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* [Bug target/112454] New: csinc (csel is though) is not being used when there is matches twice
@ 2023-11-09 6:54 pinskia at gcc dot gnu.org
2023-11-09 17:57 ` [Bug target/112454] " pinskia at gcc dot gnu.org
` (4 more replies)
0 siblings, 5 replies; 6+ messages in thread
From: pinskia at gcc dot gnu.org @ 2023-11-09 6:54 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112454
Bug ID: 112454
Summary: csinc (csel is though) is not being used when there is
matches twice
Product: gcc
Version: 14.0
Status: UNCONFIRMED
Keywords: missed-optimization
Severity: enhancement
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: pinskia at gcc dot gnu.org
Target Milestone: ---
Target: aarch64
Take:
```
int f(int a, int b, int c, int d)
{
return (a == 2 ? 1 : b) + (c == 3 ? 1 : d);
}
```
GCC produces:
```
cmp w0, 2
mov w4, 1
csel w0, w1, w4, ne
cmp w2, 3
csel w3, w3, w4, ne
add w0, w0, w3
```
But that `mov w4, 1` is useless if we use csinc .
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug target/112454] csinc (csel is though) is not being used when there is matches twice
2023-11-09 6:54 [Bug target/112454] New: csinc (csel is though) is not being used when there is matches twice pinskia at gcc dot gnu.org
@ 2023-11-09 17:57 ` pinskia at gcc dot gnu.org
2023-11-18 6:48 ` pinskia at gcc dot gnu.org
` (3 subsequent siblings)
4 siblings, 0 replies; 6+ messages in thread
From: pinskia at gcc dot gnu.org @ 2023-11-09 17:57 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112454
--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
here is another testcase which shows the issue with pulling the constant one
out of the loop when it could have been merged with the csel to use csinc:
```
int f(int *a, int n, int *b, int d)
{
for(int i = 0; i < n; i++)
b[i] = a[i] == 100 ? 1 : d;
return 0;
}
```
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug target/112454] csinc (csel is though) is not being used when there is matches twice
2023-11-09 6:54 [Bug target/112454] New: csinc (csel is though) is not being used when there is matches twice pinskia at gcc dot gnu.org
2023-11-09 17:57 ` [Bug target/112454] " pinskia at gcc dot gnu.org
@ 2023-11-18 6:48 ` pinskia at gcc dot gnu.org
2023-11-18 6:56 ` pinskia at gcc dot gnu.org
` (2 subsequent siblings)
4 siblings, 0 replies; 6+ messages in thread
From: pinskia at gcc dot gnu.org @ 2023-11-18 6:48 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112454
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |ASSIGNED
Last reconfirmed| |2023-11-18
Ever confirmed|0 |1
Assignee|unassigned at gcc dot gnu.org |pinskia at gcc dot gnu.org
--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Mine, looks like a cost issue not recording that 1 (and ~0) are free to create.
you can see the cost issue if we look at combine for the case of 1 csel:
Trying 37 -> 39:
37: r98:SI=0x1
39: r92:SI={(cc:CC!=0)?r100:SI:r98:SI}
REG_DEAD r100:SI
REG_DEAD cc:CC
REG_DEAD r98:SI
Successfully matched this instruction:
(set (reg:SI 92 [ <retval> ])
(if_then_else:SI (ne (reg:CC 66 cc)
(const_int 0 [0]))
(reg:SI 100)
(const_int 1 [0x1])))
allowing combination of insns 37 and 39
original costs 4 + 4 = 8
replacement cost 8
deferring deletion of insn with uid = 37.
modifying insn i3 39: r92:SI={(cc:CC!=0)?r100:SI:0x1}
REG_DEAD cc:CC
REG_DEAD r100:SI
deferring rescan insn with uid = 39.
The replacement cost should be still 4.
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug target/112454] csinc (csel is though) is not being used when there is matches twice
2023-11-09 6:54 [Bug target/112454] New: csinc (csel is though) is not being used when there is matches twice pinskia at gcc dot gnu.org
2023-11-09 17:57 ` [Bug target/112454] " pinskia at gcc dot gnu.org
2023-11-18 6:48 ` pinskia at gcc dot gnu.org
@ 2023-11-18 6:56 ` pinskia at gcc dot gnu.org
2023-11-26 23:52 ` pinskia at gcc dot gnu.org
2023-11-27 23:09 ` cvs-commit at gcc dot gnu.org
4 siblings, 0 replies; 6+ messages in thread
From: pinskia at gcc dot gnu.org @ 2023-11-18 6:56 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112454
--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
-1/~0 has the same issue as mentioned:
```
int finv(int a, int b, int c, int d)
{
return (a == 2 ? -1 : b) + (c == 3 ? -1 : d);
}
```
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug target/112454] csinc (csel is though) is not being used when there is matches twice
2023-11-09 6:54 [Bug target/112454] New: csinc (csel is though) is not being used when there is matches twice pinskia at gcc dot gnu.org
` (2 preceding siblings ...)
2023-11-18 6:56 ` pinskia at gcc dot gnu.org
@ 2023-11-26 23:52 ` pinskia at gcc dot gnu.org
2023-11-27 23:09 ` cvs-commit at gcc dot gnu.org
4 siblings, 0 replies; 6+ messages in thread
From: pinskia at gcc dot gnu.org @ 2023-11-26 23:52 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112454
--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
So it looks like this is not only a cost issue. I have to look into forwprop to
see if it can handle this. Note the cost issue does need to be fixed anyways
since it will be needed there; otherwise forwprop might reject it.
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug target/112454] csinc (csel is though) is not being used when there is matches twice
2023-11-09 6:54 [Bug target/112454] New: csinc (csel is though) is not being used when there is matches twice pinskia at gcc dot gnu.org
` (3 preceding siblings ...)
2023-11-26 23:52 ` pinskia at gcc dot gnu.org
@ 2023-11-27 23:09 ` cvs-commit at gcc dot gnu.org
4 siblings, 0 replies; 6+ messages in thread
From: cvs-commit at gcc dot gnu.org @ 2023-11-27 23:09 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112454
--- Comment #5 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The trunk branch has been updated by Andrew Pinski <pinskia@gcc.gnu.org>:
https://gcc.gnu.org/g:d29d27bde5df89e5357e0a33a71bb49125bd1655
commit r14-5893-gd29d27bde5df89e5357e0a33a71bb49125bd1655
Author: Andrew Pinski <quic_apinski@quicinc.com>
Date: Sun Nov 26 23:25:51 2023 +0000
aarch64: Improve cost of `a ? {-,}1 : b`
While looking into PR 112454, I found the cost for
`(if_then_else (cmp) (const_int 1) (reg))` was being recorded as 8
(or `COSTS_N_INSNS (2)`) but it should have been 4 (or `COSTS_N_INSNS
(1)`).
This improves the cost by not adding the cost of `(const_int 1)` to
the total cost.
It does not does not fully fix PR 112454 as that requires other changes to
forwprop
the `(const_int 1)` earlier than combine. Though we do fix the loop case
where the
constant was only used once.
Bootstrapped and tested on aarch64-linux-gnu with no regressions.
gcc/ChangeLog:
* config/aarch64/aarch64.cc (aarch64_if_then_else_costs):
Handle csinv/csinc case of 1/-1.
gcc/testsuite/ChangeLog:
* gcc.target/aarch64/csinc-3.c: New test.
Signed-off-by: Andrew Pinski <quic_apinski@quicinc.com>
^ permalink raw reply [flat|nested] 6+ messages in thread
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2023-11-09 6:54 [Bug target/112454] New: csinc (csel is though) is not being used when there is matches twice pinskia at gcc dot gnu.org
2023-11-09 17:57 ` [Bug target/112454] " pinskia at gcc dot gnu.org
2023-11-18 6:48 ` pinskia at gcc dot gnu.org
2023-11-18 6:56 ` pinskia at gcc dot gnu.org
2023-11-26 23:52 ` pinskia at gcc dot gnu.org
2023-11-27 23:09 ` cvs-commit at gcc dot gnu.org
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