Fix the logic to determine whether lower generic pass should run. (#5837)

Author: csyonghe

source/slang/slang-emit.cpp

@@ -429,7 +429,14 @@ void calcRequiredLoweringPassSet(
     {
         // If any instruction has an interface type, we need to run
         // the generics lowering pass.
-        auto type = inst->getDataType();
+        auto type = as<IRType>(inst) ? inst : inst->getDataType();
+        for (;;)
+        {
+            if (auto ptrType = as<IRPtrTypeBase>(type))
+                type = ptrType->getValueType();
+            else
+                break;
+        }
         if (type && type->getOp() == kIROp_InterfaceType)
         {
             result.generics = true;

tests/bugs/ptr-existential.slang

@@ -0,0 +1,20 @@
+//TEST:SIMPLE(filecheck=CHECK): -target spirv
+
+//CHECK: OpEntryPoint
+
+interface IBsdf {};
+struct Foo : IBsdf {}
+//TEST_INPUT:type_conformance Foo:IBsdf = 0
+struct Mesh {
+    float4 *vertices;
+    IBsdf *bsdf;
+}
+[[vk::push_constant]] Mesh* mesh;
+RWStructuredBuffer<float4> outputBuffer;
+
+[shader("compute")]
+[numthreads(1, 1, 1)]
+void main(uint3 dispatchThreadID: SV_DispatchThreadID)
+{
+    outputBuffer[0] = mesh.vertices[0];
+}