CGObjCRuntime.cpp

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//==- CGObjCRuntime.cpp - Interface to Shared Objective-C Runtime Features ==//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This abstract class defines the interface for Objective-C runtime-specific
// code generation.  It provides some concrete helper methods for functionality
// shared between all (or most) of the Objective-C runtimes supported by clang.
//
//===----------------------------------------------------------------------===//
 
#include "CGObjCRuntime.h"
#include "Address.h"
#include "CGCXXABI.h"
#include "CGCleanup.h"
#include "CGRecordLayout.h"
#include "CodeGenFunction.h"
#include "CodeGenModule.h"
#include "clang/AST/RecordLayout.h"
#include "clang/AST/StmtObjC.h"
#include "clang/CodeGen/CGFunctionInfo.h"
#include "clang/CodeGen/CodeGenABITypes.h"
#include "llvm/IR/Instruction.h"
#include "llvm/IR/Instructions.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/SaveAndRestore.h"
 
using namespace clang;
using namespace CodeGen;
 
uint64_t CGObjCRuntime::ComputeIvarBaseOffset(CodeGen::CodeGenModule &CGM,
                                              const ObjCInterfaceDecl *OID,
                                              const ObjCIvarDecl *Ivar) {
  return CGM.getContext().lookupFieldBitOffset(OID, Ivar) /
         CGM.getContext().getCharWidth();
}
 
uint64_t CGObjCRuntime::ComputeIvarBaseOffset(CodeGen::CodeGenModule &CGM,
                                              const ObjCImplementationDecl *OID,
                                              const ObjCIvarDecl *Ivar) {
  return CGM.getContext().lookupFieldBitOffset(OID->getClassInterface(), Ivar) /
         CGM.getContext().getCharWidth();
}
 
unsigned CGObjCRuntime::ComputeBitfieldBitOffset(
    CodeGen::CodeGenModule &CGM,
    const ObjCInterfaceDecl *ID,
    const ObjCIvarDecl *Ivar) {
  return CGM.getContext().lookupFieldBitOffset(ID, Ivar);
}
 
LValue CGObjCRuntime::EmitValueForIvarAtOffset(CodeGen::CodeGenFunction &CGF,
                                               const ObjCInterfaceDecl *OID,
                                               llvm::Value *BaseValue,
                                               const ObjCIvarDecl *Ivar,
                                               unsigned CVRQualifiers,
                                               llvm::Value *Offset) {
  // Compute (type*) ( (char *) BaseValue + Offset)
  QualType InterfaceTy{OID->getTypeForDecl(), 0};
  QualType ObjectPtrTy =
      CGF.CGM.getContext().getObjCObjectPointerType(InterfaceTy);
  QualType IvarTy =
      Ivar->getUsageType(ObjectPtrTy).withCVRQualifiers(CVRQualifiers);
  llvm::Value *V = BaseValue;
  V = CGF.Builder.CreateInBoundsGEP(CGF.Int8Ty, V, Offset, "add.ptr");
 
  if (!Ivar->isBitField()) {
    LValue LV = CGF.MakeNaturalAlignRawAddrLValue(V, IvarTy);
    return LV;
  }
 
  // We need to compute an access strategy for this bit-field. We are given the
  // offset to the first byte in the bit-field, the sub-byte offset is taken
  // from the original layout. We reuse the normal bit-field access strategy by
  // treating this as an access to a struct where the bit-field is in byte 0,
  // and adjust the containing type size as appropriate.
  //
  // FIXME: Note that currently we make a very conservative estimate of the
  // alignment of the bit-field, because (a) it is not clear what guarantees the
  // runtime makes us, and (b) we don't have a way to specify that the struct is
  // at an alignment plus offset.
  //
  // Note, there is a subtle invariant here: we can only call this routine on
  // non-synthesized ivars but we may be called for synthesized ivars.  However,
  // a synthesized ivar can never be a bit-field, so this is safe.
  uint64_t FieldBitOffset =
      CGF.CGM.getContext().lookupFieldBitOffset(OID, Ivar);
  uint64_t BitOffset = FieldBitOffset % CGF.CGM.getContext().getCharWidth();
  uint64_t AlignmentBits = CGF.CGM.getTarget().getCharAlign();
  uint64_t BitFieldSize = Ivar->getBitWidthValue();
  CharUnits StorageSize = CGF.CGM.getContext().toCharUnitsFromBits(
      llvm::alignTo(BitOffset + BitFieldSize, AlignmentBits));
  CharUnits Alignment = CGF.CGM.getContext().toCharUnitsFromBits(AlignmentBits);
 
  // Allocate a new CGBitFieldInfo object to describe this access.
  //
  // FIXME: This is incredibly wasteful, these should be uniqued or part of some
  // layout object. However, this is blocked on other cleanups to the
  // Objective-C code, so for now we just live with allocating a bunch of these
  // objects.
  CGBitFieldInfo *Info = new (CGF.CGM.getContext()) CGBitFieldInfo(
    CGBitFieldInfo::MakeInfo(CGF.CGM.getTypes(), Ivar, BitOffset, BitFieldSize,
                             CGF.CGM.getContext().toBits(StorageSize),
                             CharUnits::fromQuantity(0)));
 
  Address Addr =
      Address(V, llvm::Type::getIntNTy(CGF.getLLVMContext(), Info->StorageSize),
              Alignment);
 
  return LValue::MakeBitfield(Addr, *Info, IvarTy,
                              LValueBaseInfo(AlignmentSource::Decl),
                              TBAAAccessInfo());
}
 
namespace {
  struct CatchHandler {
    const VarDecl *Variable;
    const Stmt *Body;
    llvm::BasicBlock *Block;
    llvm::Constant *TypeInfo;
    /// Flags used to differentiate cleanups and catchalls in Windows SEH
    unsigned Flags;
  };
 
  struct CallObjCEndCatch final : EHScopeStack::Cleanup {
    CallObjCEndCatch(bool MightThrow, llvm::FunctionCallee Fn)
        : MightThrow(MightThrow), Fn(Fn) {}
    bool MightThrow;
    llvm::FunctionCallee Fn;
 
    void Emit(CodeGenFunction &CGF, Flags flags) override {
      if (MightThrow)
        CGF.EmitRuntimeCallOrInvoke(Fn);
      else
        CGF.EmitNounwindRuntimeCall(Fn);
    }
  };
}
 
void CGObjCRuntime::EmitTryCatchStmt(CodeGenFunction &CGF,
                                     const ObjCAtTryStmt &S,
                                     llvm::FunctionCallee beginCatchFn,
                                     llvm::FunctionCallee endCatchFn,
                                     llvm::FunctionCallee exceptionRethrowFn) {
  // Jump destination for falling out of catch bodies.
  CodeGenFunction::JumpDest Cont;
  if (S.getNumCatchStmts())
    Cont = CGF.getJumpDestInCurrentScope("eh.cont");
 
  bool useFunclets = getEHPersonality(CGF).usesFuncletPads();
  bool IsWasm = getEHPersonality(CGF).isWasmPersonality();
  bool IsMSVC = getEHPersonality(CGF).isMSVCPersonality();
 
  CodeGenFunction::FinallyInfo FinallyInfo;
  if (const ObjCAtFinallyStmt *Finally = S.getFinallyStmt()) {
    if (!IsMSVC) {
      // The finally statement is executed as a cleanup for the normal and
      // exceptional control flow out of a try-catch block. This is all
      // implemented in FinallyInfo. Here we enter a new EHCatchScope.
      FinallyInfo.enter(CGF, Finally->getFinallyBody(), beginCatchFn,
                        endCatchFn, exceptionRethrowFn);
    } else {
      CodeGenFunction HelperCGF(CGM, /*suppressNewContext=*/true);
      if (!CGF.CurSEHParent)
        CGF.CurSEHParent = cast<NamedDecl>(CGF.CurFuncDecl);
      const Stmt *FinallyBlock = Finally->getFinallyBody();
      HelperCGF.startOutlinedSEHHelper(CGF, /*isFilter*/ false, FinallyBlock);
      HelperCGF.EmitStmt(FinallyBlock);
      HelperCGF.FinishFunction(FinallyBlock->getEndLoc());
 
      llvm::Function *FinallyFunc = HelperCGF.CurFn;
      CGF.pushSEHCleanup(NormalAndEHCleanup, FinallyFunc);
    }
  }
 
  if (useFunclets && IsMSVC)
    if (const ObjCAtFinallyStmt *Finally = S.getFinallyStmt()) {
      CodeGenFunction HelperCGF(CGM, /*suppressNewContext=*/true);
      if (!CGF.CurSEHParent)
        CGF.CurSEHParent = cast<NamedDecl>(CGF.CurFuncDecl);
      // Outline the finally block.
      const Stmt *FinallyBlock = Finally->getFinallyBody();
      HelperCGF.startOutlinedSEHHelper(CGF, /*isFilter*/ false, FinallyBlock);
 
      // Emit the original filter expression, convert to i32, and return.
      HelperCGF.EmitStmt(FinallyBlock);
 
      HelperCGF.FinishFunction(FinallyBlock->getEndLoc());
 
      llvm::Function *FinallyFunc = HelperCGF.CurFn;
 
      // Push a cleanup for __finally blocks.
      CGF.pushSEHCleanup(NormalAndEHCleanup, FinallyFunc);
    }
 
  SmallVector<CatchHandler, 8> Handlers;
 
  // Enter the catch, if there is one.
  if (S.getNumCatchStmts()) {
    for (const ObjCAtCatchStmt *CatchStmt : S.catch_stmts()) {
      const VarDecl *CatchDecl = CatchStmt->getCatchParamDecl();
 
      Handlers.push_back(CatchHandler());
      CatchHandler &Handler = Handlers.back();
      Handler.Variable = CatchDecl;
      Handler.Body = CatchStmt->getCatchBody();
      Handler.Block = CGF.createBasicBlock("catch");
      Handler.Flags = 0;
 
      // @catch(...) always matches.
      if (!CatchDecl) {
        auto catchAll = getCatchAllTypeInfo();
        Handler.TypeInfo = catchAll.RTTI;
        Handler.Flags = catchAll.Flags;
        // Don't consider any other catches.
        break;
      }
 
      Handler.TypeInfo = GetEHType(CatchDecl->getType());
    }
 
    // Create a new catch scope
    EHCatchScope *Catch = CGF.EHStack.pushCatch(Handlers.size());
    for (unsigned I = 0, E = Handlers.size(); I != E; ++I)
      Catch->setHandler(I, { Handlers[I].TypeInfo, Handlers[I].Flags }, Handlers[I].Block);
  }
 
  // Emit the try body.
  CGF.EmitStmt(S.getTryBody());
 
  // Leave the try.
  llvm::BasicBlock *DispatchBlock = nullptr;
  if (S.getNumCatchStmts()) {
    EHCatchScope &CatchScope = cast<EHCatchScope>(*CGF.EHStack.begin());
    if (CatchScope.hasEHBranches())
      DispatchBlock = CatchScope.getCachedEHDispatchBlock();
    CGF.popCatchScope();
  }
 
  // We save the old funclet pad here before we traverse each catch handler.
  {
    SaveAndRestore RestoreCurrentFuncletPad(CGF.CurrentFuncletPad);
    llvm::BasicBlock *WasmCatchStartBlock = nullptr;
    llvm::CatchPadInst *CPI = nullptr;
    if (DispatchBlock && IsWasm) {
      auto *CatchSwitch =
          cast<llvm::CatchSwitchInst>(DispatchBlock->getFirstNonPHIIt());
      WasmCatchStartBlock = CatchSwitch->hasUnwindDest()
                                ? CatchSwitch->getSuccessor(1)
                                : CatchSwitch->getSuccessor(0);
      CPI = cast<llvm::CatchPadInst>(WasmCatchStartBlock->getFirstNonPHIIt());
      CGF.CurrentFuncletPad = CPI;
    }
 
    // Remember where we were.
    CGBuilderTy::InsertPoint SavedIP = CGF.Builder.saveAndClearIP();
 
    // Emit the handlers. If there is no catch-all handler, we need to emit a
    // fallthrough block in WASM. We therefore need to know if we have a
    // catch-all handler in this catch scope.
    bool HasCatchAll = false;
    for (CatchHandler &Handler : Handlers) {
      HasCatchAll |= Handler.TypeInfo == nullptr;
      CGF.EmitBlock(Handler.Block);
 
      CodeGenFunction::LexicalScope Cleanups(CGF,
                                             Handler.Body->getSourceRange());
      SaveAndRestore RevertAfterScope(CGF.CurrentFuncletPad);
      if (IsMSVC) {
        llvm::BasicBlock::iterator CPICandidate =
            Handler.Block->getFirstNonPHIIt();
        if (CPICandidate != Handler.Block->end()) {
          if ((CPI = dyn_cast_or_null<llvm::CatchPadInst>(CPICandidate))) {
            CGF.CurrentFuncletPad = CPI;
            CPI->setOperand(2, CGF.getExceptionSlot().emitRawPointer(CGF));
          }
        }
      }
 
      if (CPI) {
        // A catchpad requires a matching catchret instruction. We emit this in
        // form of a cleanup.
        CGF.EHStack.pushCleanup<CatchRetScope>(NormalCleanup, CPI);
      }
 
      llvm::Value *RawExn = CGF.getExceptionFromSlot();
 
      // Enter the catch.
      llvm::Value *Exn = RawExn;
      if (beginCatchFn)
        Exn = CGF.EmitNounwindRuntimeCall(beginCatchFn, RawExn, "exn.adjusted");
 
      if (endCatchFn) {
        // Add a cleanup to leave the catch.
        bool EndCatchMightThrow = (Handler.Variable == nullptr);
 
        CGF.EHStack.pushCleanup<CallObjCEndCatch>(
            NormalAndEHCleanup, EndCatchMightThrow, endCatchFn);
      }
 
      // Bind the catch parameter if it exists.
      if (const VarDecl *CatchParam = Handler.Variable) {
        llvm::Type *CatchType = CGF.ConvertType(CatchParam->getType());
        llvm::Value *CastExn = CGF.Builder.CreateBitCast(Exn, CatchType);
 
        CGF.EmitAutoVarDecl(*CatchParam);
        EmitInitOfCatchParam(CGF, CastExn, CatchParam);
      }
 
      // The body of the handler might have more try-catch blocks, so we need to
      // save the current exception before emitting the body.
      CGF.ObjCEHValueStack.push_back(Exn);
      CGF.EmitStmt(Handler.Body);
      CGF.ObjCEHValueStack.pop_back();
 
      // Leave any cleanups associated with the catch.
      Cleanups.ForceCleanup();
 
      CGF.EmitBranchThroughCleanup(Cont);
    }
 
    if (IsWasm && !HasCatchAll && WasmCatchStartBlock) {
      CGF.WasmEmitFallthroughRethrow(WasmCatchStartBlock);
    }
 
    // Go back to the try-statement fallthrough.
    CGF.Builder.restoreIP(SavedIP);
  }
 
  // Pop out of the finally.
  if (S.getFinallyStmt()) {
    if (IsMSVC) {
      CGF.PopCleanupBlock();
    } else {
      FinallyInfo.exit(CGF);
    }
  }
 
  if (Cont.isValid())
    CGF.EmitBlock(Cont.getBlock());
}
 
void CGObjCRuntime::EmitInitOfCatchParam(CodeGenFunction &CGF,
                                         llvm::Value *exn,
                                         const VarDecl *paramDecl) {
 
  Address paramAddr = CGF.GetAddrOfLocalVar(paramDecl);
 
  switch (paramDecl->getType().getQualifiers().getObjCLifetime()) {
  case Qualifiers::OCL_Strong:
    exn = CGF.EmitARCRetainNonBlock(exn);
    [[fallthrough]];
 
  case Qualifiers::OCL_None:
  case Qualifiers::OCL_ExplicitNone:
  case Qualifiers::OCL_Autoreleasing:
    CGF.Builder.CreateStore(exn, paramAddr);
    return;
 
  case Qualifiers::OCL_Weak:
    CGF.EmitARCInitWeak(paramAddr, exn);
    return;
  }
  llvm_unreachable("invalid ownership qualifier");
}
 
namespace {
  struct CallSyncExit final : EHScopeStack::Cleanup {
    llvm::FunctionCallee SyncExitFn;
    llvm::Value *SyncArg;
    CallSyncExit(llvm::FunctionCallee SyncExitFn, llvm::Value *SyncArg)
        : SyncExitFn(SyncExitFn), SyncArg(SyncArg) {}
 
    void Emit(CodeGenFunction &CGF, Flags flags) override {
      CGF.EmitNounwindRuntimeCall(SyncExitFn, SyncArg);
    }
  };
}
 
void CGObjCRuntime::EmitAtSynchronizedStmt(CodeGenFunction &CGF,
                                           const ObjCAtSynchronizedStmt &S,
                                           llvm::FunctionCallee syncEnterFn,
                                           llvm::FunctionCallee syncExitFn) {
  CodeGenFunction::RunCleanupsScope cleanups(CGF);
 
  // Evaluate the lock operand.  This is guaranteed to dominate the
  // ARC release and lock-release cleanups.
  const Expr *lockExpr = S.getSynchExpr();
  llvm::Value *lock;
  if (CGF.getLangOpts().ObjCAutoRefCount) {
    lock = CGF.EmitARCRetainScalarExpr(lockExpr);
    lock = CGF.EmitObjCConsumeObject(lockExpr->getType(), lock);
  } else {
    lock = CGF.EmitScalarExpr(lockExpr);
  }
  lock = CGF.Builder.CreateBitCast(lock, CGF.VoidPtrTy);
 
  // Acquire the lock.
  CGF.Builder.CreateCall(syncEnterFn, lock)->setDoesNotThrow();
 
  // Register an all-paths cleanup to release the lock.
  CGF.EHStack.pushCleanup<CallSyncExit>(NormalAndEHCleanup, syncExitFn, lock);
 
  // Emit the body of the statement.
  CGF.EmitStmt(S.getSynchBody());
}
 
/// Compute the pointer-to-function type to which a message send
/// should be casted in order to correctly call the given method
/// with the given arguments.
///
/// \param method - may be null
/// \param resultType - the result type to use if there's no method
/// \param callArgs - the actual arguments, including implicit ones
CGObjCRuntime::MessageSendInfo
CGObjCRuntime::getMessageSendInfo(const ObjCMethodDecl *method,
                                  QualType resultType,
                                  CallArgList &callArgs) {
  unsigned ProgramAS = CGM.getDataLayout().getProgramAddressSpace();
 
  llvm::PointerType *signatureType =
      llvm::PointerType::get(CGM.getLLVMContext(), ProgramAS);
 
  // FIXME: Pass the enclosing FunctionDecl so Objective-C message sends use
  // the caller's target features when arranging their ABI.
  // If there's a method, use information from that.
  if (method) {
    const CGFunctionInfo &signature =
      CGM.getTypes().arrangeObjCMessageSendSignature(method, callArgs[0].Ty);
 
    const CGFunctionInfo &signatureForCall =
        CGM.getTypes().arrangeCall(signature, callArgs, /*ABIInfoFD=*/nullptr);
 
    return MessageSendInfo(signatureForCall, signatureType);
  }
 
  // There's no method;  just use a default CC.
  const CGFunctionInfo &argsInfo =
    CGM.getTypes().arrangeUnprototypedObjCMessageSend(resultType, callArgs);
 
  return MessageSendInfo(argsInfo, signatureType);
}
 
bool CGObjCRuntime::canMessageReceiverBeNull(
    CodeGenFunction &CGF, const ObjCMethodDecl *method, bool isSuper,
    const ObjCInterfaceDecl *classReceiver, llvm::Value *receiver) {
  // Super dispatch assumes that self is non-null; even the messenger
  // doesn't have a null check internally.
  if (isSuper)
    return false;
 
  // If this is a direct dispatch of a class method, check whether the class,
  // or anything in its hierarchy, was weak-linked.
  if (classReceiver && method && method->isClassMethod())
    return isWeakLinkedClass(classReceiver);
 
  // If we're emitting a method, and self is const (meaning just ARC, for now),
  // and the receiver is a load of self, then self is a valid object.
  if (auto curMethod = dyn_cast_or_null<ObjCMethodDecl>(CGF.CurCodeDecl)) {
    auto self = curMethod->getSelfDecl();
    if (self->getType().isConstQualified()) {
      if (auto LI = dyn_cast<llvm::LoadInst>(receiver->stripPointerCasts())) {
        llvm::Value *selfAddr = CGF.GetAddrOfLocalVar(self).emitRawPointer(CGF);
        if (selfAddr == LI->getPointerOperand()) {
          return false;
        }
      }
    }
  }
 
  // Otherwise, assume it can be null.
  return true;
}
 
bool CGObjCRuntime::canClassObjectBeUnrealized(
    const ObjCInterfaceDecl *CalleeClassDecl, CodeGenFunction &CGF) const {
  // TODO
  // Otherwise, assume it can be unrealized.
  return true;
}
 
bool CGObjCRuntime::isWeakLinkedClass(const ObjCInterfaceDecl *ID) {
  do {
    if (ID->isWeakImported())
      return true;
  } while ((ID = ID->getSuperClass()));
 
  return false;
}
 
void CGObjCRuntime::destroyCalleeDestroyedArguments(CodeGenFunction &CGF,
                                              const ObjCMethodDecl *method,
                                              const CallArgList &callArgs) {
  CallArgList::const_iterator I = callArgs.begin();
  for (auto i = method->param_begin(), e = method->param_end();
         i != e; ++i, ++I) {
    const ParmVarDecl *param = (*i);
    if (param->hasAttr<NSConsumedAttr>()) {
      RValue RV = I->getRValue(CGF);
      assert(RV.isScalar() &&
             "NullReturnState::complete - arg not on object");
      CGF.EmitARCRelease(RV.getScalarVal(), ARCImpreciseLifetime);
    } else {
      QualType QT = param->getType();
      auto *RD = QT->getAsRecordDecl();
      if (RD && RD->isParamDestroyedInCallee()) {
        RValue RV = I->getRValue(CGF);
        QualType::DestructionKind DtorKind = QT.isDestructedType();
        switch (DtorKind) {
        case QualType::DK_cxx_destructor:
          CGF.destroyCXXObject(CGF, RV.getAggregateAddress(), QT);
          break;
        case QualType::DK_nontrivial_c_struct:
          CGF.destroyNonTrivialCStruct(CGF, RV.getAggregateAddress(), QT);
          break;
        default:
          llvm_unreachable("unexpected dtor kind");
          break;
        }
      }
    }
  }
}
 
llvm::Constant *
clang::CodeGen::emitObjCProtocolObject(CodeGenModule &CGM,
                                       const ObjCProtocolDecl *protocol) {
  return CGM.getObjCRuntime().GetOrEmitProtocol(protocol);
}
 
std::string CGObjCRuntime::getSymbolNameForMethod(const ObjCMethodDecl *OMD,
                                                  bool includeCategoryName,
                                                  bool useDirectABI) {
  std::string buffer;
  llvm::raw_string_ostream out(buffer);
  CGM.getCXXABI().getMangleContext().mangleObjCMethodName(
      OMD, out, /*includePrefixByte=*/true, includeCategoryName, useDirectABI);
  return buffer;
}