Support generic `struct` types during IR-based emit

Fixes #318

Most of the required support was actually in place, so this is just a bunch of fixes:

- Detect when we are in "full IR" mode, so that we can always emit `struct` declarations with their mangled named (which will produce different names for different specializations, since we emit decl-refs)

  - Carefully exclude builtin types from this for now. We'll need a more complete solution for mapping HLSL/Slang builtin types to their GLSL equivalents soon.

- Skip emitting types referenced by generic IR functions, since they might not be usable.

  - Also fix things up so that we emit types used in the initializer for any global variables.

- Fix bug in generic specialization where we specialize the same function more than once, with different type arguments. We were crashing on a `Dictionary::Add` call where the key already exists from a previous specialization attempt.

- Fix name-mangling logic so that when outputting a possibly-specialized generic it looks for the outer-most `GenericSubstitution` rather than just the first one in the list. This is to handle the way that we insert other substitutions willy-nilly in places where they realistically don't belong. :(

All of these changes together allow us to pass a slightly modified (more advanced) version of the test case posted to #318.

2 files changed, 41 insertions, 0 deletions

diff --git a/tests/compute/generic-struct.slang b/tests/compute/generic-struct.slang
new file mode 100644
index 000000000..fd56ae0e9
--- /dev/null
+++ b/tests/compute/generic-struct.slang
@@ -0,0 +1,37 @@
+//TEST(compute):COMPARE_COMPUTE:-xslang -use-ir
+//TEST_INPUT:ubuffer(data=[0 0 0 0], stride=4):dxbinding(0),glbinding(0),out
+
+// Check that user code can declare and use a generic
+// `struct` type.
+
+RWStructuredBuffer<int> outputBuffer;
+
+__generic<T>
+struct GenStruct
+{
+	T x;
+	T y;
+};
+
+__generic<T>
+T test(T val)
+{
+	GenStruct<T> gs;
+	gs.x = val;
+	gs.y = val;
+	return gs.x;
+}
+
+
+[numthreads(4, 1, 1)]
+void computeMain(uint3 dispatchThreadID : SV_DispatchThreadID)
+{
+	uint tid = dispatchThreadID.x;
+
+	float outVal = 0;
+
+	outVal += test<uint>(tid);
+	outVal += test<float>(tid * 16.0f);
+
+	outputBuffer[tid] = int(outVal);
+}
\ No newline at end of file
diff --git a/tests/compute/generic-struct.slang.expected.txt b/tests/compute/generic-struct.slang.expected.txt
new file mode 100644
index 000000000..d4cb1cc00
--- /dev/null
+++ b/tests/compute/generic-struct.slang.expected.txt
@@ -0,0 +1,4 @@
+0
+11
+22
+33