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Diffstat (limited to 'lib/Transforms/Scalar/RewriteStatepointsForGC.cpp')
| -rw-r--r-- | lib/Transforms/Scalar/RewriteStatepointsForGC.cpp | 1897 |
1 files changed, 1897 insertions, 0 deletions
diff --git a/lib/Transforms/Scalar/RewriteStatepointsForGC.cpp b/lib/Transforms/Scalar/RewriteStatepointsForGC.cpp new file mode 100644 index 0000000..ca9ab54 --- /dev/null +++ b/lib/Transforms/Scalar/RewriteStatepointsForGC.cpp @@ -0,0 +1,1897 @@ +//===- RewriteStatepointsForGC.cpp - Make GC relocations explicit ---------===// +// +// The LLVM Compiler Infrastructure +// +// This file is distributed under the University of Illinois Open Source +// License. See LICENSE.TXT for details. +// +//===----------------------------------------------------------------------===// +// +// Rewrite an existing set of gc.statepoints such that they make potential +// relocations performed by the garbage collector explicit in the IR. +// +//===----------------------------------------------------------------------===// + +#include "llvm/Pass.h" +#include "llvm/Analysis/CFG.h" +#include "llvm/ADT/SetOperations.h" +#include "llvm/ADT/Statistic.h" +#include "llvm/ADT/DenseSet.h" +#include "llvm/IR/BasicBlock.h" +#include "llvm/IR/CallSite.h" +#include "llvm/IR/Dominators.h" +#include "llvm/IR/Function.h" +#include "llvm/IR/IRBuilder.h" +#include "llvm/IR/InstIterator.h" +#include "llvm/IR/Instructions.h" +#include "llvm/IR/Intrinsics.h" +#include "llvm/IR/IntrinsicInst.h" +#include "llvm/IR/Module.h" +#include "llvm/IR/Statepoint.h" +#include "llvm/IR/Value.h" +#include "llvm/IR/Verifier.h" +#include "llvm/Support/Debug.h" +#include "llvm/Support/CommandLine.h" +#include "llvm/Transforms/Scalar.h" +#include "llvm/Transforms/Utils/BasicBlockUtils.h" +#include "llvm/Transforms/Utils/Cloning.h" +#include "llvm/Transforms/Utils/Local.h" +#include "llvm/Transforms/Utils/PromoteMemToReg.h" + +#define DEBUG_TYPE "rewrite-statepoints-for-gc" + +using namespace llvm; + +// Print tracing output +static cl::opt<bool> TraceLSP("trace-rewrite-statepoints", cl::Hidden, + cl::init(false)); + +// Print the liveset found at the insert location +static cl::opt<bool> PrintLiveSet("spp-print-liveset", cl::Hidden, + cl::init(false)); +static cl::opt<bool> PrintLiveSetSize("spp-print-liveset-size", + cl::Hidden, cl::init(false)); +// Print out the base pointers for debugging +static cl::opt<bool> PrintBasePointers("spp-print-base-pointers", + cl::Hidden, cl::init(false)); + +namespace { +struct RewriteStatepointsForGC : public FunctionPass { + static char ID; // Pass identification, replacement for typeid + + RewriteStatepointsForGC() : FunctionPass(ID) { + initializeRewriteStatepointsForGCPass(*PassRegistry::getPassRegistry()); + } + bool runOnFunction(Function &F) override; + + 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<DominatorTreeWrapperPass>(); + } +}; +} // namespace + +char RewriteStatepointsForGC::ID = 0; + +FunctionPass *llvm::createRewriteStatepointsForGCPass() { + return new RewriteStatepointsForGC(); +} + +INITIALIZE_PASS_BEGIN(RewriteStatepointsForGC, "rewrite-statepoints-for-gc", + "Make relocations explicit at statepoints", false, false) +INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass) +INITIALIZE_PASS_END(RewriteStatepointsForGC, "rewrite-statepoints-for-gc", + "Make relocations explicit at statepoints", false, false) + +namespace { +// The type of the internal cache used inside the findBasePointers family +// of functions. From the callers perspective, this is an opaque type and +// should not be inspected. +// +// In the actual implementation this caches two relations: +// - The base relation itself (i.e. this pointer is based on that one) +// - The base defining value relation (i.e. before base_phi insertion) +// Generally, after the execution of a full findBasePointer call, only the +// base relation will remain. Internally, we add a mixture of the two +// types, then update all the second type to the first type +typedef DenseMap<Value *, Value *> DefiningValueMapTy; +typedef DenseSet<llvm::Value *> StatepointLiveSetTy; + +struct PartiallyConstructedSafepointRecord { + /// The set of values known to be live accross this safepoint + StatepointLiveSetTy liveset; + + /// Mapping from live pointers to a base-defining-value + DenseMap<llvm::Value *, llvm::Value *> PointerToBase; + + /// Any new values which were added to the IR during base pointer analysis + /// for this safepoint + DenseSet<llvm::Value *> 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; + + /// Instruction to which exceptional gc relocates are attached + /// Makes it easier to iterate through them during relocationViaAlloca. + Instruction *UnwindToken; +}; +} + +// TODO: Once we can get to the GCStrategy, this becomes +// Optional<bool> isGCManagedPointer(const Value *V) const override { + +static bool isGCPointerType(const Type *T) { + if (const PointerType *PT = dyn_cast<PointerType>(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. + return (1 == PT->getAddressSpace()); + return false; +} + +/// Return true if the Value is a gc reference type which is potentially used +/// after the instruction 'loc'. This is only used with the edge reachability +/// liveness code. Note: It is assumed the V dominates loc. +static bool isLiveGCReferenceAt(Value &V, Instruction *loc, DominatorTree &DT, + LoopInfo *LI) { + if (!isGCPointerType(V.getType())) + return false; + + if (V.use_empty()) + return false; + + // Given assumption that V dominates loc, this may be live + return true; +} + +#ifndef NDEBUG +static bool isAggWhichContainsGCPtrType(Type *Ty) { + if (VectorType *VT = dyn_cast<VectorType>(Ty)) + return isGCPointerType(VT->getScalarType()); + if (ArrayType *AT = dyn_cast<ArrayType>(Ty)) + return isGCPointerType(AT->getElementType()) || + isAggWhichContainsGCPtrType(AT->getElementType()); + if (StructType *ST = dyn_cast<StructType>(Ty)) + return std::any_of(ST->subtypes().begin(), ST->subtypes().end(), + [](Type *SubType) { + return isGCPointerType(SubType) || + isAggWhichContainsGCPtrType(SubType); + }); + return false; +} +#endif + +// Conservatively identifies any definitions which might be live at the +// given instruction. The analysis is performed immediately before the +// given instruction. Values defined by that instruction are not considered +// live. Values used by that instruction are considered live. +// +// preconditions: valid IR graph, term is either a terminator instruction or +// a call instruction, pred is the basic block of term, DT, LI are valid +// +// side effects: none, does not mutate IR +// +// postconditions: populates liveValues as discussed above +static void findLiveGCValuesAtInst(Instruction *term, BasicBlock *pred, + DominatorTree &DT, LoopInfo *LI, + StatepointLiveSetTy &liveValues) { + liveValues.clear(); + + assert(isa<CallInst>(term) || isa<InvokeInst>(term) || term->isTerminator()); + + Function *F = pred->getParent(); + + auto is_live_gc_reference = + [&](Value &V) { return isLiveGCReferenceAt(V, term, DT, LI); }; + + // Are there any gc pointer arguments live over this point? This needs to be + // special cased since arguments aren't defined in basic blocks. + for (Argument &arg : F->args()) { + assert(!isAggWhichContainsGCPtrType(arg.getType()) && + "support for FCA unimplemented"); + + if (is_live_gc_reference(arg)) { + liveValues.insert(&arg); + } + } + + // Walk through all dominating blocks - the ones which can contain + // definitions used in this block - and check to see if any of the values + // they define are used in locations potentially reachable from the + // interesting instruction. + BasicBlock *BBI = pred; + while (true) { + if (TraceLSP) { + errs() << "[LSP] Looking at dominating block " << pred->getName() << "\n"; + } + assert(DT.dominates(BBI, pred)); + assert(isPotentiallyReachable(BBI, pred, &DT) && + "dominated block must be reachable"); + + // Walk through the instructions in dominating blocks and keep any + // that have a use potentially reachable from the block we're + // considering putting the safepoint in + for (Instruction &inst : *BBI) { + if (TraceLSP) { + errs() << "[LSP] Looking at instruction "; + inst.dump(); + } + + if (pred == BBI && (&inst) == term) { + if (TraceLSP) { + errs() << "[LSP] stopped because we encountered the safepoint " + "instruction.\n"; + } + + // If we're in the block which defines the interesting instruction, + // we don't want to include any values as live which are defined + // _after_ the interesting line or as part of the line itself + // i.e. "term" is the call instruction for a call safepoint, the + // results of the call should not be considered live in that stackmap + break; + } + + assert(!isAggWhichContainsGCPtrType(inst.getType()) && + "support for FCA unimplemented"); + + if (is_live_gc_reference(inst)) { + if (TraceLSP) { + errs() << "[LSP] found live value for this safepoint "; + inst.dump(); + term->dump(); + } + liveValues.insert(&inst); + } + } + if (!DT.getNode(BBI)->getIDom()) { + assert(BBI == &F->getEntryBlock() && + "failed to find a dominator for something other than " + "the entry block"); + break; + } + BBI = DT.getNode(BBI)->getIDom()->getBlock(); + } +} + +static bool order_by_name(llvm::Value *a, llvm::Value *b) { + if (a->hasName() && b->hasName()) { + return -1 == a->getName().compare(b->getName()); + } else if (a->hasName() && !b->hasName()) { + return true; + } else if (!a->hasName() && b->hasName()) { + return false; + } else { + // Better than nothing, but not stable + return a < b; + } +} + +/// Find the initial live set. Note that due to base pointer +/// insertion, the live set may be incomplete. +static void +analyzeParsePointLiveness(DominatorTree &DT, const CallSite &CS, + PartiallyConstructedSafepointRecord &result) { + Instruction *inst = CS.getInstruction(); + + BasicBlock *BB = inst->getParent(); + StatepointLiveSetTy liveset; + findLiveGCValuesAtInst(inst, BB, DT, nullptr, liveset); + + 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 + // by name + SmallVector<Value *, 64> 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(); + } + } + if (PrintLiveSetSize) { + errs() << "Safepoint For: " << CS.getCalledValue()->getName() << "\n"; + errs() << "Number live values: " << liveset.size() << "\n"; + } + result.liveset = liveset; +} + +/// True iff this value is the null pointer constant (of any pointer type) +static bool LLVM_ATTRIBUTE_UNUSED isNullConstant(Value *V) { + return isa<Constant>(V) && isa<PointerType>(V->getType()) && + cast<Constant>(V)->isNullValue(); +} + +/// 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) { + assert(I->getType()->isPointerTy() && + "Illegal to ask for the base pointer of a non-pointer type"); + + // There are instructions which can never return gc pointer values. Sanity + // check + // that this is actually true. + assert(!isa<InsertElementInst>(I) && !isa<ExtractElementInst>(I) && + !isa<ShuffleVectorInst>(I) && "Vector types are not gc pointers"); + assert((!isa<Instruction>(I) || isa<InvokeInst>(I) || + !cast<Instruction>(I)->isTerminator()) && + "With the exception of invoke terminators don't define values"); + assert(!isa<StoreInst>(I) && !isa<FenceInst>(I) && + "Can't be definitions to start with"); + assert(!isa<ICmpInst>(I) && !isa<FCmpInst>(I) && + "Comparisons don't give ops"); + // There's a bunch of instructions which just don't make sense to apply to + // a pointer. The only valid reason for this would be pointer bit + // twiddling which we're just not going to support. + assert((!isa<Instruction>(I) || !cast<Instruction>(I)->isBinaryOp()) && + "Binary ops on pointer values are meaningless. Unless your " + "bit-twiddling which we don't support"); + + if (Argument *Arg = dyn_cast<Argument>(I)) { + // An incoming argument to the function is a base pointer + // We should have never reached here if this argument isn't an gc value + assert(Arg->getType()->isPointerTy() && + "Base for pointer must be another pointer"); + return Arg; + } + + if (GlobalVariable *global = dyn_cast<GlobalVariable>(I)) { + // base case + assert(global->getType()->isPointerTy() && + "Base for pointer must be another pointer"); + return global; + } + + // inlining could possibly introduce phi node that contains + // undef if callee has multiple returns + if (UndefValue *undef = dyn_cast<UndefValue>(I)) { + assert(undef->getType()->isPointerTy() && + "Base for pointer must be another pointer"); + return undef; // utterly meaningless, but useful for dealing with + // partially optimized code. + } + + // Due to inheritance, this must be _after_ the global variable and undef + // checks + if (Constant *con = dyn_cast<Constant>(I)) { + assert(!isa<GlobalVariable>(I) && !isa<UndefValue>(I) && + "order of checks wrong!"); + // Note: Finding a constant base for something marked for relocation + // doesn't really make sense. The most likely case is either a) some + // screwed up the address space usage or b) your validating against + // compiled C++ code w/o the proper separation. The only real exception + // is a null pointer. You could have generic code written to index of + // 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(con->getType()->isPointerTy() && + "Base for pointer must be another pointer"); + assert(con->isNullValue() && "null is the only case which makes sense"); + return con; + } + + if (CastInst *CI = dyn_cast<CastInst>(I)) { + Value *def = CI->stripPointerCasts(); + assert(def->getType()->isPointerTy() && + "Base for pointer must be another pointer"); + // If we find a cast instruction here, it means we've found a cast which is + // not simply a pointer cast (i.e. an inttoptr). We don't know how to + // handle int->ptr conversion. + assert(!isa<CastInst>(def) && "shouldn't find another cast here"); + return findBaseDefiningValue(def); + } + + if (LoadInst *LI = dyn_cast<LoadInst>(I)) { + if (LI->getType()->isPointerTy()) { + Value *Op = LI->getOperand(0); + (void)Op; + // Has to be a pointer to an gc object, or possibly an array of such? + assert(Op->getType()->isPointerTy()); + return LI; // The value loaded is an gc base itself + } + } + if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(I)) { + Value *Op = GEP->getOperand(0); + if (Op->getType()->isPointerTy()) { + return findBaseDefiningValue(Op); // The base of this GEP is the base + } + } + + if (AllocaInst *alloc = dyn_cast<AllocaInst>(I)) { + // An alloca represents a conceptual stack slot. It's the slot itself + // that the GC needs to know about, not the value in the slot. + assert(alloc->getType()->isPointerTy() && + "Base for pointer must be another pointer"); + return alloc; + } + + if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) { + switch (II->getIntrinsicID()) { + default: + // fall through to general call handling + break; + case Intrinsic::experimental_gc_statepoint: + case Intrinsic::experimental_gc_result_float: + case Intrinsic::experimental_gc_result_int: + llvm_unreachable("these don't produce pointers"); + case Intrinsic::experimental_gc_result_ptr: + // This is just a special case of the CallInst check below to handle a + // statepoint with deopt args which hasn't been rewritten for GC yet. + // TODO: Assert that the statepoint isn't rewritten yet. + return II; + case Intrinsic::experimental_gc_relocate: { + // Rerunning safepoint insertion after safepoints are already + // inserted is not supported. It could probably be made to work, + // but why are you doing this? There's no good reason. + llvm_unreachable("repeat safepoint insertion is not supported"); + } + case Intrinsic::gcroot: + // Currently, this mechanism hasn't been extended to work with gcroot. + // There's no reason it couldn't be, but I haven't thought about the + // implications much. + llvm_unreachable( + "interaction with the gcroot mechanism is not supported"); + } + } + // We assume that functions in the source language only return base + // pointers. This should probably be generalized via attributes to support + // both source language and internal functions. + if (CallInst *call = dyn_cast<CallInst>(I)) { + assert(call->getType()->isPointerTy() && + "Base for pointer must be another pointer"); + return call; + } + if (InvokeInst *invoke = dyn_cast<InvokeInst>(I)) { + assert(invoke->getType()->isPointerTy() && + "Base for pointer must be another pointer"); + return invoke; + } + + // 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. + assert(!isa<LandingPadInst>(I) && "Landing Pad is unimplemented"); + + if (AtomicCmpXchgInst *cas = dyn_cast<AtomicCmpXchgInst>(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. We loaded a pointer from a address in memory, that value + // had better be a valid base pointer. + return cas->getPointerOperand(); + } + if (AtomicRMWInst *atomic = dyn_cast<AtomicRMWInst>(I)) { + assert(AtomicRMWInst::Xchg == atomic->getOperation() && + "All others are binary ops which don't apply to base pointers"); + // semantically, a load, store pair. Treat it the same as a standard load + return atomic->getPointerOperand(); + } + + // The aggregate ops. Aggregates can either be in the heap or on the + // 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 (ExtractValueInst *ev = dyn_cast<ExtractValueInst>(I)) { + return ev; + } + + // We should never see an insert vector since that would require we be + // tracing back a struct value not a pointer value. + assert(!isa<InsertValueInst>(I) && + "Base pointer for a struct is meaningless"); + + // The last two cases here don't return a base pointer. Instead, they + // return a value which dynamically selects from amoung several base + // derived pointers (each with it's own base potentially). It's the job of + // the caller to resolve these. + if (SelectInst *select = dyn_cast<SelectInst>(I)) { + return select; + } + + return cast<PHINode>(I); +} + +/// Returns the base defining value for this value. +static Value *findBaseDefiningValueCached(Value *I, DefiningValueMapTy &cache) { + Value *&Cached = cache[I]; + if (!Cached) { + Cached = findBaseDefiningValue(I); + } + assert(cache[I] != nullptr); + + if (TraceLSP) { + errs() << "fBDV-cached: " << I->getName() << " -> " << Cached->getName() + << "\n"; + } + return Cached; +} + +/// Return a base pointer for this value if known. Otherwise, return it's +/// base defining value. +static Value *findBaseOrBDV(Value *I, DefiningValueMapTy &cache) { + Value *def = findBaseDefiningValueCached(I, cache); + auto Found = cache.find(def); + if (Found != cache.end()) { + // Either a base-of relation, or a self reference. Caller must check. + return Found->second; + } + // Only a BDV available + return def; +} + +/// Given the result of a call to findBaseDefiningValue, or findBaseOrBDV, +/// is it known to be a base pointer? Or do we need to continue searching. +static bool isKnownBaseResult(Value *v) { + if (!isa<PHINode>(v) && !isa<SelectInst>(v)) { + // no recursion possible + return true; + } + if (cast<Instruction>(v)->getMetadata("is_base_value")) { + // This is a previously inserted base phi or select. We know + // that this is a base value. + return true; + } + + // We need to keep searching + return false; +} + +// TODO: find a better name for this +namespace { +class PhiState { +public: + enum Status { Unknown, Base, Conflict }; + + PhiState(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) {} + PhiState(const PhiState &other) : status(other.status), base(other.base) { + assert(status != Base || base); + } + + Status getStatus() const { return status; } + Value *getBase() const { return base; } + + bool isBase() const { return getStatus() == Base; } + bool isUnknown() const { return getStatus() == Unknown; } + bool isConflict() const { return getStatus() == Conflict; } + + bool operator==(const PhiState &other) const { + return base == other.base && status == other.status; + } + + bool operator!=(const PhiState &other) const { return !(*this == other); } + + void dump() { + errs() << status << " (" << base << " - " + << (base ? base->getName() : "nullptr") << "): "; + } + +private: + Status status; + Value *base; // non null only if status == base +}; + +typedef DenseMap<Value *, PhiState> ConflictStateMapTy; +// Values of type PhiState 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 { +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); + } + + PhiState 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); + } + } + + PhiState lookupFromMap(Value *V) { + auto I = phiStates.find(V); + assert(I != phiStates.end() && "lookup failed!"); + return I->second; + } + + static PhiState pureMeet(const PhiState &stateA, const PhiState &stateB) { + switch (stateA.getStatus()) { + case PhiState::Unknown: + return stateB; + + case PhiState::Base: + assert(stateA.getBase() && "can't be null"); + if (stateB.isUnknown()) + return stateA; + + if (stateB.isBase()) { + if (stateA.getBase() == stateB.getBase()) { + assert(stateA == stateB && "equality broken!"); + return stateA; + } + return PhiState(PhiState::Conflict); + } + assert(stateB.isConflict() && "only three states!"); + return PhiState(PhiState::Conflict); + + case PhiState::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<llvm::Value *> &NewInsertedDefs) { + Value *def = findBaseOrBDV(I, cache); + + if (isKnownBaseResult(def)) { + return def; + } + + // Here's the rough algorithm: + // - For every SSA value, construct a mapping to either an actual base + // pointer or a PHI which obscures the base pointer. + // - Construct a mapping from PHI to unknown TOP state. Use an + // optimistic algorithm to propagate base pointer information. Lattice + // looks like: + // UNKNOWN + // b1 b2 b3 b4 + // CONFLICT + // When algorithm terminates, all PHIs will either have a single concrete + // base or be in a conflict state. + // - For every conflict, insert a dummy PHI node without arguments. Add + // these to the base[Instruction] = BasePtr mapping. For every + // non-conflict, add the actual base. + // - For every conflict, add arguments for the base[a] of each input + // arguments. + // + // 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 + // 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 + // PERF: Yes, this is as horribly inefficient as it looks. + bool done = false; + while (!done) { + done = true; + for (auto Pair : states) { + Value *v = Pair.first; + assert(!isKnownBaseResult(v) && "why did it get added?"); + if (PHINode *phi = dyn_cast<PHINode>(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<SelectInst>(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; + } + } + } + } + + if (TraceLSP) { + errs() << "States after initialization:\n"; + for (auto Pair : states) { + Instruction *v = cast<Instruction>(Pair.first); + PhiState state = Pair.second; + state.dump(); + v->dump(); + } + } + + // TODO: come back and revisit the state transitions around inputs which + // have reached conflict state. The current version seems too conservative. + + bool progress = true; + size_t oldSize = 0; + while (progress) { + oldSize = states.size(); + progress = false; + for (auto Pair : states) { + MeetPhiStates calculateMeet(states); + Value *v = Pair.first; + assert(!isKnownBaseResult(v) && "why did it get added?"); + if (SelectInst *select = dyn_cast<SelectInst>(v)) { + calculateMeet.meetWith(findBaseOrBDV(select->getTrueValue(), cache)); + calculateMeet.meetWith(findBaseOrBDV(select->getFalseValue(), cache)); + } else + for (Value *Val : cast<PHINode>(v)->incoming_values()) + calculateMeet.meetWith(findBaseOrBDV(Val, cache)); + + PhiState oldState = states[v]; + PhiState newState = calculateMeet.getResult(); + if (oldState != newState) { + progress = true; + states[v] = newState; + } + } + + assert(oldSize <= states.size()); + assert(oldSize == states.size() || progress); + } + + if (TraceLSP) { + errs() << "States after meet iteration:\n"; + for (auto Pair : states) { + Instruction *v = cast<Instruction>(Pair.first); + PhiState state = Pair.second; + state.dump(); + v->dump(); + } + } + + // Insert Phis for all conflicts + for (auto Pair : states) { + Instruction *v = cast<Instruction>(Pair.first); + PhiState state = Pair.second; + assert(!isKnownBaseResult(v) && "why did it get added?"); + assert(!state.isUnknown() && "Optimistic algorithm didn't complete!"); + if (state.isConflict()) { + if (isa<PHINode>(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); + } else if (SelectInst *sel = dyn_cast<SelectInst>(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); + } else + llvm_unreachable("unknown conflict type"); + } + } + + // Fixup all the inputs of the new PHIs + for (auto Pair : states) { + Instruction *v = cast<Instruction>(Pair.first); + PhiState state = Pair.second; + + assert(!isKnownBaseResult(v) && "why did it get added?"); + assert(!state.isUnknown() && "Optimistic algorithm didn't complete!"); + if (state.isConflict()) { + if (PHINode *basephi = dyn_cast<PHINode>(state.getBase())) { + PHINode *phi = cast<PHINode>(v); + unsigned NumPHIValues = phi->getNumIncomingValues(); + for (unsigned i = 0; i < NumPHIValues; i++) { + Value *InVal = phi->getIncomingValue(i); + BasicBlock *InBB = phi->getIncomingBlock(i); + + // If we've already seen InBB, add the same incoming value + // we added for it earlier. The IR verifier requires phi + // nodes with multiple entries from the same basic block + // to have the same incoming value for each of those + // entries. If we don't do this check here and basephi + // has a different type than base, we'll end up adding two + // bitcasts (and hence two distinct values) as incoming + // values for the same basic block. + + int blockIndex = basephi->getBasicBlockIndex(InBB); + 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 + // 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() && + "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); + } + assert(basephi->getNumIncomingValues() == NumPHIValues); + } else if (SelectInst *basesel = dyn_cast<SelectInst>(state.getBase())) { + SelectInst *sel = cast<SelectInst>(v); + // Operand 1 & 2 are true, false path respectively. TODO: refactor to + // something more safe and less hacky. + 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); + } + } else + llvm_unreachable("unexpected conflict type"); + } + } + + // 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?"); + + 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"; + } + + assert(isKnownBaseResult(base) && + "must be something we 'know' is a base pointer"); + if (cache.count(v)) { + // Once we transition from the BDV relation being store in the cache to + // the base relation being stored, it must be stable + assert((!isKnownBaseResult(cache[v]) || cache[v] == base) && + "base relation should be stable"); + } + cache[v] = base; + } + assert(cache.find(def) != cache.end()); + return cache[def]; +} + +// For a set of live pointers (base and/or derived), identify the base +// pointer of the object which they are derived from. This routine will +// mutate the IR graph as needed to make the 'base' pointer live at the +// definition site of 'derived'. This ensures that any use of 'derived' can +// also use 'base'. This may involve the insertion of a number of +// additional PHI nodes. +// +// preconditions: live is a set of pointer type Values +// +// side effects: may insert PHI nodes into the existing CFG, will preserve +// CFG, will not remove or mutate any existing nodes +// +// post condition: PointerToBase contains one (derived, base) pair for every +// pointer in live. Note that derived can be equal to base if the original +// pointer was a base pointer. +static void findBasePointers(const StatepointLiveSetTy &live, + DenseMap<llvm::Value *, llvm::Value *> &PointerToBase, + DominatorTree *DT, DefiningValueMapTy &DVCache, + DenseSet<llvm::Value *> &NewInsertedDefs) { + for (Value *ptr : live) { + Value *base = findBasePointer(ptr, DVCache, NewInsertedDefs); + assert(base && "failed to find base pointer"); + PointerToBase[ptr] = base; + assert((!isa<Instruction>(base) || !isa<Instruction>(ptr) || + DT->dominates(cast<Instruction>(base)->getParent(), + cast<Instruction>(ptr)->getParent())) && + "The base we found better dominate the derived pointer"); + + // 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. + assert(!isNullConstant(base) && "the relocation code needs adjustment to " + "handle the relocation of a null pointer " + "constant without causing false positives " + "in the safepoint ir verifier."); + } +} + +/// Find the required based pointers (and adjust the live set) for the given +/// parse point. +static void findBasePointers(DominatorTree &DT, DefiningValueMapTy &DVCache, + const CallSite &CS, + PartiallyConstructedSafepointRecord &result) { + DenseMap<llvm::Value *, llvm::Value *> PointerToBase; + DenseSet<llvm::Value *> NewInsertedDefs; + findBasePointers(result.liveset, PointerToBase, &DT, DVCache, NewInsertedDefs); + + if (PrintBasePointers) { + errs() << "Base Pairs (w/o Relocation):\n"; + for (auto Pair : PointerToBase) { + errs() << " derived %" << Pair.first->getName() << " base %" + << Pair.second->getName() << "\n"; + } + } + + result.PointerToBase = PointerToBase; + result.NewInsertedDefs = NewInsertedDefs; +} + +/// Check for liveness of items in the insert defs and add them to the live +/// and base pointer sets +static void fixupLiveness(DominatorTree &DT, const CallSite &CS, + const DenseSet<Value *> &allInsertedDefs, + PartiallyConstructedSafepointRecord &result) { + Instruction *inst = CS.getInstruction(); + + auto liveset = result.liveset; + auto PointerToBase = result.PointerToBase; + + auto is_live_gc_reference = + [&](Value &V) { return isLiveGCReferenceAt(V, inst, DT, nullptr); }; + + // For each new definition, check to see if a) the definition dominates the + // instruction we're interested in, and b) one of the uses of that definition + // is edge-reachable from the instruction we're interested in. This is the + // same definition of liveness we used in the intial liveness analysis + for (Value *newDef : allInsertedDefs) { + if (liveset.count(newDef)) { + // already live, no action needed + continue; + } + + // PERF: Use DT to check instruction domination might not be good for + // compilation time, and we could change to optimal solution if this + // turn to be a issue + if (!DT.dominates(cast<Instruction>(newDef), inst)) { + // can't possibly be live at inst + continue; + } + + if (is_live_gc_reference(*newDef)) { + // Add the live new defs into liveset and PointerToBase + liveset.insert(newDef); + PointerToBase[newDef] = newDef; + } + } + + result.liveset = liveset; + result.PointerToBase = PointerToBase; +} + +static void fixupLiveReferences( + Function &F, DominatorTree &DT, Pass *P, + const DenseSet<llvm::Value *> &allInsertedDefs, + ArrayRef<CallSite> toUpdate, + MutableArrayRef<struct PartiallyConstructedSafepointRecord> records) { + for (size_t i = 0; i < records.size(); i++) { + struct PartiallyConstructedSafepointRecord &info = records[i]; + const CallSite &CS = toUpdate[i]; + fixupLiveness(DT, CS, allInsertedDefs, info); + } +} + +// 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; + + if (!BB->getUniquePredecessor()) { + ret = SplitBlockPredecessors(BB, InvokeParent, ""); + } + + // 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. + + return ret; +} + +static int find_index(ArrayRef<Value *> livevec, Value *val) { + auto itr = std::find(livevec.begin(), livevec.end(), val); + assert(livevec.end() != itr); + size_t index = std::distance(livevec.begin(), itr); + assert(index < livevec.size()); + return index; +} + +// Create new attribute set containing only attributes which can be transfered +// from original call to the safepoint. +static AttributeSet legalizeCallAttributes(AttributeSet AS) { + AttributeSet ret; + + for (unsigned Slot = 0; Slot < AS.getNumSlots(); Slot++) { + unsigned index = AS.getSlotIndex(Slot); + + if (index == AttributeSet::ReturnIndex || + index == AttributeSet::FunctionIndex) { + + for (auto it = AS.begin(Slot), it_end = AS.end(Slot); it != it_end; + ++it) { + Attribute attr = *it; + + // Do not allow certain attributes - just skip them + // Safepoint can not be read only or read none. + if (attr.hasAttribute(Attribute::ReadNone) || + attr.hasAttribute(Attribute::ReadOnly)) + continue; + + ret = ret.addAttributes( + AS.getContext(), index, + AttributeSet::get(AS.getContext(), index, AttrBuilder(attr))); + } + } + + // Just skip parameter attributes for now + } + + return ret; +} + +/// Helper function to place all gc relocates necessary for the given +/// statepoint. +/// Inputs: +/// liveVariables - list of variables to be relocated. +/// liveStart - index of the first live variable. +/// basePtrs - base pointers. +/// statepointToken - statepoint instruction to which relocates should be +/// bound. +/// Builder - Llvm IR builder to be used to construct new calls. +void CreateGCRelocates(ArrayRef<llvm::Value *> liveVariables, + const int liveStart, + ArrayRef<llvm::Value *> basePtrs, + Instruction *statepointToken, IRBuilder<> Builder) { + + SmallVector<Instruction *, 64> 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<Type *, 1> 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); + + // 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])); + + // 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" + : ""); + // Trick CodeGen into thinking there are lots of free registers at this + // fake call. + cast<CallInst>(reloc)->setCallingConv(CallingConv::Cold); + + NewDefs.push_back(cast<Instruction>(reloc)); + } + assert(NewDefs.size() == liveVariables.size() && + "missing or extra redefinition at safepoint"); +} + +static void +makeStatepointExplicitImpl(const CallSite &CS, /* to replace */ + const SmallVectorImpl<llvm::Value *> &basePtrs, + const SmallVectorImpl<llvm::Value *> &liveVariables, + Pass *P, + PartiallyConstructedSafepointRecord &result) { + assert(basePtrs.size() == liveVariables.size()); + assert(isStatepoint(CS) && + "This method expects to be rewriting a statepoint"); + + BasicBlock *BB = CS.getInstruction()->getParent(); + assert(BB); + Function *F = BB->getParent(); + assert(F && "must be set"); + Module *M = F->getParent(); + (void)M; + assert(M && "must be set"); + + // We're not changing the function signature of the statepoint since the gc + // arguments go into the var args section. + Function *gc_statepoint_decl = CS.getCalledFunction(); + + // Then go ahead and use the builder do actually do the inserts. We insert + // immediately before the previous instruction under the assumption that all + // arguments will be available here. We can't insert afterwards since we may + // be replacing a terminator. + Instruction *insertBefore = CS.getInstruction(); + IRBuilder<> Builder(insertBefore); + // Copy all of the arguments from the original statepoint - this includes the + // target, call args, and deopt args + SmallVector<llvm::Value *, 64> args; + args.insert(args.end(), CS.arg_begin(), CS.arg_end()); + // TODO: Clear the 'needs rewrite' flag + + // add all the pointers to be relocated (gc arguments) + // Capture the start of the live variable list for use in the gc_relocates + const int live_start = args.size(); + args.insert(args.end(), liveVariables.begin(), liveVariables.end()); + + // Create the statepoint given all the arguments + Instruction *token = nullptr; + AttributeSet return_attributes; + if (CS.isCall()) { + CallInst *toReplace = cast<CallInst>(CS.getInstruction()); + CallInst *call = + Builder.CreateCall(gc_statepoint_decl, args, "safepoint_token"); + call->setTailCall(toReplace->isTailCall()); + call->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 + // directly on statepoint and return attrs later for gc_result intrinsic. + call->setAttributes(new_attrs.getFnAttributes()); + return_attributes = new_attrs.getRetAttributes(); + + token = call; + + // Put the following gc_result and gc_relocate calls immediately after the + // the old call (which we're about to delete) + BasicBlock::iterator next(toReplace); + assert(BB->end() != next && "not a terminator, must have next"); + next++; + Instruction *IP = &*(next); + Builder.SetInsertPoint(IP); + Builder.SetCurrentDebugLocation(IP->getDebugLoc()); + + } else { + InvokeInst *toReplace = cast<InvokeInst>(CS.getInstruction()); + + // Insert the new invoke into the old block. We'll remove the old one in a + // moment at which point this will become the new terminator for the + // original block. + InvokeInst *invoke = InvokeInst::Create( + gc_statepoint_decl, toReplace->getNormalDest(), + toReplace->getUnwindDest(), args, "", 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 + // directly on statepoint and return attrs later for gc_result intrinsic. + invoke->setAttributes(new_attrs.getFnAttributes()); + return_attributes = new_attrs.getRetAttributes(); + + token = invoke; + + // Generate gc relocates in exceptional path + BasicBlock *unwindBlock = normalizeBBForInvokeSafepoint( + toReplace->getUnwindDest(), invoke->getParent(), P); + + Instruction *IP = &*(unwindBlock->getFirstInsertionPt()); + Builder.SetInsertPoint(IP); + Builder.SetCurrentDebugLocation(toReplace->getDebugLoc()); + + // Extract second element from landingpad return value. We will attach + // exceptional gc relocates to it. + const unsigned idx = 1; + Instruction *exceptional_token = + cast<Instruction>(Builder.CreateExtractValue( + 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); + + // Generate gc relocates and returns for normal block + BasicBlock *normalDest = normalizeBBForInvokeSafepoint( + toReplace->getNormalDest(), invoke->getParent(), P); + + IP = &*(normalDest->getFirstInsertionPt()); + Builder.SetInsertPoint(IP); + + // gc relocates will be generated later as if it were regular call + // statepoint + } + assert(token); + + // Take the name of the original value call if it had one. + token->takeName(CS.getInstruction()); + + // The GCResult is already inserted, we just need to find it +#ifndef NDEBUG + Instruction *toReplace = CS.getInstruction(); + assert((toReplace->hasNUses(0) || toReplace->hasNUses(1)) && + "only valid use before rewrite is gc.result"); + assert(!toReplace->hasOneUse() || + isGCResult(cast<Instruction>(*toReplace->user_begin()))); +#endif + + // Update the gc.result of the original statepoint (if any) to use the newly + // inserted statepoint. This is safe to do here since the token can't be + // considered a live reference. + CS.getInstruction()->replaceAllUsesWith(token); + + result.StatepointToken = token; + + // Second, create a gc.relocate for every live variable + CreateGCRelocates(liveVariables, live_start, basePtrs, token, Builder); + +} + +namespace { +struct name_ordering { + Value *base; + Value *derived; + bool operator()(name_ordering const &a, name_ordering const &b) { + return -1 == a.derived->getName().compare(b.derived->getName()); + } +}; +} +static void stablize_order(SmallVectorImpl<Value *> &basevec, + SmallVectorImpl<Value *> &livevec) { + assert(basevec.size() == livevec.size()); + + SmallVector<name_ordering, 64> temp; + for (size_t i = 0; i < basevec.size(); i++) { + name_ordering v; + v.base = basevec[i]; + v.derived = livevec[i]; + temp.push_back(v); + } + std::sort(temp.begin(), temp.end(), name_ordering()); + for (size_t i = 0; i < basevec.size(); i++) { + basevec[i] = temp[i].base; + livevec[i] = temp[i].derived; + } +} + +// Replace an existing gc.statepoint with a new one and a set of gc.relocates +// which make the relocations happening at this safepoint explicit. +// +// WARNING: Does not do any fixup to adjust users of the original live +// values. That's the callers responsibility. +static void +makeStatepointExplicit(DominatorTree &DT, const CallSite &CS, Pass *P, + PartiallyConstructedSafepointRecord &result) { + auto liveset = result.liveset; + auto PointerToBase = result.PointerToBase; + + // Convert to vector for efficient cross referencing. + SmallVector<Value *, 64> basevec, livevec; + livevec.reserve(liveset.size()); + basevec.reserve(liveset.size()); + for (Value *L : liveset) { + livevec.push_back(L); + + assert(PointerToBase.find(L) != PointerToBase.end()); + Value *base = PointerToBase[L]; + basevec.push_back(base); + } + assert(livevec.size() == basevec.size()); + + // To make the output IR slightly more stable (for use in diffs), ensure a + // fixed order of the values in the safepoint (by sorting the value name). + // The order is otherwise meaningless. + stablize_order(basevec, livevec); + + // Do the actual rewriting and delete the old statepoint + makeStatepointExplicitImpl(CS, basevec, livevec, P, result); + CS.getInstruction()->eraseFromParent(); +} + +// Helper function for the relocationViaAlloca. +// It receives iterator to the statepoint gc relocates and emits store to the +// assigned +// location (via allocaMap) for the each one of them. +// Add visited values into the visitedLiveValues set we will later use them +// for sanity check. +static void +insertRelocationStores(iterator_range<Value::user_iterator> gcRelocs, + DenseMap<Value *, Value *> &allocaMap, + DenseSet<Value *> &visitedLiveValues) { + + for (User *U : gcRelocs) { + if (!isa<IntrinsicInst>(U)) + continue; + + IntrinsicInst *relocatedValue = cast<IntrinsicInst>(U); + + // We only care about relocates + if (relocatedValue->getIntrinsicID() != + Intrinsic::experimental_gc_relocate) { + continue; + } + + GCRelocateOperands relocateOperands(relocatedValue); + Value *originalValue = const_cast<Value *>(relocateOperands.derivedPtr()); + assert(allocaMap.count(originalValue)); + Value *alloca = allocaMap[originalValue]; + + // Emit store into the related alloca + StoreInst *store = new StoreInst(relocatedValue, alloca); + store->insertAfter(relocatedValue); + +#ifndef NDEBUG + visitedLiveValues.insert(originalValue); +#endif + } +} + +/// do all the relocation update via allocas and mem2reg +static void relocationViaAlloca( + Function &F, DominatorTree &DT, ArrayRef<Value *> live, + ArrayRef<struct PartiallyConstructedSafepointRecord> records) { +#ifndef NDEBUG + int initialAllocaNum = 0; + + // record initial number of allocas + for (inst_iterator itr = inst_begin(F), end = inst_end(F); itr != end; + itr++) { + if (isa<AllocaInst>(*itr)) + initialAllocaNum++; + } +#endif + + // TODO-PERF: change data structures, reserve + DenseMap<Value *, Value *> allocaMap; + SmallVector<AllocaInst *, 200> PromotableAllocas; + PromotableAllocas.reserve(live.size()); + + // 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); + } + + // The next two loops are part of the same conceptual operation. We need to + // insert a store to the alloca after the original def and at each + // redefinition. We need to insert a load before each use. These are split + // into distinct loops for performance reasons. + + // update gc pointer after each statepoint + // either store a relocated value or null (if no relocated value found for + // 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; + + // This will be used for consistency check + DenseSet<Value *> visitedLiveValues; + + // Insert stores for normal statepoint gc relocates + insertRelocationStores(Statepoint->users(), allocaMap, visitedLiveValues); + + // In case if it was invoke statepoint + // we will insert stores for exceptional path gc relocates. + if (isa<InvokeInst>(Statepoint)) { + 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<AllocaInst *, 64> ToClobber; + for (auto Pair : allocaMap) { + Value *Def = Pair.first; + AllocaInst *Alloca = cast<AllocaInst>(Pair.second); + + // This value was relocated + if (visitedLiveValues.count(Def)) { + continue; + } + ToClobber.push_back(Alloca); + } + + auto InsertClobbersAt = [&](Instruction *IP) { + for (auto *AI : ToClobber) { + auto AIType = cast<PointerType>(AI->getType()); + auto PT = cast<PointerType>(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<InvokeInst>(Statepoint)) { + InsertClobbersAt(II->getNormalDest()->getFirstInsertionPt()); + InsertClobbersAt(II->getUnwindDest()->getFirstInsertionPt()); + } else { + BasicBlock::iterator Next(cast<CallInst>(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; + + // we pre-record the uses of allocas so that we dont have to worry about + // later update + // that change the user information. + SmallVector<Instruction *, 20> uses; + // PERF: trade a linear scan for repeated reallocation + uses.reserve(std::distance(def->user_begin(), def->user_end())); + for (User *U : def->users()) { + if (!isa<ConstantExpr>(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<Instruction>(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<PHINode>(use)) { + PHINode *phi = cast<PHINode>(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); + } + } + + // 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 (isa<Instruction>(def)) { + store->insertAfter(cast<Instruction>(def)); + } else { + assert((isa<Argument>(def) || isa<GlobalVariable>(def) || + (isa<Constant>(def) && cast<Constant>(def)->isNullValue())) && + "Must be argument or global"); + store->insertAfter(cast<Instruction>(alloca)); + } + } + + assert(PromotableAllocas.size() == live.size() && + "we must have the same allocas with lives"); + if (!PromotableAllocas.empty()) { + // apply mem2reg to promote alloca to SSA + PromoteMemToReg(PromotableAllocas, DT); + } + +#ifndef NDEBUG + for (inst_iterator itr = inst_begin(F), end = inst_end(F); itr != end; + itr++) { + if (isa<AllocaInst>(*itr)) + initialAllocaNum--; + } + assert(initialAllocaNum == 0 && "We must not introduce any extra allocas"); +#endif +} + +/// Implement a unique function which doesn't require we sort the input +/// 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 <typename T> static void unique_unsorted(SmallVectorImpl<T> &Vec) { + DenseSet<T> Seen; + SmallVector<T, 128> 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<Function>(M.getOrInsertFunction("__tmp_use", ftype)); + return Func; +} + +/// Insert holders so that each Value is obviously live through the entire +/// liftetime of the call. +static void insertUseHolderAfter(CallSite &CS, const ArrayRef<Value *> Values, + SmallVectorImpl<CallInst *> &holders) { + Module *M = CS.getInstruction()->getParent()->getParent()->getParent(); + Function *Func = getUseHolder(*M); + 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<InvokeInst>(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"); +} + +static void findLiveReferences( + Function &F, DominatorTree &DT, Pass *P, ArrayRef<CallSite> toUpdate, + MutableArrayRef<struct PartiallyConstructedSafepointRecord> records) { + for (size_t i = 0; i < records.size(); i++) { + struct PartiallyConstructedSafepointRecord &info = records[i]; + const CallSite &CS = toUpdate[i]; + analyzeParsePointLiveness(DT, CS, info); + } +} + +static void addBasesAsLiveValues(StatepointLiveSetTy &liveset, + DenseMap<Value *, Value *> &PointerToBase) { + // Identify any base pointers which are used in this safepoint, but not + // themselves relocated. We need to relocate them so that later inserted + // safepoints can get the properly relocated base register. + DenseSet<Value *> missing; + for (Value *L : liveset) { + assert(PointerToBase.find(L) != PointerToBase.end()); + Value *base = PointerToBase[L]; + assert(base); + if (liveset.find(base) == liveset.end()) { + assert(PointerToBase.find(base) == PointerToBase.end()); + // uniqued by set insert + missing.insert(base); + } + } + + // Note that we want these at the end of the list, otherwise + // register placement gets screwed up once we lower to STATEPOINT + // instructions. This is an utter hack, but there doesn't seem to be a + // better one. + for (Value *base : missing) { + assert(base); + liveset.insert(base); + PointerToBase[base] = base; + } + assert(liveset.size() == PointerToBase.size()); +} + +static bool insertParsePoints(Function &F, DominatorTree &DT, Pass *P, + SmallVectorImpl<CallSite> &toUpdate) { +#ifndef NDEBUG + // sanity check the input + std::set<CallSite> uniqued; + uniqued.insert(toUpdate.begin(), toUpdate.end()); + assert(uniqued.size() == toUpdate.size() && "no duplicates please!"); + + for (size_t i = 0; i < toUpdate.size(); i++) { + CallSite &CS = toUpdate[i]; + assert(CS.getInstruction()->getParent()->getParent() == &F); + assert(isStatepoint(CS) && "expected to already be a deopt statepoint"); + } +#endif + + // 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<CallInst *, 64> holders; + + // Insert a dummy call with all of the arguments to the vm_state we'll need + // for the actual safepoint insertion. This ensures reference arguments in + // the deopt argument list are considered live through the safepoint (and + // thus makes sure they get relocated.) + for (size_t i = 0; i < toUpdate.size(); i++) { + CallSite &CS = toUpdate[i]; + Statepoint StatepointCS(CS); + + SmallVector<Value *, 64> DeoptValues; + for (Use &U : StatepointCS.vm_state_args()) { + Value *Arg = cast<Value>(&U); + if (isGCPointerType(Arg->getType())) + DeoptValues.push_back(Arg); + } + insertUseHolderAfter(CS, DeoptValues, holders); + } + + SmallVector<struct PartiallyConstructedSafepointRecord, 64> records; + records.reserve(toUpdate.size()); + for (size_t i = 0; i < toUpdate.size(); i++) { + struct PartiallyConstructedSafepointRecord info; + records.push_back(info); + } + assert(records.size() == toUpdate.size()); + + // A) Identify all gc pointers which are staticly live at the given call + // site. + findLiveReferences(F, DT, P, toUpdate, records); + + // B) Find the base pointers for each live pointer + /* scope for caching */ { + // Cache the 'defining value' relation used in the computation and + // insertion of base phis and selects. This ensures that we don't insert + // large numbers of duplicate base_phis. + DefiningValueMapTy DVCache; + + for (size_t i = 0; i < records.size(); i++) { + struct PartiallyConstructedSafepointRecord &info = records[i]; + CallSite &CS = toUpdate[i]; + findBasePointers(DT, DVCache, CS, info); + } + } // end of cache scope + + // The base phi insertion logic (for any safepoint) may have inserted new + // instructions which are now live at some safepoint. The simplest such + // example is: + // loop: + // phi a <-- will be a new base_phi here + // safepoint 1 <-- that needs to be live here + // gep a + 1 + // safepoint 2 + // br loop + DenseSet<llvm::Value *> 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 + // remove the dummy calls. + holders.reserve(holders.size() + records.size()); + for (size_t i = 0; i < records.size(); i++) { + struct PartiallyConstructedSafepointRecord &info = records[i]; + CallSite &CS = toUpdate[i]; + + SmallVector<Value *, 128> Bases; + for (auto Pair : info.PointerToBase) { + Bases.push_back(Pair.second); + } + insertUseHolderAfter(CS, Bases, holders); + } + + // Add the bases explicitly to the live vector set. This may result in a few + // extra relocations, but the base has to be available whenever a pointer + // derived from it is used. Thus, we need it to be part of the statepoint's + // gc arguments list. TODO: Introduce an explicit notion (in the following + // code) of the GC argument list as seperate from the live Values at a + // given statepoint. + for (size_t i = 0; i < records.size(); i++) { + struct PartiallyConstructedSafepointRecord &info = records[i]; + addBasesAsLiveValues(info.liveset, info.PointerToBase); + } + + // If we inserted any new values, we need to adjust our notion of what is + // live at a particular safepoint. + if (!allInsertedDefs.empty()) { + fixupLiveReferences(F, DT, P, allInsertedDefs, toUpdate, records); + } + if (PrintBasePointers) { + for (size_t i = 0; i < records.size(); i++) { + struct PartiallyConstructedSafepointRecord &info = records[i]; + errs() << "Base Pairs: (w/Relocation)\n"; + for (auto Pair : info.PointerToBase) { + errs() << " derived %" << Pair.first->getName() << " base %" + << Pair.second->getName() << "\n"; + } + } + } + for (size_t i = 0; i < holders.size(); i++) { + holders[i]->eraseFromParent(); + holders[i] = nullptr; + } + holders.clear(); + + // 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 + // survive to the last iteration of this loop. (By construction, the + // previous statepoint can not be a live variable, thus we can and remove + // the old statepoint calls as we go.) + for (size_t i = 0; i < records.size(); i++) { + struct PartiallyConstructedSafepointRecord &info = records[i]; + CallSite &CS = toUpdate[i]; + makeStatepointExplicit(DT, CS, P, info); + } + 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<InvokeInst>(I)) { + FoldSingleEntryPHINodes(invoke->getNormalDest()); + assert(!isa<PHINode>(invoke->getNormalDest()->begin())); + + FoldSingleEntryPHINodes(invoke->getUnwindDest()); + assert(!isa<PHINode>(invoke->getUnwindDest()->begin())); + } + } + + // Do all the fixups of the original live variables to their relocated selves + SmallVector<Value *, 128> live; + for (size_t i = 0; i < records.size(); i++) { + struct PartiallyConstructedSafepointRecord &info = records[i]; + // We can't simply save the live set from the original insertion. One of + // the live values might be the result of a call which needs a safepoint. + // That Value* no longer exists and we need to use the new gc_result. + // Thankfully, the liveset is embedded in the statepoint (and updated), so + // we just grab that. + Statepoint statepoint(info.StatepointToken); + live.insert(live.end(), statepoint.gc_args_begin(), + statepoint.gc_args_end()); + } + unique_unsorted(live); + +#ifndef NDEBUG + // sanity check + for (auto ptr : live) { + assert(isGCPointerType(ptr->getType()) && "must be a gc pointer type"); + } +#endif + + relocationViaAlloca(F, DT, live, records); + return !records.empty(); +} + +/// 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(); + } else + return false; +} + +bool RewriteStatepointsForGC::runOnFunction(Function &F) { + // Nothing to do for declarations. + if (F.isDeclaration() || F.empty()) + return false; + + // Policy choice says not to rewrite - the most common reason is that we're + // compiling code without a GCStrategy. + if (!shouldRewriteStatepointsIn(F)) + return false; + + // Gather all the statepoints which need rewritten. + SmallVector<CallSite, 64> ParsePointNeeded; + for (Instruction &I : inst_range(F)) { + // TODO: only the ones with the flag set! + if (isStatepoint(I)) + ParsePointNeeded.push_back(CallSite(&I)); + } + + // Return early if no work to do. + if (ParsePointNeeded.empty()) + return false; + + DominatorTree &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree(); + return insertParsePoints(F, DT, this, ParsePointNeeded); +} |