Allow calling a generic function with an existential value (dynamic dispatch) (#1508)

* Allow calling a generic function with an existential value (dynamic dispatch).

* Fixes per review comments.

* Clean up implementation by having `openExistential` return `ExtractExistentialType` instead of a DeclRef to the interface with a `ThisTypeSubstitution`.

* More cleanups

Co-authored-by: Tim Foley <tfoleyNV@users.noreply.github.com>
Co-authored-by: Yong He <yhe@nvidia.com>

2 files changed, 51 insertions, 0 deletions

diff --git a/tests/compute/dynamic-dispatch-10.slang b/tests/compute/dynamic-dispatch-10.slang
new file mode 100644
index 000000000..3e1848186
--- /dev/null
+++ b/tests/compute/dynamic-dispatch-10.slang
@@ -0,0 +1,47 @@
+//TEST(compute):COMPARE_COMPUTE:-cpu -xslang -allow-dynamic-code
+//DISABLE_TEST(compute):COMPARE_COMPUTE:-cuda -xslang -allow-dynamic-code
+
+// Test dynamic dispatch code gen for specializing a generic with
+// an existential value.
+
+[anyValueSize(16)]
+interface IInterface
+{
+	int Compute(int inVal);
+};
+
+int GenericCompute0(IInterface obj, int inVal)
+{
+    return GenericCompute1(obj, obj, inVal);
+}
+
+int GenericCompute1<T:IInterface>(T obj, IInterface obj2, int inVal)
+{
+    return obj.Compute(inVal) + obj2.Compute(inVal);
+}
+
+
+struct Impl : IInterface
+{
+    int base;
+	int Compute(int inVal) { return base + inVal * inVal; }
+};
+
+int test(int inVal)
+{
+    Impl obj;
+    obj.base = 1;
+	return GenericCompute0(obj, inVal);
+}
+
+//TEST_INPUT:ubuffer(data=[0 1 2 3], stride=4):out,name=outputBuffer
+RWStructuredBuffer<int> outputBuffer : register(u0);
+
+[numthreads(4, 1, 1)]
+void computeMain(uint3 dispatchThreadID : SV_DispatchThreadID)
+{
+	uint tid = dispatchThreadID.x;
+	int inVal = outputBuffer[tid];
+	int outVal = test(inVal);
+	outputBuffer[tid] = outVal;
+}
diff --git a/tests/compute/dynamic-dispatch-10.slang.expected.txt b/tests/compute/dynamic-dispatch-10.slang.expected.txt
new file mode 100644
index 000000000..70a793021
--- /dev/null
+++ b/tests/compute/dynamic-dispatch-10.slang.expected.txt
@@ -0,0 +1,4 @@
+2
+4
+A
+14