[llvm-exegesis] Fix missing std::move.
[llvm-complete.git] / lib / CodeGen / GCRootLowering.cpp
blob31ddeadbd97a13e1576913d346e88f89bbb72ef0
1 //===-- GCRootLowering.cpp - Garbage collection infrastructure ------------===//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This file implements the lowering for the gc.root mechanism.
12 //===----------------------------------------------------------------------===//
14 #include "llvm/CodeGen/GCMetadata.h"
15 #include "llvm/CodeGen/GCStrategy.h"
16 #include "llvm/CodeGen/MachineFrameInfo.h"
17 #include "llvm/CodeGen/MachineFunctionPass.h"
18 #include "llvm/CodeGen/MachineInstrBuilder.h"
19 #include "llvm/CodeGen/MachineModuleInfo.h"
20 #include "llvm/CodeGen/Passes.h"
21 #include "llvm/CodeGen/TargetFrameLowering.h"
22 #include "llvm/CodeGen/TargetInstrInfo.h"
23 #include "llvm/CodeGen/TargetRegisterInfo.h"
24 #include "llvm/CodeGen/TargetSubtargetInfo.h"
25 #include "llvm/IR/Dominators.h"
26 #include "llvm/IR/IntrinsicInst.h"
27 #include "llvm/IR/Module.h"
28 #include "llvm/Support/Debug.h"
29 #include "llvm/Support/ErrorHandling.h"
30 #include "llvm/Support/raw_ostream.h"
32 using namespace llvm;
34 namespace {
36 /// LowerIntrinsics - This pass rewrites calls to the llvm.gcread or
37 /// llvm.gcwrite intrinsics, replacing them with simple loads and stores as
38 /// directed by the GCStrategy. It also performs automatic root initialization
39 /// and custom intrinsic lowering.
40 class LowerIntrinsics : public FunctionPass {
41 bool PerformDefaultLowering(Function &F, GCStrategy &S);
43 public:
44 static char ID;
46 LowerIntrinsics();
47 StringRef getPassName() const override;
48 void getAnalysisUsage(AnalysisUsage &AU) const override;
50 bool doInitialization(Module &M) override;
51 bool runOnFunction(Function &F) override;
54 /// GCMachineCodeAnalysis - This is a target-independent pass over the machine
55 /// function representation to identify safe points for the garbage collector
56 /// in the machine code. It inserts labels at safe points and populates a
57 /// GCMetadata record for each function.
58 class GCMachineCodeAnalysis : public MachineFunctionPass {
59 GCFunctionInfo *FI;
60 MachineModuleInfo *MMI;
61 const TargetInstrInfo *TII;
63 void FindSafePoints(MachineFunction &MF);
64 void VisitCallPoint(MachineBasicBlock::iterator CI);
65 MCSymbol *InsertLabel(MachineBasicBlock &MBB, MachineBasicBlock::iterator MI,
66 const DebugLoc &DL) const;
68 void FindStackOffsets(MachineFunction &MF);
70 public:
71 static char ID;
73 GCMachineCodeAnalysis();
74 void getAnalysisUsage(AnalysisUsage &AU) const override;
76 bool runOnMachineFunction(MachineFunction &MF) override;
80 // -----------------------------------------------------------------------------
82 INITIALIZE_PASS_BEGIN(LowerIntrinsics, "gc-lowering", "GC Lowering", false,
83 false)
84 INITIALIZE_PASS_DEPENDENCY(GCModuleInfo)
85 INITIALIZE_PASS_END(LowerIntrinsics, "gc-lowering", "GC Lowering", false, false)
87 FunctionPass *llvm::createGCLoweringPass() { return new LowerIntrinsics(); }
89 char LowerIntrinsics::ID = 0;
91 LowerIntrinsics::LowerIntrinsics() : FunctionPass(ID) {
92 initializeLowerIntrinsicsPass(*PassRegistry::getPassRegistry());
95 StringRef LowerIntrinsics::getPassName() const {
96 return "Lower Garbage Collection Instructions";
99 void LowerIntrinsics::getAnalysisUsage(AnalysisUsage &AU) const {
100 FunctionPass::getAnalysisUsage(AU);
101 AU.addRequired<GCModuleInfo>();
102 AU.addPreserved<DominatorTreeWrapperPass>();
105 static bool NeedsDefaultLoweringPass(const GCStrategy &C) {
106 // Default lowering is necessary only if read or write barriers have a default
107 // action. The default for roots is no action.
108 return !C.customWriteBarrier() || !C.customReadBarrier() ||
109 C.initializeRoots();
112 /// doInitialization - If this module uses the GC intrinsics, find them now.
113 bool LowerIntrinsics::doInitialization(Module &M) {
114 GCModuleInfo *MI = getAnalysisIfAvailable<GCModuleInfo>();
115 assert(MI && "LowerIntrinsics didn't require GCModuleInfo!?");
116 for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I)
117 if (!I->isDeclaration() && I->hasGC())
118 MI->getFunctionInfo(*I); // Instantiate the GC strategy.
120 return false;
123 /// CouldBecomeSafePoint - Predicate to conservatively determine whether the
124 /// instruction could introduce a safe point.
125 static bool CouldBecomeSafePoint(Instruction *I) {
126 // The natural definition of instructions which could introduce safe points
127 // are:
129 // - call, invoke (AfterCall, BeforeCall)
130 // - phis (Loops)
131 // - invoke, ret, unwind (Exit)
133 // However, instructions as seemingly inoccuous as arithmetic can become
134 // libcalls upon lowering (e.g., div i64 on a 32-bit platform), so instead
135 // it is necessary to take a conservative approach.
137 if (isa<AllocaInst>(I) || isa<GetElementPtrInst>(I) || isa<StoreInst>(I) ||
138 isa<LoadInst>(I))
139 return false;
141 // llvm.gcroot is safe because it doesn't do anything at runtime.
142 if (CallInst *CI = dyn_cast<CallInst>(I))
143 if (Function *F = CI->getCalledFunction())
144 if (Intrinsic::ID IID = F->getIntrinsicID())
145 if (IID == Intrinsic::gcroot)
146 return false;
148 return true;
151 static bool InsertRootInitializers(Function &F, AllocaInst **Roots,
152 unsigned Count) {
153 // Scroll past alloca instructions.
154 BasicBlock::iterator IP = F.getEntryBlock().begin();
155 while (isa<AllocaInst>(IP))
156 ++IP;
158 // Search for initializers in the initial BB.
159 SmallPtrSet<AllocaInst *, 16> InitedRoots;
160 for (; !CouldBecomeSafePoint(&*IP); ++IP)
161 if (StoreInst *SI = dyn_cast<StoreInst>(IP))
162 if (AllocaInst *AI =
163 dyn_cast<AllocaInst>(SI->getOperand(1)->stripPointerCasts()))
164 InitedRoots.insert(AI);
166 // Add root initializers.
167 bool MadeChange = false;
169 for (AllocaInst **I = Roots, **E = Roots + Count; I != E; ++I)
170 if (!InitedRoots.count(*I)) {
171 StoreInst *SI = new StoreInst(
172 ConstantPointerNull::get(cast<PointerType>((*I)->getAllocatedType())),
173 *I);
174 SI->insertAfter(*I);
175 MadeChange = true;
178 return MadeChange;
181 /// runOnFunction - Replace gcread/gcwrite intrinsics with loads and stores.
182 /// Leave gcroot intrinsics; the code generator needs to see those.
183 bool LowerIntrinsics::runOnFunction(Function &F) {
184 // Quick exit for functions that do not use GC.
185 if (!F.hasGC())
186 return false;
188 GCFunctionInfo &FI = getAnalysis<GCModuleInfo>().getFunctionInfo(F);
189 GCStrategy &S = FI.getStrategy();
191 bool MadeChange = false;
193 if (NeedsDefaultLoweringPass(S))
194 MadeChange |= PerformDefaultLowering(F, S);
196 return MadeChange;
199 bool LowerIntrinsics::PerformDefaultLowering(Function &F, GCStrategy &S) {
200 bool LowerWr = !S.customWriteBarrier();
201 bool LowerRd = !S.customReadBarrier();
202 bool InitRoots = S.initializeRoots();
204 SmallVector<AllocaInst *, 32> Roots;
206 bool MadeChange = false;
207 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) {
208 for (BasicBlock::iterator II = BB->begin(), E = BB->end(); II != E;) {
209 if (IntrinsicInst *CI = dyn_cast<IntrinsicInst>(II++)) {
210 Function *F = CI->getCalledFunction();
211 switch (F->getIntrinsicID()) {
212 case Intrinsic::gcwrite:
213 if (LowerWr) {
214 // Replace a write barrier with a simple store.
215 Value *St =
216 new StoreInst(CI->getArgOperand(0), CI->getArgOperand(2), CI);
217 CI->replaceAllUsesWith(St);
218 CI->eraseFromParent();
220 break;
221 case Intrinsic::gcread:
222 if (LowerRd) {
223 // Replace a read barrier with a simple load.
224 Value *Ld = new LoadInst(CI->getArgOperand(1), "", CI);
225 Ld->takeName(CI);
226 CI->replaceAllUsesWith(Ld);
227 CI->eraseFromParent();
229 break;
230 case Intrinsic::gcroot:
231 if (InitRoots) {
232 // Initialize the GC root, but do not delete the intrinsic. The
233 // backend needs the intrinsic to flag the stack slot.
234 Roots.push_back(
235 cast<AllocaInst>(CI->getArgOperand(0)->stripPointerCasts()));
237 break;
238 default:
239 continue;
242 MadeChange = true;
247 if (Roots.size())
248 MadeChange |= InsertRootInitializers(F, Roots.begin(), Roots.size());
250 return MadeChange;
253 // -----------------------------------------------------------------------------
255 char GCMachineCodeAnalysis::ID = 0;
256 char &llvm::GCMachineCodeAnalysisID = GCMachineCodeAnalysis::ID;
258 INITIALIZE_PASS(GCMachineCodeAnalysis, "gc-analysis",
259 "Analyze Machine Code For Garbage Collection", false, false)
261 GCMachineCodeAnalysis::GCMachineCodeAnalysis() : MachineFunctionPass(ID) {}
263 void GCMachineCodeAnalysis::getAnalysisUsage(AnalysisUsage &AU) const {
264 MachineFunctionPass::getAnalysisUsage(AU);
265 AU.setPreservesAll();
266 AU.addRequired<MachineModuleInfo>();
267 AU.addRequired<GCModuleInfo>();
270 MCSymbol *GCMachineCodeAnalysis::InsertLabel(MachineBasicBlock &MBB,
271 MachineBasicBlock::iterator MI,
272 const DebugLoc &DL) const {
273 MCSymbol *Label = MBB.getParent()->getContext().createTempSymbol();
274 BuildMI(MBB, MI, DL, TII->get(TargetOpcode::GC_LABEL)).addSym(Label);
275 return Label;
278 void GCMachineCodeAnalysis::VisitCallPoint(MachineBasicBlock::iterator CI) {
279 // Find the return address (next instruction), too, so as to bracket the call
280 // instruction.
281 MachineBasicBlock::iterator RAI = CI;
282 ++RAI;
284 if (FI->getStrategy().needsSafePoint(GC::PreCall)) {
285 MCSymbol *Label = InsertLabel(*CI->getParent(), CI, CI->getDebugLoc());
286 FI->addSafePoint(GC::PreCall, Label, CI->getDebugLoc());
289 if (FI->getStrategy().needsSafePoint(GC::PostCall)) {
290 MCSymbol *Label = InsertLabel(*CI->getParent(), RAI, CI->getDebugLoc());
291 FI->addSafePoint(GC::PostCall, Label, CI->getDebugLoc());
295 void GCMachineCodeAnalysis::FindSafePoints(MachineFunction &MF) {
296 for (MachineFunction::iterator BBI = MF.begin(), BBE = MF.end(); BBI != BBE;
297 ++BBI)
298 for (MachineBasicBlock::iterator MI = BBI->begin(), ME = BBI->end();
299 MI != ME; ++MI)
300 if (MI->isCall()) {
301 // Do not treat tail or sibling call sites as safe points. This is
302 // legal since any arguments passed to the callee which live in the
303 // remnants of the callers frame will be owned and updated by the
304 // callee if required.
305 if (MI->isTerminator())
306 continue;
307 VisitCallPoint(MI);
311 void GCMachineCodeAnalysis::FindStackOffsets(MachineFunction &MF) {
312 const TargetFrameLowering *TFI = MF.getSubtarget().getFrameLowering();
313 assert(TFI && "TargetRegisterInfo not available!");
315 for (GCFunctionInfo::roots_iterator RI = FI->roots_begin();
316 RI != FI->roots_end();) {
317 // If the root references a dead object, no need to keep it.
318 if (MF.getFrameInfo().isDeadObjectIndex(RI->Num)) {
319 RI = FI->removeStackRoot(RI);
320 } else {
321 unsigned FrameReg; // FIXME: surely GCRoot ought to store the
322 // register that the offset is from?
323 RI->StackOffset = TFI->getFrameIndexReference(MF, RI->Num, FrameReg);
324 ++RI;
329 bool GCMachineCodeAnalysis::runOnMachineFunction(MachineFunction &MF) {
330 // Quick exit for functions that do not use GC.
331 if (!MF.getFunction().hasGC())
332 return false;
334 FI = &getAnalysis<GCModuleInfo>().getFunctionInfo(MF.getFunction());
335 MMI = &getAnalysis<MachineModuleInfo>();
336 TII = MF.getSubtarget().getInstrInfo();
338 // Find the size of the stack frame. There may be no correct static frame
339 // size, we use UINT64_MAX to represent this.
340 const MachineFrameInfo &MFI = MF.getFrameInfo();
341 const TargetRegisterInfo *RegInfo = MF.getSubtarget().getRegisterInfo();
342 const bool DynamicFrameSize = MFI.hasVarSizedObjects() ||
343 RegInfo->needsStackRealignment(MF);
344 FI->setFrameSize(DynamicFrameSize ? UINT64_MAX : MFI.getStackSize());
346 // Find all safe points.
347 if (FI->getStrategy().needsSafePoints())
348 FindSafePoints(MF);
350 // Find the concrete stack offsets for all roots (stack slots)
351 FindStackOffsets(MF);
353 return false;