[SYCL][Doc] Clarify error handling in sycl_ext_oneapi_device_architec…

…ture extension (#14077)

This patch adds `unknown` field to `architecture` enum and removes error
handling based on throwing exception.
Instead, `architecture::unknown` will be returned.

sycl/doc/extensions/experimental/sycl_ext_oneapi_device_architecture.asciidoc

@@ -121,6 +121,16 @@ which version of this extension first included each of these enumerators.
 |Added in version
 |Description
 
+3+^|*Unknown architecture*
+
+a|
+[source]
+----
+unknown
+----
+|-
+|Some architecture which is not one of those listed below.
+
 3+^|*Intel CPU family*
 
 a|
@@ -1019,7 +1029,8 @@ struct architecture;
 
 _Return type:_ `sycl::ext::oneapi::experimental::architecture`
 
-_Returns:_ The architecture of the device.
+_Returns:_ The architecture of the device if architecture is supported, otherwise 
+`ext::oneapi::experimental::architecture::unknown`.
 |====
 
 
@@ -1107,6 +1118,9 @@ They currently exist only for use with the
 link:sycl_ext_matrix/sycl_ext_oneapi_matrix.asciidoc[sycl_ext_oneapi_matrix]
 extension.
 
+The architecture enumeration `unknown` is not currently supported with the 
+`if_architecture_is` function.
+
 
 == Implementation notes
 

sycl/include/sycl/ext/oneapi/experimental/device_architecture.hpp

@@ -48,13 +48,15 @@ enum class architecture : uint64_t {
   //       - DD is 2-digit number reserved for future unexpected modifications
   //         to keep uniqueness. It should be always 00 for now
   //
-  x86_64 = 0x9900000000000000,
+  unknown = 0x9900000000000000,
   //
   // Intel CPU architectures
   //
   // AA is 03,
   // CCCCCCCC is the architecture ID from the DEVICE_IP_VERSION extension of
   // underlied backend
+  // Note: CCCCCCCC for x86_64 consists of all zeros
+  x86_64 = 0x0300000000000000,
   intel_cpu_spr = 0x0300000000000800,
   intel_cpu_gnr = 0x0300000000000900,
   //

sycl/test-e2e/DeviceArchitecture/device_architecture_unknown_on_host.cpp

@@ -0,0 +1,28 @@
+// REQUIRES: accelerator
+
+// RUN: %{build} -o %t.out
+// RUN: %{run} %t.out
+
+// Test checks that device_architecture extension implementation correctly
+// handles unsupported HW. The unsupported HW in this test is any FPGA device,
+// as FPGA currently is not supported at all by the device_architecture
+// extension.
+
+#include <sycl/detail/core.hpp>
+
+int main() {
+  sycl::queue q;
+  sycl::device dev = q.get_device();
+
+  sycl::ext::oneapi::experimental::architecture arch = dev.get_info<
+      sycl::ext::oneapi::experimental::info::device::architecture>();
+
+  assert(arch == sycl::ext::oneapi::experimental::architecture::unknown);
+  // device::ext_oneapi_architecture_is(syclex::architecture::unknown) should
+  // return true if the device does not have a known architecture.
+  assert(dev.ext_oneapi_architecture_is(arch));
+
+  // No exceptions are expected in this test.
+
+  return 0;
+}