1 //===-- GCStrategy.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 // MachineCodeAnalysis identifies the GC safe points in the machine code. Roots
14 // are identified in SelectionDAGISel.
16 //===----------------------------------------------------------------------===//
18 #include "llvm/CodeGen/GCStrategy.h"
19 #include "llvm/CodeGen/Passes.h"
20 #include "llvm/IntrinsicInst.h"
21 #include "llvm/Module.h"
22 #include "llvm/CodeGen/MachineFrameInfo.h"
23 #include "llvm/CodeGen/MachineFunctionPass.h"
24 #include "llvm/CodeGen/MachineInstrBuilder.h"
25 #include "llvm/CodeGen/MachineModuleInfo.h"
26 #include "llvm/Target/TargetFrameInfo.h"
27 #include "llvm/Target/TargetInstrInfo.h"
28 #include "llvm/Target/TargetMachine.h"
29 #include "llvm/Support/Compiler.h"
35 /// LowerIntrinsics - This pass rewrites calls to the llvm.gcread or
36 /// llvm.gcwrite intrinsics, replacing them with simple loads and stores as
37 /// directed by the GCStrategy. It also performs automatic root initialization
38 /// and custom intrinsic lowering.
39 class VISIBILITY_HIDDEN LowerIntrinsics : public FunctionPass {
40 static bool NeedsDefaultLoweringPass(const GCStrategy &C);
41 static bool NeedsCustomLoweringPass(const GCStrategy &C);
42 static bool CouldBecomeSafePoint(Instruction *I);
43 bool PerformDefaultLowering(Function &F, GCStrategy &Coll);
44 static bool InsertRootInitializers(Function &F,
45 AllocaInst **Roots, unsigned Count);
51 const char *getPassName() const;
52 void getAnalysisUsage(AnalysisUsage &AU) const;
54 bool doInitialization(Module &M);
55 bool runOnFunction(Function &F);
59 /// MachineCodeAnalysis - This is a target-independent pass over the machine
60 /// function representation to identify safe points for the garbage collector
61 /// in the machine code. It inserts labels at safe points and populates a
62 /// GCMetadata record for each function.
63 class VISIBILITY_HIDDEN MachineCodeAnalysis : public MachineFunctionPass {
64 const TargetMachine *TM;
66 MachineModuleInfo *MMI;
67 const TargetInstrInfo *TII;
68 MachineFrameInfo *MFI;
70 void FindSafePoints(MachineFunction &MF);
71 void VisitCallPoint(MachineBasicBlock::iterator MI);
72 unsigned InsertLabel(MachineBasicBlock &MBB,
73 MachineBasicBlock::iterator MI) const;
75 void FindStackOffsets(MachineFunction &MF);
80 MachineCodeAnalysis();
81 const char *getPassName() const;
82 void getAnalysisUsage(AnalysisUsage &AU) const;
84 bool runOnMachineFunction(MachineFunction &MF);
89 // -----------------------------------------------------------------------------
91 template<> GCRegistry::node *GCRegistry::Head = 0;
92 template<> GCRegistry::node *GCRegistry::Tail = 0;
93 template<> GCRegistry::listener *GCRegistry::ListenerHead = 0;
94 template<> GCRegistry::listener *GCRegistry::ListenerTail = 0;
96 // -----------------------------------------------------------------------------
98 GCStrategy::GCStrategy() :
100 CustomReadBarriers(false),
101 CustomWriteBarriers(false),
107 GCStrategy::~GCStrategy() {
108 for (iterator I = begin(), E = end(); I != E; ++I)
114 bool GCStrategy::initializeCustomLowering(Module &M) { return false; }
116 bool GCStrategy::performCustomLowering(Function &F) {
117 cerr << "gc " << getName() << " must override performCustomLowering.\n";
122 GCFunctionInfo *GCStrategy::insertFunctionInfo(const Function &F) {
123 GCFunctionInfo *FI = new GCFunctionInfo(F, *this);
124 Functions.push_back(FI);
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<GCModuleInfo>();
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 GCModuleInfo *MI = getAnalysisToUpdate<GCModuleInfo>();
155 assert(MI && "LowerIntrinsics didn't require GCModuleInfo!?");
156 for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I)
157 if (!I->isDeclaration() && I->hasGC())
158 MI->getFunctionInfo(*I); // Instantiate the GC strategy.
160 bool MadeChange = false;
161 for (GCModuleInfo::iterator I = MI->begin(), E = MI->end(); I != E; ++I)
162 if (NeedsCustomLoweringPass(**I))
163 if ((*I)->initializeCustomLowering(M))
169 bool LowerIntrinsics::InsertRootInitializers(Function &F, AllocaInst **Roots,
171 // Scroll past alloca instructions.
172 BasicBlock::iterator IP = F.getEntryBlock().begin();
173 while (isa<AllocaInst>(IP)) ++IP;
175 // Search for initializers in the initial BB.
176 SmallPtrSet<AllocaInst*,16> InitedRoots;
177 for (; !CouldBecomeSafePoint(IP); ++IP)
178 if (StoreInst *SI = dyn_cast<StoreInst>(IP))
180 dyn_cast<AllocaInst>(SI->getOperand(1)->stripPointerCasts()))
181 InitedRoots.insert(AI);
183 // Add root initializers.
184 bool MadeChange = false;
186 for (AllocaInst **I = Roots, **E = Roots + Count; I != E; ++I)
187 if (!InitedRoots.count(*I)) {
188 new StoreInst(ConstantPointerNull::get(cast<PointerType>(
189 cast<PointerType>((*I)->getType())->getElementType())),
197 bool LowerIntrinsics::NeedsDefaultLoweringPass(const GCStrategy &C) {
198 // Default lowering is necessary only if read or write barriers have a default
199 // action. The default for roots is no action.
200 return !C.customWriteBarrier()
201 || !C.customReadBarrier()
202 || C.initializeRoots();
205 bool LowerIntrinsics::NeedsCustomLoweringPass(const GCStrategy &C) {
206 // Custom lowering is only necessary if enabled for some action.
207 return C.customWriteBarrier()
208 || C.customReadBarrier()
212 /// CouldBecomeSafePoint - Predicate to conservatively determine whether the
213 /// instruction could introduce a safe point.
214 bool LowerIntrinsics::CouldBecomeSafePoint(Instruction *I) {
215 // The natural definition of instructions which could introduce safe points
218 // - call, invoke (AfterCall, BeforeCall)
220 // - invoke, ret, unwind (Exit)
222 // However, instructions as seemingly inoccuous as arithmetic can become
223 // libcalls upon lowering (e.g., div i64 on a 32-bit platform), so instead
224 // it is necessary to take a conservative approach.
226 if (isa<AllocaInst>(I) || isa<GetElementPtrInst>(I) ||
227 isa<StoreInst>(I) || isa<LoadInst>(I))
230 // llvm.gcroot is safe because it doesn't do anything at runtime.
231 if (CallInst *CI = dyn_cast<CallInst>(I))
232 if (Function *F = CI->getCalledFunction())
233 if (unsigned IID = F->getIntrinsicID())
234 if (IID == Intrinsic::gcroot)
240 /// runOnFunction - Replace gcread/gcwrite intrinsics with loads and stores.
241 /// Leave gcroot intrinsics; the code generator needs to see those.
242 bool LowerIntrinsics::runOnFunction(Function &F) {
243 // Quick exit for functions that do not use GC.
247 GCFunctionInfo &FI = getAnalysis<GCModuleInfo>().getFunctionInfo(F);
248 GCStrategy &S = FI.getStrategy();
250 bool MadeChange = false;
252 if (NeedsDefaultLoweringPass(S))
253 MadeChange |= PerformDefaultLowering(F, S);
255 if (NeedsCustomLoweringPass(S))
256 MadeChange |= S.performCustomLowering(F);
261 bool LowerIntrinsics::PerformDefaultLowering(Function &F, GCStrategy &S) {
262 bool LowerWr = !S.customWriteBarrier();
263 bool LowerRd = !S.customReadBarrier();
264 bool InitRoots = S.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 CI->getOperand(1)->stripPointerCasts()));
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<GCModuleInfo>();
336 unsigned MachineCodeAnalysis::InsertLabel(MachineBasicBlock &MBB,
337 MachineBasicBlock::iterator MI) const {
338 unsigned Label = MMI->NextLabelID();
339 BuildMI(MBB, MI, TII->get(TargetInstrInfo::GC_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 (FI->getStrategy().needsSafePoint(GC::PreCall))
350 FI->addSafePoint(GC::PreCall, InsertLabel(*CI->getParent(), CI));
352 if (FI->getStrategy().needsSafePoint(GC::PostCall))
353 FI->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 (MI->getDesc().isCall())
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 (GCFunctionInfo::roots_iterator RI = FI->roots_begin(),
371 RE = FI->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()->hasGC())
381 FI = &getAnalysis<GCModuleInfo>().getFunctionInfo(*MF.getFunction());
382 if (!FI->getStrategy().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 FI->setFrameSize(MFI->getStackSize());
393 // Find all safe points.
396 // Find the stack offsets for all roots.
397 FindStackOffsets(MF);