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 // GCMachineCodeAnalysis identifies the GC safe points in the machine code.
14 // Roots are identified in SelectionDAGISel.
16 //===----------------------------------------------------------------------===//
18 #include "llvm/CodeGen/GCStrategy.h"
19 #include "llvm/CodeGen/MachineFrameInfo.h"
20 #include "llvm/CodeGen/MachineFunctionPass.h"
21 #include "llvm/CodeGen/MachineInstrBuilder.h"
22 #include "llvm/CodeGen/MachineModuleInfo.h"
23 #include "llvm/CodeGen/Passes.h"
24 #include "llvm/IR/Dominators.h"
25 #include "llvm/IR/IntrinsicInst.h"
26 #include "llvm/IR/Module.h"
27 #include "llvm/Support/Debug.h"
28 #include "llvm/Support/ErrorHandling.h"
29 #include "llvm/Support/raw_ostream.h"
30 #include "llvm/Target/TargetFrameLowering.h"
31 #include "llvm/Target/TargetInstrInfo.h"
32 #include "llvm/Target/TargetMachine.h"
33 #include "llvm/Target/TargetRegisterInfo.h"
34 #include "llvm/Target/TargetSubtargetInfo.h"
40 /// LowerIntrinsics - This pass rewrites calls to the llvm.gcread or
41 /// llvm.gcwrite intrinsics, replacing them with simple loads and stores as
42 /// directed by the GCStrategy. It also performs automatic root initialization
43 /// and custom intrinsic lowering.
44 class LowerIntrinsics : public FunctionPass {
45 static bool NeedsDefaultLoweringPass(const GCStrategy &C);
46 static bool NeedsCustomLoweringPass(const GCStrategy &C);
47 static bool CouldBecomeSafePoint(Instruction *I);
48 bool PerformDefaultLowering(Function &F, GCStrategy &Coll);
49 static bool InsertRootInitializers(Function &F,
50 AllocaInst **Roots, unsigned Count);
56 const char *getPassName() const override;
57 void getAnalysisUsage(AnalysisUsage &AU) const override;
59 bool doInitialization(Module &M) override;
60 bool runOnFunction(Function &F) override;
64 /// GCMachineCodeAnalysis - This is a target-independent pass over the machine
65 /// function representation to identify safe points for the garbage collector
66 /// in the machine code. It inserts labels at safe points and populates a
67 /// GCMetadata record for each function.
68 class GCMachineCodeAnalysis : public MachineFunctionPass {
69 const TargetMachine *TM;
71 MachineModuleInfo *MMI;
72 const TargetInstrInfo *TII;
74 void FindSafePoints(MachineFunction &MF);
75 void VisitCallPoint(MachineBasicBlock::iterator MI);
76 MCSymbol *InsertLabel(MachineBasicBlock &MBB,
77 MachineBasicBlock::iterator MI,
80 void FindStackOffsets(MachineFunction &MF);
85 GCMachineCodeAnalysis();
86 void getAnalysisUsage(AnalysisUsage &AU) const override;
88 bool runOnMachineFunction(MachineFunction &MF) override;
93 // -----------------------------------------------------------------------------
95 GCStrategy::GCStrategy() :
97 CustomReadBarriers(false),
98 CustomWriteBarriers(false),
100 CustomSafePoints(false),
105 bool GCStrategy::initializeCustomLowering(Module &M) { return false; }
107 bool GCStrategy::performCustomLowering(Function &F) {
108 dbgs() << "gc " << getName() << " must override performCustomLowering.\n";
109 llvm_unreachable("must override performCustomLowering");
113 bool GCStrategy::findCustomSafePoints(GCFunctionInfo& FI, MachineFunction &F) {
114 dbgs() << "gc " << getName() << " must override findCustomSafePoints.\n";
115 llvm_unreachable(nullptr);
118 // -----------------------------------------------------------------------------
120 INITIALIZE_PASS_BEGIN(LowerIntrinsics, "gc-lowering", "GC Lowering",
122 INITIALIZE_PASS_DEPENDENCY(GCModuleInfo)
123 INITIALIZE_PASS_END(LowerIntrinsics, "gc-lowering", "GC Lowering", false, false)
125 FunctionPass *llvm::createGCLoweringPass() {
126 return new LowerIntrinsics();
129 char LowerIntrinsics::ID = 0;
131 LowerIntrinsics::LowerIntrinsics()
133 initializeLowerIntrinsicsPass(*PassRegistry::getPassRegistry());
136 const char *LowerIntrinsics::getPassName() const {
137 return "Lower Garbage Collection Instructions";
140 void LowerIntrinsics::getAnalysisUsage(AnalysisUsage &AU) const {
141 FunctionPass::getAnalysisUsage(AU);
142 AU.addRequired<GCModuleInfo>();
143 AU.addPreserved<DominatorTreeWrapperPass>();
146 /// doInitialization - If this module uses the GC intrinsics, find them now.
147 bool LowerIntrinsics::doInitialization(Module &M) {
148 // FIXME: This is rather antisocial in the context of a JIT since it performs
149 // work against the entire module. But this cannot be done at
150 // runFunction time (initializeCustomLowering likely needs to change
152 GCModuleInfo *MI = getAnalysisIfAvailable<GCModuleInfo>();
153 assert(MI && "LowerIntrinsics didn't require GCModuleInfo!?");
154 for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I)
155 if (!I->isDeclaration() && I->hasGC())
156 MI->getFunctionInfo(*I); // Instantiate the GC strategy.
158 bool MadeChange = false;
159 for (GCModuleInfo::iterator I = MI->begin(), E = MI->end(); I != E; ++I)
160 if (NeedsCustomLoweringPass(**I))
161 if ((*I)->initializeCustomLowering(M))
167 bool LowerIntrinsics::InsertRootInitializers(Function &F, AllocaInst **Roots,
169 // Scroll past alloca instructions.
170 BasicBlock::iterator IP = F.getEntryBlock().begin();
171 while (isa<AllocaInst>(IP)) ++IP;
173 // Search for initializers in the initial BB.
174 SmallPtrSet<AllocaInst*,16> InitedRoots;
175 for (; !CouldBecomeSafePoint(IP); ++IP)
176 if (StoreInst *SI = dyn_cast<StoreInst>(IP))
178 dyn_cast<AllocaInst>(SI->getOperand(1)->stripPointerCasts()))
179 InitedRoots.insert(AI);
181 // Add root initializers.
182 bool MadeChange = false;
184 for (AllocaInst **I = Roots, **E = Roots + Count; I != E; ++I)
185 if (!InitedRoots.count(*I)) {
186 StoreInst* SI = new StoreInst(ConstantPointerNull::get(cast<PointerType>(
187 cast<PointerType>((*I)->getType())->getElementType())),
196 bool LowerIntrinsics::NeedsDefaultLoweringPass(const GCStrategy &C) {
197 // Default lowering is necessary only if read or write barriers have a default
198 // action. The default for roots is no action.
199 return !C.customWriteBarrier()
200 || !C.customReadBarrier()
201 || C.initializeRoots();
204 bool LowerIntrinsics::NeedsCustomLoweringPass(const GCStrategy &C) {
205 // Custom lowering is only necessary if enabled for some action.
206 return C.customWriteBarrier()
207 || C.customReadBarrier()
211 /// CouldBecomeSafePoint - Predicate to conservatively determine whether the
212 /// instruction could introduce a safe point.
213 bool LowerIntrinsics::CouldBecomeSafePoint(Instruction *I) {
214 // The natural definition of instructions which could introduce safe points
217 // - call, invoke (AfterCall, BeforeCall)
219 // - invoke, ret, unwind (Exit)
221 // However, instructions as seemingly inoccuous as arithmetic can become
222 // libcalls upon lowering (e.g., div i64 on a 32-bit platform), so instead
223 // it is necessary to take a conservative approach.
225 if (isa<AllocaInst>(I) || isa<GetElementPtrInst>(I) ||
226 isa<StoreInst>(I) || isa<LoadInst>(I))
229 // llvm.gcroot is safe because it doesn't do anything at runtime.
230 if (CallInst *CI = dyn_cast<CallInst>(I))
231 if (Function *F = CI->getCalledFunction())
232 if (unsigned IID = F->getIntrinsicID())
233 if (IID == Intrinsic::gcroot)
239 /// runOnFunction - Replace gcread/gcwrite intrinsics with loads and stores.
240 /// Leave gcroot intrinsics; the code generator needs to see those.
241 bool LowerIntrinsics::runOnFunction(Function &F) {
242 // Quick exit for functions that do not use GC.
246 GCFunctionInfo &FI = getAnalysis<GCModuleInfo>().getFunctionInfo(F);
247 GCStrategy &S = FI.getStrategy();
249 bool MadeChange = false;
251 if (NeedsDefaultLoweringPass(S))
252 MadeChange |= PerformDefaultLowering(F, S);
254 bool UseCustomLoweringPass = NeedsCustomLoweringPass(S);
255 if (UseCustomLoweringPass)
256 MadeChange |= S.performCustomLowering(F);
258 // Custom lowering may modify the CFG, so dominators must be recomputed.
259 if (UseCustomLoweringPass) {
260 if (DominatorTreeWrapperPass *DTWP =
261 getAnalysisIfAvailable<DominatorTreeWrapperPass>())
262 DTWP->getDomTree().recalculate(F);
268 bool LowerIntrinsics::PerformDefaultLowering(Function &F, GCStrategy &S) {
269 bool LowerWr = !S.customWriteBarrier();
270 bool LowerRd = !S.customReadBarrier();
271 bool InitRoots = S.initializeRoots();
273 SmallVector<AllocaInst*, 32> Roots;
275 bool MadeChange = false;
276 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) {
277 for (BasicBlock::iterator II = BB->begin(), E = BB->end(); II != E;) {
278 if (IntrinsicInst *CI = dyn_cast<IntrinsicInst>(II++)) {
279 Function *F = CI->getCalledFunction();
280 switch (F->getIntrinsicID()) {
281 case Intrinsic::gcwrite:
283 // Replace a write barrier with a simple store.
284 Value *St = new StoreInst(CI->getArgOperand(0),
285 CI->getArgOperand(2), CI);
286 CI->replaceAllUsesWith(St);
287 CI->eraseFromParent();
290 case Intrinsic::gcread:
292 // Replace a read barrier with a simple load.
293 Value *Ld = new LoadInst(CI->getArgOperand(1), "", CI);
295 CI->replaceAllUsesWith(Ld);
296 CI->eraseFromParent();
299 case Intrinsic::gcroot:
301 // Initialize the GC root, but do not delete the intrinsic. The
302 // backend needs the intrinsic to flag the stack slot.
303 Roots.push_back(cast<AllocaInst>(
304 CI->getArgOperand(0)->stripPointerCasts()));
317 MadeChange |= InsertRootInitializers(F, Roots.begin(), Roots.size());
322 // -----------------------------------------------------------------------------
324 char GCMachineCodeAnalysis::ID = 0;
325 char &llvm::GCMachineCodeAnalysisID = GCMachineCodeAnalysis::ID;
327 INITIALIZE_PASS(GCMachineCodeAnalysis, "gc-analysis",
328 "Analyze Machine Code For Garbage Collection", false, false)
330 GCMachineCodeAnalysis::GCMachineCodeAnalysis()
331 : MachineFunctionPass(ID) {}
333 void GCMachineCodeAnalysis::getAnalysisUsage(AnalysisUsage &AU) const {
334 MachineFunctionPass::getAnalysisUsage(AU);
335 AU.setPreservesAll();
336 AU.addRequired<MachineModuleInfo>();
337 AU.addRequired<GCModuleInfo>();
340 MCSymbol *GCMachineCodeAnalysis::InsertLabel(MachineBasicBlock &MBB,
341 MachineBasicBlock::iterator MI,
343 MCSymbol *Label = MBB.getParent()->getContext().CreateTempSymbol();
344 BuildMI(MBB, MI, DL, TII->get(TargetOpcode::GC_LABEL)).addSym(Label);
348 void GCMachineCodeAnalysis::VisitCallPoint(MachineBasicBlock::iterator CI) {
349 // Find the return address (next instruction), too, so as to bracket the call
351 MachineBasicBlock::iterator RAI = CI;
354 if (FI->getStrategy().needsSafePoint(GC::PreCall)) {
355 MCSymbol* Label = InsertLabel(*CI->getParent(), CI, CI->getDebugLoc());
356 FI->addSafePoint(GC::PreCall, Label, CI->getDebugLoc());
359 if (FI->getStrategy().needsSafePoint(GC::PostCall)) {
360 MCSymbol* Label = InsertLabel(*CI->getParent(), RAI, CI->getDebugLoc());
361 FI->addSafePoint(GC::PostCall, Label, CI->getDebugLoc());
365 void GCMachineCodeAnalysis::FindSafePoints(MachineFunction &MF) {
366 for (MachineFunction::iterator BBI = MF.begin(),
367 BBE = MF.end(); BBI != BBE; ++BBI)
368 for (MachineBasicBlock::iterator MI = BBI->begin(),
369 ME = BBI->end(); MI != ME; ++MI)
374 void GCMachineCodeAnalysis::FindStackOffsets(MachineFunction &MF) {
375 const TargetFrameLowering *TFI = TM->getSubtargetImpl()->getFrameLowering();
376 assert(TFI && "TargetRegisterInfo not available!");
378 for (GCFunctionInfo::roots_iterator RI = FI->roots_begin();
379 RI != FI->roots_end();) {
380 // If the root references a dead object, no need to keep it.
381 if (MF.getFrameInfo()->isDeadObjectIndex(RI->Num)) {
382 RI = FI->removeStackRoot(RI);
384 RI->StackOffset = TFI->getFrameIndexOffset(MF, RI->Num);
390 bool GCMachineCodeAnalysis::runOnMachineFunction(MachineFunction &MF) {
391 // Quick exit for functions that do not use GC.
392 if (!MF.getFunction()->hasGC())
395 FI = &getAnalysis<GCModuleInfo>().getFunctionInfo(*MF.getFunction());
396 if (!FI->getStrategy().needsSafePoints())
399 TM = &MF.getTarget();
400 MMI = &getAnalysis<MachineModuleInfo>();
401 TII = TM->getSubtargetImpl()->getInstrInfo();
403 // Find the size of the stack frame.
404 FI->setFrameSize(MF.getFrameInfo()->getStackSize());
406 // Find all safe points.
407 if (FI->getStrategy().customSafePoints()) {
408 FI->getStrategy().findCustomSafePoints(*FI, MF);
413 // Find the stack offsets for all roots.
414 FindStackOffsets(MF);