356 lines
12 KiB
C++
356 lines
12 KiB
C++
//===-- GCRootLowering.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 is distributed under the University of Illinois Open Source
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// 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 the lowering for the gc.root mechanism.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/CodeGen/GCMetadata.h"
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#include "llvm/CodeGen/GCStrategy.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/CodeGen/MachineModuleInfo.h"
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#include "llvm/CodeGen/Passes.h"
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#include "llvm/IR/Dominators.h"
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#include "llvm/IR/IntrinsicInst.h"
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#include "llvm/IR/Module.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/ErrorHandling.h"
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#include "llvm/Support/raw_ostream.h"
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#include "llvm/Target/TargetFrameLowering.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/Target/TargetRegisterInfo.h"
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#include "llvm/Target/TargetSubtargetInfo.h"
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using namespace llvm;
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namespace {
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/// LowerIntrinsics - This pass rewrites calls to the llvm.gcread or
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/// llvm.gcwrite intrinsics, replacing them with simple loads and stores as
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/// directed by the GCStrategy. It also performs automatic root initialization
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/// and custom intrinsic lowering.
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class LowerIntrinsics : public FunctionPass {
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bool PerformDefaultLowering(Function &F, GCStrategy &Coll);
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public:
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static char ID;
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LowerIntrinsics();
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const char *getPassName() const override;
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void getAnalysisUsage(AnalysisUsage &AU) const override;
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bool doInitialization(Module &M) override;
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bool runOnFunction(Function &F) override;
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};
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/// GCMachineCodeAnalysis - This is a target-independent pass over the machine
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/// function representation to identify safe points for the garbage collector
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/// in the machine code. It inserts labels at safe points and populates a
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/// GCMetadata record for each function.
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class GCMachineCodeAnalysis : public MachineFunctionPass {
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GCFunctionInfo *FI;
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MachineModuleInfo *MMI;
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const TargetInstrInfo *TII;
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void FindSafePoints(MachineFunction &MF);
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void VisitCallPoint(MachineBasicBlock::iterator MI);
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MCSymbol *InsertLabel(MachineBasicBlock &MBB, MachineBasicBlock::iterator MI,
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const DebugLoc &DL) 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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GCMachineCodeAnalysis();
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void getAnalysisUsage(AnalysisUsage &AU) const override;
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bool runOnMachineFunction(MachineFunction &MF) override;
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};
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}
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// -----------------------------------------------------------------------------
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INITIALIZE_PASS_BEGIN(LowerIntrinsics, "gc-lowering", "GC Lowering", false,
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false)
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INITIALIZE_PASS_DEPENDENCY(GCModuleInfo)
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INITIALIZE_PASS_END(LowerIntrinsics, "gc-lowering", "GC Lowering", false, false)
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FunctionPass *llvm::createGCLoweringPass() { return new LowerIntrinsics(); }
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char LowerIntrinsics::ID = 0;
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LowerIntrinsics::LowerIntrinsics() : FunctionPass(ID) {
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initializeLowerIntrinsicsPass(*PassRegistry::getPassRegistry());
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}
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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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void LowerIntrinsics::getAnalysisUsage(AnalysisUsage &AU) const {
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FunctionPass::getAnalysisUsage(AU);
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AU.addRequired<GCModuleInfo>();
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AU.addPreserved<DominatorTreeWrapperPass>();
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}
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static bool NeedsDefaultLoweringPass(const GCStrategy &C) {
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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 !C.customWriteBarrier() || !C.customReadBarrier() ||
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C.initializeRoots();
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}
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/// doInitialization - If this module uses the GC intrinsics, find them now.
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bool LowerIntrinsics::doInitialization(Module &M) {
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GCModuleInfo *MI = getAnalysisIfAvailable<GCModuleInfo>();
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assert(MI && "LowerIntrinsics didn't require GCModuleInfo!?");
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for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I)
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if (!I->isDeclaration() && I->hasGC())
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MI->getFunctionInfo(*I); // Instantiate the GC strategy.
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return false;
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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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static bool 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) || isa<StoreInst>(I) ||
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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 (Intrinsic::ID 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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static bool 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))
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++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 =
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dyn_cast<AllocaInst>(SI->getOperand(1)->stripPointerCasts()))
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InitedRoots.insert(AI);
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// Add root initializers.
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bool MadeChange = false;
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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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StoreInst *SI = new StoreInst(
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ConstantPointerNull::get(cast<PointerType>((*I)->getAllocatedType())),
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*I);
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SI->insertAfter(*I);
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MadeChange = true;
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}
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return MadeChange;
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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 functions that do not use GC.
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if (!F.hasGC())
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return false;
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GCFunctionInfo &FI = getAnalysis<GCModuleInfo>().getFunctionInfo(F);
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GCStrategy &S = FI.getStrategy();
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bool MadeChange = false;
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if (NeedsDefaultLoweringPass(S))
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MadeChange |= PerformDefaultLowering(F, S);
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return MadeChange;
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}
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bool LowerIntrinsics::PerformDefaultLowering(Function &F, GCStrategy &S) {
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bool LowerWr = !S.customWriteBarrier();
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bool LowerRd = !S.customReadBarrier();
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bool InitRoots = S.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 (IntrinsicInst *CI = dyn_cast<IntrinsicInst>(II++)) {
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Function *F = CI->getCalledFunction();
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switch (F->getIntrinsicID()) {
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case Intrinsic::gcwrite:
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if (LowerWr) {
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// Replace a write barrier with a simple store.
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Value *St =
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new StoreInst(CI->getArgOperand(0), CI->getArgOperand(2), CI);
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CI->replaceAllUsesWith(St);
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CI->eraseFromParent();
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}
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break;
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case Intrinsic::gcread:
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if (LowerRd) {
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// Replace a read barrier with a simple load.
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Value *Ld = new LoadInst(CI->getArgOperand(1), "", 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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}
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break;
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case Intrinsic::gcroot:
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if (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(
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cast<AllocaInst>(CI->getArgOperand(0)->stripPointerCasts()));
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}
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break;
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default:
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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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MadeChange |= 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 GCMachineCodeAnalysis::ID = 0;
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char &llvm::GCMachineCodeAnalysisID = GCMachineCodeAnalysis::ID;
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INITIALIZE_PASS(GCMachineCodeAnalysis, "gc-analysis",
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"Analyze Machine Code For Garbage Collection", false, false)
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GCMachineCodeAnalysis::GCMachineCodeAnalysis() : MachineFunctionPass(ID) {}
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void GCMachineCodeAnalysis::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<GCModuleInfo>();
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}
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MCSymbol *GCMachineCodeAnalysis::InsertLabel(MachineBasicBlock &MBB,
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MachineBasicBlock::iterator MI,
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const DebugLoc &DL) const {
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MCSymbol *Label = MBB.getParent()->getContext().createTempSymbol();
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BuildMI(MBB, MI, DL, TII->get(TargetOpcode::GC_LABEL)).addSym(Label);
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return Label;
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}
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void GCMachineCodeAnalysis::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 (FI->getStrategy().needsSafePoint(GC::PreCall)) {
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MCSymbol *Label = InsertLabel(*CI->getParent(), CI, CI->getDebugLoc());
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FI->addSafePoint(GC::PreCall, Label, CI->getDebugLoc());
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}
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if (FI->getStrategy().needsSafePoint(GC::PostCall)) {
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MCSymbol *Label = InsertLabel(*CI->getParent(), RAI, CI->getDebugLoc());
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FI->addSafePoint(GC::PostCall, Label, CI->getDebugLoc());
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}
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}
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void GCMachineCodeAnalysis::FindSafePoints(MachineFunction &MF) {
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for (MachineFunction::iterator BBI = MF.begin(), BBE = MF.end(); BBI != BBE;
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++BBI)
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for (MachineBasicBlock::iterator MI = BBI->begin(), ME = BBI->end();
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MI != ME; ++MI)
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if (MI->isCall()) {
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// Do not treat tail or sibling call sites as safe points. This is
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// legal since any arguments passed to the callee which live in the
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// remnants of the callers frame will be owned and updated by the
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// callee if required.
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if (MI->isTerminator())
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continue;
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VisitCallPoint(MI);
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}
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}
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void GCMachineCodeAnalysis::FindStackOffsets(MachineFunction &MF) {
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const TargetFrameLowering *TFI = MF.getSubtarget().getFrameLowering();
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assert(TFI && "TargetRegisterInfo not available!");
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for (GCFunctionInfo::roots_iterator RI = FI->roots_begin();
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RI != FI->roots_end();) {
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// If the root references a dead object, no need to keep it.
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if (MF.getFrameInfo()->isDeadObjectIndex(RI->Num)) {
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RI = FI->removeStackRoot(RI);
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} else {
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unsigned FrameReg; // FIXME: surely GCRoot ought to store the
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// register that the offset is from?
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RI->StackOffset = TFI->getFrameIndexReference(MF, RI->Num, FrameReg);
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++RI;
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}
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}
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}
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bool GCMachineCodeAnalysis::runOnMachineFunction(MachineFunction &MF) {
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// Quick exit for functions that do not use GC.
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if (!MF.getFunction()->hasGC())
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return false;
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FI = &getAnalysis<GCModuleInfo>().getFunctionInfo(*MF.getFunction());
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MMI = &getAnalysis<MachineModuleInfo>();
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TII = MF.getSubtarget().getInstrInfo();
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// Find the size of the stack frame. There may be no correct static frame
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// size, we use UINT64_MAX to represent this.
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const MachineFrameInfo *MFI = MF.getFrameInfo();
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const TargetRegisterInfo *RegInfo = MF.getSubtarget().getRegisterInfo();
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const bool DynamicFrameSize = MFI->hasVarSizedObjects() ||
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RegInfo->needsStackRealignment(MF);
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FI->setFrameSize(DynamicFrameSize ? UINT64_MAX : MFI->getStackSize());
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// Find all safe points.
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if (FI->getStrategy().needsSafePoints())
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FindSafePoints(MF);
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// Find the concrete stack offsets for all roots (stack slots)
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FindStackOffsets(MF);
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return false;
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}
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