build: use clang-cl for Windows CI builds (faster slicing and faster builds) (#15428)

* ci: build the Windows x64 dependencies and slicer with clang-cl

Passes -l -x from the Windows jobs, using the clang-cl and Ninja options
added in #15373. Ninja runs each dependency's build step as a plain command,
so the jobs set up a VC environment for OpenSSL's nmake. arm64 stays on MSVC
for now.

The deps cache key gains the compiler, so windows-x64 becomes
windows-x64-clang and windows-arm64 becomes windows-arm64-msvc.

* deps: select OpenSSL's ARM64 target from DEPS_ARCH

CMAKE_GENERATOR_PLATFORM is only set by -A, which Ninja never receives, so
the Ninja build selected the x64 target on ARM64. DEPS_ARCH is derived from
CMAKE_SYSTEM_PROCESSOR and is already independent of the generator.

* ci: build the Windows ARM64 dependencies and slicer with clang-cl

Three dependencies need handling first. libpng and OpenCV each build an ARM
SIMD path that does not compile with clang-cl, so those paths are off; PNG
already had the same opt-out for Apple ARM. OCCT is built with cl, since
clang-cl cannot emit one of its large generated files and there is no option
to turn that off. All three are gated to Windows ARM64 with clang.

.github/workflows/build_all.yml

@@ -81,14 +81,15 @@ jobs:
       # SELF_HOSTED skips arm64 (the self-hosted Windows server is x64-only).
       matrix:
         include: ${{ fromJSON(vars.SELF_HOSTED
-          && '[{"arch":"x64","os":"orca-win-server"}]'
-          || '[{"arch":"x64","os":"windows-latest"},{"arch":"arm64","os":"windows-11-arm"}]') }}
+          && '[{"arch":"x64","os":"orca-win-server","compiler":"clang"}]'
+          || '[{"arch":"x64","os":"windows-latest","compiler":"clang"},{"arch":"arm64","os":"windows-11-arm","compiler":"clang"}]') }}
     # Don't run scheduled builds on forks:
     if: ${{ !cancelled() && (github.event_name != 'schedule' || github.repository == 'OrcaSlicer/OrcaSlicer') }}
     uses: ./.github/workflows/build_check_cache.yml
     with:
       os: ${{ matrix.os }}
       arch: ${{ matrix.arch }}
+      compiler: ${{ matrix.compiler }}
       build-deps-only: ${{ inputs.build-deps-only || false }}
       force-build: ${{ github.event_name == 'schedule' }}
     secrets: inherit

.github/workflows/build_check_cache.yml

@@ -9,6 +9,10 @@ on:
       arch:
         required: false
         type: string
+      compiler:
+        required: false
+        type: string
+        default: msvc
       build-deps-only:
         required: false
         type: boolean
@@ -33,10 +37,10 @@ jobs:
       - name: set outputs
         id: set_outputs
         env:
-          # Keep macOS/Windows cache keys architecture-specific. amd64 Linux passes
-          # no arch (key stays 'linux-clang', preserving the existing cache);
-          # aarch64 gets its own 'linux-clang-aarch64' key.
-          cache-os: ${{ runner.os == 'macOS' && format('macos-{0}', inputs.arch) || (runner.os == 'Windows' && format('windows-{0}', inputs.arch) || format('linux-clang{0}', inputs.arch && format('-{0}', inputs.arch) || '')) }}
+          # Anything that changes how the tree is built belongs in the key, or a job
+          # restores one it cannot use. Linux amd64 passes no arch deliberately, so
+          # 'linux-clang' keeps the cache it already has.
+          cache-os: ${{ runner.os == 'macOS' && format('macos-{0}', inputs.arch) || (runner.os == 'Windows' && format('windows-{0}-{1}', inputs.arch, inputs.compiler) || format('linux-clang{0}', inputs.arch && format('-{0}', inputs.arch) || '')) }}
           # ARM64 builds use the build-arm64 tree (see build_release_vs.bat); x64/other use build.
           dep-folder-name: ${{ runner.os == 'macOS' && format('/{0}', inputs.arch) || (runner.os == 'Windows' && inputs.arch == 'arm64') && '-arm64/OrcaSlicer_dep' || '/OrcaSlicer_dep' }}
           output-cmd: ${{ runner.os == 'Windows' && '$env:GITHUB_OUTPUT' || '"$GITHUB_OUTPUT"'}}
@@ -62,6 +66,7 @@ jobs:
       valid-cache: ${{ needs.check_cache.outputs.valid-cache == 'true' }}
       os: ${{ inputs.os }}
       arch: ${{ inputs.arch }}
+      compiler: ${{ inputs.compiler }}
       build-deps-only: ${{ inputs.build-deps-only }}
       force-build: ${{ inputs.force-build }}
     secrets: inherit

.github/workflows/build_deps.yml

@@ -16,6 +16,10 @@ on:
       arch:
         required: false
         type: string
+      compiler:
+        required: false
+        type: string
+        default: msvc
       build-deps-only:
         required: false
         type: boolean
@@ -135,11 +139,22 @@ jobs:
               choco install strawberryperl
             }
             $arch = "${{ inputs.arch }}"
+            # -l selects clang-cl and -x Ninja; together they build the deps with clang.
+            $clang = "${{ inputs.compiler }}" -eq "clang"
+            $flags = if ($clang) { "-l", "-x" } else { @() }
+            if ($clang) {
+              # OpenSSL builds with nmake, which needs a VC environment.
+              $vswhere = "${env:ProgramFiles(x86)}\Microsoft Visual Studio\Installer\vswhere.exe"
+              $vs = & $vswhere -latest -property installationPath
+              $devArch = if ($arch -eq "arm64") { "arm64" } else { "amd64" }
+              Import-Module "$vs\Common7\Tools\Microsoft.VisualStudio.DevShell.dll"
+              Enter-VsDevShell -VsInstallPath $vs -SkipAutomaticLocation -DevCmdArguments "-arch=$devArch"
+            }
             if ($arch -eq "arm64") {
-              .\build_release_vs.bat deps arm64
+              .\build_release_vs.bat deps arm64 @flags
               .\build_release_vs.bat pack arm64
             } else {
-              .\build_release_vs.bat deps
+              .\build_release_vs.bat deps @flags
               .\build_release_vs.bat pack
             }
         shell: pwsh
@@ -204,4 +219,5 @@ jobs:
       cache-path: ${{ inputs.cache-path }}
       os: ${{ inputs.os }}
       arch: ${{ inputs.arch }}
+      compiler: ${{ inputs.compiler }}
     secrets: inherit

.github/workflows/build_orca.yml

@@ -13,6 +13,10 @@ on:
         arch:
           required: false
           type: string
+        compiler:
+          required: false
+          type: string
+          default: msvc
         macos-combine-only:
           required: false
           type: boolean
@@ -395,7 +399,18 @@ jobs:
         # "tests" builds the unit tests too; the unit_tests_windows_* jobs run them.
         run: |
           $arch = "${{ inputs.arch }}"
-          if ($arch -eq "arm64") { .\build_release_vs.bat slicer arm64 tests } else { .\build_release_vs.bat slicer tests }
+          # -l selects clang-cl and -x Ninja; together they build the slicer with clang.
+          $clang = "${{ inputs.compiler }}" -eq "clang"
+          $flags = if ($clang) { "-l", "-x" } else { @() }
+          if ($clang) {
+            # Build against the same VC toolchain and SDK as the dependencies.
+            $vswhere = "${env:ProgramFiles(x86)}\Microsoft Visual Studio\Installer\vswhere.exe"
+            $vs = & $vswhere -latest -property installationPath
+            $devArch = if ($arch -eq "arm64") { "arm64" } else { "amd64" }
+            Import-Module "$vs\Common7\Tools\Microsoft.VisualStudio.DevShell.dll"
+            Enter-VsDevShell -VsInstallPath $vs -SkipAutomaticLocation -DevCmdArguments "-arch=$devArch"
+          }
+          if ($arch -eq "arm64") { .\build_release_vs.bat slicer arm64 @flags tests } else { .\build_release_vs.bat slicer @flags tests }
         shell: pwsh
 
       - name: Build system preset cache (Windows)

deps/OCCT/OCCT.cmake

@@ -1,3 +1,10 @@
+# clang-cl cannot emit IGESAppli_GeneralModule.cxx on ARM64
+# (llvm/llvm-project#62081). cl and clang-cl share an ABI.
+set(_occt_compiler_args "")
+if ("${DEPS_ARCH}" STREQUAL "arm64" AND CMAKE_CXX_COMPILER_ID STREQUAL Clang)
+    set(_occt_compiler_args -DCMAKE_C_COMPILER:STRING=cl -DCMAKE_CXX_COMPILER:STRING=cl)
+endif ()
+
 if(WIN32)
     set(library_build_type "Shared")
 else()
@@ -31,6 +38,7 @@ orcaslicer_add_cmake_project(OCCT
         -DBUILD_MODULE_ModelingAlgorithms=OFF
         -DBUILD_MODULE_ModelingData=OFF
         -DBUILD_MODULE_Visualization=OFF
+        ${_occt_compiler_args}
 )
 
 # add_dependencies(dep_OCCT ${FREETYPE_PKG})

deps/OpenCV/OpenCV.cmake

@@ -10,6 +10,13 @@ else ()
     set(_options "")
 endif ()
 
+# carotene is OpenCV's ARM NEON HAL. It uses M_PI without _USE_MATH_DEFINES
+# and does not compile with clang-cl.
+set(_disable_carotene "")
+if ("${DEPS_ARCH}" STREQUAL "arm64" AND CMAKE_CXX_COMPILER_ID STREQUAL Clang)
+    set(_disable_carotene "-DWITH_CAROTENE=OFF")
+endif ()
+
 if (IN_GIT_REPO)
     set(OpenCV_DIRECTORY_FLAG --directory ${BINARY_DIR_REL}/dep_OpenCV-prefix/src/dep_OpenCV)
 endif ()
@@ -83,5 +90,6 @@ orcaslicer_add_cmake_project(OpenCV
        -DWITH_PROTOBUF=OFF
        -DWITH_WIN32UI=OFF
        -DHAVE_WIN32UI=FALSE
+       ${_disable_carotene}
 )
 

deps/OpenSSL/OpenSSL.cmake

@@ -6,7 +6,7 @@ if(DEFINED OPENSSL_ARCH)
     set(_cross_arch ${OPENSSL_ARCH})
 else()
     if(WIN32)
-        if("${CMAKE_GENERATOR_PLATFORM}" STREQUAL "ARM64")
+        if("${DEPS_ARCH}" STREQUAL "arm64")
             set(_cross_arch "VC-WIN64-ARM")
         else()
             set(_cross_arch "VC-WIN64A")

deps/PNG/PNG.cmake

@@ -1,6 +1,10 @@
 if (APPLE)
     # Only disable NEON extension for Apple ARM builds, leave it enabled for Raspberry PI.
     set(_disable_neon_extension "-DPNG_ARM_NEON=off")
+elseif ("${DEPS_ARCH}" STREQUAL "arm64" AND CMAKE_CXX_COMPILER_ID STREQUAL Clang)
+    # libpng's CMake ignores PNG_ARM_NEON on Windows ARM64 and skips the NEON
+    # sources, but pngpriv.h enables NEON anyway.
+    set(_disable_neon_extension "-DCMAKE_C_FLAGS=/DWIN32 /D_WINDOWS /DPNG_ARM_NEON_OPT=0")
 else ()
     set(_disable_neon_extension "")
 endif ()