Factor GC metadata table assembly generation out of Collector in preparation for splitting AsmPrinter into its own library.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@54881 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 441 insertions, 0 deletions

diff --git a/lib/CodeGen/ShadowStackGC.cpp b/lib/CodeGen/ShadowStackGC.cpp
new file mode 100644
index 0000000..850c005
--- /dev/null
+++ b/lib/CodeGen/ShadowStackGC.cpp
@@ -0,0 +1,441 @@
+//===-- ShadowStackCollector.cpp - GC support for uncooperative targets ---===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements lowering for the llvm.gc* intrinsics for targets that do
+// not natively support them (which includes the C backend). Note that the code
+// generated is not quite as efficient as collectors which generate stack maps
+// to identify roots.
+//
+// This pass implements the code transformation described in this paper:
+//   "Accurate Garbage Collection in an Uncooperative Environment"
+//   Fergus Henderson, ISMM, 2002
+//
+// In runtime/GC/SemiSpace.cpp is a prototype runtime which is compatible with
+// this collector.
+//
+// In order to support this particular transformation, all stack roots are
+// coallocated in the stack. This allows a fully target-independent stack map
+// while introducing only minor runtime overhead.
+//
+//===----------------------------------------------------------------------===//
+
+#define DEBUG_TYPE "shadowstackgc"
+#include "llvm/CodeGen/GCs.h"
+#include "llvm/ADT/StringExtras.h"
+#include "llvm/CodeGen/GCStrategy.h"
+#include "llvm/IntrinsicInst.h"
+#include "llvm/Module.h"
+#include "llvm/Support/IRBuilder.h"
+
+using namespace llvm;
+
+namespace {
+  
+  class VISIBILITY_HIDDEN ShadowStackCollector : public Collector {
+    /// RootChain - This is the global linked-list that contains the chain of GC
+    /// roots.
+    GlobalVariable *Head;
+    
+    /// StackEntryTy - Abstract type of a link in the shadow stack.
+    /// 
+    const StructType *StackEntryTy;
+    
+    /// Roots - GC roots in the current function. Each is a pair of the
+    /// intrinsic call and its corresponding alloca.
+    std::vector<std::pair<CallInst*,AllocaInst*> > Roots;
+    
+  public:
+    ShadowStackCollector();
+    
+    bool initializeCustomLowering(Module &M);
+    bool performCustomLowering(Function &F);
+    
+  private:
+    bool IsNullValue(Value *V);
+    Constant *GetFrameMap(Function &F);
+    const Type* GetConcreteStackEntryType(Function &F);
+    void CollectRoots(Function &F);
+    static GetElementPtrInst *CreateGEP(IRBuilder<> &B, Value *BasePtr,
+                                        int Idx1, const char *Name);
+    static GetElementPtrInst *CreateGEP(IRBuilder<> &B, Value *BasePtr,
+                                        int Idx1, int Idx2, const char *Name);
+  };
+
+}
+  
+static CollectorRegistry::Add<ShadowStackCollector>
+Y("shadow-stack",
+  "Very portable collector for uncooperative code generators");
+  
+namespace {
+  /// EscapeEnumerator - This is a little algorithm to find all escape points
+  /// from a function so that "finally"-style code can be inserted. In addition
+  /// to finding the existing return and unwind instructions, it also (if
+  /// necessary) transforms any call instructions into invokes and sends them to
+  /// a landing pad.
+  /// 
+  /// It's wrapped up in a state machine using the same transform C# uses for
+  /// 'yield return' enumerators, This transform allows it to be non-allocating.
+  class VISIBILITY_HIDDEN EscapeEnumerator {
+    Function &F;
+    const char *CleanupBBName;
+    
+    // State.
+    int State;
+    Function::iterator StateBB, StateE;
+    IRBuilder<> Builder;
+    
+  public:
+    EscapeEnumerator(Function &F, const char *N = "cleanup")
+      : F(F), CleanupBBName(N), State(0) {}
+    
+    IRBuilder<> *Next() {
+      switch (State) {
+      default:
+        return 0;
+        
+      case 0:
+        StateBB = F.begin();
+        StateE = F.end();
+        State = 1;
+        
+      case 1:
+        // Find all 'return' and 'unwind' instructions.
+        while (StateBB != StateE) {
+          BasicBlock *CurBB = StateBB++;
+          
+          // Branches and invokes do not escape, only unwind and return do.
+          TerminatorInst *TI = CurBB->getTerminator();
+          if (!isa<UnwindInst>(TI) && !isa<ReturnInst>(TI))
+            continue;
+          
+          Builder.SetInsertPoint(TI->getParent(), TI);
+          return &Builder;
+        }
+        
+        State = 2;
+        
+        // Find all 'call' instructions.
+        SmallVector<Instruction*,16> Calls;
+        for (Function::iterator BB = F.begin(),
+                                E = F.end(); BB != E; ++BB)
+          for (BasicBlock::iterator II = BB->begin(),
+                                    EE = BB->end(); II != EE; ++II)
+            if (CallInst *CI = dyn_cast<CallInst>(II))
+              if (!CI->getCalledFunction() ||
+                  !CI->getCalledFunction()->getIntrinsicID())
+                Calls.push_back(CI);
+        
+        if (Calls.empty())
+          return 0;
+        
+        // Create a cleanup block.
+        BasicBlock *CleanupBB = BasicBlock::Create(CleanupBBName, &F);
+        UnwindInst *UI = new UnwindInst(CleanupBB);
+        
+        // Transform the 'call' instructions into 'invoke's branching to the
+        // cleanup block. Go in reverse order to make prettier BB names.
+        SmallVector<Value*,16> Args;
+        for (unsigned I = Calls.size(); I != 0; ) {
+          CallInst *CI = cast<CallInst>(Calls[--I]);
+          
+          // Split the basic block containing the function call.
+          BasicBlock *CallBB = CI->getParent();
+          BasicBlock *NewBB =
+            CallBB->splitBasicBlock(CI, CallBB->getName() + ".cont");
+          
+          // Remove the unconditional branch inserted at the end of CallBB.
+          CallBB->getInstList().pop_back();
+          NewBB->getInstList().remove(CI);
+          
+          // Create a new invoke instruction.
+          Args.clear();
+          Args.append(CI->op_begin() + 1, CI->op_end());
+          
+          InvokeInst *II = InvokeInst::Create(CI->getOperand(0),
+                                              NewBB, CleanupBB,
+                                              Args.begin(), Args.end(),
+                                              CI->getName(), CallBB);
+          II->setCallingConv(CI->getCallingConv());
+          II->setParamAttrs(CI->getParamAttrs());
+          CI->replaceAllUsesWith(II);
+          delete CI;
+        }
+        
+        Builder.SetInsertPoint(UI->getParent(), UI);
+        return &Builder;
+      }
+    }
+  };
+
+}
+
+// -----------------------------------------------------------------------------
+
+Collector *llvm::createShadowStackCollector() {
+  return new ShadowStackCollector();
+}
+
+ShadowStackCollector::ShadowStackCollector() : Head(0), StackEntryTy(0) {
+  InitRoots = true;
+  CustomRoots = true;
+}
+
+Constant *ShadowStackCollector::GetFrameMap(Function &F) {
+  // doInitialization creates the abstract type of this value.
+  
+  Type *VoidPtr = PointerType::getUnqual(Type::Int8Ty);
+  
+  // Truncate the ShadowStackDescriptor if some metadata is null.
+  unsigned NumMeta = 0;
+  SmallVector<Constant*,16> Metadata;
+  for (unsigned I = 0; I != Roots.size(); ++I) {
+    Constant *C = cast<Constant>(Roots[I].first->getOperand(2));
+    if (!C->isNullValue())
+      NumMeta = I + 1;
+    Metadata.push_back(ConstantExpr::getBitCast(C, VoidPtr));
+  }
+  
+  Constant *BaseElts[] = {
+    ConstantInt::get(Type::Int32Ty, Roots.size(), false),
+    ConstantInt::get(Type::Int32Ty, NumMeta, false),
+  };
+  
+  Constant *DescriptorElts[] = {
+    ConstantStruct::get(BaseElts, 2),
+    ConstantArray::get(ArrayType::get(VoidPtr, NumMeta),
+                       Metadata.begin(), NumMeta)
+  };
+  
+  Constant *FrameMap = ConstantStruct::get(DescriptorElts, 2);
+  
+  std::string TypeName("gc_map.");
+  TypeName += utostr(NumMeta);
+  F.getParent()->addTypeName(TypeName, FrameMap->getType());
+  
+  // FIXME: Is this actually dangerous as WritingAnLLVMPass.html claims? Seems
+  //        that, short of multithreaded LLVM, it should be safe; all that is
+  //        necessary is that a simple Module::iterator loop not be invalidated.
+  //        Appending to the GlobalVariable list is safe in that sense.
+  // 
+  //        All of the output passes emit globals last. The ExecutionEngine
+  //        explicitly supports adding globals to the module after
+  //        initialization.
+  // 
+  //        Still, if it isn't deemed acceptable, then this transformation needs
+  //        to be a ModulePass (which means it cannot be in the 'llc' pipeline
+  //        (which uses a FunctionPassManager (which segfaults (not asserts) if
+  //        provided a ModulePass))).
+  Constant *GV = new GlobalVariable(FrameMap->getType(), true,
+                                    GlobalVariable::InternalLinkage,
+                                    FrameMap, "__gc_" + F.getName(),
+                                    F.getParent());
+  
+  Constant *GEPIndices[2] = { ConstantInt::get(Type::Int32Ty, 0),
+                              ConstantInt::get(Type::Int32Ty, 0) };
+  return ConstantExpr::getGetElementPtr(GV, GEPIndices, 2);
+}
+
+const Type* ShadowStackCollector::GetConcreteStackEntryType(Function &F) {
+  // doInitialization creates the generic version of this type.
+  std::vector<const Type*> EltTys;
+  EltTys.push_back(StackEntryTy);
+  for (size_t I = 0; I != Roots.size(); I++)
+    EltTys.push_back(Roots[I].second->getAllocatedType());
+  Type *Ty = StructType::get(EltTys);
+  
+  std::string TypeName("gc_stackentry.");
+  TypeName += F.getName();
+  F.getParent()->addTypeName(TypeName, Ty);
+  
+  return Ty;
+}
+
+/// doInitialization - If this module uses the GC intrinsics, find them now. If
+/// not, exit fast.
+bool ShadowStackCollector::initializeCustomLowering(Module &M) {
+  // struct FrameMap {
+  //   int32_t NumRoots; // Number of roots in stack frame.
+  //   int32_t NumMeta;  // Number of metadata descriptors. May be < NumRoots.
+  //   void *Meta[];     // May be absent for roots without metadata.
+  // };
+  std::vector<const Type*> EltTys;
+  EltTys.push_back(Type::Int32Ty); // 32 bits is ok up to a 32GB stack frame. :)
+  EltTys.push_back(Type::Int32Ty); // Specifies length of variable length array.
+  StructType *FrameMapTy = StructType::get(EltTys);
+  M.addTypeName("gc_map", FrameMapTy);
+  PointerType *FrameMapPtrTy = PointerType::getUnqual(FrameMapTy);
+  
+  // struct StackEntry {
+  //   ShadowStackEntry *Next; // Caller's stack entry.
+  //   FrameMap *Map;          // Pointer to constant FrameMap.
+  //   void *Roots[];          // Stack roots (in-place array, so we pretend).
+  // };
+  OpaqueType *RecursiveTy = OpaqueType::get();
+  
+  EltTys.clear();
+  EltTys.push_back(PointerType::getUnqual(RecursiveTy));
+  EltTys.push_back(FrameMapPtrTy);
+  PATypeHolder LinkTyH = StructType::get(EltTys);
+  
+  RecursiveTy->refineAbstractTypeTo(LinkTyH.get());
+  StackEntryTy = cast<StructType>(LinkTyH.get());
+  const PointerType *StackEntryPtrTy = PointerType::getUnqual(StackEntryTy);
+  M.addTypeName("gc_stackentry", LinkTyH.get());  // FIXME: Is this safe from
+                                                  //        a FunctionPass?
+  
+  // Get the root chain if it already exists.
+  Head = M.getGlobalVariable("llvm_gc_root_chain");
+  if (!Head) {
+    // If the root chain does not exist, insert a new one with linkonce
+    // linkage!
+    Head = new GlobalVariable(StackEntryPtrTy, false,
+                              GlobalValue::LinkOnceLinkage,
+                              Constant::getNullValue(StackEntryPtrTy),
+                              "llvm_gc_root_chain", &M);
+  } else if (Head->hasExternalLinkage() && Head->isDeclaration()) {
+    Head->setInitializer(Constant::getNullValue(StackEntryPtrTy));
+    Head->setLinkage(GlobalValue::LinkOnceLinkage);
+  }
+  
+  return true;
+}
+
+bool ShadowStackCollector::IsNullValue(Value *V) {
+  if (Constant *C = dyn_cast<Constant>(V))
+    return C->isNullValue();
+  return false;
+}
+
+void ShadowStackCollector::CollectRoots(Function &F) {
+  // FIXME: Account for original alignment. Could fragment the root array.
+  //   Approach 1: Null initialize empty slots at runtime. Yuck.
+  //   Approach 2: Emit a map of the array instead of just a count.
+  
+  assert(Roots.empty() && "Not cleaned up?");
+  
+  SmallVector<std::pair<CallInst*,AllocaInst*>,16> MetaRoots;
+  
+  for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
+    for (BasicBlock::iterator II = BB->begin(), E = BB->end(); II != E;)
+      if (IntrinsicInst *CI = dyn_cast<IntrinsicInst>(II++))
+        if (Function *F = CI->getCalledFunction())
+          if (F->getIntrinsicID() == Intrinsic::gcroot) {
+            std::pair<CallInst*,AllocaInst*> Pair = std::make_pair(
+              CI, cast<AllocaInst>(CI->getOperand(1)->stripPointerCasts()));
+            if (IsNullValue(CI->getOperand(2)))
+              Roots.push_back(Pair);
+            else
+              MetaRoots.push_back(Pair);
+          }
+  
+  // Number roots with metadata (usually empty) at the beginning, so that the
+  // FrameMap::Meta array can be elided.
+  Roots.insert(Roots.begin(), MetaRoots.begin(), MetaRoots.end());
+}
+
+GetElementPtrInst *
+ShadowStackCollector::CreateGEP(IRBuilder<> &B, Value *BasePtr,
+                                int Idx, int Idx2, const char *Name) {
+  Value *Indices[] = { ConstantInt::get(Type::Int32Ty, 0),
+                       ConstantInt::get(Type::Int32Ty, Idx),
+                       ConstantInt::get(Type::Int32Ty, Idx2) };
+  Value* Val = B.CreateGEP(BasePtr, Indices, Indices + 3, Name);
+    
+  assert(isa<GetElementPtrInst>(Val) && "Unexpected folded constant");
+    
+  return dyn_cast<GetElementPtrInst>(Val);
+}
+
+GetElementPtrInst *
+ShadowStackCollector::CreateGEP(IRBuilder<> &B, Value *BasePtr,
+                                int Idx, const char *Name) {
+  Value *Indices[] = { ConstantInt::get(Type::Int32Ty, 0),
+                       ConstantInt::get(Type::Int32Ty, Idx) };
+  Value *Val = B.CreateGEP(BasePtr, Indices, Indices + 2, Name);
+    
+  assert(isa<GetElementPtrInst>(Val) && "Unexpected folded constant");
+
+  return dyn_cast<GetElementPtrInst>(Val);
+}
+
+/// runOnFunction - Insert code to maintain the shadow stack.
+bool ShadowStackCollector::performCustomLowering(Function &F) {
+  // Find calls to llvm.gcroot.
+  CollectRoots(F);
+  
+  // If there are no roots in this function, then there is no need to add a
+  // stack map entry for it.
+  if (Roots.empty())
+    return false;
+  
+  // Build the constant map and figure the type of the shadow stack entry.
+  Value *FrameMap = GetFrameMap(F);
+  const Type *ConcreteStackEntryTy = GetConcreteStackEntryType(F);
+  
+  // Build the shadow stack entry at the very start of the function.
+  BasicBlock::iterator IP = F.getEntryBlock().begin();
+  IRBuilder<> AtEntry(IP->getParent(), IP);
+  
+  Instruction *StackEntry   = AtEntry.CreateAlloca(ConcreteStackEntryTy, 0,
+                                                   "gc_frame");
+  
+  while (isa<AllocaInst>(IP)) ++IP;
+  AtEntry.SetInsertPoint(IP->getParent(), IP);
+  
+  // Initialize the map pointer and load the current head of the shadow stack.
+  Instruction *CurrentHead  = AtEntry.CreateLoad(Head, "gc_currhead");
+  Instruction *EntryMapPtr  = CreateGEP(AtEntry, StackEntry,0,1,"gc_frame.map");
+                              AtEntry.CreateStore(FrameMap, EntryMapPtr);
+  
+  // After all the allocas...
+  for (unsigned I = 0, E = Roots.size(); I != E; ++I) {
+    // For each root, find the corresponding slot in the aggregate...
+    Value *SlotPtr = CreateGEP(AtEntry, StackEntry, 1 + I, "gc_root");
+    
+    // And use it in lieu of the alloca.
+    AllocaInst *OriginalAlloca = Roots[I].second;
+    SlotPtr->takeName(OriginalAlloca);
+    OriginalAlloca->replaceAllUsesWith(SlotPtr);
+  }
+  
+  // Move past the original stores inserted by Collector::InitRoots. This isn't
+  // really necessary (the collector would never see the intermediate state),
+  // but it's nicer not to push the half-initialized entry onto the stack.
+  while (isa<StoreInst>(IP)) ++IP;
+  AtEntry.SetInsertPoint(IP->getParent(), IP);
+  
+  // Push the entry onto the shadow stack.
+  Instruction *EntryNextPtr = CreateGEP(AtEntry,StackEntry,0,0,"gc_frame.next");
+  Instruction *NewHeadVal   = CreateGEP(AtEntry,StackEntry, 0, "gc_newhead");
+                              AtEntry.CreateStore(CurrentHead, EntryNextPtr);
+                              AtEntry.CreateStore(NewHeadVal, Head);
+  
+  // For each instruction that escapes...
+  EscapeEnumerator EE(F, "gc_cleanup");
+  while (IRBuilder<> *AtExit = EE.Next()) {
+    // Pop the entry from the shadow stack. Don't reuse CurrentHead from
+    // AtEntry, since that would make the value live for the entire function.
+    Instruction *EntryNextPtr2 = CreateGEP(*AtExit, StackEntry, 0, 0,
+                                           "gc_frame.next");
+    Value *SavedHead = AtExit->CreateLoad(EntryNextPtr2, "gc_savedhead");
+                       AtExit->CreateStore(SavedHead, Head);
+  }
+  
+  // Delete the original allocas (which are no longer used) and the intrinsic
+  // calls (which are no longer valid). Doing this last avoids invalidating
+  // iterators.
+  for (unsigned I = 0, E = Roots.size(); I != E; ++I) {
+    Roots[I].first->eraseFromParent();
+    Roots[I].second->eraseFromParent();
+  }
+  
+  Roots.clear();
+  return true;
+}