoopHeader->getFirstNonPHI(), DT, LI);
}
DEBUG(dbgs() << "Output of splitInnerLoopHeader InnerLoopHeaderSucc & "
"InnerLoopHeader\n");
}
/// \brief Move all instructions except the terminator from FromBB right before
/// InsertBefore
static void moveBBContents(BasicBlock *FromBB, Instruction *InsertBefore) {
auto &ToList = InsertBefore->getParent()->getInstList();
auto &FromList = FromBB->getInstList();
ToList.splice(InsertBefore->getIterator(), FromList, FromList.begin(),
FromBB->getTerminator()->getIterator());
}
void LoopInterchangeTransform::updateIncomingBlock(BasicBlock *CurrBlock,
BasicBlock *OldPred,
BasicBlock *NewPred) {
for (auto I = CurrBlock->begin(); isa<PHINode>(I); ++I) {
PHINode *PHI = cast<PHINode>(I);
unsigned Num = PHI->getNumIncomingValues();
for (unsigned i = 0; i < Num; ++i) {
if (PHI->getIncomingBlock(i) == OldPred)
PHI->setIncomingBlock(i, NewPred);
}
}
}
bool LoopInterchangeTransform::adjustLoopBranches() {
DEBUG(dbgs() << "adjustLoopBranches called\n");
// Adjust the loop preheader
BasicBlock *InnerLoopHeader = InnerLoop->getHeader();
BasicBlock *OuterLoopHeader = OuterLoop->getHeader();
BasicBlock *InnerLoopLatch = InnerLoop->getLoopLatch();
BasicBlock *OuterLoopLatch = OuterLoop->getLoopLatch();
BasicBlock *OuterLoopPreHeader = OuterLoop->getLoopPreheader();
BasicBlock *InnerLoopPreHeader = InnerLoop->getLoopPreheader();
BasicBlock *OuterLoopPredecessor = OuterLoopPreHeader->getUniquePredecessor();
BasicBlock *InnerLoopLatchPredecessor =
InnerLoopLatch->getUniquePredecessor();
BasicBlock *InnerLoopLatchSuccessor;
BasicBlock *OuterLoopLatchSuccessor;
BranchInst *OuterLoopLatchBI =
dyn_cast<BranchInst>(OuterLoopLatch->getTerminator());
BranchInst *InnerLoopLatchBI =
dyn_cast<BranchInst>(InnerLoopLatch->getTerminator());
BranchInst *OuterLoopHeaderBI =
dyn_cast<BranchInst>(OuterLoopHeader->getTerminator());
BranchInst *InnerLoopHeaderBI =
dyn_cast<BranchInst>(InnerLoopHeader->getTerminator());
if (!OuterLoopPredecessor || !InnerLoopLatchPredecessor ||
!OuterLoopLatchBI || !InnerLoopLatchBI || !OuterLoopHeaderBI ||
!InnerLoopHeaderBI)
return false;
BranchInst *InnerLoopLatchPredecessorBI =
dyn_cast<BranchInst>(InnerLoopLatchPredecessor->getTerminator());
BranchInst *OuterLoopPredecessorBI =
dyn_cast<BranchInst>(OuterLoopPredecessor->getTerminator());
if (!OuterLoopPredecessorBI || !InnerLoopLatchPredecessorBI)
return false;
BasicBlock *InnerLoopHeaderSuccessor = InnerLoopHeader->getUniqueSuccessor();
if (!InnerLoopHeaderSuccessor)
return false;
// Adjust Loop Preheader and headers
unsigned NumSucc = OuterLoopPredecessorBI->getNumSuccessors();
for (unsigned i = 0; i < NumSucc; ++i) {
if (OuterLoopPredecessorBI->getSuccessor(i) == OuterLoopPreHeader)
OuterLoopPredecessorBI->setSuccessor(i, InnerLoopPreHeader);
}
NumSucc = OuterLoopHeaderBI->getNumSuccessors();
for (unsigned i = 0; i < NumSucc; ++i) {
if (OuterLoopHeaderBI->getSuccessor(i) == OuterLoopLatch)
OuterLoopHeaderBI->setSuccessor(i, LoopExit);
else if (OuterLoopHeaderBI->getSuccessor(i) == InnerLoopPreHeader)
OuterLoopHeaderBI->setSuccessor(i, InnerLoopHeaderSuccessor);
}
// Adjust reduction PHI's now that the incoming block has changed.
updateIncomingBlock(InnerLoopHeaderSuccessor, InnerLoopHeader,
OuterLoopHeader);
BranchInst::Create(OuterLoopPreHeader, InnerLoopHeaderBI);
InnerLoopHeaderBI->eraseFromParent();
// -------------Adjust loop latches-----------
if (InnerLoopLatchBI->getSuccessor(0) == InnerLoopHeader)
InnerLoopLatchSuccessor = InnerLoopLatchBI->getSuccessor(1);
else
InnerLoopLatchSuccessor = InnerLoopLatchBI->getSuccessor(0);
NumSucc = InnerLoopLatchPredecessorBI->getNumSuccessors();
for (unsigned i = 0; i < NumSucc; ++i) {
if (InnerLoopLatchPredecessorBI->getSuccessor(i) == InnerLoopLatch)
InnerLoopLatchPredecessorBI->setSuccessor(i, InnerLoopLatchSuccessor);
}
// Adjust PHI nodes in InnerLoopLatchSuccessor. Update all uses of PHI with
// the value and remove this PHI node from inner loop.
SmallVector<PHINode *, 8> LcssaVec;
for (auto I = InnerLoopLatchSuccessor->begin(); isa<PHINode>(I); ++I) {
PHINode *LcssaPhi = cast<PHINode>(I);
LcssaVec.push_back(LcssaPhi);
}
for (PHINode *P : LcssaVec) {
Value *Incoming = P->getIncomingValueForBlock(InnerLoopLatch);
P->replaceAllUsesWith(Incoming);
P->eraseFromParent();
}
if (OuterLoopLatchBI->getSuccessor(0) == OuterLoopHeader)
OuterLoopLatchSuccessor = OuterLoopLatchBI->getSuccessor(1);
else
OuterLoopLatchSuccessor = OuterLoopLatchBI->getSuccessor(0);
if (InnerLoopLatchBI->getSuccessor(1) == InnerLoopLatchSuccessor)
InnerLoopLatchBI->setSuccessor(1, OuterLoopLatchSuccessor);
else
InnerLoopLatchBI->setSuccessor(0, OuterLoopLatchSuccessor);
updateIncomingBlock(OuterLoopLatchSuccessor, OuterLoopLatch, InnerLoopLatch);
if (OuterLoopLatchBI->getSuccessor(0) == OuterLoopLatchSuccessor) {
OuterLoopLatchBI->setSuccessor(0, InnerLoopLatch);
} else {
OuterLoopLatchBI->setSuccessor(1, InnerLoopLatch);
}
return true;
}
void LoopInterchangeTransform::adjustLoopPreheaders() {
// We have interchanged the preheaders so we need to interchange the data in
// the preheader as well.
// This is because the content of inner preheader was previously executed
// inside the outer loop.
BasicBlock *OuterLoopPreHeader = OuterLoop->getLoopPreheader();
BasicBlock *InnerLoopPreHeader = InnerLoop->getLoopPreheader();
BasicBlock *OuterLoopHeader = OuterLoop->getHeader();
BranchInst *InnerTermBI =
cast<BranchInst>(InnerLoopPreHeader->getTerminator());
// These instructions should now be executed inside the loop.
// Move instruction into a new block after outer header.
moveBBContents(InnerLoopPreHeader, OuterLoopHeader->getTerminator());
// These instructions were not executed previously in the loop so move them to
// the older inner loop preheader.
moveBBContents(OuterLoopPreHeader, InnerTermBI);
}
bool LoopInterchangeTransform::adjustLoopLinks() {
// Adjust all branches in the inner and outer loop.
bool Changed = adjustLoopBranches();
if (Changed)
adjustLoopPreheaders();
return Changed;
}
char LoopInterchange::ID = 0;
INITIALIZE_PASS_BEGIN(LoopInterchange, "loop-interchange",
"Interchanges loops for cache reuse", false, false)
INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass)
INITIALIZE_PASS_DEPENDENCY(DependenceAnalysisWrapperPass)
INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
INITIALIZE_PASS_DEPENDENCY(ScalarEvolutionWrapperPass)
INITIALIZE_PASS_DEPENDENCY(LoopSimplify)
INITIALIZE_PASS_DEPENDENCY(LCSSAWrapperPass)
INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
INITIALIZE_PASS_DEPENDENCY(OptimizationRemarkEmitterWrapperPass)
INITIALIZE_PASS_END(LoopInterchange, "loop-interchange",
"Interchanges loops for cache reuse", false, false)
Pass *llvm::createLoopInterchangePass() { return new LoopInterchange(); }
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