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      1 //==- CGObjCRuntime.cpp - Interface to Shared Objective-C Runtime Features ==//
      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 abstract class defines the interface for Objective-C runtime-specific
     11 // code generation.  It provides some concrete helper methods for functionality
     12 // shared between all (or most) of the Objective-C runtimes supported by clang.
     13 //
     14 //===----------------------------------------------------------------------===//
     15 
     16 #include "CGObjCRuntime.h"
     17 #include "CGCleanup.h"
     18 #include "CGRecordLayout.h"
     19 #include "CodeGenFunction.h"
     20 #include "CodeGenModule.h"
     21 #include "clang/AST/RecordLayout.h"
     22 #include "clang/AST/StmtObjC.h"
     23 #include "llvm/Support/CallSite.h"
     24 
     25 using namespace clang;
     26 using namespace CodeGen;
     27 
     28 static uint64_t LookupFieldBitOffset(CodeGen::CodeGenModule &CGM,
     29                                      const ObjCInterfaceDecl *OID,
     30                                      const ObjCImplementationDecl *ID,
     31                                      const ObjCIvarDecl *Ivar) {
     32   const ObjCInterfaceDecl *Container = Ivar->getContainingInterface();
     33 
     34   // FIXME: We should eliminate the need to have ObjCImplementationDecl passed
     35   // in here; it should never be necessary because that should be the lexical
     36   // decl context for the ivar.
     37 
     38   // If we know have an implementation (and the ivar is in it) then
     39   // look up in the implementation layout.
     40   const ASTRecordLayout *RL;
     41   if (ID && declaresSameEntity(ID->getClassInterface(), Container))
     42     RL = &CGM.getContext().getASTObjCImplementationLayout(ID);
     43   else
     44     RL = &CGM.getContext().getASTObjCInterfaceLayout(Container);
     45 
     46   // Compute field index.
     47   //
     48   // FIXME: The index here is closely tied to how ASTContext::getObjCLayout is
     49   // implemented. This should be fixed to get the information from the layout
     50   // directly.
     51   unsigned Index = 0;
     52 
     53   for (const ObjCIvarDecl *IVD = Container->all_declared_ivar_begin();
     54        IVD; IVD = IVD->getNextIvar()) {
     55     if (Ivar == IVD)
     56       break;
     57     ++Index;
     58   }
     59   assert(Index < RL->getFieldCount() && "Ivar is not inside record layout!");
     60 
     61   return RL->getFieldOffset(Index);
     62 }
     63 
     64 uint64_t CGObjCRuntime::ComputeIvarBaseOffset(CodeGen::CodeGenModule &CGM,
     65                                               const ObjCInterfaceDecl *OID,
     66                                               const ObjCIvarDecl *Ivar) {
     67   return LookupFieldBitOffset(CGM, OID, 0, Ivar) /
     68     CGM.getContext().getCharWidth();
     69 }
     70 
     71 uint64_t CGObjCRuntime::ComputeIvarBaseOffset(CodeGen::CodeGenModule &CGM,
     72                                               const ObjCImplementationDecl *OID,
     73                                               const ObjCIvarDecl *Ivar) {
     74   return LookupFieldBitOffset(CGM, OID->getClassInterface(), OID, Ivar) /
     75     CGM.getContext().getCharWidth();
     76 }
     77 
     78 unsigned CGObjCRuntime::ComputeBitfieldBitOffset(
     79     CodeGen::CodeGenModule &CGM,
     80     const ObjCInterfaceDecl *ID,
     81     const ObjCIvarDecl *Ivar) {
     82   return LookupFieldBitOffset(CGM, ID, ID->getImplementation(), Ivar);
     83 }
     84 
     85 LValue CGObjCRuntime::EmitValueForIvarAtOffset(CodeGen::CodeGenFunction &CGF,
     86                                                const ObjCInterfaceDecl *OID,
     87                                                llvm::Value *BaseValue,
     88                                                const ObjCIvarDecl *Ivar,
     89                                                unsigned CVRQualifiers,
     90                                                llvm::Value *Offset) {
     91   // Compute (type*) ( (char *) BaseValue + Offset)
     92   QualType IvarTy = Ivar->getType();
     93   llvm::Type *LTy = CGF.CGM.getTypes().ConvertTypeForMem(IvarTy);
     94   llvm::Value *V = CGF.Builder.CreateBitCast(BaseValue, CGF.Int8PtrTy);
     95   V = CGF.Builder.CreateInBoundsGEP(V, Offset, "add.ptr");
     96 
     97   if (!Ivar->isBitField()) {
     98     V = CGF.Builder.CreateBitCast(V, llvm::PointerType::getUnqual(LTy));
     99     LValue LV = CGF.MakeNaturalAlignAddrLValue(V, IvarTy);
    100     LV.getQuals().addCVRQualifiers(CVRQualifiers);
    101     return LV;
    102   }
    103 
    104   // We need to compute an access strategy for this bit-field. We are given the
    105   // offset to the first byte in the bit-field, the sub-byte offset is taken
    106   // from the original layout. We reuse the normal bit-field access strategy by
    107   // treating this as an access to a struct where the bit-field is in byte 0,
    108   // and adjust the containing type size as appropriate.
    109   //
    110   // FIXME: Note that currently we make a very conservative estimate of the
    111   // alignment of the bit-field, because (a) it is not clear what guarantees the
    112   // runtime makes us, and (b) we don't have a way to specify that the struct is
    113   // at an alignment plus offset.
    114   //
    115   // Note, there is a subtle invariant here: we can only call this routine on
    116   // non-synthesized ivars but we may be called for synthesized ivars.  However,
    117   // a synthesized ivar can never be a bit-field, so this is safe.
    118   uint64_t FieldBitOffset = LookupFieldBitOffset(CGF.CGM, OID, 0, Ivar);
    119   uint64_t BitOffset = FieldBitOffset % CGF.CGM.getContext().getCharWidth();
    120   uint64_t AlignmentBits = CGF.CGM.getContext().getTargetInfo().getCharAlign();
    121   uint64_t BitFieldSize = Ivar->getBitWidthValue(CGF.getContext());
    122   CharUnits StorageSize =
    123     CGF.CGM.getContext().toCharUnitsFromBits(
    124       llvm::RoundUpToAlignment(BitOffset + BitFieldSize, AlignmentBits));
    125   CharUnits Alignment = CGF.CGM.getContext().toCharUnitsFromBits(AlignmentBits);
    126 
    127   // Allocate a new CGBitFieldInfo object to describe this access.
    128   //
    129   // FIXME: This is incredibly wasteful, these should be uniqued or part of some
    130   // layout object. However, this is blocked on other cleanups to the
    131   // Objective-C code, so for now we just live with allocating a bunch of these
    132   // objects.
    133   CGBitFieldInfo *Info = new (CGF.CGM.getContext()) CGBitFieldInfo(
    134     CGBitFieldInfo::MakeInfo(CGF.CGM.getTypes(), Ivar, BitOffset, BitFieldSize,
    135                              CGF.CGM.getContext().toBits(StorageSize),
    136                              Alignment.getQuantity()));
    137 
    138   V = CGF.Builder.CreateBitCast(V,
    139                                 llvm::Type::getIntNPtrTy(CGF.getLLVMContext(),
    140                                                          Info->StorageSize));
    141   return LValue::MakeBitfield(V, *Info,
    142                               IvarTy.withCVRQualifiers(CVRQualifiers),
    143                               Alignment);
    144 }
    145 
    146 namespace {
    147   struct CatchHandler {
    148     const VarDecl *Variable;
    149     const Stmt *Body;
    150     llvm::BasicBlock *Block;
    151     llvm::Value *TypeInfo;
    152   };
    153 
    154   struct CallObjCEndCatch : EHScopeStack::Cleanup {
    155     CallObjCEndCatch(bool MightThrow, llvm::Value *Fn) :
    156       MightThrow(MightThrow), Fn(Fn) {}
    157     bool MightThrow;
    158     llvm::Value *Fn;
    159 
    160     void Emit(CodeGenFunction &CGF, Flags flags) {
    161       if (!MightThrow) {
    162         CGF.Builder.CreateCall(Fn)->setDoesNotThrow();
    163         return;
    164       }
    165 
    166       CGF.EmitRuntimeCallOrInvoke(Fn);
    167     }
    168   };
    169 }
    170 
    171 
    172 void CGObjCRuntime::EmitTryCatchStmt(CodeGenFunction &CGF,
    173                                      const ObjCAtTryStmt &S,
    174                                      llvm::Constant *beginCatchFn,
    175                                      llvm::Constant *endCatchFn,
    176                                      llvm::Constant *exceptionRethrowFn) {
    177   // Jump destination for falling out of catch bodies.
    178   CodeGenFunction::JumpDest Cont;
    179   if (S.getNumCatchStmts())
    180     Cont = CGF.getJumpDestInCurrentScope("eh.cont");
    181 
    182   CodeGenFunction::FinallyInfo FinallyInfo;
    183   if (const ObjCAtFinallyStmt *Finally = S.getFinallyStmt())
    184     FinallyInfo.enter(CGF, Finally->getFinallyBody(),
    185                       beginCatchFn, endCatchFn, exceptionRethrowFn);
    186 
    187   SmallVector<CatchHandler, 8> Handlers;
    188 
    189   // Enter the catch, if there is one.
    190   if (S.getNumCatchStmts()) {
    191     for (unsigned I = 0, N = S.getNumCatchStmts(); I != N; ++I) {
    192       const ObjCAtCatchStmt *CatchStmt = S.getCatchStmt(I);
    193       const VarDecl *CatchDecl = CatchStmt->getCatchParamDecl();
    194 
    195       Handlers.push_back(CatchHandler());
    196       CatchHandler &Handler = Handlers.back();
    197       Handler.Variable = CatchDecl;
    198       Handler.Body = CatchStmt->getCatchBody();
    199       Handler.Block = CGF.createBasicBlock("catch");
    200 
    201       // @catch(...) always matches.
    202       if (!CatchDecl) {
    203         Handler.TypeInfo = 0; // catch-all
    204         // Don't consider any other catches.
    205         break;
    206       }
    207 
    208       Handler.TypeInfo = GetEHType(CatchDecl->getType());
    209     }
    210 
    211     EHCatchScope *Catch = CGF.EHStack.pushCatch(Handlers.size());
    212     for (unsigned I = 0, E = Handlers.size(); I != E; ++I)
    213       Catch->setHandler(I, Handlers[I].TypeInfo, Handlers[I].Block);
    214   }
    215 
    216   // Emit the try body.
    217   CGF.EmitStmt(S.getTryBody());
    218 
    219   // Leave the try.
    220   if (S.getNumCatchStmts())
    221     CGF.popCatchScope();
    222 
    223   // Remember where we were.
    224   CGBuilderTy::InsertPoint SavedIP = CGF.Builder.saveAndClearIP();
    225 
    226   // Emit the handlers.
    227   for (unsigned I = 0, E = Handlers.size(); I != E; ++I) {
    228     CatchHandler &Handler = Handlers[I];
    229 
    230     CGF.EmitBlock(Handler.Block);
    231     llvm::Value *RawExn = CGF.getExceptionFromSlot();
    232 
    233     // Enter the catch.
    234     llvm::Value *Exn = RawExn;
    235     if (beginCatchFn) {
    236       Exn = CGF.Builder.CreateCall(beginCatchFn, RawExn, "exn.adjusted");
    237       cast<llvm::CallInst>(Exn)->setDoesNotThrow();
    238     }
    239 
    240     CodeGenFunction::LexicalScope cleanups(CGF, Handler.Body->getSourceRange());
    241 
    242     if (endCatchFn) {
    243       // Add a cleanup to leave the catch.
    244       bool EndCatchMightThrow = (Handler.Variable == 0);
    245 
    246       CGF.EHStack.pushCleanup<CallObjCEndCatch>(NormalAndEHCleanup,
    247                                                 EndCatchMightThrow,
    248                                                 endCatchFn);
    249     }
    250 
    251     // Bind the catch parameter if it exists.
    252     if (const VarDecl *CatchParam = Handler.Variable) {
    253       llvm::Type *CatchType = CGF.ConvertType(CatchParam->getType());
    254       llvm::Value *CastExn = CGF.Builder.CreateBitCast(Exn, CatchType);
    255 
    256       CGF.EmitAutoVarDecl(*CatchParam);
    257 
    258       llvm::Value *CatchParamAddr = CGF.GetAddrOfLocalVar(CatchParam);
    259 
    260       switch (CatchParam->getType().getQualifiers().getObjCLifetime()) {
    261       case Qualifiers::OCL_Strong:
    262         CastExn = CGF.EmitARCRetainNonBlock(CastExn);
    263         // fallthrough
    264 
    265       case Qualifiers::OCL_None:
    266       case Qualifiers::OCL_ExplicitNone:
    267       case Qualifiers::OCL_Autoreleasing:
    268         CGF.Builder.CreateStore(CastExn, CatchParamAddr);
    269         break;
    270 
    271       case Qualifiers::OCL_Weak:
    272         CGF.EmitARCInitWeak(CatchParamAddr, CastExn);
    273         break;
    274       }
    275     }
    276 
    277     CGF.ObjCEHValueStack.push_back(Exn);
    278     CGF.EmitStmt(Handler.Body);
    279     CGF.ObjCEHValueStack.pop_back();
    280 
    281     // Leave any cleanups associated with the catch.
    282     cleanups.ForceCleanup();
    283 
    284     CGF.EmitBranchThroughCleanup(Cont);
    285   }
    286 
    287   // Go back to the try-statement fallthrough.
    288   CGF.Builder.restoreIP(SavedIP);
    289 
    290   // Pop out of the finally.
    291   if (S.getFinallyStmt())
    292     FinallyInfo.exit(CGF);
    293 
    294   if (Cont.isValid())
    295     CGF.EmitBlock(Cont.getBlock());
    296 }
    297 
    298 namespace {
    299   struct CallSyncExit : EHScopeStack::Cleanup {
    300     llvm::Value *SyncExitFn;
    301     llvm::Value *SyncArg;
    302     CallSyncExit(llvm::Value *SyncExitFn, llvm::Value *SyncArg)
    303       : SyncExitFn(SyncExitFn), SyncArg(SyncArg) {}
    304 
    305     void Emit(CodeGenFunction &CGF, Flags flags) {
    306       CGF.Builder.CreateCall(SyncExitFn, SyncArg)->setDoesNotThrow();
    307     }
    308   };
    309 }
    310 
    311 void CGObjCRuntime::EmitAtSynchronizedStmt(CodeGenFunction &CGF,
    312                                            const ObjCAtSynchronizedStmt &S,
    313                                            llvm::Function *syncEnterFn,
    314                                            llvm::Function *syncExitFn) {
    315   CodeGenFunction::RunCleanupsScope cleanups(CGF);
    316 
    317   // Evaluate the lock operand.  This is guaranteed to dominate the
    318   // ARC release and lock-release cleanups.
    319   const Expr *lockExpr = S.getSynchExpr();
    320   llvm::Value *lock;
    321   if (CGF.getLangOpts().ObjCAutoRefCount) {
    322     lock = CGF.EmitARCRetainScalarExpr(lockExpr);
    323     lock = CGF.EmitObjCConsumeObject(lockExpr->getType(), lock);
    324   } else {
    325     lock = CGF.EmitScalarExpr(lockExpr);
    326   }
    327   lock = CGF.Builder.CreateBitCast(lock, CGF.VoidPtrTy);
    328 
    329   // Acquire the lock.
    330   CGF.Builder.CreateCall(syncEnterFn, lock)->setDoesNotThrow();
    331 
    332   // Register an all-paths cleanup to release the lock.
    333   CGF.EHStack.pushCleanup<CallSyncExit>(NormalAndEHCleanup, syncExitFn, lock);
    334 
    335   // Emit the body of the statement.
    336   CGF.EmitStmt(S.getSynchBody());
    337 }
    338 
    339 /// Compute the pointer-to-function type to which a message send
    340 /// should be casted in order to correctly call the given method
    341 /// with the given arguments.
    342 ///
    343 /// \param method - may be null
    344 /// \param resultType - the result type to use if there's no method
    345 /// \param callArgs - the actual arguments, including implicit ones
    346 CGObjCRuntime::MessageSendInfo
    347 CGObjCRuntime::getMessageSendInfo(const ObjCMethodDecl *method,
    348                                   QualType resultType,
    349                                   CallArgList &callArgs) {
    350   // If there's a method, use information from that.
    351   if (method) {
    352     const CGFunctionInfo &signature =
    353       CGM.getTypes().arrangeObjCMessageSendSignature(method, callArgs[0].Ty);
    354 
    355     llvm::PointerType *signatureType =
    356       CGM.getTypes().GetFunctionType(signature)->getPointerTo();
    357 
    358     // If that's not variadic, there's no need to recompute the ABI
    359     // arrangement.
    360     if (!signature.isVariadic())
    361       return MessageSendInfo(signature, signatureType);
    362 
    363     // Otherwise, there is.
    364     FunctionType::ExtInfo einfo = signature.getExtInfo();
    365     const CGFunctionInfo &argsInfo =
    366       CGM.getTypes().arrangeFreeFunctionCall(resultType, callArgs, einfo,
    367                                              signature.getRequiredArgs());
    368 
    369     return MessageSendInfo(argsInfo, signatureType);
    370   }
    371 
    372   // There's no method;  just use a default CC.
    373   const CGFunctionInfo &argsInfo =
    374     CGM.getTypes().arrangeFreeFunctionCall(resultType, callArgs,
    375                                            FunctionType::ExtInfo(),
    376                                            RequiredArgs::All);
    377 
    378   // Derive the signature to call from that.
    379   llvm::PointerType *signatureType =
    380     CGM.getTypes().GetFunctionType(argsInfo)->getPointerTo();
    381   return MessageSendInfo(argsInfo, signatureType);
    382 }
    383