Patchwork [PATCHv2] sysdeps/ieee754/soft-fp: ignore maybe-uninitialized with -O [BZ #19444]

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Submitter Martin Jansa
Date Sept. 30, 2018, 3:53 p.m.
Message ID <20180930155305.19266-1-Martin.Jansa@gmail.com>
Download mbox | patch
Permalink /patch/29587/
State New
Headers show

Comments

Martin Jansa - Sept. 30, 2018, 3:53 p.m.
* 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.

	Partial fix for [BZ #23716]
	* sysdeps/ieee754/soft-fp/s_fdiv.c: Fix build with -O

Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>
---
 ChangeLog                        |  4 ++++
 sysdeps/ieee754/soft-fp/s_fdiv.c | 12 ++++++++++++
 2 files changed, 16 insertions(+)
Joseph Myers - Sept. 30, 2018, 4:53 p.m.
On Sun, 30 Sep 2018, Martin Jansa wrote:

> +#include <libc-diag.h>
> +/* R_f[01] are not set in cases where it is not used in packing, but the
> +   compiler does not see that it is set in all cases where it is
> +   used, resulting in warnings that it 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 comment is missing the key information that it's specifically a 
warning seen with -O1.
Martin Jansa - Sept. 30, 2018, 5:48 p.m.
On Sun, Sep 30, 2018 at 04:53:36PM +0000, Joseph Myers wrote:
> On Sun, 30 Sep 2018, Martin Jansa wrote:
> 
> > +#include <libc-diag.h>
> > +/* R_f[01] are not set in cases where it is not used in packing, but the
> > +   compiler does not see that it is set in all cases where it is
> > +   used, resulting in warnings that it 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 comment is missing the key information that it's specifically a 
> warning seen with -O1.

The other 3 cases of the same:
https://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/ieee754/soft-fp/s_fma.c;h=41cf81a74bfc6a8c21c565fb04c90ced4bfd19e8;hb=refs/heads/master#l32
https://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/ieee754/soft-fp/s_fmaf.c;h=afe64356b3a9c5f3467c35b80f33ba946fbeee46;hb=refs/heads/master#l32
https://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/ieee754/soft-fp/s_fmal.c;h=4c2d4c5d9be09f0c8464fb20b81af3aff131e65d;hb=refs/heads/master#l32

are probably also triggered only with -O1, do you want me to update all
4 or just the new case?
Joseph Myers - Oct. 1, 2018, 3:03 p.m.
On Sun, 30 Sep 2018, Martin Jansa wrote:

> On Sun, Sep 30, 2018 at 04:53:36PM +0000, Joseph Myers wrote:
> > On Sun, 30 Sep 2018, Martin Jansa wrote:
> > 
> > > +#include <libc-diag.h>
> > > +/* R_f[01] are not set in cases where it is not used in packing, but the
> > > +   compiler does not see that it is set in all cases where it is
> > > +   used, resulting in warnings that it 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 comment is missing the key information that it's specifically a 
> > warning seen with -O1.
> 
> The other 3 cases of the same:
> https://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/ieee754/soft-fp/s_fma.c;h=41cf81a74bfc6a8c21c565fb04c90ced4bfd19e8;hb=refs/heads/master#l32
> https://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/ieee754/soft-fp/s_fmaf.c;h=afe64356b3a9c5f3467c35b80f33ba946fbeee46;hb=refs/heads/master#l32
> https://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/ieee754/soft-fp/s_fmal.c;h=4c2d4c5d9be09f0c8464fb20b81af3aff131e65d;hb=refs/heads/master#l32
> 
> are probably also triggered only with -O1, do you want me to update all
> 4 or just the new case?

They're definitely not limited to -O1 (or weren't when added in 2015, 
commit dc6b5aed1b406a53c4512d355376b4e12c7da971).  So it's only the new 
case for which a comment about being limited to -O1 is appropriate.

Patch

diff --git a/ChangeLog b/ChangeLog
index 4bafeefda5..9cdf59c9ab 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@ 
+2018-09-30  Martin Jansa  <Martin.Jansa@gmail.com>
+	Partial fix for [BZ #23716]
+	* sysdeps/ieee754/soft-fp/s_fdiv.c: Fix build with -O.
+
 2018-09-29  Martin Jansa  <Martin.Jansa@gmail.com>
 	Partial fix for [BZ #23716]
 	* sysdeps/ieee754/dbl-96/e_jnl.c: Fix build with -O
diff --git a/sysdeps/ieee754/soft-fp/s_fdiv.c b/sysdeps/ieee754/soft-fp/s_fdiv.c
index 341339f5ed..14655b77da 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 it is not used in packing, but the
+   compiler does not see that it is set in all cases where it is
+   used, resulting in warnings that it 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.  */
+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)