CI: Add native Windows arm64 job/package

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

@@ -59,8 +59,12 @@ runs:
       run: |
         set -eux
         cd ..
+        suffix='win64'
+        if [[ '${{ inputs.arch }}' == arm64 ]]; then
+          suffix='woa64'
+        fi
         curl -fL --retry 3 --max-time 300 -o clang.exe \
-          https://github.com/llvm/llvm-project/releases/download/llvmorg-20.1.3/LLVM-20.1.3-win64.exe
+          https://github.com/llvm/llvm-project/releases/download/llvmorg-20.1.3/LLVM-20.1.3-$suffix.exe
         ./clang.exe //S # double-slash for bash
         rm clang.exe
         # C:\Program Files\LLVM\bin should already be in PATH
@@ -163,7 +167,9 @@ runs:
         cd ..
 
         url='https://curl.se/windows/latest.cgi?p=win64-mingw.zip'
-        if [[ '${{ inputs.arch }}' == x86 ]]; then
+        if [[ '${{ inputs.arch }}' == arm64 ]]; then
+          url='https://curl.se/windows/latest.cgi?p=win64a-mingw.zip'
+        elif [[ '${{ inputs.arch }}' == x86 ]]; then
           url='https://curl.se/windows/latest.cgi?p=win32-mingw.zip'
         fi
 

.github/actions/5-install/action.yml

@@ -66,6 +66,11 @@ runs:
 
         cp libcurl/ldc2/* installed/bin/
 
+        if [[ '${{ inputs.arch }}' == arm64 ]]; then
+          echo "No MinGW-based libraries available for arm64 yet."
+          exit 0
+        fi
+
         curl -fL --retry 3 --max-time 60 -o mingw-w64-libs.7z \
           https://github.com/ldc-developers/mingw-w64-libs/releases/download/v8.0.0/mingw-w64-libs-v8.0.0.7z
         mkdir mingw-w64-libs

.github/actions/merge-windows/action.yml

@@ -67,6 +67,7 @@ runs:
         set PATH=%CD%\ldc2-multilib\lib32;%PATH%
         ldc2-multilib\bin\ldc2 -link-defaultlib-shared -m32 -run hello.d || exit /b
 
+    # TODO
     # preliminary arm64 cross-compilation support
     - name: Install ninja v1.12.1
       uses: Ahajha/gha-setup-ninja@69595b0cf872acdad8ce599142fbdc88724b9a2b

.github/workflows/main.yml

@@ -101,6 +101,16 @@ jobs:
               -DEXTRA_CXXFLAGS=-flto=full
             with_pgo: true
 
+          - job_name: Windows arm64
+            os: windows-11-arm
+            arch: arm64
+            base_cmake_flags: >-
+              -DCMAKE_MSVC_RUNTIME_LIBRARY=MultiThreaded
+            #extra_cmake_flags: >-
+            #  "-DD_COMPILER_FLAGS=-O -flto=full -defaultlib=phobos2-ldc-lto,druntime-ldc-lto"
+            #  -DEXTRA_CXXFLAGS=-flto=full
+            #with_pgo: true
+
           - job_name: Windows x86
             os: windows-2025
             arch: x86

CMakeLists.txt

@@ -195,7 +195,10 @@ if(NOT MSVC_IDE)
 endif()
 
 if(MSVC)
-    if(CMAKE_SIZEOF_VOID_P EQUAL 8)
+    if($ENV{VSCMD_ARG_TGT_ARCH} STREQUAL "arm64")
+        message(STATUS "Let D host compiler output arm64 object files")
+        append("-mtriple=aarch64-windows-msvc" DFLAGS_BASE)
+    elseif(CMAKE_SIZEOF_VOID_P EQUAL 8)
         message(STATUS "Let D host compiler output 64-bit object files")
         append("-m64" DFLAGS_BASE)
     else()
@@ -300,7 +303,9 @@ endif()
 if(MSVC)
     separate_arguments(LLVM_LDFLAGS WINDOWS_COMMAND "${LLVM_LDFLAGS}")
     if(NOT MSVC_IDE) # apparently not needed for VS (and spaces in path are problematic)
-        if(CMAKE_SIZEOF_VOID_P EQUAL 8)
+        if($ENV{VSCMD_ARG_TGT_ARCH} STREQUAL "arm64")
+            list(APPEND LLVM_LDFLAGS "$ENV{VSINSTALLDIR}DIA SDK\\lib\\arm64\\diaguids.lib")
+        elseif(CMAKE_SIZEOF_VOID_P EQUAL 8)
             list(APPEND LLVM_LDFLAGS "$ENV{VSINSTALLDIR}DIA SDK\\lib\\amd64\\diaguids.lib")
         else()
             list(APPEND LLVM_LDFLAGS "$ENV{VSINSTALLDIR}DIA SDK\\lib\\diaguids.lib")
@@ -898,7 +903,9 @@ if (LDC_INSTALL_LLVM_RUNTIME_LIBS)
         copy_compilerrt_lib("libclang_rt.xray-profiling${compilerrt_suffix}.a" "libldc_rt.xray-profiling.a" FALSE)
     elseif(WIN32)
         set(compilerrt_arch_suffix "x86_64")
-        if(CMAKE_SIZEOF_VOID_P EQUAL 4)
+        if($ENV{VSCMD_ARG_TGT_ARCH} STREQUAL "arm64")
+            set(compilerrt_arch_suffix "aarch64")
+        elseif(CMAKE_SIZEOF_VOID_P EQUAL 4)
             set(compilerrt_arch_suffix "i386")
         endif()
         if(LDC_LLVM_VER LESS 2000)

dmd/main.d

@@ -442,8 +442,11 @@ else
     reconcileLinkRunLib(params, files.length, target.obj_ext);
     version(CRuntime_Microsoft)
     {
-        import dmd.root.longdouble;
-        initFPU();
+        version(AArch64) { /* no longdouble_soft support on arm64 host */ } else
+        {
+            import dmd.root.longdouble;
+            initFPU();
+        }
     }
     import dmd.root.ctfloat : CTFloat;
     CTFloat.initialize();

dmd/root/ctfloat.d

@@ -27,13 +27,17 @@ private
 {
     version(CRuntime_DigitalMars) __gshared extern (C) extern const(char)* __locale_decpoint;
 
-    version(CRuntime_Microsoft) extern (C++)
+    version(CRuntime_Microsoft)
     {
-        public import dmd.root.longdouble : longdouble_soft, ld_sprint;
+        version(AArch64) { /* 64-bit real_t */ } else
+        {
+            version = MSVC_X87;
+            import dmd.root.longdouble : longdouble_soft, ld_sprint;
 version (IN_LLVM) {} else
 {
-        import dmd.root.strtold;
+            import dmd.root.strtold;
 }
+        }
     }
 }
 
@@ -193,7 +197,7 @@ extern (C++) struct CTFloat
     // the implementation of longdouble for MSVC is a struct, so mangling
     //  doesn't match with the C++ header.
     // add a wrapper just for isSNaN as this is the only function called from C++
-    version(CRuntime_Microsoft) static if (is(real_t == real))
+    version(MSVC_X87) static if (is(real_t == real))
         pure @trusted
         static bool isSNaN(longdouble_soft ld)
         {
@@ -239,7 +243,7 @@ extern (C++) struct CTFloat
     @system
     static int sprint(char* str, size_t size, char fmt, real_t x)
     {
-        version(CRuntime_Microsoft)
+        version(MSVC_X87)
         {
             auto len = cast(int) ld_sprint(str, size, fmt, longdouble_soft(x));
         }

dmd/root/longdouble.d

@@ -13,7 +13,9 @@ module dmd.root.longdouble;
 
 version (CRuntime_Microsoft)
 {
-    static if (real.sizeof > 8)
+    version (AArch64)
+        alias longdouble = real; // 64-bit
+    else static if (real.sizeof > 8)
         alias longdouble = real;
     else
         alias longdouble = longdouble_soft;
@@ -24,6 +26,7 @@ else
 // longdouble_soft needed when building the backend with
 // Visual C or the frontend with LDC on Windows
 version (CRuntime_Microsoft):
+version (AArch64) { /* cannot use x87 inline asm on arm64 host */ } else:
 extern (C++):
 nothrow:
 @nogc:

dmd/root/longdouble.h

@@ -11,7 +11,7 @@
 
 #pragma once
 
-#if !_MSC_VER // has native 10 byte doubles
+#if !defined(_MSC_VER) || defined(_M_ARM64)
 #include <stdio.h>
 typedef long double longdouble;
 typedef volatile long double volatile_longdouble;
@@ -48,7 +48,7 @@ inline size_t ld_sprint(char* str, size_t size, int fmt, longdouble x)
 #undef snprintf
 #endif
 
-#else
+#else // defined(_MSC_VER) && !defined(_M_ARM64)
 
 #include <float.h>
 #include <limits>
@@ -264,4 +264,4 @@ typedef longdouble_soft longdouble;
 // is not required.
 typedef longdouble_soft volatile_longdouble;
 
-#endif // !_MSC_VER
+#endif // defined(_MSC_VER) && !defined(_M_ARM64)

gen/ctfloat.cpp

@@ -42,8 +42,8 @@ void CTFloat::initialize() {
   if (apSemantics)
     return;
 
-#ifdef _MSC_VER
-  // MSVC hosts use dmd.root.longdouble (80-bit x87)
+#if defined(_MSC_VER) && !defined(_M_ARM64)
+  // MSVC x86[_64] hosts use dmd.root.longdouble (80-bit x87)
   apSemantics = &APFloat::x87DoubleExtended();
 #else
   static_assert(std::numeric_limits<real_t>::is_specialized,