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* [Bug middle-end/95681] New: False positive uninitialized variable usage in decNumberCompareTotalMag
@ 2020-06-15 13:54 stefansf at linux dot ibm.com
2021-07-09 1:23 ` [Bug middle-end/95681] " trnsz at pobox dot com
` (3 more replies)
0 siblings, 4 replies; 5+ messages in thread
From: stefansf at linux dot ibm.com @ 2020-06-15 13:54 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95681
Bug ID: 95681
Summary: False positive uninitialized variable usage in
decNumberCompareTotalMag
Product: gcc
Version: 11.0
Status: UNCONFIRMED
Keywords: build, diagnostic
Severity: normal
Priority: P3
Component: middle-end
Assignee: unassigned at gcc dot gnu.org
Reporter: stefansf at linux dot ibm.com
Target Milestone: ---
Target: s390
The following error/warning shows up on S/390 while bootstrapping:
libdecnumber/decNumber.c: In function 'decNumberCompareTotalMag':
libdecnumber/decNumber.c:953:14: error: '*(allocbufa).bits' may be used
uninitialized [-Werror=maybe-uninitialized]
953 | a->bits&=~DECNEG; /* .. and clear the sign */
| ^~
libdecnumber/decNumber.c:967:14: error: '*(allocbufb).bits' may be used
uninitialized [-Werror=maybe-uninitialized]
967 | b->bits&=~DECNEG; /* .. and clear the sign */
| ^~
The part of interest is:
if (decNumberIsNegative(lhs)) { /* lhs<0 */
a=bufa;
needbytes=sizeof(decNumber)+(D2U(lhs->digits)-1)*sizeof(Unit);
if (needbytes>sizeof(bufa)) { /* need malloc space */
allocbufa=(decNumber *)malloc(needbytes);
if (allocbufa==NULL) { /* hopeless -- abandon */
status|=DEC_Insufficient_storage;
break;}
a=allocbufa; /* use the allocated space */
}
decNumberCopy(a, lhs); /* copy content */
a->bits&=~DECNEG; /* .. and clear the sign */
lhs=a; /* use copy from here on */
}
While calling `decNumberCopy` variable `a` either points to `bufa` or to
`allocbufa`. Since `bufa` and `allocbufa` are both allocated inside function
`decNumberCompareTotalMag` and argument `lhs` is not changed, it is guaranteed
that `a != lhs` holds prior call `decNumberCopy(a, lhs)`. Function
`decNumberCopy` initializes `a->bits`, if `a != lhs` holds. Since this is the
case here, no warning should be printed.
Note, no warning is printed if `dest->bits=src->bits;` is shifted above `if
(dest==src) return dest;` of function `decNumberCopy` which endorses that this
is a false positive resulting from a wrong assumption that `a == lhs` may hold.
Analogous for the second warning/error which speaks about variable `b`.
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug middle-end/95681] False positive uninitialized variable usage in decNumberCompareTotalMag
2020-06-15 13:54 [Bug middle-end/95681] New: False positive uninitialized variable usage in decNumberCompareTotalMag stefansf at linux dot ibm.com
@ 2021-07-09 1:23 ` trnsz at pobox dot com
2021-07-09 17:47 ` msebor at gcc dot gnu.org
` (2 subsequent siblings)
3 siblings, 0 replies; 5+ messages in thread
From: trnsz at pobox dot com @ 2021-07-09 1:23 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95681
--- Comment #1 from Jeffrey H. Johnson <trnsz at pobox dot com> ---
Confirm this behavior and reached same analysis with gcc version 11.1.1
20210531 (Red Hat 11.1.1-3) on x86_64.
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug middle-end/95681] False positive uninitialized variable usage in decNumberCompareTotalMag
2020-06-15 13:54 [Bug middle-end/95681] New: False positive uninitialized variable usage in decNumberCompareTotalMag stefansf at linux dot ibm.com
2021-07-09 1:23 ` [Bug middle-end/95681] " trnsz at pobox dot com
@ 2021-07-09 17:47 ` msebor at gcc dot gnu.org
2021-07-16 7:05 ` stefansf at linux dot ibm.com
2021-07-16 7:09 ` stefansf at linux dot ibm.com
3 siblings, 0 replies; 5+ messages in thread
From: msebor at gcc dot gnu.org @ 2021-07-09 17:47 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95681
Martin Sebor <msebor at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Ever confirmed|0 |1
CC| |msebor at gcc dot gnu.org
Status|UNCONFIRMED |WAITING
Last reconfirmed| |2021-07-09
--- Comment #2 from Martin Sebor <msebor at gcc dot gnu.org> ---
Could you please reduce the warning to a standalone test case (or translation
unit) and attach it to the report so that it can be more easily reproduced
(with a cross-compiler) and analyzed?
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug middle-end/95681] False positive uninitialized variable usage in decNumberCompareTotalMag
2020-06-15 13:54 [Bug middle-end/95681] New: False positive uninitialized variable usage in decNumberCompareTotalMag stefansf at linux dot ibm.com
2021-07-09 1:23 ` [Bug middle-end/95681] " trnsz at pobox dot com
2021-07-09 17:47 ` msebor at gcc dot gnu.org
@ 2021-07-16 7:05 ` stefansf at linux dot ibm.com
2021-07-16 7:09 ` stefansf at linux dot ibm.com
3 siblings, 0 replies; 5+ messages in thread
From: stefansf at linux dot ibm.com @ 2021-07-16 7:05 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95681
--- Comment #3 from Stefan Schulze Frielinghaus <stefansf at linux dot ibm.com> ---
Created attachment 51160
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=51160&action=edit
Reduced program
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug middle-end/95681] False positive uninitialized variable usage in decNumberCompareTotalMag
2020-06-15 13:54 [Bug middle-end/95681] New: False positive uninitialized variable usage in decNumberCompareTotalMag stefansf at linux dot ibm.com
` (2 preceding siblings ...)
2021-07-16 7:05 ` stefansf at linux dot ibm.com
@ 2021-07-16 7:09 ` stefansf at linux dot ibm.com
3 siblings, 0 replies; 5+ messages in thread
From: stefansf at linux dot ibm.com @ 2021-07-16 7:09 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95681
--- Comment #4 from Stefan Schulze Frielinghaus <stefansf at linux dot ibm.com> ---
Running todays mainline (d97d71a1989) using options -O3 -Wall against the
reduced program on x86 as well as s390x results in
t.c: In function 'decNumberCompareTotalMag':
t.c:55:14: warning: '*allocbufa.bits' may be used uninitialized
[-Wmaybe-uninitialized]
55 | a->bits&=~0x80;
| ^~
t.c:70:14: warning: '*allocbufb.bits' may be used uninitialized
[-Wmaybe-uninitialized]
70 | b->bits&=~0x80;
| ^~
^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2021-07-16 7:09 UTC | newest]
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2020-06-15 13:54 [Bug middle-end/95681] New: False positive uninitialized variable usage in decNumberCompareTotalMag stefansf at linux dot ibm.com
2021-07-09 1:23 ` [Bug middle-end/95681] " trnsz at pobox dot com
2021-07-09 17:47 ` msebor at gcc dot gnu.org
2021-07-16 7:05 ` stefansf at linux dot ibm.com
2021-07-16 7:09 ` stefansf at linux dot ibm.com
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