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* [Bug tree-optimization/106570] New: DCE sometimes fails with depending if statements
@ 2022-08-09 11:35 tmayerl at student dot ethz.ch
2022-08-09 13:15 ` [Bug tree-optimization/106570] [12/13 Regression] DCE sometimes fails with depending if statements since r12-2305-g398572c1544d8b75 marxin at gcc dot gnu.org
` (7 more replies)
0 siblings, 8 replies; 9+ messages in thread
From: tmayerl at student dot ethz.ch @ 2022-08-09 11:35 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106570
Bug ID: 106570
Summary: DCE sometimes fails with depending if statements
Product: gcc
Version: 12.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: tmayerl at student dot ethz.ch
Target Milestone: ---
Sometimes, DCE fails when multiple if statements are used.
For example, GCC detects that the following if statements always evaluate to
false and thus removes the dead code:
#include <stdio.h>
#include <stdbool.h>
void DCEMarker0_();
void f(bool s, bool c) {
if (!c == !s) {
if (s && !c) {
DCEMarker0_();
}
}
}
In the next snippet, the if statements are used to set a variable. This
variable is then used in the next if statement. However, GCC now fails to
detect and eliminate the dead code:
#include <stdio.h>
#include <stdbool.h>
void DCEMarker0_();
void f(bool s, bool c) {
int intermediate_result = 0;
if (!c == !s) {
if (s && !c) {
intermediate_result = 1;
}
}
if (((!c == !s) && (s && !c)) || intermediate_result) {
DCEMarker0_();
}
}
This is actually a regression: It works fine until GCC 11.3.
This can also be seen via the following Compiler Explorer link:
https://godbolt.org/z/n9dKMfqsd
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug tree-optimization/106570] [12/13 Regression] DCE sometimes fails with depending if statements since r12-2305-g398572c1544d8b75
2022-08-09 11:35 [Bug tree-optimization/106570] New: DCE sometimes fails with depending if statements tmayerl at student dot ethz.ch
@ 2022-08-09 13:15 ` marxin at gcc dot gnu.org
2022-08-09 13:28 ` amacleod at redhat dot com
` (6 subsequent siblings)
7 siblings, 0 replies; 9+ messages in thread
From: marxin at gcc dot gnu.org @ 2022-08-09 13:15 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106570
Martin Liška <marxin at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Last reconfirmed| |2022-08-09
Status|UNCONFIRMED |NEW
Ever confirmed|0 |1
Summary|DCE sometimes fails with |[12/13 Regression] DCE
|depending if statements |sometimes fails with
| |depending if statements
| |since
| |r12-2305-g398572c1544d8b75
CC| |aldyh at gcc dot gnu.org,
| |amacleod at redhat dot com,
| |marxin at gcc dot gnu.org
--- Comment #1 from Martin Liška <marxin at gcc dot gnu.org> ---
Started with r12-2305-g398572c1544d8b75.
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug tree-optimization/106570] [12/13 Regression] DCE sometimes fails with depending if statements since r12-2305-g398572c1544d8b75
2022-08-09 11:35 [Bug tree-optimization/106570] New: DCE sometimes fails with depending if statements tmayerl at student dot ethz.ch
2022-08-09 13:15 ` [Bug tree-optimization/106570] [12/13 Regression] DCE sometimes fails with depending if statements since r12-2305-g398572c1544d8b75 marxin at gcc dot gnu.org
@ 2022-08-09 13:28 ` amacleod at redhat dot com
2022-08-09 13:48 ` rguenth at gcc dot gnu.org
` (5 subsequent siblings)
7 siblings, 0 replies; 9+ messages in thread
From: amacleod at redhat dot com @ 2022-08-09 13:28 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106570
--- Comment #2 from Andrew Macleod <amacleod at redhat dot com> ---
I think this is a duplicate of PR106379 . At the VRP2 stage I see:
<bb 2> [local count: 1073741824]:
if (c_6(D) == s_7(D))
goto <bb 3>; [34.00%]
else
goto <bb 5>; [66.00%]
<bb 3> [local count: 365072224]:
_1 = ~c_6(D);
_2 = _1 & s_7(D);
if (_2 != 0)
goto <bb 4>; [75.00%]
else
goto <bb 5>; [25.00%]
<bb 4> [local count: 628138969]:
DCEMarker0_ ();
<bb 5> [local count: 1073741824]:
return;
Which is basically the identical sequence.. it just took longer to get to it
:-) We aren't removing this yet with ranger as I need to get to integrate
rangers relation oracle with the simplifier so that it will see that _2 = ~s_7
& s_7.
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug tree-optimization/106570] [12/13 Regression] DCE sometimes fails with depending if statements since r12-2305-g398572c1544d8b75
2022-08-09 11:35 [Bug tree-optimization/106570] New: DCE sometimes fails with depending if statements tmayerl at student dot ethz.ch
2022-08-09 13:15 ` [Bug tree-optimization/106570] [12/13 Regression] DCE sometimes fails with depending if statements since r12-2305-g398572c1544d8b75 marxin at gcc dot gnu.org
2022-08-09 13:28 ` amacleod at redhat dot com
@ 2022-08-09 13:48 ` rguenth at gcc dot gnu.org
2022-08-10 13:53 ` rguenth at gcc dot gnu.org
` (4 subsequent siblings)
7 siblings, 0 replies; 9+ messages in thread
From: rguenth at gcc dot gnu.org @ 2022-08-09 13:48 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106570
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Target Milestone|--- |12.2
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug tree-optimization/106570] [12/13 Regression] DCE sometimes fails with depending if statements since r12-2305-g398572c1544d8b75
2022-08-09 11:35 [Bug tree-optimization/106570] New: DCE sometimes fails with depending if statements tmayerl at student dot ethz.ch
` (2 preceding siblings ...)
2022-08-09 13:48 ` rguenth at gcc dot gnu.org
@ 2022-08-10 13:53 ` rguenth at gcc dot gnu.org
2023-03-11 17:07 ` pinskia at gcc dot gnu.org
` (3 subsequent siblings)
7 siblings, 0 replies; 9+ messages in thread
From: rguenth at gcc dot gnu.org @ 2022-08-10 13:53 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106570
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords| |missed-optimization
Priority|P3 |P2
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug tree-optimization/106570] [12/13 Regression] DCE sometimes fails with depending if statements since r12-2305-g398572c1544d8b75
2022-08-09 11:35 [Bug tree-optimization/106570] New: DCE sometimes fails with depending if statements tmayerl at student dot ethz.ch
` (3 preceding siblings ...)
2022-08-10 13:53 ` rguenth at gcc dot gnu.org
@ 2023-03-11 17:07 ` pinskia at gcc dot gnu.org
2023-03-14 13:16 ` marxin at gcc dot gnu.org
` (2 subsequent siblings)
7 siblings, 0 replies; 9+ messages in thread
From: pinskia at gcc dot gnu.org @ 2023-03-11 17:07 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106570
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords| |needs-bisection
Known to fail| |12.1.0
Known to work| |11.1.0
--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Note on the trunk, now the first example fails at -O2 and not just -O3. It
might be useful to do a bisect there too.
The second example failed for -O2 for GCC 12 too.
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug tree-optimization/106570] [12/13 Regression] DCE sometimes fails with depending if statements since r12-2305-g398572c1544d8b75
2022-08-09 11:35 [Bug tree-optimization/106570] New: DCE sometimes fails with depending if statements tmayerl at student dot ethz.ch
` (4 preceding siblings ...)
2023-03-11 17:07 ` pinskia at gcc dot gnu.org
@ 2023-03-14 13:16 ` marxin at gcc dot gnu.org
2023-05-08 12:25 ` [Bug tree-optimization/106570] [12/13/14 " rguenth at gcc dot gnu.org
2023-07-13 18:38 ` pinskia at gcc dot gnu.org
7 siblings, 0 replies; 9+ messages in thread
From: marxin at gcc dot gnu.org @ 2023-03-14 13:16 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106570
Martin Liška <marxin at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords|needs-bisection |
--- Comment #5 from Martin Liška <marxin at gcc dot gnu.org> ---
(In reply to Andrew Pinski from comment #4)
> Note on the trunk, now the first example fails at -O2 and not just -O3. It
> might be useful to do a bisect there too.
That started with r13-3596-ge7310e24b1c0ca67.
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug tree-optimization/106570] [12/13/14 Regression] DCE sometimes fails with depending if statements since r12-2305-g398572c1544d8b75
2022-08-09 11:35 [Bug tree-optimization/106570] New: DCE sometimes fails with depending if statements tmayerl at student dot ethz.ch
` (5 preceding siblings ...)
2023-03-14 13:16 ` marxin at gcc dot gnu.org
@ 2023-05-08 12:25 ` rguenth at gcc dot gnu.org
2023-07-13 18:38 ` pinskia at gcc dot gnu.org
7 siblings, 0 replies; 9+ messages in thread
From: rguenth at gcc dot gnu.org @ 2023-05-08 12:25 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106570
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Target Milestone|12.3 |12.4
--- Comment #6 from Richard Biener <rguenth at gcc dot gnu.org> ---
GCC 12.3 is being released, retargeting bugs to GCC 12.4.
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug tree-optimization/106570] [12/13/14 Regression] DCE sometimes fails with depending if statements since r12-2305-g398572c1544d8b75
2022-08-09 11:35 [Bug tree-optimization/106570] New: DCE sometimes fails with depending if statements tmayerl at student dot ethz.ch
` (6 preceding siblings ...)
2023-05-08 12:25 ` [Bug tree-optimization/106570] [12/13/14 " rguenth at gcc dot gnu.org
@ 2023-07-13 18:38 ` pinskia at gcc dot gnu.org
7 siblings, 0 replies; 9+ messages in thread
From: pinskia at gcc dot gnu.org @ 2023-07-13 18:38 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106570
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
See Also| |https://gcc.gnu.org/bugzill
| |a/show_bug.cgi?id=107880
--- Comment #7 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
I suspect if we optimize:
_1 = ~c_6(D);
_2 = _1 & s_7(D);
to:
c < s;
VRP will just work now.
(that would be PR 107880 ).
^ permalink raw reply [flat|nested] 9+ messages in thread
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2022-08-09 11:35 [Bug tree-optimization/106570] New: DCE sometimes fails with depending if statements tmayerl at student dot ethz.ch
2022-08-09 13:15 ` [Bug tree-optimization/106570] [12/13 Regression] DCE sometimes fails with depending if statements since r12-2305-g398572c1544d8b75 marxin at gcc dot gnu.org
2022-08-09 13:28 ` amacleod at redhat dot com
2022-08-09 13:48 ` rguenth at gcc dot gnu.org
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