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* [Bug middle-end/115346] New: [15] Volatile load elimination with packed struct bitfields at -O2
@ 2024-06-04 17:11 patrick at rivosinc dot com
2024-06-04 17:24 ` [Bug middle-end/115346] [15] Volatile load elimination with packed struct bitfields pinskia at gcc dot gnu.org
` (3 more replies)
0 siblings, 4 replies; 5+ messages in thread
From: patrick at rivosinc dot com @ 2024-06-04 17:11 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115346
Bug ID: 115346
Summary: [15] Volatile load elimination with packed struct
bitfields at -O2
Product: gcc
Version: 15.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: middle-end
Assignee: unassigned at gcc dot gnu.org
Reporter: patrick at rivosinc dot com
Target Milestone: ---
Testcase:
#pragma pack(1)
struct a {
unsigned b;
long c : 33;
unsigned d : 31;
};
volatile struct a h[40];
int main() {
for (int i = 0; i < 40; i++) {
h[0];
}
}
-O3 asm output:
main:
xor eax, eax
ret
h:
.zero 480
Removing the pack pragma causes the loads to be emitted.
Godbolt: https://godbolt.org/z/3YfrbzdPz
GCC 4.0.4 does not eliminate the loads: https://godbolt.org/z/frsP8o7YT
^ permalink raw reply [flat|nested] 5+ messages in thread* [Bug middle-end/115346] [15] Volatile load elimination with packed struct bitfields 2024-06-04 17:11 [Bug middle-end/115346] New: [15] Volatile load elimination with packed struct bitfields at -O2 patrick at rivosinc dot com @ 2024-06-04 17:24 ` pinskia at gcc dot gnu.org 2024-06-04 17:30 ` pinskia at gcc dot gnu.org ` (2 subsequent siblings) 3 siblings, 0 replies; 5+ messages in thread From: pinskia at gcc dot gnu.org @ 2024-06-04 17:24 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115346 --- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> --- >GCC 4.0.4 does not eliminate the loads: https://godbolt.org/z/frsP8o7YT But 3.4.6 did not emit them either. ^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug middle-end/115346] [15] Volatile load elimination with packed struct bitfields 2024-06-04 17:11 [Bug middle-end/115346] New: [15] Volatile load elimination with packed struct bitfields at -O2 patrick at rivosinc dot com 2024-06-04 17:24 ` [Bug middle-end/115346] [15] Volatile load elimination with packed struct bitfields pinskia at gcc dot gnu.org @ 2024-06-04 17:30 ` pinskia at gcc dot gnu.org 2024-06-04 17:36 ` pinskia at gcc dot gnu.org 2024-06-05 7:01 ` rguenth at gcc dot gnu.org 3 siblings, 0 replies; 5+ messages in thread From: pinskia at gcc dot gnu.org @ 2024-06-04 17:30 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115346 --- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> --- Note this is not even emitted at -O0, the gimplifier removes it for some reason ... ^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug middle-end/115346] [15] Volatile load elimination with packed struct bitfields 2024-06-04 17:11 [Bug middle-end/115346] New: [15] Volatile load elimination with packed struct bitfields at -O2 patrick at rivosinc dot com 2024-06-04 17:24 ` [Bug middle-end/115346] [15] Volatile load elimination with packed struct bitfields pinskia at gcc dot gnu.org 2024-06-04 17:30 ` pinskia at gcc dot gnu.org @ 2024-06-04 17:36 ` pinskia at gcc dot gnu.org 2024-06-05 7:01 ` rguenth at gcc dot gnu.org 3 siblings, 0 replies; 5+ messages in thread From: pinskia at gcc dot gnu.org @ 2024-06-04 17:36 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115346 --- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> --- (In reply to Andrew Pinski from comment #2) > Note this is not even emitted at -O0, the gimplifier removes it for some > reason ... Oh see PR 99258 for analysis of the gimplifier (I think). with `#pragma pack(1)`, the struct becomes BLKmode. ^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug middle-end/115346] [15] Volatile load elimination with packed struct bitfields 2024-06-04 17:11 [Bug middle-end/115346] New: [15] Volatile load elimination with packed struct bitfields at -O2 patrick at rivosinc dot com ` (2 preceding siblings ...) 2024-06-04 17:36 ` pinskia at gcc dot gnu.org @ 2024-06-05 7:01 ` rguenth at gcc dot gnu.org 3 siblings, 0 replies; 5+ messages in thread From: rguenth at gcc dot gnu.org @ 2024-06-05 7:01 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115346 Richard Biener <rguenth at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Status|UNCONFIRMED |RESOLVED Resolution|--- |DUPLICATE --- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> --- duplicate *** This bug has been marked as a duplicate of bug 99258 *** ^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2024-06-05 7:01 UTC | newest] Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2024-06-04 17:11 [Bug middle-end/115346] New: [15] Volatile load elimination with packed struct bitfields at -O2 patrick at rivosinc dot com 2024-06-04 17:24 ` [Bug middle-end/115346] [15] Volatile load elimination with packed struct bitfields pinskia at gcc dot gnu.org 2024-06-04 17:30 ` pinskia at gcc dot gnu.org 2024-06-04 17:36 ` pinskia at gcc dot gnu.org 2024-06-05 7:01 ` rguenth at gcc dot gnu.org
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