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* [Bug lto/65376] New: LTO prevents use of fmadd
@ 2015-03-10 8:47 pinskia at gcc dot gnu.org
2015-03-10 9:21 ` [Bug lto/65376] " mkuvyrkov at gcc dot gnu.org
` (4 more replies)
0 siblings, 5 replies; 6+ messages in thread
From: pinskia at gcc dot gnu.org @ 2015-03-10 8:47 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65376
Bug ID: 65376
Summary: LTO prevents use of fmadd
Product: gcc
Version: 5.0
Status: UNCONFIRMED
Keywords: missed-optimization
Severity: normal
Priority: P3
Component: lto
Assignee: unassigned at gcc dot gnu.org
Reporter: pinskia at gcc dot gnu.org
Target: aarch64*
Take:
int main(void)
{
return 0;
}
double f(double a, double b, double c) __attribute__((used));
double f(double a, double b, double c)
{
return b*b+a*a;
}
--- CUT ---
Compile with -flto -Ofast t5.c -o t6.
And then dump the resulting executable, we get:
0000000000400530 <f>:
400530: 1e610821 fmul d1, d1, d1
400534: 1e600800 fmul d0, d0, d0
400538: 1e602820 fadd d0, d1, d0
40053c: d65f03c0 ret
Without -flto we get:
0000000000400530 <f>:
400530: 1e600800 fmul d0, d0, d0
400534: 1f410020 fmadd d0, d1, d1, d0
400538: d65f03c0 ret
AARCH64 is just an example, it is most likely a bug everywhere.
Using -ffp-contract=fast on the command line is a workaround.
I don't know if this is a regression either.
^ permalink raw reply [flat|nested] 6+ messages in thread* [Bug lto/65376] LTO prevents use of fmadd
2015-03-10 8:47 [Bug lto/65376] New: LTO prevents use of fmadd pinskia at gcc dot gnu.org
@ 2015-03-10 9:21 ` mkuvyrkov at gcc dot gnu.org
2015-03-10 9:31 ` rguenth at gcc dot gnu.org
` (3 subsequent siblings)
4 siblings, 0 replies; 6+ messages in thread
From: mkuvyrkov at gcc dot gnu.org @ 2015-03-10 9:21 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65376
Maxim Kuvyrkov <mkuvyrkov at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |mkuvyrkov at gcc dot gnu.org
Assignee|unassigned at gcc dot gnu.org |prathamesh3492 at gcc dot gnu.org
--- Comment #1 from Maxim Kuvyrkov <mkuvyrkov at gcc dot gnu.org> ---
Prathamesh,
Would you please look at this?
^ permalink raw reply [flat|nested] 6+ messages in thread* [Bug lto/65376] LTO prevents use of fmadd
2015-03-10 8:47 [Bug lto/65376] New: LTO prevents use of fmadd pinskia at gcc dot gnu.org
2015-03-10 9:21 ` [Bug lto/65376] " mkuvyrkov at gcc dot gnu.org
@ 2015-03-10 9:31 ` rguenth at gcc dot gnu.org
2015-03-12 15:42 ` ramana at gcc dot gnu.org
` (2 subsequent siblings)
4 siblings, 0 replies; 6+ messages in thread
From: rguenth at gcc dot gnu.org @ 2015-03-10 9:31 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65376
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords| |lto
Target|aarch64* |
Status|UNCONFIRMED |NEW
Last reconfirmed| |2015-03-10
Ever confirmed|0 |1
Known to fail| |4.8.3, 4.9.2, 5.0
--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
Confirmed on x86_64 with -mfma. Doesn't work with 4.8 or 4.9 either.
^ permalink raw reply [flat|nested] 6+ messages in thread* [Bug lto/65376] LTO prevents use of fmadd
2015-03-10 8:47 [Bug lto/65376] New: LTO prevents use of fmadd pinskia at gcc dot gnu.org
2015-03-10 9:21 ` [Bug lto/65376] " mkuvyrkov at gcc dot gnu.org
2015-03-10 9:31 ` rguenth at gcc dot gnu.org
@ 2015-03-12 15:42 ` ramana at gcc dot gnu.org
2015-03-12 15:43 ` ramana at gcc dot gnu.org
2015-03-12 20:58 ` pinskia at gcc dot gnu.org
4 siblings, 0 replies; 6+ messages in thread
From: ramana at gcc dot gnu.org @ 2015-03-12 15:42 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65376
Ramana Radhakrishnan <ramana at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |ramana at gcc dot gnu.org
Target Milestone|--- |5.0
--- Comment #4 from Ramana Radhakrishnan <ramana at gcc dot gnu.org> ---
I think this is not an issue any longer on 5.0. With a cross-compiler to
aarch64-none-linux-gnu built on 09032015, I see the following output
$GCC -flto -Ofast /tmp/fma.c -o t
0000000000400528 <f>:
400528: 1e600800 fmul d0, d0, d0
40052c: 1f410020 fmadd d0, d1, d1, d0
400530: d65f03c0 ret
400534: d503201f nop
Didn't honza do some work earlier this year in the 5.0 time frame to treat
ffp-contract similar to other options for LTO ?
regards
Ramana
^ permalink raw reply [flat|nested] 6+ messages in thread* [Bug lto/65376] LTO prevents use of fmadd
2015-03-10 8:47 [Bug lto/65376] New: LTO prevents use of fmadd pinskia at gcc dot gnu.org
` (2 preceding siblings ...)
2015-03-12 15:42 ` ramana at gcc dot gnu.org
@ 2015-03-12 15:43 ` ramana at gcc dot gnu.org
2015-03-12 20:58 ` pinskia at gcc dot gnu.org
4 siblings, 0 replies; 6+ messages in thread
From: ramana at gcc dot gnu.org @ 2015-03-12 15:43 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65376
Ramana Radhakrishnan <ramana at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |RESOLVED
Resolution|--- |FIXED
--- Comment #5 from Ramana Radhakrishnan <ramana at gcc dot gnu.org> ---
Fixed.
^ permalink raw reply [flat|nested] 6+ messages in thread* [Bug lto/65376] LTO prevents use of fmadd
2015-03-10 8:47 [Bug lto/65376] New: LTO prevents use of fmadd pinskia at gcc dot gnu.org
` (3 preceding siblings ...)
2015-03-12 15:43 ` ramana at gcc dot gnu.org
@ 2015-03-12 20:58 ` pinskia at gcc dot gnu.org
4 siblings, 0 replies; 6+ messages in thread
From: pinskia at gcc dot gnu.org @ 2015-03-12 20:58 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65376
--- Comment #6 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Works for me, I don;t know what I was doing incorrect.
^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2015-03-12 20:58 UTC | newest]
Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
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2015-03-10 8:47 [Bug lto/65376] New: LTO prevents use of fmadd pinskia at gcc dot gnu.org
2015-03-10 9:21 ` [Bug lto/65376] " mkuvyrkov at gcc dot gnu.org
2015-03-10 9:31 ` rguenth at gcc dot gnu.org
2015-03-12 15:42 ` ramana at gcc dot gnu.org
2015-03-12 15:43 ` ramana at gcc dot gnu.org
2015-03-12 20:58 ` pinskia at gcc dot gnu.org
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