fix(cmake): update C++ standard detection for torch >= 2.14 and adjust related configuration

.github/workflows/test-and-lint.yml

@@ -26,10 +26,8 @@ jobs:
       - name: Install system dependencies
         run: |
           sudo apt-get -qq update
-          sudo apt-get install -y ca-certificates libopenblas-dev gcc-9 g++-9
-          sudo update-alternatives \
-            --install /usr/bin/gcc gcc /usr/bin/gcc-9 60 \
-            --slave /usr/bin/g++ g++ /usr/bin/g++-9
+          sudo apt-get install -y ca-certificates libopenblas-dev build-essential
+          g++ --version
 
       - name: Build and install aihwkit wheel
         run: |
@@ -60,10 +58,8 @@ jobs:
       - name: Install system dependencies
         run: |
           sudo apt-get -qq update
-          sudo apt-get install -y ca-certificates libopenblas-dev gcc-9 g++-9
-          sudo update-alternatives \
-            --install /usr/bin/gcc gcc /usr/bin/gcc-9 60 \
-            --slave /usr/bin/g++ g++ /usr/bin/g++-9
+          sudo apt-get install -y ca-certificates libopenblas-dev build-essential
+          g++ --version
 
       - name: Build and install aihwkit wheel
         run: |

CHANGELOG.md

@@ -25,6 +25,7 @@ The format is based on [Keep a Changelog], and this project adheres to
 * Remove reset bias clamp in rpu_pulsed_device.h [(\#761)](https://github.com/IBM/aihwkit/pull/761)
 
 ### Fixed
+* Build against `torch >= 2.14`, whose headers require C++20: the C++ standard is now detected from the installed torch headers (C++17 for `torch <= 2.13`, C++20 for `torch >= 2.14`) and can be overridden with the new `RPU_CXX_STANDARD` cmake option
 * Improve Python executable detection and error handling in CMake [(\#757)](https://github.com/IBM/aihwkit/pull/757)
 * Retune PWU kernel when m_batch grows after initial m=1 update [(\#763)](https://github.com/IBM/aihwkit/pull/763)
 * Tests for dynamic tolerance for cuDNN TF32 precision on Ampere+ GPUs [(\#771)](https://github.com/IBM/aihwkit/pull/771)

CMakeLists.txt

@@ -21,16 +21,14 @@ option(RPU_USE_FASTMOD "Use fast mod" OFF)
 option(RPU_USE_FASTRAND "Use fastrand" OFF)
 option(RPU_USE_TORCH_BUFFERS "Use torch buffers for RPUCuda" ON)
 
+# C++ standard used for every target (17 or 20). Leave empty to pick it up from
+# the installed torch headers (see cmake/dependencies.cmake): torch <= 2.13
+# builds with C++17, torch >= 2.14 requires C++20.
+set(RPU_CXX_STANDARD "" CACHE STRING "C++ standard (17, 20). Empty: detect from torch headers")
 
 set(RPU_BLAS "OpenBLAS" CACHE STRING "BLAS backend of choice (OpenBLAS, MKL)")
 set(RPU_CUDA_ARCHITECTURES "75;80;89" CACHE STRING "Target CUDA architectures")
 
-# Internal variables.
-set(CUDA_TARGET_PROPERTIES POSITION_INDEPENDENT_CODE ON
-                           CUDA_RESOLVE_DEVICE_SYMBOLS ON
-                           CUDA_SEPARABLE_COMPILATION ON
-                           CXX_STANDARD 17)
-
 # Append the virtualenv library path to cmake.
 if(DEFINED ENV{VIRTUAL_ENV})
   include_directories("$ENV{VIRTUAL_ENV}/include")
@@ -43,10 +41,17 @@ include(cmake/dependencies.cmake)
 include(cmake/dependencies_cuda.cmake)
 include(cmake/dependencies_test.cmake)
 
+# Internal variables.
+set(CUDA_TARGET_PROPERTIES POSITION_INDEPENDENT_CODE ON
+                           CUDA_RESOLVE_DEVICE_SYMBOLS ON
+                           CUDA_SEPARABLE_COMPILATION ON
+                           CXX_STANDARD ${RPU_CXX_STANDARD}
+                           CUDA_STANDARD ${RPU_CXX_STANDARD})
+
 # Set compilation flags.
 if(WIN32)
   set(CMAKE_CXX_FLAGS_RELEASE "${CMAKE_CXX_FLAGS_RELEASE} /O2")
-  set(CMAKE_CXX_STANDARD 17)
+  set(CMAKE_CXX_STANDARD ${RPU_CXX_STANDARD})
   set(CMAKE_CXX_STANDARD_REQUIRED ON)
 else()
   set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall -Wno-narrowing -Wno-strict-overflow")
@@ -68,7 +73,7 @@ if(WIN32)
   target_link_libraries(RPU_CPU c10.lib torch_cpu.lib)
 endif()
 
-set_target_properties(RPU_CPU PROPERTIES CXX_STANDARD 17
+set_target_properties(RPU_CPU PROPERTIES CXX_STANDARD ${RPU_CXX_STANDARD}
   POSITION_INDEPENDENT_CODE ON)
 
 add_compile_definitions(RPU_USE_WITH_TORCH)
@@ -156,7 +161,7 @@ if (BUILD_EXTENSION)
 
   add_library(AIHWKIT_EXTENSION_OPS ${AIHWKIT_EXTENSION_OPS_CPU_SRCS})
 
-  set_target_properties(AIHWKIT_EXTENSION_OPS PROPERTIES CXX_STANDARD 17
+  set_target_properties(AIHWKIT_EXTENSION_OPS PROPERTIES CXX_STANDARD ${RPU_CXX_STANDARD}
     POSITION_INDEPENDENT_CODE ON)
 
   target_link_libraries(AIHWKIT_EXTENSION_OPS
@@ -198,7 +203,7 @@ if (BUILD_EXTENSION)
   target_link_libraries(${extension_module_name} PRIVATE torch_python)
   target_include_directories(${extension_module_name} PRIVATE src/aihwkit/extension/extension_src)
   target_include_directories(${extension_module_name} PRIVATE src/aihwkit/extension/extension_src/ops)
-  set_target_properties(${extension_module_name} PROPERTIES CXX_STANDARD 17
+  set_target_properties(${extension_module_name} PROPERTIES CXX_STANDARD ${RPU_CXX_STANDARD}
     POSITION_INDEPENDENT_CODE ON)
 
   if (USE_CUDA)
@@ -231,7 +236,7 @@ if(BUILD_TEST)
     add_executable(${test_name} ${test_src})
     target_link_libraries(${test_name} gtest gmock)
     target_link_libraries(${test_name} torch_python c10 torch_cpu)
-    set_target_properties(${test_name} PROPERTIES CXX_STANDARD 17
+    set_target_properties(${test_name} PROPERTIES CXX_STANDARD ${RPU_CXX_STANDARD}
       POSITION_INDEPENDENT_CODE ON)
 
     if(WIN32)

cmake/dependencies.cmake

@@ -116,6 +116,39 @@ find_package(Torch REQUIRED)
 include_directories(${TORCH_INCLUDE_DIRS})
 link_directories(${TORCH_LIB_DIR})
 
+# C++ standard. torch's headers carry a hard requirement on the language
+# standard (ATen/ATen.h: `#if __cplusplus < 202002L` / `< 201703L` followed by
+# an #error): releases up to 2.13 build with C++17, 2.14 and later need C++20.
+# Read the number out of that guard so the standard follows whichever torch is
+# installed, unless RPU_CXX_STANDARD was given explicitly.
+if(NOT RPU_CXX_STANDARD)
+  set(RPU_CXX_STANDARD 17)
+  set(_rpu_aten_h "")
+  foreach(_dir ${TORCH_INCLUDE_DIRS})
+    if(EXISTS "${_dir}/ATen/ATen.h")
+      set(_rpu_aten_h "${_dir}/ATen/ATen.h")
+      break()
+    endif()
+  endforeach()
+  if(_rpu_aten_h)
+    file(STRINGS "${_rpu_aten_h}" _rpu_aten_guard
+      REGEX "__cplusplus[ \t]*<[ \t]*20[0-9][0-9][0-9][0-9]L" LIMIT_COUNT 1)
+    if(_rpu_aten_guard MATCHES "__cplusplus[ \t]*<[ \t]*20([0-9][0-9])[0-9][0-9]L")
+      set(RPU_CXX_STANDARD ${CMAKE_MATCH_1})
+    endif()
+  endif()
+  message(STATUS "Using C++${RPU_CXX_STANDARD} (required by ${_rpu_aten_h})")
+else()
+  message(STATUS "Using C++${RPU_CXX_STANDARD} (from RPU_CXX_STANDARD)")
+endif()
+
+if(RPU_CXX_STANDARD GREATER 17 AND CMAKE_CXX_COMPILER_ID STREQUAL "GNU"
+   AND CMAKE_CXX_COMPILER_VERSION VERSION_LESS 10)
+  message(WARNING "C++${RPU_CXX_STANDARD} is required by the installed torch, but GCC "
+    "${CMAKE_CXX_COMPILER_VERSION} has no usable C++20 support (concepts, <compare>). "
+    "Use GCC 10 or newer, or install torch <= 2.13.")
+endif()
+
 if (CMAKE_COMPILER_IS_GNUCXX)
   # Prefer ABI from Torch CMake config (works even when Python build isolation
   # makes `import torch` unavailable in helper subprocesses).

docs/source/developer_install.rst

@@ -218,16 +218,22 @@ Compilation flags
 There are several ``cmake`` options that can be used for customizing the
 compilation process:
 
-==========================  ================================================  =======
+==========================  ================================================  ==============
 Flag                        Description                                       Default
-==========================  ================================================  =======
+==========================  ================================================  ==============
 ``USE_CUDA``                Build with CUDA support                           ``OFF``
 ``BUILD_TEST``              Build the C++ test binaries                       ``OFF``
 ``RPU_BLAS``                BLAS backend of choice (``OpenBLAS`` or ``MKL``)  ``OpenBLAS``
 ``RPU_USE_FASTMOD``         Use fast mod                                      ``ON``
 ``RPU_USE_FASTRAND``        Use fastrand                                      ``OFF``
 ``RPU_CUDA_ARCHITECTURES``  Target CUDA architectures                         ``60;70;75;80``
-==========================  ================================================  =======
+``RPU_CXX_STANDARD``        C++ standard (``17`` or ``20``)                   auto-detected
+==========================  ================================================  ==============
+
+The C++ standard is taken from the installed ``PyTorch`` headers when
+``RPU_CXX_STANDARD`` is not set: ``torch`` releases up to ``2.13`` are built
+with C++17, ``torch >= 2.14`` requires C++20 (and hence a C++20-capable
+compiler, e.g. ``gcc >= 10`` or ``CUDA >= 12`` for the GPU build).
 
 The options can be passed both to ``setuptools`` or to ``cmake`` directly. For
 example, for compiling and installing with CUDA support::

pyproject.toml

@@ -18,8 +18,8 @@ dependencies = [
   "scikit-build >= 0.18.1",
   "scikit-learn",
   "pybind11 >= 3.0.1",
-  "torch == 2.13.0",
-  "torchvision == 0.28.0",
+  "torch",
+  "torchvision",
   "scipy",
   "requests >= 2.32, <3",
   "numpy",

src/aihwkit/simulator/CMakeLists.txt

@@ -7,7 +7,7 @@ set(python_module_name rpu_base)
 file(GLOB RPU_BINDINGS_SRCS rpu_base_src/*.cpp)
 pybind11_add_module(${python_module_name} MODULE ${RPU_BINDINGS_SRCS})
 target_link_libraries(${python_module_name} PRIVATE torch_python)
-set_target_properties(${python_module_name} PROPERTIES CXX_STANDARD 17)
+set_target_properties(${python_module_name} PROPERTIES CXX_STANDARD ${RPU_CXX_STANDARD})
 
 if (USE_CUDA)
   target_link_libraries(${python_module_name} PRIVATE RPU_GPU)

src/rpucuda/rpu_linearstep_device.h

@@ -69,7 +69,7 @@ BUILD_PULSED_DEVICE_META_PARAMETER(
 
 template <typename T>
 struct SoftBoundsRPUDeviceMetaParameter : LinearStepRPUDeviceMetaParameter<T> {
-  SoftBoundsRPUDeviceMetaParameter<T>() {
+  SoftBoundsRPUDeviceMetaParameter() {
     // ctor, to overwrite default values to softbounds
     this->ls_decrease_up = (T)1.0;   // meaning 0 update at bounds
     this->ls_decrease_down = (T)1.0; // meaning 0 update at bounds