1 //===-- Collector.cpp - Garbage collection infrastructure -----------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file implements target- and collector-independent garbage collection
13 //===----------------------------------------------------------------------===//
15 #include "llvm/CodeGen/Collector.h"
16 #include "llvm/CodeGen/Passes.h"
17 #include "llvm/IntrinsicInst.h"
18 #include "llvm/Module.h"
19 #include "llvm/PassManager.h"
20 #include "llvm/ADT/SmallPtrSet.h"
21 #include "llvm/CodeGen/MachineFrameInfo.h"
22 #include "llvm/CodeGen/MachineFunctionPass.h"
23 #include "llvm/CodeGen/MachineInstrBuilder.h"
24 #include "llvm/CodeGen/MachineModuleInfo.h"
25 #include "llvm/Target/TargetFrameInfo.h"
26 #include "llvm/Target/TargetInstrInfo.h"
27 #include "llvm/Target/TargetMachine.h"
28 #include "llvm/Support/Compiler.h"
34 /// LowerIntrinsics - This pass rewrites calls to the llvm.gcread or
35 /// llvm.gcwrite intrinsics, replacing them with simple loads and stores as
36 /// directed by the Collector. It also performs automatic root initialization
37 /// and custom intrinsic lowering.
38 class VISIBILITY_HIDDEN LowerIntrinsics : public FunctionPass {
39 static bool NeedsDefaultLoweringPass(const Collector &C);
40 static bool NeedsCustomLoweringPass(const Collector &C);
41 static bool CouldBecomeSafePoint(Instruction *I);
42 bool PerformDefaultLowering(Function &F, Collector &Coll);
43 static bool InsertRootInitializers(Function &F,
44 AllocaInst **Roots, unsigned Count);
50 const char *getPassName() const;
51 void getAnalysisUsage(AnalysisUsage &AU) const;
53 bool doInitialization(Module &M);
54 bool runOnFunction(Function &F);
58 /// MachineCodeAnalysis - This is a target-independent pass over the machine
59 /// function representation to identify safe points for the garbage collector
60 /// in the machine code. It inserts labels at safe points and populates a
61 /// CollectorMetadata record for each function.
62 class VISIBILITY_HIDDEN MachineCodeAnalysis : public MachineFunctionPass {
63 const TargetMachine *TM;
64 CollectorMetadata *MD;
65 MachineModuleInfo *MMI;
66 const TargetInstrInfo *TII;
67 MachineFrameInfo *MFI;
69 void FindSafePoints(MachineFunction &MF);
70 void VisitCallPoint(MachineBasicBlock::iterator MI);
71 unsigned InsertLabel(MachineBasicBlock &MBB,
72 MachineBasicBlock::iterator MI) const;
74 void FindStackOffsets(MachineFunction &MF);
79 MachineCodeAnalysis();
80 const char *getPassName() const;
81 void getAnalysisUsage(AnalysisUsage &AU) const;
83 bool runOnMachineFunction(MachineFunction &MF);
88 // -----------------------------------------------------------------------------
90 Collector::Collector() :
92 CustomReadBarriers(false),
93 CustomWriteBarriers(false),
98 Collector::~Collector() {
99 for (iterator I = begin(), E = end(); I != E; ++I)
105 bool Collector::initializeCustomLowering(Module &M) { return false; }
107 bool Collector::performCustomLowering(Function &F) {
108 cerr << "gc " << getName() << " must override performCustomLowering.\n";
113 void Collector::beginAssembly(std::ostream &OS, AsmPrinter &AP,
114 const TargetAsmInfo &TAI) {
115 // Default is no action.
118 void Collector::finishAssembly(std::ostream &OS, AsmPrinter &AP,
119 const TargetAsmInfo &TAI) {
120 // Default is no action.
123 CollectorMetadata *Collector::insertFunctionMetadata(const Function &F) {
124 CollectorMetadata *CM = new CollectorMetadata(F, *this);
125 Functions.push_back(CM);
129 // -----------------------------------------------------------------------------
131 FunctionPass *llvm::createGCLoweringPass() {
132 return new LowerIntrinsics();
135 char LowerIntrinsics::ID = 0;
137 LowerIntrinsics::LowerIntrinsics()
138 : FunctionPass((intptr_t)&ID) {}
140 const char *LowerIntrinsics::getPassName() const {
141 return "Lower Garbage Collection Instructions";
144 void LowerIntrinsics::getAnalysisUsage(AnalysisUsage &AU) const {
145 FunctionPass::getAnalysisUsage(AU);
146 AU.addRequired<CollectorModuleMetadata>();
149 /// doInitialization - If this module uses the GC intrinsics, find them now.
150 bool LowerIntrinsics::doInitialization(Module &M) {
151 // FIXME: This is rather antisocial in the context of a JIT since it performs
152 // work against the entire module. But this cannot be done at
153 // runFunction time (initializeCustomLowering likely needs to change
155 CollectorModuleMetadata *CMM = getAnalysisToUpdate<CollectorModuleMetadata>();
156 assert(CMM && "LowerIntrinsics didn't require CollectorModuleMetadata!?");
157 for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I)
158 if (I->hasCollector())
159 CMM->get(*I); // Instantiate the Collector.
161 bool MadeChange = false;
162 for (CollectorModuleMetadata::iterator I = CMM->begin(),
163 E = CMM->end(); I != E; ++I)
164 if (NeedsCustomLoweringPass(**I))
165 if ((*I)->initializeCustomLowering(M))
171 bool LowerIntrinsics::InsertRootInitializers(Function &F, AllocaInst **Roots,
173 // Scroll past alloca instructions.
174 BasicBlock::iterator IP = F.getEntryBlock().begin();
175 while (isa<AllocaInst>(IP)) ++IP;
177 // Search for initializers in the initial BB.
178 SmallPtrSet<AllocaInst*,16> InitedRoots;
179 for (; !CouldBecomeSafePoint(IP); ++IP)
180 if (StoreInst *SI = dyn_cast<StoreInst>(IP))
181 if (AllocaInst *AI = dyn_cast<AllocaInst>(
182 IntrinsicInst::StripPointerCasts(SI->getOperand(1))))
183 InitedRoots.insert(AI);
185 // Add root initializers.
186 bool MadeChange = false;
188 for (AllocaInst **I = Roots, **E = Roots + Count; I != E; ++I)
189 if (!InitedRoots.count(*I)) {
190 new StoreInst(ConstantPointerNull::get(cast<PointerType>(
191 cast<PointerType>((*I)->getType())->getElementType())),
199 bool LowerIntrinsics::NeedsDefaultLoweringPass(const Collector &C) {
200 // Default lowering is necessary only if read or write barriers have a default
201 // action. The default for roots is no action.
202 return !C.customWriteBarrier()
203 || !C.customReadBarrier()
204 || C.initializeRoots();
207 bool LowerIntrinsics::NeedsCustomLoweringPass(const Collector &C) {
208 // Custom lowering is only necessary if enabled for some action.
209 return C.customWriteBarrier()
210 || C.customReadBarrier()
214 /// CouldBecomeSafePoint - Predicate to conservatively determine whether the
215 /// instruction could introduce a safe point.
216 bool LowerIntrinsics::CouldBecomeSafePoint(Instruction *I) {
217 // The natural definition of instructions which could introduce safe points
220 // - call, invoke (AfterCall, BeforeCall)
222 // - invoke, ret, unwind (Exit)
224 // However, instructions as seemingly inoccuous as arithmetic can become
225 // libcalls upon lowering (e.g., div i64 on a 32-bit platform), so instead
226 // it is necessary to take a conservative approach.
228 if (isa<AllocaInst>(I) || isa<GetElementPtrInst>(I) ||
229 isa<StoreInst>(I) || isa<LoadInst>(I))
232 // llvm.gcroot is safe because it doesn't do anything at runtime.
233 if (CallInst *CI = dyn_cast<CallInst>(I))
234 if (Function *F = CI->getCalledFunction())
235 if (unsigned IID = F->getIntrinsicID())
236 if (IID == Intrinsic::gcroot)
242 /// runOnFunction - Replace gcread/gcwrite intrinsics with loads and stores.
243 /// Leave gcroot intrinsics; the code generator needs to see those.
244 bool LowerIntrinsics::runOnFunction(Function &F) {
245 // Quick exit for functions that do not use GC.
246 if (!F.hasCollector()) return false;
248 CollectorMetadata &MD = getAnalysis<CollectorModuleMetadata>().get(F);
249 Collector &Coll = MD.getCollector();
251 bool MadeChange = false;
253 if (NeedsDefaultLoweringPass(Coll))
254 MadeChange |= PerformDefaultLowering(F, Coll);
256 if (NeedsCustomLoweringPass(Coll))
257 MadeChange |= Coll.performCustomLowering(F);
262 bool LowerIntrinsics::PerformDefaultLowering(Function &F, Collector &Coll) {
263 bool LowerWr = !Coll.customWriteBarrier();
264 bool LowerRd = !Coll.customReadBarrier();
265 bool InitRoots = Coll.initializeRoots();
267 SmallVector<AllocaInst*,32> Roots;
269 bool MadeChange = false;
270 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) {
271 for (BasicBlock::iterator II = BB->begin(), E = BB->end(); II != E;) {
272 if (IntrinsicInst *CI = dyn_cast<IntrinsicInst>(II++)) {
273 Function *F = CI->getCalledFunction();
274 switch (F->getIntrinsicID()) {
275 case Intrinsic::gcwrite:
277 // Replace a write barrier with a simple store.
278 Value *St = new StoreInst(CI->getOperand(1), CI->getOperand(3), CI);
279 CI->replaceAllUsesWith(St);
280 CI->eraseFromParent();
283 case Intrinsic::gcread:
285 // Replace a read barrier with a simple load.
286 Value *Ld = new LoadInst(CI->getOperand(2), "", CI);
288 CI->replaceAllUsesWith(Ld);
289 CI->eraseFromParent();
292 case Intrinsic::gcroot:
294 // Initialize the GC root, but do not delete the intrinsic. The
295 // backend needs the intrinsic to flag the stack slot.
296 Roots.push_back(cast<AllocaInst>(
297 IntrinsicInst::StripPointerCasts(CI->getOperand(1))));
310 MadeChange |= InsertRootInitializers(F, Roots.begin(), Roots.size());
315 // -----------------------------------------------------------------------------
317 FunctionPass *llvm::createGCMachineCodeAnalysisPass() {
318 return new MachineCodeAnalysis();
321 char MachineCodeAnalysis::ID = 0;
323 MachineCodeAnalysis::MachineCodeAnalysis()
324 : MachineFunctionPass(intptr_t(&ID)) {}
326 const char *MachineCodeAnalysis::getPassName() const {
327 return "Analyze Machine Code For Garbage Collection";
330 void MachineCodeAnalysis::getAnalysisUsage(AnalysisUsage &AU) const {
331 MachineFunctionPass::getAnalysisUsage(AU);
332 AU.setPreservesAll();
333 AU.addRequired<MachineModuleInfo>();
334 AU.addRequired<CollectorModuleMetadata>();
337 unsigned MachineCodeAnalysis::InsertLabel(MachineBasicBlock &MBB,
338 MachineBasicBlock::iterator MI) const {
339 unsigned Label = MMI->NextLabelID();
340 BuildMI(MBB, MI, TII->get(TargetInstrInfo::LABEL)).addImm(Label).addImm(2);
344 void MachineCodeAnalysis::VisitCallPoint(MachineBasicBlock::iterator CI) {
345 // Find the return address (next instruction), too, so as to bracket the call
347 MachineBasicBlock::iterator RAI = CI;
350 if (MD->getCollector().needsSafePoint(GC::PreCall))
351 MD->addSafePoint(GC::PreCall, InsertLabel(*CI->getParent(), CI));
353 if (MD->getCollector().needsSafePoint(GC::PostCall))
354 MD->addSafePoint(GC::PostCall, InsertLabel(*CI->getParent(), RAI));
357 void MachineCodeAnalysis::FindSafePoints(MachineFunction &MF) {
358 for (MachineFunction::iterator BBI = MF.begin(),
359 BBE = MF.end(); BBI != BBE; ++BBI)
360 for (MachineBasicBlock::iterator MI = BBI->begin(),
361 ME = BBI->end(); MI != ME; ++MI)
362 if (MI->getDesc().isCall())
366 void MachineCodeAnalysis::FindStackOffsets(MachineFunction &MF) {
367 uint64_t StackSize = MFI->getStackSize();
368 uint64_t OffsetAdjustment = MFI->getOffsetAdjustment();
369 uint64_t OffsetOfLocalArea = TM->getFrameInfo()->getOffsetOfLocalArea();
371 for (CollectorMetadata::roots_iterator RI = MD->roots_begin(),
372 RE = MD->roots_end(); RI != RE; ++RI)
373 RI->StackOffset = MFI->getObjectOffset(RI->Num) + StackSize
374 - OffsetOfLocalArea + OffsetAdjustment;
377 bool MachineCodeAnalysis::runOnMachineFunction(MachineFunction &MF) {
378 // Quick exit for functions that do not use GC.
379 if (!MF.getFunction()->hasCollector()) return false;
381 MD = &getAnalysis<CollectorModuleMetadata>().get(*MF.getFunction());
382 if (!MD->getCollector().needsSafePoints())
385 TM = &MF.getTarget();
386 MMI = &getAnalysis<MachineModuleInfo>();
387 TII = TM->getInstrInfo();
388 MFI = MF.getFrameInfo();
390 // Find the size of the stack frame.
391 MD->setFrameSize(MFI->getStackSize());
393 // Find all safe points.
396 // Find the stack offsets for all roots.
397 FindStackOffsets(MF);