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Diffstat (limited to 'llvm/lib/Transforms/Scalar/RewriteStatepointsForGC.cpp')
| -rw-r--r-- | llvm/lib/Transforms/Scalar/RewriteStatepointsForGC.cpp | 2846 |
1 files changed, 2846 insertions, 0 deletions
diff --git a/llvm/lib/Transforms/Scalar/RewriteStatepointsForGC.cpp b/llvm/lib/Transforms/Scalar/RewriteStatepointsForGC.cpp new file mode 100644 index 000000000000..48bbdd8d1b33 --- /dev/null +++ b/llvm/lib/Transforms/Scalar/RewriteStatepointsForGC.cpp @@ -0,0 +1,2846 @@ +//===- RewriteStatepointsForGC.cpp - Make GC relocations explicit ---------===// +// +// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. +// See https://llvm.org/LICENSE.txt for license information. +// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception +// +//===----------------------------------------------------------------------===// +// +// Rewrite call/invoke instructions so as to make potential relocations +// performed by the garbage collector explicit in the IR. +// +//===----------------------------------------------------------------------===// + +#include "llvm/Transforms/Scalar/RewriteStatepointsForGC.h" + +#include "llvm/ADT/ArrayRef.h" +#include "llvm/ADT/DenseMap.h" +#include "llvm/ADT/DenseSet.h" +#include "llvm/ADT/MapVector.h" +#include "llvm/ADT/None.h" +#include "llvm/ADT/Optional.h" +#include "llvm/ADT/STLExtras.h" +#include "llvm/ADT/SetVector.h" +#include "llvm/ADT/SmallSet.h" +#include "llvm/ADT/SmallVector.h" +#include "llvm/ADT/StringRef.h" +#include "llvm/ADT/iterator_range.h" +#include "llvm/Analysis/DomTreeUpdater.h" +#include "llvm/Analysis/TargetLibraryInfo.h" +#include "llvm/Analysis/TargetTransformInfo.h" +#include "llvm/IR/Argument.h" +#include "llvm/IR/Attributes.h" +#include "llvm/IR/BasicBlock.h" +#include "llvm/IR/CallingConv.h" +#include "llvm/IR/Constant.h" +#include "llvm/IR/Constants.h" +#include "llvm/IR/DataLayout.h" +#include "llvm/IR/DerivedTypes.h" +#include "llvm/IR/Dominators.h" +#include "llvm/IR/Function.h" +#include "llvm/IR/IRBuilder.h" +#include "llvm/IR/InstIterator.h" +#include "llvm/IR/InstrTypes.h" +#include "llvm/IR/Instruction.h" +#include "llvm/IR/Instructions.h" +#include "llvm/IR/IntrinsicInst.h" +#include "llvm/IR/Intrinsics.h" +#include "llvm/IR/LLVMContext.h" +#include "llvm/IR/MDBuilder.h" +#include "llvm/IR/Metadata.h" +#include "llvm/IR/Module.h" +#include "llvm/IR/Statepoint.h" +#include "llvm/IR/Type.h" +#include "llvm/IR/User.h" +#include "llvm/IR/Value.h" +#include "llvm/IR/ValueHandle.h" +#include "llvm/Pass.h" +#include "llvm/Support/Casting.h" +#include "llvm/Support/CommandLine.h" +#include "llvm/Support/Compiler.h" +#include "llvm/Support/Debug.h" +#include "llvm/Support/ErrorHandling.h" +#include "llvm/Support/raw_ostream.h" +#include "llvm/Transforms/Scalar.h" +#include "llvm/Transforms/Utils/BasicBlockUtils.h" +#include "llvm/Transforms/Utils/Local.h" +#include "llvm/Transforms/Utils/PromoteMemToReg.h" +#include <algorithm> +#include <cassert> +#include <cstddef> +#include <cstdint> +#include <iterator> +#include <set> +#include <string> +#include <utility> +#include <vector> + +#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 EXPENSIVE_CHECKS +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> + AllowStatepointWithNoDeoptInfo("rs4gc-allow-statepoint-with-no-deopt-info", + cl::Hidden, cl::init(true)); + +/// The IR fed into RewriteStatepointsForGC may have had attributes and +/// metadata 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. stripNonValidData (conservatively) restores +/// correctness by erasing all attributes in the module that externally imply +/// dereferenceability. Similar reasoning also applies to the noalias +/// attributes and metadata. gc.statepoint can touch the entire heap including +/// noalias objects. +/// Apart from attributes and metadata, we also remove instructions that imply +/// constant physical memory: llvm.invariant.start. +static void stripNonValidData(Module &M); + +static bool shouldRewriteStatepointsIn(Function &F); + +PreservedAnalyses RewriteStatepointsForGC::run(Module &M, + ModuleAnalysisManager &AM) { + bool Changed = false; + auto &FAM = AM.getResult<FunctionAnalysisManagerModuleProxy>(M).getManager(); + for (Function &F : M) { + // Nothing to do for declarations. + if (F.isDeclaration() || F.empty()) + continue; + + // Policy choice says not to rewrite - the most common reason is that we're + // compiling code without a GCStrategy. + if (!shouldRewriteStatepointsIn(F)) + continue; + + auto &DT = FAM.getResult<DominatorTreeAnalysis>(F); + auto &TTI = FAM.getResult<TargetIRAnalysis>(F); + auto &TLI = FAM.getResult<TargetLibraryAnalysis>(F); + Changed |= runOnFunction(F, DT, TTI, TLI); + } + if (!Changed) + return PreservedAnalyses::all(); + + // stripNonValidData 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. + stripNonValidData(M); + + PreservedAnalyses PA; + PA.preserve<TargetIRAnalysis>(); + PA.preserve<TargetLibraryAnalysis>(); + return PA; +} + +namespace { + +class RewriteStatepointsForGCLegacyPass : public ModulePass { + RewriteStatepointsForGC Impl; + +public: + static char ID; // Pass identification, replacement for typeid + + RewriteStatepointsForGCLegacyPass() : ModulePass(ID), Impl() { + initializeRewriteStatepointsForGCLegacyPassPass( + *PassRegistry::getPassRegistry()); + } + + bool runOnModule(Module &M) override { + bool Changed = false; + for (Function &F : M) { + // Nothing to do for declarations. + if (F.isDeclaration() || F.empty()) + continue; + + // Policy choice says not to rewrite - the most common reason is that + // we're compiling code without a GCStrategy. + if (!shouldRewriteStatepointsIn(F)) + continue; + + TargetTransformInfo &TTI = + getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F); + const TargetLibraryInfo &TLI = + getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(F); + auto &DT = getAnalysis<DominatorTreeWrapperPass>(F).getDomTree(); + + Changed |= Impl.runOnFunction(F, DT, TTI, TLI); + } + + if (!Changed) + return false; + + // stripNonValidData 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. + stripNonValidData(M); + return true; + } + + 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>(); + AU.addRequired<TargetLibraryInfoWrapperPass>(); + } +}; + +} // end anonymous namespace + +char RewriteStatepointsForGCLegacyPass::ID = 0; + +ModulePass *llvm::createRewriteStatepointsForGCLegacyPass() { + return new RewriteStatepointsForGCLegacyPass(); +} + +INITIALIZE_PASS_BEGIN(RewriteStatepointsForGCLegacyPass, + "rewrite-statepoints-for-gc", + "Make relocations explicit at statepoints", false, false) +INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass) +INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass) +INITIALIZE_PASS_END(RewriteStatepointsForGCLegacyPass, + "rewrite-statepoints-for-gc", + "Make relocations explicit at statepoints", false, false) + +namespace { + +struct GCPtrLivenessData { + /// Values defined in this block. + MapVector<BasicBlock *, SetVector<Value *>> KillSet; + + /// Values used in this block (and thus live); does not included values + /// killed within this block. + MapVector<BasicBlock *, SetVector<Value *>> LiveSet; + + /// Values live into this basic block (i.e. used by any + /// instruction in this basic block or ones reachable from here) + MapVector<BasicBlock *, SetVector<Value *>> LiveIn; + + /// Values live out of this basic block (i.e. live into + /// any successor block) + MapVector<BasicBlock *, SetVector<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 +using DefiningValueMapTy = MapVector<Value *, Value *>; +using StatepointLiveSetTy = SetVector<Value *>; +using RematerializedValueMapTy = + MapVector<AssertingVH<Instruction>, AssertingVH<Value>>; + +struct PartiallyConstructedSafepointRecord { + /// The set of values known to be live across this safepoint + StatepointLiveSetTy LiveSet; + + /// Mapping from live pointers to a base-defining-value + MapVector<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; +}; + +} // end anonymous namespace + +static ArrayRef<Use> GetDeoptBundleOperands(const CallBase *Call) { + Optional<OperandBundleUse> DeoptBundle = + Call->getOperandBundle(LLVMContext::OB_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 PT->getAddressSpace() == 1; + 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 llvm::any_of(ST->elements(), 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 + +// 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, CallBase *Call, + PartiallyConstructedSafepointRecord &Result) { + StatepointLiveSetTy LiveSet; + findLiveSetAtInst(Call, OriginalLivenessData, LiveSet); + + if (PrintLiveSet) { + dbgs() << "Live Variables:\n"; + for (Value *V : LiveSet) + dbgs() << " " << V->getName() << " " << *V << "\n"; + } + if (PrintLiveSetSize) { + dbgs() << "Safepoint For: " << Call->getCalledValue()->getName() << "\n"; + dbgs() << "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 + } +}; + +} // end anonymous namespace + +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)) + // Base of constant vector consists only of constant null pointers. + // For reasoning see similar case inside 'findBaseDefiningValue' function. + return BaseDefiningValueResult(ConstantAggregateZero::get(I->getType()), + 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); + + // The behavior of getelementptr instructions is the same for vector and + // non-vector data types. + if (auto *GEP = dyn_cast<GetElementPtrInst>(I)) + return findBaseDefiningValue(GEP->getPointerOperand()); + + // If the pointer comes through a bitcast of a vector of pointers to + // a vector of another type of pointer, then look through the bitcast + if (auto *BC = dyn_cast<BitCastInst>(I)) + return findBaseDefiningValue(BC->getOperand(0)); + + // 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); + + // 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. 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. + // Here we treat all of them as having single null base. By doing this we + // trying to avoid problems reporting various conflicts in a form of + // "phi (const1, const2)" or "phi (const, regular gc ptr)". + // See constant.ll file for relevant test cases. + + return BaseDefiningValueResult( + ConstantPointerNull::get(cast<PointerType>(I->getType())), 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); + + // TODO: 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; + LLVM_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() : BaseValue(nullptr) {} + + explicit BDVState(Status Status, Value *BaseValue = nullptr) + : Status(Status), BaseValue(BaseValue) { + assert(Status != Base || BaseValue); + } + + explicit BDVState(Value *BaseValue) : Status(Base), BaseValue(BaseValue) {} + + Status getStatus() const { return Status; } + Value *getBaseValue() const { return BaseValue; } + + 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 BaseValue == Other.BaseValue && 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 (getStatus()) { + case Unknown: + OS << "U"; + break; + case Base: + OS << "B"; + break; + case Conflict: + OS << "C"; + break; + } + OS << " (" << getBaseValue() << " - " + << (getBaseValue() ? getBaseValue()->getName() : "nullptr") << "): "; + } + +private: + Status Status = Unknown; + AssertingVH<Value> BaseValue; // Non-null only if Status == Base. +}; + +} // end anonymous namespace + +#ifndef NDEBUG +static raw_ostream &operator<<(raw_ostream &OS, const BDVState &State) { + State.print(OS); + return OS; +} +#endif + +static BDVState meetBDVStateImpl(const BDVState &LHS, const BDVState &RHS) { + switch (LHS.getStatus()) { + case BDVState::Unknown: + return RHS; + + case BDVState::Base: + assert(LHS.getBaseValue() && "can't be null"); + if (RHS.isUnknown()) + return LHS; + + if (RHS.isBase()) { + if (LHS.getBaseValue() == RHS.getBaseValue()) { + assert(LHS == RHS && "equality broken!"); + return LHS; + } + return BDVState(BDVState::Conflict); + } + assert(RHS.isConflict() && "only three states!"); + return BDVState(BDVState::Conflict); + + case BDVState::Conflict: + return LHS; + } + llvm_unreachable("only three states!"); +} + +// Values of type BDVState form a lattice, and this function implements the meet +// operation. +static BDVState meetBDVState(const BDVState &LHS, const BDVState &RHS) { + BDVState Result = meetBDVStateImpl(LHS, RHS); + assert(Result == meetBDVStateImpl(RHS, LHS) && + "Math is wrong: meet does not commute!"); + return Result; +} + +/// For a given value or instruction, figure out what base ptr its 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) || + isa<ShuffleVectorInst>(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({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 *PN = dyn_cast<PHINode>(Current)) { + for (Value *InVal : PN->incoming_values()) + visitIncomingValue(InVal); + } else if (SelectInst *SI = dyn_cast<SelectInst>(Current)) { + visitIncomingValue(SI->getTrueValue()); + visitIncomingValue(SI->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 if (auto *SV = dyn_cast<ShuffleVectorInst>(Current)) { + visitIncomingValue(SV->getOperand(0)); + visitIncomingValue(SV->getOperand(1)); + } + else { + llvm_unreachable("Unimplemented instruction case"); + } + } + } + +#ifndef NDEBUG + LLVM_DEBUG(dbgs() << "States after initialization:\n"); + for (auto Pair : States) { + LLVM_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); + }; + + BDVState NewState; + if (SelectInst *SI = dyn_cast<SelectInst>(BDV)) { + NewState = meetBDVState(NewState, getStateForInput(SI->getTrueValue())); + NewState = + meetBDVState(NewState, getStateForInput(SI->getFalseValue())); + } else if (PHINode *PN = dyn_cast<PHINode>(BDV)) { + for (Value *Val : PN->incoming_values()) + NewState = meetBDVState(NewState, 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. + NewState = + meetBDVState(NewState, getStateForInput(EE->getVectorOperand())); + } else if (auto *IE = dyn_cast<InsertElementInst>(BDV)){ + // Given there's a inherent type mismatch between the operands, will + // *always* produce Conflict. + NewState = meetBDVState(NewState, getStateForInput(IE->getOperand(0))); + NewState = meetBDVState(NewState, getStateForInput(IE->getOperand(1))); + } else { + // The only instance this does not return a Conflict is when both the + // vector operands are the same vector. + auto *SV = cast<ShuffleVectorInst>(BDV); + NewState = meetBDVState(NewState, getStateForInput(SV->getOperand(0))); + NewState = meetBDVState(NewState, getStateForInput(SV->getOperand(1))); + } + + BDVState OldState = States[BDV]; + 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 + LLVM_DEBUG(dbgs() << "States after meet iteration:\n"); + for (auto Pair : States) { + LLVM_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.getBaseValue()->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.getBaseValue(), 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. + assert(!isa<InsertElementInst>(I) || 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 = pred_size(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 *SI = dyn_cast<SelectInst>(I)) { + // The undef will be replaced later + UndefValue *Undef = UndefValue::get(SI->getType()); + std::string Name = suffixed_name_or(I, ".base", "base_select"); + return SelectInst::Create(SI->getCondition(), Undef, Undef, Name, SI); + } 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 if (auto *IE = dyn_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); + } else { + auto *SV = cast<ShuffleVectorInst>(I); + UndefValue *VecUndef = UndefValue::get(SV->getOperand(0)->getType()); + std::string Name = suffixed_name_or(I, ".base", "base_sv"); + return new ShuffleVectorInst(VecUndef, VecUndef, SV->getOperand(2), + Name, SV); + } + }; + 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].getBaseValue(); + } + 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.getBaseValue())) { + PHINode *PN = cast<PHINode>(BDV); + unsigned NumPHIValues = PN->getNumIncomingValues(); + for (unsigned i = 0; i < NumPHIValues; i++) { + Value *InVal = PN->getIncomingValue(i); + BasicBlock *InBB = PN->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 *BaseSI = + dyn_cast<SelectInst>(State.getBaseValue())) { + SelectInst *SI = cast<SelectInst>(BDV); + + // Find the instruction which produces the base for each input. + // We may need to insert a bitcast. + BaseSI->setTrueValue(getBaseForInput(SI->getTrueValue(), BaseSI)); + BaseSI->setFalseValue(getBaseForInput(SI->getFalseValue(), BaseSI)); + } else if (auto *BaseEE = + dyn_cast<ExtractElementInst>(State.getBaseValue())) { + Value *InVal = cast<ExtractElementInst>(BDV)->getVectorOperand(); + // Find the instruction which produces the base for each input. We may + // need to insert a bitcast. + BaseEE->setOperand(0, getBaseForInput(InVal, BaseEE)); + } else if (auto *BaseIE = dyn_cast<InsertElementInst>(State.getBaseValue())){ + 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 + } else { + auto *BaseSV = cast<ShuffleVectorInst>(State.getBaseValue()); + auto *BdvSV = cast<ShuffleVectorInst>(BDV); + auto UpdateOperand = [&](int OperandIdx) { + Value *InVal = BdvSV->getOperand(OperandIdx); + Value *Base = getBaseForInput(InVal, BaseSV); + BaseSV->setOperand(OperandIdx, Base); + }; + UpdateOperand(0); // vector operand + UpdateOperand(1); // vector operand + } + } + + // 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.getBaseValue(); + assert(BDV && Base); + assert(!isKnownBaseResult(BDV) && "why did it get added?"); + + LLVM_DEBUG( + dbgs() << "Updating base value cache" + << " for: " << BDV->getName() << " from: " + << (Cache.count(BDV) ? Cache[BDV]->getName().str() : "none") + << " to: " << Base->getName() << "\n"); + + if (Cache.count(BDV)) { + assert(isKnownBaseResult(Base) && + "must be something we 'know' is a base pointer"); + // 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, + MapVector<Value *, Value *> &PointerToBase, + DominatorTree *DT, DefiningValueMapTy &DVCache) { + for (Value *ptr : live) { + 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"); + } +} + +/// Find the required based pointers (and adjust the live set) for the given +/// parse point. +static void findBasePointers(DominatorTree &DT, DefiningValueMapTy &DVCache, + CallBase *Call, + PartiallyConstructedSafepointRecord &result) { + MapVector<Value *, Value *> PointerToBase; + findBasePointers(result.LiveSet, PointerToBase, &DT, DVCache); + + if (PrintBasePointers) { + errs() << "Base Pairs (w/o Relocation):\n"; + for (auto &Pair : PointerToBase) { + errs() << " derived "; + Pair.first->printAsOperand(errs(), false); + errs() << " base "; + Pair.second->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, + CallBase *Call, + PartiallyConstructedSafepointRecord &result); + +static void recomputeLiveInValues( + Function &F, DominatorTree &DT, ArrayRef<CallBase *> 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]; + recomputeLiveInValues(RevisedLivenessData, toUpdate[i], 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 AttributeList legalizeCallAttributes(AttributeList AL) { + if (AL.isEmpty()) + return AL; + + // Remove the readonly, readnone, and statepoint function attributes. + AttrBuilder FnAttrs = AL.getFnAttributes(); + FnAttrs.removeAttribute(Attribute::ReadNone); + FnAttrs.removeAttribute(Attribute::ReadOnly); + for (Attribute A : AL.getFnAttributes()) { + if (isStatepointDirectiveAttr(A)) + FnAttrs.remove(A); + } + + // Just skip parameter and return attributes for now + LLVMContext &Ctx = AL.getContext(); + return AttributeList::get(Ctx, AttributeList::FunctionIndex, + AttributeSet::get(Ctx, FnAttrs)); +} + +/// 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 = llvm::find(LiveVec, 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 *, Function *> 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); + Function *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; + bool IsDeoptimize = false; + + DeferredReplacement() = default; + +public: + static DeferredReplacement createRAUW(Instruction *Old, Instruction *New) { + assert(Old != New && Old && New && + "Cannot RAUW equal values or to / from null!"); + + DeferredReplacement D; + D.Old = Old; + D.New = New; + return D; + } + + static DeferredReplacement createDelete(Instruction *ToErase) { + DeferredReplacement D; + D.Old = ToErase; + return D; + } + + static DeferredReplacement createDeoptimizeReplacement(Instruction *Old) { +#ifndef NDEBUG + auto *F = cast<CallInst>(Old)->getCalledFunction(); + assert(F && F->getIntrinsicID() == Intrinsic::experimental_deoptimize && + "Only way to construct a deoptimize deferred replacement"); +#endif + DeferredReplacement D; + D.Old = Old; + D.IsDeoptimize = true; + return D; + } + + /// Does the task represented by this instance. + void doReplacement() { + Instruction *OldI = Old; + Instruction *NewI = New; + + assert(OldI != NewI && "Disallowed at construction?!"); + assert((!IsDeoptimize || !New) && + "Deoptimize intrinsics are not replaced!"); + + Old = nullptr; + New = nullptr; + + if (NewI) + OldI->replaceAllUsesWith(NewI); + + if (IsDeoptimize) { + // Note: we've inserted instructions, so the call to llvm.deoptimize may + // not necessarily be followed by the matching return. + auto *RI = cast<ReturnInst>(OldI->getParent()->getTerminator()); + new UnreachableInst(RI->getContext(), RI); + RI->eraseFromParent(); + } + + OldI->eraseFromParent(); + } +}; + +} // end anonymous namespace + +static StringRef getDeoptLowering(CallBase *Call) { + const char *DeoptLowering = "deopt-lowering"; + if (Call->hasFnAttr(DeoptLowering)) { + // FIXME: Calls have a *really* confusing interface around attributes + // with values. + const AttributeList &CSAS = Call->getAttributes(); + if (CSAS.hasAttribute(AttributeList::FunctionIndex, DeoptLowering)) + return CSAS.getAttribute(AttributeList::FunctionIndex, DeoptLowering) + .getValueAsString(); + Function *F = Call->getCalledFunction(); + assert(F && F->hasFnAttribute(DeoptLowering)); + return F->getFnAttribute(DeoptLowering).getValueAsString(); + } + return "live-through"; +} + +static void +makeStatepointExplicitImpl(CallBase *Call, /* to replace */ + const SmallVectorImpl<Value *> &BasePtrs, + const SmallVectorImpl<Value *> &LiveVariables, + PartiallyConstructedSafepointRecord &Result, + std::vector<DeferredReplacement> &Replacements) { + assert(BasePtrs.size() == LiveVariables.size()); + + // 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. + IRBuilder<> Builder(Call); + + ArrayRef<Value *> GCArgs(LiveVariables); + uint64_t StatepointID = StatepointDirectives::DefaultStatepointID; + uint32_t NumPatchBytes = 0; + uint32_t Flags = uint32_t(StatepointFlags::None); + + ArrayRef<Use> CallArgs(Call->arg_begin(), Call->arg_end()); + ArrayRef<Use> DeoptArgs = GetDeoptBundleOperands(Call); + ArrayRef<Use> TransitionArgs; + if (auto TransitionBundle = + Call->getOperandBundle(LLVMContext::OB_gc_transition)) { + Flags |= uint32_t(StatepointFlags::GCTransition); + TransitionArgs = TransitionBundle->Inputs; + } + + // Instead of lowering calls to @llvm.experimental.deoptimize as normal calls + // with a return value, we lower then as never returning calls to + // __llvm_deoptimize that are followed by unreachable to get better codegen. + bool IsDeoptimize = false; + + StatepointDirectives SD = + parseStatepointDirectivesFromAttrs(Call->getAttributes()); + if (SD.NumPatchBytes) + NumPatchBytes = *SD.NumPatchBytes; + if (SD.StatepointID) + StatepointID = *SD.StatepointID; + + // Pass through the requested lowering if any. The default is live-through. + StringRef DeoptLowering = getDeoptLowering(Call); + if (DeoptLowering.equals("live-in")) + Flags |= uint32_t(StatepointFlags::DeoptLiveIn); + else { + assert(DeoptLowering.equals("live-through") && "Unsupported value!"); + } + + Value *CallTarget = Call->getCalledValue(); + if (Function *F = dyn_cast<Function>(CallTarget)) { + if (F->getIntrinsicID() == Intrinsic::experimental_deoptimize) { + // Calls to llvm.experimental.deoptimize are lowered to calls to the + // __llvm_deoptimize symbol. We want to resolve this now, since the + // verifier does not allow taking the address of an intrinsic function. + + SmallVector<Type *, 8> DomainTy; + for (Value *Arg : CallArgs) + DomainTy.push_back(Arg->getType()); + auto *FTy = FunctionType::get(Type::getVoidTy(F->getContext()), DomainTy, + /* isVarArg = */ false); + + // Note: CallTarget can be a bitcast instruction of a symbol if there are + // calls to @llvm.experimental.deoptimize with different argument types in + // the same module. This is fine -- we assume the frontend knew what it + // was doing when generating this kind of IR. + CallTarget = F->getParent() + ->getOrInsertFunction("__llvm_deoptimize", FTy) + .getCallee(); + + IsDeoptimize = true; + } + } + + // Create the statepoint given all the arguments + Instruction *Token = nullptr; + if (auto *CI = dyn_cast<CallInst>(Call)) { + CallInst *SPCall = Builder.CreateGCStatepointCall( + StatepointID, NumPatchBytes, CallTarget, Flags, CallArgs, + TransitionArgs, DeoptArgs, GCArgs, "safepoint_token"); + + SPCall->setTailCallKind(CI->getTailCallKind()); + SPCall->setCallingConv(CI->getCallingConv()); + + // Currently we will fail on parameter attributes and on certain + // function attributes. 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. + SPCall->setAttributes(legalizeCallAttributes(CI->getAttributes())); + + Token = SPCall; + + // Put the following gc_result and gc_relocate calls immediately after the + // the old call (which we're about to delete) + assert(CI->getNextNode() && "Not a terminator, must have next!"); + Builder.SetInsertPoint(CI->getNextNode()); + Builder.SetCurrentDebugLocation(CI->getNextNode()->getDebugLoc()); + } else { + auto *II = cast<InvokeInst>(Call); + + // 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 *SPInvoke = Builder.CreateGCStatepointInvoke( + StatepointID, NumPatchBytes, CallTarget, II->getNormalDest(), + II->getUnwindDest(), Flags, CallArgs, TransitionArgs, DeoptArgs, GCArgs, + "statepoint_token"); + + SPInvoke->setCallingConv(II->getCallingConv()); + + // Currently we will fail on parameter attributes and on certain + // function attributes. 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. + SPInvoke->setAttributes(legalizeCallAttributes(II->getAttributes())); + + Token = SPInvoke; + + // Generate gc relocates in exceptional path + BasicBlock *UnwindBlock = II->getUnwindDest(); + assert(!isa<PHINode>(UnwindBlock->begin()) && + UnwindBlock->getUniquePredecessor() && + "can't safely insert in this block!"); + + Builder.SetInsertPoint(&*UnwindBlock->getFirstInsertionPt()); + Builder.SetCurrentDebugLocation(II->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 = II->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 (IsDeoptimize) { + // If we're wrapping an @llvm.experimental.deoptimize in a statepoint, we + // transform the tail-call like structure to a call to a void function + // followed by unreachable to get better codegen. + Replacements.push_back( + DeferredReplacement::createDeoptimizeReplacement(Call)); + } else { + Token->setName("statepoint_token"); + if (!Call->getType()->isVoidTy() && !Call->use_empty()) { + StringRef Name = Call->hasName() ? Call->getName() : ""; + CallInst *GCResult = Builder.CreateGCResult(Token, Call->getType(), Name); + GCResult->setAttributes( + AttributeList::get(GCResult->getContext(), AttributeList::ReturnIndex, + Call->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( + DeferredReplacement::createRAUW(Call, GCResult)); + } else { + Replacements.emplace_back(DeferredReplacement::createDelete(Call)); + } + } + + Result.StatepointToken = Token; + + // Second, create a gc.relocate for every live variable + const unsigned LiveStartIdx = Statepoint(Token).gcArgsStartIdx(); + CreateGCRelocates(LiveVariables, LiveStartIdx, BasePtrs, Token, Builder); +} + +// 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, CallBase *Call, + 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()); + + // Do the actual rewriting and delete the old statepoint + makeStatepointExplicitImpl(Call, 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 *, AllocaInst *> &AllocaMap, + DenseSet<Value *> &VisitedLiveValues) { + for (User *U : GCRelocs) { + GCRelocateInst *Relocate = dyn_cast<GCRelocateInst>(U); + if (!Relocate) + continue; + + Value *OriginalValue = 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( + const RematerializedValueMapTy &RematerializedValues, + DenseMap<Value *, AllocaInst *> &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 (Instruction &I : F.getEntryBlock()) + if (isa<AllocaInst>(I)) + InitialAllocaNum++; +#endif + + // TODO-PERF: change data structures, reserve + DenseMap<Value *, AllocaInst *> 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" + const DataLayout &DL = F.getParent()->getDataLayout(); + auto emitAllocaFor = [&](Value *LiveValue) { + AllocaInst *Alloca = new AllocaInst(LiveValue->getType(), + DL.getAllocaAddrSpace(), "", + 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 = Pair.second; + + // This value was relocated + if (VisitedLiveValues.count(Def)) { + continue; + } + ToClobber.push_back(Alloca); + } + + auto InsertClobbersAt = [&](Instruction *IP) { + for (auto *AI : ToClobber) { + auto PT = cast<PointerType>(AI->getAllocatedType()); + 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; + AllocaInst *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(Def->getNumUses()); + 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)); + } + } + + llvm::sort(Uses); + 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->getAllocatedType(), Alloca, "", + Phi->getIncomingBlock(i)->getTerminator()); + Phi->setIncomingValue(i, Load); + } + } + } else { + LoadInst *Load = + new LoadInst(Alloca->getAllocatedType(), 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 terminator 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 terminator 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(remove_if(Vec, [&](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(CallBase *Call, 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 = Call->getModule(); + // Use a dummy vararg function to actually hold the values live + FunctionCallee Func = M->getOrInsertFunction( + "__tmp_use", FunctionType::get(Type::getVoidTy(M->getContext()), true)); + if (isa<CallInst>(Call)) { + // For call safepoints insert dummy calls right after safepoint + Holders.push_back( + CallInst::Create(Func, Values, "", &*++Call->getIterator())); + return; + } + // For invoke safepooints insert dummy calls both in normal and + // exceptional destination blocks + auto *II = cast<InvokeInst>(Call); + 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<CallBase *> 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]; + analyzeParsePointLiveness(DT, OriginalLivenessData, toUpdate[i], info); + } +} + +// Helper function for the "rematerializeLiveValues". It walks use chain +// starting from the "CurrentValue" until it reaches the root of the chain, i.e. +// the base or a value it cannot process. Only "simple" values are processed +// (currently it is GEP's and casts). The returned root is examined by the +// callers of findRematerializableChainToBasePointer. Fills "ChainToBase" array +// with all visited values. +static Value* findRematerializableChainToBasePointer( + SmallVectorImpl<Instruction*> &ChainToBase, + Value *CurrentValue) { + if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(CurrentValue)) { + ChainToBase.push_back(GEP); + return findRematerializableChainToBasePointer(ChainToBase, + GEP->getPointerOperand()); + } + + if (CastInst *CI = dyn_cast<CastInst>(CurrentValue)) { + if (!CI->isNoopCast(CI->getModule()->getDataLayout())) + return CI; + + ChainToBase.push_back(CI); + return findRematerializableChainToBasePointer(ChainToBase, + CI->getOperand(0)); + } + + // We have reached the root of the chain, which is either equal to the base or + // is the first unsupported value along the use chain. + return CurrentValue; +} + +// 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, CI); + + } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Instr)) { + // Cost of the address calculation + Type *ValTy = GEP->getSourceElementType(); + 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 instruction type during rematerialization"); + } + } + + return Cost; +} + +static bool AreEquivalentPhiNodes(PHINode &OrigRootPhi, PHINode &AlternateRootPhi) { + unsigned PhiNum = OrigRootPhi.getNumIncomingValues(); + if (PhiNum != AlternateRootPhi.getNumIncomingValues() || + OrigRootPhi.getParent() != AlternateRootPhi.getParent()) + return false; + // Map of incoming values and their corresponding basic blocks of + // OrigRootPhi. + SmallDenseMap<Value *, BasicBlock *, 8> CurrentIncomingValues; + for (unsigned i = 0; i < PhiNum; i++) + CurrentIncomingValues[OrigRootPhi.getIncomingValue(i)] = + OrigRootPhi.getIncomingBlock(i); + + // Both current and base PHIs should have same incoming values and + // the same basic blocks corresponding to the incoming values. + for (unsigned i = 0; i < PhiNum; i++) { + auto CIVI = + CurrentIncomingValues.find(AlternateRootPhi.getIncomingValue(i)); + if (CIVI == CurrentIncomingValues.end()) + return false; + BasicBlock *CurrentIncomingBB = CIVI->second; + if (CurrentIncomingBB != AlternateRootPhi.getIncomingBlock(i)) + return false; + } + return true; +} + +// 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(CallBase *Call, + 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 its defining chain + SmallVector<Instruction *, 3> ChainToBase; + assert(Info.PointerToBase.count(LiveValue)); + Value *RootOfChain = + findRematerializableChainToBasePointer(ChainToBase, + LiveValue); + + // Nothing to do, or chain is too long + if ( ChainToBase.size() == 0 || + ChainToBase.size() > ChainLengthThreshold) + continue; + + // Handle the scenario where the RootOfChain is not equal to the + // Base Value, but they are essentially the same phi values. + if (RootOfChain != Info.PointerToBase[LiveValue]) { + PHINode *OrigRootPhi = dyn_cast<PHINode>(RootOfChain); + PHINode *AlternateRootPhi = dyn_cast<PHINode>(Info.PointerToBase[LiveValue]); + if (!OrigRootPhi || !AlternateRootPhi) + continue; + // PHI nodes that have the same incoming values, and belonging to the same + // basic blocks are essentially the same SSA value. When the original phi + // has incoming values with different base pointers, the original phi is + // marked as conflict, and an additional `AlternateRootPhi` with the same + // incoming values get generated by the findBasePointer function. We need + // to identify the newly generated AlternateRootPhi (.base version of phi) + // and RootOfChain (the original phi node itself) are the same, so that we + // can rematerialize the gep and casts. This is a workaround for the + // deficiency in the findBasePointer algorithm. + if (!AreEquivalentPhiNodes(*OrigRootPhi, *AlternateRootPhi)) + continue; + // Now that the phi nodes are proved to be the same, assert that + // findBasePointer's newly generated AlternateRootPhi is present in the + // liveset of the call. + assert(Info.LiveSet.count(AlternateRootPhi)); + } + // 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 (isa<InvokeInst>(Call)) { + 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, Value *RootOfChain, Value *AlternateLiveBase) { + Instruction *LastClonedValue = nullptr; + Instruction *LastValue = nullptr; + for (Instruction *Instr: ChainToBase) { + // Only GEP's and casts are supported 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 + for (auto OpValue : ClonedValue->operand_values()) { + // Assert that cloned instruction does not use any instructions from + // this chain other than LastClonedValue + assert(!is_contained(ChainToBase, OpValue) && + "incorrect use in rematerialization chain"); + // Assert that the cloned instruction does not use the RootOfChain + // or the AlternateLiveBase. + assert(OpValue != RootOfChain && OpValue != AlternateLiveBase); + } +#endif + } else { + // For the first instruction, replace the use of unrelocated base i.e. + // RootOfChain/OrigRootPhi, with the corresponding PHI present in the + // live set. They have been proved to be the same PHI nodes. Note + // that the *only* use of the RootOfChain in the ChainToBase list is + // the first Value in the list. + if (RootOfChain != AlternateLiveBase) + ClonedValue->replaceUsesOfWith(RootOfChain, AlternateLiveBase); + } + + 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 (isa<CallInst>(Call)) { + Instruction *InsertBefore = Call->getNextNode(); + assert(InsertBefore); + Instruction *RematerializedValue = rematerializeChain( + InsertBefore, RootOfChain, Info.PointerToBase[LiveValue]); + Info.RematerializedValues[RematerializedValue] = LiveValue; + } else { + auto *Invoke = cast<InvokeInst>(Call); + + Instruction *NormalInsertBefore = + &*Invoke->getNormalDest()->getFirstInsertionPt(); + Instruction *UnwindInsertBefore = + &*Invoke->getUnwindDest()->getFirstInsertionPt(); + + Instruction *NormalRematerializedValue = rematerializeChain( + NormalInsertBefore, RootOfChain, Info.PointerToBase[LiveValue]); + Instruction *UnwindRematerializedValue = rematerializeChain( + UnwindInsertBefore, RootOfChain, Info.PointerToBase[LiveValue]); + + Info.RematerializedValues[NormalRematerializedValue] = LiveValue; + Info.RematerializedValues[UnwindRematerializedValue] = LiveValue; + } + } + + // Remove rematerializaed values from the live set + for (auto LiveValue: LiveValuesToBeDeleted) { + Info.LiveSet.remove(LiveValue); + } +} + +static bool insertParsePoints(Function &F, DominatorTree &DT, + TargetTransformInfo &TTI, + SmallVectorImpl<CallBase *> &ToUpdate) { +#ifndef NDEBUG + // sanity check the input + std::set<CallBase *> Uniqued; + Uniqued.insert(ToUpdate.begin(), ToUpdate.end()); + assert(Uniqued.size() == ToUpdate.size() && "no duplicates please!"); + + for (CallBase *Call : ToUpdate) + assert(Call->getFunction() == &F); +#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 (CallBase *Call : ToUpdate) { + auto *II = dyn_cast<InvokeInst>(Call); + if (!II) + continue; + 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 deopt operands we'll need for the + // actual safepoint insertion as arguments. This ensures reference operands + // in the deopt argument list are considered live through the safepoint (and + // thus makes sure they get relocated.) + for (CallBase *Call : ToUpdate) { + SmallVector<Value *, 64> DeoptValues; + + for (Value *Arg : GetDeoptBundleOperands(Call)) { + assert(!isUnhandledGCPointerType(Arg->getType()) && + "support for FCA unimplemented"); + if (isHandledGCPointerType(Arg->getType())) + DeoptValues.push_back(Arg); + } + + insertUseHolderAfter(Call, 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.remove(BasePair.first); + + for (CallInst *CI : Holders) + CI->eraseFromParent(); + + Holders.clear(); + + // 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 calls. + + 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 calls. +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.getAttributes().hasAttribute(Index, Attribute::NoAlias)) + R.addAttribute(Attribute::NoAlias); + + if (!R.empty()) + AH.setAttributes(AH.getAttributes().removeAttributes(Ctx, Index, R)); +} + +static void stripNonValidAttributesFromPrototype(Function &F) { + LLVMContext &Ctx = F.getContext(); + + for (Argument &A : F.args()) + if (isa<PointerType>(A.getType())) + RemoveNonValidAttrAtIndex(Ctx, F, + A.getArgNo() + AttributeList::FirstArgIndex); + + if (isa<PointerType>(F.getReturnType())) + RemoveNonValidAttrAtIndex(Ctx, F, AttributeList::ReturnIndex); +} + +/// Certain metadata on instructions are invalid after running RS4GC. +/// Optimizations that run after RS4GC can incorrectly use this metadata to +/// optimize functions. We drop such metadata on the instruction. +static void stripInvalidMetadataFromInstruction(Instruction &I) { + if (!isa<LoadInst>(I) && !isa<StoreInst>(I)) + return; + // These are the attributes that are still valid on loads and stores after + // RS4GC. + // The metadata implying dereferenceability and noalias are (conservatively) + // dropped. This is because semantically, after RewriteStatepointsForGC runs, + // all calls to gc.statepoint "free" the entire heap. Also, gc.statepoint can + // touch the entire heap including noalias objects. Note: The reasoning is + // same as stripping the dereferenceability and noalias attributes that are + // analogous to the metadata counterparts. + // We also drop the invariant.load metadata on the load because that metadata + // implies the address operand to the load points to memory that is never + // changed once it became dereferenceable. This is no longer true after RS4GC. + // Similar reasoning applies to invariant.group metadata, which applies to + // loads within a group. + unsigned ValidMetadataAfterRS4GC[] = {LLVMContext::MD_tbaa, + LLVMContext::MD_range, + LLVMContext::MD_alias_scope, + LLVMContext::MD_nontemporal, + LLVMContext::MD_nonnull, + LLVMContext::MD_align, + LLVMContext::MD_type}; + + // Drops all metadata on the instruction other than ValidMetadataAfterRS4GC. + I.dropUnknownNonDebugMetadata(ValidMetadataAfterRS4GC); +} + +static void stripNonValidDataFromBody(Function &F) { + if (F.empty()) + return; + + LLVMContext &Ctx = F.getContext(); + MDBuilder Builder(Ctx); + + // Set of invariantstart instructions that we need to remove. + // Use this to avoid invalidating the instruction iterator. + SmallVector<IntrinsicInst*, 12> InvariantStartInstructions; + + for (Instruction &I : instructions(F)) { + // invariant.start on memory location implies that the referenced memory + // location is constant and unchanging. This is no longer true after + // RewriteStatepointsForGC runs because there can be calls to gc.statepoint + // which frees the entire heap and the presence of invariant.start allows + // the optimizer to sink the load of a memory location past a statepoint, + // which is incorrect. + if (auto *II = dyn_cast<IntrinsicInst>(&I)) + if (II->getIntrinsicID() == Intrinsic::invariant_start) { + InvariantStartInstructions.push_back(II); + continue; + } + + if (MDNode *Tag = I.getMetadata(LLVMContext::MD_tbaa)) { + MDNode *MutableTBAA = Builder.createMutableTBAAAccessTag(Tag); + I.setMetadata(LLVMContext::MD_tbaa, MutableTBAA); + } + + stripInvalidMetadataFromInstruction(I); + + if (auto *Call = dyn_cast<CallBase>(&I)) { + for (int i = 0, e = Call->arg_size(); i != e; i++) + if (isa<PointerType>(Call->getArgOperand(i)->getType())) + RemoveNonValidAttrAtIndex(Ctx, *Call, + i + AttributeList::FirstArgIndex); + if (isa<PointerType>(Call->getType())) + RemoveNonValidAttrAtIndex(Ctx, *Call, AttributeList::ReturnIndex); + } + } + + // Delete the invariant.start instructions and RAUW undef. + for (auto *II : InvariantStartInstructions) { + II->replaceAllUsesWith(UndefValue::get(II->getType())); + II->eraseFromParent(); + } +} + +/// 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; +} + +static void stripNonValidData(Module &M) { +#ifndef NDEBUG + assert(llvm::any_of(M, shouldRewriteStatepointsIn) && "precondition!"); +#endif + + for (Function &F : M) + stripNonValidAttributesFromPrototype(F); + + for (Function &F : M) + stripNonValidDataFromBody(F); +} + +bool RewriteStatepointsForGC::runOnFunction(Function &F, DominatorTree &DT, + TargetTransformInfo &TTI, + const TargetLibraryInfo &TLI) { + assert(!F.isDeclaration() && !F.empty() && + "need function body to rewrite statepoints in"); + assert(shouldRewriteStatepointsIn(F) && "mismatch in rewrite decision"); + + auto NeedsRewrite = [&TLI](Instruction &I) { + if (const auto *Call = dyn_cast<CallBase>(&I)) + return !callsGCLeafFunction(Call, TLI) && !isStatepoint(Call); + return 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. + DomTreeUpdater DTU(DT, DomTreeUpdater::UpdateStrategy::Lazy); + bool MadeChange = removeUnreachableBlocks(F, &DTU); + // Flush the Dominator Tree. + DTU.getDomTree(); + + // Gather all the statepoints which need rewritten. Be careful to only + // consider those in reachable code since we need to ask dominance queries + // when rewriting. We'll delete the unreachable ones in a moment. + SmallVector<CallBase *, 64> ParsePointNeeded; + for (Instruction &I : instructions(F)) { + // TODO: only the ones with the flag set! + if (NeedsRewrite(I)) { + // NOTE removeUnreachableBlocks() is stronger than + // DominatorTree::isReachableFromEntry(). In other words + // removeUnreachableBlocks can remove some blocks for which + // isReachableFromEntry() returns true. + assert(DT.isReachableFromEntry(I.getParent()) && + "no unreachable blocks expected"); + ParsePointNeeded.push_back(cast<CallBase>(&I)); + } + } + + // 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 = [](Instruction *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) { + Instruction *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); + } + } + + // Nasty workaround - The base computation code in the main algorithm doesn't + // consider the fact that a GEP can be used to convert a scalar to a vector. + // The right fix for this is to integrate GEPs into the base rewriting + // algorithm properly, this is just a short term workaround to prevent + // crashes by canonicalizing such GEPs into fully vector GEPs. + for (Instruction &I : instructions(F)) { + if (!isa<GetElementPtrInst>(I)) + continue; + + unsigned VF = 0; + for (unsigned i = 0; i < I.getNumOperands(); i++) + if (I.getOperand(i)->getType()->isVectorTy()) { + assert(VF == 0 || + VF == I.getOperand(i)->getType()->getVectorNumElements()); + VF = I.getOperand(i)->getType()->getVectorNumElements(); + } + + // It's the vector to scalar traversal through the pointer operand which + // confuses base pointer rewriting, so limit ourselves to that case. + if (!I.getOperand(0)->getType()->isVectorTy() && VF != 0) { + IRBuilder<> B(&I); + auto *Splat = B.CreateVectorSplat(VF, I.getOperand(0)); + I.setOperand(0, Splat); + MadeChange = true; + } + } + + 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 Begin, + BasicBlock::reverse_iterator End, + SetVector<Value *> &LiveTmp) { + for (auto &I : make_range(Begin, End)) { + // KILL/Def - Remove this definition from LiveIn + LiveTmp.remove(&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, SetVector<Value *> &LiveTmp) { + for (BasicBlock *Succ : successors(BB)) { + for (auto &I : *Succ) { + PHINode *PN = dyn_cast<PHINode>(&I); + if (!PN) + break; + + Value *V = PN->getIncomingValueForBlock(BB); + assert(!isUnhandledGCPointerType(V->getType()) && + "support for FCA unimplemented"); + if (isHandledGCPointerType(V->getType()) && !isa<Constant>(V)) + LiveTmp.insert(V); + } + } +} + +static SetVector<Value *> computeKillSet(BasicBlock *BB) { + SetVector<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, SetVector<Value *> &Live, + Instruction *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 *, 32> Worklist; + + // 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] = SetVector<Value *>(); + computeLiveOutSeed(&BB, Data.LiveOut[&BB]); + Data.LiveIn[&BB] = Data.LiveSet[&BB]; + Data.LiveIn[&BB].set_union(Data.LiveOut[&BB]); + Data.LiveIn[&BB].set_subtract(Data.KillSet[&BB]); + if (!Data.LiveIn[&BB].empty()) + Worklist.insert(pred_begin(&BB), pred_end(&BB)); + } + + // Propagate that liveness until stable + while (!Worklist.empty()) { + BasicBlock *BB = Worklist.pop_back_val(); + + // Compute our new liveout set, then exit early if it hasn't changed despite + // the contribution of our successor. + SetVector<Value *> LiveOut = Data.LiveOut[BB]; + const auto OldLiveOutSize = LiveOut.size(); + for (BasicBlock *Succ : successors(BB)) { + assert(Data.LiveIn.count(Succ)); + LiveOut.set_union(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 + SetVector<Value *> LiveTmp = LiveOut; + LiveTmp.set_union(Data.LiveSet[BB]); + LiveTmp.set_subtract(Data.KillSet[BB]); + + assert(Data.LiveIn.count(BB)); + const SetVector<Value *> &OldLiveIn = Data.LiveIn[BB]; + // assert: OldLiveIn is a subset of LiveTmp + if (OldLiveIn.size() != LiveTmp.size()) { + Data.LiveIn[BB] = LiveTmp; + Worklist.insert(pred_begin(BB), pred_end(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)); + SetVector<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 + computeLiveInValues(BB->rbegin(), ++Inst->getIterator().getReverse(), + LiveOut); + LiveOut.remove(Inst); + Out.insert(LiveOut.begin(), LiveOut.end()); +} + +static void recomputeLiveInValues(GCPtrLivenessData &RevisedLivenessData, + CallBase *Call, + PartiallyConstructedSafepointRecord &Info) { + StatepointLiveSetTy Updated; + findLiveSetAtInst(Call, RevisedLivenessData, Updated); + + // 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.insert({V, V}).second) { + assert(isKnownBaseResult(V) && + "Can't find base for unexpected live value!"); + 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; +} |