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/Target/TargetRegisterInfo.h"
30 #include "llvm/Support/Debug.h"
31 #include "llvm/Support/ErrorHandling.h"
32 #include "llvm/Support/raw_ostream.h"
38 /// LowerIntrinsics - This pass rewrites calls to the llvm.gcread or
39 /// llvm.gcwrite intrinsics, replacing them with simple loads and stores as
40 /// directed by the GCStrategy. It also performs automatic root initialization
41 /// and custom intrinsic lowering.
42 class LowerIntrinsics : public FunctionPass {
43 static bool NeedsDefaultLoweringPass(const GCStrategy &C);
44 static bool NeedsCustomLoweringPass(const GCStrategy &C);
45 static bool CouldBecomeSafePoint(Instruction *I);
46 bool PerformDefaultLowering(Function &F, GCStrategy &Coll);
47 static bool InsertRootInitializers(Function &F,
48 AllocaInst **Roots, unsigned Count);
54 const char *getPassName() const;
55 void getAnalysisUsage(AnalysisUsage &AU) const;
57 bool doInitialization(Module &M);
58 bool runOnFunction(Function &F);
62 /// MachineCodeAnalysis - This is a target-independent pass over the machine
63 /// function representation to identify safe points for the garbage collector
64 /// in the machine code. It inserts labels at safe points and populates a
65 /// GCMetadata record for each function.
66 class MachineCodeAnalysis : public MachineFunctionPass {
67 const TargetMachine *TM;
69 MachineModuleInfo *MMI;
70 const TargetInstrInfo *TII;
72 void FindSafePoints(MachineFunction &MF);
73 void VisitCallPoint(MachineBasicBlock::iterator MI);
74 MCSymbol *InsertLabel(MachineBasicBlock &MBB,
75 MachineBasicBlock::iterator MI,
78 void FindStackOffsets(MachineFunction &MF);
83 MachineCodeAnalysis();
84 const char *getPassName() const;
85 void getAnalysisUsage(AnalysisUsage &AU) const;
87 bool runOnMachineFunction(MachineFunction &MF);
92 // -----------------------------------------------------------------------------
94 GCStrategy::GCStrategy() :
96 CustomReadBarriers(false),
97 CustomWriteBarriers(false),
103 GCStrategy::~GCStrategy() {
104 for (iterator I = begin(), E = end(); I != E; ++I)
110 bool GCStrategy::initializeCustomLowering(Module &M) { return false; }
112 bool GCStrategy::performCustomLowering(Function &F) {
113 dbgs() << "gc " << getName() << " must override performCustomLowering.\n";
118 GCFunctionInfo *GCStrategy::insertFunctionInfo(const Function &F) {
119 GCFunctionInfo *FI = new GCFunctionInfo(F, *this);
120 Functions.push_back(FI);
124 // -----------------------------------------------------------------------------
126 FunctionPass *llvm::createGCLoweringPass() {
127 return new LowerIntrinsics();
130 char LowerIntrinsics::ID = 0;
132 LowerIntrinsics::LowerIntrinsics()
133 : FunctionPass(ID) {}
135 const char *LowerIntrinsics::getPassName() const {
136 return "Lower Garbage Collection Instructions";
139 void LowerIntrinsics::getAnalysisUsage(AnalysisUsage &AU) const {
140 FunctionPass::getAnalysisUsage(AU);
141 AU.addRequired<GCModuleInfo>();
144 /// doInitialization - If this module uses the GC intrinsics, find them now.
145 bool LowerIntrinsics::doInitialization(Module &M) {
146 // FIXME: This is rather antisocial in the context of a JIT since it performs
147 // work against the entire module. But this cannot be done at
148 // runFunction time (initializeCustomLowering likely needs to change
150 GCModuleInfo *MI = getAnalysisIfAvailable<GCModuleInfo>();
151 assert(MI && "LowerIntrinsics didn't require GCModuleInfo!?");
152 for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I)
153 if (!I->isDeclaration() && I->hasGC())
154 MI->getFunctionInfo(*I); // Instantiate the GC strategy.
156 bool MadeChange = false;
157 for (GCModuleInfo::iterator I = MI->begin(), E = MI->end(); I != E; ++I)
158 if (NeedsCustomLoweringPass(**I))
159 if ((*I)->initializeCustomLowering(M))
165 bool LowerIntrinsics::InsertRootInitializers(Function &F, AllocaInst **Roots,
167 // Scroll past alloca instructions.
168 BasicBlock::iterator IP = F.getEntryBlock().begin();
169 while (isa<AllocaInst>(IP)) ++IP;
171 // Search for initializers in the initial BB.
172 SmallPtrSet<AllocaInst*,16> InitedRoots;
173 for (; !CouldBecomeSafePoint(IP); ++IP)
174 if (StoreInst *SI = dyn_cast<StoreInst>(IP))
176 dyn_cast<AllocaInst>(SI->getOperand(1)->stripPointerCasts()))
177 InitedRoots.insert(AI);
179 // Add root initializers.
180 bool MadeChange = false;
182 for (AllocaInst **I = Roots, **E = Roots + Count; I != E; ++I)
183 if (!InitedRoots.count(*I)) {
184 StoreInst* SI = new StoreInst(ConstantPointerNull::get(cast<PointerType>(
185 cast<PointerType>((*I)->getType())->getElementType())),
194 bool LowerIntrinsics::NeedsDefaultLoweringPass(const GCStrategy &C) {
195 // Default lowering is necessary only if read or write barriers have a default
196 // action. The default for roots is no action.
197 return !C.customWriteBarrier()
198 || !C.customReadBarrier()
199 || C.initializeRoots();
202 bool LowerIntrinsics::NeedsCustomLoweringPass(const GCStrategy &C) {
203 // Custom lowering is only necessary if enabled for some action.
204 return C.customWriteBarrier()
205 || C.customReadBarrier()
209 /// CouldBecomeSafePoint - Predicate to conservatively determine whether the
210 /// instruction could introduce a safe point.
211 bool LowerIntrinsics::CouldBecomeSafePoint(Instruction *I) {
212 // The natural definition of instructions which could introduce safe points
215 // - call, invoke (AfterCall, BeforeCall)
217 // - invoke, ret, unwind (Exit)
219 // However, instructions as seemingly inoccuous as arithmetic can become
220 // libcalls upon lowering (e.g., div i64 on a 32-bit platform), so instead
221 // it is necessary to take a conservative approach.
223 if (isa<AllocaInst>(I) || isa<GetElementPtrInst>(I) ||
224 isa<StoreInst>(I) || isa<LoadInst>(I))
227 // llvm.gcroot is safe because it doesn't do anything at runtime.
228 if (CallInst *CI = dyn_cast<CallInst>(I))
229 if (Function *F = CI->getCalledFunction())
230 if (unsigned IID = F->getIntrinsicID())
231 if (IID == Intrinsic::gcroot)
237 /// runOnFunction - Replace gcread/gcwrite intrinsics with loads and stores.
238 /// Leave gcroot intrinsics; the code generator needs to see those.
239 bool LowerIntrinsics::runOnFunction(Function &F) {
240 // Quick exit for functions that do not use GC.
244 GCFunctionInfo &FI = getAnalysis<GCModuleInfo>().getFunctionInfo(F);
245 GCStrategy &S = FI.getStrategy();
247 bool MadeChange = false;
249 if (NeedsDefaultLoweringPass(S))
250 MadeChange |= PerformDefaultLowering(F, S);
252 if (NeedsCustomLoweringPass(S))
253 MadeChange |= S.performCustomLowering(F);
258 bool LowerIntrinsics::PerformDefaultLowering(Function &F, GCStrategy &S) {
259 bool LowerWr = !S.customWriteBarrier();
260 bool LowerRd = !S.customReadBarrier();
261 bool InitRoots = S.initializeRoots();
263 SmallVector<AllocaInst*, 32> Roots;
265 bool MadeChange = false;
266 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) {
267 for (BasicBlock::iterator II = BB->begin(), E = BB->end(); II != E;) {
268 if (IntrinsicInst *CI = dyn_cast<IntrinsicInst>(II++)) {
269 Function *F = CI->getCalledFunction();
270 switch (F->getIntrinsicID()) {
271 case Intrinsic::gcwrite:
273 // Replace a write barrier with a simple store.
274 Value *St = new StoreInst(CI->getArgOperand(0),
275 CI->getArgOperand(2), CI);
276 CI->replaceAllUsesWith(St);
277 CI->eraseFromParent();
280 case Intrinsic::gcread:
282 // Replace a read barrier with a simple load.
283 Value *Ld = new LoadInst(CI->getArgOperand(1), "", CI);
285 CI->replaceAllUsesWith(Ld);
286 CI->eraseFromParent();
289 case Intrinsic::gcroot:
291 // Initialize the GC root, but do not delete the intrinsic. The
292 // backend needs the intrinsic to flag the stack slot.
293 Roots.push_back(cast<AllocaInst>(
294 CI->getArgOperand(0)->stripPointerCasts()));
307 MadeChange |= InsertRootInitializers(F, Roots.begin(), Roots.size());
312 // -----------------------------------------------------------------------------
314 FunctionPass *llvm::createGCMachineCodeAnalysisPass() {
315 return new MachineCodeAnalysis();
318 char MachineCodeAnalysis::ID = 0;
320 MachineCodeAnalysis::MachineCodeAnalysis()
321 : MachineFunctionPass(ID) {}
323 const char *MachineCodeAnalysis::getPassName() const {
324 return "Analyze Machine Code For Garbage Collection";
327 void MachineCodeAnalysis::getAnalysisUsage(AnalysisUsage &AU) const {
328 MachineFunctionPass::getAnalysisUsage(AU);
329 AU.setPreservesAll();
330 AU.addRequired<MachineModuleInfo>();
331 AU.addRequired<GCModuleInfo>();
334 MCSymbol *MachineCodeAnalysis::InsertLabel(MachineBasicBlock &MBB,
335 MachineBasicBlock::iterator MI,
337 MCSymbol *Label = MBB.getParent()->getContext().CreateTempSymbol();
338 BuildMI(MBB, MI, DL, TII->get(TargetOpcode::GC_LABEL)).addSym(Label);
342 void MachineCodeAnalysis::VisitCallPoint(MachineBasicBlock::iterator CI) {
343 // Find the return address (next instruction), too, so as to bracket the call
345 MachineBasicBlock::iterator RAI = CI;
348 if (FI->getStrategy().needsSafePoint(GC::PreCall))
349 FI->addSafePoint(GC::PreCall, InsertLabel(*CI->getParent(), CI,
352 if (FI->getStrategy().needsSafePoint(GC::PostCall))
353 FI->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 const TargetRegisterInfo *TRI = TM->getRegisterInfo();
368 assert(TRI && "TargetRegisterInfo not available!");
370 for (GCFunctionInfo::roots_iterator RI = FI->roots_begin(),
371 RE = FI->roots_end(); RI != RE; ++RI)
372 RI->StackOffset = TRI->getFrameIndexOffset(MF, RI->Num);
375 bool MachineCodeAnalysis::runOnMachineFunction(MachineFunction &MF) {
376 // Quick exit for functions that do not use GC.
377 if (!MF.getFunction()->hasGC())
380 FI = &getAnalysis<GCModuleInfo>().getFunctionInfo(*MF.getFunction());
381 if (!FI->getStrategy().needsSafePoints())
384 TM = &MF.getTarget();
385 MMI = &getAnalysis<MachineModuleInfo>();
386 TII = TM->getInstrInfo();
388 // Find the size of the stack frame.
389 FI->setFrameSize(MF.getFrameInfo()->getStackSize());
391 // Find all safe points.
394 // Find the stack offsets for all roots.
395 FindStackOffsets(MF);