[win][arm64ec] Fixes to unblock building LLVM and Clang as Arm64EC #150068

dpaoliello · 2025-07-22T17:24:42Z

These changes allow LLVM and Clang to be built with Clang targeting Arm64EC using the MSVC linker.

Built with these options:

-DLLVM_ENABLE_PROJECTS="clang"
-DLLVM_HOST_TRIPLE=arm64ec-pc-windows-msvc
-DCMAKE_C_COMPILER=clang-cl.exe
-DCMAKE_C_COMPILER_TARGET=arm64ec-pc-windows-msvc
-DCMAKE_CXX_COMPILER=clang-cl.exe
-DCMAKE_CXX_COMPILER_TARGET=arm64ec-pc-windows-msvc
-DCMAKE_LINKER_TYPE=MSVC

llvmbot · 2025-07-22T17:25:10Z

@llvm/pr-subscribers-llvm-support
@llvm/pr-subscribers-tools-llvm-exegesis
@llvm/pr-subscribers-clang
@llvm/pr-subscribers-third-party-benchmark

@llvm/pr-subscribers-platform-windows

Author: Daniel Paoliello (dpaoliello)

Changes

These changes allow LLVM and Clang to be built with Clang targeting Arm64EC using the MSVC linker.

Built with these options:

-DLLVM_ENABLE_PROJECTS="clang"
-DLLVM_HOST_TRIPLE=arm64ec-pc-windows-msvc
-DCMAKE_C_COMPILER=clang-cl.exe
-DCMAKE_C_COMPILER_TARGET=arm64ec-pc-windows-msvc
-DCMAKE_CXX_COMPILER=clang-cl.exe
-DCMAKE_CXX_COMPILER_TARGET=arm64ec-pc-windows-msvc
-DCMAKE_LINKER_TYPE=MSVC
-DCMAKE_EXE_LINKER_FLAGS="-Xlinker /MACHINE:ARM64EC"
-DCMAKE_SHARED_LINKER_FLAGS="-Xlinker /MACHINE:ARM64EC"
-DLLVM_DISABLE_ASSEMBLY_FILES=On

Full diff: https://github.com/llvm/llvm-project/pull/150068.diff

4 Files Affected:

(modified) clang/tools/clang-repl/CMakeLists.txt (+9-6)
(modified) llvm/lib/TargetParser/Host.cpp (+5-5)
(modified) llvm/tools/llvm-exegesis/lib/X86/Target.cpp (+7-7)
(modified) third-party/benchmark/src/cycleclock.h (+2-2)

diff --git a/clang/tools/clang-repl/CMakeLists.txt b/clang/tools/clang-repl/CMakeLists.txt
index 68d86dd98cac3..c3d14ceb79792 100644
--- a/clang/tools/clang-repl/CMakeLists.txt
+++ b/clang/tools/clang-repl/CMakeLists.txt
@@ -19,14 +19,14 @@ if(MSVC)
   set_target_properties(clang-repl PROPERTIES WINDOWS_EXPORT_ALL_SYMBOLS 1)
 
   # RTTI/C++ symbols
-  set(clang_repl_exports ${clang_repl_exports} ??_7type_info@@6B@
-    ?__type_info_root_node@@3U__type_info_node@@A
-    ?nothrow@std@@3Unothrow_t@1@B
+  set(clang_repl_exports ${clang_repl_exports} ??_7type_info@@6B@,DATA
+    ?__type_info_root_node@@3U__type_info_node@@A,DATA
+    ?nothrow@std@@3Unothrow_t@1@B,DATA
   )
 
   # Compiler added symbols for static variables. NOT for VStudio < 2015
-  set(clang_repl_exports ${clang_repl_exports} _Init_thread_abort _Init_thread_epoch
-    _Init_thread_footer _Init_thread_header _tls_index
+  set(clang_repl_exports ${clang_repl_exports} _Init_thread_abort _Init_thread_epoch,DATA
+    _Init_thread_footer _Init_thread_header _tls_index,DATA
   )
 
   if(CMAKE_SIZEOF_VOID_P EQUAL 8)
@@ -50,7 +50,10 @@ if(MSVC)
   endif()
 
   # List to '/EXPORT:sym0 /EXPORT:sym1 /EXPORT:sym2 ...'
-  list(TRANSFORM clang_repl_exports PREPEND "LINKER:/EXPORT:")
+  # The 'SHELL' prefix tells CMake to use a space instead of comma as the
+  # separator between the driver and linker options, which we need since MSVC's
+  # linker uses `,DATA` as a suffix to indicate that data is being exported.
+  list(TRANSFORM clang_repl_exports PREPEND "LINKER:SHELL:/EXPORT:")
 
   set_property(TARGET clang-repl APPEND PROPERTY LINK_OPTIONS ${clang_repl_exports})
 
diff --git a/llvm/lib/TargetParser/Host.cpp b/llvm/lib/TargetParser/Host.cpp
index 78bd5b4b5bd25..6d089df03cf77 100644
--- a/llvm/lib/TargetParser/Host.cpp
+++ b/llvm/lib/TargetParser/Host.cpp
@@ -587,8 +587,8 @@ StringRef sys::detail::getHostCPUNameForBPF() {
 #endif
 }
 
-#if defined(__i386__) || defined(_M_IX86) || defined(__x86_64__) ||            \
-    defined(_M_X64)
+#if (defined(__i386__) || defined(_M_IX86) || defined(__x86_64__) ||            \
+    defined(_M_X64)) && !defined(_M_ARM64EC)
 
 /// getX86CpuIDAndInfo - Execute the specified cpuid and return the 4 values in
 /// the specified arguments.  If we can't run cpuid on the host, return true.
@@ -1853,8 +1853,8 @@ VendorSignatures getVendorSignature(unsigned *MaxLeaf) {
 } // namespace llvm
 #endif
 
-#if defined(__i386__) || defined(_M_IX86) || \
-    defined(__x86_64__) || defined(_M_X64)
+#if (defined(__i386__) || defined(_M_IX86) || \
+    defined(__x86_64__) || defined(_M_X64)) && !defined(_M_ARM64EC)
 StringMap<bool> sys::getHostCPUFeatures() {
   unsigned EAX = 0, EBX = 0, ECX = 0, EDX = 0;
   unsigned MaxLevel;
@@ -2067,7 +2067,7 @@ StringMap<bool> sys::getHostCPUFeatures() {
 
   return Features;
 }
-#elif defined(__linux__) && (defined(__arm__) || defined(__aarch64__))
+#elif defined(__linux__) && (defined(__arm__) || defined(__aarch64__) || defined(__arm64ec__))
 StringMap<bool> sys::getHostCPUFeatures() {
   StringMap<bool> Features;
   std::unique_ptr<llvm::MemoryBuffer> P = getProcCpuinfoContent();
diff --git a/llvm/tools/llvm-exegesis/lib/X86/Target.cpp b/llvm/tools/llvm-exegesis/lib/X86/Target.cpp
index 1659cfb31f117..f6022b6bdd428 100644
--- a/llvm/tools/llvm-exegesis/lib/X86/Target.cpp
+++ b/llvm/tools/llvm-exegesis/lib/X86/Target.cpp
@@ -30,11 +30,11 @@
 #include <memory>
 #include <string>
 #include <vector>
-#if defined(_MSC_VER) && (defined(_M_IX86) || defined(_M_X64))
+#if defined(_MSC_VER) && (defined(_M_IX86) || defined(_M_X64)) && !defined(_M_ARM64EC)
 #include <immintrin.h>
 #include <intrin.h>
 #endif
-#if defined(_MSC_VER) && defined(_M_X64)
+#if defined(_MSC_VER) && defined(_M_X64) && !defined(_M_ARM64EC)
 #include <float.h> // For _clearfp in ~X86SavedState().
 #endif
 
@@ -654,7 +654,7 @@ namespace {
 class X86SavedState : public ExegesisTarget::SavedState {
 public:
   X86SavedState() {
-#if defined(_MSC_VER) && defined(_M_X64)
+#if defined(_MSC_VER) && defined(_M_X64) && !defined(_M_ARM64EC)
     _fxsave64(FPState);
     Eflags = __readeflags();
 #elif defined(__GNUC__) && defined(__x86_64__)
@@ -668,7 +668,7 @@ class X86SavedState : public ExegesisTarget::SavedState {
   ~X86SavedState() {
     // Restoring the X87 state does not flush pending exceptions, make sure
     // these exceptions are flushed now.
-#if defined(_MSC_VER) && defined(_M_X64)
+#if defined(_MSC_VER) && defined(_M_X64) && !defined(_M_ARM64EC)
     _clearfp();
     _fxrstor64(FPState);
     __writeeflags(Eflags);
@@ -682,7 +682,7 @@ class X86SavedState : public ExegesisTarget::SavedState {
   }
 
 private:
-#if defined(__x86_64__) || defined(_M_X64)
+#if defined(__x86_64__) || defined(_M_X64) && !defined(_M_ARM64EC)
   alignas(16) char FPState[512];
   uint64_t Eflags;
 #endif
@@ -824,8 +824,8 @@ class ExegesisX86Target : public ExegesisTarget {
       // For now, only do the check if we see an Intel machine because
       // the counter uses some intel-specific magic and it could
       // be confuse and think an AMD machine actually has LBR support.
-#if defined(__i386__) || defined(_M_IX86) || defined(__x86_64__) ||            \
-    defined(_M_X64)
+#if (defined(__i386__) || defined(_M_IX86) || defined(__x86_64__) ||            \
+    defined(_M_X64)) && !defined(_M_ARM64EC)
     using namespace sys::detail::x86;
 
     if (getVendorSignature() == VendorSignatures::GENUINE_INTEL)
diff --git a/third-party/benchmark/src/cycleclock.h b/third-party/benchmark/src/cycleclock.h
index d4f1330b671db..c0dffcf4b35f6 100644
--- a/third-party/benchmark/src/cycleclock.h
+++ b/third-party/benchmark/src/cycleclock.h
@@ -79,7 +79,7 @@ inline BENCHMARK_ALWAYS_INLINE int64_t Now() {
   int64_t ret;
   __asm__ volatile("rdtsc" : "=A"(ret));
   return ret;
-#elif defined(__x86_64__) || defined(__amd64__)
+#elif (defined(__x86_64__) || defined(__amd64__)) && !defined(__arm64ec__)
   uint64_t low, high;
   __asm__ volatile("rdtsc" : "=a"(low), "=d"(high));
   return (high << 32) | low;
@@ -139,7 +139,7 @@ inline BENCHMARK_ALWAYS_INLINE int64_t Now() {
   struct timespec ts = {0, 0};
   clock_gettime(CLOCK_MONOTONIC, &ts);
   return static_cast<int64_t>(ts.tv_sec) * 1000000000 + ts.tv_nsec;
-#elif defined(__aarch64__)
+#elif defined(__aarch64__) || defined(__arm64ec__)
   // System timer of ARMv8 runs at a different frequency than the CPU's.
   // The frequency is fixed, typically in the range 1-50MHz.  It can be
   // read at CNTFRQ special register.  We assume the OS has set up

github-actions · 2025-07-22T17:28:14Z

✅ With the latest revision this PR passed the C/C++ code formatter.

efriedma-quic · 2025-07-22T21:09:22Z

llvm/lib/TargetParser/Host.cpp

@@ -2067,7 +2069,8 @@ StringMap<bool> sys::getHostCPUFeatures() {

  return Features;
 }
-#elif defined(__linux__) && (defined(__arm__) || defined(__aarch64__))
+#elif defined(__linux__) &&                                                    \
+    (defined(__arm__) || defined(__aarch64__) || defined(__arm64ec__))


__linux__ and __arm64ec__ can't be defined at the same time.

The code you want starts around line 2150.

efriedma-quic · 2025-07-22T21:15:14Z

third-party/benchmark/src/cycleclock.h

@@ -139,7 +139,7 @@ inline BENCHMARK_ALWAYS_INLINE int64_t Now() {
  struct timespec ts = {0, 0};
  clock_gettime(CLOCK_MONOTONIC, &ts);
  return static_cast<int64_t>(ts.tv_sec) * 1000000000 + ts.tv_nsec;
-#elif defined(__aarch64__)
+#elif defined(__aarch64__) || defined(__arm64ec__)


This is third-party code; can we submit this upstream?

Submitted google/benchmark#2012

efriedma-quic · 2025-07-22T21:17:08Z

-DCMAKE_EXE_LINKER_FLAGS="-Xlinker /MACHINE:ARM64EC"
-DCMAKE_SHARED_LINKER_FLAGS="-Xlinker /MACHINE:ARM64EC"

Does clang not pick the right MACHINE automatically? I thought we had code for that.

-DLLVM_DISABLE_ASSEMBLY_FILES=On

Probably should address this at some point, if only so people don't keep stumbling over it.

dpaoliello · 2025-07-24T18:58:08Z

-DCMAKE_EXE_LINKER_FLAGS="-Xlinker /MACHINE:ARM64EC"
-DCMAKE_SHARED_LINKER_FLAGS="-Xlinker /MACHINE:ARM64EC"
Does clang not pick the right MACHINE automatically? I thought we had code for that.

Trying it out now, it looks like it is working fine without this. May have been from a previous attempt when I was using clang and clang++ instead of clang-cl.

-DLLVM_DISABLE_ASSEMBLY_FILES=On
Probably should address this at some point, if only so people don't keep stumbling over it.

Yep, found the issue and pushed a fix.

efriedma-quic

Not sure if we want to wait on the upstream review in google/benchmark? Otherwise LGTM.

dpaoliello added the platform:windows label Jul 22, 2025

llvmbot added clang Clang issues not falling into any other category tools:llvm-exegesis third-party:benchmark labels Jul 22, 2025

dpaoliello force-pushed the arm64ecfixes branch from 73cfcb4 to 3c08766 Compare July 22, 2025 17:42

efriedma-quic reviewed Jul 22, 2025

View reviewed changes

dpaoliello mentioned this pull request Jul 22, 2025

Fix build when targeting Arm64EC using Clang google/benchmark#2012

Merged

dpaoliello force-pushed the arm64ecfixes branch from 3c08766 to 0231022 Compare July 24, 2025 18:58

llvmbot added the llvm:support label Jul 24, 2025

dpaoliello force-pushed the arm64ecfixes branch from 0231022 to 7c573fb Compare July 24, 2025 18:58

Fixes to unblock building LLVM and Clang as Arm64EC

8e6ec9a

dpaoliello force-pushed the arm64ecfixes branch from 7c573fb to 8e6ec9a Compare July 24, 2025 19:05

efriedma-quic approved these changes Jul 24, 2025

View reviewed changes

dpaoliello changed the title ~~Fixes to unblock building LLVM and Clang as Arm64EC~~ [win][arm64ec] Fixes to unblock building LLVM and Clang as Arm64EC Jul 30, 2025

dpaoliello merged commit 4adce33 into llvm:main Jul 31, 2025
9 checks passed

dpaoliello deleted the arm64ecfixes branch July 31, 2025 16:30

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[win][arm64ec] Fixes to unblock building LLVM and Clang as Arm64EC #150068

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