[PATCH] D71407: [TableGen] Introduce a `defvar` statement.

[Simon Tatham via Phabricator via llvm-commits]

simon_tatham added a comment.

I've been working around the lack of this for a while, so I thought it was worth at least trying to get it accepted.

This is something of a first draft. Things I'm not certain of:

- should a defvar in a foreach be local to it? (Probably)
- should I allow defvar inside a class or def as well as in a multiclass, defining variables that vanish at the closing brace but can be referred to by the definitions of proper class member values? (Possibly)
- is defvar the sensible name? (`def` and `let` were already taken; I considered C++ `using`, but thought `defvar` fits reasonably well with the existing `defset`)


Repository:
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