-Werror breaks toolchain compilation with clang

[j-stephan]

In an attempt to work around #107 I tried to compile the toolchain with Ubuntu 20.04's default clang:

> clang --version
clang version 10.0.0-4ubuntu1 
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/bin

I configured & ran the build system:

> CC=clang CXX=clang++ python buildbot/configure.py -t Release
> python buildbot/compile.py

Near the end of the compilation some warnings are triggered. Due to -Werror the build fails:

[2394/2587] Building CXX object tools/sycl/source/CMakeFiles/sycl_object.dir/backend/opencl.cpp.o
FAILED: tools/sycl/source/CMakeFiles/sycl_object.dir/backend/opencl.cpp.o 
/usr/bin/clang++ -DCL_TARGET_OPENCL_VERSION=220 -DXPTI_ENABLE_INSTRUMENTATION -DXPTI_STATIC_LIBRARY -D_DEBUG -D_GLIBCXX_ASSERTIONS=1 -D_GNU_SOURCE -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -Itools/sycl/source -I/home/jan/sycl-workspace/sycl/sycl/source -Iinclude -I/home/jan/sycl-workspace/sycl/llvm/include -I/home/jan/sycl-workspace/sycl/xpti/include -I/home/jan/sycl-workspace/sycl/sycl/include -Itools/sycl/OpenCL/inc -fPIC -fvisibility-inlines-hidden -Werror=date-time -Werror=unguarded-availability-new -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wmissing-field-initializers -pedantic -Wno-long-long -Wimplicit-fallthrough -Wcovered-switch-default -Wno-noexcept-type -Wnon-virtual-dtor -Wdelete-non-virtual-dtor -Wstring-conversion -fdiagnostics-color -ffunction-sections -fdata-sections -Wall -Wextra -Wno-deprecated-declarations -Werror -O3  -UNDEBUG -fvisibility=hidden -fvisibility-inlines-hidden -Winstantiation-after-specialization -std=c++2a -MD -MT tools/sycl/source/CMakeFiles/sycl_object.dir/backend/opencl.cpp.o -MF tools/sycl/source/CMakeFiles/sycl_object.dir/backend/opencl.cpp.o.d -o tools/sycl/source/CMakeFiles/sycl_object.dir/backend/opencl.cpp.o -c /home/jan/sycl-workspace/sycl/sycl/source/backend/opencl.cpp

In file included from /home/jan/sycl-workspace/sycl/sycl/source/backend/opencl.cpp:10:
In file included from /home/jan/sycl-workspace/sycl/sycl/source/detail/platform_impl.hpp:14:
In file included from /home/jan/sycl-workspace/sycl/sycl/source/detail/platform_info.hpp:14:
In file included from /home/jan/sycl-workspace/sycl/sycl/source/detail/plugin.hpp:14:
/home/jan/sycl-workspace/sycl/sycl/source/detail/plugin_printers.hpp:120:14: error: unused parameter 'val' [-Werror,-Wunused-parameter]
  printOut(T val) {}
             ^
In file included from /home/jan/sycl-workspace/sycl/sycl/source/backend/opencl.cpp:12:
In file included from /home/jan/sycl-workspace/sycl/sycl/source/detail/program_impl.hpp:17:
In file included from /home/jan/sycl-workspace/sycl/sycl/source/detail/context_impl.hpp:17:
In file included from /home/jan/sycl-workspace/sycl/sycl/source/detail/device_impl.hpp:14:
/home/jan/sycl-workspace/sycl/sycl/source/detail/device_info.hpp:282:3: error: default label in switch which covers all enumeration values [-Werror,-Wcovered-switch-default]
  default:
  ^
2 warnings and 2 errors generated.

(I removed some harmless warnings that are triggered by including cl_ext_intel.h.)

Let me know if I can do something to investigate or help.

[j-stephan]

This is still an issue with clang 12, although the warning changed:

[11/146] Building CXX object tools/sycl/source/CMakeFiles/sycl_object.dir/detail/memory_manager.cpp.o
FAILED: tools/sycl/source/CMakeFiles/sycl_object.dir/detail/memory_manager.cpp.o 
/usr/bin/clang++ -DCL_TARGET_OPENCL_VERSION=220 -DSYCL2020_DISABLE_DEPRECATION_WARNINGS -DXPTI_ENABLE_INSTRUMENTATION -DXPTI_STATIC_LIBRARY -D_DEBUG -D_GLIBCXX_ASSERTIONS=1 -D_GNU_SOURCE -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -I/home/jan/sycl-workspace/sycl/build/tools/sycl/source -I/home/jan/sycl-workspace/sycl/sycl/source -I/home/jan/sycl-workspace/sycl/build/include -I/home/jan/sycl-workspace/sycl/llvm/include -I/home/jan/sycl-workspace/sycl/xpti/include -I/home/jan/sycl-workspace/sycl/sycl/include -isystem /home/jan/sycl-workspace/sycl/build/_deps/ocl-headers-src -fPIC -fvisibility-inlines-hidden -Werror=date-time -Werror=unguarded-availability-new -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wmissing-field-initializers -pedantic -Wno-long-long -Wc++98-compat-extra-semi -Wimplicit-fallthrough -Wcovered-switch-default -Wno-noexcept-type -Wnon-virtual-dtor -Wdelete-non-virtual-dtor -Wsuggest-override -Wstring-conversion -Wmisleading-indentation -fdiagnostics-color -ffunction-sections -fdata-sections -Wall -Wextra -Wno-deprecated-declarations -Werror -O3 -DNDEBUG -UNDEBUG -fvisibility=hidden -fvisibility-inlines-hidden -Winstantiation-after-specialization -std=c++20 -MD -MT tools/sycl/source/CMakeFiles/sycl_object.dir/detail/memory_manager.cpp.o -MF tools/sycl/source/CMakeFiles/sycl_object.dir/detail/memory_manager.cpp.o.d -o tools/sycl/source/CMakeFiles/sycl_object.dir/detail/memory_manager.cpp.o -c /home/jan/sycl-workspace/sycl/sycl/source/detail/memory_manager.cpp
/home/jan/sycl-workspace/sycl/sycl/source/detail/memory_manager.cpp:29:21: error: ISO C++20 considers use of overloaded operator '==' (with operand types 'const sycl::id<3>' and 'sycl::id<3>') to be ambiguous despite there being a unique best viable function [-Werror,-Wambiguous-reversed-operator]
  return (SrcOffset == sycl::id<3>{0, 0, 0}) && (SrcSize == DstAccessRange) &&
          ~~~~~~~~~ ^  ~~~~~~~~~~~~~~~~~~~~
/home/jan/sycl-workspace/sycl/sycl/include/CL/sycl/detail/array.hpp:89:8: note: ambiguity is between a regular call to this operator and a call with the argument order reversed
  bool operator==(const array<dimensions> &rhs) const {
       ^
/home/jan/sycl-workspace/sycl/sycl/source/detail/memory_manager.cpp:31:21: error: ISO C++20 considers use of overloaded operator '==' (with operand types 'const sycl::id<3>' and 'const sycl::id<3>') to be ambiguous despite there being a unique best viable function [-Werror,-Wambiguous-reversed-operator]
         (SrcOffset == DstOffset);
          ~~~~~~~~~ ^  ~~~~~~~~~
/home/jan/sycl-workspace/sycl/sycl/include/CL/sycl/detail/array.hpp:89:8: note: ambiguity is between a regular call to this operator and a call with the argument order reversed
  bool operator==(const array<dimensions> &rhs) const {
       ^
/home/jan/sycl-workspace/sycl/sycl/source/detail/memory_manager.cpp:548:18: error: ISO C++20 considers use of overloaded operator '!=' (with operand types 'sycl::id<3>' and 'sycl::id<3>') to be ambiguous despite there being a unique best viable function [-Werror,-Wambiguous-reversed-operator]
      (SrcOffset != sycl::id<3>{0, 0, 0} || DstOffset != sycl::id<3>{0, 0, 0} ||
       ~~~~~~~~~ ^  ~~~~~~~~~~~~~~~~~~~~
/home/jan/sycl-workspace/sycl/sycl/include/CL/sycl/detail/array.hpp:89:8: note: ambiguity is between a regular call to this operator and a call with the argument order reversed
  bool operator==(const array<dimensions> &rhs) const {
       ^
/home/jan/sycl-workspace/sycl/sycl/source/detail/memory_manager.cpp:548:55: error: ISO C++20 considers use of overloaded operator '!=' (with operand types 'sycl::id<3>' and 'sycl::id<3>') to be ambiguous despite there being a unique best viable function [-Werror,-Wambiguous-reversed-operator]
      (SrcOffset != sycl::id<3>{0, 0, 0} || DstOffset != sycl::id<3>{0, 0, 0} ||
                                            ~~~~~~~~~ ^  ~~~~~~~~~~~~~~~~~~~~
/home/jan/sycl-workspace/sycl/sycl/include/CL/sycl/detail/array.hpp:89:8: note: ambiguity is between a regular call to this operator and a call with the argument order reversed
  bool operator==(const array<dimensions> &rhs) const {
       ^
4 errors generated.

[gogo2]

You can use --no-werror parameter with configure.py to suppress this. That's what I do.

I'm not a triSYCL/sycl dev, but I suppose they just don't care about this kind o warnings at this stage of development.

[j-stephan]

Thanks, that helps.

[keryell]

I have seen that upstream they have removed some warnings when compiling with C++20. Perhaps there will be less warning after next merge from upstream. But not before CppCon 2021...