Fix kernel return type in DISubroutineType debug metadata

Author: jiel-nv

numba_cuda/numba/cuda/compiler.py

@@ -880,7 +880,8 @@ def kernel_fixup(kernel, debug):
     kernel.return_value = ir.ReturnValue(kernel, ir.VoidType())
     kernel.args = kernel.args[1:]
 
-    # If debug metadata is present, remove the return value from it
+    # If debug metadata is present, fix the return type to void by replacing
+    # the first element of the types tuple with null (representing void).
 
     if kernel_metadata := getattr(kernel, "metadata", None):
         if dbg_metadata := kernel_metadata.get("dbg", None):
@@ -890,7 +891,8 @@ def kernel_fixup(kernel, debug):
                     for tm_name, tm_value in type_metadata.operands:
                         if tm_name == "types":
                             types = tm_value
-                            types.operands = types.operands[1:]
+                            null_metadata = ir.Constant(ir.MetaDataType(), None)
+                            types.operands = (null_metadata,) + types.operands[1:]
                             if config.DUMP_LLVM:
                                 types._clear_string_cache()
 

numba_cuda/numba/cuda/tests/cudapy/test_debuginfo.py

@@ -291,7 +291,8 @@ def f(x, y):
         mdnode_id = match.group(1)
 
         # extract the metadata node ids from the flexible node of types
-        pat = rf"!{mdnode_id}\s+=\s+!{{\s+!(\d+),\s+!(\d+)\s+}}"
+        # The first element is null (void return type), followed by param types
+        pat = rf"!{mdnode_id}\s+=\s+!{{\s+null,\s+!(\d+),\s+!(\d+)\s+}}"
         match = re.compile(pat).search(llvm_ir)
         self.assertIsNotNone(match, msg=llvm_ir)
         mdnode_id1 = match.group(1)