Re: totalorder, totalorderf: Fix handling of SNaN on i386 and x86_64 CPUs

[Bruno Haible]

I wrote:
> This patch does it and thus fixes the test failures on Linux and NetBSD.

Well, it fixes them only when not optimizing. With -O2, I see the
same miscompilation with gcc as with clang. This patch works around it.


2024-04-09  Bruno Haible  <bruno@clisp.org>

        totalorder, totalorderf: Avoid miscompilation by gcc on NetBSD/i386.
        * lib/totalorder.c (totalorder): Use the a compiler optimization barrier
        also for GCC.
        * lib/totalorderf.c (totalorderf): Likewise.

diff --git a/lib/totalorder.c b/lib/totalorder.c
index eaef9a582d..445b8f84d6 100644
--- a/lib/totalorder.c
+++ b/lib/totalorder.c
@@ -57,9 +57,11 @@ totalorder (double const *x, double const *y)
   xu.f = *x;
   yu.f = *y;
 #else
-# ifdef __clang__
-  /* Prevent clang 16.0.6 on OpenBSD 7.5 from reusing the values of *x and *y
-     (fetched above) in optimized inlined memcpy expansions.  */
+# if defined __GNUC__ || defined __clang__
+  /* Prevent gcc and clang from reusing the values of *x and *y (fetched above)
+     in optimized inlined memcpy expansions.
+     Seen with gcc <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114659>
+     and with clang 16.0.6 on OpenBSD 7.5.  */
   __asm__ __volatile__ ("" : : : "memory");
 # endif
   /* On 32-bit x86 processors, as well as on x86_64 processors with
diff --git a/lib/totalorderf.c b/lib/totalorderf.c
index f5f1b40112..70bc02cd90 100644
--- a/lib/totalorderf.c
+++ b/lib/totalorderf.c
@@ -57,9 +57,11 @@ totalorderf (float const *x, float const *y)
   xu.f = *x;
   yu.f = *y;
 #else
-# ifdef __clang__
-  /* Prevent clang 16.0.6 on OpenBSD 7.5 from reusing the values of *x and *y
-     (fetched above) in optimized inlined memcpy expansions.  */
+# if defined __GNUC__ || defined __clang__
+  /* Prevent gcc and clang from reusing the values of *x and *y (fetched above)
+     in optimized inlined memcpy expansions.
+     Seen with gcc <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114659>
+     and with clang 16.0.6 on OpenBSD 7.5.  */
   __asm__ __volatile__ ("" : : : "memory");
 # endif
   /* On 32-bit x86 processors, as well as on x86_64 processors with