#include "llvm/Pass.h"
#include "llvm/Analysis/CFG.h"
+#include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/Analysis/TargetTransformInfo.h"
#include "llvm/ADT/SetOperations.h"
#include "llvm/ADT/Statistic.h"
typedef DenseMap<Instruction *, Value *> RematerializedValueMapTy;
struct PartiallyConstructedSafepointRecord {
- /// The set of values known to be live accross this safepoint
+ /// The set of values known to be live across this safepoint
StatepointLiveSetTy liveset;
/// Mapping from live pointers to a base-defining-value
if (PrintLiveSet) {
// Note: This output is used by several of the test cases
- // The order of elemtns in a set is not stable, put them in a vec and sort
+ // The order of elements in a set is not stable, put them in a vec and sort
// by name
SmallVector<Value *, 64> temp;
temp.insert(temp.end(), liveset.begin(), liveset.end());
static bool isKnownBaseResult(Value *V);
/// Helper function for findBasePointer - Will return a value which either a)
-/// defines the base pointer for the input or b) blocks the simple search
-/// (i.e. a PHI or Select of two derived pointers)
+/// defines the base pointer for the input, b) blocks the simple search
+/// (i.e. a PHI or Select of two derived pointers), or c) involves a change
+/// from pointer to vector type or back.
static Value *findBaseDefiningValue(Value *I) {
if (I->getType()->isVectorTy())
return findBaseDefiningValueOfVector(I).first;
assert(I->getType()->isPointerTy() &&
"Illegal to ask for the base pointer of a non-pointer type");
- // This case is a bit of a hack - it only handles extracts from vectors which
- // trivially contain only base pointers or cases where we can directly match
- // the index of the original extract element to an insertion into the vector.
- // See note inside the function for how to improve this.
- if (auto *EEI = dyn_cast<ExtractElementInst>(I)) {
- Value *VectorOperand = EEI->getVectorOperand();
- Value *Index = EEI->getIndexOperand();
- std::pair<Value *, bool> pair =
- findBaseDefiningValueOfVector(VectorOperand, Index);
- Value *VectorBase = pair.first;
- if (VectorBase->getType()->isPointerTy())
- // We found a BDV for this specific element with the vector. This is an
- // optimization, but in practice it covers most of the useful cases
- // created via scalarization.
- return VectorBase;
- else {
- assert(VectorBase->getType()->isVectorTy());
- if (pair.second)
- // If the entire vector returned is known to be entirely base pointers,
- // then the extractelement is valid base for this value.
- return EEI;
- else {
- // Otherwise, we have an instruction which potentially produces a
- // derived pointer and we need findBasePointers to clone code for us
- // such that we can create an instruction which produces the
- // accompanying base pointer.
- // Note: This code is currently rather incomplete. We don't currently
- // support the general form of shufflevector of insertelement.
- // Conceptually, these are just 'base defining values' of the same
- // variety as phi or select instructions. We need to update the
- // findBasePointers algorithm to insert new 'base-only' versions of the
- // original instructions. This is relative straight forward to do, but
- // the case which would motivate the work hasn't shown up in real
- // workloads yet.
- assert((isa<PHINode>(VectorBase) || isa<SelectInst>(VectorBase)) &&
- "need to extend findBasePointers for generic vector"
- "instruction cases");
- return VectorBase;
- }
- }
- }
-
if (isa<Argument>(I))
// An incoming argument to the function is a base pointer
// We should have never reached here if this argument isn't an gc value
return I;
// I have absolutely no idea how to implement this part yet. It's not
- // neccessarily hard, I just haven't really looked at it yet.
+ // necessarily hard, I just haven't really looked at it yet.
assert(!isa<LandingPadInst>(I) && "Landing Pad is unimplemented");
if (isa<AtomicCmpXchgInst>(I))
assert(!isa<InsertValueInst>(I) &&
"Base pointer for a struct is meaningless");
+ // An extractelement produces a base result exactly when it's input does.
+ // We may need to insert a parallel instruction to extract the appropriate
+ // element out of the base vector corresponding to the input. Given this,
+ // it's analogous to the phi and select case even though it's not a merge.
+ if (auto *EEI = dyn_cast<ExtractElementInst>(I)) {
+ Value *VectorOperand = EEI->getVectorOperand();
+ Value *Index = EEI->getIndexOperand();
+ std::pair<Value *, bool> pair =
+ findBaseDefiningValueOfVector(VectorOperand, Index);
+ Value *VectorBase = pair.first;
+ if (VectorBase->getType()->isPointerTy())
+ // We found a BDV for this specific element with the vector. This is an
+ // optimization, but in practice it covers most of the useful cases
+ // created via scalarization. Note: The peephole optimization here is
+ // currently needed for correctness since the general algorithm doesn't
+ // yet handle insertelements. That will change shortly.
+ return VectorBase;
+ else {
+ assert(VectorBase->getType()->isVectorTy());
+ // Otherwise, we have an instruction which potentially produces a
+ // derived pointer and we need findBasePointers to clone code for us
+ // such that we can create an instruction which produces the
+ // accompanying base pointer.
+ return EEI;
+ }
+ }
+
// The last two cases here don't return a base pointer. Instead, they
- // return a value which dynamically selects from amoung several base
+ // return a value which dynamically selects from among several base
// derived pointers (each with it's own base potentially). It's the job of
// the caller to resolve these.
assert((isa<SelectInst>(I) || isa<PHINode>(I)) &&
/// Given the result of a call to findBaseDefiningValue, or findBaseOrBDV,
/// is it known to be a base pointer? Or do we need to continue searching.
static bool isKnownBaseResult(Value *V) {
- if (!isa<PHINode>(V) && !isa<SelectInst>(V)) {
+ if (!isa<PHINode>(V) && !isa<SelectInst>(V) && !isa<ExtractElementInst>(V)) {
// no recursion possible
return true;
}
//
// Note: A simpler form of this would be to add the conflict form of all
// PHIs without running the optimistic algorithm. This would be
- // analougous to pessimistic data flow and would likely lead to an
+ // analogous to pessimistic data flow and would likely lead to an
// overall worse solution.
#ifndef NDEBUG
auto isExpectedBDVType = [](Value *BDV) {
- return isa<PHINode>(BDV) || isa<SelectInst>(BDV);
+ return isa<PHINode>(BDV) || isa<SelectInst>(BDV) || isa<ExtractElementInst>(BDV);
};
#endif
if (PHINode *Phi = dyn_cast<PHINode>(Current)) {
for (Value *InVal : Phi->incoming_values())
visitIncomingValue(InVal);
- } else {
- SelectInst *Sel = cast<SelectInst>(Current);
+ } else if (SelectInst *Sel = dyn_cast<SelectInst>(Current)) {
visitIncomingValue(Sel->getTrueValue());
visitIncomingValue(Sel->getFalseValue());
+ } else if (auto *EE = dyn_cast<ExtractElementInst>(Current)) {
+ visitIncomingValue(EE->getVectorOperand());
+ } else {
+ // There are two classes of instructions we know we don't handle.
+ assert(isa<ShuffleVectorInst>(Current) ||
+ isa<InsertElementInst>(Current));
+ llvm_unreachable("unimplemented instruction case");
}
}
// The frontier of visited instructions are the ones we might need to
if (TraceLSP) {
errs() << "States after initialization:\n";
for (auto Pair : states)
- dbgs() << " " << Pair.second << " for " << Pair.first << "\n";
+ dbgs() << " " << Pair.second << " for " << *Pair.first << "\n";
}
// TODO: come back and revisit the state transitions around inputs which
if (SelectInst *select = dyn_cast<SelectInst>(v)) {
calculateMeet.meetWith(getStateForInput(select->getTrueValue()));
calculateMeet.meetWith(getStateForInput(select->getFalseValue()));
- } else
- for (Value *Val : cast<PHINode>(v)->incoming_values())
+ } else if (PHINode *Phi = dyn_cast<PHINode>(v)) {
+ for (Value *Val : Phi->incoming_values())
calculateMeet.meetWith(getStateForInput(Val));
+ } else {
+ // The 'meet' for an extractelement is slightly trivial, but it's still
+ // useful in that it drives us to conflict if our input is.
+ auto *EE = cast<ExtractElementInst>(v);
+ calculateMeet.meetWith(getStateForInput(EE->getVectorOperand()));
+ }
+
BDVState oldState = states[v];
BDVState newState = calculateMeet.getResult();
if (TraceLSP) {
errs() << "States after meet iteration:\n";
for (auto Pair : states)
- dbgs() << " " << Pair.second << " for " << Pair.first << "\n";
+ dbgs() << " " << Pair.second << " for " << *Pair.first << "\n";
}
// Insert Phis for all conflicts
BDVState State = states[I];
assert(!isKnownBaseResult(I) && "why did it get added?");
assert(!State.isUnknown() && "Optimistic algorithm didn't complete!");
+
+ // extractelement instructions are a bit special in that we may need to
+ // insert an extract even when we know an exact base for the instruction.
+ // The problem is that we need to convert from a vector base to a scalar
+ // base for the particular indice we're interested in.
+ if (State.isBase() && isa<ExtractElementInst>(I) &&
+ isa<VectorType>(State.getBase()->getType())) {
+ auto *EE = cast<ExtractElementInst>(I);
+ // TODO: In many cases, the new instruction is just EE itself. We should
+ // exploit this, but can't do it here since it would break the invariant
+ // about the BDV not being known to be a base.
+ auto *BaseInst = ExtractElementInst::Create(State.getBase(),
+ EE->getIndexOperand(),
+ "base_ee", EE);
+ BaseInst->setMetadata("is_base_value", MDNode::get(I->getContext(), {}));
+ states[I] = BDVState(BDVState::Base, BaseInst);
+ }
+
if (!State.isConflict())
continue;
std::string Name = I->hasName() ?
(I->getName() + ".base").str() : "base_phi";
return PHINode::Create(I->getType(), NumPreds, Name, I);
+ } else if (SelectInst *Sel = dyn_cast<SelectInst>(I)) {
+ // The undef will be replaced later
+ UndefValue *Undef = UndefValue::get(Sel->getType());
+ std::string Name = I->hasName() ?
+ (I->getName() + ".base").str() : "base_select";
+ return SelectInst::Create(Sel->getCondition(), Undef,
+ Undef, Name, Sel);
+ } else {
+ auto *EE = cast<ExtractElementInst>(I);
+ UndefValue *Undef = UndefValue::get(EE->getVectorOperand()->getType());
+ std::string Name = I->hasName() ?
+ (I->getName() + ".base").str() : "base_ee";
+ return ExtractElementInst::Create(Undef, EE->getIndexOperand(), Name,
+ EE);
}
- SelectInst *Sel = cast<SelectInst>(I);
- // The undef will be replaced later
- UndefValue *Undef = UndefValue::get(Sel->getType());
- std::string Name = I->hasName() ?
- (I->getName() + ".base").str() : "base_select";
- return SelectInst::Create(Sel->getCondition(), Undef,
- Undef, Name, Sel);
};
Instruction *BaseInst = MakeBaseInstPlaceholder(I);
// Add metadata marking this as a base value
assert(base != nullptr && "unknown BDVState!");
}
- // In essense this assert states: the only way two
+ // In essence this assert states: the only way two
// values incoming from the same basic block may be
// different is by being different bitcasts of the same
// value. A cleanup that remains TODO is changing
basephi->addIncoming(base, InBB);
}
assert(basephi->getNumIncomingValues() == NumPHIValues);
- } else {
- SelectInst *basesel = cast<SelectInst>(state.getBase());
+ } else if (SelectInst *basesel = dyn_cast<SelectInst>(state.getBase())) {
SelectInst *sel = cast<SelectInst>(v);
// Operand 1 & 2 are true, false path respectively. TODO: refactor to
// something more safe and less hacky.
}
basesel->setOperand(i, base);
}
+ } else {
+ auto *BaseEE = cast<ExtractElementInst>(state.getBase());
+ Value *InVal = cast<ExtractElementInst>(v)->getVectorOperand();
+ Value *Base = findBaseOrBDV(InVal, cache);
+ if (!isKnownBaseResult(Base)) {
+ // Either conflict or base.
+ assert(states.count(Base));
+ Base = states[Base].getBase();
+ assert(Base != nullptr && "unknown BDVState!");
+ }
+ assert(Base && "can't be null");
+ BaseEE->setOperand(0, Base);
+ }
+ }
+
+ // Now that we're done with the algorithm, see if we can optimize the
+ // results slightly by reducing the number of new instructions needed.
+ // Arguably, this should be integrated into the algorithm above, but
+ // doing as a post process step is easier to reason about for the moment.
+ DenseMap<Value *, Value *> ReverseMap;
+ SmallPtrSet<Instruction *, 16> NewInsts;
+ SmallSetVector<Instruction *, 16> Worklist;
+ for (auto Item : states) {
+ Value *V = Item.first;
+ Value *Base = Item.second.getBase();
+ assert(V && Base);
+ assert(!isKnownBaseResult(V) && "why did it get added?");
+ assert(isKnownBaseResult(Base) &&
+ "must be something we 'know' is a base pointer");
+ if (!Item.second.isConflict())
+ continue;
+
+ ReverseMap[Base] = V;
+ if (auto *BaseI = dyn_cast<Instruction>(Base)) {
+ NewInsts.insert(BaseI);
+ Worklist.insert(BaseI);
+ }
+ }
+ auto PushNewUsers = [&](Instruction *I) {
+ for (User *U : I->users())
+ if (auto *UI = dyn_cast<Instruction>(U))
+ if (NewInsts.count(UI))
+ Worklist.insert(UI);
+ };
+ const DataLayout &DL = cast<Instruction>(def)->getModule()->getDataLayout();
+ while (!Worklist.empty()) {
+ Instruction *BaseI = Worklist.pop_back_val();
+ Value *Bdv = ReverseMap[BaseI];
+ if (auto *BdvI = dyn_cast<Instruction>(Bdv))
+ if (BaseI->isIdenticalTo(BdvI)) {
+ DEBUG(dbgs() << "Identical Base: " << *BaseI << "\n");
+ PushNewUsers(BaseI);
+ BaseI->replaceAllUsesWith(Bdv);
+ BaseI->eraseFromParent();
+ states[Bdv] = BDVState(BDVState::Conflict, Bdv);
+ NewInsts.erase(BaseI);
+ ReverseMap.erase(BaseI);
+ continue;
+ }
+ if (Value *V = SimplifyInstruction(BaseI, DL)) {
+ DEBUG(dbgs() << "Base " << *BaseI << " simplified to " << *V << "\n");
+ PushNewUsers(BaseI);
+ BaseI->replaceAllUsesWith(V);
+ BaseI->eraseFromParent();
+ states[Bdv] = BDVState(BDVState::Conflict, V);
+ NewInsts.erase(BaseI);
+ ReverseMap.erase(BaseI);
+ continue;
}
}
Value *v = item.first;
Value *base = item.second.getBase();
assert(v && base);
- assert(!isKnownBaseResult(v) && "why did it get added?");
if (TraceLSP) {
std::string fromstr =
<< " to: " << (base->hasName() ? base->getName() : "") << "\n";
}
- assert(isKnownBaseResult(base) &&
- "must be something we 'know' is a base pointer");
if (cache.count(v)) {
// Once we transition from the BDV relation being store in the cache to
// the base relation being stored, it must be stable
// If you see this trip and like to live really dangerously, the code should
// be correct, just with idioms the verifier can't handle. You can try
- // disabling the verifier at your own substaintial risk.
+ // disabling the verifier at your own substantial risk.
assert(!isa<ConstantPointerNull>(base) &&
"the relocation code needs adjustment to handle the relocation of "
"a null pointer constant without causing false positives in the "
Function &F, DominatorTree &DT, Pass *P, ArrayRef<CallSite> toUpdate,
MutableArrayRef<struct PartiallyConstructedSafepointRecord> records) {
// TODO-PERF: reuse the original liveness, then simply run the dataflow
- // again. The old values are still live and will help it stablize quickly.
+ // again. The old values are still live and will help it stabilize quickly.
GCPtrLivenessData RevisedLivenessData;
computeLiveInValues(DT, F, RevisedLivenessData);
for (size_t i = 0; i < records.size(); i++) {
return index;
}
-// Create new attribute set containing only attributes which can be transfered
+// Create new attribute set containing only attributes which can be transferred
// from original call to the safepoint.
static AttributeSet legalizeCallAttributes(AttributeSet AS) {
AttributeSet ret;
// Currently we will fail on parameter attributes and on certain
// function attributes.
AttributeSet new_attrs = legalizeCallAttributes(toReplace->getAttributes());
- // In case if we can handle this set of sttributes - set up function attrs
+ // In case if we can handle this set of attributes - set up function attrs
// directly on statepoint and return attrs later for gc_result intrinsic.
call->setAttributes(new_attrs.getFnAttributes());
return_attributes = new_attrs.getRetAttributes();
// Currently we will fail on parameter attributes and on certain
// function attributes.
AttributeSet new_attrs = legalizeCallAttributes(toReplace->getAttributes());
- // In case if we can handle this set of sttributes - set up function attrs
+ // In case if we can handle this set of attributes - set up function attrs
// directly on statepoint and return attrs later for gc_result intrinsic.
invoke->setAttributes(new_attrs.getFnAttributes());
return_attributes = new_attrs.getRetAttributes();
VisitedLiveValues);
if (ClobberNonLive) {
- // As a debuging aid, pretend that an unrelocated pointer becomes null at
+ // As a debugging aid, pretend that an unrelocated pointer becomes null at
// the gc.statepoint. This will turn some subtle GC problems into
// slightly easier to debug SEGVs. Note that on large IR files with
// lots of gc.statepoints this is extremely costly both memory and time
/// Remove any vector of pointers from the liveset by scalarizing them over the
/// statepoint instruction. Adds the scalarized pieces to the liveset. It
-/// would be preferrable to include the vector in the statepoint itself, but
+/// would be preferable to include the vector in the statepoint itself, but
/// the lowering code currently does not handle that. Extending it would be
/// slightly non-trivial since it requires a format change. Given how rare
-/// such cases are (for the moment?) scalarizing is an acceptable comprimise.
+/// such cases are (for the moment?) scalarizing is an acceptable compromise.
static void splitVectorValues(Instruction *StatepointInst,
StatepointLiveSetTy &LiveSet,
DenseMap<Value *, Value *>& PointerToBase,
// Helper function for the "rematerializeLiveValues". It walks use chain
// starting from the "CurrentValue" until it meets "BaseValue". Only "simple"
// values are visited (currently it is GEP's and casts). Returns true if it
-// sucessfully reached "BaseValue" and false otherwise.
+// successfully reached "BaseValue" and false otherwise.
// Fills "ChainToBase" array with all visited values. "BaseValue" is not
// recorded.
static bool findRematerializableChainToBasePointer(
}
assert(records.size() == toUpdate.size());
- // A) Identify all gc pointers which are staticly live at the given call
+ // A) Identify all gc pointers which are statically live at the given call
// site.
findLiveReferences(F, DT, P, toUpdate, records);
}
// In order to reduce live set of statepoint we might choose to rematerialize
- // some values instead of relocating them. This is purelly an optimization and
+ // some values instead of relocating them. This is purely an optimization and
// does not influence correctness.
TargetTransformInfo &TTI =
P->getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F);
LLVMContext &Ctx = F.getContext();
MDBuilder Builder(Ctx);
- for (Instruction &I : inst_range(F)) {
+ for (Instruction &I : instructions(F)) {
if (const MDNode *MD = I.getMetadata(LLVMContext::MD_tbaa)) {
assert(MD->getNumOperands() < 5 && "unrecognized metadata shape!");
bool IsImmutableTBAA =
// when rewriting. We'll delete the unreachable ones in a moment.
SmallVector<CallSite, 64> ParsePointNeeded;
bool HasUnreachableStatepoint = false;
- for (Instruction &I : inst_range(F)) {
+ for (Instruction &I : instructions(F)) {
// TODO: only the ones with the flag set!
if (isStatepoint(I)) {
if (DT.isReachableFromEntry(I.getParent()))
FoldSingleEntryPHINodes(&BB);
}
+ // Before we start introducing relocations, we want to tweak the IR a bit to
+ // avoid unfortunate code generation effects. The main example is that we
+ // want to try to make sure the comparison feeding a branch is after any
+ // safepoints. Otherwise, we end up with a comparison of pre-relocation
+ // values feeding a branch after relocation. This is semantically correct,
+ // but results in extra register pressure since both the pre-relocation and
+ // post-relocation copies must be available in registers. For code without
+ // relocations this is handled elsewhere, but teaching the scheduler to
+ // reverse the transform we're about to do would be slightly complex.
+ // Note: This may extend the live range of the inputs to the icmp and thus
+ // increase the liveset of any statepoint we move over. This is profitable
+ // as long as all statepoints are in rare blocks. If we had in-register
+ // lowering for live values this would be a much safer transform.
+ auto getConditionInst = [](TerminatorInst *TI) -> Instruction* {
+ if (auto *BI = dyn_cast<BranchInst>(TI))
+ if (BI->isConditional())
+ return dyn_cast<Instruction>(BI->getCondition());
+ // TODO: Extend this to handle switches
+ return nullptr;
+ };
+ for (BasicBlock &BB : F) {
+ TerminatorInst *TI = BB.getTerminator();
+ if (auto *Cond = getConditionInst(TI))
+ // TODO: Handle more than just ICmps here. We should be able to move
+ // most instructions without side effects or memory access.
+ if (isa<ICmpInst>(Cond) && Cond->hasOneUse()) {
+ MadeChange = true;
+ Cond->moveBefore(TI);
+ }
+ }
+
MadeChange |= insertParsePoints(F, DT, this, ParsePointNeeded);
return MadeChange;
}
"support for FCA unimplemented");
if (isHandledGCPointerType(V->getType()) && !isa<Constant>(V)) {
// The choice to exclude all things constant here is slightly subtle.
- // There are two idependent reasons:
+ // There are two independent reasons:
// - We assume that things which are constant (from LLVM's definition)
// do not move at runtime. For example, the address of a global
// variable is fixed, even though it's contents may not be.
} // while( !worklist.empty() )
#ifndef NDEBUG
- // Sanity check our ouput against SSA properties. This helps catch any
+ // Sanity check our output against SSA properties. This helps catch any
// missing kills during the above iteration.
for (BasicBlock &BB : F) {
checkBasicSSA(DT, Data, BB);
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