public inbox for gcc-bugs@sourceware.org
help / color / mirror / Atom feed
* [Bug tree-optimization/115202] New: [14/15 Regression] Missed optimization: std::min(f ? (unsigned short)m : a, ~0)
@ 2024-05-23 7:44 652023330028 at smail dot nju.edu.cn
2024-05-23 9:02 ` [Bug tree-optimization/115202] " rguenth at gcc dot gnu.org
2024-05-23 12:18 ` [Bug tree-optimization/115202] [11/12/13/14/15 " pinskia at gcc dot gnu.org
0 siblings, 2 replies; 3+ messages in thread
From: 652023330028 at smail dot nju.edu.cn @ 2024-05-23 7:44 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115202
Bug ID: 115202
Summary: [14/15 Regression] Missed optimization: std::min(f ?
(unsigned short)m : a, ~0)
Product: gcc
Version: 15.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: 652023330028 at smail dot nju.edu.cn
Target Milestone: ---
Hello, we noticed that the code below can be optimized to be independent of
'm', but gcc -O3 seems to have missed it.
https://godbolt.org/z/a6MoofoYK
unsigned short m;
#include <algorithm>
unsigned short func(int a, int f) {
return std::min(f ? m : a, ~0);
}
GCC-trunk -O3:
func(int, int):
movzx eax, WORD PTR m[rip]
test esi, esi
mov edx, -1
cmove eax, edi
test eax, eax
cmovns eax, edx
ret
Expected code (gcc-13.2):
func(int, int):
mov eax, edi
test edi, edi
jns .L4
test esi, esi
jne .L4
ret
.L4:
mov eax, 65535
ret
If we did it correctly, it's caused by
https://github.com/gcc-mirror/gcc/commit/7b34cacc5735385e7e2855d7c0a6fad60ef4a99b
Thank you very much for your time and effort! We look forward to hearing from
you.
^ permalink raw reply [flat|nested] 3+ messages in thread
* [Bug tree-optimization/115202] [14/15 Regression] Missed optimization: std::min(f ? (unsigned short)m : a, ~0)
2024-05-23 7:44 [Bug tree-optimization/115202] New: [14/15 Regression] Missed optimization: std::min(f ? (unsigned short)m : a, ~0) 652023330028 at smail dot nju.edu.cn
@ 2024-05-23 9:02 ` rguenth at gcc dot gnu.org
2024-05-23 12:18 ` [Bug tree-optimization/115202] [11/12/13/14/15 " pinskia at gcc dot gnu.org
1 sibling, 0 replies; 3+ messages in thread
From: rguenth at gcc dot gnu.org @ 2024-05-23 9:02 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115202
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords| |missed-optimization
Target Milestone|--- |14.2
^ permalink raw reply [flat|nested] 3+ messages in thread
* [Bug tree-optimization/115202] [11/12/13/14/15 Regression] Missed optimization: std::min(f ? (unsigned short)m : a, ~0)
2024-05-23 7:44 [Bug tree-optimization/115202] New: [14/15 Regression] Missed optimization: std::min(f ? (unsigned short)m : a, ~0) 652023330028 at smail dot nju.edu.cn
2024-05-23 9:02 ` [Bug tree-optimization/115202] " rguenth at gcc dot gnu.org
@ 2024-05-23 12:18 ` pinskia at gcc dot gnu.org
1 sibling, 0 replies; 3+ messages in thread
From: pinskia at gcc dot gnu.org @ 2024-05-23 12:18 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115202
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Target Milestone|14.2 |11.5
Status|UNCONFIRMED |NEW
Last reconfirmed| |2024-05-23
Summary|[14/15 Regression] Missed |[11/12/13/14/15 Regression]
|optimization: std::min(f ? |Missed optimization:
|(unsigned short)m : a, ~0) |std::min(f ? (unsigned
| |short)m : a, ~0)
Ever confirmed|0 |1
--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Confirmed.
Here is a reduced testcase:
```
unsigned short m;
template<typename T>
const T min(const T a, const T b)
{
if (a < b)
return a;
return b;
}
unsigned short func(int a, int f) {
return min(f ? m : a, ~0);
}
```
The above is a regression from GCC 8 where in GCC 9 adds an early phiopt.
And here is a version which is not a regression:
```
unsigned short m;
template<typename T>
inline const T min(const T a, const T b)
{
return a < b ? a : b;
}
unsigned short func(int a, int f) {
return min(f ? m : a, ~0);
}
```
The real issue is we don't optimize MIN<PHI<>, -1>.
From the IR:
```
# RANGE [irange] int [0, 65535] MASK 0xffff VALUE 0x0
iftmp.0_6 = (intD.9) m.1_1;
;; succ: 4 [always] count:536870912 (estimated locally, freq 0.5000)
(FALLTHRU,EXECUTABLE)
;; basic block 4, loop depth 0, count 1073741824 (estimated locally, freq
1.0000), maybe hot
;; prev block 3, next block 1, flags: (NEW, REACHABLE, VISITED)
;; pred: 3 [always] count:536870912 (estimated locally, freq 0.5000)
(FALLTHRU,EXECUTABLE)
;; 2 [50.0% (guessed)] count:536870912 (estimated locally, freq
0.5000) (FALSE_VALUE,EXECUTABLE)
# iftmp.0_2 = PHI <iftmp.0_6(3), a_4(D)(2)>
# RANGE [irange] int [-INF, -1]
_7 = MIN_EXPR <iftmp.0_2, -1>;
```
Obviously here `MIN_EXPR <X, -1>` for the iftmp.0_6 part of the PHI, it will be
-1.
^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2024-05-23 12:18 UTC | newest]
Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2024-05-23 7:44 [Bug tree-optimization/115202] New: [14/15 Regression] Missed optimization: std::min(f ? (unsigned short)m : a, ~0) 652023330028 at smail dot nju.edu.cn
2024-05-23 9:02 ` [Bug tree-optimization/115202] " rguenth at gcc dot gnu.org
2024-05-23 12:18 ` [Bug tree-optimization/115202] [11/12/13/14/15 " pinskia at gcc dot gnu.org
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).