1. Function type variables should not include class type variables,
because they are not bound to the function.
2. Defer type variable constraint evaluation until we get all fields
definition.
Fixes nondeterministic error messages due to nondeterministic
unification order. As all unification operations will be restored, the
error messages should not be affected by the unification order before
the failure operation.
Raise error when index out of range. Note that we use llvm.expect to
tell the optimizer that we expect not to raise an exception, so the
normal path performance would be better. If this assumption is violated,
the exception overhead might be slightly larger, but the percentage
increase in overhead should not be high since exception unwinding is
already pretty slow.
- No longer check if the statement will return. Instead, we check if
the current basic block is terminated, which is simpler and handles
exception/break/continue better.
- Use invoke statement when unwind is needed.
- Moved codegen for a block of statements into a separate function.
- Added `Exception` primitive type and some builtin exception types.
Note that all exception types share the same layout, and should
inherit from the base `Exception` type. There are some hacks in the
toplevel module for handling exception types, we should revisit and
fix them later.
- Added new primitive types to concrete type module, otherwise there
would be some weird type errors.
- Changed the representation of strings to CSlice<u8>, instead of
CString.
