Work towards target-specific function overloads (#210)

* Checkpoint: interface conformance work

- Add explicit definition of `saturate` for the GLSL target, which calls through to `clamp`

- Needed to add explicit initializer to `__BuiltinFloatingPointType` to allow initialization from a single `float`, so that the `saturate` implementation can be sure that it can initialize a `T` from `0.0` or `1.0`.

- This triggered errors in overload resolution, because the logic in place could not figure out that the `T` of the outer generic (`saturate<T>()`) conformed to the interface required by the callee.

At this point I have the call to the scalar `clamp()` getting past type-checking, but not the vector or matrix cases.

* More fixups for overload resolution inside generics

- Make sure value parameters are treated the same as type parameters: we only want to solve for the parameters of the generic actually being applied, and not accidentally generate constraints for outer generics (e.g., when checking the body of a generic function).

- Make sure that the diagnostics stuff uses the correct source manager when expanding the location of a builtin.

* Fixes for function redeclaration

- Handle case of redeclaring a generic function
  - Enumerate siblings in the parent of the *generic* not the parent of the *function*
  - Add logic to compare generic signatures
  - When generic signatures match, specialize functions to compatible generic arguments before comparing the function signatures

- Fix redeclaration logic to *not* detect prefix/postifx operators as redeclarations of one another

- Build an explicit representation of function redeclaration groups
  - First declaration is the "primary" and others are stored in a linked list

- Make overload resolution handle redeclared functions
  - Only consider the primary declaration and skip others

1 files changed, 6 insertions, 1 deletions

diff --git a/source/slang/lower-to-ir.cpp b/source/slang/lower-to-ir.cpp
index 2f3456d0c..e0dbd5dae 100644
--- a/source/slang/lower-to-ir.cpp
+++ b/source/slang/lower-to-ir.cpp
@@ -785,7 +785,12 @@ struct ValLoweringVisitor : ValVisitor<ValLoweringVisitor, LoweredValInfo, Lower
 
     LoweredTypeInfo visitType(Type* type)
     {
-        SLANG_UNIMPLEMENTED_X("type lowering");
+        // TODO(tfoley): Now that we use the AST types directly in the IR, there
+        // isn't much to do in the "lowering" step. Still, there might be cases
+        // where certain kinds of legalization need to take place, so this
+        // visitor setup might still be needed in the long run.
+        return LoweredTypeInfo(type);
+//        SLANG_UNIMPLEMENTED_X("type lowering");
     }
 
     LoweredTypeInfo visitFuncType(FuncType* type)