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