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, 20 insertions, 2 deletions

diff --git a/source/slang/slang.cpp b/source/slang/slang.cpp
index fe24fbd19..17f8ea96d 100644
--- a/source/slang/slang.cpp
+++ b/source/slang/slang.cpp
@@ -746,12 +746,30 @@ SLANG_API void spSetCodeGenTarget(
     req->addTarget(Slang::CodeGenTarget(target));
 }
 
-SLANG_API void spAddCodeGenTarget(
+SLANG_API int spAddCodeGenTarget(
     SlangCompileRequest*    request,
     SlangCompileTarget      target)
 {
     auto req = REQ(request);
-    req->addTarget(Slang::CodeGenTarget(target));
+    return (int) req->addTarget(Slang::CodeGenTarget(target));
+}
+
+SLANG_API void spSetTargetProfile(
+    SlangCompileRequest*    request,
+    int                     targetIndex,
+    SlangProfileID          profile)
+{
+    auto req = REQ(request);
+    req->targets[targetIndex]->targetProfile = profile;
+}
+
+SLANG_API void spSetTargetFlags(
+    SlangCompileRequest*    request,
+    int                     targetIndex,
+    SlangTargetFlags        flags)
+{
+    auto req = REQ(request);
+    req->targets[targetIndex]->targetFlags = flags;
 }
 
 SLANG_API void spSetOutputContainerFormat(