[SYCL] Ignore some symbols during ABI check (#6993)

MSVC and clang-cl have minor differences in how the exported symbols are
created under some circumstances. We hit some of them in SYCL RT but we
believe they don't affect customers and so could be excluded from the
ABI check so that it would pass when the library is compiled with either
toolchain.

Co-authored-by: Steffen Larsen <steffen.larsen@intel.com>

Author: aelovikov-intel

sycl/test/abi/sycl_symbols_windows.dump

@@ -411,9 +411,7 @@
 ??0gpu_selector@_V1@sycl@@QEAA@$$QEAV012@@Z
 ??0gpu_selector@_V1@sycl@@QEAA@AEBV012@@Z
 ??0gpu_selector@_V1@sycl@@QEAA@XZ
-??0half@host_half_impl@detail@_V1@sycl@@QEAA@$$QEAV01234@@Z
 ??0half@host_half_impl@detail@_V1@sycl@@QEAA@AEBM@Z
-??0half@host_half_impl@detail@_V1@sycl@@QEAA@AEBV01234@@Z
 ??0half@host_half_impl@detail@_V1@sycl@@QEAA@G@Z
 ??0handler@_V1@sycl@@AEAA@V?$shared_ptr@Vqueue_impl@detail@_V1@sycl@@@std@@00_N@Z
 ??0handler@_V1@sycl@@AEAA@V?$shared_ptr@Vqueue_impl@detail@_V1@sycl@@@std@@_N@Z

sycl/tools/abi_check.py

@@ -102,9 +102,52 @@ def check_symbols(ref_path, target_path):
     readobj_out = subprocess.check_output([get_llvm_bin_path()+"llvm-readobj",
                                            readobj_opts, target_path])
     symbols = parse_readobj_output(readobj_out)
+
     # Presence of _dl_relocate_static_pie depends on whether ld.gold or ld.lld
     # is used. Ignore it for the purpose of the library ABI check.
     ignore_symbols = ["_dl_relocate_static_pie"]
+
+    # In some scenarios MSVC and clang-cl exhibit differences in regards to the exported symbols they generate.
+    # Some of them happen in the SYCL RT library and we think clang-cl's behavior is more reasonable.
+    #
+    # Case 1:
+    # pi.hpp:
+    #   template <backend BE> __SYCL_EXPORT const plugin &getPlugin();
+    #
+    # pi.cpp:
+    #   template <backend BE> const plugin &getPlugin() {
+    #     static const plugin *Plugin = nullptr;
+    #     ...
+    #   }
+    #   // explicit dllexport instantiations.
+    #
+    # clang-cl generates exported symbols for the static variables Plugin. These are never referenced
+    # in the user's headers so cannot be used outside DLL and not exporting them should not affect any
+    # usage scenario.
+    #
+    # In general, the compiler doesn't know if the definition is in the DLL or in the header and inline
+    # dllexport/dllimport functions have to be supported, hence clang-cl's behavior.
+    #
+    # See also https://devblogs.microsoft.com/oldnewthing/20140109-00/?p=2123.
+    ignore_symbols += ["?Plugin@?1???$getPlugin@$01@pi@detail@_V1@sycl@@YAAEBVplugin@234@XZ@4PEBV5234@EB",
+                       "?Plugin@?1???$getPlugin@$00@pi@detail@_V1@sycl@@YAAEBVplugin@234@XZ@4PEBV5234@EB",
+                       "?Plugin@?1???$getPlugin@$04@pi@detail@_V1@sycl@@YAAEBVplugin@234@XZ@4PEBV5234@EB",
+                       "?Plugin@?1???$getPlugin@$02@pi@detail@_V1@sycl@@YAAEBVplugin@234@XZ@4PEBV5234@EB"]
+    # Case 2:
+    # half_type.hpp:
+    #   class __SYCL_EXPORT half {
+    #     ...
+    #     constexpr half(const half &) = default;
+    #     constexpr half(half &&) = default;
+    #     ...
+    #   };
+    #
+    # For some reason MSVC creates exported symbols for the constexpr versions of those defaulted ctors
+    # although it never calls them at use point. Instead, those trivially copyable/moveable objects are
+    # memcpy/memmove'ed. We don't expect these symbols are ever referenced directly so having or not
+    # having them won't cause ABI issues.
+    ignore_symbols += ["??0half@host_half_impl@detail@_V1@sycl@@QEAA@AEBV01234@@Z",
+                       "??0half@host_half_impl@detail@_V1@sycl@@QEAA@$$QEAV01234@@Z"]
     symbols = [s for s in symbols if s not in ignore_symbols]
 
     missing_symbols, new_symbols = compare_results(ref_symbols, symbols)