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Diffstat (limited to 'lib/CodeGen/GCRootLowering.cpp')
| -rw-r--r-- | lib/CodeGen/GCRootLowering.cpp | 351 |
1 files changed, 351 insertions, 0 deletions
diff --git a/lib/CodeGen/GCRootLowering.cpp b/lib/CodeGen/GCRootLowering.cpp new file mode 100644 index 0000000..9d38e4c --- /dev/null +++ b/lib/CodeGen/GCRootLowering.cpp @@ -0,0 +1,351 @@ +//===-- GCRootLowering.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 the lowering for the gc.root mechanism. +// +//===----------------------------------------------------------------------===// + +#include "llvm/CodeGen/GCMetadata.h" +#include "llvm/CodeGen/GCStrategy.h" +#include "llvm/CodeGen/MachineFrameInfo.h" +#include "llvm/CodeGen/MachineFunctionPass.h" +#include "llvm/CodeGen/MachineInstrBuilder.h" +#include "llvm/CodeGen/MachineModuleInfo.h" +#include "llvm/CodeGen/Passes.h" +#include "llvm/IR/Dominators.h" +#include "llvm/IR/IntrinsicInst.h" +#include "llvm/IR/Module.h" +#include "llvm/Support/Debug.h" +#include "llvm/Support/ErrorHandling.h" +#include "llvm/Support/raw_ostream.h" +#include "llvm/Target/TargetFrameLowering.h" +#include "llvm/Target/TargetInstrInfo.h" +#include "llvm/Target/TargetMachine.h" +#include "llvm/Target/TargetRegisterInfo.h" +#include "llvm/Target/TargetSubtargetInfo.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 GCStrategy. It also performs automatic root initialization +/// and custom intrinsic lowering. +class LowerIntrinsics : public FunctionPass { + bool PerformDefaultLowering(Function &F, GCStrategy &Coll); + +public: + static char ID; + + LowerIntrinsics(); + const char *getPassName() const override; + void getAnalysisUsage(AnalysisUsage &AU) const override; + + bool doInitialization(Module &M) override; + bool runOnFunction(Function &F) override; +}; + +/// GCMachineCodeAnalysis - 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 +/// GCMetadata record for each function. +class GCMachineCodeAnalysis : public MachineFunctionPass { + GCFunctionInfo *FI; + MachineModuleInfo *MMI; + const TargetInstrInfo *TII; + + void FindSafePoints(MachineFunction &MF); + void VisitCallPoint(MachineBasicBlock::iterator MI); + MCSymbol *InsertLabel(MachineBasicBlock &MBB, MachineBasicBlock::iterator MI, + DebugLoc DL) const; + + void FindStackOffsets(MachineFunction &MF); + +public: + static char ID; + + GCMachineCodeAnalysis(); + void getAnalysisUsage(AnalysisUsage &AU) const override; + + bool runOnMachineFunction(MachineFunction &MF) override; +}; +} + +// ----------------------------------------------------------------------------- + +INITIALIZE_PASS_BEGIN(LowerIntrinsics, "gc-lowering", "GC Lowering", false, + false) +INITIALIZE_PASS_DEPENDENCY(GCModuleInfo) +INITIALIZE_PASS_END(LowerIntrinsics, "gc-lowering", "GC Lowering", false, false) + +FunctionPass *llvm::createGCLoweringPass() { return new LowerIntrinsics(); } + +char LowerIntrinsics::ID = 0; + +LowerIntrinsics::LowerIntrinsics() : FunctionPass(ID) { + initializeLowerIntrinsicsPass(*PassRegistry::getPassRegistry()); +} + +const char *LowerIntrinsics::getPassName() const { + return "Lower Garbage Collection Instructions"; +} + +void LowerIntrinsics::getAnalysisUsage(AnalysisUsage &AU) const { + FunctionPass::getAnalysisUsage(AU); + AU.addRequired<GCModuleInfo>(); + AU.addPreserved<DominatorTreeWrapperPass>(); +} + +static bool NeedsDefaultLoweringPass(const GCStrategy &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(); +} + +/// doInitialization - If this module uses the GC intrinsics, find them now. +bool LowerIntrinsics::doInitialization(Module &M) { + GCModuleInfo *MI = getAnalysisIfAvailable<GCModuleInfo>(); + assert(MI && "LowerIntrinsics didn't require GCModuleInfo!?"); + for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I) + if (!I->isDeclaration() && I->hasGC()) + MI->getFunctionInfo(*I); // Instantiate the GC strategy. + + return false; +} + +/// CouldBecomeSafePoint - Predicate to conservatively determine whether the +/// instruction could introduce a safe point. +static bool 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; +} + +static bool 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)) { + StoreInst *SI = new StoreInst( + ConstantPointerNull::get(cast<PointerType>( + cast<PointerType>((*I)->getType())->getElementType())), + *I); + SI->insertAfter(*I); + MadeChange = true; + } + + return MadeChange; +} + +/// 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.hasGC()) + return false; + + GCFunctionInfo &FI = getAnalysis<GCModuleInfo>().getFunctionInfo(F); + GCStrategy &S = FI.getStrategy(); + + bool MadeChange = false; + + if (NeedsDefaultLoweringPass(S)) + MadeChange |= PerformDefaultLowering(F, S); + + return MadeChange; +} + +bool LowerIntrinsics::PerformDefaultLowering(Function &F, GCStrategy &S) { + bool LowerWr = !S.customWriteBarrier(); + bool LowerRd = !S.customReadBarrier(); + bool InitRoots = S.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->getArgOperand(0), CI->getArgOperand(2), 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->getArgOperand(1), "", 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->getArgOperand(0)->stripPointerCasts())); + } + break; + default: + continue; + } + + MadeChange = true; + } + } + } + + if (Roots.size()) + MadeChange |= InsertRootInitializers(F, Roots.begin(), Roots.size()); + + return MadeChange; +} + +// ----------------------------------------------------------------------------- + +char GCMachineCodeAnalysis::ID = 0; +char &llvm::GCMachineCodeAnalysisID = GCMachineCodeAnalysis::ID; + +INITIALIZE_PASS(GCMachineCodeAnalysis, "gc-analysis", + "Analyze Machine Code For Garbage Collection", false, false) + +GCMachineCodeAnalysis::GCMachineCodeAnalysis() : MachineFunctionPass(ID) {} + +void GCMachineCodeAnalysis::getAnalysisUsage(AnalysisUsage &AU) const { + MachineFunctionPass::getAnalysisUsage(AU); + AU.setPreservesAll(); + AU.addRequired<MachineModuleInfo>(); + AU.addRequired<GCModuleInfo>(); +} + +MCSymbol *GCMachineCodeAnalysis::InsertLabel(MachineBasicBlock &MBB, + MachineBasicBlock::iterator MI, + DebugLoc DL) const { + MCSymbol *Label = MBB.getParent()->getContext().CreateTempSymbol(); + BuildMI(MBB, MI, DL, TII->get(TargetOpcode::GC_LABEL)).addSym(Label); + return Label; +} + +void GCMachineCodeAnalysis::VisitCallPoint(MachineBasicBlock::iterator CI) { + // Find the return address (next instruction), too, so as to bracket the call + // instruction. + MachineBasicBlock::iterator RAI = CI; + ++RAI; + + if (FI->getStrategy().needsSafePoint(GC::PreCall)) { + MCSymbol *Label = InsertLabel(*CI->getParent(), CI, CI->getDebugLoc()); + FI->addSafePoint(GC::PreCall, Label, CI->getDebugLoc()); + } + + if (FI->getStrategy().needsSafePoint(GC::PostCall)) { + MCSymbol *Label = InsertLabel(*CI->getParent(), RAI, CI->getDebugLoc()); + FI->addSafePoint(GC::PostCall, Label, CI->getDebugLoc()); + } +} + +void GCMachineCodeAnalysis::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->isCall()) { + // Do not treat tail or sibling call sites as safe points. This is + // legal since any arguments passed to the callee which live in the + // remnants of the callers frame will be owned and updated by the + // callee if required. + if (MI->isTerminator()) + continue; + VisitCallPoint(MI); + } +} + +void GCMachineCodeAnalysis::FindStackOffsets(MachineFunction &MF) { + const TargetFrameLowering *TFI = MF.getSubtarget().getFrameLowering(); + assert(TFI && "TargetRegisterInfo not available!"); + + for (GCFunctionInfo::roots_iterator RI = FI->roots_begin(); + RI != FI->roots_end();) { + // If the root references a dead object, no need to keep it. + if (MF.getFrameInfo()->isDeadObjectIndex(RI->Num)) { + RI = FI->removeStackRoot(RI); + } else { + RI->StackOffset = TFI->getFrameIndexOffset(MF, RI->Num); + ++RI; + } + } +} + +bool GCMachineCodeAnalysis::runOnMachineFunction(MachineFunction &MF) { + // Quick exit for functions that do not use GC. + if (!MF.getFunction()->hasGC()) + return false; + + FI = &getAnalysis<GCModuleInfo>().getFunctionInfo(*MF.getFunction()); + if (!FI->getStrategy().needsSafePoints()) + return false; + + MMI = &getAnalysis<MachineModuleInfo>(); + TII = MF.getSubtarget().getInstrInfo(); + + // Find the size of the stack frame. + FI->setFrameSize(MF.getFrameInfo()->getStackSize()); + + // Find all safe points. + FindSafePoints(MF); + + // Find the stack offsets for all roots. + FindStackOffsets(MF); + + return false; +} |