MS ABI: Implement support for throwing a C++ exception

Throwing a C++ exception, under the MS ABI, is implemented using three
components:
- ThrowInfo structure which contains information like CV qualifiers,
  what destructor to call and a pointer to the CatchableTypeArray.
- In a significant departure from the Itanium ABI, copying by-value
  occurs in the runtime and not at the catch site.  This means we need
  to enumerate all possible types that this exception could be caught as
  and encode the necessary information to convert from the exception
  object's type to the catch handler's type.  This includes complicated
  derived to base conversions and the execution of copy-constructors.

N.B. This implementation doesn't support the execution of a
copy-constructor from within the runtime for now.  Adding support for
that functionality is quite difficult due to things like default
argument expressions which may evaluate arbitrary code hiding in the
copy-constructor's parameters.

Differential Revision: http://reviews.llvm.org/D8066

llvm-svn: 231328

1 files changed, 18 insertions, 96 deletions

diff --git a/clang/lib/CodeGen/CGException.cpp b/clang/lib/CodeGen/CGException.cpp
index a80af4c20a1..80292d5bd6f 100644
--- a/clang/lib/CodeGen/CGException.cpp
+++ b/clang/lib/CodeGen/CGException.cpp
@@ -25,15 +25,6 @@
 using namespace clang;
 using namespace CodeGen;
 
-static llvm::Constant *getAllocateExceptionFn(CodeGenModule &CGM) {
-  // void *__cxa_allocate_exception(size_t thrown_size);
-
-  llvm::FunctionType *FTy =
-    llvm::FunctionType::get(CGM.Int8PtrTy, CGM.SizeTy, /*IsVarArgs=*/false);
-
-  return CGM.CreateRuntimeFunction(FTy, "__cxa_allocate_exception");
-}
-
 static llvm::Constant *getFreeExceptionFn(CodeGenModule &CGM) {
   // void __cxa_free_exception(void *thrown_exception);
 
@@ -43,17 +34,6 @@ static llvm::Constant *getFreeExceptionFn(CodeGenModule &CGM) {
   return CGM.CreateRuntimeFunction(FTy, "__cxa_free_exception");
 }
 
-static llvm::Constant *getThrowFn(CodeGenModule &CGM) {
-  // void __cxa_throw(void *thrown_exception, std::type_info *tinfo,
-  //                  void (*dest) (void *));
-
-  llvm::Type *Args[3] = { CGM.Int8PtrTy, CGM.Int8PtrTy, CGM.Int8PtrTy };
-  llvm::FunctionType *FTy =
-    llvm::FunctionType::get(CGM.VoidTy, Args, /*IsVarArgs=*/false);
-
-  return CGM.CreateRuntimeFunction(FTy, "__cxa_throw");
-}
-
 static llvm::Constant *getUnexpectedFn(CodeGenModule &CGM) {
   // void __cxa_call_unexpected(void *thrown_exception);
 
@@ -381,17 +361,16 @@ namespace {
 // differs from EmitAnyExprToMem only in that, if a final copy-ctor
 // call is required, an exception within that copy ctor causes
 // std::terminate to be invoked.
-static void EmitAnyExprToExn(CodeGenFunction &CGF, const Expr *e,
-                             llvm::Value *addr) {
+void CodeGenFunction::EmitAnyExprToExn(const Expr *e, llvm::Value *addr) {
   // Make sure the exception object is cleaned up if there's an
   // exception during initialization.
-  CGF.pushFullExprCleanup<FreeException>(EHCleanup, addr);
-  EHScopeStack::stable_iterator cleanup = CGF.EHStack.stable_begin();
+  pushFullExprCleanup<FreeException>(EHCleanup, addr);
+  EHScopeStack::stable_iterator cleanup = EHStack.stable_begin();
 
   // __cxa_allocate_exception returns a void*;  we need to cast this
   // to the appropriate type for the object.
-  llvm::Type *ty = CGF.ConvertTypeForMem(e->getType())->getPointerTo();
-  llvm::Value *typedAddr = CGF.Builder.CreateBitCast(addr, ty);
+  llvm::Type *ty = ConvertTypeForMem(e->getType())->getPointerTo();
+  llvm::Value *typedAddr = Builder.CreateBitCast(addr, ty);
 
   // FIXME: this isn't quite right!  If there's a final unelided call
   // to a copy constructor, then according to [except.terminate]p1 we
@@ -400,11 +379,11 @@ static void EmitAnyExprToExn(CodeGenFunction &CGF, const Expr *e,
   // evaluated but before the exception is caught.  But the best way
   // to handle that is to teach EmitAggExpr to do the final copy
   // differently if it can't be elided.
-  CGF.EmitAnyExprToMem(e, typedAddr, e->getType().getQualifiers(), 
-                       /*IsInit*/ true);
+  EmitAnyExprToMem(e, typedAddr, e->getType().getQualifiers(),
+                   /*IsInit*/ true);
 
   // Deactivate the cleanup block.
-  CGF.DeactivateCleanupBlock(cleanup, cast<llvm::Instruction>(typedAddr));
+  DeactivateCleanupBlock(cleanup, cast<llvm::Instruction>(typedAddr));
 }
 
 llvm::Value *CodeGenFunction::getExceptionSlot() {
@@ -436,75 +415,18 @@ llvm::Value *CodeGenFunction::getAbnormalTerminationSlot() {
 
 void CodeGenFunction::EmitCXXThrowExpr(const CXXThrowExpr *E,
                                        bool KeepInsertionPoint) {
-  if (!E->getSubExpr()) {
-    CGM.getCXXABI().emitRethrow(*this, /*isNoReturn*/true);
-
-    // throw is an expression, and the expression emitters expect us
-    // to leave ourselves at a valid insertion point.
-    if (KeepInsertionPoint)
-      EmitBlock(createBasicBlock("throw.cont"));
-
-    return;
-  }
-
-  if (CGM.getTarget().getTriple().isKnownWindowsMSVCEnvironment()) {
-    // Call std::terminate().
-    llvm::CallInst *TermCall = EmitNounwindRuntimeCall(CGM.getTerminateFn());
-    TermCall->setDoesNotReturn();
-
-    // throw is an expression, and the expression emitters expect us
-    // to leave ourselves at a valid insertion point.
-    if (KeepInsertionPoint)
-      EmitBlock(createBasicBlock("throw.cont"));
-
-    return;
-  }
-
-  QualType ThrowType = E->getSubExpr()->getType();
-
-  if (ThrowType->isObjCObjectPointerType()) {
-    const Stmt *ThrowStmt = E->getSubExpr();
-    const ObjCAtThrowStmt S(E->getExprLoc(),
-                            const_cast<Stmt *>(ThrowStmt));
-    CGM.getObjCRuntime().EmitThrowStmt(*this, S, false);
-    // This will clear insertion point which was not cleared in
-    // call to EmitThrowStmt.
-    if (KeepInsertionPoint)
-      EmitBlock(createBasicBlock("throw.cont"));
-    return;
-  }
-  
-  // Now allocate the exception object.
-  llvm::Type *SizeTy = ConvertType(getContext().getSizeType());
-  uint64_t TypeSize = getContext().getTypeSizeInChars(ThrowType).getQuantity();
-
-  llvm::Constant *AllocExceptionFn = getAllocateExceptionFn(CGM);
-  llvm::CallInst *ExceptionPtr =
-    EmitNounwindRuntimeCall(AllocExceptionFn,
-                            llvm::ConstantInt::get(SizeTy, TypeSize),
-                            "exception");
-  
-  EmitAnyExprToExn(*this, E->getSubExpr(), ExceptionPtr);
-
-  // Now throw the exception.
-  llvm::Constant *TypeInfo = CGM.GetAddrOfRTTIDescriptor(ThrowType, 
-                                                         /*ForEH=*/true);
-
-  // The address of the destructor.  If the exception type has a
-  // trivial destructor (or isn't a record), we just pass null.
-  llvm::Constant *Dtor = nullptr;
-  if (const RecordType *RecordTy = ThrowType->getAs<RecordType>()) {
-    CXXRecordDecl *Record = cast<CXXRecordDecl>(RecordTy->getDecl());
-    if (!Record->hasTrivialDestructor()) {
-      CXXDestructorDecl *DtorD = Record->getDestructor();
-      Dtor = CGM.getAddrOfCXXStructor(DtorD, StructorType::Complete);
-      Dtor = llvm::ConstantExpr::getBitCast(Dtor, Int8PtrTy);
+  if (const Expr *SubExpr = E->getSubExpr()) {
+    QualType ThrowType = SubExpr->getType();
+    if (ThrowType->isObjCObjectPointerType()) {
+      const Stmt *ThrowStmt = E->getSubExpr();
+      const ObjCAtThrowStmt S(E->getExprLoc(), const_cast<Stmt *>(ThrowStmt));
+      CGM.getObjCRuntime().EmitThrowStmt(*this, S, false);
+    } else {
+      CGM.getCXXABI().emitThrow(*this, E);
     }
+  } else {
+    CGM.getCXXABI().emitRethrow(*this, /*isNoReturn=*/true);
   }
-  if (!Dtor) Dtor = llvm::Constant::getNullValue(Int8PtrTy);
-
-  llvm::Value *args[] = { ExceptionPtr, TypeInfo, Dtor };
-  EmitNoreturnRuntimeCallOrInvoke(getThrowFn(CGM), args);
 
   // throw is an expression, and the expression emitters expect us
   // to leave ourselves at a valid insertion point.