LLVM  12.0.0git
GCRootLowering.cpp
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1 //===-- GCRootLowering.cpp - Garbage collection infrastructure ------------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // This file implements the lowering for the gc.root mechanism.
10 //
11 //===----------------------------------------------------------------------===//
12 
19 #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/InitializePasses.h"
28 #include "llvm/Support/Debug.h"
31 
32 using namespace llvm;
33 
34 namespace {
35 
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 DoLowering(Function &F, GCStrategy &S);
42 
43 public:
44  static char ID;
45 
46  LowerIntrinsics();
47  StringRef getPassName() const override;
48  void getAnalysisUsage(AnalysisUsage &AU) const override;
49 
50  bool doInitialization(Module &M) override;
51  bool runOnFunction(Function &F) override;
52 };
53 
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  const TargetInstrInfo *TII;
61 
62  void FindSafePoints(MachineFunction &MF);
63  void VisitCallPoint(MachineBasicBlock::iterator CI);
65  const DebugLoc &DL) const;
66 
67  void FindStackOffsets(MachineFunction &MF);
68 
69 public:
70  static char ID;
71 
72  GCMachineCodeAnalysis();
73  void getAnalysisUsage(AnalysisUsage &AU) const override;
74 
75  bool runOnMachineFunction(MachineFunction &MF) override;
76 };
77 }
78 
79 // -----------------------------------------------------------------------------
80 
81 INITIALIZE_PASS_BEGIN(LowerIntrinsics, "gc-lowering", "GC Lowering", false,
82  false)
84 INITIALIZE_PASS_END(LowerIntrinsics, "gc-lowering", "GC Lowering", false, false)
85 
86 FunctionPass *llvm::createGCLoweringPass() { return new LowerIntrinsics(); }
87 
88 char LowerIntrinsics::ID = 0;
89 
90 LowerIntrinsics::LowerIntrinsics() : FunctionPass(ID) {
91  initializeLowerIntrinsicsPass(*PassRegistry::getPassRegistry());
92 }
93 
94 StringRef LowerIntrinsics::getPassName() const {
95  return "Lower Garbage Collection Instructions";
96 }
97 
98 void LowerIntrinsics::getAnalysisUsage(AnalysisUsage &AU) const {
99  FunctionPass::getAnalysisUsage(AU);
102 }
103 
104 /// doInitialization - If this module uses the GC intrinsics, find them now.
105 bool LowerIntrinsics::doInitialization(Module &M) {
106  GCModuleInfo *MI = getAnalysisIfAvailable<GCModuleInfo>();
107  assert(MI && "LowerIntrinsics didn't require GCModuleInfo!?");
108  for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I)
109  if (!I->isDeclaration() && I->hasGC())
110  MI->getFunctionInfo(*I); // Instantiate the GC strategy.
111 
112  return false;
113 }
114 
115 /// CouldBecomeSafePoint - Predicate to conservatively determine whether the
116 /// instruction could introduce a safe point.
118  // The natural definition of instructions which could introduce safe points
119  // are:
120  //
121  // - call, invoke (AfterCall, BeforeCall)
122  // - phis (Loops)
123  // - invoke, ret, unwind (Exit)
124  //
125  // However, instructions as seemingly inoccuous as arithmetic can become
126  // libcalls upon lowering (e.g., div i64 on a 32-bit platform), so instead
127  // it is necessary to take a conservative approach.
128 
129  if (isa<AllocaInst>(I) || isa<GetElementPtrInst>(I) || isa<StoreInst>(I) ||
130  isa<LoadInst>(I))
131  return false;
132 
133  // llvm.gcroot is safe because it doesn't do anything at runtime.
134  if (CallInst *CI = dyn_cast<CallInst>(I))
135  if (Function *F = CI->getCalledFunction())
136  if (Intrinsic::ID IID = F->getIntrinsicID())
137  if (IID == Intrinsic::gcroot)
138  return false;
139 
140  return true;
141 }
142 
144  // Scroll past alloca instructions.
145  BasicBlock::iterator IP = F.getEntryBlock().begin();
146  while (isa<AllocaInst>(IP))
147  ++IP;
148 
149  // Search for initializers in the initial BB.
150  SmallPtrSet<AllocaInst *, 16> InitedRoots;
151  for (; !CouldBecomeSafePoint(&*IP); ++IP)
152  if (StoreInst *SI = dyn_cast<StoreInst>(IP))
153  if (AllocaInst *AI =
154  dyn_cast<AllocaInst>(SI->getOperand(1)->stripPointerCasts()))
155  InitedRoots.insert(AI);
156 
157  // Add root initializers.
158  bool MadeChange = false;
159 
160  for (AllocaInst *Root : Roots)
161  if (!InitedRoots.count(Root)) {
162  new StoreInst(
163  ConstantPointerNull::get(cast<PointerType>(Root->getAllocatedType())),
164  Root, Root->getNextNode());
165  MadeChange = true;
166  }
167 
168  return MadeChange;
169 }
170 
171 /// runOnFunction - Replace gcread/gcwrite intrinsics with loads and stores.
172 /// Leave gcroot intrinsics; the code generator needs to see those.
174  // Quick exit for functions that do not use GC.
175  if (!F.hasGC())
176  return false;
177 
178  GCFunctionInfo &FI = getAnalysis<GCModuleInfo>().getFunctionInfo(F);
179  GCStrategy &S = FI.getStrategy();
180 
181  return DoLowering(F, S);
182 }
183 
184 /// Lower barriers out of existance (if the associated GCStrategy hasn't
185 /// already done so...), and insert initializing stores to roots as a defensive
186 /// measure. Given we're going to report all roots live at all safepoints, we
187 /// need to be able to ensure each root has been initialized by the point the
188 /// first safepoint is reached. This really should have been done by the
189 /// frontend, but the old API made this non-obvious, so we do a potentially
190 /// redundant store just in case.
191 bool LowerIntrinsics::DoLowering(Function &F, GCStrategy &S) {
193 
194  bool MadeChange = false;
195  for (BasicBlock &BB : F)
196  for (BasicBlock::iterator II = BB.begin(), E = BB.end(); II != E;) {
197  IntrinsicInst *CI = dyn_cast<IntrinsicInst>(II++);
198  if (!CI)
199  continue;
200 
201  Function *F = CI->getCalledFunction();
202  switch (F->getIntrinsicID()) {
203  default: break;
204  case Intrinsic::gcwrite: {
205  // Replace a write barrier with a simple store.
206  Value *St = new StoreInst(CI->getArgOperand(0),
207  CI->getArgOperand(2), CI);
208  CI->replaceAllUsesWith(St);
209  CI->eraseFromParent();
210  MadeChange = true;
211  break;
212  }
213  case Intrinsic::gcread: {
214  // Replace a read barrier with a simple load.
215  Value *Ld = new LoadInst(CI->getType(), CI->getArgOperand(1), "", CI);
216  Ld->takeName(CI);
217  CI->replaceAllUsesWith(Ld);
218  CI->eraseFromParent();
219  MadeChange = true;
220  break;
221  }
222  case Intrinsic::gcroot: {
223  // Initialize the GC root, but do not delete the intrinsic. The
224  // backend needs the intrinsic to flag the stack slot.
225  Roots.push_back(
226  cast<AllocaInst>(CI->getArgOperand(0)->stripPointerCasts()));
227  break;
228  }
229  }
230  }
231 
232  if (Roots.size())
233  MadeChange |= InsertRootInitializers(F, Roots);
234 
235  return MadeChange;
236 }
237 
238 // -----------------------------------------------------------------------------
239 
242 
243 INITIALIZE_PASS(GCMachineCodeAnalysis, "gc-analysis",
244  "Analyze Machine Code For Garbage Collection", false, false)
245 
246 GCMachineCodeAnalysis::GCMachineCodeAnalysis() : MachineFunctionPass(ID) {}
247 
248 void GCMachineCodeAnalysis::getAnalysisUsage(AnalysisUsage &AU) const {
249  MachineFunctionPass::getAnalysisUsage(AU);
250  AU.setPreservesAll();
252 }
253 
254 MCSymbol *GCMachineCodeAnalysis::InsertLabel(MachineBasicBlock &MBB,
256  const DebugLoc &DL) const {
258  BuildMI(MBB, MI, DL, TII->get(TargetOpcode::GC_LABEL)).addSym(Label);
259  return Label;
260 }
261 
262 void GCMachineCodeAnalysis::VisitCallPoint(MachineBasicBlock::iterator CI) {
263  // Find the return address (next instruction), since that's what will be on
264  // the stack when the call is suspended and we need to inspect the stack.
266  ++RAI;
267 
268  MCSymbol *Label = InsertLabel(*CI->getParent(), RAI, CI->getDebugLoc());
269  FI->addSafePoint(Label, CI->getDebugLoc());
270 }
271 
272 void GCMachineCodeAnalysis::FindSafePoints(MachineFunction &MF) {
273  for (MachineBasicBlock &MBB : MF)
274  for (MachineBasicBlock::iterator MI = MBB.begin(), ME = MBB.end();
275  MI != ME; ++MI)
276  if (MI->isCall()) {
277  // Do not treat tail or sibling call sites as safe points. This is
278  // legal since any arguments passed to the callee which live in the
279  // remnants of the callers frame will be owned and updated by the
280  // callee if required.
281  if (MI->isTerminator())
282  continue;
283  VisitCallPoint(MI);
284  }
285 }
286 
287 void GCMachineCodeAnalysis::FindStackOffsets(MachineFunction &MF) {
289  assert(TFI && "TargetRegisterInfo not available!");
290 
292  RI != FI->roots_end();) {
293  // If the root references a dead object, no need to keep it.
294  if (MF.getFrameInfo().isDeadObjectIndex(RI->Num)) {
295  RI = FI->removeStackRoot(RI);
296  } else {
297  Register FrameReg; // FIXME: surely GCRoot ought to store the
298  // register that the offset is from?
299  auto FrameOffset = TFI->getFrameIndexReference(MF, RI->Num, FrameReg);
300  assert(!FrameOffset.getScalable() &&
301  "Frame offsets with a scalable component are not supported");
302  RI->StackOffset = FrameOffset.getFixed();
303  ++RI;
304  }
305  }
306 }
307 
308 bool GCMachineCodeAnalysis::runOnMachineFunction(MachineFunction &MF) {
309  // Quick exit for functions that do not use GC.
310  if (!MF.getFunction().hasGC())
311  return false;
312 
313  FI = &getAnalysis<GCModuleInfo>().getFunctionInfo(MF.getFunction());
314  TII = MF.getSubtarget().getInstrInfo();
315 
316  // Find the size of the stack frame. There may be no correct static frame
317  // size, we use UINT64_MAX to represent this.
318  const MachineFrameInfo &MFI = MF.getFrameInfo();
319  const TargetRegisterInfo *RegInfo = MF.getSubtarget().getRegisterInfo();
320  const bool DynamicFrameSize = MFI.hasVarSizedObjects() ||
321  RegInfo->needsStackRealignment(MF);
322  FI->setFrameSize(DynamicFrameSize ? UINT64_MAX : MFI.getStackSize());
323 
324  // Find all safe points.
325  if (FI->getStrategy().needsSafePoints())
326  FindSafePoints(MF);
327 
328  // Find the concrete stack offsets for all roots (stack slots)
329  FindStackOffsets(MF);
330 
331  return false;
332 }
INITIALIZE_PASS(GCMachineCodeAnalysis, "gc-analysis", "Analyze Machine Code For Garbage Collection", false, false) GCMachineCodeAnalysis
MCSymbol * createTempSymbol()
Create a temporary symbol with a unique name.
Definition: MCContext.cpp:253
SymbolTableList< Instruction >::iterator eraseFromParent()
This method unlinks 'this' from the containing basic block and deletes it.
Definition: Instruction.cpp:77
AnalysisUsage & addPreserved()
Add the specified Pass class to the set of analyses preserved by this pass.
This class represents lattice values for constants.
Definition: AllocatorList.h:23
MCSymbol - Instances of this class represent a symbol name in the MC file, and MCSymbols are created ...
Definition: MCSymbol.h:41
A Module instance is used to store all the information related to an LLVM module.
Definition: Module.h:67
static bool InsertRootInitializers(Function &F, ArrayRef< AllocaInst * > Roots)
Shadow Stack GC Lowering
virtual const TargetRegisterInfo * getRegisterInfo() const
getRegisterInfo - If register information is available, return it.
bool isDeadObjectIndex(int ObjectIdx) const
Returns true if the specified index corresponds to a dead object.
This class represents a function call, abstracting a target machine's calling convention.
static bool CouldBecomeSafePoint(Instruction *I)
CouldBecomeSafePoint - Predicate to conservatively determine whether the instruction could introduce ...
A debug info location.
Definition: DebugLoc.h:33
F(f)
An instruction for reading from memory.
Definition: Instructions.h:174
Function & getFunction()
Return the LLVM function that this machine code represents.
MachineBasicBlock & MBB
Value * getArgOperand(unsigned i) const
Definition: InstrTypes.h:1323
AnalysisUsage & addRequired()
MachineFunctionPass - This class adapts the FunctionPass interface to allow convenient creation of pa...
const HexagonInstrInfo * TII
FunctionPass * createGCLoweringPass()
GCLowering Pass - Used by gc.root to perform its default lowering operations.
void initializeLowerIntrinsicsPass(PassRegistry &)
The MachineFrameInfo class represents an abstract stack frame until prolog/epilog code is inserted.
bool hasVarSizedObjects() const
This method may be called any time after instruction selection is complete to determine if the stack ...
An analysis pass which caches information about the entire Module.
Definition: GCMetadata.h:152
#define UINT64_MAX
Definition: DataTypes.h:77
Type * getType() const
All values are typed, get the type of this value.
Definition: Value.h:246
ArrayRef - Represent a constant reference to an array (0 or more elements consecutively in memory),...
Definition: APInt.h:32
An instruction for storing to memory.
Definition: Instructions.h:303
void replaceAllUsesWith(Value *V)
Change all uses of this to point to a new Value.
Definition: Value.cpp:523
virtual const TargetInstrInfo * getInstrInfo() const
void takeName(Value *V)
Transfer the name from V to this value.
Definition: Value.cpp:373
TargetInstrInfo - Interface to description of machine instruction set.
MCContext & getContext() const
MachineInstrBuilder BuildMI(MachineFunction &MF, const DebugLoc &DL, const MCInstrDesc &MCID)
Builder interface. Specify how to create the initial instruction itself.
static bool runOnFunction(Function &F, bool PostInlining)
roots_iterator roots_end()
Definition: GCMetadata.h:140
Root(llvm::StringRef Name="")
Definition: JSON.h:571
LLVM Basic Block Representation.
Definition: BasicBlock.h:58
const TargetSubtargetInfo & getSubtarget() const
getSubtarget - Return the subtarget for which this machine code is being compiled.
MachineFrameInfo & getFrameInfo()
getFrameInfo - Return the frame info object for the current function.
static GCRegistry::Add< CoreCLRGC > E("coreclr", "CoreCLR-compatible GC")
virtual StackOffset getFrameIndexReference(const MachineFunction &MF, int FI, Register &FrameReg) const
getFrameIndexReference - This method should return the base register and offset used to reference a f...
roots_iterator removeStackRoot(roots_iterator position)
removeStackRoot - Removes a root.
Definition: GCMetadata.h:118
std::pair< iterator, bool > insert(PtrType Ptr)
Inserts Ptr if and only if there is no element in the container equal to Ptr.
Definition: SmallPtrSet.h:364
GCStrategy & getStrategy()
getStrategy - Return the GC strategy for the function.
Definition: GCMetadata.h:108
Represent the analysis usage information of a pass.
void addSafePoint(MCSymbol *Label, const DebugLoc &DL)
addSafePoint - Notes the existence of a safe point.
Definition: GCMetadata.h:125
FunctionPass class - This class is used to implement most global optimizations.
Definition: Pass.h:298
size_type count(ConstPtrType Ptr) const
count - Return 1 if the specified pointer is in the set, 0 otherwise.
Definition: SmallPtrSet.h:375
rewrite statepoints for gc
roots_iterator roots_begin()
roots_begin/roots_end - Iterators for all roots in the function.
Definition: GCMetadata.h:139
const Value * stripPointerCasts() const
Strip off pointer casts, all-zero GEPs and address space casts.
Definition: Value.cpp:630
TargetRegisterInfo base class - We assume that the target defines a static array of TargetRegisterDes...
INITIALIZE_PASS_END(RegBankSelect, DEBUG_TYPE, "Assign register bank of generic virtual registers", false, false) RegBankSelect
std::vector< GCRoot >::iterator roots_iterator
Definition: GCMetadata.h:80
Iterator for intrusive lists based on ilist_node.
SmallPtrSet - This class implements a set which is optimized for holding SmallSize or less elements.
Definition: SmallPtrSet.h:442
This is a 'vector' (really, a variable-sized array), optimized for the case when the array is small.
Definition: SmallVector.h:1116
Module.h This file contains the declarations for the Module class.
Information about stack frame layout on the target.
void setPreservesAll()
Set by analyses that do not transform their input at all.
const MachineFunction * getParent() const
Return the MachineFunction containing this basic block.
GCStrategy describes a garbage collector algorithm's code generation requirements,...
Definition: GCStrategy.h:66
bool hasGC() const
hasGC/getGC/setGC/clearGC - The name of the garbage collection algorithm to use during code generatio...
Definition: Function.h:383
char & GCMachineCodeAnalysisID
GCMachineCodeAnalysis - Target-independent pass to mark safe points in machine code.
Function * getCalledFunction() const
Returns the function called, or null if this is an indirect function invocation.
Definition: InstrTypes.h:1378
#define I(x, y, z)
Definition: MD5.cpp:59
virtual const TargetFrameLowering * getFrameLowering() const
void setFrameSize(uint64_t S)
Definition: GCMetadata.h:131
assert(ImpDefSCC.getReg()==AMDGPU::SCC &&ImpDefSCC.isDef())
bool needsStackRealignment(const MachineFunction &MF) const
True if storage within the function requires the stack pointer to be aligned more than the normal cal...
LLVM Value Representation.
Definition: Value.h:75
IRTranslator LLVM IR MI
bool needsSafePoints() const
True if safe points need to be inferred on call sites.
Definition: GCStrategy.h:111
StringRef - Represent a constant reference to a string, i.e.
Definition: StringRef.h:57
Garbage collection metadata for a single function.
Definition: GCMetadata.h:77
Legacy analysis pass which computes a DominatorTree.
Definition: Dominators.h:278
INITIALIZE_PASS_BEGIN(LowerIntrinsics, "gc-lowering", "GC Lowering", false, false) FunctionPass *llvm
amdgpu printf runtime AMDGPU Printf lowering
uint64_t getStackSize() const
Return the number of bytes that must be allocated to hold all of the fixed size frame objects.
Wrapper class representing virtual and physical registers.
Definition: Register.h:19
A wrapper class for inspecting calls to intrinsic functions.
Definition: IntrinsicInst.h:44
an instruction to allocate memory on the stack
Definition: Instructions.h:61
INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
MachineBasicBlock MachineBasicBlock::iterator DebugLoc DL