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[Tolk] throw interrupts control flow; never type

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In FunC (and in Tolk before) throwing an exception is just
calling a built-in function:
> throw 123; // actually, __throw(123)
Since it's a regular function, the compiler was not aware
that execution will stop, and all following code is unreachable.
For instance, `throw` in the end on function needed to be
followed by `return` statement.

Now, `throw` interrupts control flow, all statements after
it are considered unreachable. At IR level, code Ops are
also not produced.

This works because a built-in __throw() now has `never` type.
It can also be applied to custom functions:
> fun alwaysThrow(): never { throw 123; }
The code after alwaysThrow() call will also be unreachable.
This commit is contained in:
tolk-vm 2025-02-24 20:15:24 +03:00
parent 7bcb8b895f
commit ef0328837f
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GPG key ID: 7905DD7FE0324B12
10 changed files with 227 additions and 25 deletions
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5
tolk/builtins.cpp
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@ -1088,6 +1088,7 @@ void define_builtins() {
TypePtr Slice = TypeDataSlice::create();
TypePtr Builder = TypeDataBuilder::create();
TypePtr Tuple = TypeDataTuple::create();
TypePtr Never = TypeDataNever::create();
std::vector<GenericsDeclaration::GenericsItem> itemsT;
itemsT.emplace_back("T");
@ -1201,10 +1202,10 @@ void define_builtins() {
define_builtin_func("__isNull", {typeT}, Bool, declGenericT,
compile_is_null,
FunctionData::flagMarkedAsPure);
define_builtin_func("__throw", ParamsInt1, Unit, nullptr,
define_builtin_func("__throw", ParamsInt1, Never, nullptr,
compile_throw,
0);
define_builtin_func("__throw_arg", {typeT, Int}, Unit, declGenericT,
define_builtin_func("__throw_arg", {typeT, Int}, Never, declGenericT,
compile_throw_arg,
0);
define_builtin_func("__throw_if_unless", ParamsInt3, Unit, nullptr,