Fix maybe-uninitialized error on powerpc

The build has been failing on powerpc64le-linux-gnu with GCC 10
due to a maybe-uninitialized error:

../sysdeps/ieee754/dbl-64/mpa.c:875:6: error: ‘w.e’ may be used
uninitialized in this function [-Werror=maybe-uninitialized]
  875 |   EY -= EX;
      |      ^~

The warning is thrown because when __inv is called by __dvd *y is not
initialized and if t == 0 before calling __dbl_mp, EY will stay
uninitialized, as the function does not touch it in this case.

However, since t will be set to 1/t before calling __dbl_mp, t == 0 will
never happen, so we can instruct the compiler to ignore this case, which
suppresses the warning.

Tested on powerpc64le.

Reviewed-by: Tulio Magno Quites Machado Filho <tuliom@linux.ibm.com>

1 files changed, 7 insertions, 0 deletions

diff --git a/sysdeps/ieee754/dbl-64/mpa.c b/sysdeps/ieee754/dbl-64/mpa.c
index 3bb8bff90d..aed4354bac 100644
--- a/sysdeps/ieee754/dbl-64/mpa.c
+++ b/sysdeps/ieee754/dbl-64/mpa.c
@@ -871,6 +871,13 @@ __inv (const mp_no *x, mp_no *y, int p)
   z.e = 0;
   __mp_dbl (&z, &t, p);
   t = 1 / t;
+
+  /* t == 0 will never happen at this point, since 1/t can only be 0 if t is
+     infinity, but before the division t == mantissa of x (exponent is 0).  We
+     can instruct the compiler to ignore this case.  */
+  if (t == 0)
+    __builtin_unreachable ();
+
   __dbl_mp (t, y, p);
   EY -= EX;