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Diffstat (limited to 'gnu/llvm/lib/Transforms/Scalar/RewriteStatepointsForGC.cpp')
| -rw-r--r-- | gnu/llvm/lib/Transforms/Scalar/RewriteStatepointsForGC.cpp | 2826 |
1 files changed, 0 insertions, 2826 deletions
diff --git a/gnu/llvm/lib/Transforms/Scalar/RewriteStatepointsForGC.cpp b/gnu/llvm/lib/Transforms/Scalar/RewriteStatepointsForGC.cpp deleted file mode 100644 index 42d7ed5bc53..00000000000 --- a/gnu/llvm/lib/Transforms/Scalar/RewriteStatepointsForGC.cpp +++ /dev/null @@ -1,2826 +0,0 @@ -//===- RewriteStatepointsForGC.cpp - Make GC relocations explicit ---------===// -// -// The LLVM Compiler Infrastructure -// -// This file is distributed under the University of Illinois Open Source -// License. See LICENSE.TXT for details. -// -//===----------------------------------------------------------------------===// -// -// Rewrite 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/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/CallSite.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/DomTreeUpdater.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; - const TargetLibraryInfo &TLI = - getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(); - 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); - 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(ImmutableCallSite CS) { - Optional<OperandBundleUse> DeoptBundle = - CS.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, CallSite CS, - PartiallyConstructedSafepointRecord &Result) { - Instruction *Inst = CS.getInstruction(); - - StatepointLiveSetTy LiveSet; - findLiveSetAtInst(Inst, OriginalLivenessData, LiveSet); - - if (PrintLiveSet) { - dbgs() << "Live Variables:\n"; - for (Value *V : LiveSet) - dbgs() << " " << V->getName() << " " << *V << "\n"; - } - if (PrintLiveSetSize) { - dbgs() << "Safepoint For: " << CS.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, - CallSite CS, - 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, - CallSite CS, - PartiallyConstructedSafepointRecord &result); - -static void recomputeLiveInValues( - Function &F, DominatorTree &DT, ArrayRef<CallSite> toUpdate, - MutableArrayRef<struct PartiallyConstructedSafepointRecord> records) { - // TODO-PERF: reuse the original liveness, then simply run the dataflow - // again. The old values are still live and will help it stabilize quickly. - GCPtrLivenessData RevisedLivenessData; - computeLiveInValues(DT, F, RevisedLivenessData); - for (size_t i = 0; i < records.size(); i++) { - struct PartiallyConstructedSafepointRecord &info = records[i]; - 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*, Value*> TypeToDeclMap; - - for (unsigned i = 0; i < LiveVariables.size(); i++) { - // Generate the gc.relocate call and save the result - Value *BaseIdx = - Builder.getInt32(LiveStart + FindIndex(LiveVariables, BasePtrs[i])); - Value *LiveIdx = Builder.getInt32(LiveStart + i); - - Type *Ty = LiveVariables[i]->getType(); - if (!TypeToDeclMap.count(Ty)) - TypeToDeclMap[Ty] = getGCRelocateDecl(Ty); - Value *GCRelocateDecl = TypeToDeclMap[Ty]; - - // only specify a debug name if we can give a useful one - CallInst *Reloc = Builder.CreateCall( - GCRelocateDecl, {StatepointToken, BaseIdx, LiveIdx}, - suffixed_name_or(LiveVariables[i], ".relocated", "")); - // Trick CodeGen into thinking there are lots of free registers at this - // fake call. - Reloc->setCallingConv(CallingConv::Cold); - } -} - -namespace { - -/// This struct is used to defer RAUWs and `eraseFromParent` s. Using this -/// avoids having to worry about keeping around dangling pointers to Values. -class DeferredReplacement { - AssertingVH<Instruction> Old; - AssertingVH<Instruction> New; - 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(CallSite CS) { - const char *DeoptLowering = "deopt-lowering"; - if (CS.hasFnAttr(DeoptLowering)) { - // FIXME: CallSite has a *really* confusing interface around attributes - // with values. - const AttributeList &CSAS = CS.getAttributes(); - if (CSAS.hasAttribute(AttributeList::FunctionIndex, DeoptLowering)) - return CSAS.getAttribute(AttributeList::FunctionIndex, DeoptLowering) - .getValueAsString(); - Function *F = CS.getCalledFunction(); - assert(F && F->hasFnAttribute(DeoptLowering)); - return F->getFnAttribute(DeoptLowering).getValueAsString(); - } - return "live-through"; -} - -static void -makeStatepointExplicitImpl(const CallSite CS, /* to replace */ - const SmallVectorImpl<Value *> &BasePtrs, - const SmallVectorImpl<Value *> &LiveVariables, - PartiallyConstructedSafepointRecord &Result, - std::vector<DeferredReplacement> &Replacements) { - assert(BasePtrs.size() == LiveVariables.size()); - - // Then go ahead and use the builder do actually do the inserts. We insert - // immediately before the previous instruction under the assumption that all - // arguments will be available here. We can't insert afterwards since we may - // be replacing a terminator. - Instruction *InsertBefore = CS.getInstruction(); - IRBuilder<> Builder(InsertBefore); - - ArrayRef<Value *> GCArgs(LiveVariables); - uint64_t StatepointID = StatepointDirectives::DefaultStatepointID; - uint32_t NumPatchBytes = 0; - uint32_t Flags = uint32_t(StatepointFlags::None); - - ArrayRef<Use> CallArgs(CS.arg_begin(), CS.arg_end()); - ArrayRef<Use> DeoptArgs = GetDeoptBundleOperands(CS); - ArrayRef<Use> TransitionArgs; - if (auto TransitionBundle = - CS.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(CS.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(CS); - if (DeoptLowering.equals("live-in")) - Flags |= uint32_t(StatepointFlags::DeoptLiveIn); - else { - assert(DeoptLowering.equals("live-through") && "Unsupported value!"); - } - - Value *CallTarget = CS.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); - - IsDeoptimize = true; - } - } - - // Create the statepoint given all the arguments - Instruction *Token = nullptr; - if (CS.isCall()) { - CallInst *ToReplace = cast<CallInst>(CS.getInstruction()); - CallInst *Call = Builder.CreateGCStatepointCall( - StatepointID, NumPatchBytes, CallTarget, Flags, CallArgs, - TransitionArgs, DeoptArgs, GCArgs, "safepoint_token"); - - Call->setTailCallKind(ToReplace->getTailCallKind()); - Call->setCallingConv(ToReplace->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. - Call->setAttributes(legalizeCallAttributes(ToReplace->getAttributes())); - - Token = Call; - - // Put the following gc_result and gc_relocate calls immediately after the - // the old call (which we're about to delete) - assert(ToReplace->getNextNode() && "Not a terminator, must have next!"); - Builder.SetInsertPoint(ToReplace->getNextNode()); - Builder.SetCurrentDebugLocation(ToReplace->getNextNode()->getDebugLoc()); - } else { - InvokeInst *ToReplace = cast<InvokeInst>(CS.getInstruction()); - - // Insert the new invoke into the old block. We'll remove the old one in a - // moment at which point this will become the new terminator for the - // original block. - InvokeInst *Invoke = Builder.CreateGCStatepointInvoke( - StatepointID, NumPatchBytes, CallTarget, ToReplace->getNormalDest(), - ToReplace->getUnwindDest(), Flags, CallArgs, TransitionArgs, DeoptArgs, - GCArgs, "statepoint_token"); - - Invoke->setCallingConv(ToReplace->getCallingConv()); - - // Currently we will fail on parameter attributes and on certain - // function attributes. In case if we can handle this set of attributes - - // set up function attrs directly on statepoint and return attrs later for - // gc_result intrinsic. - Invoke->setAttributes(legalizeCallAttributes(ToReplace->getAttributes())); - - Token = Invoke; - - // Generate gc relocates in exceptional path - BasicBlock *UnwindBlock = ToReplace->getUnwindDest(); - assert(!isa<PHINode>(UnwindBlock->begin()) && - UnwindBlock->getUniquePredecessor() && - "can't safely insert in this block!"); - - Builder.SetInsertPoint(&*UnwindBlock->getFirstInsertionPt()); - Builder.SetCurrentDebugLocation(ToReplace->getDebugLoc()); - - // Attach exceptional gc relocates to the landingpad. - Instruction *ExceptionalToken = UnwindBlock->getLandingPadInst(); - Result.UnwindToken = ExceptionalToken; - - const unsigned LiveStartIdx = Statepoint(Token).gcArgsStartIdx(); - CreateGCRelocates(LiveVariables, LiveStartIdx, BasePtrs, ExceptionalToken, - Builder); - - // Generate gc relocates and returns for normal block - BasicBlock *NormalDest = ToReplace->getNormalDest(); - assert(!isa<PHINode>(NormalDest->begin()) && - NormalDest->getUniquePredecessor() && - "can't safely insert in this block!"); - - Builder.SetInsertPoint(&*NormalDest->getFirstInsertionPt()); - - // gc relocates will be generated later as if it were regular call - // statepoint - } - assert(Token && "Should be set in one of the above branches!"); - - if (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(CS.getInstruction())); - } else { - Token->setName("statepoint_token"); - if (!CS.getType()->isVoidTy() && !CS.getInstruction()->use_empty()) { - StringRef Name = - CS.getInstruction()->hasName() ? CS.getInstruction()->getName() : ""; - CallInst *GCResult = Builder.CreateGCResult(Token, CS.getType(), Name); - GCResult->setAttributes( - AttributeList::get(GCResult->getContext(), AttributeList::ReturnIndex, - CS.getAttributes().getRetAttributes())); - - // We cannot RAUW or delete CS.getInstruction() because it could be in the - // live set of some other safepoint, in which case that safepoint's - // PartiallyConstructedSafepointRecord will hold a raw pointer to this - // llvm::Instruction. Instead, we defer the replacement and deletion to - // after the live sets have been made explicit in the IR, and we no longer - // have raw pointers to worry about. - Replacements.emplace_back( - DeferredReplacement::createRAUW(CS.getInstruction(), GCResult)); - } else { - Replacements.emplace_back( - DeferredReplacement::createDelete(CS.getInstruction())); - } - } - - 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, CallSite CS, - PartiallyConstructedSafepointRecord &Result, - std::vector<DeferredReplacement> &Replacements) { - const auto &LiveSet = Result.LiveSet; - const auto &PointerToBase = Result.PointerToBase; - - // Convert to vector for efficient cross referencing. - SmallVector<Value *, 64> BaseVec, LiveVec; - LiveVec.reserve(LiveSet.size()); - BaseVec.reserve(LiveSet.size()); - for (Value *L : LiveSet) { - LiveVec.push_back(L); - assert(PointerToBase.count(L)); - Value *Base = PointerToBase.find(L)->second; - BaseVec.push_back(Base); - } - assert(LiveVec.size() == BaseVec.size()); - - // Do the actual rewriting and delete the old statepoint - makeStatepointExplicitImpl(CS, BaseVec, LiveVec, Result, Replacements); -} - -// Helper function for the relocationViaAlloca. -// -// It receives iterator to the statepoint gc relocates and emits a store to the -// assigned location (via allocaMap) for the each one of them. It adds the -// visited values into the visitedLiveValues set, which we will later use them -// for sanity checking. -static void -insertRelocationStores(iterator_range<Value::user_iterator> GCRelocs, - DenseMap<Value *, Value *> &AllocaMap, - DenseSet<Value *> &VisitedLiveValues) { - for (User *U : GCRelocs) { - GCRelocateInst *Relocate = dyn_cast<GCRelocateInst>(U); - if (!Relocate) - continue; - - Value *OriginalValue = 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 *, Value *> &AllocaMap, - DenseSet<Value *> &VisitedLiveValues) { - for (auto RematerializedValuePair: RematerializedValues) { - Instruction *RematerializedValue = RematerializedValuePair.first; - Value *OriginalValue = RematerializedValuePair.second; - - assert(AllocaMap.count(OriginalValue) && - "Can not find alloca for rematerialized value"); - Value *Alloca = AllocaMap[OriginalValue]; - - StoreInst *Store = new StoreInst(RematerializedValue, Alloca); - Store->insertAfter(RematerializedValue); - -#ifndef NDEBUG - VisitedLiveValues.insert(OriginalValue); -#endif - } -} - -/// Do all the relocation update via allocas and mem2reg -static void relocationViaAlloca( - Function &F, DominatorTree &DT, ArrayRef<Value *> Live, - ArrayRef<PartiallyConstructedSafepointRecord> Records) { -#ifndef NDEBUG - // record initial number of (static) allocas; we'll check we have the same - // number when we get done. - int InitialAllocaNum = 0; - for (Instruction &I : F.getEntryBlock()) - if (isa<AllocaInst>(I)) - InitialAllocaNum++; -#endif - - // TODO-PERF: change data structures, reserve - DenseMap<Value *, Value *> AllocaMap; - SmallVector<AllocaInst *, 200> PromotableAllocas; - // Used later to chack that we have enough allocas to store all values - std::size_t NumRematerializedValues = 0; - PromotableAllocas.reserve(Live.size()); - - // Emit alloca for "LiveValue" and record it in "allocaMap" and - // "PromotableAllocas" - 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 = cast<AllocaInst>(Pair.second); - - // This value was relocated - if (VisitedLiveValues.count(Def)) { - continue; - } - ToClobber.push_back(Alloca); - } - - auto InsertClobbersAt = [&](Instruction *IP) { - for (auto *AI : ToClobber) { - auto 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; - Value *Alloca = Pair.second; - - // We pre-record the uses of allocas so that we dont have to worry about - // later update that changes the user information.. - - SmallVector<Instruction *, 20> Uses; - // PERF: trade a linear scan for repeated reallocation - Uses.reserve(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, "", Phi->getIncomingBlock(i)->getTerminator()); - Phi->setIncomingValue(i, Load); - } - } - } else { - LoadInst *Load = new LoadInst(Alloca, "", Use); - Use->replaceUsesOfWith(Def, Load); - } - } - - // Emit store for the initial gc value. Store must be inserted after load, - // otherwise store will be in alloca's use list and an extra load will be - // inserted before it. - StoreInst *Store = new StoreInst(Def, Alloca); - if (Instruction *Inst = dyn_cast<Instruction>(Def)) { - if (InvokeInst *Invoke = dyn_cast<InvokeInst>(Inst)) { - // InvokeInst is a 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(CallSite &CS, const ArrayRef<Value *> Values, - SmallVectorImpl<CallInst *> &Holders) { - if (Values.empty()) - // No values to hold live, might as well not insert the empty holder - return; - - Module *M = CS.getInstruction()->getModule(); - // Use a dummy vararg function to actually hold the values live - Function *Func = cast<Function>(M->getOrInsertFunction( - "__tmp_use", FunctionType::get(Type::getVoidTy(M->getContext()), true))); - if (CS.isCall()) { - // For call safepoints insert dummy calls right after safepoint - Holders.push_back(CallInst::Create(Func, Values, "", - &*++CS.getInstruction()->getIterator())); - return; - } - // For invoke safepooints insert dummy calls both in normal and - // exceptional destination blocks - auto *II = cast<InvokeInst>(CS.getInstruction()); - Holders.push_back(CallInst::Create( - Func, Values, "", &*II->getNormalDest()->getFirstInsertionPt())); - Holders.push_back(CallInst::Create( - Func, Values, "", &*II->getUnwindDest()->getFirstInsertionPt())); -} - -static void findLiveReferences( - Function &F, DominatorTree &DT, ArrayRef<CallSite> toUpdate, - MutableArrayRef<struct PartiallyConstructedSafepointRecord> records) { - GCPtrLivenessData OriginalLivenessData; - computeLiveInValues(DT, F, OriginalLivenessData); - for (size_t i = 0; i < records.size(); i++) { - struct PartiallyConstructedSafepointRecord &info = records[i]; - 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(CallSite CS, - PartiallyConstructedSafepointRecord &Info, - TargetTransformInfo &TTI) { - const unsigned int ChainLengthThreshold = 10; - - // Record values we are going to delete from this statepoint live set. - // We can not di this in following loop due to iterator invalidation. - SmallVector<Value *, 32> LiveValuesToBeDeleted; - - for (Value *LiveValue: Info.LiveSet) { - // For each live pointer find 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 (CS.isInvoke()) { - Cost *= 2; - } - // If it's too expensive - skip it - if (Cost >= RematerializationThreshold) - continue; - - // Remove value from the live set - LiveValuesToBeDeleted.push_back(LiveValue); - - // Clone instructions and record them inside "Info" structure - - // Walk backwards to visit top-most instructions first - std::reverse(ChainToBase.begin(), ChainToBase.end()); - - // Utility function which clones all instructions from "ChainToBase" - // and inserts them before "InsertBefore". Returns rematerialized value - // which should be used after statepoint. - auto rematerializeChain = [&ChainToBase]( - Instruction *InsertBefore, 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 (CS.isCall()) { - Instruction *InsertBefore = CS.getInstruction()->getNextNode(); - assert(InsertBefore); - Instruction *RematerializedValue = rematerializeChain( - InsertBefore, RootOfChain, Info.PointerToBase[LiveValue]); - Info.RematerializedValues[RematerializedValue] = LiveValue; - } else { - InvokeInst *Invoke = cast<InvokeInst>(CS.getInstruction()); - - Instruction *NormalInsertBefore = - &*Invoke->getNormalDest()->getFirstInsertionPt(); - Instruction *UnwindInsertBefore = - &*Invoke->getUnwindDest()->getFirstInsertionPt(); - - Instruction *NormalRematerializedValue = rematerializeChain( - NormalInsertBefore, 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<CallSite> &ToUpdate) { -#ifndef NDEBUG - // sanity check the input - std::set<CallSite> Uniqued; - Uniqued.insert(ToUpdate.begin(), ToUpdate.end()); - assert(Uniqued.size() == ToUpdate.size() && "no duplicates please!"); - - for (CallSite CS : ToUpdate) - assert(CS.getInstruction()->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 (CallSite CS : ToUpdate) { - if (!CS.isInvoke()) - continue; - auto *II = cast<InvokeInst>(CS.getInstruction()); - normalizeForInvokeSafepoint(II->getNormalDest(), II->getParent(), DT); - normalizeForInvokeSafepoint(II->getUnwindDest(), II->getParent(), DT); - } - - // A list of dummy calls added to the IR to keep various values obviously - // live in the IR. We'll remove all of these when done. - SmallVector<CallInst *, 64> Holders; - - // Insert a dummy call with all of the 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 (CallSite CS : ToUpdate) { - SmallVector<Value *, 64> DeoptValues; - - for (Value *Arg : GetDeoptBundleOperands(CS)) { - assert(!isUnhandledGCPointerType(Arg->getType()) && - "support for FCA unimplemented"); - if (isHandledGCPointerType(Arg->getType())) - DeoptValues.push_back(Arg); - } - - insertUseHolderAfter(CS, DeoptValues, Holders); - } - - SmallVector<PartiallyConstructedSafepointRecord, 64> Records(ToUpdate.size()); - - // A) Identify all gc pointers which are statically live at the given call - // site. - findLiveReferences(F, DT, ToUpdate, Records); - - // B) Find the base pointers for each live pointer - /* scope for caching */ { - // Cache the 'defining value' relation used in the computation and - // insertion of base phis and selects. This ensures that we don't insert - // large numbers of duplicate base_phis. - DefiningValueMapTy DVCache; - - for (size_t i = 0; i < Records.size(); i++) { - PartiallyConstructedSafepointRecord &info = Records[i]; - findBasePointers(DT, DVCache, ToUpdate[i], info); - } - } // end of cache scope - - // The base phi insertion logic (for any safepoint) may have inserted new - // instructions which are now live at some safepoint. The simplest such - // example is: - // loop: - // phi a <-- will be a new base_phi here - // safepoint 1 <-- that needs to be live here - // gep a + 1 - // safepoint 2 - // br loop - // We insert some dummy calls after each safepoint to definitely hold live - // the base pointers which were identified for that safepoint. We'll then - // ask liveness for _every_ base inserted to see what is now live. Then we - // remove the dummy calls. - Holders.reserve(Holders.size() + Records.size()); - for (size_t i = 0; i < Records.size(); i++) { - PartiallyConstructedSafepointRecord &Info = Records[i]; - - SmallVector<Value *, 128> Bases; - for (auto Pair : Info.PointerToBase) - Bases.push_back(Pair.second); - - insertUseHolderAfter(ToUpdate[i], Bases, Holders); - } - - // By selecting base pointers, we've effectively inserted new uses. Thus, we - // need to rerun liveness. We may *also* have inserted new defs, but that's - // not the key issue. - recomputeLiveInValues(F, DT, ToUpdate, Records); - - if (PrintBasePointers) { - for (auto &Info : Records) { - errs() << "Base Pairs: (w/Relocation)\n"; - for (auto Pair : Info.PointerToBase) { - errs() << " derived "; - Pair.first->printAsOperand(errs(), false); - errs() << " base "; - Pair.second->printAsOperand(errs(), false); - errs() << "\n"; - } - } - } - - // It is possible that non-constant live variables have a constant base. For - // example, a GEP with a variable offset from a global. In this case we can - // remove it from the liveset. We already don't add constants to the liveset - // because we assume they won't move at runtime and the GC doesn't need to be - // informed about them. The same reasoning applies if the base is constant. - // Note that the relocation placement code relies on this filtering for - // correctness as it expects the base to be in the liveset, which isn't true - // if the base is constant. - for (auto &Info : Records) - for (auto &BasePair : Info.PointerToBase) - if (isa<Constant>(BasePair.second)) - Info.LiveSet.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 CallSites - - for (auto &PR : Replacements) - PR.doReplacement(); - - Replacements.clear(); - - for (auto &Info : Records) { - // These live sets may contain state Value pointers, since we replaced calls - // with operand bundles with calls wrapped in gc.statepoint, and some of - // those calls may have been def'ing live gc pointers. Clear these out to - // avoid accidentally using them. - // - // TODO: We should create a separate data structure that does not contain - // these live sets, and migrate to using that data structure from this point - // onward. - Info.LiveSet.clear(); - Info.PointerToBase.clear(); - } - - // Do all the fixups of the original live variables to their relocated selves - SmallVector<Value *, 128> Live; - for (size_t i = 0; i < Records.size(); i++) { - PartiallyConstructedSafepointRecord &Info = Records[i]; - - // We can't simply save the live set from the original insertion. One of - // the live values might be the result of a call which needs a safepoint. - // That Value* no longer exists and we need to use the new gc_result. - // Thankfully, the live set is embedded in the statepoint (and updated), so - // we just grab that. - Statepoint Statepoint(Info.StatepointToken); - Live.insert(Live.end(), Statepoint.gc_args_begin(), - Statepoint.gc_args_end()); -#ifndef NDEBUG - // Do some basic sanity checks on our liveness results before performing - // relocation. Relocation can and will turn mistakes in liveness results - // into non-sensical code which is must harder to debug. - // TODO: It would be nice to test consistency as well - assert(DT.isReachableFromEntry(Info.StatepointToken->getParent()) && - "statepoint must be reachable or liveness is meaningless"); - for (Value *V : Statepoint.gc_args()) { - if (!isa<Instruction>(V)) - // Non-instruction values trivial dominate all possible uses - continue; - auto *LiveInst = cast<Instruction>(V); - assert(DT.isReachableFromEntry(LiveInst->getParent()) && - "unreachable values should never be live"); - assert(DT.dominates(LiveInst, Info.StatepointToken) && - "basic SSA liveness expectation violated by liveness analysis"); - } -#endif - } - unique_unsorted(Live); - -#ifndef NDEBUG - // sanity check - for (auto *Ptr : Live) - assert(isHandledGCPointerType(Ptr->getType()) && - "must be a gc pointer type"); -#endif - - relocationViaAlloca(F, DT, Live, Records); - return !Records.empty(); -} - -// Handles both return values and arguments for Functions and CallSites. -template <typename AttrHolder> -static void RemoveNonValidAttrAtIndex(LLVMContext &Ctx, AttrHolder &AH, - unsigned Index) { - AttrBuilder R; - if (AH.getDereferenceableBytes(Index)) - R.addAttribute(Attribute::get(Ctx, Attribute::Dereferenceable, - AH.getDereferenceableBytes(Index))); - if (AH.getDereferenceableOrNullBytes(Index)) - R.addAttribute(Attribute::get(Ctx, Attribute::DereferenceableOrNull, - AH.getDereferenceableOrNullBytes(Index))); - if (AH.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 (CallSite CS = CallSite(&I)) { - for (int i = 0, e = CS.arg_size(); i != e; i++) - if (isa<PointerType>(CS.getArgument(i)->getType())) - RemoveNonValidAttrAtIndex(Ctx, CS, i + AttributeList::FirstArgIndex); - if (isa<PointerType>(CS.getType())) - RemoveNonValidAttrAtIndex(Ctx, CS, 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 (ImmutableCallSite CS = ImmutableCallSite(&I)) - return !callsGCLeafFunction(CS, TLI) && !isStatepoint(CS); - 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, nullptr, &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<CallSite, 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(CallSite(&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); - } - } - - 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, - CallSite CS, - PartiallyConstructedSafepointRecord &Info) { - Instruction *Inst = CS.getInstruction(); - StatepointLiveSetTy Updated; - findLiveSetAtInst(Inst, 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; -} |