fix: detect GNU inline asm support on clang-cl

Author: DiamonDinoia

include/xsimd/arch/common/xsimd_common_details.hpp

@@ -120,7 +120,7 @@ namespace xsimd
             template <class T>
             XSIMD_INLINE void reassociation_barrier(T& x, memory_barrier_tag) noexcept
             {
-#if defined(__GNUC__)
+#if XSIMD_WITH_GNU_INLINE_ASM
                 __asm__ volatile("" : : "r"(&x) : "memory");
 #else
                 (void)x;

include/xsimd/arch/xsimd_neon.hpp

@@ -167,7 +167,7 @@ namespace xsimd
             template <class T>
             XSIMD_INLINE void reassociation_barrier(T& x, arm_barrier_tag) noexcept
             {
-#if defined(__GNUC__)
+#if XSIMD_WITH_GNU_INLINE_ASM
                 __asm__ volatile("" : "+w"(x));
 #else
                 detail::reassociation_barrier(x, memory_barrier_tag {});

include/xsimd/arch/xsimd_neon64.hpp

@@ -709,7 +709,7 @@ namespace xsimd
             return vcvtnq_s32_f32(self);
         }
 
-#if !defined(__GNUC__)
+#if !XSIMD_WITH_GNU_INLINE_ASM
         template <class A>
         XSIMD_INLINE batch<int64_t, A> nearbyint_as_int(batch<double, A> const& self,
                                                         requires_arch<neon64>) noexcept

include/xsimd/arch/xsimd_rvv.hpp

@@ -297,7 +297,7 @@ namespace xsimd
             template <class T>
             XSIMD_INLINE void reassociation_barrier(T& x, rvv_barrier_tag) noexcept
             {
-#if defined(__GNUC__)
+#if XSIMD_WITH_GNU_INLINE_ASM
                 __asm__ volatile("" : "+vr"(x));
 #else
                 detail::reassociation_barrier(x, memory_barrier_tag {});

include/xsimd/arch/xsimd_sse2.hpp

@@ -45,7 +45,7 @@ namespace xsimd
             template <class T>
             XSIMD_INLINE void reassociation_barrier(T& x, x86_barrier_tag) noexcept
             {
-#if defined(__GNUC__) && XSIMD_TARGET_X86
+#if XSIMD_WITH_GNU_INLINE_ASM && XSIMD_TARGET_X86
                 __asm__ volatile("" : "+x"(x));
 #else
                 detail::reassociation_barrier(x, memory_barrier_tag {});

include/xsimd/arch/xsimd_vsx.hpp

@@ -44,7 +44,7 @@ namespace xsimd
             template <class T>
             XSIMD_INLINE void reassociation_barrier(T& x, vsx_barrier_tag) noexcept
             {
-#if defined(__GNUC__)
+#if XSIMD_WITH_GNU_INLINE_ASM
                 __asm__ volatile("" : "+wa"(x));
 #else
                 detail::reassociation_barrier(x, memory_barrier_tag {});

include/xsimd/config/xsimd_config.hpp

@@ -44,6 +44,23 @@
 #define XSIMD_TARGET_X86 0
 #endif
 
+/**
+ * @ingroup xsimd_config_macro
+ *
+ * Set to 1 if GNU-style extended inline assembly is available, to 0 otherwise.
+ */
+/* clang-cl runs in MSVC-compatibility mode and does not define __GNUC__
+ * by default. Clang only emits __GNUC__ when GNUCVersion != 0:
+ * https://github.com/llvm/llvm-project/blob/main/clang/lib/Frontend/InitPreprocessor.cpp
+ * and GNUCVersion defaults to 0:
+ * https://github.com/llvm/llvm-project/blob/main/clang/include/clang/Basic/LangOptions.def
+ * Clang still supports GNU-style extended asm there. */
+#if defined(__GNUC__) || defined(__clang__)
+#define XSIMD_WITH_GNU_INLINE_ASM 1
+#else
+#define XSIMD_WITH_GNU_INLINE_ASM 0
+#endif
+
 /**
  * @ingroup xsimd_config_macro
  *

include/xsimd/config/xsimd_cpu_features_x86.hpp

@@ -533,7 +533,7 @@ namespace xsimd
             __cpuid(buf, leaf);
             std::memcpy(reg.data(), buf, sizeof(buf));
 
-#elif defined(__GNUC__) || defined(__clang__)
+#elif XSIMD_WITH_GNU_INLINE_ASM
 
 #if defined(__i386__) && defined(__PIC__)
             // %ebx may be the PIC register
@@ -561,7 +561,7 @@ namespace xsimd
 #error "_MSC_VER < 1400 is not supported"
 #endif
 
-#elif defined(__GNUC__)
+#elif XSIMD_WITH_GNU_INLINE_ASM
             x86_reg32_t xcr0 = {};
             __asm__(
                 "xorl %%ecx, %%ecx\n"

test/test_arch.cpp

@@ -25,6 +25,10 @@ static_assert(xsimd::supported_architectures::contains<xsimd::default_arch>(), "
 static_assert(xsimd::all_architectures::contains<xsimd::default_arch>(), "default arch is a valid arch");
 #endif
 
+#if defined(__clang__) && defined(_MSC_VER)
+static_assert(XSIMD_WITH_GNU_INLINE_ASM, "clang-cl should expose GNU-style inline asm support");
+#endif
+
 #if !XSIMD_WITH_SVE
 static_assert((std::is_base_of<xsimd::neon64, xsimd::default_arch>::value || !xsimd::neon64::supported()), "on arm, without sve, the best we can do is neon64");
 #endif