//===----------------------------------------------------------------------===//
#include "llvm/Transforms/Scalar.h"
+#include "llvm/ADT/MapVector.h"
#include "llvm/ADT/STLExtras.h"
+#include "llvm/ADT/SmallBitVector.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/AliasAnalysis.h"
// br %cmp, header, exit
namespace {
+ enum IterationLimits {
+ /// The maximum number of iterations that we'll try and reroll. This
+ /// has to be less than 25 in order to fit into a SmallBitVector.
+ IL_MaxRerollIterations = 16,
+ /// The bitvector index used by loop induction variables and other
+ /// instructions that belong to no one particular iteration.
+ IL_LoopIncIdx,
+ IL_End
+ };
+
class LoopReroll : public LoopPass {
public:
static char ID; // Pass ID, replacement for typeid
AU.addRequired<TargetLibraryInfoWrapperPass>();
}
-protected:
+ protected:
AliasAnalysis *AA;
LoopInfo *LI;
ScalarEvolution *SE;
void replace(const SCEV *IterCount);
protected:
+ typedef MapVector<Instruction*, SmallBitVector> UsesTy;
+
bool findScaleFromMul();
bool collectAllRoots();
+ bool collectUsedInstructions(SmallInstructionSet &PossibleRedSet);
void collectInLoopUserSet(const SmallInstructionVector &Roots,
const SmallInstructionSet &Exclude,
const SmallInstructionSet &Final,
const SmallInstructionSet &Final,
DenseSet<Instruction *> &Users);
+ UsesTy::iterator nextInstr(int Val, UsesTy &In, UsesTy::iterator I);
+
LoopReroll *Parent;
// Members of Parent, replicated here for brevity.
SmallInstructionVector Roots;
// All increment instructions for IV.
SmallInstructionVector LoopIncs;
- // All instructions transitively used by any root.
- DenseSet<Instruction *> AllRootUses;
- // All instructions transitively used by the base.
- DenseSet<Instruction *> BaseUseSet;
- // All instructions transitively used by the increments.
- DenseSet<Instruction *> LoopIncUseSet;
+ // Map of all instructions in the loop (in order) to the iterations
+ // they are used in (or specially, IL_LoopIncIdx for instructions
+ // used in the loop increment mechanism).
+ UsesTy Uses;
};
void collectPossibleIVs(Loop *L, SmallInstructionVector &PossibleIVs);
// 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())
+ for (User *U : I->users()) {
if (!L->contains(cast<Instruction>(U)))
return true;
-
+ }
return false;
}
return;
// C is now the (potential) last instruction in the reduction chain.
- for (User *U : C->users())
+ 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;
if (!collectAllRoots())
return false;
+ if (Roots.size() > IL_MaxRerollIterations) {
+ DEBUG(dbgs() << "LRR: Aborting - too many iterations found. "
+ << "#Found=" << Roots.size() << ", #Max=" << IL_MaxRerollIterations
+ << "\n");
+ return false;
+ }
+
return true;
}
return true;
}
-bool LoopReroll::DAGRootTracker::validate(ReductionTracker &Reductions) {
- BasicBlock *Header = L->getHeader();
+bool LoopReroll::DAGRootTracker::collectUsedInstructions(SmallInstructionSet &PossibleRedSet) {
+ // Populate the MapVector with all instructions in the block, in order first,
+ // so we can iterate over the contents later in perfect order.
+ for (auto &I : *L->getHeader()) {
+ Uses[&I].resize(IL_End);
+ }
+
+ SmallInstructionSet Exclude;
+ Exclude.insert(Roots.begin(), Roots.end());
+ Exclude.insert(LoopIncs.begin(), LoopIncs.end());
+ DenseSet<Instruction*> VBase;
+ collectInLoopUserSet(IV, Exclude, PossibleRedSet, VBase);
+ for (auto *I : VBase) {
+ Uses[I].set(0);
+ }
+
+ unsigned Idx = 1;
+ for (auto *Root : Roots) {
+ DenseSet<Instruction*> V;
+ collectInLoopUserSet(Root, Exclude, PossibleRedSet, V);
+
+ // While we're here, check the use sets are the same size.
+ if (V.size() != VBase.size()) {
+ DEBUG(dbgs() << "LRR: Aborting - use sets are different sizes\n");
+ return false;
+ }
+
+ for (auto *I : V) {
+ Uses[I].set(Idx);
+ }
+ ++Idx;
+ }
+
+ // Make sure the loop increments are also accounted for.
+ Exclude.clear();
+ Exclude.insert(Roots.begin(), Roots.end());
+
+ DenseSet<Instruction*> V;
+ collectInLoopUserSet(LoopIncs, Exclude, PossibleRedSet, V);
+ for (auto *I : V) {
+ Uses[I].set(IL_LoopIncIdx);
+ }
+ if (IV != RealIV)
+ Uses[RealIV].set(IL_LoopIncIdx);
+
+ return true;
+
+}
+
+LoopReroll::DAGRootTracker::UsesTy::iterator
+LoopReroll::DAGRootTracker::nextInstr(int Val, UsesTy &In,
+ UsesTy::iterator I) {
+ while (I != In.end() && I->second.test(Val) == 0)
+ ++I;
+ return I;
+}
+
+bool LoopReroll::DAGRootTracker::validate(ReductionTracker &Reductions) {
// 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
// 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;
- Exclude.insert(Roots.begin(), Roots.end());
- Exclude.insert(LoopIncs.begin(), LoopIncs.end());
// 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
SmallInstructionSet PossibleRedPHISet;
Reductions.restrictToScale(Scale, PossibleRedSet,
PossibleRedPHISet, PossibleRedLastSet);
-
-
- collectInLoopUserSet(IV, Exclude, PossibleRedSet, BaseUseSet);
- std::vector<DenseSet<Instruction *> > RootUseSets(Scale-1);
+ // Populate "Uses" with where each instruction is used.
+ if (!collectUsedInstructions(PossibleRedSet))
+ return false;
- bool MatchFailed = false;
- for (unsigned i = 0; i < Scale-1 && !MatchFailed; ++i) {
- DenseSet<Instruction *> &RootUseSet = RootUseSets[i];
- collectInLoopUserSet(Roots[i], SmallInstructionSet(),
- PossibleRedSet, RootUseSet);
+ // Make sure we mark the reduction PHIs as used in all iterations.
+ for (auto *I : PossibleRedPHISet) {
+ Uses[I].set(IL_LoopIncIdx);
+ }
- DEBUG(dbgs() << "LRR: base use set size: " << BaseUseSet.size() <<
- " vs. iteration increment " << (i+1) <<
- " use set size: " << RootUseSet.size() << "\n");
+ // Make sure all instructions in the loop are in one and only one
+ // set.
+ for (auto &KV : Uses) {
+ if (KV.second.count() != 1) {
+ DEBUG(dbgs() << "LRR: Aborting - instruction is not used in 1 iteration: "
+ << *KV.first << " (#uses=" << KV.second.count() << ")\n");
+ return false;
+ }
+ }
- if (BaseUseSet.size() != RootUseSet.size()) {
- MatchFailed = true;
- break;
+ DEBUG(
+ for (auto &KV : Uses) {
+ dbgs() << "LRR: " << KV.second.find_first() << "\t" << *KV.first << "\n";
}
+ );
+ for (unsigned Iter = 1; Iter < Scale; ++Iter) {
// 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;
+ // Compare iteration Iter to the base.
+ auto BaseIt = nextInstr(0, Uses, Uses.begin());
+ auto RootIt = nextInstr(Iter, Uses, Uses.begin());
+ auto LastRootIt = Uses.begin();
- while (J2 != JE && (!RootUseSet.count(J2) || Roots[i] == J2)) {
- // 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;
- }
+ while (BaseIt != Uses.end() && RootIt != Uses.end()) {
+ Instruction *BaseInst = BaseIt->first;
+ Instruction *RootInst = RootIt->first;
- ++J2;
+ // Skip over the IV or root instructions; only match their users.
+ bool Continue = false;
+ if (BaseInst == RealIV || BaseInst == IV) {
+ BaseIt = nextInstr(0, Uses, ++BaseIt);
+ Continue = true;
+ }
+ if (std::find(Roots.begin(), Roots.end(), RootInst) != Roots.end()) {
+ LastRootIt = RootIt;
+ RootIt = nextInstr(Iter, Uses, ++RootIt);
+ Continue = true;
+ }
+ if (Continue) continue;
+
+ // All instructions between the last root and this root
+ // belong to some other iteration. If they belong to a
+ // future iteration, then they're dangerous to alias with.
+ for (; LastRootIt != RootIt; ++LastRootIt) {
+ Instruction *I = LastRootIt->first;
+ if (LastRootIt->second.find_first() < (int)Iter)
+ continue;
+ if (I->mayWriteToMemory())
+ AST.add(I);
+ // 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 (!isa<PHINode>(I) && !isSimpleLoadStore(I) &&
+ !isSafeToSpeculativelyExecute(I, DL))
+ // Intervening instructions cause side effects.
+ FutureSideEffects = true;
}
- if (!J1->isSameOperationAs(J2)) {
- DEBUG(dbgs() << "LRR: iteration root match failed at " << *J1 <<
- " vs. " << *J2 << "\n");
- MatchFailed = true;
- break;
+ if (!BaseInst->isSameOperationAs(RootInst)) {
+ DEBUG(dbgs() << "LRR: iteration root match failed at " << *BaseInst <<
+ " vs. " << *RootInst << "\n");
+ return false;
}
// 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;
+ // some other root instruction.
+ if (RootIt->second.count() > 1) {
+ DEBUG(dbgs() << "LRR: iteration root match failed at " << *BaseInst <<
+ " vs. " << *RootInst << " (prev. case overlap)\n");
+ return false;
}
// 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 (RootInst->mayReadFromMemory())
+ for (auto &K : AST) {
+ if (K.aliasesUnknownInst(RootInst, *AA)) {
+ DEBUG(dbgs() << "LRR: iteration root match failed at " << *BaseInst <<
+ " vs. " << *RootInst << " (depends on future store)\n");
+ return false;
}
}
- }
// 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, DL)) ||
- (!isSimpleLoadStore(J2) &&
- !isSafeToSpeculativelyExecute(J2, DL)))) {
- DEBUG(dbgs() << "LRR: iteration root match failed at " << *J1 <<
- " vs. " << *J2 <<
+ ((!isSimpleLoadStore(BaseInst) &&
+ !isSafeToSpeculativelyExecute(BaseInst, DL)) ||
+ (!isSimpleLoadStore(RootInst) &&
+ !isSafeToSpeculativelyExecute(RootInst, DL)))) {
+ DEBUG(dbgs() << "LRR: iteration root match failed at " << *BaseInst <<
+ " vs. " << *RootInst <<
" (side effects prevent reordering)\n");
- MatchFailed = true;
- break;
+ return false;
}
// For instructions that are part of a reduction, if the operation is
// 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);
+ bool InReduction = Reductions.isPairInSame(BaseInst, RootInst);
- if (!(InReduction && J1->isAssociative())) {
+ if (!(InReduction && BaseInst->isAssociative())) {
bool Swapped = false, SomeOpMatched = false;
- for (unsigned j = 0; j < J1->getNumOperands() && !MatchFailed; ++j) {
- Value *Op2 = J2->getOperand(j);
+ for (unsigned j = 0; j < BaseInst->getNumOperands(); ++j) {
+ Value *Op2 = RootInst->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))
+ if (Reductions.isPairInSame(RootInst, Op2I))
continue;
DenseMap<Value *, Value *>::iterator BMI = BaseMap.find(Op2);
if (BMI != BaseMap.end())
Op2 = BMI->second;
- else if (Roots[i] == (Instruction*) Op2)
+ else if (Roots[Iter-1] == (Instruction*) Op2)
Op2 = IV;
- if (J1->getOperand(Swapped ? unsigned(!j) : j) != Op2) {
+ if (BaseInst->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) {
+ if (!Swapped && BaseInst->isCommutative() && !SomeOpMatched &&
+ BaseInst->getOperand(!j) == Op2) {
Swapped = true;
} else {
- DEBUG(dbgs() << "LRR: iteration root match failed at " << *J1 <<
- " vs. " << *J2 << " (operand " << j << ")\n");
- MatchFailed = true;
- break;
+ DEBUG(dbgs() << "LRR: iteration root match failed at " << *BaseInst
+ << " vs. " << *RootInst << " (operand " << j << ")\n");
+ return false;
}
}
}
}
- 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 ((!PossibleRedLastSet.count(BaseInst) &&
+ hasUsesOutsideLoop(BaseInst, L)) ||
+ (!PossibleRedLastSet.count(RootInst) &&
+ hasUsesOutsideLoop(RootInst, L))) {
+ DEBUG(dbgs() << "LRR: iteration root match failed at " << *BaseInst <<
+ " vs. " << *RootInst << " (uses outside loop)\n");
+ return false;
}
- if (!MatchFailed)
- BaseMap.insert(std::pair<Value *, Value *>(J2, J1));
-
- AllRootUses.insert(J2);
- Reductions.recordPair(J1, J2, i+1);
+ Reductions.recordPair(BaseInst, RootInst, Iter);
+ BaseMap.insert(std::make_pair(RootInst, BaseInst));
- ++J2;
+ LastRootIt = RootIt;
+ BaseIt = nextInstr(0, Uses, ++BaseIt);
+ RootIt = nextInstr(Iter, Uses, ++RootIt);
}
+ assert (BaseIt == Uses.end() && RootIt == Uses.end() &&
+ "Mismatched set sizes!");
}
- if (MatchFailed)
- return false;
-
DEBUG(dbgs() << "LRR: Matched all iteration increments for " <<
*RealIV << "\n");
- collectInLoopUserSet(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 (std::find(Roots.begin(), Roots.end(), J) != Roots.end())
- 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");
return true;
}
// Remove instructions associated with non-base iterations.
for (BasicBlock::reverse_iterator J = Header->rbegin();
J != Header->rend();) {
- if (AllRootUses.count(&*J)) {
+ unsigned I = Uses[&*J].find_first();
+ if (I > 0 && I < IL_LoopIncIdx) {
Instruction *D = &*J;
DEBUG(dbgs() << "LRR: removing: " << *D << "\n");
D->eraseFromParent();
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);
+ for (auto &KV : Uses) {
+ if (KV.second.find_first() == 0)
+ KV.first->replaceUsesOfWith(IV, NewIV);
+ }
if (BranchInst *BI = dyn_cast<BranchInst>(Header->getTerminator())) {
- if (LoopIncUseSet.count(BI)) {
+ // FIXME: Why do we need this check?
+ if (Uses[BI].find_first() == IL_LoopIncIdx) {
const SCEV *ICSCEV = RealIVSCEV->evaluateAtIteration(IterCount, *SE);
if (Inc == 1)
ICSCEV =
// Replace users with the new end-of-chain value.
SmallInstructionVector Users;
- for (User *U : PossibleReds[i].getReducedValue()->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)
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