ChuanqiXu9 wrote:
> Thanks! With all the explanation, the patch makes a lot of sense. Generally
> LG, I just have a few more NITs and feel it's good to go.
Thanks.
>
> I am surprised to hear we have less TypeIDs than DeclIDs. My mental model was
> that for every type Decl we introduce, we'd have at least a few types with it
> (the type itself, pointer to that type, reference to that type, functions
> returning that type, etc). And every non-type declaration will have it's own
> type (the functions often have unique signatures). Do we end up reusing the
> types from the current compilation and other modules we imported often enough
> that the amount of newly introduced types ends up being small? Or is my logic
> flawed in some ways?
Since most of the time, the types are reused. For example, if we have,
```
export module A;
export struct A { int a; }
export A getA(A) { return {43}; }
```
```
export module B;
import A;
export struct B {
A v1;
A v2;
A v3;
};
export A getAFromB(A p) { ... }
```
In the above example, in module B, there will be (in my mind, I didn't
experiment actually) 6 new decls (a new `struct decl` for `B`, 3 new `field
decl` for `v1`, `v2` and `v3`. a new `function decl` for `getAFromB` and a new
parm decl for `p`). However, there will only be only one new type, the struct
type B. The function type `A *(A)` is reused.
So I feel it pretty makes sense that the number of type ID is much less than
Decl ID.
https://github.com/llvm/llvm-project/pull/92511
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