1 //===-- Collector.cpp - Garbage collection infrastructure -----------------===//
3 // The LLVM Compiler Infrastructure
5 // This file was developed by Gordon Henriksen and is distributed under
6 // the University of Illinois Open Source 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/Target/TargetFrameInfo.h"
25 #include "llvm/Target/TargetInstrInfo.h"
26 #include "llvm/Target/TargetMachine.h"
27 #include "llvm/Support/Compiler.h"
33 /// LowerIntrinsics - This pass rewrites calls to the llvm.gcread or
34 /// llvm.gcwrite intrinsics, replacing them with simple loads and stores as
35 /// directed by the Collector. It also performs automatic root initialization
36 /// and custom intrinsic lowering.
37 class VISIBILITY_HIDDEN LowerIntrinsics : public FunctionPass {
38 static bool NeedsDefaultLoweringPass(const Collector &C);
39 static bool NeedsCustomLoweringPass(const Collector &C);
40 static bool CouldBecomeSafePoint(Instruction *I);
41 bool PerformDefaultLowering(Function &F, Collector &Coll);
42 static bool InsertRootInitializers(Function &F,
43 AllocaInst **Roots, unsigned Count);
49 const char *getPassName() const;
50 void getAnalysisUsage(AnalysisUsage &AU) const;
52 bool doInitialization(Module &M);
53 bool runOnFunction(Function &F);
57 /// MachineCodeAnalysis - This is a target-independent pass over the machine
58 /// function representation to identify safe points for the garbage collector
59 /// in the machine code. It inserts labels at safe points and populates a
60 /// CollectorMetadata record for each function.
61 class VISIBILITY_HIDDEN MachineCodeAnalysis : public MachineFunctionPass {
62 const TargetMachine *TM;
63 CollectorMetadata *MD;
64 MachineModuleInfo *MMI;
65 const TargetInstrInfo *TII;
66 MachineFrameInfo *MFI;
68 void FindSafePoints(MachineFunction &MF);
69 void VisitCallPoint(MachineBasicBlock::iterator MI);
70 unsigned InsertLabel(MachineBasicBlock &MBB,
71 MachineBasicBlock::iterator MI) const;
73 void FindStackOffsets(MachineFunction &MF);
78 MachineCodeAnalysis();
79 const char *getPassName() const;
80 void getAnalysisUsage(AnalysisUsage &AU) const;
82 bool runOnMachineFunction(MachineFunction &MF);
87 // -----------------------------------------------------------------------------
89 Collector::Collector() :
91 CustomReadBarriers(false),
92 CustomWriteBarriers(false),
97 Collector::~Collector() {
98 for (iterator I = begin(), E = end(); I != E; ++I)
104 bool Collector::initializeCustomLowering(Module &M) { return false; }
106 bool Collector::performCustomLowering(Function &F) {
107 cerr << "gc " << getName() << " must override performCustomLowering.\n";
112 void Collector::beginAssembly(std::ostream &OS, AsmPrinter &AP,
113 const TargetAsmInfo &TAI) {
114 // Default is no action.
117 void Collector::finishAssembly(std::ostream &OS, AsmPrinter &AP,
118 const TargetAsmInfo &TAI) {
119 // Default is no action.
122 CollectorMetadata *Collector::insertFunctionMetadata(const Function &F) {
123 CollectorMetadata *CM = new CollectorMetadata(F, *this);
124 Functions.push_back(CM);
128 // -----------------------------------------------------------------------------
130 FunctionPass *llvm::createGCLoweringPass() {
131 return new LowerIntrinsics();
134 char LowerIntrinsics::ID = 0;
136 LowerIntrinsics::LowerIntrinsics()
137 : FunctionPass((intptr_t)&ID) {}
139 const char *LowerIntrinsics::getPassName() const {
140 return "Lower Garbage Collection Instructions";
143 void LowerIntrinsics::getAnalysisUsage(AnalysisUsage &AU) const {
144 FunctionPass::getAnalysisUsage(AU);
145 AU.addRequired<CollectorModuleMetadata>();
148 /// doInitialization - If this module uses the GC intrinsics, find them now.
149 bool LowerIntrinsics::doInitialization(Module &M) {
150 // FIXME: This is rather antisocial in the context of a JIT since it performs
151 // work against the entire module. But this cannot be done at
152 // runFunction time (initializeCustomLowering likely needs to change
154 CollectorModuleMetadata *CMM = getAnalysisToUpdate<CollectorModuleMetadata>();
155 assert(CMM && "LowerIntrinsics didn't require CollectorModuleMetadata!?");
156 for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I)
157 if (I->hasCollector())
158 CMM->get(*I); // Instantiate the Collector.
160 bool MadeChange = false;
161 for (CollectorModuleMetadata::iterator I = CMM->begin(),
162 E = CMM->end(); I != E; ++I)
163 if (NeedsCustomLoweringPass(**I))
164 if ((*I)->initializeCustomLowering(M))
170 bool LowerIntrinsics::InsertRootInitializers(Function &F, AllocaInst **Roots,
172 // Scroll past alloca instructions.
173 BasicBlock::iterator IP = F.getEntryBlock().begin();
174 while (isa<AllocaInst>(IP)) ++IP;
176 // Search for initializers in the initial BB.
177 SmallPtrSet<AllocaInst*,16> InitedRoots;
178 for (; !CouldBecomeSafePoint(IP); ++IP)
179 if (StoreInst *SI = dyn_cast<StoreInst>(IP))
180 if (AllocaInst *AI = dyn_cast<AllocaInst>(
181 IntrinsicInst::StripPointerCasts(SI->getOperand(1))))
182 InitedRoots.insert(AI);
184 // Add root initializers.
185 bool MadeChange = false;
187 for (AllocaInst **I = Roots, **E = Roots + Count; I != E; ++I)
188 if (!InitedRoots.count(*I)) {
189 new StoreInst(ConstantPointerNull::get(cast<PointerType>(
190 cast<PointerType>((*I)->getType())->getElementType())),
198 bool LowerIntrinsics::NeedsDefaultLoweringPass(const Collector &C) {
199 // Default lowering is necessary only if read or write barriers have a default
200 // action. The default for roots is no action.
201 return !C.customWriteBarrier()
202 || !C.customReadBarrier()
203 || C.initializeRoots();
206 bool LowerIntrinsics::NeedsCustomLoweringPass(const Collector &C) {
207 // Custom lowering is only necessary if enabled for some action.
208 return C.customWriteBarrier()
209 || C.customReadBarrier()
213 /// CouldBecomeSafePoint - Predicate to conservatively determine whether the
214 /// instruction could introduce a safe point.
215 bool LowerIntrinsics::CouldBecomeSafePoint(Instruction *I) {
216 // The natural definition of instructions which could introduce safe points
219 // - call, invoke (AfterCall, BeforeCall)
221 // - invoke, ret, unwind (Exit)
223 // However, instructions as seemingly inoccuous as arithmetic can become
224 // libcalls upon lowering (e.g., div i64 on a 32-bit platform), so instead
225 // it is necessary to take a conservative approach.
227 if (isa<AllocaInst>(I) || isa<GetElementPtrInst>(I) ||
228 isa<StoreInst>(I) || isa<LoadInst>(I))
231 // llvm.gcroot is safe because it doesn't do anything at runtime.
232 if (CallInst *CI = dyn_cast<CallInst>(I))
233 if (Function *F = CI->getCalledFunction())
234 if (unsigned IID = F->getIntrinsicID())
235 if (IID == Intrinsic::gcroot)
241 /// runOnFunction - Replace gcread/gcwrite intrinsics with loads and stores.
242 /// Leave gcroot intrinsics; the code generator needs to see those.
243 bool LowerIntrinsics::runOnFunction(Function &F) {
244 // Quick exit for functions that do not use GC.
245 if (!F.hasCollector()) return false;
247 CollectorMetadata &MD = getAnalysis<CollectorModuleMetadata>().get(F);
248 Collector &Coll = MD.getCollector();
250 bool MadeChange = false;
252 if (NeedsDefaultLoweringPass(Coll))
253 MadeChange |= PerformDefaultLowering(F, Coll);
255 if (NeedsCustomLoweringPass(Coll))
256 MadeChange |= Coll.performCustomLowering(F);
261 bool LowerIntrinsics::PerformDefaultLowering(Function &F, Collector &Coll) {
262 bool LowerWr = !Coll.customWriteBarrier();
263 bool LowerRd = !Coll.customReadBarrier();
264 bool InitRoots = Coll.initializeRoots();
266 SmallVector<AllocaInst*,32> Roots;
268 bool MadeChange = false;
269 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) {
270 for (BasicBlock::iterator II = BB->begin(), E = BB->end(); II != E;) {
271 if (IntrinsicInst *CI = dyn_cast<IntrinsicInst>(II++)) {
272 Function *F = CI->getCalledFunction();
273 switch (F->getIntrinsicID()) {
274 case Intrinsic::gcwrite:
276 // Replace a write barrier with a simple store.
277 Value *St = new StoreInst(CI->getOperand(1), CI->getOperand(3), CI);
278 CI->replaceAllUsesWith(St);
279 CI->eraseFromParent();
282 case Intrinsic::gcread:
284 // Replace a read barrier with a simple load.
285 Value *Ld = new LoadInst(CI->getOperand(2), "", CI);
287 CI->replaceAllUsesWith(Ld);
288 CI->eraseFromParent();
291 case Intrinsic::gcroot:
293 // Initialize the GC root, but do not delete the intrinsic. The
294 // backend needs the intrinsic to flag the stack slot.
295 Roots.push_back(cast<AllocaInst>(
296 IntrinsicInst::StripPointerCasts(CI->getOperand(1))));
309 MadeChange |= InsertRootInitializers(F, Roots.begin(), Roots.size());
314 // -----------------------------------------------------------------------------
316 FunctionPass *llvm::createGCMachineCodeAnalysisPass() {
317 return new MachineCodeAnalysis();
320 char MachineCodeAnalysis::ID = 0;
322 MachineCodeAnalysis::MachineCodeAnalysis()
323 : MachineFunctionPass(intptr_t(&ID)) {}
325 const char *MachineCodeAnalysis::getPassName() const {
326 return "Analyze Machine Code For Garbage Collection";
329 void MachineCodeAnalysis::getAnalysisUsage(AnalysisUsage &AU) const {
330 MachineFunctionPass::getAnalysisUsage(AU);
331 AU.setPreservesAll();
332 AU.addRequired<MachineModuleInfo>();
333 AU.addRequired<CollectorModuleMetadata>();
336 unsigned MachineCodeAnalysis::InsertLabel(MachineBasicBlock &MBB,
337 MachineBasicBlock::iterator MI) const {
338 unsigned Label = MMI->NextLabelID();
339 BuildMI(MBB, MI, TII->get(TargetInstrInfo::LABEL)).addImm(Label);
343 void MachineCodeAnalysis::VisitCallPoint(MachineBasicBlock::iterator CI) {
344 // Find the return address (next instruction), too, so as to bracket the call
346 MachineBasicBlock::iterator RAI = CI;
349 if (MD->getCollector().needsSafePoint(GC::PreCall))
350 MD->addSafePoint(GC::PreCall, InsertLabel(*CI->getParent(), CI));
352 if (MD->getCollector().needsSafePoint(GC::PostCall))
353 MD->addSafePoint(GC::PostCall, InsertLabel(*CI->getParent(), RAI));
356 void MachineCodeAnalysis::FindSafePoints(MachineFunction &MF) {
357 for (MachineFunction::iterator BBI = MF.begin(),
358 BBE = MF.end(); BBI != BBE; ++BBI)
359 for (MachineBasicBlock::iterator MI = BBI->begin(),
360 ME = BBI->end(); MI != ME; ++MI)
361 if (TII->isCall(MI->getOpcode()))
365 void MachineCodeAnalysis::FindStackOffsets(MachineFunction &MF) {
366 uint64_t StackSize = MFI->getStackSize();
367 uint64_t OffsetAdjustment = MFI->getOffsetAdjustment();
368 uint64_t OffsetOfLocalArea = TM->getFrameInfo()->getOffsetOfLocalArea();
370 for (CollectorMetadata::roots_iterator RI = MD->roots_begin(),
371 RE = MD->roots_end(); RI != RE; ++RI)
372 RI->StackOffset = MFI->getObjectOffset(RI->Num) + StackSize
373 - OffsetOfLocalArea + OffsetAdjustment;
376 bool MachineCodeAnalysis::runOnMachineFunction(MachineFunction &MF) {
377 // Quick exit for functions that do not use GC.
378 if (!MF.getFunction()->hasCollector()) return false;
380 MD = &getAnalysis<CollectorModuleMetadata>().get(*MF.getFunction());
381 if (!MD->getCollector().needsSafePoints())
384 TM = &MF.getTarget();
385 MMI = &getAnalysis<MachineModuleInfo>();
386 TII = TM->getInstrInfo();
387 MFI = MF.getFrameInfo();
389 // Find the size of the stack frame.
390 MD->setFrameSize(MFI->getStackSize());
392 // Find all safe points.
395 // Find the stack offsets for all roots.
396 FindStackOffsets(MF);