[try matching clang from GitHub on macOS arm64]

Author: kinke

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

@@ -49,6 +49,19 @@ runs:
           sudo ln -sf $tool-19 /usr/bin/$tool
           $tool --version
         done
+    - name: 'macOS arm64: Install clang 19 from GitHub' # see mimalloc comment in ../3-build-native/action.yml
+      if: runner.os == 'macOS' && inputs.arch == 'arm64'
+      shell: bash
+      run: |
+        set -eux
+        cd ..
+        curl -fL --retry 3 --max-time 300 -o clang.tar.xz \
+          https://github.com/llvm/llvm-project/releases/download/llvmorg-19.1.7/LLVM-19.1.7-macOS-ARM64.tar.xz
+        mkdir clang
+        tar -xf clang.tar.xz --strip 1 -C clang
+        rm clang.tar.xz
+        # prepend its bin/ dir to PATH for subsequent steps
+        echo "$PWD/clang/bin" >> "$GITHUB_PATH"
     - name: 'Windows: Install clang v19.1.3 from GitHub'
       if: runner.os == 'Windows'
       shell: bash

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

@@ -22,11 +22,13 @@ runs:
         build_dir: build
         host_dc: ../bootstrap-ldc/bin/ldmd2
         specify_install_dir: true
-        # FIXME: 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!`
-        #        on x86_64, this is 'fixed' by using LTO - on arm64, this doesn't suffice
+        # 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!`
+        # On x86_64, this is 'fixed' by using LTO (for both D and C++ parts of ldc2).
+        # On arm64, we need a matching clang to enable C++ LTO anyway, due to `LLVM ERROR: Unsupported stack probing method` with Xcode clang.
         cmake_flags: >-
-          ${{ (runner.os != 'Windows' && !(runner.os == 'macOS' && inputs.arch == 'arm64')) && '-DALTERNATIVE_MALLOC_O="$PWD/../build-mimalloc/CMakeFiles/mimalloc-obj.dir/src/static.c.o"' || '' }}
+          ${{ runner.os != 'Windows' && '-DALTERNATIVE_MALLOC_O="$PWD/../build-mimalloc/CMakeFiles/mimalloc-obj.dir/src/static.c.o"' || '' }}
           ${{ inputs.cmake_flags }}
           ${{ inputs.with_pgo == 'true' && '-DDFLAGS_LDC=-fprofile-use=../pgo-ldc/merged.profdata' || '' }}
         build_targets: all ldc2-unittest all-test-runners

.github/workflows/main.yml

@@ -85,10 +85,10 @@ jobs:
             os: macos-14
             arch: arm64
             extra_cmake_flags: >-
+              -DCMAKE_C_COMPILER=clang
+              -DCMAKE_CXX_COMPILER=clang++
               -DD_COMPILER_FLAGS="-O -flto=full -defaultlib=phobos2-ldc-lto,druntime-ldc-lto -L-exported_symbol '-L__*' -L-w"
-            # FIXME: cannot enable LTO for C++ parts too, due to: `LLVM ERROR: Unsupported stack probing method` when linking ldc2
-            #        (apparently from bitcode files compiled with older Xcode clang)
-            #  -DEXTRA_CXXFLAGS=-flto=full
+              -DEXTRA_CXXFLAGS=-flto=full
             with_pgo: true
 
           - job_name: Windows x64