Add a new CMake extension to detect the CUDA architecture

CMakeLists.txt

@@ -12,7 +12,6 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-set(CMAKE_CXX_STANDARD 17)
 cmake_minimum_required(VERSION 3.31)
 project(qsim LANGUAGES CXX)
 
@@ -48,21 +47,25 @@ endif()
 find_package(OpenMP REQUIRED)
 
 # Always build the basic part.
-ADD_SUBDIRECTORY(pybind_interface/basic)
-ADD_SUBDIRECTORY(pybind_interface/decide)
+add_subdirectory(pybind_interface/basic)
+add_subdirectory(pybind_interface/decide)
 
 # Add subdirectories based on the architecture or available compilers.
 if(NOT CMAKE_APPLE_SILICON_PROCESSOR)
     if(CMAKE_CUDA_COMPILER)
-        ADD_SUBDIRECTORY(pybind_interface/cuda)
+        add_subdirectory(pybind_interface/cuda)
         if(DEFINED ENV{CUQUANTUM_ROOT})
-            ADD_SUBDIRECTORY(pybind_interface/custatevec)
+            add_subdirectory(pybind_interface/custatevec)
         endif()
     elseif(has_hipcc)
-        ADD_SUBDIRECTORY(pybind_interface/hip)
+        add_subdirectory(pybind_interface/hip)
     endif()
 
-    ADD_SUBDIRECTORY(pybind_interface/sse)
-    ADD_SUBDIRECTORY(pybind_interface/avx512)
-    ADD_SUBDIRECTORY(pybind_interface/avx2)
+    add_subdirectory(pybind_interface/sse)
+    add_subdirectory(pybind_interface/avx512)
+    add_subdirectory(pybind_interface/avx2)
 endif()
+
+# The following settings mirror what is in our hand-written Makefiles.
+set(CMAKE_CXX_STANDARD 17)
+set(CMAKE_POSITION_INDEPENDENT_CODE ON)

pybind_interface/GetCUDAARCHS.cmake

@@ -0,0 +1,49 @@
+# Copyright 2025 Google LLC. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+
+# Check whether the user has provided info about the GPU(s) installed
+# on their system. If not, try to determine what it is automaticaly.
+if(DEFINED ENV{CUDAARCHS})
+    set(CMAKE_CUDA_ARCHITECTURES "$ENV{CUDAARCHS}")
+    message(STATUS "qsim: using CUDA archs string $ENV{CUDAARCHS}")
+else()
+    find_program(NVIDIA_SMI nvidia-smi)
+    if(NVIDIA_SMI)
+        execute_process(
+            COMMAND ${NVIDIA_SMI} --query-gpu=compute_cap --format=csv,noheader
+            COMMAND tr -d .
+            OUTPUT_VARIABLE DETECTED_ARCHS
+            RESULT_VARIABLE NVIDIA_SMI_RESULT
+            OUTPUT_STRIP_TRAILING_WHITESPACE
+        )
+        if(NVIDIA_SMI_RESULT EQUAL 0 AND DETECTED_ARCHS)
+            # The command was successful. The output may contain
+            # multiple lines if there are multiple GPUs.
+            string(REPLACE "\n" ";" ARCHS_LIST "${DETECTED_ARCHS}")
+            set(CMAKE_CUDA_ARCHITECTURES "${ARCHS_LIST}")
+        else()
+            message(FATAL_ERROR "nvidia-smi failed or returned no GPU"
+                                " architectures. Please check your"
+                                " NVIDIA driver installation and your"
+                                " command search PATH variable.")
+        endif()
+    else()
+        message(FATAL_ERROR "nvidia-smi not found. Cannot autodetect"
+                            " the current GPU architecture(s). Please"
+                            " set the environment variable CUDAARCHS"
+                            " to an appropriate value and try again.")
+    endif()
+endif()
+

pybind_interface/cuda/CMakeLists.txt

@@ -36,7 +36,9 @@ if(APPLE)
     )
 endif()
 
-INCLUDE(../GetPybind11.cmake)
+include(../GetPybind11.cmake)
+include(../GetCUDAARCHS.cmake)
+
 find_package(Python 3.10 REQUIRED)
 
 include_directories(${PYTHON_INCLUDE_DIRS})
@@ -48,7 +50,7 @@ endif()
 
 add_library(qsim_cuda MODULE pybind_main_cuda.cpp)
 set_target_properties(qsim_cuda PROPERTIES
-    CUDA_ARCHITECTURES "$ENV{CUDAARCHS}"
+    CUDA_ARCHITECTURES "${CMAKE_CUDA_ARCHITECTURES}"
     PREFIX "${PYTHON_MODULE_PREFIX}"
     SUFFIX "${PYTHON_MODULE_EXTENSION}"
 )

pybind_interface/decide/CMakeLists.txt

@@ -43,6 +43,7 @@ include(../GetPybind11.cmake)
 
 # Configure based on the detected platform
 if(CMAKE_CUDA_COMPILER)
+    include(../GetCUDAARCHS.cmake)
     add_library(qsim_decide MODULE decide.cpp)
     if(DEFINED ENV{CUQUANTUM_ROOT})
         target_compile_options(qsim_decide PRIVATE
@@ -52,7 +53,7 @@ if(CMAKE_CUDA_COMPILER)
     find_package(Python3 3.10 REQUIRED COMPONENTS Interpreter Development)
     include_directories(${PYTHON_INCLUDE_DIRS} ${pybind11_SOURCE_DIR}/include)
     set_target_properties(qsim_decide PROPERTIES
-        CUDA_ARCHITECTURES "$ENV{CUDAARCHS}"
+        CUDA_ARCHITECTURES "${CMAKE_CUDA_ARCHITECTURES}"
         PREFIX "${PYTHON_MODULE_PREFIX}"
         SUFFIX "${PYTHON_MODULE_EXTENSION}"
     )