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+//===-- GCStrategy.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.
+//
+// GCMachineCodeAnalysis identifies the GC safe points in the machine code.
+// Roots are identified in SelectionDAGISel.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/CodeGen/GCStrategy.h"
+#include "llvm/CodeGen/Passes.h"
+#include "llvm/IntrinsicInst.h"
+#include "llvm/Module.h"
+#include "llvm/Analysis/Dominators.h"
+#include "llvm/CodeGen/MachineFrameInfo.h"
+#include "llvm/CodeGen/MachineFunctionPass.h"
+#include "llvm/CodeGen/MachineInstrBuilder.h"
+#include "llvm/CodeGen/MachineModuleInfo.h"
+#include "llvm/Target/TargetFrameLowering.h"
+#include "llvm/Target/TargetInstrInfo.h"
+#include "llvm/Target/TargetMachine.h"
+#include "llvm/Target/TargetRegisterInfo.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/ErrorHandling.h"
+#include "llvm/Support/raw_ostream.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 {
+ static bool NeedsDefaultLoweringPass(const GCStrategy &C);
+ static bool NeedsCustomLoweringPass(const GCStrategy &C);
+ static bool CouldBecomeSafePoint(Instruction *I);
+ bool PerformDefaultLowering(Function &F, GCStrategy &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);
+ };
+
+
+ /// 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 {
+ const TargetMachine *TM;
+ 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;
+
+ bool runOnMachineFunction(MachineFunction &MF);
+ };
+
+}
+
+// -----------------------------------------------------------------------------
+
+GCStrategy::GCStrategy() :
+ NeededSafePoints(0),
+ CustomReadBarriers(false),
+ CustomWriteBarriers(false),
+ CustomRoots(false),
+ CustomSafePoints(false),
+ InitRoots(true),
+ UsesMetadata(false)
+{}
+
+GCStrategy::~GCStrategy() {
+ for (iterator I = begin(), E = end(); I != E; ++I)
+ delete *I;
+
+ Functions.clear();
+}
+
+bool GCStrategy::initializeCustomLowering(Module &M) { return false; }
+
+bool GCStrategy::performCustomLowering(Function &F) {
+ dbgs() << "gc " << getName() << " must override performCustomLowering.\n";
+ llvm_unreachable("must override performCustomLowering");
+}
+
+
+bool GCStrategy::findCustomSafePoints(GCFunctionInfo& FI, MachineFunction &F) {
+ dbgs() << "gc " << getName() << " must override findCustomSafePoints.\n";
+ llvm_unreachable(0);
+}
+
+
+GCFunctionInfo *GCStrategy::insertFunctionInfo(const Function &F) {
+ GCFunctionInfo *FI = new GCFunctionInfo(F, *this);
+ Functions.push_back(FI);
+ return FI;
+}
+
+// -----------------------------------------------------------------------------
+
+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<DominatorTree>();
+}
+
+/// 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).
+ 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.
+
+ bool MadeChange = false;
+ for (GCModuleInfo::iterator I = MI->begin(), E = MI->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)) {
+ StoreInst* SI = new StoreInst(ConstantPointerNull::get(cast<PointerType>(
+ cast<PointerType>((*I)->getType())->getElementType())),
+ *I);
+ SI->insertAfter(*I);
+ MadeChange = true;
+ }
+
+ return MadeChange;
+}
+
+bool LowerIntrinsics::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();
+}
+
+bool LowerIntrinsics::NeedsCustomLoweringPass(const GCStrategy &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.hasGC())
+ return false;
+
+ GCFunctionInfo &FI = getAnalysis<GCModuleInfo>().getFunctionInfo(F);
+ GCStrategy &S = FI.getStrategy();
+
+ bool MadeChange = false;
+
+ if (NeedsDefaultLoweringPass(S))
+ MadeChange |= PerformDefaultLowering(F, S);
+
+ bool UseCustomLoweringPass = NeedsCustomLoweringPass(S);
+ if (UseCustomLoweringPass)
+ MadeChange |= S.performCustomLowering(F);
+
+ // Custom lowering may modify the CFG, so dominators must be recomputed.
+ if (UseCustomLoweringPass) {
+ if (DominatorTree *DT = getAnalysisIfAvailable<DominatorTree>())
+ DT->DT->recalculate(F);
+ }
+
+ 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())
+ VisitCallPoint(MI);
+}
+
+void GCMachineCodeAnalysis::FindStackOffsets(MachineFunction &MF) {
+ const TargetFrameLowering *TFI = TM->getFrameLowering();
+ assert(TFI && "TargetRegisterInfo not available!");
+
+ for (GCFunctionInfo::roots_iterator RI = FI->roots_begin(),
+ RE = FI->roots_end(); RI != RE; ++RI)
+ RI->StackOffset = TFI->getFrameIndexOffset(MF, RI->Num);
+}
+
+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;
+
+ TM = &MF.getTarget();
+ MMI = &getAnalysis<MachineModuleInfo>();
+ TII = TM->getInstrInfo();
+
+ // Find the size of the stack frame.
+ FI->setFrameSize(MF.getFrameInfo()->getStackSize());
+
+ // Find all safe points.
+ if (FI->getStrategy().customSafePoints()) {
+ FI->getStrategy().findCustomSafePoints(*FI, MF);
+ } else {
+ FindSafePoints(MF);
+ }
+
+ // Find the stack offsets for all roots.
+ FindStackOffsets(MF);
+
+ return false;
+}
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