qemu/compiler: Wrap __attribute__((flatten)) in a macro

Older versions of Clang (before 3.5) and GCC (before 4.1) do not
support the "__attribute__((flatten))" yet. We don't care about
such old versions of GCC anymore, but since Clang 3.4 is still
used in EPEL for RHEL7 / CentOS 7, we should not use this attribute
directly but with a wrapper macro instead.
Reviewed-by: NAlex Bennée <alex.bennee@linaro.org>
Reviewed-by: NRichard Henderson <richard.henderson@linaro.org>
Signed-off-by: NThomas Huth <thuth@redhat.com>

fpu/softfloat.c

@@ -726,8 +726,7 @@ static FloatParts addsub_floats(FloatParts a, FloatParts b, bool subtract,
  * IEC/IEEE Standard for Binary Floating-Point Arithmetic.
  */
 
-float16  __attribute__((flatten)) float16_add(float16 a, float16 b,
-                                              float_status *status)
+float16 QEMU_FLATTEN float16_add(float16 a, float16 b, float_status *status)
 {
     FloatParts pa = float16_unpack_canonical(a, status);
     FloatParts pb = float16_unpack_canonical(b, status);
@@ -736,8 +735,7 @@ float16  __attribute__((flatten)) float16_add(float16 a, float16 b,
     return float16_round_pack_canonical(pr, status);
 }
 
-float32 __attribute__((flatten)) float32_add(float32 a, float32 b,
-                                             float_status *status)
+float32 QEMU_FLATTEN float32_add(float32 a, float32 b, float_status *status)
 {
     FloatParts pa = float32_unpack_canonical(a, status);
     FloatParts pb = float32_unpack_canonical(b, status);
@@ -746,8 +744,7 @@ float32 __attribute__((flatten)) float32_add(float32 a, float32 b,
     return float32_round_pack_canonical(pr, status);
 }
 
-float64 __attribute__((flatten)) float64_add(float64 a, float64 b,
-                                             float_status *status)
+float64 QEMU_FLATTEN float64_add(float64 a, float64 b, float_status *status)
 {
     FloatParts pa = float64_unpack_canonical(a, status);
     FloatParts pb = float64_unpack_canonical(b, status);
@@ -756,8 +753,7 @@ float64 __attribute__((flatten)) float64_add(float64 a, float64 b,
     return float64_round_pack_canonical(pr, status);
 }
 
-float16 __attribute__((flatten)) float16_sub(float16 a, float16 b,
-                                             float_status *status)
+float16 QEMU_FLATTEN float16_sub(float16 a, float16 b, float_status *status)
 {
     FloatParts pa = float16_unpack_canonical(a, status);
     FloatParts pb = float16_unpack_canonical(b, status);
@@ -766,8 +762,7 @@ float16 __attribute__((flatten)) float16_sub(float16 a, float16 b,
     return float16_round_pack_canonical(pr, status);
 }
 
-float32 __attribute__((flatten)) float32_sub(float32 a, float32 b,
-                                             float_status *status)
+float32 QEMU_FLATTEN float32_sub(float32 a, float32 b, float_status *status)
 {
     FloatParts pa = float32_unpack_canonical(a, status);
     FloatParts pb = float32_unpack_canonical(b, status);
@@ -776,8 +771,7 @@ float32 __attribute__((flatten)) float32_sub(float32 a, float32 b,
     return float32_round_pack_canonical(pr, status);
 }
 
-float64 __attribute__((flatten)) float64_sub(float64 a, float64 b,
-                                             float_status *status)
+float64 QEMU_FLATTEN float64_sub(float64 a, float64 b, float_status *status)
 {
     FloatParts pa = float64_unpack_canonical(a, status);
     FloatParts pb = float64_unpack_canonical(b, status);
@@ -835,8 +829,7 @@ static FloatParts mul_floats(FloatParts a, FloatParts b, float_status *s)
     g_assert_not_reached();
 }
 
-float16 __attribute__((flatten)) float16_mul(float16 a, float16 b,
-                                             float_status *status)
+float16 QEMU_FLATTEN float16_mul(float16 a, float16 b, float_status *status)
 {
     FloatParts pa = float16_unpack_canonical(a, status);
     FloatParts pb = float16_unpack_canonical(b, status);
@@ -845,8 +838,7 @@ float16 __attribute__((flatten)) float16_mul(float16 a, float16 b,
     return float16_round_pack_canonical(pr, status);
 }
 
-float32 __attribute__((flatten)) float32_mul(float32 a, float32 b,
-                                             float_status *status)
+float32 QEMU_FLATTEN float32_mul(float32 a, float32 b, float_status *status)
 {
     FloatParts pa = float32_unpack_canonical(a, status);
     FloatParts pb = float32_unpack_canonical(b, status);
@@ -855,8 +847,7 @@ float32 __attribute__((flatten)) float32_mul(float32 a, float32 b,
     return float32_round_pack_canonical(pr, status);
 }
 
-float64 __attribute__((flatten)) float64_mul(float64 a, float64 b,
-                                             float_status *status)
+float64 QEMU_FLATTEN float64_mul(float64 a, float64 b, float_status *status)
 {
     FloatParts pa = float64_unpack_canonical(a, status);
     FloatParts pb = float64_unpack_canonical(b, status);
@@ -1068,7 +1059,7 @@ static FloatParts muladd_floats(FloatParts a, FloatParts b, FloatParts c,
     return a;
 }
 
-float16 __attribute__((flatten)) float16_muladd(float16 a, float16 b, float16 c,
+float16 QEMU_FLATTEN float16_muladd(float16 a, float16 b, float16 c,
                                                 int flags, float_status *status)
 {
     FloatParts pa = float16_unpack_canonical(a, status);
@@ -1079,7 +1070,7 @@ float16 __attribute__((flatten)) float16_muladd(float16 a, float16 b, float16 c,
     return float16_round_pack_canonical(pr, status);
 }
 
-float32 __attribute__((flatten)) float32_muladd(float32 a, float32 b, float32 c,
+float32 QEMU_FLATTEN float32_muladd(float32 a, float32 b, float32 c,
                                                 int flags, float_status *status)
 {
     FloatParts pa = float32_unpack_canonical(a, status);
@@ -1090,7 +1081,7 @@ float32 __attribute__((flatten)) float32_muladd(float32 a, float32 b, float32 c,
     return float32_round_pack_canonical(pr, status);
 }
 
-float64 __attribute__((flatten)) float64_muladd(float64 a, float64 b, float64 c,
+float64 QEMU_FLATTEN float64_muladd(float64 a, float64 b, float64 c,
                                                 int flags, float_status *status)
 {
     FloatParts pa = float64_unpack_canonical(a, status);
@@ -2414,21 +2405,21 @@ static FloatParts sqrt_float(FloatParts a, float_status *s, const FloatFmt *p)
     return a;
 }
 
-float16 __attribute__((flatten)) float16_sqrt(float16 a, float_status *status)
+float16 QEMU_FLATTEN float16_sqrt(float16 a, float_status *status)
 {
     FloatParts pa = float16_unpack_canonical(a, status);
     FloatParts pr = sqrt_float(pa, status, &float16_params);
     return float16_round_pack_canonical(pr, status);
 }
 
-float32 __attribute__((flatten)) float32_sqrt(float32 a, float_status *status)
+float32 QEMU_FLATTEN float32_sqrt(float32 a, float_status *status)
 {
     FloatParts pa = float32_unpack_canonical(a, status);
     FloatParts pr = sqrt_float(pa, status, &float32_params);
     return float32_round_pack_canonical(pr, status);
 }
 
-float64 __attribute__((flatten)) float64_sqrt(float64 a, float_status *status)
+float64 QEMU_FLATTEN float64_sqrt(float64 a, float_status *status)
 {
     FloatParts pa = float64_unpack_canonical(a, status);
     FloatParts pr = sqrt_float(pa, status, &float64_params);

include/qemu/compiler.h

@@ -131,6 +131,21 @@
 #define HAS_ASSUME_ALIGNED
 #endif
 
+#ifndef __has_attribute
+#define __has_attribute(x) 0 /* compatibility with older GCC */
+#endif
+
+/*
+ * GCC doesn't provide __has_attribute() until GCC 5, but we know all the GCC
+ * versions we support have the "flatten" attribute. Clang may not have the
+ * "flatten" attribute but always has __has_attribute() to check for it.
+ */
+#if __has_attribute(flatten) || !defined(__clang__)
+# define QEMU_FLATTEN __attribute__((flatten))
+#else
+# define QEMU_FLATTEN
+#endif
+
 /* Implement C11 _Generic via GCC builtins.  Example:
  *
  *    QEMU_GENERIC(x, (float, sinf), (long double, sinl), sin) (x)