lib/CodeGen/CGObjCRuntime.cpp

//==- CGObjCRuntime.cpp - Interface to Shared Objective-C Runtime Features ==//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// 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 "CGRecordLayout.h"
#include "CodeGenModule.h"
#include "CodeGenFunction.h"
#include "CGCleanup.h"

#include "clang/AST/RecordLayout.h"
#include "clang/AST/StmtObjC.h"

#include "llvm/Support/CallSite.h"

using namespace clang;
using namespace CodeGen;

static uint64_t LookupFieldBitOffset(CodeGen::CodeGenModule &CGM,
                                     const ObjCInterfaceDecl *OID,
                                     const ObjCImplementationDecl *ID,
                                     const ObjCIvarDecl *Ivar) {
  const ObjCInterfaceDecl *Container = Ivar->getContainingInterface();

  // FIXME: We should eliminate the need to have ObjCImplementationDecl passed
  // in here; it should never be necessary because that should be the lexical
  // decl context for the ivar.

  // If we know have an implementation (and the ivar is in it) then
  // look up in the implementation layout.
  const ASTRecordLayout *RL;
  if (ID && ID->getClassInterface() == Container)
    RL = &CGM.getContext().getASTObjCImplementationLayout(ID);
  else
    RL = &CGM.getContext().getASTObjCInterfaceLayout(Container);

  // Compute field index.
  //
  // FIXME: The index here is closely tied to how ASTContext::getObjCLayout is
  // implemented. This should be fixed to get the information from the layout
  // directly.
  unsigned Index = 0;
  llvm::SmallVector<ObjCIvarDecl*, 16> Ivars;
  CGM.getContext().ShallowCollectObjCIvars(Container, Ivars);
  for (unsigned k = 0, e = Ivars.size(); k != e; ++k) {
    if (Ivar == Ivars[k])
      break;
    ++Index;
  }
  assert(Index != Ivars.size() && "Ivar is not inside container!");
  assert(Index < RL->getFieldCount() && "Ivar is not inside record layout!");

  return RL->getFieldOffset(Index);
}

uint64_t CGObjCRuntime::ComputeIvarBaseOffset(CodeGen::CodeGenModule &CGM,
                                              const ObjCInterfaceDecl *OID,
                                              const ObjCIvarDecl *Ivar) {
  return LookupFieldBitOffset(CGM, OID, 0, Ivar) / 8;
}

uint64_t CGObjCRuntime::ComputeIvarBaseOffset(CodeGen::CodeGenModule &CGM,
                                              const ObjCImplementationDecl *OID,
                                              const ObjCIvarDecl *Ivar) {
  return LookupFieldBitOffset(CGM, OID->getClassInterface(), OID, Ivar) / 8;
}

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)
  const llvm::Type *I8Ptr = llvm::Type::getInt8PtrTy(CGF.getLLVMContext());
  QualType IvarTy = Ivar->getType();
  const llvm::Type *LTy = CGF.CGM.getTypes().ConvertTypeForMem(IvarTy);
  llvm::Value *V = CGF.Builder.CreateBitCast(BaseValue, I8Ptr);
  V = CGF.Builder.CreateInBoundsGEP(V, Offset, "add.ptr");
  V = CGF.Builder.CreateBitCast(V, llvm::PointerType::getUnqual(LTy));

  if (!Ivar->isBitField()) {
    LValue LV = CGF.MakeAddrLValue(V, IvarTy);
    LV.getQuals().addCVRQualifiers(CVRQualifiers);
    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.
  const ASTRecordLayout &RL =
    CGF.CGM.getContext().getASTObjCInterfaceLayout(OID);
  uint64_t TypeSizeInBits = CGF.CGM.getContext().toBits(RL.getSize());
  uint64_t FieldBitOffset = LookupFieldBitOffset(CGF.CGM, OID, 0, Ivar);
  uint64_t BitOffset = FieldBitOffset % 8;
  uint64_t ContainingTypeAlign = 8;
  uint64_t ContainingTypeSize = TypeSizeInBits - (FieldBitOffset - BitOffset);
  uint64_t BitFieldSize =
    Ivar->getBitWidth()->EvaluateAsInt(CGF.getContext()).getZExtValue();

  // 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,
                             ContainingTypeSize, ContainingTypeAlign));

  return LValue::MakeBitfield(V, *Info,
                              IvarTy.getCVRQualifiers() | CVRQualifiers);
}

namespace {
  struct CatchHandler {
    const VarDecl *Variable;
    const Stmt *Body;
    llvm::BasicBlock *Block;
    llvm::Value *TypeInfo;
  };

  struct CallObjCEndCatch : EHScopeStack::Cleanup {
    CallObjCEndCatch(bool MightThrow, llvm::Value *Fn) :
      MightThrow(MightThrow), Fn(Fn) {}
    bool MightThrow;
    llvm::Value *Fn;

    void Emit(CodeGenFunction &CGF, bool IsForEH) {
      if (!MightThrow) {
        CGF.Builder.CreateCall(Fn)->setDoesNotThrow();
        return;
      }

      CGF.EmitCallOrInvoke(Fn, 0, 0);
    }
  };
}


void CGObjCRuntime::EmitTryCatchStmt(CodeGenFunction &CGF,
                                     const ObjCAtTryStmt &S,
                                     llvm::Function *beginCatchFn,
                                     llvm::Function *endCatchFn,
                                     llvm::Function *exceptionRethrowFn) {
  // Jump destination for falling out of catch bodies.
  CodeGenFunction::JumpDest Cont;
  if (S.getNumCatchStmts())
    Cont = CGF.getJumpDestInCurrentScope("eh.cont");

  CodeGenFunction::FinallyInfo FinallyInfo;
  if (const ObjCAtFinallyStmt *Finally = S.getFinallyStmt())
    FinallyInfo = CGF.EnterFinallyBlock(Finally->getFinallyBody(),
                                        beginCatchFn,
                                        endCatchFn,
                                        exceptionRethrowFn);

  llvm::SmallVector<CatchHandler, 8> Handlers;

  // Enter the catch, if there is one.
  if (S.getNumCatchStmts()) {
    for (unsigned I = 0, N = S.getNumCatchStmts(); I != N; ++I) {
      const ObjCAtCatchStmt *CatchStmt = S.getCatchStmt(I);
      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");

      // @catch(...) always matches.
      if (!CatchDecl) {
        Handler.TypeInfo = 0; // catch-all
        // Don't consider any other catches.
        break;
      }

      Handler.TypeInfo = GetEHType(CatchDecl->getType());
    }

    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].Block);
  }
  
  // Emit the try body.
  CGF.EmitStmt(S.getTryBody());

  // Leave the try.
  if (S.getNumCatchStmts())
    CGF.EHStack.popCatch();

  // Remember where we were.
  CGBuilderTy::InsertPoint SavedIP = CGF.Builder.saveAndClearIP();

  // Emit the handlers.
  for (unsigned I = 0, E = Handlers.size(); I != E; ++I) {
    CatchHandler &Handler = Handlers[I];

    CGF.EmitBlock(Handler.Block);
    llvm::Value *RawExn = CGF.Builder.CreateLoad(CGF.getExceptionSlot());

    // Enter the catch.
    llvm::Value *Exn = RawExn;
    if (beginCatchFn) {
      Exn = CGF.Builder.CreateCall(beginCatchFn, RawExn, "exn.adjusted");
      cast<llvm::CallInst>(Exn)->setDoesNotThrow();
    }

    if (endCatchFn) {
      // Add a cleanup to leave the catch.
      bool EndCatchMightThrow = (Handler.Variable == 0);

      CGF.EHStack.pushCleanup<CallObjCEndCatch>(NormalAndEHCleanup,
                                                EndCatchMightThrow,
                                                endCatchFn);
    }

    // Bind the catch parameter if it exists.
    if (const VarDecl *CatchParam = Handler.Variable) {
      const llvm::Type *CatchType = CGF.ConvertType(CatchParam->getType());
      llvm::Value *CastExn = CGF.Builder.CreateBitCast(Exn, CatchType);

      CGF.EmitAutoVarDecl(*CatchParam);
      CGF.Builder.CreateStore(CastExn, CGF.GetAddrOfLocalVar(CatchParam));
    }

    CGF.ObjCEHValueStack.push_back(Exn);
    CGF.EmitStmt(Handler.Body);
    CGF.ObjCEHValueStack.pop_back();

    // Leave the earlier cleanup.
    if (endCatchFn) 
      CGF.PopCleanupBlock();

    CGF.EmitBranchThroughCleanup(Cont);
  }  

  // Go back to the try-statement fallthrough.
  CGF.Builder.restoreIP(SavedIP);

  // Pop out of the normal cleanup on the finally.
  if (S.getFinallyStmt())
    CGF.ExitFinallyBlock(FinallyInfo);

  if (Cont.isValid())
    CGF.EmitBlock(Cont.getBlock());
}

namespace {
  struct CallSyncExit : EHScopeStack::Cleanup {
    llvm::Value *SyncExitFn;
    llvm::Value *SyncArg;
    CallSyncExit(llvm::Value *SyncExitFn, llvm::Value *SyncArg)
      : SyncExitFn(SyncExitFn), SyncArg(SyncArg) {}

    void Emit(CodeGenFunction &CGF, bool IsForEHCleanup) {
      CGF.Builder.CreateCall(SyncExitFn, SyncArg)->setDoesNotThrow();
    }
  };
}

void CGObjCRuntime::EmitAtSynchronizedStmt(CodeGenFunction &CGF,
                                           const ObjCAtSynchronizedStmt &S,
                                           llvm::Function *syncEnterFn,
                                           llvm::Function *syncExitFn) {
  // Evaluate the lock operand.  This should dominate the cleanup.
  llvm::Value *SyncArg =
    CGF.EmitScalarExpr(S.getSynchExpr());

  // Acquire the lock.
  SyncArg = CGF.Builder.CreateBitCast(SyncArg, syncEnterFn->getFunctionType()->getParamType(0));
  CGF.Builder.CreateCall(syncEnterFn, SyncArg);

  // Register an all-paths cleanup to release the lock.
  CGF.EHStack.pushCleanup<CallSyncExit>(NormalAndEHCleanup, syncExitFn,
      SyncArg);

  // Emit the body of the statement.
  CGF.EmitStmt(S.getSynchBody());

  // Pop the lock-release cleanup.
  CGF.PopCleanupBlock();
}