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* [Bug middle-end/67194] New: Missed jump thread and false positive from -Wuninitialized
@ 2015-08-12 17:19 law at redhat dot com
2021-03-31 19:12 ` [Bug middle-end/67194] [9/10/11 Regression] " msebor at gcc dot gnu.org
` (7 more replies)
0 siblings, 8 replies; 9+ messages in thread
From: law at redhat dot com @ 2015-08-12 17:19 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67194
Bug ID: 67194
Summary: Missed jump thread and false positive from
-Wuninitialized
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: middle-end
Assignee: unassigned at gcc dot gnu.org
Reporter: law at redhat dot com
Target Milestone: ---
Extracted from bz55035:
Reconfirmed.
Nowadays (trunk@221914) also breaks all-gcc for nios2-linux-gnu.
Reminds me of bug #36550
Smallish testcase:
$ cat reload1.i ; echo EOF
/* PR target/55035 */
/* { dg-do compile } */
/* { dg-options "-O2 -W -Wall -Werror" } */
struct rtx_def;
typedef struct rtx_def *rtx;
enum rtx_code {
UNKNOWN,
INSN,
ASM_INPUT,
CLOBBER
};
struct rtx_def {
enum rtx_code code: 4;
};
class rtx_def;
class rtx_insn : public rtx_def {};
struct recog_data_d
{
rtx operand[30];
rtx *operand_loc[30];
rtx *dup_loc[1];
char dup_num[1];
char n_operands;
char n_dups;
};
extern struct recog_data_d recog_data;
extern int get_int(void);
void
elimination_costs_in_insn (rtx_insn *insn)
{
int icode = get_int ();
int i;
rtx orig_operand[30];
rtx orig_dup[30];
if (icode < 0)
{
if (((enum rtx_code) insn->code) == INSN)
__builtin_abort();
return;
}
for (i = 0; i < recog_data.n_dups; i++)
orig_dup[i] = *recog_data.dup_loc[i];
for (i = 0; i < recog_data.n_operands; i++)
{
orig_operand[i] = recog_data.operand[i];
if (orig_operand[i]->code == CLOBBER)
*recog_data.operand_loc[i] = 0;
}
for (i = 0; i < recog_data.n_dups; i++)
*recog_data.dup_loc[i]
= *recog_data.operand_loc[(int) recog_data.dup_num[i]];
for (i = 0; i < recog_data.n_dups; i++)
*recog_data.dup_loc[i] = orig_dup[i];
}
EOF
$ g++ -O2 -W -Wall -Werror -c reload1.i -o reload1.o
reload1.i: In function ‘void elimination_costs_in_insn(rtx_insn*)’:
reload1.i:53:41: error: ‘orig_dup[0]’ may be used uninitialized in this
function [-Werror=maybe-uninitialized]
*recog_data.dup_loc[i] = orig_dup[i];
^
cc1plus: all warnings being treated as errors
And a second, related testcase:
typedef struct rtx_def *rtx;
struct recog_data_d
{
rtx operand;
char n_dups;
};
rtx *operand_loc;
rtx dup_loc;
struct recog_data_d recog_data;
void elimination_costs_in_insn ()
{
rtx orig_dup;
if (recog_data.n_dups)
orig_dup = dup_loc;
*operand_loc = 0;
if (recog_data.n_dups)
dup_loc = orig_dup;
}
A warning is issued even at -O1. If I remove "rtx operand" field from struct
recog_data_d (or if I change the type of n_dups to int), then it disappears at
-O2 (but still present at -O1).
In both cases the -Wuninitialized warning is bogus and points to a miss jump
threading opportunity.
>From gcc-bugs-return-494667-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Wed Aug 12 17:26:01 2015
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From: "mpolacek at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/55095] Wshift-overflow
Date: Wed, 12 Aug 2015 17:26:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?idU095
--- Comment #19 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Author: mpolacek
Date: Wed Aug 12 17:25:23 2015
New Revision: 226826
URL: https://gcc.gnu.org/viewcvs?rev"6826&root=gcc&view=rev
Log:
PR c++/55095
* c-common.c (maybe_warn_shift_overflow): Properly handle
left-shifting 1 into the sign bit.
* c-c++-common/Wshift-overflow-6.c: New test.
* c-c++-common/Wshift-overflow-7.c: New test.
* g++.dg/cpp1y/left-shift-2.C: New test.
Added:
trunk/gcc/testsuite/c-c++-common/Wshift-overflow-6.c
trunk/gcc/testsuite/c-c++-common/Wshift-overflow-7.c
trunk/gcc/testsuite/g++.dg/cpp1y/left-shift-2.C
Modified:
trunk/gcc/c-family/ChangeLog
trunk/gcc/c-family/c-common.c
trunk/gcc/testsuite/ChangeLog
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug middle-end/67194] [9/10/11 Regression] Missed jump thread and false positive from -Wuninitialized
2015-08-12 17:19 [Bug middle-end/67194] New: Missed jump thread and false positive from -Wuninitialized law at redhat dot com
@ 2021-03-31 19:12 ` msebor at gcc dot gnu.org
2021-04-08 14:24 ` rguenth at gcc dot gnu.org
` (6 subsequent siblings)
7 siblings, 0 replies; 9+ messages in thread
From: msebor at gcc dot gnu.org @ 2021-03-31 19:12 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67194
Martin Sebor <msebor at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Version|unknown |4.8.0
Summary|Missed jump thread and |[9/10/11 Regression] Missed
|false positive from |jump thread and false
|-Wuninitialized |positive from
| |-Wuninitialized
CC| |msebor at gcc dot gnu.org
Status|UNCONFIRMED |NEW
Ever confirmed|0 |1
Last reconfirmed| |2021-03-31
Known to fail| |10.2.0, 11.0, 4.8.4, 4.9.4,
| |5.5.0, 6.4.0, 7.2.0, 8.3.0,
| |9.1.0
--- Comment #1 from Martin Sebor <msebor at gcc dot gnu.org> ---
Confirmed with GCC 11 as a regression introduced in r192537 (4.8.0 20121017):
$ gcc -O2 -S -Wall -xc++ pr67194.c
pr67194.c: In function ‘void elimination_costs_in_insn(rtx_insn*)’:
pr67194.c:53:28: warning: ‘orig_dup[0]’ may be used uninitialized in this
function [-Wmaybe-uninitialized]
53 | *recog_data.dup_loc[i] = orig_dup[i];
| ~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~
pr67194.c:34:7: note: ‘orig_dup[0]’ was declared here
34 | rtx orig_dup[30];
| ^~~~~~~~
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug middle-end/67194] [9/10/11 Regression] Missed jump thread and false positive from -Wuninitialized
2015-08-12 17:19 [Bug middle-end/67194] New: Missed jump thread and false positive from -Wuninitialized law at redhat dot com
2021-03-31 19:12 ` [Bug middle-end/67194] [9/10/11 Regression] " msebor at gcc dot gnu.org
@ 2021-04-08 14:24 ` rguenth at gcc dot gnu.org
2021-06-01 8:06 ` [Bug middle-end/67194] [9/10/11/12 " rguenth at gcc dot gnu.org
` (5 subsequent siblings)
7 siblings, 0 replies; 9+ messages in thread
From: rguenth at gcc dot gnu.org @ 2021-04-08 14:24 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67194
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Target Milestone|--- |9.4
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug middle-end/67194] [9/10/11/12 Regression] Missed jump thread and false positive from -Wuninitialized
2015-08-12 17:19 [Bug middle-end/67194] New: Missed jump thread and false positive from -Wuninitialized law at redhat dot com
2021-03-31 19:12 ` [Bug middle-end/67194] [9/10/11 Regression] " msebor at gcc dot gnu.org
2021-04-08 14:24 ` rguenth at gcc dot gnu.org
@ 2021-06-01 8:06 ` rguenth at gcc dot gnu.org
2022-01-21 13:54 ` [Bug tree-optimization/67194] " rguenth at gcc dot gnu.org
` (4 subsequent siblings)
7 siblings, 0 replies; 9+ messages in thread
From: rguenth at gcc dot gnu.org @ 2021-06-01 8:06 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67194
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Target Milestone|9.4 |9.5
--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
GCC 9.4 is being released, retargeting bugs to GCC 9.5.
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug tree-optimization/67194] [9/10/11/12 Regression] Missed jump thread and false positive from -Wuninitialized
2015-08-12 17:19 [Bug middle-end/67194] New: Missed jump thread and false positive from -Wuninitialized law at redhat dot com
` (2 preceding siblings ...)
2021-06-01 8:06 ` [Bug middle-end/67194] [9/10/11/12 " rguenth at gcc dot gnu.org
@ 2022-01-21 13:54 ` rguenth at gcc dot gnu.org
2022-05-27 9:35 ` [Bug tree-optimization/67194] [10/11/12/13 " rguenth at gcc dot gnu.org
` (3 subsequent siblings)
7 siblings, 0 replies; 9+ messages in thread
From: rguenth at gcc dot gnu.org @ 2022-01-21 13:54 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67194
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Priority|P3 |P2
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug tree-optimization/67194] [10/11/12/13 Regression] Missed jump thread and false positive from -Wuninitialized
2015-08-12 17:19 [Bug middle-end/67194] New: Missed jump thread and false positive from -Wuninitialized law at redhat dot com
` (3 preceding siblings ...)
2022-01-21 13:54 ` [Bug tree-optimization/67194] " rguenth at gcc dot gnu.org
@ 2022-05-27 9:35 ` rguenth at gcc dot gnu.org
2022-06-28 10:31 ` jakub at gcc dot gnu.org
` (2 subsequent siblings)
7 siblings, 0 replies; 9+ messages in thread
From: rguenth at gcc dot gnu.org @ 2022-05-27 9:35 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67194
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Target Milestone|9.5 |10.4
--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
GCC 9 branch is being closed
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug tree-optimization/67194] [10/11/12/13 Regression] Missed jump thread and false positive from -Wuninitialized
2015-08-12 17:19 [Bug middle-end/67194] New: Missed jump thread and false positive from -Wuninitialized law at redhat dot com
` (4 preceding siblings ...)
2022-05-27 9:35 ` [Bug tree-optimization/67194] [10/11/12/13 " rguenth at gcc dot gnu.org
@ 2022-06-28 10:31 ` jakub at gcc dot gnu.org
2022-08-30 9:03 ` rguenth at gcc dot gnu.org
2023-07-07 10:30 ` [Bug tree-optimization/67194] [11/12/13/14 " rguenth at gcc dot gnu.org
7 siblings, 0 replies; 9+ messages in thread
From: jakub at gcc dot gnu.org @ 2022-06-28 10:31 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67194
Jakub Jelinek <jakub at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Target Milestone|10.4 |10.5
--- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
GCC 10.4 is being released, retargeting bugs to GCC 10.5.
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug tree-optimization/67194] [10/11/12/13 Regression] Missed jump thread and false positive from -Wuninitialized
2015-08-12 17:19 [Bug middle-end/67194] New: Missed jump thread and false positive from -Wuninitialized law at redhat dot com
` (5 preceding siblings ...)
2022-06-28 10:31 ` jakub at gcc dot gnu.org
@ 2022-08-30 9:03 ` rguenth at gcc dot gnu.org
2023-07-07 10:30 ` [Bug tree-optimization/67194] [11/12/13/14 " rguenth at gcc dot gnu.org
7 siblings, 0 replies; 9+ messages in thread
From: rguenth at gcc dot gnu.org @ 2022-08-30 9:03 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67194
--- Comment #5 from Richard Biener <rguenth at gcc dot gnu.org> ---
For the second testcase the issue is the aliasing store *operand_loc = 0;
which can invalidate the predicate value. Fixed with -fstrict-aliasing (or
-O2).
Nothing uninit analysis can do here.
The first testcase has a similar issue at -O2 because of the union now
containing rtx *.
I don't see what we can do here - if there's no aliasing the code needs to say
that or be optimized in source.
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug tree-optimization/67194] [11/12/13/14 Regression] Missed jump thread and false positive from -Wuninitialized
2015-08-12 17:19 [Bug middle-end/67194] New: Missed jump thread and false positive from -Wuninitialized law at redhat dot com
` (6 preceding siblings ...)
2022-08-30 9:03 ` rguenth at gcc dot gnu.org
@ 2023-07-07 10:30 ` rguenth at gcc dot gnu.org
7 siblings, 0 replies; 9+ messages in thread
From: rguenth at gcc dot gnu.org @ 2023-07-07 10:30 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67194
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Target Milestone|10.5 |11.5
--- Comment #6 from Richard Biener <rguenth at gcc dot gnu.org> ---
GCC 10 branch is being closed.
^ permalink raw reply [flat|nested] 9+ messages in thread
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2015-08-12 17:19 [Bug middle-end/67194] New: Missed jump thread and false positive from -Wuninitialized law at redhat dot com
2021-03-31 19:12 ` [Bug middle-end/67194] [9/10/11 Regression] " msebor at gcc dot gnu.org
2021-04-08 14:24 ` rguenth at gcc dot gnu.org
2021-06-01 8:06 ` [Bug middle-end/67194] [9/10/11/12 " rguenth at gcc dot gnu.org
2022-01-21 13:54 ` [Bug tree-optimization/67194] " rguenth at gcc dot gnu.org
2022-05-27 9:35 ` [Bug tree-optimization/67194] [10/11/12/13 " rguenth at gcc dot gnu.org
2022-06-28 10:31 ` jakub at gcc dot gnu.org
2022-08-30 9:03 ` rguenth at gcc dot gnu.org
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