Re: test-free: fails with -flto=auto

[Bruno Haible]

Hi Berny,

> hmm, I tried a couple of things like declaring the variable err as static.
> The only combination I found to work is:
> 
> diff --git a/lib/free.c b/lib/free.c
> index 135c3eb..e923ee5 100644
> --- a/lib/free.c
> +++ b/lib/free.c
> @@ -27,7 +27,10 @@ void
>  rpl_free (void *p)
>  #undef free
>  {
> -  int err = errno;
> +  int err[2];
> +  err[0] = errno;
> +  err[1] = errno;
> +  errno = 0;
>    free (p);
> -  errno = err;
> +  errno = err[errno==0];
>  }
> 
> It's slow and ugly. ;-(

It's not that slow. I like it :-) Installed as follows:


2021-01-03  Bruno Haible  <bruno@clisp.org>

        free-posix: Work around GCC mis-optimization bug.
        Code by Bernhard Voelker <mail@bernhard-voelker.de>.
        * lib/free.c (rpl_free): Add alternative complicated code for GCC.

diff --git a/lib/free.c b/lib/free.c
index 135c3eb..5c89787 100644
--- a/lib/free.c
+++ b/lib/free.c
@@ -27,7 +27,21 @@ void
 rpl_free (void *p)
 #undef free
 {
+#if defined __GNUC__ && !defined __clang__
+  /* An invalid GCC optimization
+     <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98396>
+     would optimize away the assignments in the code below, when link-time
+     optimization (LTO) is enabled.  Make the code more complicated, so that
+     GCC does not grok how to optimize it.  */
+  int err[2];
+  err[0] = errno;
+  err[1] = errno;
+  errno = 0;
+  free (p);
+  errno = err[errno == 0];
+#else
   int err = errno;
   free (p);
   errno = err;
+#endif
 }