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, 4 insertions, 2 deletions

diff --git a/source/slang/compiler.h b/source/slang/compiler.h
index 7a045d23c..f42f36c1f 100644
--- a/source/slang/compiler.h
+++ b/source/slang/compiler.h
@@ -176,8 +176,10 @@ namespace Slang
     class TargetRequest : public RefObject
     {
     public:
-        CompileRequest* compileRequest;
-        CodeGenTarget   target;
+        CompileRequest*     compileRequest;
+        CodeGenTarget       target;
+        SlangTargetFlags    targetFlags = 0;
+        Slang::Profile      targetProfile = Slang::Profile::Unknown;
 
         // The resulting reflection layout information
         RefPtr<ProgramLayout> layout;