CUDA: Add CUDA_ARCHITECTURES target property

Simplifies CUDA target architecture handling.

Required for Clang support as Clang doesn't automatically select a supported architecture.
We detect a supported architecture during compiler identification and set CMAKE_CUDA_ARCHITECTURES to it.

Introduces CMP0104 for backwards compatibility with manually setting code generation flags with NVCC.

Implements #17963.

8 files changed, 94 insertions, 0 deletions

diff --git a/Help/manual/cmake-policies.7.rst b/Help/manual/cmake-policies.7.rst
index 08d59e7..869ae41 100644
--- a/Help/manual/cmake-policies.7.rst
+++ b/Help/manual/cmake-policies.7.rst
@@ -57,6 +57,7 @@ Policies Introduced by CMake 3.18
 .. toctree::
    :maxdepth: 1
 
+   CMP0104: CMAKE_CUDA_ARCHITECTURES now detected for NVCC, empty CUDA_ARCHITECTURES not allowed. </policy/CMP0104>
    CMP0103: Multiple export() with same FILE without APPEND is not allowed. </policy/CMP0103>
 
 Policies Introduced by CMake 3.17
diff --git a/Help/manual/cmake-properties.7.rst b/Help/manual/cmake-properties.7.rst
index cbb2298..4966f86 100644
--- a/Help/manual/cmake-properties.7.rst
+++ b/Help/manual/cmake-properties.7.rst
@@ -172,6 +172,7 @@ Properties on Targets
    /prop_tgt/CONFIG_OUTPUT_NAME
    /prop_tgt/CONFIG_POSTFIX
    /prop_tgt/CROSSCOMPILING_EMULATOR
+   /prop_tgt/CUDA_ARCHITECTURES
    /prop_tgt/CUDA_PTX_COMPILATION
    /prop_tgt/CUDA_SEPARABLE_COMPILATION
    /prop_tgt/CUDA_RESOLVE_DEVICE_SYMBOLS
diff --git a/Help/manual/cmake-variables.7.rst b/Help/manual/cmake-variables.7.rst
index 1642772..7d802e1 100644
--- a/Help/manual/cmake-variables.7.rst
+++ b/Help/manual/cmake-variables.7.rst
@@ -488,6 +488,7 @@ Variables for Languages
    /variable/CMAKE_COMPILER_IS_GNUCC
    /variable/CMAKE_COMPILER_IS_GNUCXX
    /variable/CMAKE_COMPILER_IS_GNUG77
+   /variable/CMAKE_CUDA_ARCHITECTURES
    /variable/CMAKE_CUDA_COMPILE_FEATURES
    /variable/CMAKE_CUDA_HOST_COMPILER
    /variable/CMAKE_CUDA_EXTENSIONS
diff --git a/Help/policy/CMP0104.rst b/Help/policy/CMP0104.rst
new file mode 100644
index 0000000..ca2c571
--- /dev/null
+++ b/Help/policy/CMP0104.rst
@@ -0,0 +1,31 @@
+CMP0104
+-------
+
+Initialize :variable:`CMAKE_CUDA_ARCHITECTURES` when
+:variable:`CMAKE_CUDA_COMPILER_ID <CMAKE_<LANG>_COMPILER_ID>` is ``NVIDIA``.
+Raise an error if :prop_tgt:`CUDA_ARCHITECTURES` is empty.
+
+:variable:`CMAKE_CUDA_ARCHITECTURES` introduced in CMake 3.18 is used to
+initialize :prop_tgt:`CUDA_ARCHITECTURES`, which passes correct code generation
+flags to the CUDA compiler.
+
+Previous to this users had to manually specify the code generation flags. This
+policy is for backwards compatibility with manually specifying code generation
+flags.
+
+The ``OLD`` behavior for this policy is to not initialize
+:variable:`CMAKE_CUDA_ARCHITECTURES` when
+:variable:`CMAKE_CUDA_COMPILER_ID <CMAKE_<LANG>_COMPILER_ID>` is ``NVIDIA``.
+Empty :prop_tgt:`CUDA_ARCHITECTURES` is allowed.
+
+The ``NEW`` behavior of this policy is to initialize
+:variable:`CMAKE_CUDA_ARCHITECTURES` when
+:variable:`CMAKE_CUDA_COMPILER_ID <CMAKE_<LANG>_COMPILER_ID>` is ``NVIDIA``
+and raise an error if :prop_tgt:`CUDA_ARCHITECTURES` is empty during generation.
+
+This policy was introduced in CMake version 3.18.  CMake version
+|release| warns when the policy is not set and uses ``OLD`` behavior.
+Use the :command:`cmake_policy` command to set it to ``OLD`` or ``NEW``
+explicitly.
+
+.. include:: DEPRECATED.txt
diff --git a/Help/prop_tgt/CUDA_ARCHITECTURES.rst b/Help/prop_tgt/CUDA_ARCHITECTURES.rst
new file mode 100644
index 0000000..328f40b
--- /dev/null
+++ b/Help/prop_tgt/CUDA_ARCHITECTURES.rst
@@ -0,0 +1,30 @@
+CUDA_ARCHITECTURES
+------------------
+
+List of architectures to generate device code for.
+
+An architecture can be suffixed by either ``-real`` or ``-virtual`` to specify
+the kind of architecture to generate code for.
+If no suffix is given then code is generated for both real and virtual
+architectures.
+
+This property is initialized by the value of the :variable:`CMAKE_CUDA_ARCHITECTURES`
+variable if it is set when a target is created.
+
+The ``CUDA_ARCHITECTURES`` target property must be set to a non-empty value on targets
+that compile CUDA sources, or it is an error.  See policy :policy:`CMP0104`.
+
+Examples
+^^^^^^^^
+
+.. code-block:: cmake
+
+  set_property(TARGET tgt PROPERTY CUDA_ARCHITECTURES 35 50 72)
+
+Generates code for real and virtual architectures ``30``, ``50`` and ``72``.
+
+.. code-block:: cmake
+
+  set_property(TARGET tgt PROPERTY CUDA_ARCHITECTURES 70-real 72-virtual)
+
+Generates code for real architecture ``70`` and virtual architecture ``72``.
diff --git a/Help/release/dev/cuda-architectures-empty.rst b/Help/release/dev/cuda-architectures-empty.rst
new file mode 100644
index 0000000..b0fc327
--- /dev/null
+++ b/Help/release/dev/cuda-architectures-empty.rst
@@ -0,0 +1,7 @@
+cuda-architectures-empty
+------------------------
+
+* :variable:`CMAKE_CUDA_ARCHITECTURES` is now initialized when
+  :variable:`CMAKE_CUDA_COMPILER_ID <CMAKE_<LANG>_COMPILER_ID>` is ``NVIDIA``.
+  Empty :prop_tgt:`CUDA_ARCHITECTURES` raises an error. See policy
+  :policy:`CMP0104`.
diff --git a/Help/release/dev/cuda-architectures.rst b/Help/release/dev/cuda-architectures.rst
new file mode 100644
index 0000000..dc6c55b
--- /dev/null
+++ b/Help/release/dev/cuda-architectures.rst
@@ -0,0 +1,6 @@
+cuda-architectures
+------------------
+
+* Added :prop_tgt:`CUDA_ARCHITECTURES` target property for specifying CUDA
+  output architectures. Users are encouraged to use this instead of specifying
+  options manually, as this approach is compiler-agnostic.
diff --git a/Help/variable/CMAKE_CUDA_ARCHITECTURES.rst b/Help/variable/CMAKE_CUDA_ARCHITECTURES.rst
new file mode 100644
index 0000000..149bffa
--- /dev/null
+++ b/Help/variable/CMAKE_CUDA_ARCHITECTURES.rst
@@ -0,0 +1,17 @@
+CMAKE_CUDA_ARCHITECTURES
+------------------------
+
+Default value for :prop_tgt:`CUDA_ARCHITECTURES` property of targets.
+
+This is initialized as follows depending on :variable:`CMAKE_CUDA_COMPILER_ID <CMAKE_<LANG>_COMPILER_ID>`:
+
+- For ``Clang``: the oldest architecture that works.
+
+- For ``NVIDIA``: the default architecture chosen by the compiler.
+  See policy :policy:`CMP0104`.
+
+Users are encouraged to override this, as the default varies across compilers
+and compiler versions.
+
+This variable is used to initialize the :prop_tgt:`CUDA_ARCHITECTURES` property
+on all targets. See the target property for additional information.