X-Git-Url: http://plrg.eecs.uci.edu/git/?a=blobdiff_plain;f=lib%2FTransforms%2FScalar%2FRewriteStatepointsForGC.cpp;h=031f40e2caa6c0a11adc2700080893b2ce22d0d9;hb=b4f6a50926a9b2c684594f1ec4366cae09a82976;hp=f2cdcfe02a5302d9668c1d21d0fbb43eeb9c6eb5;hpb=d92e9ef1705f8f78a7b67d6462953419559bc44c;p=oota-llvm.git diff --git a/lib/Transforms/Scalar/RewriteStatepointsForGC.cpp b/lib/Transforms/Scalar/RewriteStatepointsForGC.cpp index f2cdcfe02a5..031f40e2caa 100644 --- a/lib/Transforms/Scalar/RewriteStatepointsForGC.cpp +++ b/lib/Transforms/Scalar/RewriteStatepointsForGC.cpp @@ -14,9 +14,14 @@ #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" #include "llvm/ADT/DenseSet.h" +#include "llvm/ADT/SetVector.h" +#include "llvm/ADT/StringRef.h" +#include "llvm/ADT/MapVector.h" #include "llvm/IR/BasicBlock.h" #include "llvm/IR/CallSite.h" #include "llvm/IR/Dominators.h" @@ -27,6 +32,7 @@ #include "llvm/IR/Intrinsics.h" #include "llvm/IR/IntrinsicInst.h" #include "llvm/IR/Module.h" +#include "llvm/IR/MDBuilder.h" #include "llvm/IR/Statepoint.h" #include "llvm/IR/Value.h" #include "llvm/IR/Verifier.h" @@ -42,10 +48,6 @@ using namespace llvm; -// Print tracing output -static cl::opt TraceLSP("trace-rewrite-statepoints", cl::Hidden, - cl::init(false)); - // Print the liveset found at the insert location static cl::opt PrintLiveSet("spp-print-liveset", cl::Hidden, cl::init(false)); @@ -55,26 +57,70 @@ static cl::opt PrintLiveSetSize("spp-print-liveset-size", cl::Hidden, static cl::opt PrintBasePointers("spp-print-base-pointers", cl::Hidden, cl::init(false)); +// Cost threshold measuring when it is profitable to rematerialize value instead +// of relocating it +static cl::opt +RematerializationThreshold("spp-rematerialization-threshold", cl::Hidden, + cl::init(6)); + +#ifdef XDEBUG +static bool ClobberNonLive = true; +#else +static bool ClobberNonLive = false; +#endif +static cl::opt ClobberNonLiveOverride("rs4gc-clobber-non-live", + cl::location(ClobberNonLive), + cl::Hidden); + namespace { -struct RewriteStatepointsForGC : public FunctionPass { +struct RewriteStatepointsForGC : public ModulePass { static char ID; // Pass identification, replacement for typeid - RewriteStatepointsForGC() : FunctionPass(ID) { + RewriteStatepointsForGC() : ModulePass(ID) { initializeRewriteStatepointsForGCPass(*PassRegistry::getPassRegistry()); } - bool runOnFunction(Function &F) override; + bool runOnFunction(Function &F); + bool runOnModule(Module &M) override { + bool Changed = false; + for (Function &F : M) + Changed |= runOnFunction(F); + + if (Changed) { + // stripDereferenceabilityInfo asserts that shouldRewriteStatepointsIn + // returns true for at least one function in the module. Since at least + // one function changed, we know that the precondition is satisfied. + stripDereferenceabilityInfo(M); + } + + return Changed; + } void getAnalysisUsage(AnalysisUsage &AU) const override { // We add and rewrite a bunch of instructions, but don't really do much // else. We could in theory preserve a lot more analyses here. AU.addRequired(); - } + AU.addRequired(); + } + + /// The IR fed into RewriteStatepointsForGC may have had attributes implying + /// dereferenceability that are no longer valid/correct after + /// RewriteStatepointsForGC has run. This is because semantically, after + /// RewriteStatepointsForGC runs, all calls to gc.statepoint "free" the entire + /// heap. stripDereferenceabilityInfo (conservatively) restores correctness + /// by erasing all attributes in the module that externally imply + /// dereferenceability. + /// + void stripDereferenceabilityInfo(Module &M); + + // Helpers for stripDereferenceabilityInfo + void stripDereferenceabilityInfoFromBody(Function &F); + void stripDereferenceabilityInfoFromPrototype(Function &F); }; } // namespace char RewriteStatepointsForGC::ID = 0; -FunctionPass *llvm::createRewriteStatepointsForGCPass() { +ModulePass *llvm::createRewriteStatepointsForGCPass() { return new RewriteStatepointsForGC(); } @@ -113,18 +159,15 @@ struct GCPtrLivenessData { // types, then update all the second type to the first type typedef DenseMap DefiningValueMapTy; typedef DenseSet StatepointLiveSetTy; +typedef DenseMap 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 DenseMap PointerToBase; - /// Any new values which were added to the IR during base pointer analysis - /// for this safepoint - DenseSet NewInsertedDefs; - /// The *new* gc.statepoint instruction itself. This produces the token /// that normal path gc.relocates and the gc.result are tied to. Instruction *StatepointToken; @@ -132,6 +175,11 @@ struct PartiallyConstructedSafepointRecord { /// Instruction to which exceptional gc relocates are attached /// Makes it easier to iterate through them during relocationViaAlloca. Instruction *UnwindToken; + + /// Record live values we are rematerialized instead of relocating. + /// They are not included into 'liveset' field. + /// Maps rematerialized copy to it's original value. + RematerializedValueMapTy RematerializedValues; }; } @@ -147,8 +195,8 @@ static void findLiveSetAtInst(Instruction *inst, GCPtrLivenessData &Data, // TODO: Once we can get to the GCStrategy, this becomes // Optional isGCManagedPointer(const Value *V) const override { -static bool isGCPointerType(const Type *T) { - if (const PointerType *PT = dyn_cast(T)) +static bool isGCPointerType(Type *T) { + if (auto *PT = dyn_cast(T)) // For the sake of this example GC, we arbitrarily pick addrspace(1) as our // GC managed heap. We know that a pointer into this heap needs to be // updated and that no other pointer does. @@ -224,16 +272,14 @@ static void analyzeParsePointLiveness( 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 temp; - temp.insert(temp.end(), liveset.begin(), liveset.end()); - std::sort(temp.begin(), temp.end(), order_by_name); + SmallVector Temp; + Temp.insert(Temp.end(), liveset.begin(), liveset.end()); + std::sort(Temp.begin(), Temp.end(), order_by_name); errs() << "Live Variables:\n"; - for (Value *V : temp) { - errs() << " " << V->getName(); // no newline - V->dump(); - } + for (Value *V : Temp) + dbgs() << " " << V->getName() << " " << *V << "\n"; } if (PrintLiveSetSize) { errs() << "Safepoint For: " << CS.getCalledValue()->getName() << "\n"; @@ -242,9 +288,47 @@ static void analyzeParsePointLiveness( result.liveset = liveset; } -/// If we can trivially determine that this vector contains only base pointers, -/// return the base instruction. -static Value *findBaseOfVector(Value *I) { +static bool isKnownBaseResult(Value *V); +namespace { +/// A single base defining value - An immediate base defining value for an +/// instruction 'Def' is an input to 'Def' whose base is also a base of 'Def'. +/// For instructions which have multiple pointer [vector] inputs or that +/// transition between vector and scalar types, there is no immediate base +/// defining value. The 'base defining value' for 'Def' is the transitive +/// closure of this relation stopping at the first instruction which has no +/// immediate base defining value. The b.d.v. might itself be a base pointer, +/// but it can also be an arbitrary derived pointer. +struct BaseDefiningValueResult { + /// Contains the value which is the base defining value. + Value * const BDV; + /// True if the base defining value is also known to be an actual base + /// pointer. + const bool IsKnownBase; + BaseDefiningValueResult(Value *BDV, bool IsKnownBase) + : BDV(BDV), IsKnownBase(IsKnownBase) { +#ifndef NDEBUG + // Check consistency between new and old means of checking whether a BDV is + // a base. + bool MustBeBase = isKnownBaseResult(BDV); + assert(!MustBeBase || MustBeBase == IsKnownBase); +#endif + } +}; +} + +static BaseDefiningValueResult findBaseDefiningValue(Value *I); + +/// Return a base defining value for the 'Index' element of the given vector +/// instruction 'I'. If Index is null, returns a BDV for the entire vector +/// 'I'. As an optimization, this method will try to determine when the +/// element is known to already be a base pointer. If this can be established, +/// the second value in the returned pair will be true. Note that either a +/// vector or a pointer typed value can be returned. For the former, the +/// vector returned is a BDV (and possibly a base) of the entire vector 'I'. +/// If the later, the return pointer is a BDV (or possibly a base) for the +/// particular element in 'I'. +static BaseDefiningValueResult +findBaseDefiningValueOfVector(Value *I, Value *Index = nullptr) { assert(I->getType()->isVectorTy() && cast(I->getType())->getElementType()->isPointerTy() && "Illegal to ask for the base pointer of a non-pointer type"); @@ -254,7 +338,7 @@ static Value *findBaseOfVector(Value *I) { if (isa(I)) // An incoming argument to the function is a base pointer - return I; + return BaseDefiningValueResult(I, true); // We shouldn't see the address of a global as a vector value? assert(!isa(I) && @@ -265,7 +349,7 @@ static Value *findBaseOfVector(Value *I) { if (isa(I)) // utterly meaningless, but useful for dealing with partially optimized // code. - return I; + return BaseDefiningValueResult(I, true); // Due to inheritance, this must be _after_ the global variable and undef // checks @@ -273,57 +357,86 @@ static Value *findBaseOfVector(Value *I) { assert(!isa(I) && !isa(I) && "order of checks wrong!"); assert(Con->isNullValue() && "null is the only case which makes sense"); - return Con; + return BaseDefiningValueResult(Con, true); } - + if (isa(I)) - return I; - - // Note: This code is currently rather incomplete. We are essentially only - // handling cases where the vector element is trivially a base pointer. We - // need to update the entire base pointer construction algorithm to know how - // to track vector elements and potentially scalarize, but the case which - // would motivate the work hasn't shown up in real workloads yet. - llvm_unreachable("no base found for vector element"); + return BaseDefiningValueResult(I, true); + + // For an insert element, we might be able to look through it if we know + // something about the indexes. + if (InsertElementInst *IEI = dyn_cast(I)) { + if (Index) { + Value *InsertIndex = IEI->getOperand(2); + // This index is inserting the value, look for its BDV + if (InsertIndex == Index) + return findBaseDefiningValue(IEI->getOperand(1)); + // Both constant, and can't be equal per above. This insert is definitely + // not relevant, look back at the rest of the vector and keep trying. + if (isa(Index) && isa(InsertIndex)) + return findBaseDefiningValueOfVector(IEI->getOperand(0), Index); + } + + // If both inputs to the insertelement are known bases, then so is the + // insertelement itself. NOTE: This should be handled within the generic + // base pointer inference code and after http://reviews.llvm.org/D12583, + // will be. However, when strengthening asserts I needed to add this to + // keep an existing test passing which was 'working'. FIXME + if (findBaseDefiningValue(IEI->getOperand(0)).IsKnownBase && + findBaseDefiningValue(IEI->getOperand(1)).IsKnownBase) + return BaseDefiningValueResult(IEI, true); + + // We don't know whether this vector contains entirely base pointers or + // not. To be conservatively correct, we treat it as a BDV and will + // duplicate code as needed to construct a parallel vector of bases. + return BaseDefiningValueResult(IEI, false); + } + + if (isa(I)) + // We don't know whether this vector contains entirely base pointers or + // not. To be conservatively correct, we treat it as a BDV and will + // duplicate code as needed to construct a parallel vector of bases. + // TODO: There a number of local optimizations which could be applied here + // for particular sufflevector patterns. + return BaseDefiningValueResult(I, false); + + // A PHI or Select is a base defining value. The outer findBasePointer + // algorithm is responsible for constructing a base value for this BDV. + assert((isa(I) || isa(I)) && + "unknown vector instruction - no base found for vector element"); + return BaseDefiningValueResult(I, false); } /// 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) -static Value *findBaseDefiningValue(Value *I) { +/// 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 BaseDefiningValueResult findBaseDefiningValue(Value *I) { + if (I->getType()->isVectorTy()) + return findBaseDefiningValueOfVector(I); + 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. See note inside the function for - // how to improve this. - if (auto *EEI = dyn_cast(I)) { - Value *VectorOperand = EEI->getVectorOperand(); - Value *VectorBase = findBaseOfVector(VectorOperand); - (void)VectorBase; - assert(VectorBase && "extract element not known to be a trivial base"); - return EEI; - } - if (isa(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; + return BaseDefiningValueResult(I, true); if (isa(I)) // base case - return I; + return BaseDefiningValueResult(I, true); // inlining could possibly introduce phi node that contains // undef if callee has multiple returns if (isa(I)) // utterly meaningless, but useful for dealing with // partially optimized code. - return I; + return BaseDefiningValueResult(I, true); // Due to inheritance, this must be _after_ the global variable and undef // checks - if (Constant *Con = dyn_cast(I)) { + if (isa(I)) { assert(!isa(I) && !isa(I) && "order of checks wrong!"); // Note: Finding a constant base for something marked for relocation @@ -334,9 +447,9 @@ static Value *findBaseDefiningValue(Value *I) { // off a potentially null value and have proven it null. We also use // null pointers in dead paths of relocation phis (which we might later // want to find a base pointer for). - assert(isa(Con) && + assert(isa(I) && "null is the only case which makes sense"); - return Con; + return BaseDefiningValueResult(I, true); } if (CastInst *CI = dyn_cast(I)) { @@ -349,7 +462,9 @@ static Value *findBaseDefiningValue(Value *I) { } if (isa(I)) - return I; // The value loaded is an gc base itself + // The value loaded is an gc base itself + return BaseDefiningValueResult(I, true); + if (GetElementPtrInst *GEP = dyn_cast(I)) // The base of this GEP is the base @@ -383,17 +498,17 @@ static Value *findBaseDefiningValue(Value *I) { // pointers. This should probably be generalized via attributes to support // both source language and internal functions. if (isa(I) || isa(I)) - return I; + return BaseDefiningValueResult(I, true); // 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(I) && "Landing Pad is unimplemented"); if (isa(I)) // A CAS is effectively a atomic store and load combined under a // predicate. From the perspective of base pointers, we just treat it // like a load. - return I; + return BaseDefiningValueResult(I, true); assert(!isa(I) && "Xchg handled above, all others are " "binary ops which don't apply to pointers"); @@ -402,34 +517,57 @@ static Value *findBaseDefiningValue(Value *I) { // stack, but in either case, this is simply a field load. As a result, // this is a defining definition of the base just like a load is. if (isa(I)) - return I; + return BaseDefiningValueResult(I, true); // We should never see an insert vector since that would require we be // tracing back a struct value not a pointer value. assert(!isa(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(I)) { + Value *VectorOperand = EEI->getVectorOperand(); + Value *Index = EEI->getIndexOperand(); + auto VecResult = findBaseDefiningValueOfVector(VectorOperand, Index); + Value *VectorBase = VecResult.BDV; + 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 BaseDefiningValueResult(VectorBase, VecResult.IsKnownBase); + 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 BaseDefiningValueResult(I, VecResult.IsKnownBase); + } + } + // 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(I) || isa(I)) && "missing instruction case in findBaseDefiningValing"); - return I; + return BaseDefiningValueResult(I, false); } /// Returns the base defining value for this value. static Value *findBaseDefiningValueCached(Value *I, DefiningValueMapTy &Cache) { Value *&Cached = Cache[I]; if (!Cached) { - Cached = findBaseDefiningValue(I); + Cached = findBaseDefiningValue(I).BDV; + DEBUG(dbgs() << "fBDV-cached: " << I->getName() << " -> " + << Cached->getName() << "\n"); } assert(Cache[I] != nullptr); - - if (TraceLSP) { - dbgs() << "fBDV-cached: " << I->getName() << " -> " << Cached->getName() - << "\n"; - } return Cached; } @@ -449,7 +587,7 @@ static Value *findBaseOrBDV(Value *I, DefiningValueMapTy &Cache) { /// 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(V) && !isa(V)) { + if (!isa(V) && !isa(V) && !isa(V)) { // no recursion possible return true; } @@ -464,17 +602,19 @@ static bool isKnownBaseResult(Value *V) { return false; } -// TODO: find a better name for this namespace { -class PhiState { +/// Models the state of a single base defining value in the findBasePointer +/// algorithm for determining where a new instruction is needed to propagate +/// the base of this BDV. +class BDVState { public: enum Status { Unknown, Base, Conflict }; - PhiState(Status s, Value *b = nullptr) : status(s), base(b) { + BDVState(Status s, Value *b = nullptr) : status(s), base(b) { assert(status != Base || b); } - PhiState(Value *b) : status(Base), base(b) {} - PhiState() : status(Unknown), base(nullptr) {} + explicit BDVState(Value *b) : status(Base), base(b) {} + BDVState() : status(Unknown), base(nullptr) {} Status getStatus() const { return status; } Value *getBase() const { return base; } @@ -483,72 +623,80 @@ public: bool isUnknown() const { return getStatus() == Unknown; } bool isConflict() const { return getStatus() == Conflict; } - bool operator==(const PhiState &other) const { + bool operator==(const BDVState &other) const { return base == other.base && status == other.status; } - bool operator!=(const PhiState &other) const { return !(*this == other); } + bool operator!=(const BDVState &other) const { return !(*this == other); } - void dump() { - errs() << status << " (" << base << " - " - << (base ? base->getName() : "nullptr") << "): "; + LLVM_DUMP_METHOD + void dump() const { print(dbgs()); dbgs() << '\n'; } + + void print(raw_ostream &OS) const { + switch (status) { + case Unknown: + OS << "U"; + break; + case Base: + OS << "B"; + break; + case Conflict: + OS << "C"; + break; + }; + OS << " (" << base << " - " + << (base ? base->getName() : "nullptr") << "): "; } private: Status status; Value *base; // non null only if status == base }; +} -typedef DenseMap ConflictStateMapTy; -// Values of type PhiState form a lattice, and this is a helper +#ifndef NDEBUG +static raw_ostream &operator<<(raw_ostream &OS, const BDVState &State) { + State.print(OS); + return OS; +} +#endif + +namespace { +// Values of type BDVState form a lattice, and this is a helper // class that implementes the meet operation. The meat of the meet -// operation is implemented in MeetPhiStates::pureMeet -class MeetPhiStates { +// operation is implemented in MeetBDVStates::pureMeet +class MeetBDVStates { public: - // phiStates is a mapping from PHINodes and SelectInst's to PhiStates. - explicit MeetPhiStates(const ConflictStateMapTy &phiStates) - : phiStates(phiStates) {} - - // Destructively meet the current result with the base V. V can - // either be a merge instruction (SelectInst / PHINode), in which - // case its status is looked up in the phiStates map; or a regular - // SSA value, in which case it is assumed to be a base. - void meetWith(Value *V) { - PhiState otherState = getStateForBDV(V); - assert((MeetPhiStates::pureMeet(otherState, currentResult) == - MeetPhiStates::pureMeet(currentResult, otherState)) && - "math is wrong: meet does not commute!"); - currentResult = MeetPhiStates::pureMeet(otherState, currentResult); + /// Initializes the currentResult to the TOP state so that if can be met with + /// any other state to produce that state. + MeetBDVStates() {} + + // Destructively meet the current result with the given BDVState + void meetWith(BDVState otherState) { + currentResult = meet(otherState, currentResult); } - PhiState getResult() const { return currentResult; } + BDVState getResult() const { return currentResult; } private: - const ConflictStateMapTy &phiStates; - PhiState currentResult; - - /// Return a phi state for a base defining value. We'll generate a new - /// base state for known bases and expect to find a cached state otherwise - PhiState getStateForBDV(Value *baseValue) { - if (isKnownBaseResult(baseValue)) { - return PhiState(baseValue); - } else { - return lookupFromMap(baseValue); - } - } + BDVState currentResult; - PhiState lookupFromMap(Value *V) { - auto I = phiStates.find(V); - assert(I != phiStates.end() && "lookup failed!"); - return I->second; + /// Perform a meet operation on two elements of the BDVState lattice. + static BDVState meet(BDVState LHS, BDVState RHS) { + assert((pureMeet(LHS, RHS) == pureMeet(RHS, LHS)) && + "math is wrong: meet does not commute!"); + BDVState Result = pureMeet(LHS, RHS); + DEBUG(dbgs() << "meet of " << LHS << " with " << RHS + << " produced " << Result << "\n"); + return Result; } - static PhiState pureMeet(const PhiState &stateA, const PhiState &stateB) { + static BDVState pureMeet(const BDVState &stateA, const BDVState &stateB) { switch (stateA.getStatus()) { - case PhiState::Unknown: + case BDVState::Unknown: return stateB; - case PhiState::Base: + case BDVState::Base: assert(stateA.getBase() && "can't be null"); if (stateB.isUnknown()) return stateA; @@ -558,24 +706,25 @@ private: assert(stateA == stateB && "equality broken!"); return stateA; } - return PhiState(PhiState::Conflict); + return BDVState(BDVState::Conflict); } assert(stateB.isConflict() && "only three states!"); - return PhiState(PhiState::Conflict); + return BDVState(BDVState::Conflict); - case PhiState::Conflict: + case BDVState::Conflict: return stateA; } llvm_unreachable("only three states!"); } }; } + + /// For a given value or instruction, figure out what base ptr it's derived /// from. For gc objects, this is simply itself. On success, returns a value /// which is the base pointer. (This is reliable and can be used for /// relocation.) On failure, returns nullptr. -static Value *findBasePointer(Value *I, DefiningValueMapTy &cache, - DenseSet &NewInsertedDefs) { +static Value *findBasePointer(Value *I, DefiningValueMapTy &cache) { Value *def = findBaseOrBDV(I, cache); if (isKnownBaseResult(def)) { @@ -601,64 +750,76 @@ static Value *findBasePointer(Value *I, DefiningValueMapTy &cache, // // 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. - ConflictStateMapTy states; - states[def] = PhiState(); - // Recursively fill in all phis & selects reachable from the initial one - // for which we don't already know a definite base value for - // TODO: This should be rewritten with a worklist - bool done = false; - while (!done) { - done = true; - // Since we're adding elements to 'states' as we run, we can't keep - // iterators into the set. - SmallVector Keys; - Keys.reserve(states.size()); - for (auto Pair : states) { - Value *V = Pair.first; - Keys.push_back(V); - } - for (Value *v : Keys) { - assert(!isKnownBaseResult(v) && "why did it get added?"); - if (PHINode *phi = dyn_cast(v)) { - assert(phi->getNumIncomingValues() > 0 && - "zero input phis are illegal"); - for (Value *InVal : phi->incoming_values()) { - Value *local = findBaseOrBDV(InVal, cache); - if (!isKnownBaseResult(local) && states.find(local) == states.end()) { - states[local] = PhiState(); - done = false; - } - } - } else if (SelectInst *sel = dyn_cast(v)) { - Value *local = findBaseOrBDV(sel->getTrueValue(), cache); - if (!isKnownBaseResult(local) && states.find(local) == states.end()) { - states[local] = PhiState(); - done = false; - } - local = findBaseOrBDV(sel->getFalseValue(), cache); - if (!isKnownBaseResult(local) && states.find(local) == states.end()) { - states[local] = PhiState(); - done = false; - } +#ifndef NDEBUG + auto isExpectedBDVType = [](Value *BDV) { + return isa(BDV) || isa(BDV) || isa(BDV); + }; +#endif + + // Once populated, will contain a mapping from each potentially non-base BDV + // to a lattice value (described above) which corresponds to that BDV. + // We use the order of insertion (DFS over the def/use graph) to provide a + // stable deterministic ordering for visiting DenseMaps (which are unordered) + // below. This is important for deterministic compilation. + MapVector states; + + // Recursively fill in all base defining values reachable from the initial + // one for which we don't already know a definite base value for + /* scope */ { + SmallVector Worklist; + Worklist.push_back(def); + states.insert(std::make_pair(def, BDVState())); + while (!Worklist.empty()) { + Value *Current = Worklist.pop_back_val(); + assert(!isKnownBaseResult(Current) && "why did it get added?"); + + auto visitIncomingValue = [&](Value *InVal) { + Value *Base = findBaseOrBDV(InVal, cache); + if (isKnownBaseResult(Base)) + // Known bases won't need new instructions introduced and can be + // ignored safely + return; + assert(isExpectedBDVType(Base) && "the only non-base values " + "we see should be base defining values"); + if (states.insert(std::make_pair(Base, BDVState())).second) + Worklist.push_back(Base); + }; + if (PHINode *Phi = dyn_cast(Current)) { + for (Value *InVal : Phi->incoming_values()) + visitIncomingValue(InVal); + } else if (SelectInst *Sel = dyn_cast(Current)) { + visitIncomingValue(Sel->getTrueValue()); + visitIncomingValue(Sel->getFalseValue()); + } else if (auto *EE = dyn_cast(Current)) { + visitIncomingValue(EE->getVectorOperand()); + } else { + // There are two classes of instructions we know we don't handle. + assert(isa(Current) || + isa(Current)); + llvm_unreachable("unimplemented instruction case"); } } } - if (TraceLSP) { - errs() << "States after initialization:\n"; - for (auto Pair : states) { - Instruction *v = cast(Pair.first); - PhiState state = Pair.second; - state.dump(); - v->dump(); - } +#ifndef NDEBUG + DEBUG(dbgs() << "States after initialization:\n"); + for (auto Pair : states) { + DEBUG(dbgs() << " " << Pair.second << " for " << *Pair.first << "\n"); } +#endif - // TODO: come back and revisit the state transitions around inputs which - // have reached conflict state. The current version seems too conservative. + // Return a phi state for a base defining value. We'll generate a new + // base state for known bases and expect to find a cached state otherwise. + auto getStateForBDV = [&](Value *baseValue) { + if (isKnownBaseResult(baseValue)) + return BDVState(baseValue); + auto I = states.find(baseValue); + assert(I != states.end() && "lookup failed!"); + return I->second; + }; bool progress = true; while (progress) { @@ -666,20 +827,37 @@ static Value *findBasePointer(Value *I, DefiningValueMapTy &cache, size_t oldSize = states.size(); #endif progress = false; - // We're only changing keys in this loop, thus safe to keep iterators + // We're only changing values in this loop, thus safe to keep iterators. + // Since this is computing a fixed point, the order of visit does not + // effect the result. TODO: We could use a worklist here and make this run + // much faster. for (auto Pair : states) { - MeetPhiStates calculateMeet(states); Value *v = Pair.first; assert(!isKnownBaseResult(v) && "why did it get added?"); + + // Given an input value for the current instruction, return a BDVState + // instance which represents the BDV of that value. + auto getStateForInput = [&](Value *V) mutable { + Value *BDV = findBaseOrBDV(V, cache); + return getStateForBDV(BDV); + }; + + MeetBDVStates calculateMeet; if (SelectInst *select = dyn_cast(v)) { - calculateMeet.meetWith(findBaseOrBDV(select->getTrueValue(), cache)); - calculateMeet.meetWith(findBaseOrBDV(select->getFalseValue(), cache)); - } else - for (Value *Val : cast(v)->incoming_values()) - calculateMeet.meetWith(findBaseOrBDV(Val, cache)); - - PhiState oldState = states[v]; - PhiState newState = calculateMeet.getResult(); + calculateMeet.meetWith(getStateForInput(select->getTrueValue())); + calculateMeet.meetWith(getStateForInput(select->getFalseValue())); + } else if (PHINode *Phi = dyn_cast(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(v); + calculateMeet.meetWith(getStateForInput(EE->getVectorOperand())); + } + + BDVState oldState = states[v]; + BDVState newState = calculateMeet.getResult(); if (oldState != newState) { progress = true; states[v] = newState; @@ -690,76 +868,107 @@ static Value *findBasePointer(Value *I, DefiningValueMapTy &cache, assert(oldSize == states.size() || progress); } - if (TraceLSP) { - errs() << "States after meet iteration:\n"; - for (auto Pair : states) { - Instruction *v = cast(Pair.first); - PhiState state = Pair.second; - state.dump(); - v->dump(); - } - } - - // Insert Phis for all conflicts - // We want to keep naming deterministic in the loop that follows, so - // sort the keys before iteration. This is useful in allowing us to - // write stable tests. Note that there is no invalidation issue here. - SmallVector Keys; - Keys.reserve(states.size()); +#ifndef NDEBUG + DEBUG(dbgs() << "States after meet iteration:\n"); for (auto Pair : states) { - Value *V = Pair.first; - Keys.push_back(V); + DEBUG(dbgs() << " " << Pair.second << " for " << *Pair.first << "\n"); } - std::sort(Keys.begin(), Keys.end(), order_by_name); +#endif + + // Insert Phis for all conflicts // TODO: adjust naming patterns to avoid this order of iteration dependency - for (Value *V : Keys) { - Instruction *v = cast(V); - PhiState state = states[V]; - assert(!isKnownBaseResult(v) && "why did it get added?"); - assert(!state.isUnknown() && "Optimistic algorithm didn't complete!"); - if (!state.isConflict()) + for (auto Pair : states) { + Instruction *I = cast(Pair.first); + BDVState State = Pair.second; + 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(I) && + isa(State.getBase()->getType())) { + auto *EE = cast(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; - if (isa(v)) { - int num_preds = - std::distance(pred_begin(v->getParent()), pred_end(v->getParent())); - assert(num_preds > 0 && "how did we reach here"); - PHINode *phi = PHINode::Create(v->getType(), num_preds, "base_phi", v); - NewInsertedDefs.insert(phi); - // Add metadata marking this as a base value - auto *const_1 = ConstantInt::get( - Type::getInt32Ty( - v->getParent()->getParent()->getParent()->getContext()), - 1); - auto MDConst = ConstantAsMetadata::get(const_1); - MDNode *md = MDNode::get( - v->getParent()->getParent()->getParent()->getContext(), MDConst); - phi->setMetadata("is_base_value", md); - states[v] = PhiState(PhiState::Conflict, phi); + /// Create and insert a new instruction which will represent the base of + /// the given instruction 'I'. + auto MakeBaseInstPlaceholder = [](Instruction *I) -> Instruction* { + if (isa(I)) { + BasicBlock *BB = I->getParent(); + int NumPreds = std::distance(pred_begin(BB), pred_end(BB)); + assert(NumPreds > 0 && "how did we reach here"); + 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(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(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); + } + }; + Instruction *BaseInst = MakeBaseInstPlaceholder(I); + // Add metadata marking this as a base value + BaseInst->setMetadata("is_base_value", MDNode::get(I->getContext(), {})); + states[I] = BDVState(BDVState::Conflict, BaseInst); + } + + // Returns a instruction which produces the base pointer for a given + // instruction. The instruction is assumed to be an input to one of the BDVs + // seen in the inference algorithm above. As such, we must either already + // know it's base defining value is a base, or have inserted a new + // instruction to propagate the base of it's BDV and have entered that newly + // introduced instruction into the state table. In either case, we are + // assured to be able to determine an instruction which produces it's base + // pointer. + auto getBaseForInput = [&](Value *Input, Instruction *InsertPt) { + Value *BDV = findBaseOrBDV(Input, cache); + Value *Base = nullptr; + if (isKnownBaseResult(BDV)) { + Base = BDV; } else { - SelectInst *sel = cast(v); - // The undef will be replaced later - UndefValue *undef = UndefValue::get(sel->getType()); - SelectInst *basesel = SelectInst::Create(sel->getCondition(), undef, - undef, "base_select", sel); - NewInsertedDefs.insert(basesel); - // Add metadata marking this as a base value - auto *const_1 = ConstantInt::get( - Type::getInt32Ty( - v->getParent()->getParent()->getParent()->getContext()), - 1); - auto MDConst = ConstantAsMetadata::get(const_1); - MDNode *md = MDNode::get( - v->getParent()->getParent()->getParent()->getContext(), MDConst); - basesel->setMetadata("is_base_value", md); - states[v] = PhiState(PhiState::Conflict, basesel); + // Either conflict or base. + assert(states.count(BDV)); + Base = states[BDV].getBase(); } - } + assert(Base && "can't be null"); + // The cast is needed since base traversal may strip away bitcasts + if (Base->getType() != Input->getType() && + InsertPt) { + Base = new BitCastInst(Base, Input->getType(), "cast", + InsertPt); + } + return Base; + }; - // Fixup all the inputs of the new PHIs + // Fixup all the inputs of the new PHIs. Visit order needs to be + // deterministic and predictable because we're naming newly created + // instructions. for (auto Pair : states) { Instruction *v = cast(Pair.first); - PhiState state = Pair.second; + BDVState state = Pair.second; assert(!isKnownBaseResult(v) && "why did it get added?"); assert(!state.isUnknown() && "Optimistic algorithm didn't complete!"); @@ -786,106 +995,135 @@ static Value *findBasePointer(Value *I, DefiningValueMapTy &cache, if (blockIndex != -1) { Value *oldBase = basephi->getIncomingValue(blockIndex); basephi->addIncoming(oldBase, InBB); + #ifndef NDEBUG - Value *base = findBaseOrBDV(InVal, cache); - if (!isKnownBaseResult(base)) { - // Either conflict or base. - assert(states.count(base)); - base = states[base].getBase(); - assert(base != nullptr && "unknown PhiState!"); - assert(NewInsertedDefs.count(base) && - "should have already added this in a prev. iteration!"); - } - - // In essense this assert states: the only way two + Value *Base = getBaseForInput(InVal, nullptr); + // 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 // findBaseOrBDV to return an llvm::Value of the correct // type (and still remain pure). This will remove the // need to add bitcasts. - assert(base->stripPointerCasts() == oldBase->stripPointerCasts() && + assert(Base->stripPointerCasts() == oldBase->stripPointerCasts() && "sanity -- findBaseOrBDV should be pure!"); #endif continue; } - // Find either the defining value for the PHI or the normal base for - // a non-phi node - Value *base = findBaseOrBDV(InVal, cache); - if (!isKnownBaseResult(base)) { - // Either conflict or base. - assert(states.count(base)); - base = states[base].getBase(); - assert(base != nullptr && "unknown PhiState!"); - } - assert(base && "can't be null"); - // Must use original input BB since base may not be Instruction - // The cast is needed since base traversal may strip away bitcasts - if (base->getType() != basephi->getType()) { - base = new BitCastInst(base, basephi->getType(), "cast", - InBB->getTerminator()); - NewInsertedDefs.insert(base); - } - basephi->addIncoming(base, InBB); + // Find the instruction which produces the base for each input. We may + // need to insert a bitcast in the incoming block. + // TODO: Need to split critical edges if insertion is needed + Value *Base = getBaseForInput(InVal, InBB->getTerminator()); + basephi->addIncoming(Base, InBB); } assert(basephi->getNumIncomingValues() == NumPHIValues); - } else { - SelectInst *basesel = cast(state.getBase()); - SelectInst *sel = cast(v); + } else if (SelectInst *BaseSel = dyn_cast(state.getBase())) { + SelectInst *Sel = cast(v); // Operand 1 & 2 are true, false path respectively. TODO: refactor to // something more safe and less hacky. for (int i = 1; i <= 2; i++) { - Value *InVal = sel->getOperand(i); - // Find either the defining value for the PHI or the normal base for - // a non-phi node - Value *base = findBaseOrBDV(InVal, cache); - if (!isKnownBaseResult(base)) { - // Either conflict or base. - assert(states.count(base)); - base = states[base].getBase(); - assert(base != nullptr && "unknown PhiState!"); - } - assert(base && "can't be null"); - // Must use original input BB since base may not be Instruction - // The cast is needed since base traversal may strip away bitcasts - if (base->getType() != basesel->getType()) { - base = new BitCastInst(base, basesel->getType(), "cast", basesel); - NewInsertedDefs.insert(base); - } - basesel->setOperand(i, base); + Value *InVal = Sel->getOperand(i); + // Find the instruction which produces the base for each input. We may + // need to insert a bitcast. + Value *Base = getBaseForInput(InVal, BaseSel); + BaseSel->setOperand(i, Base); } + } else { + auto *BaseEE = cast(state.getBase()); + Value *InVal = cast(v)->getVectorOperand(); + // Find the instruction which produces the base for each input. We may + // need to insert a bitcast. + Value *Base = getBaseForInput(InVal, BaseEE); + BaseEE->setOperand(0, Base); } } - // Cache all of our results so we can cheaply reuse them - // NOTE: This is actually two caches: one of the base defining value - // relation and one of the base pointer relation! FIXME - for (auto item : states) { - Value *v = item.first; - Value *base = item.second.getBase(); - assert(v && base); - assert(!isKnownBaseResult(v) && "why did it get added?"); + // 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 ReverseMap; + SmallPtrSet NewInsts; + SmallSetVector, 16> Worklist; + // Note: We need to visit the states in a deterministic order. We uses the + // Keys we sorted above for this purpose. Note that we are papering over a + // bigger problem with the algorithm above - it's visit order is not + // deterministic. A larger change is needed to fix this. + for (auto Pair : states) { + auto *BDV = Pair.first; + auto State = Pair.second; + Value *Base = State.getBase(); + assert(BDV && Base); + assert(!isKnownBaseResult(BDV) && "why did it get added?"); + assert(isKnownBaseResult(Base) && + "must be something we 'know' is a base pointer"); + if (!State.isConflict()) + continue; - if (TraceLSP) { - std::string fromstr = - cache.count(v) ? (cache[v]->hasName() ? cache[v]->getName() : "") - : "none"; - errs() << "Updating base value cache" - << " for: " << (v->hasName() ? v->getName() : "") - << " from: " << fromstr - << " to: " << (base->hasName() ? base->getName() : "") << "\n"; + ReverseMap[Base] = BDV; + if (auto *BaseI = dyn_cast(Base)) { + NewInsts.insert(BaseI); + Worklist.insert(BaseI); + } + } + auto ReplaceBaseInstWith = [&](Value *BDV, Instruction *BaseI, + Value *Replacement) { + // Add users which are new instructions (excluding self references) + for (User *U : BaseI->users()) + if (auto *UI = dyn_cast(U)) + if (NewInsts.count(UI) && UI != BaseI) + Worklist.insert(UI); + // Then do the actual replacement + NewInsts.erase(BaseI); + ReverseMap.erase(BaseI); + BaseI->replaceAllUsesWith(Replacement); + BaseI->eraseFromParent(); + assert(states.count(BDV)); + assert(states[BDV].isConflict() && states[BDV].getBase() == BaseI); + states[BDV] = BDVState(BDVState::Conflict, Replacement); + }; + const DataLayout &DL = cast(def)->getModule()->getDataLayout(); + while (!Worklist.empty()) { + Instruction *BaseI = Worklist.pop_back_val(); + assert(NewInsts.count(BaseI)); + Value *Bdv = ReverseMap[BaseI]; + if (auto *BdvI = dyn_cast(Bdv)) + if (BaseI->isIdenticalTo(BdvI)) { + DEBUG(dbgs() << "Identical Base: " << *BaseI << "\n"); + ReplaceBaseInstWith(Bdv, BaseI, Bdv); + continue; + } + if (Value *V = SimplifyInstruction(BaseI, DL)) { + DEBUG(dbgs() << "Base " << *BaseI << " simplified to " << *V << "\n"); + ReplaceBaseInstWith(Bdv, BaseI, V); + continue; } + } - assert(isKnownBaseResult(base) && - "must be something we 'know' is a base pointer"); - if (cache.count(v)) { + // Cache all of our results so we can cheaply reuse them + // NOTE: This is actually two caches: one of the base defining value + // relation and one of the base pointer relation! FIXME + for (auto Pair : states) { + auto *BDV = Pair.first; + Value *base = Pair.second.getBase(); + assert(BDV && base); + + std::string fromstr = + cache.count(BDV) ? (cache[BDV]->hasName() ? cache[BDV]->getName() : "") + : "none"; + DEBUG(dbgs() << "Updating base value cache" + << " for: " << (BDV->hasName() ? BDV->getName() : "") + << " from: " << fromstr + << " to: " << (base->hasName() ? base->getName() : "") << "\n"); + + if (cache.count(BDV)) { // Once we transition from the BDV relation being store in the cache to // the base relation being stored, it must be stable - assert((!isKnownBaseResult(cache[v]) || cache[v] == base) && + assert((!isKnownBaseResult(cache[BDV]) || cache[BDV] == base) && "base relation should be stable"); } - cache[v] = base; + cache[BDV] = base; } assert(cache.find(def) != cache.end()); return cache[def]; @@ -909,8 +1147,7 @@ static Value *findBasePointer(Value *I, DefiningValueMapTy &cache, static void findBasePointers(const StatepointLiveSetTy &live, DenseMap &PointerToBase, - DominatorTree *DT, DefiningValueMapTy &DVCache, - DenseSet &NewInsertedDefs) { + DominatorTree *DT, DefiningValueMapTy &DVCache) { // For the naming of values inserted to be deterministic - which makes for // much cleaner and more stable tests - we need to assign an order to the // live values. DenseSets do not provide a deterministic order across runs. @@ -918,7 +1155,7 @@ findBasePointers(const StatepointLiveSetTy &live, Temp.insert(Temp.end(), live.begin(), live.end()); std::sort(Temp.begin(), Temp.end(), order_by_name); for (Value *ptr : Temp) { - Value *base = findBasePointer(ptr, DVCache, NewInsertedDefs); + Value *base = findBasePointer(ptr, DVCache); assert(base && "failed to find base pointer"); PointerToBase[ptr] = base; assert((!isa(base) || !isa(ptr) || @@ -928,7 +1165,7 @@ findBasePointers(const StatepointLiveSetTy &live, // 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(base) && "the relocation code needs adjustment to handle the relocation of " "a null pointer constant without causing false positives in the " @@ -942,9 +1179,7 @@ static void findBasePointers(DominatorTree &DT, DefiningValueMapTy &DVCache, const CallSite &CS, PartiallyConstructedSafepointRecord &result) { DenseMap PointerToBase; - DenseSet NewInsertedDefs; - findBasePointers(result.liveset, PointerToBase, &DT, DVCache, - NewInsertedDefs); + findBasePointers(result.liveset, PointerToBase, &DT, DVCache); if (PrintBasePointers) { // Note: Need to print these in a stable order since this is checked in @@ -964,7 +1199,6 @@ static void findBasePointers(DominatorTree &DT, DefiningValueMapTy &DVCache, } result.PointerToBase = PointerToBase; - result.NewInsertedDefs = NewInsertedDefs; } /// Given an updated version of the dataflow liveness results, update the @@ -977,7 +1211,7 @@ static void recomputeLiveInValues( Function &F, DominatorTree &DT, Pass *P, ArrayRef toUpdate, MutableArrayRef 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++) { @@ -987,27 +1221,28 @@ static void recomputeLiveInValues( } } -// Normalize basic block to make it ready to be target of invoke statepoint. -// It means spliting it to have single predecessor. Return newly created BB -// ready to be successor of invoke statepoint. -static BasicBlock *normalizeBBForInvokeSafepoint(BasicBlock *BB, - BasicBlock *InvokeParent, - Pass *P) { - BasicBlock *ret = BB; - +// When inserting gc.relocate calls, we need to ensure there are no uses +// of the original value between the gc.statepoint and the gc.relocate call. +// One case which can arise is a phi node starting one of the successor blocks. +// We also need to be able to insert the gc.relocates only on the path which +// goes through the statepoint. We might need to split an edge to make this +// possible. +static BasicBlock * +normalizeForInvokeSafepoint(BasicBlock *BB, BasicBlock *InvokeParent, + DominatorTree &DT) { + BasicBlock *Ret = BB; if (!BB->getUniquePredecessor()) { - ret = SplitBlockPredecessors(BB, InvokeParent, ""); + Ret = SplitBlockPredecessors(BB, InvokeParent, "", &DT); } - // Another requirement for such basic blocks is to not have any phi nodes. - // Since we just ensured that new BB will have single predecessor, - // all phi nodes in it will have one value. Here it would be naturall place - // to - // remove them all. But we can not do this because we are risking to remove - // one of the values stored in liveset of another statepoint. We will do it - // later after placing all safepoints. + // Now that 'ret' has unique predecessor we can safely remove all phi nodes + // from it + FoldSingleEntryPHINodes(Ret); + assert(!isa(Ret->begin())); - return ret; + // At this point, we can safely insert a gc.relocate as the first instruction + // in Ret if needed. + return Ret; } static int find_index(ArrayRef livevec, Value *val) { @@ -1018,7 +1253,7 @@ static int find_index(ArrayRef livevec, Value *val) { 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; @@ -1060,47 +1295,42 @@ static AttributeSet legalizeCallAttributes(AttributeSet AS) { /// statepointToken - statepoint instruction to which relocates should be /// bound. /// Builder - Llvm IR builder to be used to construct new calls. -static void CreateGCRelocates(ArrayRef liveVariables, - const int liveStart, - ArrayRef basePtrs, - Instruction *statepointToken, +static void CreateGCRelocates(ArrayRef LiveVariables, + const int LiveStart, + ArrayRef BasePtrs, + Instruction *StatepointToken, IRBuilder<> Builder) { - SmallVector NewDefs; - NewDefs.reserve(liveVariables.size()); - - Module *M = statepointToken->getParent()->getParent()->getParent(); - - for (unsigned i = 0; i < liveVariables.size(); i++) { - // We generate a (potentially) unique declaration for every pointer type - // combination. This results is some blow up the function declarations in - // the IR, but removes the need for argument bitcasts which shrinks the IR - // greatly and makes it much more readable. - SmallVector types; // one per 'any' type - types.push_back(liveVariables[i]->getType()); // result type - Value *gc_relocate_decl = Intrinsic::getDeclaration( - M, Intrinsic::experimental_gc_relocate, types); - + if (LiveVariables.empty()) + return; + + // All gc_relocate are set to i8 addrspace(1)* type. We originally generated + // unique declarations for each pointer type, but this proved problematic + // because the intrinsic mangling code is incomplete and fragile. Since + // we're moving towards a single unified pointer type anyways, we can just + // cast everything to an i8* of the right address space. A bitcast is added + // later to convert gc_relocate to the actual value's type. + Module *M = StatepointToken->getModule(); + auto AS = cast(LiveVariables[0]->getType())->getAddressSpace(); + Type *Types[] = {Type::getInt8PtrTy(M->getContext(), AS)}; + Value *GCRelocateDecl = + Intrinsic::getDeclaration(M, Intrinsic::experimental_gc_relocate, Types); + + for (unsigned i = 0; i < LiveVariables.size(); i++) { // Generate the gc.relocate call and save the result - Value *baseIdx = - ConstantInt::get(Type::getInt32Ty(M->getContext()), - liveStart + find_index(liveVariables, basePtrs[i])); - Value *liveIdx = ConstantInt::get( - Type::getInt32Ty(M->getContext()), - liveStart + find_index(liveVariables, liveVariables[i])); + Value *BaseIdx = + Builder.getInt32(LiveStart + find_index(LiveVariables, BasePtrs[i])); + Value *LiveIdx = + Builder.getInt32(LiveStart + find_index(LiveVariables, LiveVariables[i])); // only specify a debug name if we can give a useful one - Value *reloc = Builder.CreateCall3( - gc_relocate_decl, statepointToken, baseIdx, liveIdx, - liveVariables[i]->hasName() ? liveVariables[i]->getName() + ".relocated" + CallInst *Reloc = Builder.CreateCall( + GCRelocateDecl, {StatepointToken, BaseIdx, LiveIdx}, + LiveVariables[i]->hasName() ? LiveVariables[i]->getName() + ".relocated" : ""); // Trick CodeGen into thinking there are lots of free registers at this // fake call. - cast(reloc)->setCallingConv(CallingConv::Cold); - - NewDefs.push_back(cast(reloc)); + Reloc->setCallingConv(CallingConv::Cold); } - assert(NewDefs.size() == liveVariables.size() && - "missing or extra redefinition at safepoint"); } static void @@ -1155,7 +1385,7 @@ makeStatepointExplicitImpl(const CallSite &CS, /* to replace */ // 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(); @@ -1179,13 +1409,13 @@ makeStatepointExplicitImpl(const CallSite &CS, /* to replace */ // original block. InvokeInst *invoke = InvokeInst::Create( gc_statepoint_decl, toReplace->getNormalDest(), - toReplace->getUnwindDest(), args, "", toReplace->getParent()); + toReplace->getUnwindDest(), args, "statepoint_token", toReplace->getParent()); invoke->setCallingConv(toReplace->getCallingConv()); // 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(); @@ -1193,8 +1423,10 @@ makeStatepointExplicitImpl(const CallSite &CS, /* to replace */ token = invoke; // Generate gc relocates in exceptional path - BasicBlock *unwindBlock = normalizeBBForInvokeSafepoint( - toReplace->getUnwindDest(), invoke->getParent(), P); + BasicBlock *unwindBlock = toReplace->getUnwindDest(); + assert(!isa(unwindBlock->begin()) && + unwindBlock->getUniquePredecessor() && + "can't safely insert in this block!"); Instruction *IP = &*(unwindBlock->getFirstInsertionPt()); Builder.SetInsertPoint(IP); @@ -1208,14 +1440,14 @@ makeStatepointExplicitImpl(const CallSite &CS, /* to replace */ unwindBlock->getLandingPadInst(), idx, "relocate_token")); result.UnwindToken = exceptional_token; - // Just throw away return value. We will use the one we got for normal - // block. - (void)CreateGCRelocates(liveVariables, live_start, basePtrs, - exceptional_token, Builder); + CreateGCRelocates(liveVariables, live_start, basePtrs, + exceptional_token, Builder); // Generate gc relocates and returns for normal block - BasicBlock *normalDest = normalizeBBForInvokeSafepoint( - toReplace->getNormalDest(), invoke->getParent(), P); + BasicBlock *normalDest = toReplace->getNormalDest(); + assert(!isa(normalDest->begin()) && + normalDest->getUniquePredecessor() && + "can't safely insert in this block!"); IP = &*(normalDest->getFirstInsertionPt()); Builder.SetInsertPoint(IP); @@ -1292,8 +1524,7 @@ makeStatepointExplicit(DominatorTree &DT, const CallSite &CS, Pass *P, basevec.reserve(liveset.size()); for (Value *L : liveset) { livevec.push_back(L); - - assert(PointerToBase.find(L) != PointerToBase.end()); + assert(PointerToBase.count(L)); Value *base = PointerToBase[L]; basevec.push_back(base); } @@ -1316,41 +1547,75 @@ makeStatepointExplicit(DominatorTree &DT, const CallSite &CS, Pass *P, // Add visited values into the visitedLiveValues set we will later use them // for sanity check. static void -insertRelocationStores(iterator_range gcRelocs, - DenseMap &allocaMap, - DenseSet &visitedLiveValues) { +insertRelocationStores(iterator_range GCRelocs, + DenseMap &AllocaMap, + DenseSet &VisitedLiveValues) { - for (User *U : gcRelocs) { + for (User *U : GCRelocs) { if (!isa(U)) continue; - IntrinsicInst *relocatedValue = cast(U); + IntrinsicInst *RelocatedValue = cast(U); // We only care about relocates - if (relocatedValue->getIntrinsicID() != + if (RelocatedValue->getIntrinsicID() != Intrinsic::experimental_gc_relocate) { continue; } - GCRelocateOperands relocateOperands(relocatedValue); - Value *originalValue = const_cast(relocateOperands.derivedPtr()); - assert(allocaMap.count(originalValue)); - Value *alloca = allocaMap[originalValue]; + GCRelocateOperands RelocateOperands(RelocatedValue); + Value *OriginalValue = + const_cast(RelocateOperands.getDerivedPtr()); + assert(AllocaMap.count(OriginalValue)); + Value *Alloca = AllocaMap[OriginalValue]; // Emit store into the related alloca - StoreInst *store = new StoreInst(relocatedValue, alloca); - store->insertAfter(relocatedValue); + // All gc_relocate are i8 addrspace(1)* typed, and it must be bitcasted to + // the correct type according to alloca. + assert(RelocatedValue->getNextNode() && "Should always have one since it's not a terminator"); + IRBuilder<> Builder(RelocatedValue->getNextNode()); + Value *CastedRelocatedValue = + Builder.CreateBitCast(RelocatedValue, cast(Alloca)->getAllocatedType(), + RelocatedValue->hasName() ? RelocatedValue->getName() + ".casted" : ""); + + StoreInst *Store = new StoreInst(CastedRelocatedValue, Alloca); + Store->insertAfter(cast(CastedRelocatedValue)); + +#ifndef NDEBUG + VisitedLiveValues.insert(OriginalValue); +#endif + } +} + +// Helper function for the "relocationViaAlloca". Similar to the +// "insertRelocationStores" but works for rematerialized values. +static void +insertRematerializationStores( + RematerializedValueMapTy RematerializedValues, + DenseMap &AllocaMap, + DenseSet &VisitedLiveValues) { + + for (auto RematerializedValuePair: RematerializedValues) { + Instruction *RematerializedValue = RematerializedValuePair.first; + Value *OriginalValue = RematerializedValuePair.second; + + assert(AllocaMap.count(OriginalValue) && + "Can not find alloca for rematerialized value"); + Value *Alloca = AllocaMap[OriginalValue]; + + StoreInst *Store = new StoreInst(RematerializedValue, Alloca); + Store->insertAfter(RematerializedValue); #ifndef NDEBUG - visitedLiveValues.insert(originalValue); + VisitedLiveValues.insert(OriginalValue); #endif } } /// do all the relocation update via allocas and mem2reg static void relocationViaAlloca( - Function &F, DominatorTree &DT, ArrayRef live, - ArrayRef records) { + Function &F, DominatorTree &DT, ArrayRef Live, + ArrayRef Records) { #ifndef NDEBUG // record initial number of (static) allocas; we'll check we have the same // number when we get done. @@ -1362,17 +1627,38 @@ static void relocationViaAlloca( #endif // TODO-PERF: change data structures, reserve - DenseMap allocaMap; + DenseMap AllocaMap; SmallVector PromotableAllocas; - PromotableAllocas.reserve(live.size()); + // Used later to chack that we have enough allocas to store all values + std::size_t NumRematerializedValues = 0; + PromotableAllocas.reserve(Live.size()); + + // Emit alloca for "LiveValue" and record it in "allocaMap" and + // "PromotableAllocas" + auto emitAllocaFor = [&](Value *LiveValue) { + AllocaInst *Alloca = new AllocaInst(LiveValue->getType(), "", + F.getEntryBlock().getFirstNonPHI()); + AllocaMap[LiveValue] = Alloca; + PromotableAllocas.push_back(Alloca); + }; // emit alloca for each live gc pointer - for (unsigned i = 0; i < live.size(); i++) { - Value *liveValue = live[i]; - AllocaInst *alloca = new AllocaInst(liveValue->getType(), "", - F.getEntryBlock().getFirstNonPHI()); - allocaMap[liveValue] = alloca; - PromotableAllocas.push_back(alloca); + for (unsigned i = 0; i < Live.size(); i++) { + emitAllocaFor(Live[i]); + } + + // emit allocas for rematerialized values + for (size_t i = 0; i < Records.size(); i++) { + const struct PartiallyConstructedSafepointRecord &Info = Records[i]; + + for (auto RematerializedValuePair : Info.RematerializedValues) { + Value *OriginalValue = RematerializedValuePair.second; + if (AllocaMap.count(OriginalValue) != 0) + continue; + + emitAllocaFor(OriginalValue); + ++NumRematerializedValues; + } } // The next two loops are part of the same conceptual operation. We need to @@ -1385,128 +1671,132 @@ static void relocationViaAlloca( // this gc pointer and it is not a gc_result) // this must happen before we update the statepoint with load of alloca // otherwise we lose the link between statepoint and old def - for (size_t i = 0; i < records.size(); i++) { - const struct PartiallyConstructedSafepointRecord &info = records[i]; - Value *Statepoint = info.StatepointToken; + for (size_t i = 0; i < Records.size(); i++) { + const struct PartiallyConstructedSafepointRecord &Info = Records[i]; + Value *Statepoint = Info.StatepointToken; // This will be used for consistency check - DenseSet visitedLiveValues; + DenseSet VisitedLiveValues; // Insert stores for normal statepoint gc relocates - insertRelocationStores(Statepoint->users(), allocaMap, visitedLiveValues); + insertRelocationStores(Statepoint->users(), AllocaMap, VisitedLiveValues); // In case if it was invoke statepoint // we will insert stores for exceptional path gc relocates. if (isa(Statepoint)) { - insertRelocationStores(info.UnwindToken->users(), allocaMap, - visitedLiveValues); + insertRelocationStores(Info.UnwindToken->users(), AllocaMap, + VisitedLiveValues); } -#ifndef NDEBUG - // As a debuging 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 - SmallVector ToClobber; - for (auto Pair : allocaMap) { - Value *Def = Pair.first; - AllocaInst *Alloca = cast(Pair.second); - - // This value was relocated - if (visitedLiveValues.count(Def)) { - continue; + // Do similar thing with rematerialized values + insertRematerializationStores(Info.RematerializedValues, AllocaMap, + VisitedLiveValues); + + if (ClobberNonLive) { + // 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 + // wise. + SmallVector ToClobber; + for (auto Pair : AllocaMap) { + Value *Def = Pair.first; + AllocaInst *Alloca = cast(Pair.second); + + // This value was relocated + if (VisitedLiveValues.count(Def)) { + continue; + } + ToClobber.push_back(Alloca); } - ToClobber.push_back(Alloca); - } - auto InsertClobbersAt = [&](Instruction *IP) { - for (auto *AI : ToClobber) { - auto AIType = cast(AI->getType()); - auto PT = cast(AIType->getElementType()); - Constant *CPN = ConstantPointerNull::get(PT); - StoreInst *store = new StoreInst(CPN, AI); - store->insertBefore(IP); - } - }; + auto InsertClobbersAt = [&](Instruction *IP) { + for (auto *AI : ToClobber) { + auto AIType = cast(AI->getType()); + auto PT = cast(AIType->getElementType()); + Constant *CPN = ConstantPointerNull::get(PT); + StoreInst *Store = new StoreInst(CPN, AI); + Store->insertBefore(IP); + } + }; - // Insert the clobbering stores. These may get intermixed with the - // gc.results and gc.relocates, but that's fine. - if (auto II = dyn_cast(Statepoint)) { - InsertClobbersAt(II->getNormalDest()->getFirstInsertionPt()); - InsertClobbersAt(II->getUnwindDest()->getFirstInsertionPt()); - } else { - BasicBlock::iterator Next(cast(Statepoint)); - Next++; - InsertClobbersAt(Next); + // Insert the clobbering stores. These may get intermixed with the + // gc.results and gc.relocates, but that's fine. + if (auto II = dyn_cast(Statepoint)) { + InsertClobbersAt(II->getNormalDest()->getFirstInsertionPt()); + InsertClobbersAt(II->getUnwindDest()->getFirstInsertionPt()); + } else { + BasicBlock::iterator Next(cast(Statepoint)); + Next++; + InsertClobbersAt(Next); + } } -#endif } // update use with load allocas and add store for gc_relocated - for (auto Pair : allocaMap) { - Value *def = Pair.first; - Value *alloca = Pair.second; + for (auto Pair : AllocaMap) { + Value *Def = Pair.first; + Value *Alloca = Pair.second; // we pre-record the uses of allocas so that we dont have to worry about // later update // that change the user information. - SmallVector uses; + SmallVector Uses; // PERF: trade a linear scan for repeated reallocation - uses.reserve(std::distance(def->user_begin(), def->user_end())); - for (User *U : def->users()) { + Uses.reserve(std::distance(Def->user_begin(), Def->user_end())); + for (User *U : Def->users()) { if (!isa(U)) { // If the def has a ConstantExpr use, then the def is either a // ConstantExpr use itself or null. In either case // (recursively in the first, directly in the second), the oop // it is ultimately dependent on is null and this particular // use does not need to be fixed up. - uses.push_back(cast(U)); + Uses.push_back(cast(U)); } } - std::sort(uses.begin(), uses.end()); - auto last = std::unique(uses.begin(), uses.end()); - uses.erase(last, uses.end()); - - for (Instruction *use : uses) { - if (isa(use)) { - PHINode *phi = cast(use); - for (unsigned i = 0; i < phi->getNumIncomingValues(); i++) { - if (def == phi->getIncomingValue(i)) { - LoadInst *load = new LoadInst( - alloca, "", phi->getIncomingBlock(i)->getTerminator()); - phi->setIncomingValue(i, load); + std::sort(Uses.begin(), Uses.end()); + auto Last = std::unique(Uses.begin(), Uses.end()); + Uses.erase(Last, Uses.end()); + + for (Instruction *Use : Uses) { + if (isa(Use)) { + PHINode *Phi = cast(Use); + for (unsigned i = 0; i < Phi->getNumIncomingValues(); i++) { + if (Def == Phi->getIncomingValue(i)) { + LoadInst *Load = new LoadInst( + Alloca, "", Phi->getIncomingBlock(i)->getTerminator()); + Phi->setIncomingValue(i, Load); } } } else { - LoadInst *load = new LoadInst(alloca, "", use); - use->replaceUsesOfWith(def, load); + LoadInst *Load = new LoadInst(Alloca, "", Use); + Use->replaceUsesOfWith(Def, Load); } } // emit store for the initial gc value // store must be inserted after load, otherwise store will be in alloca's // use list and an extra load will be inserted before it - StoreInst *store = new StoreInst(def, alloca); - if (Instruction *inst = dyn_cast(def)) { - if (InvokeInst *invoke = dyn_cast(inst)) { + StoreInst *Store = new StoreInst(Def, Alloca); + if (Instruction *Inst = dyn_cast(Def)) { + if (InvokeInst *Invoke = dyn_cast(Inst)) { // InvokeInst is a TerminatorInst so the store need to be inserted // into its normal destination block. - BasicBlock *normalDest = invoke->getNormalDest(); - store->insertBefore(normalDest->getFirstNonPHI()); + BasicBlock *NormalDest = Invoke->getNormalDest(); + Store->insertBefore(NormalDest->getFirstNonPHI()); } else { - assert(!inst->isTerminator() && + assert(!Inst->isTerminator() && "The only TerminatorInst that can produce a value is " "InvokeInst which is handled above."); - store->insertAfter(inst); + Store->insertAfter(Inst); } } else { - assert((isa(def) || isa(def) || - isa(def)) && - "Must be argument or global"); - store->insertAfter(cast(alloca)); + assert(isa(Def)); + Store->insertAfter(cast(Alloca)); } } - assert(PromotableAllocas.size() == live.size() && + assert(PromotableAllocas.size() == Live.size() + NumRematerializedValues && "we must have the same allocas with lives"); if (!PromotableAllocas.empty()) { // apply mem2reg to promote alloca to SSA @@ -1526,50 +1816,38 @@ static void relocationViaAlloca( /// vector. Doing so has the effect of changing the output of a couple of /// tests in ways which make them less useful in testing fused safepoints. template static void unique_unsorted(SmallVectorImpl &Vec) { - DenseSet Seen; - SmallVector TempVec; - TempVec.reserve(Vec.size()); - for (auto Element : Vec) - TempVec.push_back(Element); - Vec.clear(); - for (auto V : TempVec) { - if (Seen.insert(V).second) { - Vec.push_back(V); - } - } -} - -static Function *getUseHolder(Module &M) { - FunctionType *ftype = - FunctionType::get(Type::getVoidTy(M.getContext()), true); - Function *Func = cast(M.getOrInsertFunction("__tmp_use", ftype)); - return Func; + SmallSet Seen; + Vec.erase(std::remove_if(Vec.begin(), Vec.end(), [&](const T &V) { + return !Seen.insert(V).second; + }), Vec.end()); } /// Insert holders so that each Value is obviously live through the entire -/// liftetime of the call. +/// lifetime of the call. static void insertUseHolderAfter(CallSite &CS, const ArrayRef Values, - SmallVectorImpl &holders) { + SmallVectorImpl &Holders) { + if (Values.empty()) + // No values to hold live, might as well not insert the empty holder + return; + Module *M = CS.getInstruction()->getParent()->getParent()->getParent(); - Function *Func = getUseHolder(*M); + // Use a dummy vararg function to actually hold the values live + Function *Func = cast(M->getOrInsertFunction( + "__tmp_use", FunctionType::get(Type::getVoidTy(M->getContext()), true))); if (CS.isCall()) { // For call safepoints insert dummy calls right after safepoint - BasicBlock::iterator next(CS.getInstruction()); - next++; - CallInst *base_holder = CallInst::Create(Func, Values, "", next); - holders.push_back(base_holder); - } else if (CS.isInvoke()) { - // For invoke safepooints insert dummy calls both in normal and - // exceptional destination blocks - InvokeInst *invoke = cast(CS.getInstruction()); - CallInst *normal_holder = CallInst::Create( - Func, Values, "", invoke->getNormalDest()->getFirstInsertionPt()); - CallInst *unwind_holder = CallInst::Create( - Func, Values, "", invoke->getUnwindDest()->getFirstInsertionPt()); - holders.push_back(normal_holder); - holders.push_back(unwind_holder); - } else - llvm_unreachable("unsupported call type"); + BasicBlock::iterator Next(CS.getInstruction()); + Next++; + Holders.push_back(CallInst::Create(Func, Values, "", Next)); + return; + } + // For invoke safepooints insert dummy calls both in normal and + // exceptional destination blocks + auto *II = cast(CS.getInstruction()); + Holders.push_back(CallInst::Create( + Func, Values, "", II->getNormalDest()->getFirstInsertionPt())); + Holders.push_back(CallInst::Create( + Func, Values, "", II->getUnwindDest()->getFirstInsertionPt())); } static void findLiveReferences( @@ -1586,12 +1864,14 @@ static void findLiveReferences( /// 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, DominatorTree &DT) { + StatepointLiveSetTy &LiveSet, + DenseMap& PointerToBase, + DominatorTree &DT) { SmallVector ToSplit; for (Value *V : LiveSet) if (isa(V->getType())) @@ -1600,14 +1880,14 @@ static void splitVectorValues(Instruction *StatepointInst, if (ToSplit.empty()) return; + DenseMap> ElementMapping; + Function &F = *(StatepointInst->getParent()->getParent()); DenseMap AllocaMap; // First is normal return, second is exceptional return (invoke only) DenseMap> Replacements; for (Value *V : ToSplit) { - LiveSet.erase(V); - AllocaInst *Alloca = new AllocaInst(V->getType(), "", F.getEntryBlock().getFirstNonPHI()); AllocaMap[V] = Alloca; @@ -1617,7 +1897,7 @@ static void splitVectorValues(Instruction *StatepointInst, SmallVector Elements; for (unsigned i = 0; i < VT->getNumElements(); i++) Elements.push_back(Builder.CreateExtractElement(V, Builder.getInt32(i))); - LiveSet.insert(Elements.begin(), Elements.end()); + ElementMapping[V] = Elements; auto InsertVectorReform = [&](Instruction *IP) { Builder.SetInsertPoint(IP); @@ -1650,6 +1930,7 @@ static void splitVectorValues(Instruction *StatepointInst, Replacements[V].second = InsertVectorReform(IP); } } + for (Value *V : ToSplit) { AllocaInst *Alloca = AllocaMap[V]; @@ -1693,6 +1974,220 @@ static void splitVectorValues(Instruction *StatepointInst, for (Value *V : ToSplit) Allocas.push_back(AllocaMap[V]); PromoteMemToReg(Allocas, DT); + + // Update our tracking of live pointers and base mappings to account for the + // changes we just made. + for (Value *V : ToSplit) { + auto &Elements = ElementMapping[V]; + + LiveSet.erase(V); + LiveSet.insert(Elements.begin(), Elements.end()); + // We need to update the base mapping as well. + assert(PointerToBase.count(V)); + Value *OldBase = PointerToBase[V]; + auto &BaseElements = ElementMapping[OldBase]; + PointerToBase.erase(V); + assert(Elements.size() == BaseElements.size()); + for (unsigned i = 0; i < Elements.size(); i++) { + Value *Elem = Elements[i]; + PointerToBase[Elem] = BaseElements[i]; + } + } +} + +// 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 +// successfully reached "BaseValue" and false otherwise. +// Fills "ChainToBase" array with all visited values. "BaseValue" is not +// recorded. +static bool findRematerializableChainToBasePointer( + SmallVectorImpl &ChainToBase, + Value *CurrentValue, Value *BaseValue) { + + // We have found a base value + if (CurrentValue == BaseValue) { + return true; + } + + if (GetElementPtrInst *GEP = dyn_cast(CurrentValue)) { + ChainToBase.push_back(GEP); + return findRematerializableChainToBasePointer(ChainToBase, + GEP->getPointerOperand(), + BaseValue); + } + + if (CastInst *CI = dyn_cast(CurrentValue)) { + Value *Def = CI->stripPointerCasts(); + + // This two checks are basically similar. First one is here for the + // consistency with findBasePointers logic. + assert(!isa(Def) && "not a pointer cast found"); + if (!CI->isNoopCast(CI->getModule()->getDataLayout())) + return false; + + ChainToBase.push_back(CI); + return findRematerializableChainToBasePointer(ChainToBase, Def, BaseValue); + } + + // Not supported instruction in the chain + return false; +} + +// Helper function for the "rematerializeLiveValues". Compute cost of the use +// chain we are going to rematerialize. +static unsigned +chainToBasePointerCost(SmallVectorImpl &Chain, + TargetTransformInfo &TTI) { + unsigned Cost = 0; + + for (Instruction *Instr : Chain) { + if (CastInst *CI = dyn_cast(Instr)) { + assert(CI->isNoopCast(CI->getModule()->getDataLayout()) && + "non noop cast is found during rematerialization"); + + Type *SrcTy = CI->getOperand(0)->getType(); + Cost += TTI.getCastInstrCost(CI->getOpcode(), CI->getType(), SrcTy); + + } else if (GetElementPtrInst *GEP = dyn_cast(Instr)) { + // Cost of the address calculation + Type *ValTy = GEP->getPointerOperandType()->getPointerElementType(); + Cost += TTI.getAddressComputationCost(ValTy); + + // And cost of the GEP itself + // TODO: Use TTI->getGEPCost here (it exists, but appears to be not + // allowed for the external usage) + if (!GEP->hasAllConstantIndices()) + Cost += 2; + + } else { + llvm_unreachable("unsupported instruciton type during rematerialization"); + } + } + + return Cost; +} + +// From the statepoint liveset pick values that are cheaper to recompute then to +// relocate. Remove this values from the liveset, rematerialize them after +// statepoint and record them in "Info" structure. Note that similar to +// relocated values we don't do any user adjustments here. +static void rematerializeLiveValues(CallSite CS, + PartiallyConstructedSafepointRecord &Info, + TargetTransformInfo &TTI) { + const unsigned int ChainLengthThreshold = 10; + + // Record values we are going to delete from this statepoint live set. + // We can not di this in following loop due to iterator invalidation. + SmallVector LiveValuesToBeDeleted; + + for (Value *LiveValue: Info.liveset) { + // For each live pointer find it's defining chain + SmallVector ChainToBase; + assert(Info.PointerToBase.count(LiveValue)); + bool FoundChain = + findRematerializableChainToBasePointer(ChainToBase, + LiveValue, + Info.PointerToBase[LiveValue]); + // Nothing to do, or chain is too long + if (!FoundChain || + ChainToBase.size() == 0 || + ChainToBase.size() > ChainLengthThreshold) + continue; + + // Compute cost of this chain + unsigned Cost = chainToBasePointerCost(ChainToBase, TTI); + // TODO: We can also account for cases when we will be able to remove some + // of the rematerialized values by later optimization passes. I.e if + // we rematerialized several intersecting chains. Or if original values + // don't have any uses besides this statepoint. + + // For invokes we need to rematerialize each chain twice - for normal and + // for unwind basic blocks. Model this by multiplying cost by two. + if (CS.isInvoke()) { + Cost *= 2; + } + // If it's too expensive - skip it + if (Cost >= RematerializationThreshold) + continue; + + // Remove value from the live set + LiveValuesToBeDeleted.push_back(LiveValue); + + // Clone instructions and record them inside "Info" structure + + // Walk backwards to visit top-most instructions first + std::reverse(ChainToBase.begin(), ChainToBase.end()); + + // Utility function which clones all instructions from "ChainToBase" + // and inserts them before "InsertBefore". Returns rematerialized value + // which should be used after statepoint. + auto rematerializeChain = [&ChainToBase](Instruction *InsertBefore) { + Instruction *LastClonedValue = nullptr; + Instruction *LastValue = nullptr; + for (Instruction *Instr: ChainToBase) { + // Only GEP's and casts are suported as we need to be careful to not + // introduce any new uses of pointers not in the liveset. + // Note that it's fine to introduce new uses of pointers which were + // otherwise not used after this statepoint. + assert(isa(Instr) || isa(Instr)); + + Instruction *ClonedValue = Instr->clone(); + ClonedValue->insertBefore(InsertBefore); + ClonedValue->setName(Instr->getName() + ".remat"); + + // If it is not first instruction in the chain then it uses previously + // cloned value. We should update it to use cloned value. + if (LastClonedValue) { + assert(LastValue); + ClonedValue->replaceUsesOfWith(LastValue, LastClonedValue); +#ifndef NDEBUG + // Assert that cloned instruction does not use any instructions from + // this chain other than LastClonedValue + for (auto OpValue : ClonedValue->operand_values()) { + assert(std::find(ChainToBase.begin(), ChainToBase.end(), OpValue) == + ChainToBase.end() && + "incorrect use in rematerialization chain"); + } +#endif + } + + LastClonedValue = ClonedValue; + LastValue = Instr; + } + assert(LastClonedValue); + return LastClonedValue; + }; + + // Different cases for calls and invokes. For invokes we need to clone + // instructions both on normal and unwind path. + if (CS.isCall()) { + Instruction *InsertBefore = CS.getInstruction()->getNextNode(); + assert(InsertBefore); + Instruction *RematerializedValue = rematerializeChain(InsertBefore); + Info.RematerializedValues[RematerializedValue] = LiveValue; + } else { + InvokeInst *Invoke = cast(CS.getInstruction()); + + Instruction *NormalInsertBefore = + Invoke->getNormalDest()->getFirstInsertionPt(); + Instruction *UnwindInsertBefore = + Invoke->getUnwindDest()->getFirstInsertionPt(); + + Instruction *NormalRematerializedValue = + rematerializeChain(NormalInsertBefore); + Instruction *UnwindRematerializedValue = + rematerializeChain(UnwindInsertBefore); + + Info.RematerializedValues[NormalRematerializedValue] = LiveValue; + Info.RematerializedValues[UnwindRematerializedValue] = LiveValue; + } + } + + // Remove rematerializaed values from the live set + for (auto LiveValue: LiveValuesToBeDeleted) { + Info.liveset.erase(LiveValue); + } } static bool insertParsePoints(Function &F, DominatorTree &DT, Pass *P, @@ -1710,6 +2205,20 @@ static bool insertParsePoints(Function &F, DominatorTree &DT, Pass *P, } #endif + // When inserting gc.relocates for invokes, we need to be able to insert at + // the top of the successor blocks. See the comment on + // normalForInvokeSafepoint on exactly what is needed. Note that this step + // may restructure the CFG. + for (CallSite CS : toUpdate) { + if (!CS.isInvoke()) + continue; + InvokeInst *invoke = cast(CS.getInstruction()); + normalizeForInvokeSafepoint(invoke->getNormalDest(), invoke->getParent(), + DT); + normalizeForInvokeSafepoint(invoke->getUnwindDest(), invoke->getParent(), + DT); + } + // A list of dummy calls added to the IR to keep various values obviously // live in the IR. We'll remove all of these when done. SmallVector holders; @@ -1741,21 +2250,10 @@ static bool insertParsePoints(Function &F, DominatorTree &DT, Pass *P, } 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); - // Do a limited scalarization of any live at safepoint vector values which - // contain pointers. This enables this pass to run after vectorization at - // the cost of some possible performance loss. TODO: it would be nice to - // natively support vectors all the way through the backend so we don't need - // to scalarize here. - for (size_t i = 0; i < records.size(); i++) { - struct PartiallyConstructedSafepointRecord &info = records[i]; - Instruction *statepoint = toUpdate[i].getInstruction(); - splitVectorValues(cast(statepoint), info.liveset, DT); - } - // B) Find the base pointers for each live pointer /* scope for caching */ { // Cache the 'defining value' relation used in the computation and @@ -1779,13 +2277,6 @@ static bool insertParsePoints(Function &F, DominatorTree &DT, Pass *P, // gep a + 1 // safepoint 2 // br loop - DenseSet allInsertedDefs; - for (size_t i = 0; i < records.size(); i++) { - struct PartiallyConstructedSafepointRecord &info = records[i]; - allInsertedDefs.insert(info.NewInsertedDefs.begin(), - info.NewInsertedDefs.end()); - } - // We insert some dummy calls after each safepoint to definitely hold live // the base pointers which were identified for that safepoint. We'll then // ask liveness for _every_ base inserted to see what is now live. Then we @@ -1823,6 +2314,31 @@ static bool insertParsePoints(Function &F, DominatorTree &DT, Pass *P, } holders.clear(); + // Do a limited scalarization of any live at safepoint vector values which + // contain pointers. This enables this pass to run after vectorization at + // the cost of some possible performance loss. TODO: it would be nice to + // natively support vectors all the way through the backend so we don't need + // to scalarize here. + for (size_t i = 0; i < records.size(); i++) { + struct PartiallyConstructedSafepointRecord &info = records[i]; + Instruction *statepoint = toUpdate[i].getInstruction(); + splitVectorValues(cast(statepoint), info.liveset, + info.PointerToBase, DT); + } + + // In order to reduce live set of statepoint we might choose to rematerialize + // some values instead of relocating them. This is purely an optimization and + // does not influence correctness. + TargetTransformInfo &TTI = + P->getAnalysis().getTTI(F); + + for (size_t i = 0; i < records.size(); i++) { + struct PartiallyConstructedSafepointRecord &info = records[i]; + CallSite &CS = toUpdate[i]; + + rematerializeLiveValues(CS, info, TTI); + } + // Now run through and replace the existing statepoints with new ones with // the live variables listed. We do not yet update uses of the values being // relocated. We have references to live variables that need to @@ -1836,25 +2352,6 @@ static bool insertParsePoints(Function &F, DominatorTree &DT, Pass *P, } toUpdate.clear(); // prevent accident use of invalid CallSites - // In case if we inserted relocates in a different basic block than the - // original safepoint (this can happen for invokes). We need to be sure that - // original values were not used in any of the phi nodes at the - // beginning of basic block containing them. Because we know that all such - // blocks will have single predecessor we can safely assume that all phi - // nodes have single entry (because of normalizeBBForInvokeSafepoint). - // Just remove them all here. - for (size_t i = 0; i < records.size(); i++) { - Instruction *I = records[i].StatepointToken; - - if (InvokeInst *invoke = dyn_cast(I)) { - FoldSingleEntryPHINodes(invoke->getNormalDest()); - assert(!isa(invoke->getNormalDest()->begin())); - - FoldSingleEntryPHINodes(invoke->getUnwindDest()); - assert(!isa(invoke->getUnwindDest()->begin())); - } - } - // Do all the fixups of the original live variables to their relocated selves SmallVector live; for (size_t i = 0; i < records.size(); i++) { @@ -1867,6 +2364,24 @@ static bool insertParsePoints(Function &F, DominatorTree &DT, Pass *P, Statepoint statepoint(info.StatepointToken); live.insert(live.end(), statepoint.gc_args_begin(), statepoint.gc_args_end()); +#ifndef NDEBUG + // Do some basic sanity checks on our liveness results before performing + // relocation. Relocation can and will turn mistakes in liveness results + // into non-sensical code which is must harder to debug. + // TODO: It would be nice to test consistency as well + assert(DT.isReachableFromEntry(info.StatepointToken->getParent()) && + "statepoint must be reachable or liveness is meaningless"); + for (Value *V : statepoint.gc_args()) { + if (!isa(V)) + // Non-instruction values trivial dominate all possible uses + continue; + auto LiveInst = cast(V); + assert(DT.isReachableFromEntry(LiveInst->getParent()) && + "unreachable values should never be live"); + assert(DT.dominates(LiveInst, info.StatepointToken) && + "basic SSA liveness expectation violated by liveness analysis"); + } +#endif } unique_unsorted(live); @@ -1881,17 +2396,99 @@ static bool insertParsePoints(Function &F, DominatorTree &DT, Pass *P, return !records.empty(); } +// Handles both return values and arguments for Functions and CallSites. +template +static void RemoveDerefAttrAtIndex(LLVMContext &Ctx, AttrHolder &AH, + unsigned Index) { + AttrBuilder R; + if (AH.getDereferenceableBytes(Index)) + R.addAttribute(Attribute::get(Ctx, Attribute::Dereferenceable, + AH.getDereferenceableBytes(Index))); + if (AH.getDereferenceableOrNullBytes(Index)) + R.addAttribute(Attribute::get(Ctx, Attribute::DereferenceableOrNull, + AH.getDereferenceableOrNullBytes(Index))); + + if (!R.empty()) + AH.setAttributes(AH.getAttributes().removeAttributes( + Ctx, Index, AttributeSet::get(Ctx, Index, R))); +} + +void +RewriteStatepointsForGC::stripDereferenceabilityInfoFromPrototype(Function &F) { + LLVMContext &Ctx = F.getContext(); + + for (Argument &A : F.args()) + if (isa(A.getType())) + RemoveDerefAttrAtIndex(Ctx, F, A.getArgNo() + 1); + + if (isa(F.getReturnType())) + RemoveDerefAttrAtIndex(Ctx, F, AttributeSet::ReturnIndex); +} + +void RewriteStatepointsForGC::stripDereferenceabilityInfoFromBody(Function &F) { + if (F.empty()) + return; + + LLVMContext &Ctx = F.getContext(); + MDBuilder Builder(Ctx); + + for (Instruction &I : instructions(F)) { + if (const MDNode *MD = I.getMetadata(LLVMContext::MD_tbaa)) { + assert(MD->getNumOperands() < 5 && "unrecognized metadata shape!"); + bool IsImmutableTBAA = + MD->getNumOperands() == 4 && + mdconst::extract(MD->getOperand(3))->getValue() == 1; + + if (!IsImmutableTBAA) + continue; // no work to do, MD_tbaa is already marked mutable + + MDNode *Base = cast(MD->getOperand(0)); + MDNode *Access = cast(MD->getOperand(1)); + uint64_t Offset = + mdconst::extract(MD->getOperand(2))->getZExtValue(); + + MDNode *MutableTBAA = + Builder.createTBAAStructTagNode(Base, Access, Offset); + I.setMetadata(LLVMContext::MD_tbaa, MutableTBAA); + } + + if (CallSite CS = CallSite(&I)) { + for (int i = 0, e = CS.arg_size(); i != e; i++) + if (isa(CS.getArgument(i)->getType())) + RemoveDerefAttrAtIndex(Ctx, CS, i + 1); + if (isa(CS.getType())) + RemoveDerefAttrAtIndex(Ctx, CS, AttributeSet::ReturnIndex); + } + } +} + /// Returns true if this function should be rewritten by this pass. The main /// point of this function is as an extension point for custom logic. static bool shouldRewriteStatepointsIn(Function &F) { // TODO: This should check the GCStrategy if (F.hasGC()) { - const std::string StatepointExampleName("statepoint-example"); - return StatepointExampleName == F.getGC(); + const char *FunctionGCName = F.getGC(); + const StringRef StatepointExampleName("statepoint-example"); + const StringRef CoreCLRName("coreclr"); + return (StatepointExampleName == FunctionGCName) || + (CoreCLRName == FunctionGCName); } else return false; } +void RewriteStatepointsForGC::stripDereferenceabilityInfo(Module &M) { +#ifndef NDEBUG + assert(std::any_of(M.begin(), M.end(), shouldRewriteStatepointsIn) && + "precondition!"); +#endif + + for (Function &F : M) + stripDereferenceabilityInfoFromPrototype(F); + + for (Function &F : M) + stripDereferenceabilityInfoFromBody(F); +} + bool RewriteStatepointsForGC::runOnFunction(Function &F) { // Nothing to do for declarations. if (F.isDeclaration() || F.empty()) @@ -1902,14 +2499,14 @@ bool RewriteStatepointsForGC::runOnFunction(Function &F) { if (!shouldRewriteStatepointsIn(F)) return false; - DominatorTree &DT = getAnalysis().getDomTree(); + DominatorTree &DT = getAnalysis(F).getDomTree(); // Gather all the statepoints which need rewritten. Be careful to only // consider those in reachable code since we need to ask dominance queries // when rewriting. We'll delete the unreachable ones in a moment. SmallVector 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())) @@ -1942,6 +2539,37 @@ bool RewriteStatepointsForGC::runOnFunction(Function &F) { 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(TI)) + if (BI->isConditional()) + return dyn_cast(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(Cond) && Cond->hasOneUse()) { + MadeChange = true; + Cond->moveBefore(TI); + } + } + MadeChange |= insertParsePoints(F, DT, this, ParsePointNeeded); return MadeChange; } @@ -1952,11 +2580,6 @@ bool RewriteStatepointsForGC::runOnFunction(Function &F) { // TODO: Consider using bitvectors for liveness, the set of potentially // interesting values should be small and easy to pre-compute. -/// Is this value a constant consisting of entirely null values? -static bool isConstantNull(Value *V) { - return isa(V) && cast(V)->isNullValue(); -} - /// Compute the live-in set for the location rbegin starting from /// the live-out set of the basic block static void computeLiveInValues(BasicBlock::reverse_iterator rbegin, @@ -1978,9 +2601,17 @@ static void computeLiveInValues(BasicBlock::reverse_iterator rbegin, for (Value *V : I->operands()) { assert(!isUnhandledGCPointerType(V->getType()) && "support for FCA unimplemented"); - if (isHandledGCPointerType(V->getType()) && !isConstantNull(V) && - !isa(V)) { - // The choice to exclude null and undef is arbitrary here. Reconsider? + if (isHandledGCPointerType(V->getType()) && !isa(V)) { + // The choice to exclude all things constant here is slightly subtle. + // 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. + // - Second, we can't disallow arbitrary inttoptr constants even + // if the language frontend does. Optimization passes are free to + // locally exploit facts without respect to global reachability. This + // can create sections of code which are dynamically unreachable and + // contain just about anything. (see constants.ll in tests) LiveTmp.insert(V); } } @@ -1996,9 +2627,7 @@ static void computeLiveOutSeed(BasicBlock *BB, DenseSet &LiveTmp) { Value *V = Phi->getIncomingValueForBlock(BB); assert(!isUnhandledGCPointerType(V->getType()) && "support for FCA unimplemented"); - if (isHandledGCPointerType(V->getType()) && !isConstantNull(V) && - !isa(V)) { - // The choice to exclude null and undef is arbitrary here. Reconsider? + if (isHandledGCPointerType(V->getType()) && !isa(V)) { LiveTmp.insert(V); } } @@ -2013,11 +2642,11 @@ static DenseSet computeKillSet(BasicBlock *BB) { return KillSet; } +#ifndef NDEBUG /// Check that the items in 'Live' dominate 'TI'. This is used as a basic /// sanity check for the liveness computation. static void checkBasicSSA(DominatorTree &DT, DenseSet &Live, TerminatorInst *TI, bool TermOkay = false) { -#ifndef NDEBUG for (Value *V : Live) { if (auto *I = dyn_cast(V)) { // The terminator can be a member of the LiveOut set. LLVM's definition @@ -2029,7 +2658,6 @@ static void checkBasicSSA(DominatorTree &DT, DenseSet &Live, "basic SSA liveness expectation violated by liveness analysis"); } } -#endif } /// Check that all the liveness sets used during the computation of liveness @@ -2041,21 +2669,19 @@ static void checkBasicSSA(DominatorTree &DT, GCPtrLivenessData &Data, checkBasicSSA(DT, Data.LiveOut[&BB], BB.getTerminator(), true); checkBasicSSA(DT, Data.LiveIn[&BB], BB.getTerminator()); } +#endif static void computeLiveInValues(DominatorTree &DT, Function &F, GCPtrLivenessData &Data) { - DenseSet WorklistSet; - SmallVector Worklist; + SmallSetVector Worklist; auto AddPredsToWorklist = [&](BasicBlock *BB) { - for (BasicBlock *Pred : predecessors(BB)) - if (WorklistSet.insert(Pred).second) - Worklist.push_back(Pred); + // We use a SetVector so that we don't have duplicates in the worklist. + Worklist.insert(pred_begin(BB), pred_end(BB)); }; auto NextItem = [&]() { BasicBlock *BB = Worklist.back(); Worklist.pop_back(); - WorklistSet.erase(BB); return BB; }; @@ -2115,7 +2741,7 @@ static void computeLiveInValues(DominatorTree &DT, Function &F, } // 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);