[PATCHv4] sysdeps/ieee754: prevent maybe-uninitialized errors with -O [BZ #19444]
Commit Message
With -O included in CFLAGS it fails to build with:
../sysdeps/ieee754/ldbl-96/e_jnl.c: In function '__ieee754_jnl':
../sysdeps/ieee754/ldbl-96/e_jnl.c:146:20: error: 'temp' may be used uninitialized in this function [-Werror=maybe-uninitialized]
b = invsqrtpi * temp / sqrtl (x);
~~~~~~~~~~^~~~~~
../sysdeps/ieee754/ldbl-96/e_jnl.c: In function '__ieee754_ynl':
../sysdeps/ieee754/ldbl-96/e_jnl.c:375:16: error: 'temp' may be used uninitialized in this function [-Werror=maybe-uninitialized]
b = invsqrtpi * temp / sqrtl (x);
~~~~~~~~~~^~~~~~
../sysdeps/ieee754/dbl-64/e_jn.c: In function '__ieee754_jn':
../sysdeps/ieee754/dbl-64/e_jn.c:113:20: error: 'temp' may be used uninitialized in this function [-Werror=maybe-uninitialized]
b = invsqrtpi * temp / sqrt (x);
~~~~~~~~~~^~~~~~
../sysdeps/ieee754/dbl-64/e_jn.c: In function '__ieee754_yn':
../sysdeps/ieee754/dbl-64/e_jn.c:320:16: error: 'temp' may be used uninitialized in this function [-Werror=maybe-uninitialized]
b = invsqrtpi * temp / sqrt (x);
~~~~~~~~~~^~~~~~
Build tested with Yocto for ARM, AARCH64, X86, X86_64, PPC, MIPS, MIPS64
with -O, -O1, -Os.
For soft-fp ARM it needs one more fix for -O1:
https://sourceware.org/ml/libc-alpha/2018-09/msg00300.html
For AARCH64 it needs one more fix in locale for -Os.
[BZ #23716]
* sysdeps/ieee754/dbl-96/e_jnl.c: Fix build with -O
* sysdeps/ieee754/ldbl-96/e_jnl.c: Likewise.
* sysdeps/ieee754/ldbl-128/e_jnl.c: Likewise.
* sysdeps/ieee754/ldbl-128ibm/e_jnl.c: Likewise.
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>
---
ChangeLog | 7 +++++++
sysdeps/ieee754/dbl-64/e_jn.c | 21 +++++++++++++++++++++
sysdeps/ieee754/ldbl-128/e_jnl.c | 21 +++++++++++++++++++++
sysdeps/ieee754/ldbl-128ibm/e_jnl.c | 21 +++++++++++++++++++++
sysdeps/ieee754/ldbl-96/e_jnl.c | 21 +++++++++++++++++++++
5 files changed, 91 insertions(+)
Comments
On Sep 30 2018, Martin Jansa <martin.jansa@gmail.com> wrote:
> @@ -110,7 +111,17 @@ __ieee754_jn (int n, double x)
> case 2: temp = -c - s; break;
> case 3: temp = c - s; break;
> }
> + /* With GCC 8 (and older) when compiling with -O the compiler
> + warns that the variable 'temp', may be used uninitialized.
> + The switch above covers all possible values of n & 3
> + but GCC without VRP enabled isn't able to figure out the
> + range of possible values is [0,3] as explained in:
> + https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69230
> + so it's false ositive with -O1. */
> + DIAG_PUSH_NEEDS_COMMENT;
> + DIAG_IGNORE_NEEDS_COMMENT (8, "-Wmaybe-uninitialized");
> b = invsqrtpi * temp / sqrt (x);
> + DIAG_POP_NEEDS_COMMENT;
How about adding __builtin_unreachable instead? That doesn't add any
code, but helps the compiler seeing the whole picture.
Andreas.
On Mon, 1 Oct 2018, Andreas Schwab wrote:
> How about adding __builtin_unreachable instead? That doesn't add any
> code, but helps the compiler seeing the whole picture.
Yes, adding default: __builtin_unreachable (); to the switch statements in
question seems reasonable as an approach for these particular
uninitialized warnings (it only works for cases like this where there's a
suitable place to add such a call, of course).
@@ -1,3 +1,10 @@
+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
+ * sysdeps/ieee754/ldbl-96/e_jnl.c: Likewise.
+ * sysdeps/ieee754/ldbl-128/e_jnl.c: Likewise.
+ * sysdeps/ieee754/ldbl-128ibm/e_jnl.c: Likewise.
+
2018-09-28 Joseph Myers <joseph@codesourcery.com>
* math/fromfp.h: Do not include <math_private.h>.
@@ -43,6 +43,7 @@
#include <math_private.h>
#include <fenv_private.h>
#include <math-underflow.h>
+#include <libc-diag.h>
static const double
invsqrtpi = 5.64189583547756279280e-01, /* 0x3FE20DD7, 0x50429B6D */
@@ -110,7 +111,17 @@ __ieee754_jn (int n, double x)
case 2: temp = -c - s; break;
case 3: temp = c - s; break;
}
+ /* With GCC 8 (and older) when compiling with -O the compiler
+ warns that the variable 'temp', may be used uninitialized.
+ The switch above covers all possible values of n & 3
+ but GCC without VRP enabled isn't able to figure out the
+ range of possible values is [0,3] as explained in:
+ https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69230
+ so it's false ositive with -O1. */
+ DIAG_PUSH_NEEDS_COMMENT;
+ DIAG_IGNORE_NEEDS_COMMENT (8, "-Wmaybe-uninitialized");
b = invsqrtpi * temp / sqrt (x);
+ DIAG_POP_NEEDS_COMMENT;
}
else
{
@@ -317,7 +328,17 @@ __ieee754_yn (int n, double x)
case 2: temp = -s + c; break;
case 3: temp = s + c; break;
}
+ /* With GCC 8 (and older) when compiling with -O the compiler
+ warns that the variable 'temp', may be used uninitialized.
+ The switch above covers all possible values of n & 3
+ but GCC without VRP enabled isn't able to figure out the
+ range of possible values is [0,3] as explained in:
+ https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69230
+ so it's false ositive with -O1. */
+ DIAG_PUSH_NEEDS_COMMENT;
+ DIAG_IGNORE_NEEDS_COMMENT (8, "-Wmaybe-uninitialized");
b = invsqrtpi * temp / sqrt (x);
+ DIAG_POP_NEEDS_COMMENT;
}
else
{
@@ -62,6 +62,7 @@
#include <math_private.h>
#include <fenv_private.h>
#include <math-underflow.h>
+#include <libc-diag.h>
static const _Float128
invsqrtpi = L(5.6418958354775628694807945156077258584405E-1),
@@ -151,7 +152,17 @@ __ieee754_jnl (int n, _Float128 x)
temp = c - s;
break;
}
+ /* With GCC 8 (and older) when compiling with -O the compiler
+ warns that the variable 'temp', may be used uninitialized.
+ The switch above covers all possible values of n & 3
+ but GCC without VRP enabled isn't able to figure out the
+ range of possible values is [0,3] as explained in:
+ https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69230
+ so it's false ositive with -O1. */
+ DIAG_PUSH_NEEDS_COMMENT;
+ DIAG_IGNORE_NEEDS_COMMENT (8, "-Wmaybe-uninitialized");
b = invsqrtpi * temp / sqrtl (x);
+ DIAG_POP_NEEDS_COMMENT;
}
else
{
@@ -387,7 +398,17 @@ __ieee754_ynl (int n, _Float128 x)
temp = s + c;
break;
}
+ /* With GCC 8 (and older) when compiling with -O the compiler
+ warns that the variable 'temp', may be used uninitialized.
+ The switch above covers all possible values of n & 3
+ but GCC without VRP enabled isn't able to figure out the
+ range of possible values is [0,3] as explained in:
+ https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69230
+ so it's false ositive with -O1. */
+ DIAG_PUSH_NEEDS_COMMENT;
+ DIAG_IGNORE_NEEDS_COMMENT (8, "-Wmaybe-uninitialized");
b = invsqrtpi * temp / sqrtl (x);
+ DIAG_POP_NEEDS_COMMENT;
}
else
{
@@ -62,6 +62,7 @@
#include <math_private.h>
#include <fenv_private.h>
#include <math-underflow.h>
+#include <libc-diag.h>
static const long double
invsqrtpi = 5.6418958354775628694807945156077258584405E-1L,
@@ -151,7 +152,17 @@ __ieee754_jnl (int n, long double x)
temp = c - s;
break;
}
+ /* With GCC 8 (and older) when compiling with -O the compiler
+ warns that the variable 'temp', may be used uninitialized.
+ The switch above covers all possible values of n & 3
+ but GCC without VRP enabled isn't able to figure out the
+ range of possible values is [0,3] as explained in:
+ https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69230
+ so it's false ositive with -O1. */
+ DIAG_PUSH_NEEDS_COMMENT;
+ DIAG_IGNORE_NEEDS_COMMENT (8, "-Wmaybe-uninitialized");
b = invsqrtpi * temp / sqrtl (x);
+ DIAG_POP_NEEDS_COMMENT;
}
else
{
@@ -387,7 +398,17 @@ __ieee754_ynl (int n, long double x)
temp = s + c;
break;
}
+ /* With GCC 8 (and older) when compiling with -O the compiler
+ warns that the variable 'temp', may be used uninitialized.
+ The switch above covers all possible values of n & 3
+ but GCC without VRP enabled isn't able to figure out the
+ range of possible values is [0,3] as explained in:
+ https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69230
+ so it's false ositive with -O1. */
+ DIAG_PUSH_NEEDS_COMMENT;
+ DIAG_IGNORE_NEEDS_COMMENT (8, "-Wmaybe-uninitialized");
b = invsqrtpi * temp / sqrtl (x);
+ DIAG_POP_NEEDS_COMMENT;
}
else
{
@@ -62,6 +62,7 @@
#include <math_private.h>
#include <fenv_private.h>
#include <math-underflow.h>
+#include <libc-diag.h>
static const long double
invsqrtpi = 5.64189583547756286948079e-1L, two = 2.0e0L, one = 1.0e0L;
@@ -144,7 +145,17 @@ __ieee754_jnl (int n, long double x)
temp = c - s;
break;
}
+ /* With GCC 8 (and older) when compiling with -O the compiler
+ warns that the variable 'temp', may be used uninitialized.
+ The switch above covers all possible values of n & 3
+ but GCC without VRP enabled isn't able to figure out the
+ range of possible values is [0,3] as explained in:
+ https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69230
+ so it's false ositive with -O1. */
+ DIAG_PUSH_NEEDS_COMMENT;
+ DIAG_IGNORE_NEEDS_COMMENT (8, "-Wmaybe-uninitialized");
b = invsqrtpi * temp / sqrtl (x);
+ DIAG_POP_NEEDS_COMMENT;
}
else
{
@@ -373,7 +384,17 @@ __ieee754_ynl (int n, long double x)
temp = s + c;
break;
}
+ /* With GCC 8 (and older) when compiling with -O the compiler
+ warns that the variable 'temp', may be used uninitialized.
+ The switch above covers all possible values of n & 3
+ but GCC without VRP enabled isn't able to figure out the
+ range of possible values is [0,3] as explained in:
+ https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69230
+ so it's false ositive with -O1. */
+ DIAG_PUSH_NEEDS_COMMENT;
+ DIAG_IGNORE_NEEDS_COMMENT (8, "-Wmaybe-uninitialized");
b = invsqrtpi * temp / sqrtl (x);
+ DIAG_POP_NEEDS_COMMENT;
}
else
{