[llvm-dev] Adding new a new type

[Friedman, Eli via llvm-dev]

On 5/14/2018 4:38 PM, Jason Ott wrote:
> Ok, so I can use the structure-type to represent base or acid or 
> salts.  My next question is how union-typing works in LLVM.  After 
> reading a bit about, it's unclear to me if it is a "thing" anymore; my 
> intuition -- and poking around in the sources is that it's a "no", 
> it's been deprecated.

No, LLVM doesn't have unions; you just bitcast pointers between 
different struct types.  (In general, if you're having trouble 
understanding how to lower something to LLVM IR, it's often useful to 
use "clang -S -emit-llvm" to see what clang emits for a simple C testcase.)

> Which then means that it doesn't much matter about typing LLVM.  I can 
> pass that up to a python script and handle typing up there.

Yes, you should only use LLVM types as far as they're actually helpful.

-Eli

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