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Diffstat (limited to 'gnu/llvm/lib/Transforms/Scalar/RewriteStatepointsForGC.cpp')
| -rw-r--r-- | gnu/llvm/lib/Transforms/Scalar/RewriteStatepointsForGC.cpp | 2915 |
1 files changed, 2915 insertions, 0 deletions
diff --git a/gnu/llvm/lib/Transforms/Scalar/RewriteStatepointsForGC.cpp b/gnu/llvm/lib/Transforms/Scalar/RewriteStatepointsForGC.cpp new file mode 100644 index 00000000000..d77d5745e60 --- /dev/null +++ b/gnu/llvm/lib/Transforms/Scalar/RewriteStatepointsForGC.cpp @@ -0,0 +1,2915 @@ +//===- 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/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" +#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/MDBuilder.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 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)); + +// Cost threshold measuring when it is profitable to rematerialize value instead +// of relocating it +static cl::opt<unsigned> +RematerializationThreshold("spp-rematerialization-threshold", cl::Hidden, + cl::init(6)); + +#ifdef XDEBUG +static bool ClobberNonLive = true; +#else +static bool ClobberNonLive = false; +#endif +static cl::opt<bool, true> ClobberNonLiveOverride("rs4gc-clobber-non-live", + cl::location(ClobberNonLive), + cl::Hidden); + +static cl::opt<bool> UseDeoptBundles("rs4gc-use-deopt-bundles", cl::Hidden, + cl::init(false)); +static cl::opt<bool> + AllowStatepointWithNoDeoptInfo("rs4gc-allow-statepoint-with-no-deopt-info", + cl::Hidden, cl::init(true)); + +/// Should we split vectors of pointers into their individual elements? This +/// is known to be buggy, but the alternate implementation isn't yet ready. +/// This is purely to provide a debugging and dianostic hook until the vector +/// split is replaced with vector relocations. +static cl::opt<bool> UseVectorSplit("rs4gc-split-vector-values", cl::Hidden, + cl::init(true)); + +namespace { +struct RewriteStatepointsForGC : public ModulePass { + static char ID; // Pass identification, replacement for typeid + + RewriteStatepointsForGC() : ModulePass(ID) { + initializeRewriteStatepointsForGCPass(*PassRegistry::getPassRegistry()); + } + bool runOnFunction(Function &F); + bool runOnModule(Module &M) override { + bool Changed = false; + for (Function &F : M) + Changed |= runOnFunction(F); + + if (Changed) { + // stripNonValidAttributes 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. + stripNonValidAttributes(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<DominatorTreeWrapperPass>(); + AU.addRequired<TargetTransformInfoWrapperPass>(); + } + + /// 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. stripNonValidAttributes (conservatively) restores correctness + /// by erasing all attributes in the module that externally imply + /// dereferenceability. + /// Similar reasoning also applies to the noalias attributes. gc.statepoint + /// can touch the entire heap including noalias objects. + void stripNonValidAttributes(Module &M); + + // Helpers for stripNonValidAttributes + void stripNonValidAttributesFromBody(Function &F); + void stripNonValidAttributesFromPrototype(Function &F); +}; +} // namespace + +char RewriteStatepointsForGC::ID = 0; + +ModulePass *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 { +struct GCPtrLivenessData { + /// Values defined in this block. + DenseMap<BasicBlock *, DenseSet<Value *>> KillSet; + /// Values used in this block (and thus live); does not included values + /// killed within this block. + DenseMap<BasicBlock *, DenseSet<Value *>> LiveSet; + + /// Values live into this basic block (i.e. used by any + /// instruction in this basic block or ones reachable from here) + DenseMap<BasicBlock *, DenseSet<Value *>> LiveIn; + + /// Values live out of this basic block (i.e. live into + /// any successor block) + DenseMap<BasicBlock *, DenseSet<Value *>> LiveOut; +}; + +// 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<Value *> StatepointLiveSetTy; +typedef DenseMap<AssertingVH<Instruction>, AssertingVH<Value>> + RematerializedValueMapTy; + +struct PartiallyConstructedSafepointRecord { + /// The set of values known to be live across this safepoint + StatepointLiveSetTy LiveSet; + + /// Mapping from live pointers to a base-defining-value + DenseMap<Value *, Value *> PointerToBase; + + /// 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; + + /// 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; +}; +} + +static ArrayRef<Use> GetDeoptBundleOperands(ImmutableCallSite CS) { + assert(UseDeoptBundles && "Should not be called otherwise!"); + + Optional<OperandBundleUse> DeoptBundle = CS.getOperandBundle("deopt"); + + if (!DeoptBundle.hasValue()) { + assert(AllowStatepointWithNoDeoptInfo && + "Found non-leaf call without deopt info!"); + return None; + } + + return DeoptBundle.getValue().Inputs; +} + +/// Compute the live-in set for every basic block in the function +static void computeLiveInValues(DominatorTree &DT, Function &F, + GCPtrLivenessData &Data); + +/// Given results from the dataflow liveness computation, find the set of live +/// Values at a particular instruction. +static void findLiveSetAtInst(Instruction *inst, GCPtrLivenessData &Data, + StatepointLiveSetTy &out); + +// TODO: Once we can get to the GCStrategy, this becomes +// Optional<bool> isGCManagedPointer(const Type *Ty) const override { + +static bool isGCPointerType(Type *T) { + if (auto *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 this type is one which a) is a gc pointer or contains a GC +// pointer and b) is of a type this code expects to encounter as a live value. +// (The insertion code will assert that a type which matches (a) and not (b) +// is not encountered.) +static bool isHandledGCPointerType(Type *T) { + // We fully support gc pointers + if (isGCPointerType(T)) + return true; + // We partially support vectors of gc pointers. The code will assert if it + // can't handle something. + if (auto VT = dyn_cast<VectorType>(T)) + if (isGCPointerType(VT->getElementType())) + return true; + return false; +} + +#ifndef NDEBUG +/// Returns true if this type contains a gc pointer whether we know how to +/// handle that type or not. +static bool containsGCPtrType(Type *Ty) { + if (isGCPointerType(Ty)) + return true; + if (VectorType *VT = dyn_cast<VectorType>(Ty)) + return isGCPointerType(VT->getScalarType()); + if (ArrayType *AT = dyn_cast<ArrayType>(Ty)) + return containsGCPtrType(AT->getElementType()); + if (StructType *ST = dyn_cast<StructType>(Ty)) + return std::any_of(ST->subtypes().begin(), ST->subtypes().end(), + containsGCPtrType); + return false; +} + +// Returns true if this is a type which a) is a gc pointer or contains a GC +// pointer and b) is of a type which the code doesn't expect (i.e. first class +// aggregates). Used to trip assertions. +static bool isUnhandledGCPointerType(Type *Ty) { + return containsGCPtrType(Ty) && !isHandledGCPointerType(Ty); +} +#endif + +static bool order_by_name(Value *a, 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; + } +} + +// Return the name of the value suffixed with the provided value, or if the +// value didn't have a name, the default value specified. +static std::string suffixed_name_or(Value *V, StringRef Suffix, + StringRef DefaultName) { + return V->hasName() ? (V->getName() + Suffix).str() : DefaultName.str(); +} + +// 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. +static void analyzeParsePointLiveness( + DominatorTree &DT, GCPtrLivenessData &OriginalLivenessData, + const CallSite &CS, PartiallyConstructedSafepointRecord &result) { + Instruction *inst = CS.getInstruction(); + + StatepointLiveSetTy LiveSet; + findLiveSetAtInst(inst, OriginalLivenessData, LiveSet); + + if (PrintLiveSet) { + // Note: This output is used by several of the test cases + // The order of elements in a set is not stable, put them in a vec and sort + // by name + SmallVector<Value *, 64> Temp; + Temp.insert(Temp.end(), LiveSet.begin(), LiveSet.end()); + std::sort(Temp.begin(), Temp.end(), order_by_name); + errs() << "Live Variables:\n"; + for (Value *V : Temp) + dbgs() << " " << V->getName() << " " << *V << "\n"; + } + if (PrintLiveSetSize) { + errs() << "Safepoint For: " << CS.getCalledValue()->getName() << "\n"; + errs() << "Number live values: " << LiveSet.size() << "\n"; + } + result.LiveSet = LiveSet; +} + +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) { + // Each case parallels findBaseDefiningValue below, see that code for + // detailed motivation. + + if (isa<Argument>(I)) + // An incoming argument to the function is a base pointer + return BaseDefiningValueResult(I, true); + + if (isa<Constant>(I)) + // Constant vectors consist only of constant pointers. + return BaseDefiningValueResult(I, true); + + if (isa<LoadInst>(I)) + return BaseDefiningValueResult(I, true); + + if (isa<InsertElementInst>(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. + return BaseDefiningValueResult(I, false); + + if (isa<ShuffleVectorInst>(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<SelectInst>(I) || isa<PHINode>(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, 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) { + assert(I->getType()->isPtrOrPtrVectorTy() && + "Illegal to ask for the base pointer of a non-pointer type"); + + if (I->getType()->isVectorTy()) + return findBaseDefiningValueOfVector(I); + + if (isa<Argument>(I)) + // An incoming argument to the function is a base pointer + // We should have never reached here if this argument isn't an gc value + return BaseDefiningValueResult(I, true); + + if (isa<Constant>(I)) + // We assume that objects with a constant base (e.g. a global) can't move + // and don't need to be reported to the collector because they are always + // live. All constants have constant bases. Besides global references, all + // kinds of constants (e.g. undef, constant expressions, null pointers) can + // be introduced by the inliner or the optimizer, especially on dynamically + // dead paths. See e.g. test4 in constants.ll. + return BaseDefiningValueResult(I, true); + + if (CastInst *CI = dyn_cast<CastInst>(I)) { + Value *Def = CI->stripPointerCasts(); + // If stripping pointer casts changes the address space there is an + // addrspacecast in between. + assert(cast<PointerType>(Def->getType())->getAddressSpace() == + cast<PointerType>(CI->getType())->getAddressSpace() && + "unsupported addrspacecast"); + // 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 (isa<LoadInst>(I)) + // The value loaded is an gc base itself + return BaseDefiningValueResult(I, true); + + + if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(I)) + // The base of this GEP is the base + return findBaseDefiningValue(GEP->getPointerOperand()); + + if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) { + switch (II->getIntrinsicID()) { + default: + // fall through to general call handling + break; + case Intrinsic::experimental_gc_statepoint: + llvm_unreachable("statepoints don't produce pointers"); + 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 (isa<CallInst>(I) || isa<InvokeInst>(I)) + return BaseDefiningValueResult(I, true); + + // I have absolutely no idea how to implement this part yet. It's not + // necessarily hard, I just haven't really looked at it yet. + assert(!isa<LandingPadInst>(I) && "Landing Pad is unimplemented"); + + if (isa<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. + return BaseDefiningValueResult(I, true); + + assert(!isa<AtomicRMWInst>(I) && "Xchg handled above, all others are " + "binary ops which don't apply to pointers"); + + // 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 (isa<ExtractValueInst>(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<InsertValueInst>(I) && + "Base pointer for a struct is meaningless"); + + // An extractelement produces a base result exactly when it's input does. + // We may need to insert a parallel instruction to extract the appropriate + // element out of the base vector corresponding to the input. Given this, + // it's analogous to the phi and select case even though it's not a merge. + if (isa<ExtractElementInst>(I)) + // Note: There a lot of obvious peephole cases here. This are deliberately + // handled after the main base pointer inference algorithm to make writing + // test cases to exercise that code easier. + return BaseDefiningValueResult(I, false); + + // The last two cases here don't return a base pointer. Instead, they + // return a value which dynamically selects from among several base + // derived pointers (each with it's own base potentially). It's the job of + // the caller to resolve these. + assert((isa<SelectInst>(I) || isa<PHINode>(I)) && + "missing instruction case in findBaseDefiningValing"); + 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).BDV; + DEBUG(dbgs() << "fBDV-cached: " << I->getName() << " -> " + << Cached->getName() << "\n"); + } + assert(Cache[I] != nullptr); + 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) && + !isa<ExtractElementInst>(V) && !isa<InsertElementInst>(V) && + !isa<ShuffleVectorInst>(V)) { + // no recursion possible + return true; + } + if (isa<Instruction>(V) && + 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; +} + +namespace { +/// 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 }; + + BDVState(Status s, Value *b = nullptr) : status(s), base(b) { + assert(status != Base || b); + } + explicit BDVState(Value *b) : status(Base), base(b) {} + BDVState() : status(Unknown), base(nullptr) {} + + 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 BDVState &other) const { + return base == other.base && status == other.status; + } + + bool operator!=(const BDVState &other) const { return !(*this == other); } + + 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; + AssertingVH<Value> base; // non null only if status == base +}; +} + +#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 MeetBDVStates::pureMeet +class MeetBDVStates { +public: + /// 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); + } + + BDVState getResult() const { return currentResult; } + +private: + BDVState currentResult; + + /// 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 BDVState pureMeet(const BDVState &stateA, const BDVState &stateB) { + switch (stateA.getStatus()) { + case BDVState::Unknown: + return stateB; + + case BDVState::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 BDVState(BDVState::Conflict); + } + assert(stateB.isConflict() && "only three states!"); + return BDVState(BDVState::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) { + 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 + // analogous to pessimistic data flow and would likely lead to an + // overall worse solution. + +#ifndef NDEBUG + auto isExpectedBDVType = [](Value *BDV) { + return isa<PHINode>(BDV) || isa<SelectInst>(BDV) || + isa<ExtractElementInst>(BDV) || isa<InsertElementInst>(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<Value *, BDVState> 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<Value*, 16> 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<PHINode>(Current)) { + for (Value *InVal : Phi->incoming_values()) + visitIncomingValue(InVal); + } else if (SelectInst *Sel = dyn_cast<SelectInst>(Current)) { + visitIncomingValue(Sel->getTrueValue()); + visitIncomingValue(Sel->getFalseValue()); + } else if (auto *EE = dyn_cast<ExtractElementInst>(Current)) { + visitIncomingValue(EE->getVectorOperand()); + } else if (auto *IE = dyn_cast<InsertElementInst>(Current)) { + visitIncomingValue(IE->getOperand(0)); // vector operand + visitIncomingValue(IE->getOperand(1)); // scalar operand + } else { + // There is one known class of instructions we know we don't handle. + assert(isa<ShuffleVectorInst>(Current)); + llvm_unreachable("unimplemented instruction case"); + } + } + } + +#ifndef NDEBUG + DEBUG(dbgs() << "States after initialization:\n"); + for (auto Pair : States) { + DEBUG(dbgs() << " " << Pair.second << " for " << *Pair.first << "\n"); + } +#endif + + // 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) { +#ifndef NDEBUG + const size_t oldSize = States.size(); +#endif + progress = false; + // 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) { + Value *BDV = Pair.first; + assert(!isKnownBaseResult(BDV) && "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<SelectInst>(BDV)) { + calculateMeet.meetWith(getStateForInput(select->getTrueValue())); + calculateMeet.meetWith(getStateForInput(select->getFalseValue())); + } else if (PHINode *Phi = dyn_cast<PHINode>(BDV)) { + for (Value *Val : Phi->incoming_values()) + calculateMeet.meetWith(getStateForInput(Val)); + } else if (auto *EE = dyn_cast<ExtractElementInst>(BDV)) { + // The 'meet' for an extractelement is slightly trivial, but it's still + // useful in that it drives us to conflict if our input is. + calculateMeet.meetWith(getStateForInput(EE->getVectorOperand())); + } else { + // Given there's a inherent type mismatch between the operands, will + // *always* produce Conflict. + auto *IE = cast<InsertElementInst>(BDV); + calculateMeet.meetWith(getStateForInput(IE->getOperand(0))); + calculateMeet.meetWith(getStateForInput(IE->getOperand(1))); + } + + BDVState oldState = States[BDV]; + BDVState newState = calculateMeet.getResult(); + if (oldState != newState) { + progress = true; + States[BDV] = newState; + } + } + + assert(oldSize == States.size() && + "fixed point shouldn't be adding any new nodes to state"); + } + +#ifndef NDEBUG + DEBUG(dbgs() << "States after meet iteration:\n"); + for (auto Pair : States) { + DEBUG(dbgs() << " " << Pair.second << " for " << *Pair.first << "\n"); + } +#endif + + // Insert Phis for all conflicts + // TODO: adjust naming patterns to avoid this order of iteration dependency + for (auto Pair : States) { + Instruction *I = cast<Instruction>(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<ExtractElementInst>(I) && + isa<VectorType>(State.getBase()->getType())) { + auto *EE = cast<ExtractElementInst>(I); + // TODO: In many cases, the new instruction is just EE itself. We should + // exploit this, but can't do it here since it would break the invariant + // about the BDV not being known to be a base. + auto *BaseInst = ExtractElementInst::Create(State.getBase(), + EE->getIndexOperand(), + "base_ee", EE); + BaseInst->setMetadata("is_base_value", MDNode::get(I->getContext(), {})); + States[I] = BDVState(BDVState::Base, BaseInst); + } + + // Since we're joining a vector and scalar base, they can never be the + // same. As a result, we should always see insert element having reached + // the conflict state. + if (isa<InsertElementInst>(I)) { + assert(State.isConflict()); + } + + if (!State.isConflict()) + continue; + + /// Create and insert a new instruction which will represent the base of + /// the given instruction 'I'. + auto MakeBaseInstPlaceholder = [](Instruction *I) -> Instruction* { + if (isa<PHINode>(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 = suffixed_name_or(I, ".base", "base_phi"); + return PHINode::Create(I->getType(), NumPreds, Name, I); + } else if (SelectInst *Sel = dyn_cast<SelectInst>(I)) { + // The undef will be replaced later + UndefValue *Undef = UndefValue::get(Sel->getType()); + std::string Name = suffixed_name_or(I, ".base", "base_select"); + return SelectInst::Create(Sel->getCondition(), Undef, + Undef, Name, Sel); + } else if (auto *EE = dyn_cast<ExtractElementInst>(I)) { + UndefValue *Undef = UndefValue::get(EE->getVectorOperand()->getType()); + std::string Name = suffixed_name_or(I, ".base", "base_ee"); + return ExtractElementInst::Create(Undef, EE->getIndexOperand(), Name, + EE); + } else { + auto *IE = cast<InsertElementInst>(I); + UndefValue *VecUndef = UndefValue::get(IE->getOperand(0)->getType()); + UndefValue *ScalarUndef = UndefValue::get(IE->getOperand(1)->getType()); + std::string Name = suffixed_name_or(I, ".base", "base_ie"); + return InsertElementInst::Create(VecUndef, ScalarUndef, + IE->getOperand(2), Name, IE); + } + + }; + 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 { + // 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. Visit order needs to be + // deterministic and predictable because we're naming newly created + // instructions. + for (auto Pair : States) { + Instruction *BDV = cast<Instruction>(Pair.first); + BDVState State = Pair.second; + + assert(!isKnownBaseResult(BDV) && "why did it get added?"); + assert(!State.isUnknown() && "Optimistic algorithm didn't complete!"); + if (!State.isConflict()) + continue; + + if (PHINode *basephi = dyn_cast<PHINode>(State.getBase())) { + PHINode *phi = cast<PHINode>(BDV); + 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 = 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() && + "sanity -- findBaseOrBDV should be pure!"); +#endif + continue; + } + + // 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 if (SelectInst *BaseSel = dyn_cast<SelectInst>(State.getBase())) { + SelectInst *Sel = cast<SelectInst>(BDV); + // 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 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 if (auto *BaseEE = dyn_cast<ExtractElementInst>(State.getBase())) { + Value *InVal = cast<ExtractElementInst>(BDV)->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); + } else { + auto *BaseIE = cast<InsertElementInst>(State.getBase()); + auto *BdvIE = cast<InsertElementInst>(BDV); + auto UpdateOperand = [&](int OperandIdx) { + Value *InVal = BdvIE->getOperand(OperandIdx); + Value *Base = getBaseForInput(InVal, BaseIE); + BaseIE->setOperand(OperandIdx, Base); + }; + UpdateOperand(0); // vector operand + UpdateOperand(1); // scalar operand + } + + } + + // Now that we're done with the algorithm, see if we can optimize the + // results slightly by reducing the number of new instructions needed. + // Arguably, this should be integrated into the algorithm above, but + // doing as a post process step is easier to reason about for the moment. + DenseMap<Value *, Value *> ReverseMap; + SmallPtrSet<Instruction *, 16> NewInsts; + SmallSetVector<AssertingVH<Instruction>, 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; + + ReverseMap[Base] = BDV; + if (auto *BaseI = dyn_cast<Instruction>(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<Instruction>(U)) + if (NewInsts.count(UI) && UI != BaseI) + Worklist.insert(UI); + // Then do the actual replacement + NewInsts.erase(BaseI); + ReverseMap.erase(BaseI); + BaseI->replaceAllUsesWith(Replacement); + assert(States.count(BDV)); + assert(States[BDV].isConflict() && States[BDV].getBase() == BaseI); + States[BDV] = BDVState(BDVState::Conflict, Replacement); + BaseI->eraseFromParent(); + }; + const DataLayout &DL = cast<Instruction>(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<Instruction>(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; + } + } + + // 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]->getName() : "none"; + DEBUG(dbgs() << "Updating base value cache" + << " for: " << BDV->getName() + << " from: " << fromstr + << " to: " << 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[BDV]) || cache[BDV] == base) && + "base relation should be stable"); + } + cache[BDV] = base; + } + assert(cache.count(def)); + 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<Value *, Value *> &PointerToBase, + 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. + SmallVector<Value *, 64> Temp; + 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); + 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 substantial risk. + assert(!isa<ConstantPointerNull>(base) && + "the relocation code needs adjustment to handle the relocation of " + "a null pointer constant without causing false positives in the " + "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<Value *, Value *> PointerToBase; + findBasePointers(result.LiveSet, PointerToBase, &DT, DVCache); + + if (PrintBasePointers) { + // Note: Need to print these in a stable order since this is checked in + // some tests. + errs() << "Base Pairs (w/o Relocation):\n"; + SmallVector<Value *, 64> Temp; + Temp.reserve(PointerToBase.size()); + for (auto Pair : PointerToBase) { + Temp.push_back(Pair.first); + } + std::sort(Temp.begin(), Temp.end(), order_by_name); + for (Value *Ptr : Temp) { + Value *Base = PointerToBase[Ptr]; + errs() << " derived "; + Ptr->printAsOperand(errs(), false); + errs() << " base "; + Base->printAsOperand(errs(), false); + errs() << "\n";; + } + } + + result.PointerToBase = PointerToBase; +} + +/// Given an updated version of the dataflow liveness results, update the +/// liveset and base pointer maps for the call site CS. +static void recomputeLiveInValues(GCPtrLivenessData &RevisedLivenessData, + const CallSite &CS, + PartiallyConstructedSafepointRecord &result); + +static void recomputeLiveInValues( + Function &F, DominatorTree &DT, ArrayRef<CallSite> toUpdate, + MutableArrayRef<struct PartiallyConstructedSafepointRecord> records) { + // TODO-PERF: reuse the original liveness, then simply run the dataflow + // again. The old values are still live and will help it stabilize quickly. + GCPtrLivenessData RevisedLivenessData; + computeLiveInValues(DT, F, RevisedLivenessData); + for (size_t i = 0; i < records.size(); i++) { + struct PartiallyConstructedSafepointRecord &info = records[i]; + const CallSite &CS = toUpdate[i]; + recomputeLiveInValues(RevisedLivenessData, CS, info); + } +} + +// When inserting gc.relocate and gc.result calls, we need to ensure there are +// no uses of the original value / return value between the gc.statepoint and +// the gc.relocate / gc.result 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, "", &DT); + + // Now that 'Ret' has unique predecessor we can safely remove all phi nodes + // from it + FoldSingleEntryPHINodes(Ret); + assert(!isa<PHINode>(Ret->begin()) && + "All PHI nodes should have been removed!"); + + // At this point, we can safely insert a gc.relocate or gc.result as the first + // instruction in Ret if needed. + return Ret; +} + +// Create new attribute set containing only attributes which can be transferred +// 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 (Attribute Attr : make_range(AS.begin(Slot), AS.end(Slot))) { + + // 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; + + // These attributes control the generation of the gc.statepoint call / + // invoke itself; and once the gc.statepoint is in place, they're of no + // use. + if (Attr.hasAttribute("statepoint-num-patch-bytes") || + Attr.hasAttribute("statepoint-id")) + 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. +static void CreateGCRelocates(ArrayRef<Value *> LiveVariables, + const int LiveStart, + ArrayRef<Value *> BasePtrs, + Instruction *StatepointToken, + IRBuilder<> Builder) { + if (LiveVariables.empty()) + return; + + auto FindIndex = [](ArrayRef<Value *> LiveVec, Value *Val) { + auto ValIt = std::find(LiveVec.begin(), LiveVec.end(), Val); + assert(ValIt != LiveVec.end() && "Val not found in LiveVec!"); + size_t Index = std::distance(LiveVec.begin(), ValIt); + assert(Index < LiveVec.size() && "Bug in std::find?"); + return Index; + }; + Module *M = StatepointToken->getModule(); + + // All gc_relocate are generated as i8 addrspace(1)* (or a vector type whose + // element type is i8 addrspace(1)*). 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. + auto getGCRelocateDecl = [&] (Type *Ty) { + assert(isHandledGCPointerType(Ty)); + auto AS = Ty->getScalarType()->getPointerAddressSpace(); + Type *NewTy = Type::getInt8PtrTy(M->getContext(), AS); + if (auto *VT = dyn_cast<VectorType>(Ty)) + NewTy = VectorType::get(NewTy, VT->getNumElements()); + return Intrinsic::getDeclaration(M, Intrinsic::experimental_gc_relocate, + {NewTy}); + }; + + // Lazily populated map from input types to the canonicalized form mentioned + // in the comment above. This should probably be cached somewhere more + // broadly. + DenseMap<Type*, Value*> TypeToDeclMap; + + for (unsigned i = 0; i < LiveVariables.size(); i++) { + // Generate the gc.relocate call and save the result + Value *BaseIdx = + Builder.getInt32(LiveStart + FindIndex(LiveVariables, BasePtrs[i])); + Value *LiveIdx = Builder.getInt32(LiveStart + i); + + Type *Ty = LiveVariables[i]->getType(); + if (!TypeToDeclMap.count(Ty)) + TypeToDeclMap[Ty] = getGCRelocateDecl(Ty); + Value *GCRelocateDecl = TypeToDeclMap[Ty]; + + // only specify a debug name if we can give a useful one + CallInst *Reloc = Builder.CreateCall( + GCRelocateDecl, {StatepointToken, BaseIdx, LiveIdx}, + suffixed_name_or(LiveVariables[i], ".relocated", "")); + // Trick CodeGen into thinking there are lots of free registers at this + // fake call. + Reloc->setCallingConv(CallingConv::Cold); + } +} + +namespace { + +/// This struct is used to defer RAUWs and `eraseFromParent` s. Using this +/// avoids having to worry about keeping around dangling pointers to Values. +class DeferredReplacement { + AssertingVH<Instruction> Old; + AssertingVH<Instruction> New; + +public: + explicit DeferredReplacement(Instruction *Old, Instruction *New) : + Old(Old), New(New) { + assert(Old != New && "Not allowed!"); + } + + /// Does the task represented by this instance. + void doReplacement() { + Instruction *OldI = Old; + Instruction *NewI = New; + + assert(OldI != NewI && "Disallowed at construction?!"); + + Old = nullptr; + New = nullptr; + + if (NewI) + OldI->replaceAllUsesWith(NewI); + OldI->eraseFromParent(); + } +}; +} + +static void +makeStatepointExplicitImpl(const CallSite CS, /* to replace */ + const SmallVectorImpl<Value *> &BasePtrs, + const SmallVectorImpl<Value *> &LiveVariables, + PartiallyConstructedSafepointRecord &Result, + std::vector<DeferredReplacement> &Replacements) { + assert(BasePtrs.size() == LiveVariables.size()); + assert((UseDeoptBundles || isStatepoint(CS)) && + "This method expects to be rewriting a statepoint"); + + // 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); + + ArrayRef<Value *> GCArgs(LiveVariables); + uint64_t StatepointID = 0xABCDEF00; + uint32_t NumPatchBytes = 0; + uint32_t Flags = uint32_t(StatepointFlags::None); + + ArrayRef<Use> CallArgs; + ArrayRef<Use> DeoptArgs; + ArrayRef<Use> TransitionArgs; + + Value *CallTarget = nullptr; + + if (UseDeoptBundles) { + CallArgs = {CS.arg_begin(), CS.arg_end()}; + DeoptArgs = GetDeoptBundleOperands(CS); + // TODO: we don't fill in TransitionArgs or Flags in this branch, but we + // could have an operand bundle for that too. + AttributeSet OriginalAttrs = CS.getAttributes(); + + Attribute AttrID = OriginalAttrs.getAttribute(AttributeSet::FunctionIndex, + "statepoint-id"); + if (AttrID.isStringAttribute()) + AttrID.getValueAsString().getAsInteger(10, StatepointID); + + Attribute AttrNumPatchBytes = OriginalAttrs.getAttribute( + AttributeSet::FunctionIndex, "statepoint-num-patch-bytes"); + if (AttrNumPatchBytes.isStringAttribute()) + AttrNumPatchBytes.getValueAsString().getAsInteger(10, NumPatchBytes); + + CallTarget = CS.getCalledValue(); + } else { + // This branch will be gone soon, and we will soon only support the + // UseDeoptBundles == true configuration. + Statepoint OldSP(CS); + StatepointID = OldSP.getID(); + NumPatchBytes = OldSP.getNumPatchBytes(); + Flags = OldSP.getFlags(); + + CallArgs = {OldSP.arg_begin(), OldSP.arg_end()}; + DeoptArgs = {OldSP.vm_state_begin(), OldSP.vm_state_end()}; + TransitionArgs = {OldSP.gc_transition_args_begin(), + OldSP.gc_transition_args_end()}; + CallTarget = OldSP.getCalledValue(); + } + + // Create the statepoint given all the arguments + Instruction *Token = nullptr; + AttributeSet ReturnAttrs; + if (CS.isCall()) { + CallInst *ToReplace = cast<CallInst>(CS.getInstruction()); + CallInst *Call = Builder.CreateGCStatepointCall( + StatepointID, NumPatchBytes, CallTarget, Flags, CallArgs, + TransitionArgs, DeoptArgs, GCArgs, "safepoint_token"); + + Call->setTailCall(ToReplace->isTailCall()); + Call->setCallingConv(ToReplace->getCallingConv()); + + // Currently we will fail on parameter attributes and on certain + // function attributes. + AttributeSet NewAttrs = legalizeCallAttributes(ToReplace->getAttributes()); + // 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(NewAttrs.getFnAttributes()); + ReturnAttrs = NewAttrs.getRetAttributes(); + + Token = Call; + + // Put the following gc_result and gc_relocate calls immediately after the + // the old call (which we're about to delete) + assert(ToReplace->getNextNode() && "Not a terminator, must have next!"); + Builder.SetInsertPoint(ToReplace->getNextNode()); + Builder.SetCurrentDebugLocation(ToReplace->getNextNode()->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 = Builder.CreateGCStatepointInvoke( + StatepointID, NumPatchBytes, CallTarget, ToReplace->getNormalDest(), + ToReplace->getUnwindDest(), Flags, CallArgs, TransitionArgs, DeoptArgs, + GCArgs, "statepoint_token"); + + Invoke->setCallingConv(ToReplace->getCallingConv()); + + // Currently we will fail on parameter attributes and on certain + // function attributes. + AttributeSet NewAttrs = legalizeCallAttributes(ToReplace->getAttributes()); + // 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(NewAttrs.getFnAttributes()); + ReturnAttrs = NewAttrs.getRetAttributes(); + + Token = Invoke; + + // Generate gc relocates in exceptional path + BasicBlock *UnwindBlock = ToReplace->getUnwindDest(); + assert(!isa<PHINode>(UnwindBlock->begin()) && + UnwindBlock->getUniquePredecessor() && + "can't safely insert in this block!"); + + Builder.SetInsertPoint(&*UnwindBlock->getFirstInsertionPt()); + Builder.SetCurrentDebugLocation(ToReplace->getDebugLoc()); + + // Attach exceptional gc relocates to the landingpad. + Instruction *ExceptionalToken = UnwindBlock->getLandingPadInst(); + Result.UnwindToken = ExceptionalToken; + + const unsigned LiveStartIdx = Statepoint(Token).gcArgsStartIdx(); + CreateGCRelocates(LiveVariables, LiveStartIdx, BasePtrs, ExceptionalToken, + Builder); + + // Generate gc relocates and returns for normal block + BasicBlock *NormalDest = ToReplace->getNormalDest(); + assert(!isa<PHINode>(NormalDest->begin()) && + NormalDest->getUniquePredecessor() && + "can't safely insert in this block!"); + + Builder.SetInsertPoint(&*NormalDest->getFirstInsertionPt()); + + // gc relocates will be generated later as if it were regular call + // statepoint + } + assert(Token && "Should be set in one of the above branches!"); + + if (UseDeoptBundles) { + Token->setName("statepoint_token"); + if (!CS.getType()->isVoidTy() && !CS.getInstruction()->use_empty()) { + StringRef Name = + CS.getInstruction()->hasName() ? CS.getInstruction()->getName() : ""; + CallInst *GCResult = Builder.CreateGCResult(Token, CS.getType(), Name); + GCResult->setAttributes(CS.getAttributes().getRetAttributes()); + + // We cannot RAUW or delete CS.getInstruction() because it could be in the + // live set of some other safepoint, in which case that safepoint's + // PartiallyConstructedSafepointRecord will hold a raw pointer to this + // llvm::Instruction. Instead, we defer the replacement and deletion to + // after the live sets have been made explicit in the IR, and we no longer + // have raw pointers to worry about. + Replacements.emplace_back(CS.getInstruction(), GCResult); + } else { + Replacements.emplace_back(CS.getInstruction(), nullptr); + } + } else { + assert(!CS.getInstruction()->hasNUsesOrMore(2) && + "only valid use before rewrite is gc.result"); + assert(!CS.getInstruction()->hasOneUse() || + isGCResult(cast<Instruction>(*CS.getInstruction()->user_begin()))); + + // Take the name of the original statepoint token if there was one. + Token->takeName(CS.getInstruction()); + + // 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); + CS.getInstruction()->eraseFromParent(); + } + + Result.StatepointToken = Token; + + // Second, create a gc.relocate for every live variable + const unsigned LiveStartIdx = Statepoint(Token).gcArgsStartIdx(); + CreateGCRelocates(LiveVariables, LiveStartIdx, BasePtrs, Token, Builder); +} + +namespace { +struct NameOrdering { + Value *Base; + Value *Derived; + + bool operator()(NameOrdering const &a, NameOrdering const &b) { + return -1 == a.Derived->getName().compare(b.Derived->getName()); + } +}; +} + +static void StabilizeOrder(SmallVectorImpl<Value *> &BaseVec, + SmallVectorImpl<Value *> &LiveVec) { + assert(BaseVec.size() == LiveVec.size()); + + SmallVector<NameOrdering, 64> Temp; + for (size_t i = 0; i < BaseVec.size(); i++) { + NameOrdering v; + v.Base = BaseVec[i]; + v.Derived = LiveVec[i]; + Temp.push_back(v); + } + + std::sort(Temp.begin(), Temp.end(), NameOrdering()); + 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, + PartiallyConstructedSafepointRecord &Result, + std::vector<DeferredReplacement> &Replacements) { + const auto &LiveSet = Result.LiveSet; + const 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.count(L)); + Value *Base = PointerToBase.find(L)->second; + 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. + StabilizeOrder(BaseVec, LiveVec); + + // Do the actual rewriting and delete the old statepoint + makeStatepointExplicitImpl(CS, BaseVec, LiveVec, Result, Replacements); +} + +// Helper function for the relocationViaAlloca. +// +// It receives iterator to the statepoint gc relocates and emits a store to the +// assigned location (via allocaMap) for the each one of them. It adds the +// visited values into the visitedLiveValues set, which we will later use them +// for sanity checking. +static void +insertRelocationStores(iterator_range<Value::user_iterator> GCRelocs, + DenseMap<Value *, Value *> &AllocaMap, + DenseSet<Value *> &VisitedLiveValues) { + + for (User *U : GCRelocs) { + GCRelocateInst *Relocate = dyn_cast<GCRelocateInst>(U); + if (!Relocate) + continue; + + Value *OriginalValue = const_cast<Value *>(Relocate->getDerivedPtr()); + assert(AllocaMap.count(OriginalValue)); + Value *Alloca = AllocaMap[OriginalValue]; + + // Emit store into the related alloca + // All gc_relocates are i8 addrspace(1)* typed, and it must be bitcasted to + // the correct type according to alloca. + assert(Relocate->getNextNode() && + "Should always have one since it's not a terminator"); + IRBuilder<> Builder(Relocate->getNextNode()); + Value *CastedRelocatedValue = + Builder.CreateBitCast(Relocate, + cast<AllocaInst>(Alloca)->getAllocatedType(), + suffixed_name_or(Relocate, ".casted", "")); + + StoreInst *Store = new StoreInst(CastedRelocatedValue, Alloca); + Store->insertAfter(cast<Instruction>(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<Value *, Value *> &AllocaMap, + DenseSet<Value *> &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); +#endif + } +} + +/// Do all the relocation update via allocas and mem2reg +static void relocationViaAlloca( + Function &F, DominatorTree &DT, ArrayRef<Value *> Live, + ArrayRef<PartiallyConstructedSafepointRecord> Records) { +#ifndef NDEBUG + // record initial number of (static) allocas; we'll check we have the same + // number when we get done. + int InitialAllocaNum = 0; + for (auto I = F.getEntryBlock().begin(), E = F.getEntryBlock().end(); I != E; + I++) + if (isa<AllocaInst>(*I)) + InitialAllocaNum++; +#endif + + // TODO-PERF: change data structures, reserve + DenseMap<Value *, Value *> AllocaMap; + SmallVector<AllocaInst *, 200> PromotableAllocas; + // 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 (Value *V : Live) + emitAllocaFor(V); + + // Emit allocas for rematerialized values + for (const auto &Info : Records) + 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 + // 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 was 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 (const auto &Info : Records) { + 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); + } + + // 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<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 { + InsertClobbersAt(cast<Instruction>(Statepoint)->getNextNode()); + } + } + } + + // 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 changes 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 (Instruction *Inst = dyn_cast<Instruction>(Def)) { + if (InvokeInst *Invoke = dyn_cast<InvokeInst>(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()); + } else { + assert(!Inst->isTerminator() && + "The only TerminatorInst that can produce a value is " + "InvokeInst which is handled above."); + Store->insertAfter(Inst); + } + } else { + assert(isa<Argument>(Def)); + Store->insertAfter(cast<Instruction>(Alloca)); + } + } + + assert(PromotableAllocas.size() == Live.size() + NumRematerializedValues && + "we must have the same allocas with lives"); + if (!PromotableAllocas.empty()) { + // Apply mem2reg to promote alloca to SSA + PromoteMemToReg(PromotableAllocas, DT); + } + +#ifndef NDEBUG + for (auto &I : F.getEntryBlock()) + if (isa<AllocaInst>(I)) + 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) { + SmallSet<T, 8> 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 +/// lifetime of the call. +static void insertUseHolderAfter(CallSite &CS, const ArrayRef<Value *> Values, + SmallVectorImpl<CallInst *> &Holders) { + if (Values.empty()) + // No values to hold live, might as well not insert the empty holder + return; + + Module *M = CS.getInstruction()->getModule(); + // Use a dummy vararg function to actually hold the values live + Function *Func = cast<Function>(M->getOrInsertFunction( + "__tmp_use", FunctionType::get(Type::getVoidTy(M->getContext()), true))); + if (CS.isCall()) { + // For call safepoints insert dummy calls right after safepoint + Holders.push_back(CallInst::Create(Func, Values, "", + &*++CS.getInstruction()->getIterator())); + return; + } + // For invoke safepooints insert dummy calls both in normal and + // exceptional destination blocks + auto *II = cast<InvokeInst>(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( + Function &F, DominatorTree &DT, ArrayRef<CallSite> toUpdate, + MutableArrayRef<struct PartiallyConstructedSafepointRecord> records) { + GCPtrLivenessData OriginalLivenessData; + computeLiveInValues(DT, F, OriginalLivenessData); + for (size_t i = 0; i < records.size(); i++) { + struct PartiallyConstructedSafepointRecord &info = records[i]; + const CallSite &CS = toUpdate[i]; + analyzeParsePointLiveness(DT, OriginalLivenessData, CS, info); + } +} + +/// Remove any vector of pointers from the live set by scalarizing them over the +/// statepoint instruction. Adds the scalarized pieces to the live set. It +/// 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 compromise. +static void splitVectorValues(Instruction *StatepointInst, + StatepointLiveSetTy &LiveSet, + DenseMap<Value *, Value *>& PointerToBase, + DominatorTree &DT) { + SmallVector<Value *, 16> ToSplit; + for (Value *V : LiveSet) + if (isa<VectorType>(V->getType())) + ToSplit.push_back(V); + + if (ToSplit.empty()) + return; + + DenseMap<Value *, SmallVector<Value *, 16>> ElementMapping; + + Function &F = *(StatepointInst->getParent()->getParent()); + + DenseMap<Value *, AllocaInst *> AllocaMap; + // First is normal return, second is exceptional return (invoke only) + DenseMap<Value *, std::pair<Value *, Value *>> Replacements; + for (Value *V : ToSplit) { + AllocaInst *Alloca = + new AllocaInst(V->getType(), "", F.getEntryBlock().getFirstNonPHI()); + AllocaMap[V] = Alloca; + + VectorType *VT = cast<VectorType>(V->getType()); + IRBuilder<> Builder(StatepointInst); + SmallVector<Value *, 16> Elements; + for (unsigned i = 0; i < VT->getNumElements(); i++) + Elements.push_back(Builder.CreateExtractElement(V, Builder.getInt32(i))); + ElementMapping[V] = Elements; + + auto InsertVectorReform = [&](Instruction *IP) { + Builder.SetInsertPoint(IP); + Builder.SetCurrentDebugLocation(IP->getDebugLoc()); + Value *ResultVec = UndefValue::get(VT); + for (unsigned i = 0; i < VT->getNumElements(); i++) + ResultVec = Builder.CreateInsertElement(ResultVec, Elements[i], + Builder.getInt32(i)); + return ResultVec; + }; + + if (isa<CallInst>(StatepointInst)) { + BasicBlock::iterator Next(StatepointInst); + Next++; + Instruction *IP = &*(Next); + Replacements[V].first = InsertVectorReform(IP); + Replacements[V].second = nullptr; + } else { + InvokeInst *Invoke = cast<InvokeInst>(StatepointInst); + // We've already normalized - check that we don't have shared destination + // blocks + BasicBlock *NormalDest = Invoke->getNormalDest(); + assert(!isa<PHINode>(NormalDest->begin())); + BasicBlock *UnwindDest = Invoke->getUnwindDest(); + assert(!isa<PHINode>(UnwindDest->begin())); + // Insert insert element sequences in both successors + Instruction *IP = &*(NormalDest->getFirstInsertionPt()); + Replacements[V].first = InsertVectorReform(IP); + IP = &*(UnwindDest->getFirstInsertionPt()); + Replacements[V].second = InsertVectorReform(IP); + } + } + + for (Value *V : ToSplit) { + AllocaInst *Alloca = AllocaMap[V]; + + // Capture all users before we start mutating use lists + SmallVector<Instruction *, 16> Users; + for (User *U : V->users()) + Users.push_back(cast<Instruction>(U)); + + for (Instruction *I : Users) { + if (auto Phi = dyn_cast<PHINode>(I)) { + for (unsigned i = 0; i < Phi->getNumIncomingValues(); i++) + if (V == Phi->getIncomingValue(i)) { + LoadInst *Load = new LoadInst( + Alloca, "", Phi->getIncomingBlock(i)->getTerminator()); + Phi->setIncomingValue(i, Load); + } + } else { + LoadInst *Load = new LoadInst(Alloca, "", I); + I->replaceUsesOfWith(V, Load); + } + } + + // Store the original value and the replacement value into the alloca + StoreInst *Store = new StoreInst(V, Alloca); + if (auto I = dyn_cast<Instruction>(V)) + Store->insertAfter(I); + else + Store->insertAfter(Alloca); + + // Normal return for invoke, or call return + Instruction *Replacement = cast<Instruction>(Replacements[V].first); + (new StoreInst(Replacement, Alloca))->insertAfter(Replacement); + // Unwind return for invoke only + Replacement = cast_or_null<Instruction>(Replacements[V].second); + if (Replacement) + (new StoreInst(Replacement, Alloca))->insertAfter(Replacement); + } + + // apply mem2reg to promote alloca to SSA + SmallVector<AllocaInst *, 16> Allocas; + 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<Instruction*> &ChainToBase, + Value *CurrentValue, Value *BaseValue) { + + // We have found a base value + if (CurrentValue == BaseValue) { + return true; + } + + if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(CurrentValue)) { + ChainToBase.push_back(GEP); + return findRematerializableChainToBasePointer(ChainToBase, + GEP->getPointerOperand(), + BaseValue); + } + + if (CastInst *CI = dyn_cast<CastInst>(CurrentValue)) { + if (!CI->isNoopCast(CI->getModule()->getDataLayout())) + return false; + + ChainToBase.push_back(CI); + return findRematerializableChainToBasePointer(ChainToBase, + CI->getOperand(0), 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<Instruction*> &Chain, + TargetTransformInfo &TTI) { + unsigned Cost = 0; + + for (Instruction *Instr : Chain) { + if (CastInst *CI = dyn_cast<CastInst>(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<GetElementPtrInst>(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 live set pick values that are cheaper to recompute then +// to relocate. Remove this values from the live set, 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<Value *, 32> LiveValuesToBeDeleted; + + for (Value *LiveValue: Info.LiveSet) { + // For each live pointer find it's defining chain + SmallVector<Instruction *, 3> 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<GetElementPtrInst>(Instr) || isa<CastInst>(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<InvokeInst>(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, + TargetTransformInfo &TTI, + 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 (CallSite CS : ToUpdate) { + assert(CS.getInstruction()->getParent()->getParent() == &F); + assert((UseDeoptBundles || isStatepoint(CS)) && + "expected to already be a deopt statepoint"); + } +#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; + auto *II = cast<InvokeInst>(CS.getInstruction()); + normalizeForInvokeSafepoint(II->getNormalDest(), II->getParent(), DT); + normalizeForInvokeSafepoint(II->getUnwindDest(), II->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<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 (CallSite CS : ToUpdate) { + SmallVector<Value *, 64> DeoptValues; + + iterator_range<const Use *> DeoptStateRange = + UseDeoptBundles + ? iterator_range<const Use *>(GetDeoptBundleOperands(CS)) + : iterator_range<const Use *>(Statepoint(CS).vm_state_args()); + + for (Value *Arg : DeoptStateRange) { + assert(!isUnhandledGCPointerType(Arg->getType()) && + "support for FCA unimplemented"); + if (isHandledGCPointerType(Arg->getType())) + DeoptValues.push_back(Arg); + } + + insertUseHolderAfter(CS, DeoptValues, Holders); + } + + SmallVector<PartiallyConstructedSafepointRecord, 64> Records(ToUpdate.size()); + + // A) Identify all gc pointers which are statically live at the given call + // site. + findLiveReferences(F, DT, 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++) { + PartiallyConstructedSafepointRecord &info = Records[i]; + findBasePointers(DT, DVCache, ToUpdate[i], 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 + // 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++) { + PartiallyConstructedSafepointRecord &Info = Records[i]; + + SmallVector<Value *, 128> Bases; + for (auto Pair : Info.PointerToBase) + Bases.push_back(Pair.second); + + insertUseHolderAfter(ToUpdate[i], Bases, Holders); + } + + // By selecting base pointers, we've effectively inserted new uses. Thus, we + // need to rerun liveness. We may *also* have inserted new defs, but that's + // not the key issue. + recomputeLiveInValues(F, DT, ToUpdate, Records); + + if (PrintBasePointers) { + for (auto &Info : Records) { + errs() << "Base Pairs: (w/Relocation)\n"; + for (auto Pair : Info.PointerToBase) { + errs() << " derived "; + Pair.first->printAsOperand(errs(), false); + errs() << " base "; + Pair.second->printAsOperand(errs(), false); + errs() << "\n"; + } + } + } + + // It is possible that non-constant live variables have a constant base. For + // example, a GEP with a variable offset from a global. In this case we can + // remove it from the liveset. We already don't add constants to the liveset + // because we assume they won't move at runtime and the GC doesn't need to be + // informed about them. The same reasoning applies if the base is constant. + // Note that the relocation placement code relies on this filtering for + // correctness as it expects the base to be in the liveset, which isn't true + // if the base is constant. + for (auto &Info : Records) + for (auto &BasePair : Info.PointerToBase) + if (isa<Constant>(BasePair.second)) + Info.LiveSet.erase(BasePair.first); + + for (CallInst *CI : Holders) + CI->eraseFromParent(); + + 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. Note: This is known to not + // handle updating of the side tables correctly which can lead to relocation + // bugs when the same vector is live at multiple statepoints. We're in the + // process of implementing the alternate lowering - relocating the + // vector-of-pointers as first class item and updating the backend to + // understand that - but that's not yet complete. + if (UseVectorSplit) + for (size_t i = 0; i < Records.size(); i++) { + PartiallyConstructedSafepointRecord &Info = Records[i]; + Instruction *Statepoint = ToUpdate[i].getInstruction(); + splitVectorValues(cast<Instruction>(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. + for (size_t i = 0; i < Records.size(); i++) + rematerializeLiveValues(ToUpdate[i], Records[i], TTI); + + // We need this to safely RAUW and delete call or invoke return values that + // may themselves be live over a statepoint. For details, please see usage in + // makeStatepointExplicitImpl. + std::vector<DeferredReplacement> Replacements; + + // 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++) + makeStatepointExplicit(DT, ToUpdate[i], Records[i], Replacements); + + ToUpdate.clear(); // prevent accident use of invalid CallSites + + for (auto &PR : Replacements) + PR.doReplacement(); + + Replacements.clear(); + + for (auto &Info : Records) { + // These live sets may contain state Value pointers, since we replaced calls + // with operand bundles with calls wrapped in gc.statepoint, and some of + // those calls may have been def'ing live gc pointers. Clear these out to + // avoid accidentally using them. + // + // TODO: We should create a separate data structure that does not contain + // these live sets, and migrate to using that data structure from this point + // onward. + Info.LiveSet.clear(); + Info.PointerToBase.clear(); + } + + // 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++) { + 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 live set 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()); +#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<Instruction>(V)) + // Non-instruction values trivial dominate all possible uses + continue; + auto *LiveInst = cast<Instruction>(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); + +#ifndef NDEBUG + // sanity check + for (auto *Ptr : Live) + assert(isHandledGCPointerType(Ptr->getType()) && + "must be a gc pointer type"); +#endif + + relocationViaAlloca(F, DT, Live, Records); + return !Records.empty(); +} + +// Handles both return values and arguments for Functions and CallSites. +template <typename AttrHolder> +static void RemoveNonValidAttrAtIndex(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 (AH.doesNotAlias(Index)) + R.addAttribute(Attribute::NoAlias); + + if (!R.empty()) + AH.setAttributes(AH.getAttributes().removeAttributes( + Ctx, Index, AttributeSet::get(Ctx, Index, R))); +} + +void +RewriteStatepointsForGC::stripNonValidAttributesFromPrototype(Function &F) { + LLVMContext &Ctx = F.getContext(); + + for (Argument &A : F.args()) + if (isa<PointerType>(A.getType())) + RemoveNonValidAttrAtIndex(Ctx, F, A.getArgNo() + 1); + + if (isa<PointerType>(F.getReturnType())) + RemoveNonValidAttrAtIndex(Ctx, F, AttributeSet::ReturnIndex); +} + +void RewriteStatepointsForGC::stripNonValidAttributesFromBody(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<ConstantInt>(MD->getOperand(3))->getValue() == 1; + + if (!IsImmutableTBAA) + continue; // no work to do, MD_tbaa is already marked mutable + + MDNode *Base = cast<MDNode>(MD->getOperand(0)); + MDNode *Access = cast<MDNode>(MD->getOperand(1)); + uint64_t Offset = + mdconst::extract<ConstantInt>(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<PointerType>(CS.getArgument(i)->getType())) + RemoveNonValidAttrAtIndex(Ctx, CS, i + 1); + if (isa<PointerType>(CS.getType())) + RemoveNonValidAttrAtIndex(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 auto &FunctionGCName = F.getGC(); + const StringRef StatepointExampleName("statepoint-example"); + const StringRef CoreCLRName("coreclr"); + return (StatepointExampleName == FunctionGCName) || + (CoreCLRName == FunctionGCName); + } else + return false; +} + +void RewriteStatepointsForGC::stripNonValidAttributes(Module &M) { +#ifndef NDEBUG + assert(std::any_of(M.begin(), M.end(), shouldRewriteStatepointsIn) && + "precondition!"); +#endif + + for (Function &F : M) + stripNonValidAttributesFromPrototype(F); + + for (Function &F : M) + stripNonValidAttributesFromBody(F); +} + +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; + + DominatorTree &DT = getAnalysis<DominatorTreeWrapperPass>(F).getDomTree(); + TargetTransformInfo &TTI = + getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F); + + auto NeedsRewrite = [](Instruction &I) { + if (UseDeoptBundles) { + if (ImmutableCallSite CS = ImmutableCallSite(&I)) + return !callsGCLeafFunction(CS); + return false; + } + + return isStatepoint(I); + }; + + // 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<CallSite, 64> ParsePointNeeded; + bool HasUnreachableStatepoint = false; + for (Instruction &I : instructions(F)) { + // TODO: only the ones with the flag set! + if (NeedsRewrite(I)) { + if (DT.isReachableFromEntry(I.getParent())) + ParsePointNeeded.push_back(CallSite(&I)); + else + HasUnreachableStatepoint = true; + } + } + + bool MadeChange = false; + + // Delete any unreachable statepoints so that we don't have unrewritten + // statepoints surviving this pass. This makes testing easier and the + // resulting IR less confusing to human readers. Rather than be fancy, we + // just reuse a utility function which removes the unreachable blocks. + if (HasUnreachableStatepoint) + MadeChange |= removeUnreachableBlocks(F); + + // Return early if no work to do. + if (ParsePointNeeded.empty()) + return MadeChange; + + // As a prepass, go ahead and aggressively destroy single entry phi nodes. + // These are created by LCSSA. They have the effect of increasing the size + // of liveness sets for no good reason. It may be harder to do this post + // insertion since relocations and base phis can confuse things. + for (BasicBlock &BB : F) + if (BB.getUniquePredecessor()) { + MadeChange = true; + FoldSingleEntryPHINodes(&BB); + } + + // Before we start introducing relocations, we want to tweak the IR a bit to + // avoid unfortunate code generation effects. The main example is that we + // want to try to make sure the comparison feeding a branch is after any + // safepoints. Otherwise, we end up with a comparison of pre-relocation + // values feeding a branch after relocation. This is semantically correct, + // but results in extra register pressure since both the pre-relocation and + // post-relocation copies must be available in registers. For code without + // relocations this is handled elsewhere, but teaching the scheduler to + // reverse the transform we're about to do would be slightly complex. + // Note: This may extend the live range of the inputs to the icmp and thus + // increase the liveset of any statepoint we move over. This is profitable + // as long as all statepoints are in rare blocks. If we had in-register + // lowering for live values this would be a much safer transform. + auto getConditionInst = [](TerminatorInst *TI) -> Instruction* { + if (auto *BI = dyn_cast<BranchInst>(TI)) + if (BI->isConditional()) + return dyn_cast<Instruction>(BI->getCondition()); + // TODO: Extend this to handle switches + return nullptr; + }; + for (BasicBlock &BB : F) { + TerminatorInst *TI = BB.getTerminator(); + if (auto *Cond = getConditionInst(TI)) + // TODO: Handle more than just ICmps here. We should be able to move + // most instructions without side effects or memory access. + if (isa<ICmpInst>(Cond) && Cond->hasOneUse()) { + MadeChange = true; + Cond->moveBefore(TI); + } + } + + MadeChange |= insertParsePoints(F, DT, TTI, ParsePointNeeded); + return MadeChange; +} + +// liveness computation via standard dataflow +// ------------------------------------------------------------------- + +// TODO: Consider using bitvectors for liveness, the set of potentially +// interesting values should be small and easy to pre-compute. + +/// 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, + BasicBlock::reverse_iterator rend, + DenseSet<Value *> &LiveTmp) { + + for (BasicBlock::reverse_iterator ritr = rbegin; ritr != rend; ritr++) { + Instruction *I = &*ritr; + + // KILL/Def - Remove this definition from LiveIn + LiveTmp.erase(I); + + // Don't consider *uses* in PHI nodes, we handle their contribution to + // predecessor blocks when we seed the LiveOut sets + if (isa<PHINode>(I)) + continue; + + // USE - Add to the LiveIn set for this instruction + for (Value *V : I->operands()) { + assert(!isUnhandledGCPointerType(V->getType()) && + "support for FCA unimplemented"); + if (isHandledGCPointerType(V->getType()) && !isa<Constant>(V)) { + // The choice to exclude all things constant here is slightly subtle. + // There are two 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); + } + } + } +} + +static void computeLiveOutSeed(BasicBlock *BB, DenseSet<Value *> &LiveTmp) { + + for (BasicBlock *Succ : successors(BB)) { + const BasicBlock::iterator E(Succ->getFirstNonPHI()); + for (BasicBlock::iterator I = Succ->begin(); I != E; I++) { + PHINode *Phi = cast<PHINode>(&*I); + Value *V = Phi->getIncomingValueForBlock(BB); + assert(!isUnhandledGCPointerType(V->getType()) && + "support for FCA unimplemented"); + if (isHandledGCPointerType(V->getType()) && !isa<Constant>(V)) { + LiveTmp.insert(V); + } + } + } +} + +static DenseSet<Value *> computeKillSet(BasicBlock *BB) { + DenseSet<Value *> KillSet; + for (Instruction &I : *BB) + if (isHandledGCPointerType(I.getType())) + KillSet.insert(&I); + 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<Value *> &Live, + TerminatorInst *TI, bool TermOkay = false) { + for (Value *V : Live) { + if (auto *I = dyn_cast<Instruction>(V)) { + // The terminator can be a member of the LiveOut set. LLVM's definition + // of instruction dominance states that V does not dominate itself. As + // such, we need to special case this to allow it. + if (TermOkay && TI == I) + continue; + assert(DT.dominates(I, TI) && + "basic SSA liveness expectation violated by liveness analysis"); + } + } +} + +/// Check that all the liveness sets used during the computation of liveness +/// obey basic SSA properties. This is useful for finding cases where we miss +/// a def. +static void checkBasicSSA(DominatorTree &DT, GCPtrLivenessData &Data, + BasicBlock &BB) { + checkBasicSSA(DT, Data.LiveSet[&BB], BB.getTerminator()); + 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) { + + SmallSetVector<BasicBlock *, 200> Worklist; + auto AddPredsToWorklist = [&](BasicBlock *BB) { + // 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(); + return BB; + }; + + // Seed the liveness for each individual block + for (BasicBlock &BB : F) { + Data.KillSet[&BB] = computeKillSet(&BB); + Data.LiveSet[&BB].clear(); + computeLiveInValues(BB.rbegin(), BB.rend(), Data.LiveSet[&BB]); + +#ifndef NDEBUG + for (Value *Kill : Data.KillSet[&BB]) + assert(!Data.LiveSet[&BB].count(Kill) && "live set contains kill"); +#endif + + Data.LiveOut[&BB] = DenseSet<Value *>(); + computeLiveOutSeed(&BB, Data.LiveOut[&BB]); + Data.LiveIn[&BB] = Data.LiveSet[&BB]; + set_union(Data.LiveIn[&BB], Data.LiveOut[&BB]); + set_subtract(Data.LiveIn[&BB], Data.KillSet[&BB]); + if (!Data.LiveIn[&BB].empty()) + AddPredsToWorklist(&BB); + } + + // Propagate that liveness until stable + while (!Worklist.empty()) { + BasicBlock *BB = NextItem(); + + // Compute our new liveout set, then exit early if it hasn't changed + // despite the contribution of our successor. + DenseSet<Value *> LiveOut = Data.LiveOut[BB]; + const auto OldLiveOutSize = LiveOut.size(); + for (BasicBlock *Succ : successors(BB)) { + assert(Data.LiveIn.count(Succ)); + set_union(LiveOut, Data.LiveIn[Succ]); + } + // assert OutLiveOut is a subset of LiveOut + if (OldLiveOutSize == LiveOut.size()) { + // If the sets are the same size, then we didn't actually add anything + // when unioning our successors LiveIn Thus, the LiveIn of this block + // hasn't changed. + continue; + } + Data.LiveOut[BB] = LiveOut; + + // Apply the effects of this basic block + DenseSet<Value *> LiveTmp = LiveOut; + set_union(LiveTmp, Data.LiveSet[BB]); + set_subtract(LiveTmp, Data.KillSet[BB]); + + assert(Data.LiveIn.count(BB)); + const DenseSet<Value *> &OldLiveIn = Data.LiveIn[BB]; + // assert: OldLiveIn is a subset of LiveTmp + if (OldLiveIn.size() != LiveTmp.size()) { + Data.LiveIn[BB] = LiveTmp; + AddPredsToWorklist(BB); + } + } // while( !worklist.empty() ) + +#ifndef NDEBUG + // 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); + } +#endif +} + +static void findLiveSetAtInst(Instruction *Inst, GCPtrLivenessData &Data, + StatepointLiveSetTy &Out) { + + BasicBlock *BB = Inst->getParent(); + + // Note: The copy is intentional and required + assert(Data.LiveOut.count(BB)); + DenseSet<Value *> LiveOut = Data.LiveOut[BB]; + + // We want to handle the statepoint itself oddly. It's + // call result is not live (normal), nor are it's arguments + // (unless they're used again later). This adjustment is + // specifically what we need to relocate + BasicBlock::reverse_iterator rend(Inst->getIterator()); + computeLiveInValues(BB->rbegin(), rend, LiveOut); + LiveOut.erase(Inst); + Out.insert(LiveOut.begin(), LiveOut.end()); +} + +static void recomputeLiveInValues(GCPtrLivenessData &RevisedLivenessData, + const CallSite &CS, + PartiallyConstructedSafepointRecord &Info) { + Instruction *Inst = CS.getInstruction(); + StatepointLiveSetTy Updated; + findLiveSetAtInst(Inst, RevisedLivenessData, Updated); + +#ifndef NDEBUG + DenseSet<Value *> Bases; + for (auto KVPair : Info.PointerToBase) { + Bases.insert(KVPair.second); + } +#endif + // We may have base pointers which are now live that weren't before. We need + // to update the PointerToBase structure to reflect this. + for (auto V : Updated) + if (!Info.PointerToBase.count(V)) { + assert(Bases.count(V) && "can't find base for unexpected live value"); + Info.PointerToBase[V] = V; + continue; + } + +#ifndef NDEBUG + for (auto V : Updated) { + assert(Info.PointerToBase.count(V) && + "must be able to find base for live value"); + } +#endif + + // Remove any stale base mappings - this can happen since our liveness is + // more precise then the one inherent in the base pointer analysis + DenseSet<Value *> ToErase; + for (auto KVPair : Info.PointerToBase) + if (!Updated.count(KVPair.first)) + ToErase.insert(KVPair.first); + for (auto V : ToErase) + Info.PointerToBase.erase(V); + +#ifndef NDEBUG + for (auto KVPair : Info.PointerToBase) + assert(Updated.count(KVPair.first) && "record for non-live value"); +#endif + + Info.LiveSet = Updated; +} |