[libc][fenv] Refactor x86 fenv implementations to make it work for various fenv_t.

Author: lntue

libc/src/__support/CPP/bit.h

@@ -26,6 +26,16 @@ namespace cpp {
 #define LLVM_LIBC_HAS_BUILTIN_MEMCPY_INLINE
 #endif
 
+template <unsigned N>
+LIBC_INLINE static void inline_copy(const char *from, char *to) {
+#if __has_builtin(__builtin_memcpy_inline)
+  __builtin_memcpy_inline(to, from, N);
+#else
+  for (unsigned i = 0; i < N; ++i)
+    to[i] = from[i];
+#endif // __has_builtin(__builtin_memcpy_inline)
+}
+
 // This implementation of bit_cast requires trivially-constructible To, to avoid
 // UB in the implementation.
 template <typename To, typename From>
@@ -43,16 +53,30 @@ bit_cast(const From &from) {
   To to{};
   char *dst = reinterpret_cast<char *>(&to);
   const char *src = reinterpret_cast<const char *>(&from);
-#if __has_builtin(__builtin_memcpy_inline)
-  __builtin_memcpy_inline(dst, src, sizeof(To));
-#else
-  for (unsigned i = 0; i < sizeof(To); ++i)
-    dst[i] = src[i];
-#endif // __has_builtin(__builtin_memcpy_inline)
+  inline_copy<sizeof(From)>(src, dst);
   return to;
 #endif // __has_builtin(__builtin_bit_cast)
 }
 
+// The following simple bit copy from a smaller type to maybe-larger type.
+template <typename To, typename From>
+LIBC_INLINE constexpr cpp::enable_if_t<
+    (sizeof(To) >= sizeof(From)) &&
+        cpp::is_trivially_constructible<To>::value &&
+        cpp::is_trivially_copyable<To>::value &&
+        cpp::is_trivially_copyable<From>::value,
+    void>
+bit_copy(const From &from, To &to) {
+  MSAN_UNPOISON(&from, sizeof(From));
+  if constexpr (sizeof(To) == sizeof(From)) {
+    to = bit_cast<To>(from);
+  } else {
+    char *dst = reinterpret_cast<char *>(&to);
+    const char *src = reinterpret_cast<const char *>(&from);
+    inline_copy<sizeof(From)>(src, dst);
+  }
+}
+
 template <typename T>
 [[nodiscard]] LIBC_INLINE constexpr cpp::enable_if_t<cpp::is_unsigned_v<T>,
                                                      bool>

libc/src/__support/FPUtil/FEnvImpl.h

@@ -31,8 +31,7 @@
 // the dummy implementations below. Once a proper x86_64 darwin fenv is set up,
 // the apple condition here should be removed.
 // TODO: fully support fenv for MSVC.
-#elif defined(LIBC_TARGET_ARCH_IS_X86) && !defined(__APPLE__) &&               \
-    !defined(LIBC_COMPILER_IS_MSVC)
+#elif defined(LIBC_TARGET_ARCH_IS_X86) && !defined(__APPLE__)
 #include "x86_64/FEnvImpl.h"
 #elif defined(LIBC_TARGET_ARCH_IS_ARM) && defined(__ARM_FP) &&                 \
     !defined(LIBC_COMPILER_IS_MSVC)
@@ -110,12 +109,7 @@ raise_except_if_required([[maybe_unused]] int excepts) {
   } else {
 #ifndef LIBC_MATH_HAS_NO_EXCEPT
     if (math_errhandling & MATH_ERREXCEPT)
-#ifdef LIBC_TARGET_ARCH_IS_X86_64
-      return raise_except</*SKIP_X87_FPU*/ true>(excepts);
-#else  // !LIBC_TARGET_ARCH_IS_X86
       return raise_except(excepts);
-#endif // LIBC_TARGET_ARCH_IS_X86
-
 #endif // LIBC_MATH_HAS_NO_EXCEPT
     return 0;
   }