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);
119 GCFunctionInfo *GCStrategy::insertFunctionInfo(const Function &F) {
120 Functions.push_back(make_unique<GCFunctionInfo>(F, *this));
121 return Functions.back().get();
124 // -----------------------------------------------------------------------------
126 INITIALIZE_PASS_BEGIN(LowerIntrinsics, "gc-lowering", "GC Lowering",
128 INITIALIZE_PASS_DEPENDENCY(GCModuleInfo)
129 INITIALIZE_PASS_END(LowerIntrinsics, "gc-lowering", "GC Lowering", false, false)
131 FunctionPass *llvm::createGCLoweringPass() {
132 return new LowerIntrinsics();
135 char LowerIntrinsics::ID = 0;
137 LowerIntrinsics::LowerIntrinsics()
139 initializeLowerIntrinsicsPass(*PassRegistry::getPassRegistry());
142 const char *LowerIntrinsics::getPassName() const {
143 return "Lower Garbage Collection Instructions";
146 void LowerIntrinsics::getAnalysisUsage(AnalysisUsage &AU) const {
147 FunctionPass::getAnalysisUsage(AU);
148 AU.addRequired<GCModuleInfo>();
149 AU.addPreserved<DominatorTreeWrapperPass>();
152 /// doInitialization - If this module uses the GC intrinsics, find them now.
153 bool LowerIntrinsics::doInitialization(Module &M) {
154 // FIXME: This is rather antisocial in the context of a JIT since it performs
155 // work against the entire module. But this cannot be done at
156 // runFunction time (initializeCustomLowering likely needs to change
158 GCModuleInfo *MI = getAnalysisIfAvailable<GCModuleInfo>();
159 assert(MI && "LowerIntrinsics didn't require GCModuleInfo!?");
160 for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I)
161 if (!I->isDeclaration() && I->hasGC())
162 MI->getFunctionInfo(*I); // Instantiate the GC strategy.
164 bool MadeChange = false;
165 for (GCModuleInfo::iterator I = MI->begin(), E = MI->end(); I != E; ++I)
166 if (NeedsCustomLoweringPass(**I))
167 if ((*I)->initializeCustomLowering(M))
173 bool LowerIntrinsics::InsertRootInitializers(Function &F, AllocaInst **Roots,
175 // Scroll past alloca instructions.
176 BasicBlock::iterator IP = F.getEntryBlock().begin();
177 while (isa<AllocaInst>(IP)) ++IP;
179 // Search for initializers in the initial BB.
180 SmallPtrSet<AllocaInst*,16> InitedRoots;
181 for (; !CouldBecomeSafePoint(IP); ++IP)
182 if (StoreInst *SI = dyn_cast<StoreInst>(IP))
184 dyn_cast<AllocaInst>(SI->getOperand(1)->stripPointerCasts()))
185 InitedRoots.insert(AI);
187 // Add root initializers.
188 bool MadeChange = false;
190 for (AllocaInst **I = Roots, **E = Roots + Count; I != E; ++I)
191 if (!InitedRoots.count(*I)) {
192 StoreInst* SI = new StoreInst(ConstantPointerNull::get(cast<PointerType>(
193 cast<PointerType>((*I)->getType())->getElementType())),
202 bool LowerIntrinsics::NeedsDefaultLoweringPass(const GCStrategy &C) {
203 // Default lowering is necessary only if read or write barriers have a default
204 // action. The default for roots is no action.
205 return !C.customWriteBarrier()
206 || !C.customReadBarrier()
207 || C.initializeRoots();
210 bool LowerIntrinsics::NeedsCustomLoweringPass(const GCStrategy &C) {
211 // Custom lowering is only necessary if enabled for some action.
212 return C.customWriteBarrier()
213 || C.customReadBarrier()
217 /// CouldBecomeSafePoint - Predicate to conservatively determine whether the
218 /// instruction could introduce a safe point.
219 bool LowerIntrinsics::CouldBecomeSafePoint(Instruction *I) {
220 // The natural definition of instructions which could introduce safe points
223 // - call, invoke (AfterCall, BeforeCall)
225 // - invoke, ret, unwind (Exit)
227 // However, instructions as seemingly inoccuous as arithmetic can become
228 // libcalls upon lowering (e.g., div i64 on a 32-bit platform), so instead
229 // it is necessary to take a conservative approach.
231 if (isa<AllocaInst>(I) || isa<GetElementPtrInst>(I) ||
232 isa<StoreInst>(I) || isa<LoadInst>(I))
235 // llvm.gcroot is safe because it doesn't do anything at runtime.
236 if (CallInst *CI = dyn_cast<CallInst>(I))
237 if (Function *F = CI->getCalledFunction())
238 if (unsigned IID = F->getIntrinsicID())
239 if (IID == Intrinsic::gcroot)
245 /// runOnFunction - Replace gcread/gcwrite intrinsics with loads and stores.
246 /// Leave gcroot intrinsics; the code generator needs to see those.
247 bool LowerIntrinsics::runOnFunction(Function &F) {
248 // Quick exit for functions that do not use GC.
252 GCFunctionInfo &FI = getAnalysis<GCModuleInfo>().getFunctionInfo(F);
253 GCStrategy &S = FI.getStrategy();
255 bool MadeChange = false;
257 if (NeedsDefaultLoweringPass(S))
258 MadeChange |= PerformDefaultLowering(F, S);
260 bool UseCustomLoweringPass = NeedsCustomLoweringPass(S);
261 if (UseCustomLoweringPass)
262 MadeChange |= S.performCustomLowering(F);
264 // Custom lowering may modify the CFG, so dominators must be recomputed.
265 if (UseCustomLoweringPass) {
266 if (DominatorTreeWrapperPass *DTWP =
267 getAnalysisIfAvailable<DominatorTreeWrapperPass>())
268 DTWP->getDomTree().recalculate(F);
274 bool LowerIntrinsics::PerformDefaultLowering(Function &F, GCStrategy &S) {
275 bool LowerWr = !S.customWriteBarrier();
276 bool LowerRd = !S.customReadBarrier();
277 bool InitRoots = S.initializeRoots();
279 SmallVector<AllocaInst*, 32> Roots;
281 bool MadeChange = false;
282 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) {
283 for (BasicBlock::iterator II = BB->begin(), E = BB->end(); II != E;) {
284 if (IntrinsicInst *CI = dyn_cast<IntrinsicInst>(II++)) {
285 Function *F = CI->getCalledFunction();
286 switch (F->getIntrinsicID()) {
287 case Intrinsic::gcwrite:
289 // Replace a write barrier with a simple store.
290 Value *St = new StoreInst(CI->getArgOperand(0),
291 CI->getArgOperand(2), CI);
292 CI->replaceAllUsesWith(St);
293 CI->eraseFromParent();
296 case Intrinsic::gcread:
298 // Replace a read barrier with a simple load.
299 Value *Ld = new LoadInst(CI->getArgOperand(1), "", CI);
301 CI->replaceAllUsesWith(Ld);
302 CI->eraseFromParent();
305 case Intrinsic::gcroot:
307 // Initialize the GC root, but do not delete the intrinsic. The
308 // backend needs the intrinsic to flag the stack slot.
309 Roots.push_back(cast<AllocaInst>(
310 CI->getArgOperand(0)->stripPointerCasts()));
323 MadeChange |= InsertRootInitializers(F, Roots.begin(), Roots.size());
328 // -----------------------------------------------------------------------------
330 char GCMachineCodeAnalysis::ID = 0;
331 char &llvm::GCMachineCodeAnalysisID = GCMachineCodeAnalysis::ID;
333 INITIALIZE_PASS(GCMachineCodeAnalysis, "gc-analysis",
334 "Analyze Machine Code For Garbage Collection", false, false)
336 GCMachineCodeAnalysis::GCMachineCodeAnalysis()
337 : MachineFunctionPass(ID) {}
339 void GCMachineCodeAnalysis::getAnalysisUsage(AnalysisUsage &AU) const {
340 MachineFunctionPass::getAnalysisUsage(AU);
341 AU.setPreservesAll();
342 AU.addRequired<MachineModuleInfo>();
343 AU.addRequired<GCModuleInfo>();
346 MCSymbol *GCMachineCodeAnalysis::InsertLabel(MachineBasicBlock &MBB,
347 MachineBasicBlock::iterator MI,
349 MCSymbol *Label = MBB.getParent()->getContext().CreateTempSymbol();
350 BuildMI(MBB, MI, DL, TII->get(TargetOpcode::GC_LABEL)).addSym(Label);
354 void GCMachineCodeAnalysis::VisitCallPoint(MachineBasicBlock::iterator CI) {
355 // Find the return address (next instruction), too, so as to bracket the call
357 MachineBasicBlock::iterator RAI = CI;
360 if (FI->getStrategy().needsSafePoint(GC::PreCall)) {
361 MCSymbol* Label = InsertLabel(*CI->getParent(), CI, CI->getDebugLoc());
362 FI->addSafePoint(GC::PreCall, Label, CI->getDebugLoc());
365 if (FI->getStrategy().needsSafePoint(GC::PostCall)) {
366 MCSymbol* Label = InsertLabel(*CI->getParent(), RAI, CI->getDebugLoc());
367 FI->addSafePoint(GC::PostCall, Label, CI->getDebugLoc());
371 void GCMachineCodeAnalysis::FindSafePoints(MachineFunction &MF) {
372 for (MachineFunction::iterator BBI = MF.begin(),
373 BBE = MF.end(); BBI != BBE; ++BBI)
374 for (MachineBasicBlock::iterator MI = BBI->begin(),
375 ME = BBI->end(); MI != ME; ++MI)
380 void GCMachineCodeAnalysis::FindStackOffsets(MachineFunction &MF) {
381 const TargetFrameLowering *TFI = TM->getSubtargetImpl()->getFrameLowering();
382 assert(TFI && "TargetRegisterInfo not available!");
384 for (GCFunctionInfo::roots_iterator RI = FI->roots_begin();
385 RI != FI->roots_end();) {
386 // If the root references a dead object, no need to keep it.
387 if (MF.getFrameInfo()->isDeadObjectIndex(RI->Num)) {
388 RI = FI->removeStackRoot(RI);
390 RI->StackOffset = TFI->getFrameIndexOffset(MF, RI->Num);
396 bool GCMachineCodeAnalysis::runOnMachineFunction(MachineFunction &MF) {
397 // Quick exit for functions that do not use GC.
398 if (!MF.getFunction()->hasGC())
401 FI = &getAnalysis<GCModuleInfo>().getFunctionInfo(*MF.getFunction());
402 if (!FI->getStrategy().needsSafePoints())
405 TM = &MF.getTarget();
406 MMI = &getAnalysis<MachineModuleInfo>();
407 TII = TM->getSubtargetImpl()->getInstrInfo();
409 // Find the size of the stack frame.
410 FI->setFrameSize(MF.getFrameInfo()->getStackSize());
412 // Find all safe points.
413 if (FI->getStrategy().customSafePoints()) {
414 FI->getStrategy().findCustomSafePoints(*FI, MF);
419 // Find the stack offsets for all roots.
420 FindStackOffsets(MF);