sysdeps/ieee754/soft-fp: ignore maybe-uninitialized with -O [BZ #19444]

* with -O, -O1, -Os it fails with:

In file included from ../soft-fp/soft-fp.h:318,
                 from ../sysdeps/ieee754/soft-fp/s_fdiv.c:28:
../sysdeps/ieee754/soft-fp/s_fdiv.c: In function '__fdiv':
../soft-fp/op-2.h:98:25: error: 'R_f1' may be used uninitialized in this function [-Werror=maybe-uninitialized]
        X##_f0 = (X##_f1 << (_FP_W_TYPE_SIZE - (N)) | X##_f0 >> (N) \
                         ^~
../sysdeps/ieee754/soft-fp/s_fdiv.c:38:14: note: 'R_f1' was declared here
   FP_DECL_D (R);
              ^
../soft-fp/op-2.h:37:36: note: in definition of macro '_FP_FRAC_DECL_2'
   _FP_W_TYPE X##_f0 _FP_ZERO_INIT, X##_f1 _FP_ZERO_INIT
                                    ^
../soft-fp/double.h:95:24: note: in expansion of macro '_FP_DECL'
 # define FP_DECL_D(X)  _FP_DECL (2, X)
                        ^~~~~~~~
../sysdeps/ieee754/soft-fp/s_fdiv.c:38:3: note: in expansion of macro 'FP_DECL_D'
   FP_DECL_D (R);
   ^~~~~~~~~
../soft-fp/op-2.h:101:17: error: 'R_f0' may be used uninitialized in this function [-Werror=maybe-uninitialized]
       : (X##_f0 << (_FP_W_TYPE_SIZE - (N))) != 0)); \
                 ^~
../sysdeps/ieee754/soft-fp/s_fdiv.c:38:14: note: 'R_f0' was declared here
   FP_DECL_D (R);
              ^
../soft-fp/op-2.h:37:14: note: in definition of macro '_FP_FRAC_DECL_2'
   _FP_W_TYPE X##_f0 _FP_ZERO_INIT, X##_f1 _FP_ZERO_INIT
              ^
../soft-fp/double.h:95:24: note: in expansion of macro '_FP_DECL'
 # define FP_DECL_D(X)  _FP_DECL (2, X)
                        ^~~~~~~~
../sysdeps/ieee754/soft-fp/s_fdiv.c:38:3: note: in expansion of macro 'FP_DECL_D'
   FP_DECL_D (R);
   ^~~~~~~~~

Build tested with Yocto for ARM, AARCH64, X86, X86_64, PPC, MIPS, MIPS64
with -O, -O1, -Os.
For AARCH64 it needs one more fix in locale for -Os.

	[BZ #19444]
	* sysdeps/ieee754/soft-fp/s_fdiv.c: Include <libc-diag.h> and use
	DIAG_PUSH_NEEDS_COMMENT, DIAG_IGNORE_NEEDS_COMMENT and
	DIAG_POP_NEEDS_COMMENT to disable -Wmaybe-uninitialized.

(cherry picked from commit 4a06ceea33ecc220bbfe264d8f1e74de2f04e90d)

3 files changed, 20 insertions, 0 deletions

diff --git a/ChangeLog b/ChangeLog
index 54b37a6ccf..feca77e0b5 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+2019-01-03  Martin Jansa  <Martin.Jansa@gmail.com>
+
+	[BZ #19444]
+	* sysdeps/ieee754/soft-fp/s_fdiv.c: Include <libc-diag.h> and use
+	DIAG_PUSH_NEEDS_COMMENT, DIAG_IGNORE_NEEDS_COMMENT and
+	DIAG_POP_NEEDS_COMMENT to disable -Wmaybe-uninitialized.
+
 2019-01-02  Aurelien Jarno  <aurelien@aurel32.net>
 
 	[BZ #24034]
diff --git a/NEWS b/NEWS
index 13b8795e6e..af2be85488 100644
--- a/NEWS
+++ b/NEWS
@@ -9,6 +9,7 @@ Version 2.28.1
 
 The following bugs are resolved with this release:
 
+  [19444] build failures with -O1 due to -Wmaybe-uninitialized
   [20209] localedata: Spelling mistake for Sunday in Greenlandic kl_GL
   [22927] libanl: properly cleanup if first helper thread creation failed
   [23400] stdlib/test-bz22786.c creates temporary files in glibc source tree
diff --git a/sysdeps/ieee754/soft-fp/s_fdiv.c b/sysdeps/ieee754/soft-fp/s_fdiv.c
index 341339f5ed..7a15cbeee6 100644
--- a/sysdeps/ieee754/soft-fp/s_fdiv.c
+++ b/sysdeps/ieee754/soft-fp/s_fdiv.c
@@ -25,6 +25,16 @@
 #undef fdivl
 
 #include <math-narrow.h>
+#include <libc-diag.h>
+
+/* R_f[01] are not set in cases where they are not used in packing,
+   but the compiler does not see that they are set in all cases where
+   they are used, resulting in warnings that they may be used
+   uninitialized.  The location of the warning differs in different
+   versions of GCC, it may be where R is defined using a macro or it
+   may be where the macro is defined.  This happens only with -O1.  */
+DIAG_PUSH_NEEDS_COMMENT;
+DIAG_IGNORE_NEEDS_COMMENT (8, "-Wmaybe-uninitialized");
 #include <soft-fp.h>
 #include <single.h>
 #include <double.h>
@@ -53,4 +63,6 @@ __fdiv (double x, double y)
   CHECK_NARROW_DIV (ret, x, y);
   return ret;
 }
+DIAG_POP_NEEDS_COMMENT;
+
 libm_alias_float_double (div)