/// <inheritdoc/>
public override BlockCodegen Emit(BasicBlockBuilder BasicBlock)
{
if (CatchClauses.Count == 0)
{
return(TryBody.Emit(BasicBlock));
}
var exceptionDataType = StructType(new[] { PointerType(Int8Type(), 0), Int32Type() }, false);
var catchBlock = BasicBlock.CreateChildBlock("catch");
var catchLandingPadBlock = BasicBlock.CreateChildBlock("catch_landingpad");
var leaveBlock = BasicBlock.CreateChildBlock("leave");
// The try block is a regular block that jumps to the 'leave' block.
//
// try:
// <try body>
// br label %leave
var tryCodegen = TryBody.Emit(BasicBlock.WithUnwindTarget(catchLandingPadBlock, catchBlock));
BuildBr(tryCodegen.BasicBlock.Builder, leaveBlock.Block);
PopulateCatchBlock(catchBlock, leaveBlock);
ItaniumCxxFinallyBlock.PopulateThunkLandingPadBlock(catchLandingPadBlock, catchBlock.Block, false);
return(new BlockCodegen(leaveBlock, tryCodegen.Value));
}
/// <summary>
/// Populates the given 'catch' block.
/// </summary>
/// <param name="CatchBlock">The 'catch' block to populate.</param>
/// <param name="LeaveBlock">The 'leave' block to jump to when the 'catch' is done.</param>
private void PopulateCatchBlock(BasicBlockBuilder CatchBlock, BasicBlockBuilder LeaveBlock)
{
var catchBlockEntry = CatchBlock;
// Before we even get started on the catch block's body, we should first
// take the time to ensure that the '__cxa_begin_catch' environment set up
// by the catch block is properly terminated by a '__cxa_end_catch' call,
// even if an exception is thrown from the catch block itself. We can do
// so by creating a 'catch_end' block and a thunk landing pad.
var catchEndBlock = CatchBlock.CreateChildBlock("catch_end");
var catchExceptionBlock = CatchBlock.CreateChildBlock("catch_exception");
var catchEndLandingPadBlock = CatchBlock.CreateChildBlock("catch_end_landingpad");
ItaniumCxxFinallyBlock.PopulateThunkLandingPadBlock(
catchEndLandingPadBlock,
catchExceptionBlock.Block,
true);
CatchBlock = CatchBlock.WithUnwindTarget(catchEndLandingPadBlock, catchEndBlock);
// The catch block starts like this:
//
// catch:
// %exception_data = load { i8*, i32 }* %exception_data_alloca
// %exception_obj = extractvalue { i8*, i32 } %exception_data, 0
// %exception_ptr_opaque = call i8* @__cxa_begin_catch(i8* %exception_obj)
// %exception_ptr = bitcast i8* %exception_ptr_opaque to i8**
// %exception = load i8*, i8** %exception_ptr
// %exception_vtable_ptr_ptr = bitcast i8* %exception to i8**
// %exception_vtable_ptr = load i8*, i8** %exception_vtable_ptr_ptr
// %exception_typeid = <typeid> i64, i8* %exception_vtable_ptr
var exceptionData = BuildLoad(
CatchBlock.Builder,
CatchBlock.FunctionBody.ExceptionDataStorage.Value,
"exception_data");
var exceptionObj = BuildExtractValue(
CatchBlock.Builder,
exceptionData,
0,
"exception_obj");
var exceptionPtrOpaque = BuildCall(
CatchBlock.Builder,
CatchBlock.FunctionBody.Module.Declare(IntrinsicValue.CxaBeginCatch),
new LLVMValueRef[] { exceptionObj },
"exception_ptr_opaque");
var exceptionPtr = BuildBitCast(
CatchBlock.Builder,
exceptionPtrOpaque,
PointerType(PointerType(Int8Type(), 0), 0),
"exception_ptr");
var exception = BuildLoad(CatchBlock.Builder, exceptionPtr, "exception");
var exceptionVtablePtrPtr = BuildBitCast(
CatchBlock.Builder,
exception,
PointerType(PointerType(Int8Type(), 0), 0),
"exception_vtable_ptr_ptr");
var exceptionVtablePtr = AtAddressEmitVariable.BuildConstantLoad(
CatchBlock.Builder,
exceptionVtablePtrPtr,
"exception_vtable_ptr");
var exceptionTypeid = TypeIdBlock.BuildTypeid(
CatchBlock.Builder,
exceptionVtablePtr);
// Next, we need to figure out if we have a catch block that can handle the
// exception we've thrown. We do so by iterating over all catch blocks and
// testing if they're a match for the exception's type.
var fallthroughBlock = CatchBlock.CreateChildBlock("catch_test");
for (int i = 0; i < CatchClauses.Count; i++)
{
var clause = CatchClauses[i];
var catchBodyBlock = CatchBlock.CreateChildBlock("catch_body");
var catchBodyBlockTail = catchBodyBlock;
// First, emit the catch body. This is just a regular block that
// clears the exception value variable when it gets started and
// jumps to the 'catch_end' when it's done.
//
// catch_body:
// %exception_val = bitcast i8* %exception to <clause_type>
// store <clause_type> %exception_val, <clause_type>* %clause_exception_variable_alloca
// <catch clause body>
// br catch_end
var ehVarAddressAndBlock = clause.LLVMHeader
.AtAddressExceptionVariable.Address.Emit(catchBodyBlockTail);
catchBodyBlockTail = ehVarAddressAndBlock.BasicBlock;
BuildStore(
catchBodyBlockTail.Builder,
BuildBitCast(
catchBodyBlockTail.Builder,
exception,
catchBodyBlockTail.FunctionBody.Module.Declare(clause.ExceptionType),
"exception_val"),
ehVarAddressAndBlock.Value);
catchBodyBlockTail = clause.Body.Emit(catchBodyBlockTail).BasicBlock;
BuildBr(catchBodyBlockTail.Builder, catchEndBlock.Block);
// Each clause is implemented as:
//
// catch_clause:
// %clause_typeid = <typeid> i64, clause-exception-type
// %typeid_rem = urem i64 %exception_typeid_tmp, %clause_typeid
// %is_subtype = cmp eq i64 %typeid_rem, 0
// br i1 %is_subtype, label %catch_body, label %fallthrough
//
var clauseTypeid = CatchBlock.FunctionBody.Module.GetTypeId((LLVMType)clause.ExceptionType);
var typeIdRem = BuildURem(
CatchBlock.Builder,
exceptionTypeid,
ConstInt(exceptionTypeid.TypeOf(), clauseTypeid, false),
"typeid_rem");
var isSubtype = BuildICmp(
CatchBlock.Builder,
LLVMIntPredicate.LLVMIntEQ,
typeIdRem,
ConstInt(exceptionTypeid.TypeOf(), 0, false),
"is_subtype");
BuildCondBr(CatchBlock.Builder, isSubtype, catchBodyBlock.Block, fallthroughBlock.Block);
CatchBlock = fallthroughBlock;
fallthroughBlock = CatchBlock.CreateChildBlock("catch_test");
}
// If we didn't match any catch clauses, then we'll rethrow the exception and
// unwind to the end-catch landing pad.
//
// no_matching_clause:
// invoke void @__cxa_rethrow() to label %unreachable unwind label %catch_end_landingpad
//
// unreachable:
// unreachable
BuildInvoke(
CatchBlock.Builder,
CatchBlock.FunctionBody.Module.Declare(IntrinsicValue.CxaRethrow),
new LLVMValueRef[] { },
fallthroughBlock.Block,
catchEndLandingPadBlock.Block,
"");
BuildUnreachable(fallthroughBlock.Builder);
// The catch end block simply calls '__cxa_end_catch' and jumps to the 'leave'
// block. Like so:
//
// catch_end:
// call void @__cxa_end_catch()
// br label %leave
BuildCall(
catchEndBlock.Builder,
CatchBlock.FunctionBody.Module.Declare(IntrinsicValue.CxaEndCatch),
new LLVMValueRef[] { },
"");
BuildBr(catchEndBlock.Builder, LeaveBlock.Block);
// The 'catch exception' block is entered when an exception is thrown from
// the 'catch' block, or if the catch block is ill-equipped to handle the
// exception. Its responsibility is to end the catch block and jump to
// the manual unwind target.
//
// catch_exception:
// call void @__cxa_end_catch()
// br label %manual_unwind_target
BuildCall(
catchExceptionBlock.Builder,
catchExceptionBlock.FunctionBody.Module.Declare(IntrinsicValue.CxaEndCatch),
new LLVMValueRef[] { },
"");
BuildBr(catchExceptionBlock.Builder, ItaniumCxxFinallyBlock.GetManualUnwindTarget(catchBlockEntry));
}
