Added diagnostics & built-in type lowering for `[CUDAKernel]` functions (#4042)

* Added diagnostics & built-in type lowering for `[CUDAKernel]` functions

This PR adds
- Diagnostics for non-void return from a cuda kernel entry point
- Diagnostics for using differentiable types in a differentiable cuda kernel entry point
- Logic for converting built-in types (float3, float3x3, etc..) to portable struct types and unpacks the parameter back into a built-in type on the CUDA side. This is because built-in types have different implementations in CUDA & CPP targets, which causes signature mis-match when linking.

* Fix error codes

* Add ability to lower structs and arrays that contain built-in types.

+ Added tests
+ Fix issue where the host-side was not marshalling data to lowered types.

* Update slang-ir-pytorch-cpp-binding.cpp

---------

Co-authored-by: Yong He <yonghe@outlook.com>

1 files changed, 2 insertions, 3 deletions

diff --git a/source/slang/slang-emit-c-like.cpp b/source/slang/slang-emit-c-like.cpp
index fa380e061..626c372e9 100644
--- a/source/slang/slang-emit-c-like.cpp
+++ b/source/slang/slang-emit-c-like.cpp
@@ -3518,14 +3518,13 @@ bool CLikeSourceEmitter::isTargetIntrinsic(IRInst* inst)
     return findTargetIntrinsicDefinition(inst, intrinsicDef);
 }
 
-bool shouldWrappInExternCBlock(IRFunc* func)
+bool shouldWrapInExternCBlock(IRFunc* func)
 {
     for (auto decor : func->getDecorations())
     {
         switch (decor->getOp())
         {
         case kIROp_ExternCDecoration:
-        case kIROp_CudaKernelDecoration:
             return true;
         }
     }
@@ -3540,7 +3539,7 @@ void CLikeSourceEmitter::emitFunc(IRFunc* func)
     if (isTargetIntrinsic(func))
         return;
 
-    bool shouldCloseExternCBlock = shouldWrappInExternCBlock(func);
+    bool shouldCloseExternCBlock = shouldWrapInExternCBlock(func);
     if (shouldCloseExternCBlock)
     {
         // If this is a C++ `extern "C"` function, then we need to emit