Parameter block work (#276)

* Don't auto-enable IR use for compute tests

The `COMPARE_COMPUTE` and `COMPARE_RENDER_COMPUTE` test fixtures were set up to always enable the `-use-ir` flag on Slang, which precludes having any tests that confirm functionality on the old non-IR path (which is still required by our main customer).

This change adds the `-xslang -use-ir` flags explicitly to any compute test cases that left them out, and makes the fixture no longer add it by default.

* Continue building out parameter block support

The initial front-end logic for parameter blocks was already added, but they are still missing a bunch of functionality. This change addresses some of the known issues:

- Bug fix: don't try to emit HLSL `register` bindings for variables that consume whole register spaces/sets

- Overhaul type layout logic so that it can make decisions based on a given code generation target (currently passed in as a `TargetRequest`), which allows us to decide whether or not a parameter block should get its own register set on a per-target basis.
  - Always use a register space/set for Vulkan
  - Never use a register space/set for HLSL SM 5.0 and lower
  - By default, don't use register spaces/sets for HLSL output
  - Add a command-line flag and some "target flags" to enable register-space usage for D3D targets

- Hackily add initial support for parameter blocks in the AST-to-AST path
  - This just blindly lowers `ParameterBlock<T>` to `T`, which shouldn't quite work
  - A more complete overhaul will probably need to wait until the AST-to-AST legalization is changed to use the `LegalType`s from the IR legalization pass.

- Add a compute-based test case to actually run code using parameter blocks
  - This file runs test cases both with and without the IR

1 files changed, 14 insertions, 0 deletions

diff --git a/source/slang/lower.cpp b/source/slang/lower.cpp
index ccf302027..a15104d6a 100644
--- a/source/slang/lower.cpp
+++ b/source/slang/lower.cpp
@@ -797,6 +797,20 @@ struct LoweringVisitor
             lowerType(type->valueType));
     }
 
+    RefPtr<Type> visitParameterBlockType(ParameterBlockType* type)
+    {
+        // TODO: When doing AST-to-AST lowering, we want to lower
+        // a `ParameterBlock<T>` just like a `ConstantBuffer<T>`.
+        //
+        // HACK: for now we will try to simply lower the type
+        // directly to its stated element type, and see how
+        // that works.
+
+        return lowerType(type->getElementType());
+//        return getSession()->getConstantBufferType(
+//            lowerType(type->getElementType());
+    }
+
     RefPtr<Type> transformSyntaxField(Type* type)
     {
         return lowerType(type);