Get rid of array-bounds warning in __kernel_rem_pio2[f] with gcc 6.1 -O3.
Commit Message
On 07/20/2016 06:33 PM, Joseph Myers wrote:
> On Thu, 7 Jul 2016, Stefan Liebler wrote:
>
>> Hi,
>>
>> while testing, I've got the following werror on s390x when build with gcc 6.1
>> (or current gcc head) and -O3:
>> ../sysdeps/ieee754/dbl-64/k_rem_pio2.c: In function ‘__kernel_rem_pio2’:
>> ../sysdeps/ieee754/dbl-64/k_rem_pio2.c:254:18: error: array subscript is below
>> array bounds [-Werror=array-bounds]
>> for (k = 1; iq[jk - k] == 0; k++)
>> ~~^~~~~~~~
>>
>> I get the same error with sysdeps/ieee754/flt-32/k_rem_pio2f.c.
>>
>> Does anybody else get this warning on another architecture, too?
>>
>> This patch adds a check so that the index is always >= 0.
>
> Such an unnecessary check is not how we deal with bogus warnings.
> Rather, use the DIAG_*_NEEDS_COMMENT macros from include/libc-internal.h,
> with a detailed comment explaining what the warning is and why it is a
> false positive.
>
Sorry for the delay. Here is the updated patch with DIAG_* macros.
Is this okay?
Bye Stefan
ChangeLog:
ChangeLog:
* sysdeps/ieee754/dbl-64/k_rem_pio2.c (__kernel_rem_pio2):
Use DIAG_*_NEEDS_COMMENT macro to get rid of array-bounds
warning.
* sysdeps/ieee754/flt-32/k_rem_pio2f.c (__kernel_rem_pio2f):
Likewise.
Comments
On 25 Jul 2016 17:55, Stefan Liebler wrote:
> + /* On s390x gcc 6.1 -O3 produces the warning "array subscript is below
> + array bounds [-Werror=array-bounds]". Only __ieee754_rem_pio2l()
> + calls __kernel_rem_pio2f() for normal numbers and |x| > 3pi/4. Thus
> + x can't be zero and ipio2 is not zero, too. Thus not all iq[]
> + values can't be zero. */
GNU style puts two spaces after the period
-mike
@@ -132,6 +132,7 @@ static char rcsid[] = "$NetBSD: k_rem_pio2.c,v 1.7 1995/05/10 20:46:25 jtc Exp $
#include <math.h>
#include <math_private.h>
+#include <libc-internal.h>
static const int init_jk[] = {2,3,4,6}; /* initial value for jk */
@@ -251,8 +252,16 @@ recompute:
j |= iq[i];
if (j == 0) /* need recomputation */
{
+ /* On s390x gcc 6.1 -O3 produces the warning "array subscript is below
+ array bounds [-Werror=array-bounds]". Only __ieee754_rem_pio2l()
+ calls __kernel_rem_pio2f() for normal numbers and |x| > 3pi/4. Thus
+ x can't be zero and ipio2 is not zero, too. Thus not all iq[]
+ values can't be zero. */
+ DIAG_PUSH_NEEDS_COMMENT;
+ DIAG_IGNORE_NEEDS_COMMENT (6.1, "-Warray-bounds");
for (k = 1; iq[jk - k] == 0; k++)
; /* k = no. of terms needed */
+ DIAG_POP_NEEDS_COMMENT;
for (i = jz + 1; i <= jz + k; i++) /* add q[jz+1] to q[jz+k] */
{
@@ -19,6 +19,7 @@ static char rcsid[] = "$NetBSD: k_rem_pio2f.c,v 1.4 1995/05/10 20:46:28 jtc Exp
#include <math.h>
#include <math_private.h>
+#include <libc-internal.h>
/* In the float version, the input parameter x contains 8 bit
integers, not 24 bit integers. 113 bit precision is not supported. */
@@ -122,7 +123,15 @@ recompute:
j = 0;
for (i=jz-1;i>=jk;i--) j |= iq[i];
if(j==0) { /* need recomputation */
+ /* On s390x gcc 6.1 -O3 produces the warning "array subscript is
+ below array bounds [-Werror=array-bounds]". Only
+ __ieee754_rem_pio2f() calls __kernel_rem_pio2f() for normal
+ numbers and |x| ~> 2^7*(pi/2). Thus x can't be zero and ipio2
+ is not zero, too. Thus not all iq[] values can't be zero. */
+ DIAG_PUSH_NEEDS_COMMENT;
+ DIAG_IGNORE_NEEDS_COMMENT (6.1, "-Warray-bounds");
for(k=1;iq[jk-k]==0;k++); /* k = no. of terms needed */
+ DIAG_POP_NEEDS_COMMENT;
for(i=jz+1;i<=jz+k;i++) { /* add q[jz+1] to q[jz+k] */
f[jx+i] = (float) ipio2[jv+i];