GHA macOS: Enable bootstrap stage again (#4912)

And the latest stable LDC release as first host compiler.

Fixes #4899 for good.

Author: kinke

.github/actions/1-setup/action.yml

@@ -49,6 +49,10 @@ runs:
           sudo ln -sf $tool-19 /usr/bin/$tool
           $tool --version
         done
+    - name: 'macOS arm64: Install Homebrew clang 19' # see mimalloc comment in ../3-build-native/action.yml
+      if: runner.os == 'macOS' && inputs.arch == 'arm64'
+      shell: bash
+      run: brew install llvm@19
     - name: 'Windows: Install clang v19.1.3 from GitHub'
       if: runner.os == 'Windows'
       shell: bash
@@ -121,8 +125,7 @@ runs:
     - name: Install D host compiler
       uses: dlang-community/setup-dlang@v1
       with:
-        # macOS: use LDC with LLVM version matching Xcode - v1.39.0 (LLVM 17) on arm64 with Xcode 16, v1.35.0 (LLVM 16) on x86_64 with Xcode 15
-        compiler: ${{ runner.os != 'macOS' && 'ldc-latest' || (inputs.arch == 'arm64' && 'ldc-1.39.0' || 'ldc-1.35.0') }}
+        compiler: ldc-latest
     - name: 'Posix: Clear LD_LIBRARY_PATH env variable' # don't use host druntime/Phobos .so/.dylib etc.
       if: runner.os != 'Windows'
       shell: bash

.github/actions/3-build-native/action.yml

@@ -4,7 +4,7 @@ inputs:
     required: false
     default: ''
   arch:
-    required: false # Windows only
+    required: true
   with_pgo:
     required: false
     default: false
@@ -15,13 +15,23 @@ runs:
     - name: 'Posix: Build mimalloc'
       if: runner.os != 'Windows'
       uses: ./.github/actions/helper-mimalloc
+      with:
+        cmake_flags: ${{ inputs.cmake_flags }} # propagate C(++) compilers and ignored LDC-specific vars
 
     - name: Build LDC & LDC D unittests & defaultlib unittest runners
       uses: ./.github/actions/helper-build-ldc
       with:
         build_dir: build
         host_dc: ../bootstrap-ldc/bin/ldmd2
         specify_install_dir: true
+        # NOTE:
+        # mimalloc on macOS is tricky - when mixing newer LLVM from bootstrap LDC with older LLVM from Xcode clang,
+        # causing *sporadic* compiler crashes: `libc++abi: Pure virtual function called!`
+        # What apparently makes it work with newer LLVM versions on both x86_64 and arm64 is using mixed LTO for both
+        # C++ and D parts of ldc2 (with prebuilt non-LTO'd LLVM compiled with Xcode clang); the compiler used for
+        # non-LTO'd mimalloc doesn't seem to play a role.
+        # On macOS arm64, we need a matching Homebrew clang to get C++ LTO to work, otherwise hitting linker error
+        # `LLVM ERROR: Unsupported stack probing method` with bitcode files produced by older Xcode clang.
         cmake_flags: >-
           ${{ runner.os != 'Windows' && '-DALTERNATIVE_MALLOC_O="$PWD/../build-mimalloc/CMakeFiles/mimalloc-obj.dir/src/static.c.o"' || '' }}
           ${{ inputs.cmake_flags }}

.github/workflows/main.yml

@@ -76,20 +76,18 @@ jobs:
             # https://github.com/ldc-developers/ldc/issues/4462:
             # When using LTO, we need to explicitly export ~all symbols for plugin support via `ld64 -exported_symbol '__*'`.
             # Additionally `-w` to suppress resulting linker warnings.
-            #
-            # We also need to work around issues with the used LDC v1.35.0 host/bootstrap compiler:
-            # * Specify a macOS triple with OS version. And exclude LTO-able host druntime/Phobos because precompiled without OS version.
-            # * Manually specify the path to the bundled libLTO.dylib (broken for *universal* packages for LDC <= v1.40.0).
             extra_cmake_flags: >-
-              -DD_COMPILER_FLAGS="-O -flto=full -L-exported_symbol '-L__*' -L-w -flto-binary=$PWD/../bootstrap-ldc/lib-x86_64/libLTO.dylib -mtriple=x86_64-apple-macos$MACOSX_DEPLOYMENT_TARGET"
+              -DD_COMPILER_FLAGS="-O -flto=full -defaultlib=phobos2-ldc-lto,druntime-ldc-lto -L-exported_symbol '-L__*' -L-w"
               -DEXTRA_CXXFLAGS=-flto=full
             with_pgo: true
 
           - job_name: macOS arm64
             os: macos-14
             arch: arm64
             extra_cmake_flags: >-
-              -DD_COMPILER_FLAGS="-O -flto=full -defaultlib=phobos2-ldc-lto,druntime-ldc-lto -L-exported_symbol '-L__*' -L-w -flto-binary=$PWD/../bootstrap-ldc/lib-arm64/libLTO.dylib"
+              -DCMAKE_C_COMPILER=/opt/homebrew/opt/llvm@19/bin/clang
+              -DCMAKE_CXX_COMPILER=/opt/homebrew/opt/llvm@19/bin/clang++
+              -DD_COMPILER_FLAGS="-O -flto=full -defaultlib=phobos2-ldc-lto,druntime-ldc-lto -L-exported_symbol '-L__*' -L-w"
               -DEXTRA_CXXFLAGS=-flto=full
             with_pgo: true
 
@@ -161,25 +159,14 @@ jobs:
         uses: ./.github/actions/helper-build-gdb
         with:
           arch: ${{ matrix.arch }}
+      - name: 'macOS arm64: Switch to Xcode 16'
+        if: runner.os == 'macOS' && matrix.arch == 'arm64'
+        run: sudo xcode-select -switch /Applications/Xcode_16.1.app
       - name: Build bootstrap LDC
-        if: runner.os != 'macOS'
         uses: ./.github/actions/2-build-bootstrap
         with:
           cmake_flags: -DBUILD_LTO_LIBS=ON ${{ matrix.base_cmake_flags }}
           arch: ${{ matrix.arch }}
-      # FIXME: on macOS, mixing newer LLVM from bootstrap LDC with older LLVM from Xcode clang is problematic,
-      #        leading to sporadic 'libc++abi: Pure virtual function called!' compiler crashes etc.
-      - name: 'macOS: Use host LDC (with Xcode-compatible LLVM version) as bootstrap LDC'
-        if: runner.os == 'macOS'
-        run: |
-          ln -s $(dirname $(dirname $(which ldmd2))) ../bootstrap-ldc
-          if [[ '${{ matrix.arch }}' == 'x86_64' ]]; then
-            # work around a v1.35.0 bug - need to rename libLTO-ldc.dylib to make it loadable
-            mv ../bootstrap-ldc/lib-x86_64/libLTO-ldc.dylib ../bootstrap-ldc/lib-x86_64/libLTO.dylib
-          else
-            # use Xcode v16 on arm64
-            sudo xcode-select -switch /Applications/Xcode_16.1.app
-          fi
       - name: Build LDC with PGO instrumentation & gather profile from compiling default libs
         if: matrix.with_pgo
         uses: ./.github/actions/2a-build-pgo

CMakeLists.txt

@@ -317,7 +317,7 @@ if(UNIX AND LDC_FULLY_STATIC)
 endif()
 
 # Suppress superfluous randlib warnings about "*.a" having no symbols on MacOSX.
-if (APPLE)
+if (${CMAKE_CXX_COMPILER_ID} STREQUAL "AppleClang") # not supported by llvm-ranlib used with Homebrew clang
     set(CMAKE_C_ARCHIVE_CREATE   "<CMAKE_AR> Scr <TARGET> <LINK_FLAGS> <OBJECTS>")
     set(CMAKE_CXX_ARCHIVE_CREATE "<CMAKE_AR> Scr <TARGET> <LINK_FLAGS> <OBJECTS>")
     set(CMAKE_C_ARCHIVE_FINISH   "<CMAKE_RANLIB> -no_warning_for_no_symbols -c <TARGET>")