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* [Bug rtl-optimization/57448] New: GCSE generates incorrect code with acquire barrier
@ 2013-05-29 9:26 jleahy+gcc at gmail dot com
2013-05-29 9:34 ` [Bug rtl-optimization/57448] " rguenth at gcc dot gnu.org
` (4 more replies)
0 siblings, 5 replies; 6+ messages in thread
From: jleahy+gcc at gmail dot com @ 2013-05-29 9:26 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57448
Bug ID: 57448
Summary: GCSE generates incorrect code with acquire barrier
Product: gcc
Version: 4.8.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: rtl-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: jleahy+gcc at gmail dot com
The following code:
extern int seq;
extern int data;
int reader() {
int data_copy;
int seq_copy;
for (int i=0; i<10; ++i) {
__atomic_load(&seq, &seq_copy, __ATOMIC_ACQUIRE);
data_copy = data;
}
return data_copy + seq_copy;
}
Compiled with "g++ -masm=intel -std=c++11 -S -O -fgcse test.cpp" using gcc
4.8.0 on x86_64 Linux, generates the following assembler:
.file "test.cpp"
.intel_syntax noprefix
.text
.globl _Z6readerv
.type _Z6readerv, @function
_Z6readerv:
.LFB0:
.cfi_startproc
mov edx, 10
mov ecx, DWORD PTR data[rip]
.L3:
mov eax, DWORD PTR seq[rip]
sub edx, 1
jne .L3
add eax, ecx
ret
.cfi_endproc
.LFE0:
.size _Z6readerv, .-_Z6readerv
.ident "GCC: (GNU) 4.8.0"
.section .note.GNU-stack,"",@progbits
Here the load of data was hoisted above the load of seq, which is in violation
of the acquire memory ordering.
On the wiki here (http://gcc.gnu.org/wiki/Atomic/GCCMM/Optimizations/Details)
it says "acquire is a barrier to hoisting code" and "CSE basically hoists
subexpressions into temporaries, so it would have the same logic apply as PRE:
valid across release, invalid across an acquire."
^ permalink raw reply [flat|nested] 6+ messages in thread* [Bug rtl-optimization/57448] GCSE generates incorrect code with acquire barrier 2013-05-29 9:26 [Bug rtl-optimization/57448] New: GCSE generates incorrect code with acquire barrier jleahy+gcc at gmail dot com @ 2013-05-29 9:34 ` rguenth at gcc dot gnu.org 2013-05-29 20:21 ` steven at gcc dot gnu.org ` (3 subsequent siblings) 4 siblings, 0 replies; 6+ messages in thread From: rguenth at gcc dot gnu.org @ 2013-05-29 9:34 UTC (permalink / raw) To: gcc-bugs http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57448 Richard Biener <rguenth at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Status|UNCONFIRMED |NEW Last reconfirmed| |2013-05-29 CC| |stevenb.gcc at gmail dot com Ever confirmed|0 |1 --- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> --- ;; _7 = __atomic_load_4 (&seq, 2); (insn 13 12 0 (set (reg:SI 61 [ D.2227 ]) (mem/v:SI (symbol_ref:DI ("seq") [flags 0x40] <var_decl 0x7ffff6e67558 seq>) [-1 S4 A32])) t.c:8 -1 (nil)) the MEM alias-set of -1 (ALIAS_SET_MEMORY_BARRIER) is supposed to prevent this, but PRE does not know about this special property (it should "kill" all refs crossing it). ^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug rtl-optimization/57448] GCSE generates incorrect code with acquire barrier 2013-05-29 9:26 [Bug rtl-optimization/57448] New: GCSE generates incorrect code with acquire barrier jleahy+gcc at gmail dot com 2013-05-29 9:34 ` [Bug rtl-optimization/57448] " rguenth at gcc dot gnu.org @ 2013-05-29 20:21 ` steven at gcc dot gnu.org 2013-05-29 22:07 ` steven at gcc dot gnu.org ` (2 subsequent siblings) 4 siblings, 0 replies; 6+ messages in thread From: steven at gcc dot gnu.org @ 2013-05-29 20:21 UTC (permalink / raw) To: gcc-bugs http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57448 Steven Bosscher <steven at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Status|NEW |ASSIGNED CC|jleahy+gcc at gmail dot com, |steven at gcc dot gnu.org |stevenb.gcc at gmail dot com | Assignee|unassigned at gcc dot gnu.org |steven at gcc dot gnu.org ^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug rtl-optimization/57448] GCSE generates incorrect code with acquire barrier 2013-05-29 9:26 [Bug rtl-optimization/57448] New: GCSE generates incorrect code with acquire barrier jleahy+gcc at gmail dot com 2013-05-29 9:34 ` [Bug rtl-optimization/57448] " rguenth at gcc dot gnu.org 2013-05-29 20:21 ` steven at gcc dot gnu.org @ 2013-05-29 22:07 ` steven at gcc dot gnu.org 2021-08-22 20:03 ` pinskia at gcc dot gnu.org 2021-08-22 20:04 ` pinskia at gcc dot gnu.org 4 siblings, 0 replies; 6+ messages in thread From: steven at gcc dot gnu.org @ 2013-05-29 22:07 UTC (permalink / raw) To: gcc-bugs http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57448 --- Comment #2 from Steven Bosscher <steven at gcc dot gnu.org> --- Created attachment 30219 --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=30219&action=edit Handle ALIAS_SET_MEMORY_BARRIER loads and stores It feels like too-big-a-hammer but I don't see any other way... ^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug rtl-optimization/57448] GCSE generates incorrect code with acquire barrier 2013-05-29 9:26 [Bug rtl-optimization/57448] New: GCSE generates incorrect code with acquire barrier jleahy+gcc at gmail dot com ` (2 preceding siblings ...) 2013-05-29 22:07 ` steven at gcc dot gnu.org @ 2021-08-22 20:03 ` pinskia at gcc dot gnu.org 2021-08-22 20:04 ` pinskia at gcc dot gnu.org 4 siblings, 0 replies; 6+ messages in thread From: pinskia at gcc dot gnu.org @ 2021-08-22 20:03 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57448 Andrew Pinski <pinskia at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Target Milestone|--- |8.0 Keywords| |wrong-code ^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug rtl-optimization/57448] GCSE generates incorrect code with acquire barrier 2013-05-29 9:26 [Bug rtl-optimization/57448] New: GCSE generates incorrect code with acquire barrier jleahy+gcc at gmail dot com ` (3 preceding siblings ...) 2021-08-22 20:03 ` pinskia at gcc dot gnu.org @ 2021-08-22 20:04 ` pinskia at gcc dot gnu.org 4 siblings, 0 replies; 6+ messages in thread From: pinskia at gcc dot gnu.org @ 2021-08-22 20:04 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57448 Andrew Pinski <pinskia at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |lucenadeveloper at gmail dot com --- Comment #5 from Andrew Pinski <pinskia at gcc dot gnu.org> --- *** Bug 70889 has been marked as a duplicate of this bug. *** ^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2021-08-22 20:04 UTC | newest] Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2013-05-29 9:26 [Bug rtl-optimization/57448] New: GCSE generates incorrect code with acquire barrier jleahy+gcc at gmail dot com 2013-05-29 9:34 ` [Bug rtl-optimization/57448] " rguenth at gcc dot gnu.org 2013-05-29 20:21 ` steven at gcc dot gnu.org 2013-05-29 22:07 ` steven at gcc dot gnu.org 2021-08-22 20:03 ` pinskia at gcc dot gnu.org 2021-08-22 20:04 ` pinskia at gcc dot gnu.org
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