Implement D3663R2 (Future-proof submdspan_mapping)

CMakeLists.txt

@@ -27,10 +27,15 @@ option(MDSPAN_INSTALL_STDMODE_HEADERS "Whether to install headers to emulate sta
 
 # Option to override which C++ standard to use
 set(MDSPAN_CXX_STANDARD DETECT CACHE STRING "Override the default CXX_STANDARD to compile with.")
-set_property(CACHE MDSPAN_CXX_STANDARD PROPERTY STRINGS DETECT 14 17 20 23)
+set_property(CACHE MDSPAN_CXX_STANDARD PROPERTY STRINGS DETECT 14 17 20 23 26)
 
 option(MDSPAN_ENABLE_CONCEPTS "Try to enable concepts support by giving extra flags." On)
 
+option(MDSPAN_ENABLE_P3663 "Enable implementation of P3663 (Future-proof submdspan_mapping)." Off)
+
+# Defaults to ON, because this has only been tested with Clang 21 (development Clang).
+option(MDSPAN_CONSTANT_WRAPPER_WORKAROUND "If MDSPAN_ENABLE_P3663 is enabled, work around some compilers' inability to build constant_wrapper." ON)
+
 ################################################################################
 
 # Decide on the standard to use
@@ -62,8 +67,18 @@ elseif(MDSPAN_CXX_STANDARD STREQUAL "23")
   else()
     message(FATAL_ERROR "Requested MDSPAN_CXX_STANDARD \"23\" not supported by provided C++ compiler")
   endif()
+elseif(MDSPAN_CXX_STANDARD STREQUAL "26")
+  if("cxx_std_26" IN_LIST CMAKE_CXX_COMPILE_FEATURES)
+    message(STATUS "Using C++26 standard")
+    set(CMAKE_CXX_STANDARD 26)
+  else()
+    message(WARNING "Requested MDSPAN_CXX_STANDARD \"26\" not supported by provided C++ compiler")
+  endif()
 else()
-  if("cxx_std_23" IN_LIST CMAKE_CXX_COMPILE_FEATURES)
+  if("cxx_std_26" IN_LIST CMAKE_CXX_COMPILE_FEATURES)
+    set(CMAKE_CXX_STANDARD 26)
+    message(STATUS "Detected support for C++26 standard")
+  elseif("cxx_std_23" IN_LIST CMAKE_CXX_COMPILE_FEATURES)
     set(CMAKE_CXX_STANDARD 23)
     message(STATUS "Detected support for C++23 standard")
   elseif("cxx_std_20" IN_LIST CMAKE_CXX_COMPILE_FEATURES)

benchmarks/CMakeLists.txt

@@ -7,6 +7,15 @@ function(mdspan_add_benchmark EXENAME)
   )
   # Set flag to build with parenthesis enabled
   target_compile_definitions(${EXENAME} PRIVATE MDSPAN_USE_PAREN_OPERATOR=1)
+  if(MDSPAN_ENABLE_P3663)
+    target_compile_definitions(${EXENAME} PUBLIC MDSPAN_ENABLE_P3663=1)
+  endif()
+  if(MDSPAN_CONSTANT_WRAPPER_WORKAROUND)
+    target_compile_definitions(${EXENAME}
+      PUBLIC
+      MDSPAN_CONSTANT_WRAPPER_WORKAROUND=1
+    )
+  endif()
 endfunction()
 
 if(MDSPAN_USE_SYSTEM_BENCHMARK)
@@ -66,6 +75,15 @@ function(mdspan_add_cuda_benchmark EXENAME)
   if(_benchmark_libs_old MATCHES "-pthread")
     target_compile_options(${EXENAME} PUBLIC "-Xcompiler=-pthread")
   endif()
+  if(MDSPAN_ENABLE_P3663)
+    target_compile_definitions(${EXENAME} PUBLIC MDSPAN_ENABLE_P3663=1)
+  endif()
+  if(MDSPAN_CONSTANT_WRAPPER_WORKAROUND)
+    target_compile_definitions(${EXENAME}
+      PUBLIC
+      MDSPAN_CONSTANT_WRAPPER_WORKAROUND=1
+    )
+  endif()
 endfunction()
 
 if(MDSPAN_ENABLE_OPENMP)
@@ -81,6 +99,15 @@ function(mdspan_add_openmp_benchmark EXENAME)
         $<BUILD_INTERFACE:${CMAKE_SOURCE_DIR}/benchmarks>
       )
       target_compile_definitions(${EXENAME} PRIVATE MDSPAN_USE_PAREN_OPERATOR=1)
+      if(MDSPAN_ENABLE_P3663)
+        target_compile_definitions(${EXENAME} PUBLIC MDSPAN_ENABLE_P3663=1)
+      endif()
+      if(MDSPAN_CONSTANT_WRAPPER_WORKAROUND)
+        target_compile_definitions(${EXENAME}
+          PUBLIC
+          MDSPAN_CONSTANT_WRAPPER_WORKAROUND=1
+        )
+      endif() 
     else()
       message(WARNING "Not adding target ${EXENAME} because OpenMP was not found")
     endif()
@@ -92,3 +119,4 @@ add_subdirectory(matvec)
 add_subdirectory(copy)
 add_subdirectory(stencil)
 add_subdirectory(tiny_matrix_add)
+add_subdirectory(submdspan)

benchmarks/submdspan/CMakeLists.txt

@@ -0,0 +1,6 @@
+
+mdspan_add_benchmark(submdspan)
+
+#if(MDSPAN_ENABLE_CUDA)
+#  add_subdirectory(cuda)
+#endif()

benchmarks/submdspan/cuda/CMakeLists.txt

@@ -0,0 +1,9 @@
+
+if(CMAKE_CUDA_COMPILER_ID STREQUAL "NVIDIA")
+  set(CMAKE_CUDA_FLAGS "${CMAKE_CUDA_FLAGS} --extended-lambda")
+endif()
+
+mdspan_add_cuda_benchmark(submdspan_cuda)
+target_include_directories(submdspan_cuda PUBLIC
+    $<BUILD_INTERFACE:${CMAKE_SOURCE_DIR}/benchmarks/submdspan>
+)