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llvm-6502/lib/Transforms/Scalar/LoopRerollPass.cpp
Chandler Carruth 36b699f2b1 [C++11] Add range based accessors for the Use-Def chain of a Value. 
This requires a number of steps.
1) Move value_use_iterator into the Value class as an implementation
   detail
2) Change it to actually be a *Use* iterator rather than a *User*
   iterator.
3) Add an adaptor which is a User iterator that always looks through the
   Use to the User.
4) Wrap these in Value::use_iterator and Value::user_iterator typedefs.
5) Add the range adaptors as Value::uses() and Value::users().
6) Update *all* of the callers to correctly distinguish between whether
   they wanted a use_iterator (and to explicitly dig out the User when
   needed), or a user_iterator which makes the Use itself totally
   opaque.

Because #6 requires churning essentially everything that walked the
Use-Def chains, I went ahead and added all of the range adaptors and
switched them to range-based loops where appropriate. Also because the
renaming requires at least churning every line of code, it didn't make
any sense to split these up into multiple commits -- all of which would
touch all of the same lies of code.

The result is still not quite optimal. The Value::use_iterator is a nice
regular iterator, but Value::user_iterator is an iterator over User*s
rather than over the User objects themselves. As a consequence, it fits
a bit awkwardly into the range-based world and it has the weird
extra-dereferencing 'operator->' that so many of our iterators have.
I think this could be fixed by providing something which transforms
a range of T&s into a range of T*s, but that *can* be separated into
another patch, and it isn't yet 100% clear whether this is the right
move.

However, this change gets us most of the benefit and cleans up
a substantial amount of code around Use and User. =]

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@203364 91177308-0d34-0410-b5e6-96231b3b80d8
2014-03-09 03:16:01 +00:00

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//===-- LoopReroll.cpp - Loop rerolling pass ------------------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This pass implements a simple loop reroller.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "loop-reroll"
#include "llvm/Transforms/Scalar.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/AliasSetTracker.h"
#include "llvm/Analysis/LoopPass.h"
#include "llvm/Analysis/ScalarEvolution.h"
#include "llvm/Analysis/ScalarEvolutionExpander.h"
#include "llvm/Analysis/ScalarEvolutionExpressions.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Target/TargetLibraryInfo.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/Transforms/Utils/LoopUtils.h"
using namespace llvm;
STATISTIC(NumRerolledLoops, "Number of rerolled loops");
static cl::opt<unsigned>
MaxInc("max-reroll-increment", cl::init(2048), cl::Hidden,
cl::desc("The maximum increment for loop rerolling"));
// This loop re-rolling transformation aims to transform loops like this:
//
// int foo(int a);
// void bar(int *x) {
// for (int i = 0; i < 500; i += 3) {
// foo(i);
// foo(i+1);
// foo(i+2);
// }
// }
//
// into a loop like this:
//
// void bar(int *x) {
// for (int i = 0; i < 500; ++i)
// foo(i);
// }
//
// It does this by looking for loops that, besides the latch code, are composed
// of isomorphic DAGs of instructions, with each DAG rooted at some increment
// to the induction variable, and where each DAG is isomorphic to the DAG
// rooted at the induction variable (excepting the sub-DAGs which root the
// other induction-variable increments). In other words, we're looking for loop
// bodies of the form:
//
// %iv = phi [ (preheader, ...), (body, %iv.next) ]
// f(%iv)
// %iv.1 = add %iv, 1 <-- a root increment
// f(%iv.1)
// %iv.2 = add %iv, 2 <-- a root increment
// f(%iv.2)
// %iv.scale_m_1 = add %iv, scale-1 <-- a root increment
// f(%iv.scale_m_1)
// ...
// %iv.next = add %iv, scale
// %cmp = icmp(%iv, ...)
// br %cmp, header, exit
//
// where each f(i) is a set of instructions that, collectively, are a function
// only of i (and other loop-invariant values).
//
// As a special case, we can also reroll loops like this:
//
// int foo(int);
// void bar(int *x) {
// for (int i = 0; i < 500; ++i) {
// x[3*i] = foo(0);
// x[3*i+1] = foo(0);
// x[3*i+2] = foo(0);
// }
// }
//
// into this:
//
// void bar(int *x) {
// for (int i = 0; i < 1500; ++i)
// x[i] = foo(0);
// }
//
// in which case, we're looking for inputs like this:
//
// %iv = phi [ (preheader, ...), (body, %iv.next) ]
// %scaled.iv = mul %iv, scale
// f(%scaled.iv)
// %scaled.iv.1 = add %scaled.iv, 1
// f(%scaled.iv.1)
// %scaled.iv.2 = add %scaled.iv, 2
// f(%scaled.iv.2)
// %scaled.iv.scale_m_1 = add %scaled.iv, scale-1
// f(%scaled.iv.scale_m_1)
// ...
// %iv.next = add %iv, 1
// %cmp = icmp(%iv, ...)
// br %cmp, header, exit
namespace {
class LoopReroll : public LoopPass {
public:
static char ID; // Pass ID, replacement for typeid
LoopReroll() : LoopPass(ID) {
initializeLoopRerollPass(*PassRegistry::getPassRegistry());
}
bool runOnLoop(Loop *L, LPPassManager &LPM) override;
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.addRequired<AliasAnalysis>();
AU.addRequired<LoopInfo>();
AU.addPreserved<LoopInfo>();
AU.addRequired<DominatorTreeWrapperPass>();
AU.addPreserved<DominatorTreeWrapperPass>();
AU.addRequired<ScalarEvolution>();
AU.addRequired<TargetLibraryInfo>();
}
protected:
AliasAnalysis *AA;
LoopInfo *LI;
ScalarEvolution *SE;
const DataLayout *DL;
TargetLibraryInfo *TLI;
DominatorTree *DT;
typedef SmallVector<Instruction *, 16> SmallInstructionVector;
typedef SmallSet<Instruction *, 16> SmallInstructionSet;
// A chain of isomorphic instructions, indentified by a single-use PHI,
// representing a reduction. Only the last value may be used outside the
// loop.
struct SimpleLoopReduction {
SimpleLoopReduction(Instruction *P, Loop *L)
: Valid(false), Instructions(1, P) {
assert(isa<PHINode>(P) && "First reduction instruction must be a PHI");
add(L);
}
bool valid() const {
return Valid;
}
Instruction *getPHI() const {
assert(Valid && "Using invalid reduction");
return Instructions.front();
}
Instruction *getReducedValue() const {
assert(Valid && "Using invalid reduction");
return Instructions.back();
}
Instruction *get(size_t i) const {
assert(Valid && "Using invalid reduction");
return Instructions[i+1];
}
Instruction *operator [] (size_t i) const { return get(i); }
// The size, ignoring the initial PHI.
size_t size() const {
assert(Valid && "Using invalid reduction");
return Instructions.size()-1;
}
typedef SmallInstructionVector::iterator iterator;
typedef SmallInstructionVector::const_iterator const_iterator;
iterator begin() {
assert(Valid && "Using invalid reduction");
return std::next(Instructions.begin());
}
const_iterator begin() const {
assert(Valid && "Using invalid reduction");
return std::next(Instructions.begin());
}
iterator end() { return Instructions.end(); }
const_iterator end() const { return Instructions.end(); }
protected:
bool Valid;
SmallInstructionVector Instructions;
void add(Loop *L);
};
// The set of all reductions, and state tracking of possible reductions
// during loop instruction processing.
struct ReductionTracker {
typedef SmallVector<SimpleLoopReduction, 16> SmallReductionVector;
// Add a new possible reduction.
void addSLR(SimpleLoopReduction &SLR) {
PossibleReds.push_back(SLR);
}
// Setup to track possible reductions corresponding to the provided
// rerolling scale. Only reductions with a number of non-PHI instructions
// that is divisible by the scale are considered. Three instructions sets
// are filled in:
// - A set of all possible instructions in eligible reductions.
// - A set of all PHIs in eligible reductions
// - A set of all reduced values (last instructions) in eligible reductions.
void restrictToScale(uint64_t Scale,
SmallInstructionSet &PossibleRedSet,
SmallInstructionSet &PossibleRedPHISet,
SmallInstructionSet &PossibleRedLastSet) {
PossibleRedIdx.clear();
PossibleRedIter.clear();
Reds.clear();
for (unsigned i = 0, e = PossibleReds.size(); i != e; ++i)
if (PossibleReds[i].size() % Scale == 0) {
PossibleRedLastSet.insert(PossibleReds[i].getReducedValue());
PossibleRedPHISet.insert(PossibleReds[i].getPHI());
PossibleRedSet.insert(PossibleReds[i].getPHI());
PossibleRedIdx[PossibleReds[i].getPHI()] = i;
for (SimpleLoopReduction::iterator J = PossibleReds[i].begin(),
JE = PossibleReds[i].end(); J != JE; ++J) {
PossibleRedSet.insert(*J);
PossibleRedIdx[*J] = i;
}
}
}
// The functions below are used while processing the loop instructions.
// Are the two instructions both from reductions, and furthermore, from
// the same reduction?
bool isPairInSame(Instruction *J1, Instruction *J2) {
DenseMap<Instruction *, int>::iterator J1I = PossibleRedIdx.find(J1);
if (J1I != PossibleRedIdx.end()) {
DenseMap<Instruction *, int>::iterator J2I = PossibleRedIdx.find(J2);
if (J2I != PossibleRedIdx.end() && J1I->second == J2I->second)
return true;
}
return false;
}
// The two provided instructions, the first from the base iteration, and
// the second from iteration i, form a matched pair. If these are part of
// a reduction, record that fact.
void recordPair(Instruction *J1, Instruction *J2, unsigned i) {
if (PossibleRedIdx.count(J1)) {
assert(PossibleRedIdx.count(J2) &&
"Recording reduction vs. non-reduction instruction?");
PossibleRedIter[J1] = 0;
PossibleRedIter[J2] = i;
int Idx = PossibleRedIdx[J1];
assert(Idx == PossibleRedIdx[J2] &&
"Recording pair from different reductions?");
Reds.insert(Idx);
}
}
// The functions below can be called after we've finished processing all
// instructions in the loop, and we know which reductions were selected.
// Is the provided instruction the PHI of a reduction selected for
// rerolling?
bool isSelectedPHI(Instruction *J) {
if (!isa<PHINode>(J))
return false;
for (DenseSet<int>::iterator RI = Reds.begin(), RIE = Reds.end();
RI != RIE; ++RI) {
int i = *RI;
if (cast<Instruction>(J) == PossibleReds[i].getPHI())
return true;
}
return false;
}
bool validateSelected();
void replaceSelected();
protected:
// The vector of all possible reductions (for any scale).
SmallReductionVector PossibleReds;
DenseMap<Instruction *, int> PossibleRedIdx;
DenseMap<Instruction *, int> PossibleRedIter;
DenseSet<int> Reds;
};
void collectPossibleIVs(Loop *L, SmallInstructionVector &PossibleIVs);
void collectPossibleReductions(Loop *L,
ReductionTracker &Reductions);
void collectInLoopUserSet(Loop *L,
const SmallInstructionVector &Roots,
const SmallInstructionSet &Exclude,
const SmallInstructionSet &Final,
DenseSet<Instruction *> &Users);
void collectInLoopUserSet(Loop *L,
Instruction * Root,
const SmallInstructionSet &Exclude,
const SmallInstructionSet &Final,
DenseSet<Instruction *> &Users);
bool findScaleFromMul(Instruction *RealIV, uint64_t &Scale,
Instruction *&IV,
SmallInstructionVector &LoopIncs);
bool collectAllRoots(Loop *L, uint64_t Inc, uint64_t Scale, Instruction *IV,
SmallVector<SmallInstructionVector, 32> &Roots,
SmallInstructionSet &AllRoots,
SmallInstructionVector &LoopIncs);
bool reroll(Instruction *IV, Loop *L, BasicBlock *Header, const SCEV *IterCount,
ReductionTracker &Reductions);
};
}
char LoopReroll::ID = 0;
INITIALIZE_PASS_BEGIN(LoopReroll, "loop-reroll", "Reroll loops", false, false)
INITIALIZE_AG_DEPENDENCY(AliasAnalysis)
INITIALIZE_PASS_DEPENDENCY(LoopInfo)
INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
INITIALIZE_PASS_DEPENDENCY(ScalarEvolution)
INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfo)
INITIALIZE_PASS_END(LoopReroll, "loop-reroll", "Reroll loops", false, false)
Pass *llvm::createLoopRerollPass() {
return new LoopReroll;
}
// Returns true if the provided instruction is used outside the given loop.
// This operates like Instruction::isUsedOutsideOfBlock, but considers PHIs in
// non-loop blocks to be outside the loop.
static bool hasUsesOutsideLoop(Instruction *I, Loop *L) {
for (User *U : I->users())
if (!L->contains(cast<Instruction>(U)))
return true;
return false;
}
// Collect the list of loop induction variables with respect to which it might
// be possible to reroll the loop.
void LoopReroll::collectPossibleIVs(Loop *L,
SmallInstructionVector &PossibleIVs) {
BasicBlock *Header = L->getHeader();
for (BasicBlock::iterator I = Header->begin(),
IE = Header->getFirstInsertionPt(); I != IE; ++I) {
if (!isa<PHINode>(I))
continue;
if (!I->getType()->isIntegerTy())
continue;
if (const SCEVAddRecExpr *PHISCEV =
dyn_cast<SCEVAddRecExpr>(SE->getSCEV(I))) {
if (PHISCEV->getLoop() != L)
continue;
if (!PHISCEV->isAffine())
continue;
if (const SCEVConstant *IncSCEV =
dyn_cast<SCEVConstant>(PHISCEV->getStepRecurrence(*SE))) {
if (!IncSCEV->getValue()->getValue().isStrictlyPositive())
continue;
if (IncSCEV->getValue()->uge(MaxInc))
continue;
DEBUG(dbgs() << "LRR: Possible IV: " << *I << " = " <<
*PHISCEV << "\n");
PossibleIVs.push_back(I);
}
}
}
}
// Add the remainder of the reduction-variable chain to the instruction vector
// (the initial PHINode has already been added). If successful, the object is
// marked as valid.
void LoopReroll::SimpleLoopReduction::add(Loop *L) {
assert(!Valid && "Cannot add to an already-valid chain");
// The reduction variable must be a chain of single-use instructions
// (including the PHI), except for the last value (which is used by the PHI
// and also outside the loop).
Instruction *C = Instructions.front();
do {
C = cast<Instruction>(*C->user_begin());
if (C->hasOneUse()) {
if (!C->isBinaryOp())
return;
if (!(isa<PHINode>(Instructions.back()) ||
C->isSameOperationAs(Instructions.back())))
return;
Instructions.push_back(C);
}
} while (C->hasOneUse());
if (Instructions.size() < 2 ||
!C->isSameOperationAs(Instructions.back()) ||
C->use_empty())
return;
// C is now the (potential) last instruction in the reduction chain.
for (User *U : C->users())
// The only in-loop user can be the initial PHI.
if (L->contains(cast<Instruction>(U)))
if (cast<Instruction>(U) != Instructions.front())
return;
Instructions.push_back(C);
Valid = true;
}
// Collect the vector of possible reduction variables.
void LoopReroll::collectPossibleReductions(Loop *L,
ReductionTracker &Reductions) {
BasicBlock *Header = L->getHeader();
for (BasicBlock::iterator I = Header->begin(),
IE = Header->getFirstInsertionPt(); I != IE; ++I) {
if (!isa<PHINode>(I))
continue;
if (!I->getType()->isSingleValueType())
continue;
SimpleLoopReduction SLR(I, L);
if (!SLR.valid())
continue;
DEBUG(dbgs() << "LRR: Possible reduction: " << *I << " (with " <<
SLR.size() << " chained instructions)\n");
Reductions.addSLR(SLR);
}
}
// Collect the set of all users of the provided root instruction. This set of
// users contains not only the direct users of the root instruction, but also
// all users of those users, and so on. There are two exceptions:
//
// 1. Instructions in the set of excluded instructions are never added to the
// use set (even if they are users). This is used, for example, to exclude
// including root increments in the use set of the primary IV.
//
// 2. Instructions in the set of final instructions are added to the use set
// if they are users, but their users are not added. This is used, for
// example, to prevent a reduction update from forcing all later reduction
// updates into the use set.
void LoopReroll::collectInLoopUserSet(Loop *L,
Instruction *Root, const SmallInstructionSet &Exclude,
const SmallInstructionSet &Final,
DenseSet<Instruction *> &Users) {
SmallInstructionVector Queue(1, Root);
while (!Queue.empty()) {
Instruction *I = Queue.pop_back_val();
if (!Users.insert(I).second)
continue;
if (!Final.count(I))
for (Use &U : I->uses()) {
Instruction *User = cast<Instruction>(U.getUser());
if (PHINode *PN = dyn_cast<PHINode>(User)) {
// Ignore "wrap-around" uses to PHIs of this loop's header.
if (PN->getIncomingBlock(U) == L->getHeader())
continue;
}
if (L->contains(User) && !Exclude.count(User)) {
Queue.push_back(User);
}
}
// We also want to collect single-user "feeder" values.
for (User::op_iterator OI = I->op_begin(),
OIE = I->op_end(); OI != OIE; ++OI) {
if (Instruction *Op = dyn_cast<Instruction>(*OI))
if (Op->hasOneUse() && L->contains(Op) && !Exclude.count(Op) &&
!Final.count(Op))
Queue.push_back(Op);
}
}
}
// Collect all of the users of all of the provided root instructions (combined
// into a single set).
void LoopReroll::collectInLoopUserSet(Loop *L,
const SmallInstructionVector &Roots,
const SmallInstructionSet &Exclude,
const SmallInstructionSet &Final,
DenseSet<Instruction *> &Users) {
for (SmallInstructionVector::const_iterator I = Roots.begin(),
IE = Roots.end(); I != IE; ++I)
collectInLoopUserSet(L, *I, Exclude, Final, Users);
}
static bool isSimpleLoadStore(Instruction *I) {
if (LoadInst *LI = dyn_cast<LoadInst>(I))
return LI->isSimple();
if (StoreInst *SI = dyn_cast<StoreInst>(I))
return SI->isSimple();
if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(I))
return !MI->isVolatile();
return false;
}
// Recognize loops that are setup like this:
//
// %iv = phi [ (preheader, ...), (body, %iv.next) ]
// %scaled.iv = mul %iv, scale
// f(%scaled.iv)
// %scaled.iv.1 = add %scaled.iv, 1
// f(%scaled.iv.1)
// %scaled.iv.2 = add %scaled.iv, 2
// f(%scaled.iv.2)
// %scaled.iv.scale_m_1 = add %scaled.iv, scale-1
// f(%scaled.iv.scale_m_1)
// ...
// %iv.next = add %iv, 1
// %cmp = icmp(%iv, ...)
// br %cmp, header, exit
//
// and, if found, set IV = %scaled.iv, and add %iv.next to LoopIncs.
bool LoopReroll::findScaleFromMul(Instruction *RealIV, uint64_t &Scale,
Instruction *&IV,
SmallInstructionVector &LoopIncs) {
// This is a special case: here we're looking for all uses (except for
// the increment) to be multiplied by a common factor. The increment must
// be by one. This is to capture loops like:
// for (int i = 0; i < 500; ++i) {
// foo(3*i); foo(3*i+1); foo(3*i+2);
// }
if (RealIV->getNumUses() != 2)
return false;
const SCEVAddRecExpr *RealIVSCEV = cast<SCEVAddRecExpr>(SE->getSCEV(RealIV));
Instruction *User1 = cast<Instruction>(*RealIV->user_begin()),
*User2 = cast<Instruction>(*std::next(RealIV->user_begin()));
if (!SE->isSCEVable(User1->getType()) || !SE->isSCEVable(User2->getType()))
return false;
const SCEVAddRecExpr *User1SCEV =
dyn_cast<SCEVAddRecExpr>(SE->getSCEV(User1)),
*User2SCEV =
dyn_cast<SCEVAddRecExpr>(SE->getSCEV(User2));
if (!User1SCEV || !User1SCEV->isAffine() ||
!User2SCEV || !User2SCEV->isAffine())
return false;
// We assume below that User1 is the scale multiply and User2 is the
// increment. If this can't be true, then swap them.
if (User1SCEV == RealIVSCEV->getPostIncExpr(*SE)) {
std::swap(User1, User2);
std::swap(User1SCEV, User2SCEV);
}
if (User2SCEV != RealIVSCEV->getPostIncExpr(*SE))
return false;
assert(User2SCEV->getStepRecurrence(*SE)->isOne() &&
"Invalid non-unit step for multiplicative scaling");
LoopIncs.push_back(User2);
if (const SCEVConstant *MulScale =
dyn_cast<SCEVConstant>(User1SCEV->getStepRecurrence(*SE))) {
// Make sure that both the start and step have the same multiplier.
if (RealIVSCEV->getStart()->getType() != MulScale->getType())
return false;
if (SE->getMulExpr(RealIVSCEV->getStart(), MulScale) !=
User1SCEV->getStart())
return false;
ConstantInt *MulScaleCI = MulScale->getValue();
if (!MulScaleCI->uge(2) || MulScaleCI->uge(MaxInc))
return false;
Scale = MulScaleCI->getZExtValue();
IV = User1;
} else
return false;
DEBUG(dbgs() << "LRR: Found possible scaling " << *User1 << "\n");
return true;
}
// Collect all root increments with respect to the provided induction variable
// (normally the PHI, but sometimes a multiply). A root increment is an
// instruction, normally an add, with a positive constant less than Scale. In a
// rerollable loop, each of these increments is the root of an instruction
// graph isomorphic to the others. Also, we collect the final induction
// increment (the increment equal to the Scale), and its users in LoopIncs.
bool LoopReroll::collectAllRoots(Loop *L, uint64_t Inc, uint64_t Scale,
Instruction *IV,
SmallVector<SmallInstructionVector, 32> &Roots,
SmallInstructionSet &AllRoots,
SmallInstructionVector &LoopIncs) {
for (User *U : IV->users()) {
Instruction *UI = cast<Instruction>(U);
if (!SE->isSCEVable(UI->getType()))
continue;
if (UI->getType() != IV->getType())
continue;
if (!L->contains(UI))
continue;
if (hasUsesOutsideLoop(UI, L))
continue;
if (const SCEVConstant *Diff = dyn_cast<SCEVConstant>(SE->getMinusSCEV(
SE->getSCEV(UI), SE->getSCEV(IV)))) {
uint64_t Idx = Diff->getValue()->getValue().getZExtValue();
if (Idx > 0 && Idx < Scale) {
Roots[Idx-1].push_back(UI);
AllRoots.insert(UI);
} else if (Idx == Scale && Inc > 1) {
LoopIncs.push_back(UI);
}
}
}
if (Roots[0].empty())
return false;
bool AllSame = true;
for (unsigned i = 1; i < Scale-1; ++i)
if (Roots[i].size() != Roots[0].size()) {
AllSame = false;
break;
}
if (!AllSame)
return false;
return true;
}
// Validate the selected reductions. All iterations must have an isomorphic
// part of the reduction chain and, for non-associative reductions, the chain
// entries must appear in order.
bool LoopReroll::ReductionTracker::validateSelected() {
// For a non-associative reduction, the chain entries must appear in order.
for (DenseSet<int>::iterator RI = Reds.begin(), RIE = Reds.end();
RI != RIE; ++RI) {
int i = *RI;
int PrevIter = 0, BaseCount = 0, Count = 0;
for (SimpleLoopReduction::iterator J = PossibleReds[i].begin(),
JE = PossibleReds[i].end(); J != JE; ++J) {
// Note that all instructions in the chain must have been found because
// all instructions in the function must have been assigned to some
// iteration.
int Iter = PossibleRedIter[*J];
if (Iter != PrevIter && Iter != PrevIter + 1 &&
!PossibleReds[i].getReducedValue()->isAssociative()) {
DEBUG(dbgs() << "LRR: Out-of-order non-associative reduction: " <<
*J << "\n");
return false;
}
if (Iter != PrevIter) {
if (Count != BaseCount) {
DEBUG(dbgs() << "LRR: Iteration " << PrevIter <<
" reduction use count " << Count <<
" is not equal to the base use count " <<
BaseCount << "\n");
return false;
}
Count = 0;
}
++Count;
if (Iter == 0)
++BaseCount;
PrevIter = Iter;
}
}
return true;
}
// For all selected reductions, remove all parts except those in the first
// iteration (and the PHI). Replace outside uses of the reduced value with uses
// of the first-iteration reduced value (in other words, reroll the selected
// reductions).
void LoopReroll::ReductionTracker::replaceSelected() {
// Fixup reductions to refer to the last instruction associated with the
// first iteration (not the last).
for (DenseSet<int>::iterator RI = Reds.begin(), RIE = Reds.end();
RI != RIE; ++RI) {
int i = *RI;
int j = 0;
for (int e = PossibleReds[i].size(); j != e; ++j)
if (PossibleRedIter[PossibleReds[i][j]] != 0) {
--j;
break;
}
// Replace users with the new end-of-chain value.
SmallInstructionVector Users;
for (User *U : PossibleReds[i].getReducedValue()->users())
Users.push_back(cast<Instruction>(U));
for (SmallInstructionVector::iterator J = Users.begin(),
JE = Users.end(); J != JE; ++J)
(*J)->replaceUsesOfWith(PossibleReds[i].getReducedValue(),
PossibleReds[i][j]);
}
}
// Reroll the provided loop with respect to the provided induction variable.
// Generally, we're looking for a loop like this:
//
// %iv = phi [ (preheader, ...), (body, %iv.next) ]
// f(%iv)
// %iv.1 = add %iv, 1 <-- a root increment
// f(%iv.1)
// %iv.2 = add %iv, 2 <-- a root increment
// f(%iv.2)
// %iv.scale_m_1 = add %iv, scale-1 <-- a root increment
// f(%iv.scale_m_1)
// ...
// %iv.next = add %iv, scale
// %cmp = icmp(%iv, ...)
// br %cmp, header, exit
//
// Notably, we do not require that f(%iv), f(%iv.1), etc. be isolated groups of
// instructions. In other words, the instructions in f(%iv), f(%iv.1), etc. can
// be intermixed with eachother. The restriction imposed by this algorithm is
// that the relative order of the isomorphic instructions in f(%iv), f(%iv.1),
// etc. be the same.
//
// First, we collect the use set of %iv, excluding the other increment roots.
// This gives us f(%iv). Then we iterate over the loop instructions (scale-1)
// times, having collected the use set of f(%iv.(i+1)), during which we:
// - Ensure that the next unmatched instruction in f(%iv) is isomorphic to
// the next unmatched instruction in f(%iv.(i+1)).
// - Ensure that both matched instructions don't have any external users
// (with the exception of last-in-chain reduction instructions).
// - Track the (aliasing) write set, and other side effects, of all
// instructions that belong to future iterations that come before the matched
// instructions. If the matched instructions read from that write set, then
// f(%iv) or f(%iv.(i+1)) has some dependency on instructions in
// f(%iv.(j+1)) for some j > i, and we cannot reroll the loop. Similarly,
// if any of these future instructions had side effects (could not be
// speculatively executed), and so do the matched instructions, when we
// cannot reorder those side-effect-producing instructions, and rerolling
// fails.
//
// Finally, we make sure that all loop instructions are either loop increment
// roots, belong to simple latch code, parts of validated reductions, part of
// f(%iv) or part of some f(%iv.i). If all of that is true (and all reductions
// have been validated), then we reroll the loop.
bool LoopReroll::reroll(Instruction *IV, Loop *L, BasicBlock *Header,
const SCEV *IterCount,
ReductionTracker &Reductions) {
const SCEVAddRecExpr *RealIVSCEV = cast<SCEVAddRecExpr>(SE->getSCEV(IV));
uint64_t Inc = cast<SCEVConstant>(RealIVSCEV->getOperand(1))->
getValue()->getZExtValue();
// The collection of loop increment instructions.
SmallInstructionVector LoopIncs;
uint64_t Scale = Inc;
// The effective induction variable, IV, is normally also the real induction
// variable. When we're dealing with a loop like:
// for (int i = 0; i < 500; ++i)
// x[3*i] = ...;
// x[3*i+1] = ...;
// x[3*i+2] = ...;
// then the real IV is still i, but the effective IV is (3*i).
Instruction *RealIV = IV;
if (Inc == 1 && !findScaleFromMul(RealIV, Scale, IV, LoopIncs))
return false;
assert(Scale <= MaxInc && "Scale is too large");
assert(Scale > 1 && "Scale must be at least 2");
// The set of increment instructions for each increment value.
SmallVector<SmallInstructionVector, 32> Roots(Scale-1);
SmallInstructionSet AllRoots;
if (!collectAllRoots(L, Inc, Scale, IV, Roots, AllRoots, LoopIncs))
return false;
DEBUG(dbgs() << "LRR: Found all root induction increments for: " <<
*RealIV << "\n");
// An array of just the possible reductions for this scale factor. When we
// collect the set of all users of some root instructions, these reduction
// instructions are treated as 'final' (their uses are not considered).
// This is important because we don't want the root use set to search down
// the reduction chain.
SmallInstructionSet PossibleRedSet;
SmallInstructionSet PossibleRedLastSet, PossibleRedPHISet;
Reductions.restrictToScale(Scale, PossibleRedSet, PossibleRedPHISet,
PossibleRedLastSet);
// We now need to check for equivalence of the use graph of each root with
// that of the primary induction variable (excluding the roots). Our goal
// here is not to solve the full graph isomorphism problem, but rather to
// catch common cases without a lot of work. As a result, we will assume
// that the relative order of the instructions in each unrolled iteration
// is the same (although we will not make an assumption about how the
// different iterations are intermixed). Note that while the order must be
// the same, the instructions may not be in the same basic block.
SmallInstructionSet Exclude(AllRoots);
Exclude.insert(LoopIncs.begin(), LoopIncs.end());
DenseSet<Instruction *> BaseUseSet;
collectInLoopUserSet(L, IV, Exclude, PossibleRedSet, BaseUseSet);
DenseSet<Instruction *> AllRootUses;
std::vector<DenseSet<Instruction *> > RootUseSets(Scale-1);
bool MatchFailed = false;
for (unsigned i = 0; i < Scale-1 && !MatchFailed; ++i) {
DenseSet<Instruction *> &RootUseSet = RootUseSets[i];
collectInLoopUserSet(L, Roots[i], SmallInstructionSet(),
PossibleRedSet, RootUseSet);
DEBUG(dbgs() << "LRR: base use set size: " << BaseUseSet.size() <<
" vs. iteration increment " << (i+1) <<
" use set size: " << RootUseSet.size() << "\n");
if (BaseUseSet.size() != RootUseSet.size()) {
MatchFailed = true;
break;
}
// In addition to regular aliasing information, we need to look for
// instructions from later (future) iterations that have side effects
// preventing us from reordering them past other instructions with side
// effects.
bool FutureSideEffects = false;
AliasSetTracker AST(*AA);
// The map between instructions in f(%iv.(i+1)) and f(%iv).
DenseMap<Value *, Value *> BaseMap;
assert(L->getNumBlocks() == 1 && "Cannot handle multi-block loops");
for (BasicBlock::iterator J1 = Header->begin(), J2 = Header->begin(),
JE = Header->end(); J1 != JE && !MatchFailed; ++J1) {
if (cast<Instruction>(J1) == RealIV)
continue;
if (cast<Instruction>(J1) == IV)
continue;
if (!BaseUseSet.count(J1))
continue;
if (PossibleRedPHISet.count(J1)) // Skip reduction PHIs.
continue;
while (J2 != JE && (!RootUseSet.count(J2) ||
std::find(Roots[i].begin(), Roots[i].end(), J2) !=
Roots[i].end())) {
// As we iterate through the instructions, instructions that don't
// belong to previous iterations (or the base case), must belong to
// future iterations. We want to track the alias set of writes from
// previous iterations.
if (!isa<PHINode>(J2) && !BaseUseSet.count(J2) &&
!AllRootUses.count(J2)) {
if (J2->mayWriteToMemory())
AST.add(J2);
// Note: This is specifically guarded by a check on isa<PHINode>,
// which while a valid (somewhat arbitrary) micro-optimization, is
// needed because otherwise isSafeToSpeculativelyExecute returns
// false on PHI nodes.
if (!isSimpleLoadStore(J2) && !isSafeToSpeculativelyExecute(J2, DL))
FutureSideEffects = true;
}
++J2;
}
if (!J1->isSameOperationAs(J2)) {
DEBUG(dbgs() << "LRR: iteration root match failed at " << *J1 <<
" vs. " << *J2 << "\n");
MatchFailed = true;
break;
}
// Make sure that this instruction, which is in the use set of this
// root instruction, does not also belong to the base set or the set of
// some previous root instruction.
if (BaseUseSet.count(J2) || AllRootUses.count(J2)) {
DEBUG(dbgs() << "LRR: iteration root match failed at " << *J1 <<
" vs. " << *J2 << " (prev. case overlap)\n");
MatchFailed = true;
break;
}
// Make sure that we don't alias with any instruction in the alias set
// tracker. If we do, then we depend on a future iteration, and we
// can't reroll.
if (J2->mayReadFromMemory()) {
for (AliasSetTracker::iterator K = AST.begin(), KE = AST.end();
K != KE && !MatchFailed; ++K) {
if (K->aliasesUnknownInst(J2, *AA)) {
DEBUG(dbgs() << "LRR: iteration root match failed at " << *J1 <<
" vs. " << *J2 << " (depends on future store)\n");
MatchFailed = true;
break;
}
}
}
// If we've past an instruction from a future iteration that may have
// side effects, and this instruction might also, then we can't reorder
// them, and this matching fails. As an exception, we allow the alias
// set tracker to handle regular (simple) load/store dependencies.
if (FutureSideEffects &&
((!isSimpleLoadStore(J1) && !isSafeToSpeculativelyExecute(J1)) ||
(!isSimpleLoadStore(J2) && !isSafeToSpeculativelyExecute(J2)))) {
DEBUG(dbgs() << "LRR: iteration root match failed at " << *J1 <<
" vs. " << *J2 <<
" (side effects prevent reordering)\n");
MatchFailed = true;
break;
}
// For instructions that are part of a reduction, if the operation is
// associative, then don't bother matching the operands (because we
// already know that the instructions are isomorphic, and the order
// within the iteration does not matter). For non-associative reductions,
// we do need to match the operands, because we need to reject
// out-of-order instructions within an iteration!
// For example (assume floating-point addition), we need to reject this:
// x += a[i]; x += b[i];
// x += a[i+1]; x += b[i+1];
// x += b[i+2]; x += a[i+2];
bool InReduction = Reductions.isPairInSame(J1, J2);
if (!(InReduction && J1->isAssociative())) {
bool Swapped = false, SomeOpMatched = false;;
for (unsigned j = 0; j < J1->getNumOperands() && !MatchFailed; ++j) {
Value *Op2 = J2->getOperand(j);
// If this is part of a reduction (and the operation is not
// associatve), then we match all operands, but not those that are
// part of the reduction.
if (InReduction)
if (Instruction *Op2I = dyn_cast<Instruction>(Op2))
if (Reductions.isPairInSame(J2, Op2I))
continue;
DenseMap<Value *, Value *>::iterator BMI = BaseMap.find(Op2);
if (BMI != BaseMap.end())
Op2 = BMI->second;
else if (std::find(Roots[i].begin(), Roots[i].end(),
(Instruction*) Op2) != Roots[i].end())
Op2 = IV;
if (J1->getOperand(Swapped ? unsigned(!j) : j) != Op2) {
// If we've not already decided to swap the matched operands, and
// we've not already matched our first operand (note that we could
// have skipped matching the first operand because it is part of a
// reduction above), and the instruction is commutative, then try
// the swapped match.
if (!Swapped && J1->isCommutative() && !SomeOpMatched &&
J1->getOperand(!j) == Op2) {
Swapped = true;
} else {
DEBUG(dbgs() << "LRR: iteration root match failed at " << *J1 <<
" vs. " << *J2 << " (operand " << j << ")\n");
MatchFailed = true;
break;
}
}
SomeOpMatched = true;
}
}
if ((!PossibleRedLastSet.count(J1) && hasUsesOutsideLoop(J1, L)) ||
(!PossibleRedLastSet.count(J2) && hasUsesOutsideLoop(J2, L))) {
DEBUG(dbgs() << "LRR: iteration root match failed at " << *J1 <<
" vs. " << *J2 << " (uses outside loop)\n");
MatchFailed = true;
break;
}
if (!MatchFailed)
BaseMap.insert(std::pair<Value *, Value *>(J2, J1));
AllRootUses.insert(J2);
Reductions.recordPair(J1, J2, i+1);
++J2;
}
}
if (MatchFailed)
return false;
DEBUG(dbgs() << "LRR: Matched all iteration increments for " <<
*RealIV << "\n");
DenseSet<Instruction *> LoopIncUseSet;
collectInLoopUserSet(L, LoopIncs, SmallInstructionSet(),
SmallInstructionSet(), LoopIncUseSet);
DEBUG(dbgs() << "LRR: Loop increment set size: " <<
LoopIncUseSet.size() << "\n");
// Make sure that all instructions in the loop have been included in some
// use set.
for (BasicBlock::iterator J = Header->begin(), JE = Header->end();
J != JE; ++J) {
if (isa<DbgInfoIntrinsic>(J))
continue;
if (cast<Instruction>(J) == RealIV)
continue;
if (cast<Instruction>(J) == IV)
continue;
if (BaseUseSet.count(J) || AllRootUses.count(J) ||
(LoopIncUseSet.count(J) && (J->isTerminator() ||
isSafeToSpeculativelyExecute(J, DL))))
continue;
if (AllRoots.count(J))
continue;
if (Reductions.isSelectedPHI(J))
continue;
DEBUG(dbgs() << "LRR: aborting reroll based on " << *RealIV <<
" unprocessed instruction found: " << *J << "\n");
MatchFailed = true;
break;
}
if (MatchFailed)
return false;
DEBUG(dbgs() << "LRR: all instructions processed from " <<
*RealIV << "\n");
if (!Reductions.validateSelected())
return false;
// At this point, we've validated the rerolling, and we're committed to
// making changes!
Reductions.replaceSelected();
// Remove instructions associated with non-base iterations.
for (BasicBlock::reverse_iterator J = Header->rbegin();
J != Header->rend();) {
if (AllRootUses.count(&*J)) {
Instruction *D = &*J;
DEBUG(dbgs() << "LRR: removing: " << *D << "\n");
D->eraseFromParent();
continue;
}
++J;
}
// Insert the new induction variable.
const SCEV *Start = RealIVSCEV->getStart();
if (Inc == 1)
Start = SE->getMulExpr(Start,
SE->getConstant(Start->getType(), Scale));
const SCEVAddRecExpr *H =
cast<SCEVAddRecExpr>(SE->getAddRecExpr(Start,
SE->getConstant(RealIVSCEV->getType(), 1),
L, SCEV::FlagAnyWrap));
{ // Limit the lifetime of SCEVExpander.
SCEVExpander Expander(*SE, "reroll");
Value *NewIV = Expander.expandCodeFor(H, IV->getType(), Header->begin());
for (DenseSet<Instruction *>::iterator J = BaseUseSet.begin(),
JE = BaseUseSet.end(); J != JE; ++J)
(*J)->replaceUsesOfWith(IV, NewIV);
if (BranchInst *BI = dyn_cast<BranchInst>(Header->getTerminator())) {
if (LoopIncUseSet.count(BI)) {
const SCEV *ICSCEV = RealIVSCEV->evaluateAtIteration(IterCount, *SE);
if (Inc == 1)
ICSCEV =
SE->getMulExpr(ICSCEV, SE->getConstant(ICSCEV->getType(), Scale));
// Iteration count SCEV minus 1
const SCEV *ICMinus1SCEV =
SE->getMinusSCEV(ICSCEV, SE->getConstant(ICSCEV->getType(), 1));
Value *ICMinus1; // Iteration count minus 1
if (isa<SCEVConstant>(ICMinus1SCEV)) {
ICMinus1 = Expander.expandCodeFor(ICMinus1SCEV, NewIV->getType(), BI);
} else {
BasicBlock *Preheader = L->getLoopPreheader();
if (!Preheader)
Preheader = InsertPreheaderForLoop(L, this);
ICMinus1 = Expander.expandCodeFor(ICMinus1SCEV, NewIV->getType(),
Preheader->getTerminator());
}
Value *Cond = new ICmpInst(BI, CmpInst::ICMP_EQ, NewIV, ICMinus1,
"exitcond");
BI->setCondition(Cond);
if (BI->getSuccessor(1) != Header)
BI->swapSuccessors();
}
}
}
SimplifyInstructionsInBlock(Header, DL, TLI);
DeleteDeadPHIs(Header, TLI);
++NumRerolledLoops;
return true;
}
bool LoopReroll::runOnLoop(Loop *L, LPPassManager &LPM) {
if (skipOptnoneFunction(L))
return false;
AA = &getAnalysis<AliasAnalysis>();
LI = &getAnalysis<LoopInfo>();
SE = &getAnalysis<ScalarEvolution>();
TLI = &getAnalysis<TargetLibraryInfo>();
DataLayoutPass *DLP = getAnalysisIfAvailable<DataLayoutPass>();
DL = DLP ? &DLP->getDataLayout() : 0;
DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
BasicBlock *Header = L->getHeader();
DEBUG(dbgs() << "LRR: F[" << Header->getParent()->getName() <<
"] Loop %" << Header->getName() << " (" <<
L->getNumBlocks() << " block(s))\n");
bool Changed = false;
// For now, we'll handle only single BB loops.
if (L->getNumBlocks() > 1)
return Changed;
if (!SE->hasLoopInvariantBackedgeTakenCount(L))
return Changed;
const SCEV *LIBETC = SE->getBackedgeTakenCount(L);
const SCEV *IterCount =
SE->getAddExpr(LIBETC, SE->getConstant(LIBETC->getType(), 1));
DEBUG(dbgs() << "LRR: iteration count = " << *IterCount << "\n");
// First, we need to find the induction variable with respect to which we can
// reroll (there may be several possible options).
SmallInstructionVector PossibleIVs;
collectPossibleIVs(L, PossibleIVs);
if (PossibleIVs.empty()) {
DEBUG(dbgs() << "LRR: No possible IVs found\n");
return Changed;
}
ReductionTracker Reductions;
collectPossibleReductions(L, Reductions);
// For each possible IV, collect the associated possible set of 'root' nodes
// (i+1, i+2, etc.).
for (SmallInstructionVector::iterator I = PossibleIVs.begin(),
IE = PossibleIVs.end(); I != IE; ++I)
if (reroll(*I, L, Header, IterCount, Reductions)) {
Changed = true;
break;
}
return Changed;
}
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