forked from OSchip/llvm-project
634484885c
We can cast a string to a record via !cast, but we have no mechanism
to check if it is valid and TableGen will raise an error if failed to
cast. Besides, we have no semantic null in TableGen (we have `?` but
different backends handle uninitialized value differently), so operator
like `dyn_cast<>` is hard to implement.
In this patch, we add a new operator `!exists<T>(s)` to check whether
a record with type `T` and name `s` exists. Self-references are allowed
just like `!cast`.
By doing these, we can write code like:
```
class dyn_cast_to_record<string name> {
R value = !if(!exists<R>(name), !cast<R>(name), default_value);
}
defvar v = dyn_cast_to_record<"R0">.value; // R0 or default_value.
```
Reviewed By: tra, nhaehnle
Differential Revision: https://reviews.llvm.org/D127948
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| BackEnds.rst | ||
| BackGuide.rst | ||
| ProgRef.rst | ||
| index.rst | ||