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This version enhances the previous patch to add root initialization as discussed here: http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20070910/053455.html Collector gives its subclasses control over generic algorithms: unsigned NeededSafePoints; //< Bitmask of required safe points. bool CustomReadBarriers; //< Default is to insert loads. bool CustomWriteBarriers; //< Default is to insert stores. bool CustomRoots; //< Default is to pass through to backend. bool InitRoots; //< If set, roots are nulled during lowering. It also has callbacks which collectors can hook: /// If any of the actions are set to Custom, this is expected to /// be overriden to create a transform to lower those actions to /// LLVM IR. virtual Pass *createCustomLoweringPass() const; /// beginAssembly/finishAssembly - Emit module metadata as /// assembly code. virtual void beginAssembly(Module &M, std::ostream &OS, AsmPrinter &AP, const TargetAsmInfo &TAI) const; virtual void finishAssembly(Module &M, CollectorModuleMetadata &CMM, std::ostream &OS, AsmPrinter &AP, const TargetAsmInfo &TAI) const; Various other independent algorithms could be implemented, but were not necessary for the initial two collectors. Some examples are listed here: http://llvm.org/docs/GarbageCollection.html#collector-algos git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@42466 91177308-0d34-0410-b5e6-96231b3b80d8
354 lines
12 KiB
C++
354 lines
12 KiB
C++
//===-- Collector.cpp - Garbage collection infrastructure -----------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file was developed by Gordon Henriksen and is distributed under
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// the University of Illinois Open Source License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file implements target- and collector-independent garbage collection
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// infrastructure.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/CodeGen/Collector.h"
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#include "llvm/IntrinsicInst.h"
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#include "llvm/Module.h"
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#include "llvm/PassManager.h"
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#include "llvm/ADT/SmallPtrSet.h"
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#include "llvm/CodeGen/MachineFrameInfo.h"
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#include "llvm/CodeGen/MachineFunctionPass.h"
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#include "llvm/CodeGen/MachineInstrBuilder.h"
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#include "llvm/Target/TargetFrameInfo.h"
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#include "llvm/Target/TargetInstrInfo.h"
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#include "llvm/Target/TargetMachine.h"
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#include "llvm/Support/Compiler.h"
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using namespace llvm;
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namespace {
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/// This pass rewrites calls to the llvm.gcread or llvm.gcwrite intrinsics,
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/// replacing them with simple loads and stores as directed by the Collector.
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/// This is useful for most garbage collectors.
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class VISIBILITY_HIDDEN LowerIntrinsics : public FunctionPass {
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const Collector &Coll;
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/// GCRootInt, GCReadInt, GCWriteInt - The function prototypes for the
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/// llvm.gc* intrinsics.
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Function *GCRootInt, *GCReadInt, *GCWriteInt;
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static bool CouldBecomeSafePoint(Instruction *I);
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static void InsertRootInitializers(Function &F,
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AllocaInst **Roots, unsigned Count);
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public:
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static char ID;
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LowerIntrinsics(const Collector &GC);
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const char *getPassName() const;
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bool doInitialization(Module &M);
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bool runOnFunction(Function &F);
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};
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/// This is a target-independent pass over the machine function representation
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/// to identify safe points for the garbage collector in the machine code. It
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/// inserts labels at safe points and populates the GCInfo class.
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class VISIBILITY_HIDDEN MachineCodeAnalysis : public MachineFunctionPass {
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const Collector &Coll;
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const TargetMachine &Targ;
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CollectorMetadata *MD;
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MachineModuleInfo *MMI;
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const TargetInstrInfo *TII;
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MachineFrameInfo *MFI;
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void FindSafePoints(MachineFunction &MF);
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void VisitCallPoint(MachineBasicBlock::iterator MI);
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unsigned InsertLabel(MachineBasicBlock &MBB,
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MachineBasicBlock::iterator MI) const;
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void FindStackOffsets(MachineFunction &MF);
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public:
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static char ID;
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MachineCodeAnalysis(const Collector &C, const TargetMachine &T);
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const char *getPassName() const;
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void getAnalysisUsage(AnalysisUsage &AU) const;
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bool runOnMachineFunction(MachineFunction &MF);
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};
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}
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// -----------------------------------------------------------------------------
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const Collector *llvm::TheCollector = 0;
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Collector::Collector() :
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NeededSafePoints(0),
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CustomReadBarriers(false),
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CustomWriteBarriers(false),
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CustomRoots(false),
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InitRoots(true)
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{}
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Collector::~Collector() {}
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void Collector::addLoweringPasses(FunctionPassManager &PM) const {
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if (NeedsDefaultLoweringPass())
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PM.add(new LowerIntrinsics(*this));
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if (NeedsCustomLoweringPass())
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PM.add(createCustomLoweringPass());
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}
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void Collector::addLoweringPasses(PassManager &PM) const {
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if (NeedsDefaultLoweringPass())
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PM.add(new LowerIntrinsics(*this));
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if (NeedsCustomLoweringPass())
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PM.add(createCustomLoweringPass());
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}
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void Collector::addGenericMachineCodePass(FunctionPassManager &PM,
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const TargetMachine &TM,
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bool Fast) const {
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if (needsSafePoints())
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PM.add(new MachineCodeAnalysis(*this, TM));
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}
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bool Collector::NeedsDefaultLoweringPass() const {
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// Default lowering is necessary only if read or write barriers have a default
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// action. The default for roots is no action.
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return !customWriteBarrier()
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|| !customReadBarrier()
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|| initializeRoots();
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}
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bool Collector::NeedsCustomLoweringPass() const {
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// Custom lowering is only necessary if enabled for some action.
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return customWriteBarrier()
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|| customReadBarrier()
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|| customRoots();
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}
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Pass *Collector::createCustomLoweringPass() const {
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cerr << "Collector must override createCustomLoweringPass.\n";
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abort();
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return 0;
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}
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void Collector::beginAssembly(Module &M, std::ostream &OS, AsmPrinter &AP,
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const TargetAsmInfo &TAI) const {
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// Default is no action.
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}
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void Collector::finishAssembly(Module &M, CollectorModuleMetadata &CMM,
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std::ostream &OS, AsmPrinter &AP,
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const TargetAsmInfo &TAI) const {
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// Default is no action.
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}
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// -----------------------------------------------------------------------------
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char LowerIntrinsics::ID = 0;
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LowerIntrinsics::LowerIntrinsics(const Collector &C)
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: FunctionPass((intptr_t)&ID), Coll(C),
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GCRootInt(0), GCReadInt(0), GCWriteInt(0) {}
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const char *LowerIntrinsics::getPassName() const {
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return "Lower Garbage Collection Instructions";
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}
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/// doInitialization - If this module uses the GC intrinsics, find them now. If
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/// not, this pass does not do anything.
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bool LowerIntrinsics::doInitialization(Module &M) {
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GCReadInt = M.getFunction("llvm.gcread");
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GCWriteInt = M.getFunction("llvm.gcwrite");
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GCRootInt = M.getFunction("llvm.gcroot");
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return false;
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}
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void LowerIntrinsics::InsertRootInitializers(Function &F, AllocaInst **Roots,
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unsigned Count) {
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// Scroll past alloca instructions.
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BasicBlock::iterator IP = F.getEntryBlock().begin();
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while (isa<AllocaInst>(IP)) ++IP;
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// Search for initializers in the initial BB.
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SmallPtrSet<AllocaInst*,16> InitedRoots;
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for (; !CouldBecomeSafePoint(IP); ++IP)
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if (StoreInst *SI = dyn_cast<StoreInst>(IP))
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if (AllocaInst *AI = dyn_cast<AllocaInst>(
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IntrinsicInst::StripPointerCasts(SI->getOperand(1))))
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InitedRoots.insert(AI);
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// Add root initializers.
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for (AllocaInst **I = Roots, **E = Roots + Count; I != E; ++I)
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if (!InitedRoots.count(*I))
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new StoreInst(ConstantPointerNull::get(cast<PointerType>(
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cast<PointerType>((*I)->getType())->getElementType())),
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*I, IP);
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}
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/// CouldBecomeSafePoint - Predicate to conservatively determine whether the
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/// instruction could introduce a safe point.
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bool LowerIntrinsics::CouldBecomeSafePoint(Instruction *I) {
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// The natural definition of instructions which could introduce safe points
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// are:
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//
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// - call, invoke (AfterCall, BeforeCall)
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// - phis (Loops)
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// - invoke, ret, unwind (Exit)
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//
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// However, instructions as seemingly inoccuous as arithmetic can become
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// libcalls upon lowering (e.g., div i64 on a 32-bit platform), so instead
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// it is necessary to take a conservative approach.
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if (isa<AllocaInst>(I) || isa<GetElementPtrInst>(I) ||
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isa<StoreInst>(I) || isa<LoadInst>(I))
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return false;
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// llvm.gcroot is safe because it doesn't do anything at runtime.
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if (CallInst *CI = dyn_cast<CallInst>(I))
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if (Function *F = CI->getCalledFunction())
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if (unsigned IID = F->getIntrinsicID())
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if (IID == Intrinsic::gcroot)
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return false;
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return true;
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}
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/// runOnFunction - Replace gcread/gcwrite intrinsics with loads and stores.
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/// Leave gcroot intrinsics; the code generator needs to see those.
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bool LowerIntrinsics::runOnFunction(Function &F) {
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// Quick exit for programs that do not declare the intrinsics.
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if (!GCReadInt && !GCWriteInt && !GCRootInt) return false;
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bool LowerWr = !Coll.customWriteBarrier();
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bool LowerRd = !Coll.customReadBarrier();
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bool InitRoots = Coll.initializeRoots();
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SmallVector<AllocaInst*,32> Roots;
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bool MadeChange = false;
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for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) {
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for (BasicBlock::iterator II = BB->begin(), E = BB->end(); II != E;) {
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if (CallInst *CI = dyn_cast<CallInst>(II++)) {
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Function *F = CI->getCalledFunction();
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if (F == GCWriteInt && LowerWr) {
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// Replace a write barrier with a simple store.
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Value *St = new StoreInst(CI->getOperand(1), CI->getOperand(3), CI);
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CI->replaceAllUsesWith(St);
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CI->eraseFromParent();
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} else if (F == GCReadInt && LowerRd) {
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// Replace a read barrier with a simple load.
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Value *Ld = new LoadInst(CI->getOperand(2), "", CI);
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Ld->takeName(CI);
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CI->replaceAllUsesWith(Ld);
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CI->eraseFromParent();
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} else if (F == GCRootInt && InitRoots) {
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// Initialize the GC root, but do not delete the intrinsic. The
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// backend needs the intrinsic to flag the stack slot.
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Roots.push_back(cast<AllocaInst>(
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IntrinsicInst::StripPointerCasts(CI->getOperand(1))));
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} else {
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continue;
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}
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MadeChange = true;
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}
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}
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}
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if (Roots.size())
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InsertRootInitializers(F, Roots.begin(), Roots.size());
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return MadeChange;
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}
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// -----------------------------------------------------------------------------
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char MachineCodeAnalysis::ID = 0;
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MachineCodeAnalysis::MachineCodeAnalysis(const Collector &C, const TargetMachine &T)
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: MachineFunctionPass(intptr_t(&ID)), Coll(C), Targ(T) {}
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const char *MachineCodeAnalysis::getPassName() const {
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return "Analyze Machine Code For Garbage Collection";
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}
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void MachineCodeAnalysis::getAnalysisUsage(AnalysisUsage &AU) const {
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MachineFunctionPass::getAnalysisUsage(AU);
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AU.setPreservesAll();
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AU.addRequired<MachineModuleInfo>();
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AU.addRequired<CollectorModuleMetadata>();
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}
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unsigned MachineCodeAnalysis::InsertLabel(MachineBasicBlock &MBB,
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MachineBasicBlock::iterator MI) const {
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unsigned Label = MMI->NextLabelID();
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BuildMI(MBB, MI, TII->get(TargetInstrInfo::LABEL)).addImm(Label);
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return Label;
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}
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void MachineCodeAnalysis::VisitCallPoint(MachineBasicBlock::iterator CI) {
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// Find the return address (next instruction), too, so as to bracket the call
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// instruction.
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MachineBasicBlock::iterator RAI = CI;
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++RAI;
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if (Coll.needsSafePoint(GC::PreCall))
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MD->addSafePoint(GC::PreCall, InsertLabel(*CI->getParent(), CI));
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if (Coll.needsSafePoint(GC::PostCall))
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MD->addSafePoint(GC::PostCall, InsertLabel(*CI->getParent(), RAI));
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}
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void MachineCodeAnalysis::FindSafePoints(MachineFunction &MF) {
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for (MachineFunction::iterator BBI = MF.begin(),
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BBE = MF.end(); BBI != BBE; ++BBI)
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for (MachineBasicBlock::iterator MI = BBI->begin(),
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ME = BBI->end(); MI != ME; ++MI)
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if (TII->isCall(MI->getOpcode()))
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VisitCallPoint(*MI);
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}
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void MachineCodeAnalysis::FindStackOffsets(MachineFunction &MF) {
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uint64_t StackSize = MFI->getStackSize();
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uint64_t OffsetAdjustment = MFI->getOffsetAdjustment();
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uint64_t OffsetOfLocalArea = Targ.getFrameInfo()->getOffsetOfLocalArea();
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for (CollectorMetadata::roots_iterator RI = MD->roots_begin(),
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RE = MD->roots_end(); RI != RE; ++RI)
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RI->StackOffset = MFI->getObjectOffset(RI->Num) + StackSize
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- OffsetOfLocalArea + OffsetAdjustment;
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}
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bool MachineCodeAnalysis::runOnMachineFunction(MachineFunction &MF) {
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if (!Coll.needsSafePoints())
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return false;
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MD = getAnalysis<CollectorModuleMetadata>().get(MF.getFunction());
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MMI = &getAnalysis<MachineModuleInfo>();
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TII = MF.getTarget().getInstrInfo();
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MFI = MF.getFrameInfo();
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// Find the size of the stack frame.
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MD->setFrameSize(MFI->getStackSize());
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// Find all safe points.
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FindSafePoints(MF);
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// Find the stack offsets for all roots.
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FindStackOffsets(MF);
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return false;
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}
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