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Diffstat (limited to 'lib/CodeGen/GCStrategy.cpp')
| -rw-r--r-- | lib/CodeGen/GCStrategy.cpp | 389 |
1 files changed, 389 insertions, 0 deletions
diff --git a/lib/CodeGen/GCStrategy.cpp b/lib/CodeGen/GCStrategy.cpp new file mode 100644 index 0000000000..629a2e13de --- /dev/null +++ b/lib/CodeGen/GCStrategy.cpp @@ -0,0 +1,389 @@ +//===-- Collector.cpp - Garbage collection infrastructure -----------------===// +// +// The LLVM Compiler Infrastructure +// +// This file is distributed under the University of Illinois Open Source +// License. See LICENSE.TXT for details. +// +//===----------------------------------------------------------------------===// +// +// This file implements target- and collector-independent garbage collection +// infrastructure. +// +//===----------------------------------------------------------------------===// + +#include "llvm/CodeGen/GCStrategy.h" +#include "llvm/CodeGen/Passes.h" +#include "llvm/IntrinsicInst.h" +#include "llvm/Module.h" +#include "llvm/CodeGen/MachineFrameInfo.h" +#include "llvm/CodeGen/MachineFunctionPass.h" +#include "llvm/CodeGen/MachineInstrBuilder.h" +#include "llvm/CodeGen/MachineModuleInfo.h" +#include "llvm/Target/TargetFrameInfo.h" +#include "llvm/Target/TargetInstrInfo.h" +#include "llvm/Target/TargetMachine.h" +#include "llvm/Support/Compiler.h" + +using namespace llvm; + +namespace { + + /// LowerIntrinsics - This pass rewrites calls to the llvm.gcread or + /// llvm.gcwrite intrinsics, replacing them with simple loads and stores as + /// directed by the Collector. It also performs automatic root initialization + /// and custom intrinsic lowering. + class VISIBILITY_HIDDEN LowerIntrinsics : public FunctionPass { + static bool NeedsDefaultLoweringPass(const Collector &C); + static bool NeedsCustomLoweringPass(const Collector &C); + static bool CouldBecomeSafePoint(Instruction *I); + bool PerformDefaultLowering(Function &F, Collector &Coll); + static bool InsertRootInitializers(Function &F, + AllocaInst **Roots, unsigned Count); + + public: + static char ID; + + LowerIntrinsics(); + const char *getPassName() const; + void getAnalysisUsage(AnalysisUsage &AU) const; + + bool doInitialization(Module &M); + bool runOnFunction(Function &F); + }; + + + /// MachineCodeAnalysis - This is a target-independent pass over the machine + /// function representation to identify safe points for the garbage collector + /// in the machine code. It inserts labels at safe points and populates a + /// CollectorMetadata record for each function. + class VISIBILITY_HIDDEN MachineCodeAnalysis : public MachineFunctionPass { + const TargetMachine *TM; + CollectorMetadata *MD; + MachineModuleInfo *MMI; + const TargetInstrInfo *TII; + MachineFrameInfo *MFI; + + void FindSafePoints(MachineFunction &MF); + void VisitCallPoint(MachineBasicBlock::iterator MI); + unsigned InsertLabel(MachineBasicBlock &MBB, + MachineBasicBlock::iterator MI) const; + + void FindStackOffsets(MachineFunction &MF); + + public: + static char ID; + + MachineCodeAnalysis(); + const char *getPassName() const; + void getAnalysisUsage(AnalysisUsage &AU) const; + + bool runOnMachineFunction(MachineFunction &MF); + }; + +} + +// ----------------------------------------------------------------------------- + +Collector::Collector() : + NeededSafePoints(0), + CustomReadBarriers(false), + CustomWriteBarriers(false), + CustomRoots(false), + InitRoots(true), + UsesMetadata(false) +{} + +Collector::~Collector() { + for (iterator I = begin(), E = end(); I != E; ++I) + delete *I; + + Functions.clear(); +} + +bool Collector::initializeCustomLowering(Module &M) { return false; } + +bool Collector::performCustomLowering(Function &F) { + cerr << "gc " << getName() << " must override performCustomLowering.\n"; + abort(); + return 0; +} + +CollectorMetadata *Collector::insertFunctionMetadata(const Function &F) { + CollectorMetadata *CM = new CollectorMetadata(F, *this); + Functions.push_back(CM); + return CM; +} + +// ----------------------------------------------------------------------------- + +FunctionPass *llvm::createGCLoweringPass() { + return new LowerIntrinsics(); +} + +char LowerIntrinsics::ID = 0; + +LowerIntrinsics::LowerIntrinsics() + : FunctionPass((intptr_t)&ID) {} + +const char *LowerIntrinsics::getPassName() const { + return "Lower Garbage Collection Instructions"; +} + +void LowerIntrinsics::getAnalysisUsage(AnalysisUsage &AU) const { + FunctionPass::getAnalysisUsage(AU); + AU.addRequired<CollectorModuleMetadata>(); +} + +/// doInitialization - If this module uses the GC intrinsics, find them now. +bool LowerIntrinsics::doInitialization(Module &M) { + // FIXME: This is rather antisocial in the context of a JIT since it performs + // work against the entire module. But this cannot be done at + // runFunction time (initializeCustomLowering likely needs to change + // the module). + CollectorModuleMetadata *CMM = getAnalysisToUpdate<CollectorModuleMetadata>(); + assert(CMM && "LowerIntrinsics didn't require CollectorModuleMetadata!?"); + for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I) + if (I->hasCollector()) + CMM->get(*I); // Instantiate the Collector. + + bool MadeChange = false; + for (CollectorModuleMetadata::iterator I = CMM->begin(), + E = CMM->end(); I != E; ++I) + if (NeedsCustomLoweringPass(**I)) + if ((*I)->initializeCustomLowering(M)) + MadeChange = true; + + return MadeChange; +} + +bool LowerIntrinsics::InsertRootInitializers(Function &F, AllocaInst **Roots, + unsigned Count) { + // Scroll past alloca instructions. + BasicBlock::iterator IP = F.getEntryBlock().begin(); + while (isa<AllocaInst>(IP)) ++IP; + + // Search for initializers in the initial BB. + SmallPtrSet<AllocaInst*,16> InitedRoots; + for (; !CouldBecomeSafePoint(IP); ++IP) + if (StoreInst *SI = dyn_cast<StoreInst>(IP)) + if (AllocaInst *AI = + dyn_cast<AllocaInst>(SI->getOperand(1)->stripPointerCasts())) + InitedRoots.insert(AI); + + // Add root initializers. + bool MadeChange = false; + + for (AllocaInst **I = Roots, **E = Roots + Count; I != E; ++I) + if (!InitedRoots.count(*I)) { + new StoreInst(ConstantPointerNull::get(cast<PointerType>( + cast<PointerType>((*I)->getType())->getElementType())), + *I, IP); + MadeChange = true; + } + + return MadeChange; +} + +bool LowerIntrinsics::NeedsDefaultLoweringPass(const Collector &C) { + // Default lowering is necessary only if read or write barriers have a default + // action. The default for roots is no action. + return !C.customWriteBarrier() + || !C.customReadBarrier() + || C.initializeRoots(); +} + +bool LowerIntrinsics::NeedsCustomLoweringPass(const Collector &C) { + // Custom lowering is only necessary if enabled for some action. + return C.customWriteBarrier() + || C.customReadBarrier() + || C.customRoots(); +} + +/// CouldBecomeSafePoint - Predicate to conservatively determine whether the +/// instruction could introduce a safe point. +bool LowerIntrinsics::CouldBecomeSafePoint(Instruction *I) { + // The natural definition of instructions which could introduce safe points + // are: + // + // - call, invoke (AfterCall, BeforeCall) + // - phis (Loops) + // - invoke, ret, unwind (Exit) + // + // However, instructions as seemingly inoccuous as arithmetic can become + // libcalls upon lowering (e.g., div i64 on a 32-bit platform), so instead + // it is necessary to take a conservative approach. + + if (isa<AllocaInst>(I) || isa<GetElementPtrInst>(I) || + isa<StoreInst>(I) || isa<LoadInst>(I)) + return false; + + // llvm.gcroot is safe because it doesn't do anything at runtime. + if (CallInst *CI = dyn_cast<CallInst>(I)) + if (Function *F = CI->getCalledFunction()) + if (unsigned IID = F->getIntrinsicID()) + if (IID == Intrinsic::gcroot) + return false; + + return true; +} + +/// runOnFunction - Replace gcread/gcwrite intrinsics with loads and stores. +/// Leave gcroot intrinsics; the code generator needs to see those. +bool LowerIntrinsics::runOnFunction(Function &F) { + // Quick exit for functions that do not use GC. + if (!F.hasCollector()) return false; + + CollectorMetadata &MD = getAnalysis<CollectorModuleMetadata>().get(F); + Collector &Coll = MD.getCollector(); + + bool MadeChange = false; + + if (NeedsDefaultLoweringPass(Coll)) + MadeChange |= PerformDefaultLowering(F, Coll); + + if (NeedsCustomLoweringPass(Coll)) + MadeChange |= Coll.performCustomLowering(F); + + return MadeChange; +} + +bool LowerIntrinsics::PerformDefaultLowering(Function &F, Collector &Coll) { + bool LowerWr = !Coll.customWriteBarrier(); + bool LowerRd = !Coll.customReadBarrier(); + bool InitRoots = Coll.initializeRoots(); + + SmallVector<AllocaInst*,32> Roots; + + bool MadeChange = false; + for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) { + for (BasicBlock::iterator II = BB->begin(), E = BB->end(); II != E;) { + if (IntrinsicInst *CI = dyn_cast<IntrinsicInst>(II++)) { + Function *F = CI->getCalledFunction(); + switch (F->getIntrinsicID()) { + case Intrinsic::gcwrite: + if (LowerWr) { + // Replace a write barrier with a simple store. + Value *St = new StoreInst(CI->getOperand(1), CI->getOperand(3), CI); + CI->replaceAllUsesWith(St); + CI->eraseFromParent(); + } + break; + case Intrinsic::gcread: + if (LowerRd) { + // Replace a read barrier with a simple load. + Value *Ld = new LoadInst(CI->getOperand(2), "", CI); + Ld->takeName(CI); + CI->replaceAllUsesWith(Ld); + CI->eraseFromParent(); + } + break; + case Intrinsic::gcroot: + if (InitRoots) { + // Initialize the GC root, but do not delete the intrinsic. The + // backend needs the intrinsic to flag the stack slot. + Roots.push_back(cast<AllocaInst>( + CI->getOperand(1)->stripPointerCasts())); + } + break; + default: + continue; + } + + MadeChange = true; + } + } + } + + if (Roots.size()) + MadeChange |= InsertRootInitializers(F, Roots.begin(), Roots.size()); + + return MadeChange; +} + +// ----------------------------------------------------------------------------- + +FunctionPass *llvm::createGCMachineCodeAnalysisPass() { + return new MachineCodeAnalysis(); +} + +char MachineCodeAnalysis::ID = 0; + +MachineCodeAnalysis::MachineCodeAnalysis() + : MachineFunctionPass(intptr_t(&ID)) {} + +const char *MachineCodeAnalysis::getPassName() const { + return "Analyze Machine Code For Garbage Collection"; +} + +void MachineCodeAnalysis::getAnalysisUsage(AnalysisUsage &AU) const { + MachineFunctionPass::getAnalysisUsage(AU); + AU.setPreservesAll(); + AU.addRequired<MachineModuleInfo>(); + AU.addRequired<CollectorModuleMetadata>(); +} + +unsigned MachineCodeAnalysis::InsertLabel(MachineBasicBlock &MBB, + MachineBasicBlock::iterator MI) const { + unsigned Label = MMI->NextLabelID(); + BuildMI(MBB, MI, TII->get(TargetInstrInfo::GC_LABEL)).addImm(Label); + return Label; +} + +void MachineCodeAnalysis::VisitCallPoint(MachineBasicBlock::iterator CI) { + // Find the return address (next instruction), too, so as to bracket the call + // instruction. + MachineBasicBlock::iterator RAI = CI; + ++RAI; + + if (MD->getCollector().needsSafePoint(GC::PreCall)) + MD->addSafePoint(GC::PreCall, InsertLabel(*CI->getParent(), CI)); + + if (MD->getCollector().needsSafePoint(GC::PostCall)) + MD->addSafePoint(GC::PostCall, InsertLabel(*CI->getParent(), RAI)); +} + +void MachineCodeAnalysis::FindSafePoints(MachineFunction &MF) { + for (MachineFunction::iterator BBI = MF.begin(), + BBE = MF.end(); BBI != BBE; ++BBI) + for (MachineBasicBlock::iterator MI = BBI->begin(), + ME = BBI->end(); MI != ME; ++MI) + if (MI->getDesc().isCall()) + VisitCallPoint(MI); +} + +void MachineCodeAnalysis::FindStackOffsets(MachineFunction &MF) { + uint64_t StackSize = MFI->getStackSize(); + uint64_t OffsetAdjustment = MFI->getOffsetAdjustment(); + uint64_t OffsetOfLocalArea = TM->getFrameInfo()->getOffsetOfLocalArea(); + + for (CollectorMetadata::roots_iterator RI = MD->roots_begin(), + RE = MD->roots_end(); RI != RE; ++RI) + RI->StackOffset = MFI->getObjectOffset(RI->Num) + StackSize + - OffsetOfLocalArea + OffsetAdjustment; +} + +bool MachineCodeAnalysis::runOnMachineFunction(MachineFunction &MF) { + // Quick exit for functions that do not use GC. + if (!MF.getFunction()->hasCollector()) return false; + + MD = &getAnalysis<CollectorModuleMetadata>().get(*MF.getFunction()); + if (!MD->getCollector().needsSafePoints()) + return false; + + TM = &MF.getTarget(); + MMI = &getAnalysis<MachineModuleInfo>(); + TII = TM->getInstrInfo(); + MFI = MF.getFrameInfo(); + + // Find the size of the stack frame. + MD->setFrameSize(MFI->getStackSize()); + + // Find all safe points. + FindSafePoints(MF); + + // Find the stack offsets for all roots. + FindStackOffsets(MF); + + return false; +} |