1 //===-- GCRootLowering.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 the lowering for the gc.root mechanism.
12 //===----------------------------------------------------------------------===//
14 #include "llvm/CodeGen/GCMetadata.h"
15 #include "llvm/CodeGen/MachineFrameInfo.h"
16 #include "llvm/CodeGen/MachineFunctionPass.h"
17 #include "llvm/CodeGen/MachineInstrBuilder.h"
18 #include "llvm/CodeGen/MachineModuleInfo.h"
19 #include "llvm/CodeGen/GCStrategy.h"
20 #include "llvm/CodeGen/Passes.h"
21 #include "llvm/IR/Dominators.h"
22 #include "llvm/IR/IntrinsicInst.h"
23 #include "llvm/IR/Module.h"
24 #include "llvm/Support/Debug.h"
25 #include "llvm/Support/ErrorHandling.h"
26 #include "llvm/Support/raw_ostream.h"
27 #include "llvm/Target/TargetFrameLowering.h"
28 #include "llvm/Target/TargetInstrInfo.h"
29 #include "llvm/Target/TargetMachine.h"
30 #include "llvm/Target/TargetRegisterInfo.h"
31 #include "llvm/Target/TargetSubtargetInfo.h"
37 /// LowerIntrinsics - This pass rewrites calls to the llvm.gcread or
38 /// llvm.gcwrite intrinsics, replacing them with simple loads and stores as
39 /// directed by the GCStrategy. It also performs automatic root initialization
40 /// and custom intrinsic lowering.
41 class LowerIntrinsics : public FunctionPass {
42 bool PerformDefaultLowering(Function &F, GCStrategy &Coll);
48 const char *getPassName() const override;
49 void getAnalysisUsage(AnalysisUsage &AU) const override;
51 bool doInitialization(Module &M) override;
52 bool runOnFunction(Function &F) override;
55 /// GCMachineCodeAnalysis - This is a target-independent pass over the machine
56 /// function representation to identify safe points for the garbage collector
57 /// in the machine code. It inserts labels at safe points and populates a
58 /// GCMetadata record for each function.
59 class GCMachineCodeAnalysis : public MachineFunctionPass {
60 const TargetMachine *TM;
62 MachineModuleInfo *MMI;
63 const TargetInstrInfo *TII;
65 void FindSafePoints(MachineFunction &MF);
66 void VisitCallPoint(MachineBasicBlock::iterator MI);
67 MCSymbol *InsertLabel(MachineBasicBlock &MBB, MachineBasicBlock::iterator MI,
70 void FindStackOffsets(MachineFunction &MF);
75 GCMachineCodeAnalysis();
76 void getAnalysisUsage(AnalysisUsage &AU) const override;
78 bool runOnMachineFunction(MachineFunction &MF) override;
82 // -----------------------------------------------------------------------------
84 INITIALIZE_PASS_BEGIN(LowerIntrinsics, "gc-lowering", "GC Lowering", false,
86 INITIALIZE_PASS_DEPENDENCY(GCModuleInfo)
87 INITIALIZE_PASS_END(LowerIntrinsics, "gc-lowering", "GC Lowering", false, false)
89 FunctionPass *llvm::createGCLoweringPass() { return new LowerIntrinsics(); }
91 char LowerIntrinsics::ID = 0;
93 LowerIntrinsics::LowerIntrinsics() : FunctionPass(ID) {
94 initializeLowerIntrinsicsPass(*PassRegistry::getPassRegistry());
97 const char *LowerIntrinsics::getPassName() const {
98 return "Lower Garbage Collection Instructions";
101 void LowerIntrinsics::getAnalysisUsage(AnalysisUsage &AU) const {
102 FunctionPass::getAnalysisUsage(AU);
103 AU.addRequired<GCModuleInfo>();
104 AU.addPreserved<DominatorTreeWrapperPass>();
107 static bool NeedsDefaultLoweringPass(const GCStrategy &C) {
108 // Default lowering is necessary only if read or write barriers have a default
109 // action. The default for roots is no action.
110 return !C.customWriteBarrier() || !C.customReadBarrier() ||
114 static bool NeedsCustomLoweringPass(const GCStrategy &C) {
115 // Custom lowering is only necessary if enabled for some action.
116 return C.customWriteBarrier() || C.customReadBarrier() || C.customRoots();
119 /// doInitialization - If this module uses the GC intrinsics, find them now.
120 bool LowerIntrinsics::doInitialization(Module &M) {
121 // FIXME: This is rather antisocial in the context of a JIT since it performs
122 // work against the entire module. But this cannot be done at
123 // runFunction time (initializeCustomLowering likely needs to change
125 GCModuleInfo *MI = getAnalysisIfAvailable<GCModuleInfo>();
126 assert(MI && "LowerIntrinsics didn't require GCModuleInfo!?");
127 for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I)
128 if (!I->isDeclaration() && I->hasGC())
129 MI->getFunctionInfo(*I); // Instantiate the GC strategy.
131 bool MadeChange = false;
132 for (GCModuleInfo::iterator I = MI->begin(), E = MI->end(); I != E; ++I)
133 if (NeedsCustomLoweringPass(**I))
134 if ((*I)->initializeCustomLowering(M))
140 /// CouldBecomeSafePoint - Predicate to conservatively determine whether the
141 /// instruction could introduce a safe point.
142 static bool CouldBecomeSafePoint(Instruction *I) {
143 // The natural definition of instructions which could introduce safe points
146 // - call, invoke (AfterCall, BeforeCall)
148 // - invoke, ret, unwind (Exit)
150 // However, instructions as seemingly inoccuous as arithmetic can become
151 // libcalls upon lowering (e.g., div i64 on a 32-bit platform), so instead
152 // it is necessary to take a conservative approach.
154 if (isa<AllocaInst>(I) || isa<GetElementPtrInst>(I) || isa<StoreInst>(I) ||
158 // llvm.gcroot is safe because it doesn't do anything at runtime.
159 if (CallInst *CI = dyn_cast<CallInst>(I))
160 if (Function *F = CI->getCalledFunction())
161 if (unsigned IID = F->getIntrinsicID())
162 if (IID == Intrinsic::gcroot)
168 static bool InsertRootInitializers(Function &F, AllocaInst **Roots,
170 // Scroll past alloca instructions.
171 BasicBlock::iterator IP = F.getEntryBlock().begin();
172 while (isa<AllocaInst>(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 StoreInst *SI = new StoreInst(
189 ConstantPointerNull::get(cast<PointerType>(
190 cast<PointerType>((*I)->getType())->getElementType())),
199 /// runOnFunction - Replace gcread/gcwrite intrinsics with loads and stores.
200 /// Leave gcroot intrinsics; the code generator needs to see those.
201 bool LowerIntrinsics::runOnFunction(Function &F) {
202 // Quick exit for functions that do not use GC.
206 GCFunctionInfo &FI = getAnalysis<GCModuleInfo>().getFunctionInfo(F);
207 GCStrategy &S = FI.getStrategy();
209 bool MadeChange = false;
211 if (NeedsDefaultLoweringPass(S))
212 MadeChange |= PerformDefaultLowering(F, S);
214 bool UseCustomLoweringPass = NeedsCustomLoweringPass(S);
215 if (UseCustomLoweringPass)
216 MadeChange |= S.performCustomLowering(F);
218 // Custom lowering may modify the CFG, so dominators must be recomputed.
219 if (UseCustomLoweringPass) {
220 if (DominatorTreeWrapperPass *DTWP =
221 getAnalysisIfAvailable<DominatorTreeWrapperPass>())
222 DTWP->getDomTree().recalculate(F);
228 bool LowerIntrinsics::PerformDefaultLowering(Function &F, GCStrategy &S) {
229 bool LowerWr = !S.customWriteBarrier();
230 bool LowerRd = !S.customReadBarrier();
231 bool InitRoots = S.initializeRoots();
233 SmallVector<AllocaInst *, 32> Roots;
235 bool MadeChange = false;
236 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) {
237 for (BasicBlock::iterator II = BB->begin(), E = BB->end(); II != E;) {
238 if (IntrinsicInst *CI = dyn_cast<IntrinsicInst>(II++)) {
239 Function *F = CI->getCalledFunction();
240 switch (F->getIntrinsicID()) {
241 case Intrinsic::gcwrite:
243 // Replace a write barrier with a simple store.
245 new StoreInst(CI->getArgOperand(0), CI->getArgOperand(2), CI);
246 CI->replaceAllUsesWith(St);
247 CI->eraseFromParent();
250 case Intrinsic::gcread:
252 // Replace a read barrier with a simple load.
253 Value *Ld = new LoadInst(CI->getArgOperand(1), "", CI);
255 CI->replaceAllUsesWith(Ld);
256 CI->eraseFromParent();
259 case Intrinsic::gcroot:
261 // Initialize the GC root, but do not delete the intrinsic. The
262 // backend needs the intrinsic to flag the stack slot.
264 cast<AllocaInst>(CI->getArgOperand(0)->stripPointerCasts()));
277 MadeChange |= InsertRootInitializers(F, Roots.begin(), Roots.size());
282 // -----------------------------------------------------------------------------
284 char GCMachineCodeAnalysis::ID = 0;
285 char &llvm::GCMachineCodeAnalysisID = GCMachineCodeAnalysis::ID;
287 INITIALIZE_PASS(GCMachineCodeAnalysis, "gc-analysis",
288 "Analyze Machine Code For Garbage Collection", false, false)
290 GCMachineCodeAnalysis::GCMachineCodeAnalysis() : MachineFunctionPass(ID) {}
292 void GCMachineCodeAnalysis::getAnalysisUsage(AnalysisUsage &AU) const {
293 MachineFunctionPass::getAnalysisUsage(AU);
294 AU.setPreservesAll();
295 AU.addRequired<MachineModuleInfo>();
296 AU.addRequired<GCModuleInfo>();
299 MCSymbol *GCMachineCodeAnalysis::InsertLabel(MachineBasicBlock &MBB,
300 MachineBasicBlock::iterator MI,
302 MCSymbol *Label = MBB.getParent()->getContext().CreateTempSymbol();
303 BuildMI(MBB, MI, DL, TII->get(TargetOpcode::GC_LABEL)).addSym(Label);
307 void GCMachineCodeAnalysis::VisitCallPoint(MachineBasicBlock::iterator CI) {
308 // Find the return address (next instruction), too, so as to bracket the call
310 MachineBasicBlock::iterator RAI = CI;
313 if (FI->getStrategy().needsSafePoint(GC::PreCall)) {
314 MCSymbol *Label = InsertLabel(*CI->getParent(), CI, CI->getDebugLoc());
315 FI->addSafePoint(GC::PreCall, Label, CI->getDebugLoc());
318 if (FI->getStrategy().needsSafePoint(GC::PostCall)) {
319 MCSymbol *Label = InsertLabel(*CI->getParent(), RAI, CI->getDebugLoc());
320 FI->addSafePoint(GC::PostCall, Label, CI->getDebugLoc());
324 void GCMachineCodeAnalysis::FindSafePoints(MachineFunction &MF) {
325 for (MachineFunction::iterator BBI = MF.begin(), BBE = MF.end(); BBI != BBE;
327 for (MachineBasicBlock::iterator MI = BBI->begin(), ME = BBI->end();
330 // Do not treat tail or sibling call sites as safe points. This is
331 // legal since any arguments passed to the callee which live in the
332 // remnants of the callers frame will be owned and updated by the
333 // callee if required.
334 if (MI->isTerminator())
340 void GCMachineCodeAnalysis::FindStackOffsets(MachineFunction &MF) {
341 const TargetFrameLowering *TFI = TM->getSubtargetImpl()->getFrameLowering();
342 assert(TFI && "TargetRegisterInfo not available!");
344 for (GCFunctionInfo::roots_iterator RI = FI->roots_begin();
345 RI != FI->roots_end();) {
346 // If the root references a dead object, no need to keep it.
347 if (MF.getFrameInfo()->isDeadObjectIndex(RI->Num)) {
348 RI = FI->removeStackRoot(RI);
350 RI->StackOffset = TFI->getFrameIndexOffset(MF, RI->Num);
356 bool GCMachineCodeAnalysis::runOnMachineFunction(MachineFunction &MF) {
357 // Quick exit for functions that do not use GC.
358 if (!MF.getFunction()->hasGC())
361 FI = &getAnalysis<GCModuleInfo>().getFunctionInfo(*MF.getFunction());
362 if (!FI->getStrategy().needsSafePoints())
365 TM = &MF.getTarget();
366 MMI = &getAnalysis<MachineModuleInfo>();
367 TII = TM->getSubtargetImpl()->getInstrInfo();
369 // Find the size of the stack frame.
370 FI->setFrameSize(MF.getFrameInfo()->getStackSize());
372 // Find all safe points.
375 // Find the stack offsets for all roots.
376 FindStackOffsets(MF);