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* [Bug tree-optimization/102893] New: [8/9/10/11/12 Regression] CDDCE does not detect empty infinite nested loops
@ 2021-10-22 9:40 tnfchris at gcc dot gnu.org
2021-10-22 10:44 ` [Bug tree-optimization/102893] [9/10/11/12 " rguenth at gcc dot gnu.org
` (8 more replies)
0 siblings, 9 replies; 10+ messages in thread
From: tnfchris at gcc dot gnu.org @ 2021-10-22 9:40 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102893
Bug ID: 102893
Summary: [8/9/10/11/12 Regression] CDDCE does not detect empty
infinite nested loops
Product: gcc
Version: 8.5.0
Status: UNCONFIRMED
Keywords: missed-optimization
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: tnfchris at gcc dot gnu.org
Target Milestone: ---
The following example
int main() {
while(1) {
for(int i=0; i<9000000; i++){}
}
}
In GCC 7 compiled to
main:
.L2:
b .L2
but since GCC 8 compiles to
main:
.L3:
mov w0, 21568
movk w0, 0x89, lsl 16
.L2:
subs w0, w0, #1
bne .L2
b .L3
The difference seems to be in cddce which previously was able to detect the
code as dead:
;; 3 loops found
;;
;; Loop 0
;; header 0, latch 1
;; depth 0, outer -1
;; nodes: 0 1 2 3 4 5 6
;;
;; Loop 1
;; header 3, latch 6
;; depth 1, outer 0
;; nodes: 3 6 5 4
;;
;; Loop 2
;; header 5, latch 4
;; depth 2, outer 1
;; nodes: 5 4
;; 2 succs { 3 }
;; 3 succs { 5 }
;; 4 succs { 5 }
;; 5 succs { 4 6 }
;; 6 succs { 3 }
can not prove finiteness of loop 1
Removing basic block 4
Merging blocks 3 and 5
Removing basic block 6
but since GCC 8 does
;; 3 loops found
;;
;; Loop 0
;; header 0, latch 1
;; depth 0, outer -1
;; nodes: 0 1 2 3 4 5 6
;;
;; Loop 1
;; header 3, latch 6
;; depth 1, outer 0
;; nodes: 3 6 5 4
;;
;; Loop 2
;; header 5, latch 4
;; depth 2, outer 1
;; nodes: 5 4
;; 2 succs { 3 }
;; 3 succs { 5 }
;; 4 succs { 5 }
;; 5 succs { 4 6 }
;; 6 succs { 3 }
cannot prove finiteness of loop 1
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug tree-optimization/102893] [9/10/11/12 Regression] CDDCE does not detect empty infinite nested loops
2021-10-22 9:40 [Bug tree-optimization/102893] New: [8/9/10/11/12 Regression] CDDCE does not detect empty infinite nested loops tnfchris at gcc dot gnu.org
@ 2021-10-22 10:44 ` rguenth at gcc dot gnu.org
2021-10-22 11:43 ` cvs-commit at gcc dot gnu.org
` (7 subsequent siblings)
8 siblings, 0 replies; 10+ messages in thread
From: rguenth at gcc dot gnu.org @ 2021-10-22 10:44 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102893
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |ASSIGNED
Ever confirmed|0 |1
Assignee|unassigned at gcc dot gnu.org |rguenth at gcc dot gnu.org
Target Milestone|--- |9.5
Last reconfirmed| |2021-10-22
Summary|[8/9/10/11/12 Regression] |[9/10/11/12 Regression]
|CDDCE does not detect empty |CDDCE does not detect empty
|infinite nested loops |infinite nested loops
--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
Hm, there's
/* For loops without an exit do not mark any condition. */
if (loop->exits->next && !finite_loop_p (loop))
but here
(gdb) p loop->exits
$2 = (loop_exit *) 0x7ffff6690440
(gdb) p loop->exits->next
$3 = (loop_exit *) 0x7ffff6690440
(gdb) p *loop->exits
$5 = {e = <edge 0x0>, prev = 0x7ffff6690440, next = 0x7ffff6690440,
next_e = 0x0}
so I suppose I misunderstood how loop->exits works, looks like ->e has to be
non-NULL as well. But that means the testcase I added this check for
somehow did not have loop->exits->next?!
Mine.
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug tree-optimization/102893] [9/10/11/12 Regression] CDDCE does not detect empty infinite nested loops
2021-10-22 9:40 [Bug tree-optimization/102893] New: [8/9/10/11/12 Regression] CDDCE does not detect empty infinite nested loops tnfchris at gcc dot gnu.org
2021-10-22 10:44 ` [Bug tree-optimization/102893] [9/10/11/12 " rguenth at gcc dot gnu.org
@ 2021-10-22 11:43 ` cvs-commit at gcc dot gnu.org
2021-10-22 11:43 ` [Bug tree-optimization/102893] [9/10/11 " rguenth at gcc dot gnu.org
` (6 subsequent siblings)
8 siblings, 0 replies; 10+ messages in thread
From: cvs-commit at gcc dot gnu.org @ 2021-10-22 11:43 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102893
--- Comment #2 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Richard Biener <rguenth@gcc.gnu.org>:
https://gcc.gnu.org/g:c2a9a98a369528c8689ecb68db576f8e7dc2fa45
commit r12-4627-gc2a9a98a369528c8689ecb68db576f8e7dc2fa45
Author: Richard Biener <rguenther@suse.de>
Date: Fri Oct 22 12:45:32 2021 +0200
tree-optimization/102893 - properly DCE empty loops inside infinite loops
The following fixes the test for an exit edge I put in place for
the fix for PR45178 where I somehow misunderstood how the cyclic
list works.
2021-10-22 Richard Biener <rguenther@suse.de>
PR tree-optimization/102893
* tree-ssa-dce.c (find_obviously_necessary_stmts): Fix the
test for an exit edge.
* gcc.dg/tree-ssa/ssa-dce-9.c: New testcase.
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug tree-optimization/102893] [9/10/11 Regression] CDDCE does not detect empty infinite nested loops
2021-10-22 9:40 [Bug tree-optimization/102893] New: [8/9/10/11/12 Regression] CDDCE does not detect empty infinite nested loops tnfchris at gcc dot gnu.org
2021-10-22 10:44 ` [Bug tree-optimization/102893] [9/10/11/12 " rguenth at gcc dot gnu.org
2021-10-22 11:43 ` cvs-commit at gcc dot gnu.org
@ 2021-10-22 11:43 ` rguenth at gcc dot gnu.org
2021-10-22 12:07 ` tnfchris at gcc dot gnu.org
` (5 subsequent siblings)
8 siblings, 0 replies; 10+ messages in thread
From: rguenth at gcc dot gnu.org @ 2021-10-22 11:43 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102893
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Priority|P3 |P2
Known to work| |12.0
Summary|[9/10/11/12 Regression] |[9/10/11 Regression] CDDCE
|CDDCE does not detect empty |does not detect empty
|infinite nested loops |infinite nested loops
--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
Not sure if worth backporting.
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug tree-optimization/102893] [9/10/11 Regression] CDDCE does not detect empty infinite nested loops
2021-10-22 9:40 [Bug tree-optimization/102893] New: [8/9/10/11/12 Regression] CDDCE does not detect empty infinite nested loops tnfchris at gcc dot gnu.org
` (2 preceding siblings ...)
2021-10-22 11:43 ` [Bug tree-optimization/102893] [9/10/11 " rguenth at gcc dot gnu.org
@ 2021-10-22 12:07 ` tnfchris at gcc dot gnu.org
2022-02-17 10:17 ` rguenth at gcc dot gnu.org
` (4 subsequent siblings)
8 siblings, 0 replies; 10+ messages in thread
From: tnfchris at gcc dot gnu.org @ 2021-10-22 12:07 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102893
--- Comment #4 from Tamar Christina <tnfchris at gcc dot gnu.org> ---
Thanks for the fix!
This was reported to us by a user of the arm embedded toolchains that was
upgrading from gcc 7. We won't be releasing any new releases for GCC 8 and 9,
but may be for 10 and 11 is certain.
So a backport to 11 and if possible 10 would be great as it avoids us having to
possibly carry the patch in a vendor branch.
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug tree-optimization/102893] [9/10/11 Regression] CDDCE does not detect empty infinite nested loops
2021-10-22 9:40 [Bug tree-optimization/102893] New: [8/9/10/11/12 Regression] CDDCE does not detect empty infinite nested loops tnfchris at gcc dot gnu.org
` (3 preceding siblings ...)
2021-10-22 12:07 ` tnfchris at gcc dot gnu.org
@ 2022-02-17 10:17 ` rguenth at gcc dot gnu.org
2022-02-17 11:26 ` cvs-commit at gcc dot gnu.org
` (3 subsequent siblings)
8 siblings, 0 replies; 10+ messages in thread
From: rguenth at gcc dot gnu.org @ 2022-02-17 10:17 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102893
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Depends on| |45178
--- Comment #5 from Richard Biener <rguenth at gcc dot gnu.org> ---
The fix depends on the fix for PR45178.
Referenced Bugs:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=45178
[Bug 45178] CDDCE doesn't eliminate conditional code in infinite loop
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug tree-optimization/102893] [9/10/11 Regression] CDDCE does not detect empty infinite nested loops
2021-10-22 9:40 [Bug tree-optimization/102893] New: [8/9/10/11/12 Regression] CDDCE does not detect empty infinite nested loops tnfchris at gcc dot gnu.org
` (4 preceding siblings ...)
2022-02-17 10:17 ` rguenth at gcc dot gnu.org
@ 2022-02-17 11:26 ` cvs-commit at gcc dot gnu.org
2022-05-27 9:46 ` [Bug tree-optimization/102893] [10 " rguenth at gcc dot gnu.org
` (2 subsequent siblings)
8 siblings, 0 replies; 10+ messages in thread
From: cvs-commit at gcc dot gnu.org @ 2022-02-17 11:26 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102893
--- Comment #6 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-11 branch has been updated by Richard Biener
<rguenth@gcc.gnu.org>:
https://gcc.gnu.org/g:6d9c2ed02128ddf327465333f5563500b6cf8886
commit r11-9587-g6d9c2ed02128ddf327465333f5563500b6cf8886
Author: Richard Biener <rguenther@suse.de>
Date: Fri Oct 22 12:45:32 2021 +0200
tree-optimization/102893 - properly DCE empty loops inside infinite loops
The following fixes the test for an exit edge I put in place for
the fix for PR45178 where I somehow misunderstood how the cyclic
list works.
2021-10-22 Richard Biener <rguenther@suse.de>
PR tree-optimization/102893
* tree-ssa-dce.c (find_obviously_necessary_stmts): Fix the
test for an exit edge.
* gcc.dg/tree-ssa/ssa-dce-9.c: New testcase.
(cherry picked from commit c2a9a98a369528c8689ecb68db576f8e7dc2fa45)
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug tree-optimization/102893] [10 Regression] CDDCE does not detect empty infinite nested loops
2021-10-22 9:40 [Bug tree-optimization/102893] New: [8/9/10/11/12 Regression] CDDCE does not detect empty infinite nested loops tnfchris at gcc dot gnu.org
` (5 preceding siblings ...)
2022-02-17 11:26 ` cvs-commit at gcc dot gnu.org
@ 2022-05-27 9:46 ` rguenth at gcc dot gnu.org
2022-06-28 10:46 ` jakub at gcc dot gnu.org
2023-07-07 9:47 ` rguenth at gcc dot gnu.org
8 siblings, 0 replies; 10+ messages in thread
From: rguenth at gcc dot gnu.org @ 2022-05-27 9:46 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102893
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Target Milestone|9.5 |10.4
--- Comment #7 from Richard Biener <rguenth at gcc dot gnu.org> ---
GCC 9 branch is being closed
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug tree-optimization/102893] [10 Regression] CDDCE does not detect empty infinite nested loops
2021-10-22 9:40 [Bug tree-optimization/102893] New: [8/9/10/11/12 Regression] CDDCE does not detect empty infinite nested loops tnfchris at gcc dot gnu.org
` (6 preceding siblings ...)
2022-05-27 9:46 ` [Bug tree-optimization/102893] [10 " rguenth at gcc dot gnu.org
@ 2022-06-28 10:46 ` jakub at gcc dot gnu.org
2023-07-07 9:47 ` rguenth at gcc dot gnu.org
8 siblings, 0 replies; 10+ messages in thread
From: jakub at gcc dot gnu.org @ 2022-06-28 10:46 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102893
Jakub Jelinek <jakub at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Target Milestone|10.4 |10.5
--- Comment #8 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] 10+ messages in thread
* [Bug tree-optimization/102893] [10 Regression] CDDCE does not detect empty infinite nested loops
2021-10-22 9:40 [Bug tree-optimization/102893] New: [8/9/10/11/12 Regression] CDDCE does not detect empty infinite nested loops tnfchris at gcc dot gnu.org
` (7 preceding siblings ...)
2022-06-28 10:46 ` jakub at gcc dot gnu.org
@ 2023-07-07 9:47 ` rguenth at gcc dot gnu.org
8 siblings, 0 replies; 10+ messages in thread
From: rguenth at gcc dot gnu.org @ 2023-07-07 9:47 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102893
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Target Milestone|10.5 |11.3
Status|ASSIGNED |RESOLVED
Known to fail| |10.5.0
Resolution|--- |FIXED
--- Comment #9 from Richard Biener <rguenth at gcc dot gnu.org> ---
Fixed.
^ permalink raw reply [flat|nested] 10+ messages in thread
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2021-10-22 10:44 ` [Bug tree-optimization/102893] [9/10/11/12 " rguenth at gcc dot gnu.org
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