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, 28 insertions, 0 deletions

diff --git a/tests/compute/parameter-block.slang b/tests/compute/parameter-block.slang
new file mode 100644
index 000000000..d10a1e9c2
--- /dev/null
+++ b/tests/compute/parameter-block.slang
@@ -0,0 +1,28 @@
+//TEST(compute):COMPARE_COMPUTE:-xslang -use-ir
+//TEST(compute):COMPARE_COMPUTE:
+
+//TEST_INPUT:ubuffer(data=[0 0 0 0], stride=4):dxbinding(0),glbinding(0),out
+//TEST_INPUT:ubuffer(data=[0 1 2 3], stride=4):dxbinding(1),glbinding(1)
+
+// Ensure that Slang `ParameterBlock` type is lowered
+// to HLSL in the fashion that we expect.
+
+struct P
+{
+	RWStructuredBuffer<int> buffer;
+};
+
+ParameterBlock<P> block0;
+ParameterBlock<P> block1;
+
+[numthreads(4, 1, 1)]
+void computeMain(uint3 dispatchThreadID : SV_DispatchThreadID)
+{
+	uint tid = dispatchThreadID.x;
+
+	int inVal = block1.buffer[tid];
+
+	int outVal = inVal;
+
+	block0.buffer[tid] = outVal;
+}
\ No newline at end of file