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* Fix up test runner output for compute.
We want compute-based tests to produce a `.actual` file when compilation fails, so we can easily diagnose the issue. I thought I'd added this capability previous, but it seemst to not be present any more.
* Compute result types for constructor decls
Fixes #246
When the parser sees an `init()` declaration, it can't easily know what type is is supposed to return, so it leaves the type as NULL. This was causing some downstream crashes.
Rather than special-case every site that cares about the result type of a callable, we will instead ensure that we install an actual result type on an initializer/constructor as part of its semantic checking.
This code needs to handle both the case where the initializer is declared inside a type, as well as the case where it is declared inside an `extension`.
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This change includes a lot of infrastructure work, but the main point is to allow code like the following:
```
// define an interface
interface Helper { float help(); }
// define a generic function that uses the interface
float test<T : Helper>( T t ) { return t.help(); }
// define a type that implements the interface
struct A : Helper { float help() { return 1.0 } }
// define an ordinary function that calls the
// generic function with a concrete type:
float doIt()
{
A a;
return test<A>(a);
}
```
Getting this to generate valid code involves a lot of steps. This change includes the initial version of all of these steps, but leaves a lot of gaps where more complete implementation is required.
The changes include:
- Member lookup on types has been centralized, and now handles the case where the type we are looking for a member in is a generic parameter (e.g., given `t.help()` we can now look up `help` in `Helper` by knowing that `t` is a `T` and `T` conforms to `Helper`).
- There is an obvious cleanup still to be done here where the same exact logic should be used to look up available "constructor" declarations inside a type when the type is used like a function.
- Add a notion of subtype constraint "wittnesses" to the type system. When a generic is declared as taking `<T : Helper>` it really takes two generic parameters: the type `T` and a proof that `T` conforms to `Helper`. The actual arguments to a generic will then include both the type argument and a suitable witness argument (both type-level values).
- As it stands right now, a witness wraps a `DeclRef` to the declaration that represents the appropriate subtype relationship. So if we have `struct A : Helper`, that `: Helper` part turns into an `InheritanceDecl` member, and a reference to that member can serve as a witness to the fact that `A` conforms to `Helper`.
- Make explicit generic application `G<A,B>` synthesize the additional arguments that represent conformances required by the generic.
- This does *not* yet deal with the case where a generic is implicitly specialized as part of an ordinary call `G(a,b)`
- A bug fix to not auto-specialize generics during lookup. The problem here was related to an attempted fix of an earlier issue.
During checking of a method nested in a generic type, we were running into problems where `DeclRefType::create()` was getting called on an un-specialized reference to `vector`, and this was leading to a crash when the code looked for the arguments for the generic. This was worked around by having name lookup automatically specialize any generics it runs into while going through lookup contexts.
That choice creates the problem that in a generic method like this:
```
void test<T>(T val) { ... }
```
any reference to `val` inside the body of `test` will end up getting specialized so that it is effectively `test<T>::val`, when that isn't really needed.
- Add front-end logic to check that when a type claims to conform to an interface it actually must provide the methods required by the interface. The checking process goes ahead and builds a front-end "witness table" that maps declarations in the interface being conformed to over to their concrete implementations for the type.
- At the moment the checking is completely broken and bad: it assumes that *any* member with the right name is an appropriate declaration to satisfy a requirement. That obviously needs to be fixed.
- Add an explicit operation to the IR for lookup of methods: `lookup_interface_method(w, r)` where `w` is a reference to the "witness" value and `r` is an `IRDeclRef` for the member we want to look up.
- Add an explicit notion of witness tables to the IR. These end up being the IR representation of an `InheritanceDecl` in a type, and they are generated by enumerating the members that satisfy the interface requirements (which were handily already enumerated by the front-end checking). The witness table is an explicit IR value, and so it will be referenced/used at the site where conformance is being exploited (e.g., as part of a `specialize` call), so it should be safe to eliminate witness tables that are unused (since they represent conformances that aren't actually exploited). Similarly, the entries in a witness table are uses of the functions that implement interface methods, and so keep those live.
- In order to implement the above, I did a bit of a cleanup pass on the IR representation so that there is an `IRUser` base that `IRInst` inherits from, so that we can have users of values that aren't instructions.
- One annoying thing is that because of how types and generics are handled in the IR, we needed a way to have a type-level `Val` that wraps an IR-level value: e.g., to allow an IR-level witness table to be used as one of the arguments for specialization of a generic. The design I chose here is to have a "proxy" `Val` subclass (`IRProxyVal`) that wraps an `IRValue*`. These should only ever appear as part of types and `DeclRef`s that are used by the IR.
- One annoying bit here is that an IR value might then have a use that is not manifest in the set of IR instructions, and instead only appears as part of a type somewhere.
- I'm not 100% happy with this design, but it seems like we'd have to tackle similar issues if/when we eventually allow functions to have `constexpr` or `@Constant` parameters
- Make generic specialization also propagate witness table arguments through to their use sites (this is mostly just the existing substitution machinery, once we have `IRProxyVal`), and then include logic to specialize `lookup_interface_method` instructions when their first operand is a concrete witness table.
All of this work allows a single limited test using generics with constraints to pass, but more work is needed to make the solution robust.
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There are two big changes here:
- Add logic during the initial IR cloning pass for an entry point + target that tries to pick the best possible version of any target-overloaded function. This allows us to pick the intrinsic version of `saturate()` when compiling for HLSL output, but then pick the non-intrinsic version (that is implemented in terms of `clamp()`) when targetting GLSL.
- Add an initial specialization pass that tries to deal with generics. This required some fixing work to IR generation, so that we correctly generate explicit operations to specialize a generic for specific types (this is currently implemented as a `specialize` instruction that takes the generic to specialize plus a declaration-reference that represents the specialized form). With that work in place, we can scan for `specialize` instructions inside of non-generic functions, and use them to trigger generation of specialized code. We rely on the name-mangling scheme to help us find pre-existing specializations when possible.
There are also a bunch of cleanups encountered along the way:
- Don't use the explicit `layout(offset=...)` for uniforms, because it isn't supported by all current drivers. For now we will just assume that our layout rules compute the same values that the driver would for un-marked-up code. We can come back later and try to implement a workaround in the cases where this doesn't apply (e.g., by re-running the layout logic as part of emission, and dropping layout modifiers from variables that don't need explicit layout).
- Fix some issues in IR dump printing so that we print function declarations more nicely.
- Testing: print out failing pixel when image-diff fails
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None of these changes are made "live" at the moment. I'm just trying to get them checked in to avoid divering too far from `master` at any point during development.
- Add basic emit logic to produce GLSL from the IR in a few cases (the existing IR emit logic was ad hoc and HLSL-specific)
- When lowering a function declaration, walk up its chain of parent declarations to collect additional parameters as needed
- When lowering a call, make sure to add generic arguments that come from the declaration reference being called
- Attach a "mangled name" to symbols when lowering, so that we can eventually use that name to resolve things for linkage.
- After the above work, I had to apply some fixups to make sure that generic arguments *don't* get added when the user is calling an `__intrinsic_op` function, since those should map 1-to-1 down to instructions with just their ordinary parameter list.
A big open question right now is whether I should continue to represent the generic arguments as just part of the ordinary argument list for a function, or split them out into separate `applyGeneric` and `apply` steps.
A strongly related question is whether a declaration with generic parameters should lower into a single declaration, or one declaration nested inside an outer generic declaration.
A good future step at this point would be to eliminate a lot of the `__intrinsic_op` stuff in favor of having the builtin functions include their own definitions, which might be in terms of a new expression-level construct for writing inline IR operations. This can't be done until the existing AST-to-AST path is no longer needed for cross-compilation purposes.
More immediate next steps here:
- We need a way to round-trip calls to external declaration that get handled by this mangled-name logic. Basically, if we are asked to output HLSL and we see a call to `_S...GetDimensions...(float4, t, a, ...)` we need to be able to walk the mangled name and get back to `t.getDimensions(a, ...)` without a whole lot of manual definitions to make things round-trip.
- In the other case, where a declaration isn't built-in for the chosen target, we need to be able to load a module of target-specific definitions (which will somehow map back to symbols with certain mangled names) and then look these up (by mangled name) and then load/link/inline them into the user's IR to satisfy requirements in their code.
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