* [Bug target/62011] False Data Dependency in popcnt instruction
2014-08-04 14:29 [Bug rtl-optimization/62011] New: False Data Dependency in popcnt instruction debiandev at gmail dot com
@ 2014-08-05 9:07 ` rguenth at gcc dot gnu.org
2014-08-05 11:49 ` amonakov at gcc dot gnu.org
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From: rguenth at gcc dot gnu.org @ 2014-08-05 9:07 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62011
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords| |missed-optimization
Target|X86_64-*-* |x86_64-*-*, i?86-*-*
--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
Please clarify - this is a defect in the CPU? Can you point to an official
errata?
In which case we might want to adjust the scheduler description used for
GENERIC tuning (and for the specific broken CPUs). Not sure if we want to
disable popcnt use completely.
^ permalink raw reply [flat|nested] 13+ messages in thread* [Bug target/62011] False Data Dependency in popcnt instruction
2014-08-04 14:29 [Bug rtl-optimization/62011] New: False Data Dependency in popcnt instruction debiandev at gmail dot com
2014-08-05 9:07 ` [Bug target/62011] " rguenth at gcc dot gnu.org
@ 2014-08-05 11:49 ` amonakov at gcc dot gnu.org
2014-08-05 13:40 ` debiandev at gmail dot com
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From: amonakov at gcc dot gnu.org @ 2014-08-05 11:49 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62011
Alexander Monakov <amonakov at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |amonakov at gcc dot gnu.org
--- Comment #2 from Alexander Monakov <amonakov at gcc dot gnu.org> ---
I think adjusting for scheduling won't help much: rather than making the
compiler aware of increased latency, you'd need that either the register
allocator avoids using a recently written hard register for popcnt (I'm not
aware of such capability), or as a stopgap measure the compiler can issue a
dependency-breaking instruction (xor %reg %reg) just before popcnt.
^ permalink raw reply [flat|nested] 13+ messages in thread* [Bug target/62011] False Data Dependency in popcnt instruction
2014-08-04 14:29 [Bug rtl-optimization/62011] New: False Data Dependency in popcnt instruction debiandev at gmail dot com
2014-08-05 9:07 ` [Bug target/62011] " rguenth at gcc dot gnu.org
2014-08-05 11:49 ` amonakov at gcc dot gnu.org
@ 2014-08-05 13:40 ` debiandev at gmail dot com
2014-08-07 9:22 ` finis at in dot tum.de
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From: debiandev at gmail dot com @ 2014-08-05 13:40 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62011
--- Comment #3 from Andev <debiandev at gmail dot com> ---
This seems to be specific to some latest Intel CPUs. I am not sure which other
CPUs are affected. There is no official errata for this behavior AFAIK.
As Alexander suggested, it would be a great idea to have a work around for this
in gcc for these specific CPUs.
^ permalink raw reply [flat|nested] 13+ messages in thread* [Bug target/62011] False Data Dependency in popcnt instruction
2014-08-04 14:29 [Bug rtl-optimization/62011] New: False Data Dependency in popcnt instruction debiandev at gmail dot com
` (2 preceding siblings ...)
2014-08-05 13:40 ` debiandev at gmail dot com
@ 2014-08-07 9:22 ` finis at in dot tum.de
2014-08-11 14:37 ` ysrumyan at gmail dot com
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From: finis at in dot tum.de @ 2014-08-07 9:22 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62011
--- Comment #5 from finis at in dot tum.de ---
Maybe there are a lot more instructions with such a false dependency. popcnt
may only be the tip of the ice berg. I don't think Intel only got this
operation wrong and all other SSE/AVX/... instructions are correct. I rather
think a group of operations is implemented like popcnt. The source code in the
linked SO question yields a good testbed for other operations as well: Simply
replace popcount by another intrinsic and check if the performance deviations
occur.
^ permalink raw reply [flat|nested] 13+ messages in thread* [Bug target/62011] False Data Dependency in popcnt instruction
2014-08-04 14:29 [Bug rtl-optimization/62011] New: False Data Dependency in popcnt instruction debiandev at gmail dot com
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2014-08-07 9:22 ` finis at in dot tum.de
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From: ysrumyan at gmail dot com @ 2014-08-11 14:37 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62011
Yuri Rumyantsev <ysrumyan at gmail dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |ysrumyan at gmail dot com
--- Comment #6 from Yuri Rumyantsev <ysrumyan at gmail dot com> ---
I don't see any issues with 'false dependency' on HSW. I've got sep data on it:
for unsigned veriant (with LEA instructions):
0x400b30 52 161 lea 0x1(%rdx),%ecx
0x400b33 53 0 popcnt (%rbx,%rax,8),%rax
0x400b39 54 353 lea 0x2(%rdx),%r8d
0x400b3d 55 0 popcnt (%rbx,%rcx,8),%rcx
0x400b43 56 170 add %rax,%rcx
0x400b46 57 25 lea 0x3(%rdx),%esi
0x400b49 58 332 popcnt (%rbx,%r8,8),%rax
0x400b4f 59 196 add %rax,%rcx
0x400b52 60 199 popcnt (%rbx,%rsi,8),%rax
0x400b58 61 235 add %rax,%rcx
0x400b5b 62 414 lea 0x4(%rdx),%eax
0x400b5e 63 0 add %rcx,%r14
0x400b61 64 312 mov %rax,%rdx
0x400b64 65 0 cmp %rax,%r12
0x400b67 66 0 ja 400b30 <main+0xb0>
and we don't see any performance anomaly with popcnt.
But for 2nd loop we have
0x400c50 118 0 popcnt -0x8(%rdx),%rax
0x400c56 119 0 popcnt (%rdx),%rcx
0x400c5b 120 1086 add %rax,%rcx
0x400c5e 121 492 popcnt 0x8(%rdx),%rax
0x400c64 122 3 add %rcx,%rax
0x400c67 123 507 add $0x20,%rdx
0x400c6b 124 0 popcnt -0x10(%rdx),%rcx
0x400c71 125 955 add %rax,%rcx
0x400c74 126 479 add %rcx,%r13
0x400c77 127 489 cmp %rsi,%rdx
0x400c7a 128 0 jne 400c50 <main+0x1d0>
So far I can't imagine what the problem is.
^ permalink raw reply [flat|nested] 13+ messages in thread* [Bug target/62011] False Data Dependency in popcnt instruction
2014-08-04 14:29 [Bug rtl-optimization/62011] New: False Data Dependency in popcnt instruction debiandev at gmail dot com
` (4 preceding siblings ...)
2014-08-11 14:37 ` ysrumyan at gmail dot com
@ 2014-08-12 8:38 ` ysrumyan at gmail dot com
2014-08-12 10:49 ` finis at in dot tum.de
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From: ysrumyan at gmail dot com @ 2014-08-12 8:38 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62011
--- Comment #7 from Yuri Rumyantsev <ysrumyan at gmail dot com> ---
Please ignore my previous comment - if we insert nullifying of destination
register before each popcnt (and lzcnt) performance will restore:
original test results:
unsigned 83886630000 0.848533 sec 24.715 GB/s
uint64_t 83886630000 1.37436 sec 15.2592 GB/s
fixed popcnt:
unsigned 90440370000 0.853753 sec 24.5639 GB/s
uint64_t 83886630000 0.694458 sec 30.1984 GB/s
Here is assembly for 2nd loop:
.L16:
xorq %rax, %rax
popcntq -8(%rdx), %rax
xorq %rcx, %rcx
popcntq (%rdx), %rcx
addq %rax, %rcx
xorq %rax, %rax
popcntq 8(%rdx), %rax
addq %rcx, %rax
addq $32, %rdx
xorq %rcx, %rcx
popcntq -16(%rdx), %rcx
addq %rax, %rcx
addq %rcx, %r13
cmpq %rsi, %rdx
jne .L16
^ permalink raw reply [flat|nested] 13+ messages in thread* [Bug target/62011] False Data Dependency in popcnt instruction
2014-08-04 14:29 [Bug rtl-optimization/62011] New: False Data Dependency in popcnt instruction debiandev at gmail dot com
` (5 preceding siblings ...)
2014-08-12 8:38 ` ysrumyan at gmail dot com
@ 2014-08-12 10:49 ` finis at in dot tum.de
2014-08-12 11:26 ` ysrumyan at gmail dot com
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From: finis at in dot tum.de @ 2014-08-12 10:49 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62011
--- Comment #8 from finis at in dot tum.de ---
@Yuri: Note however, that the result of your fixed u32 version seems to be
wrong.
^ permalink raw reply [flat|nested] 13+ messages in thread* [Bug target/62011] False Data Dependency in popcnt instruction
2014-08-04 14:29 [Bug rtl-optimization/62011] New: False Data Dependency in popcnt instruction debiandev at gmail dot com
` (6 preceding siblings ...)
2014-08-12 10:49 ` finis at in dot tum.de
@ 2014-08-12 11:26 ` ysrumyan at gmail dot com
2014-08-13 8:23 ` rguenth at gcc dot gnu.org
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From: ysrumyan at gmail dot com @ 2014-08-12 11:26 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62011
--- Comment #9 from Yuri Rumyantsev <ysrumyan at gmail dot com> ---
This is not u32 version but u64. The first loop (u32) version looks like:
.L23:
leal 1(%rdx), %ecx
xorq %rax, %rax
popcntq (%rbx,%rax,8), %rax
leal 2(%rdx), %r8d
xorq %rcx, %rcx
popcntq (%rbx,%rcx,8), %rcx
addq %rax, %rcx
leal 3(%rdx), %esi
xorq %rax, %rax
popcntq (%rbx,%r8,8), %rax
addq %rax, %rcx
xorq %rax, %rax
popcntq (%rbx,%rsi,8), %rax
addq %rax, %rcx
leal 4(%rdx), %eax
addq %rcx, %r14
movq %rax, %rdx
cmpq %rax, %r12
ja .L23
^ permalink raw reply [flat|nested] 13+ messages in thread* [Bug target/62011] False Data Dependency in popcnt instruction
2014-08-04 14:29 [Bug rtl-optimization/62011] New: False Data Dependency in popcnt instruction debiandev at gmail dot com
` (7 preceding siblings ...)
2014-08-12 11:26 ` ysrumyan at gmail dot com
@ 2014-08-13 8:23 ` rguenth at gcc dot gnu.org
2014-08-21 18:04 ` uros at gcc dot gnu.org
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From: rguenth at gcc dot gnu.org @ 2014-08-13 8:23 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62011
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |NEW
Last reconfirmed| |2014-08-13
Ever confirmed|0 |1
--- Comment #10 from Richard Biener <rguenth at gcc dot gnu.org> ---
Confirmed at least.
^ permalink raw reply [flat|nested] 13+ messages in thread* [Bug target/62011] False Data Dependency in popcnt instruction
2014-08-04 14:29 [Bug rtl-optimization/62011] New: False Data Dependency in popcnt instruction debiandev at gmail dot com
` (8 preceding siblings ...)
2014-08-13 8:23 ` rguenth at gcc dot gnu.org
@ 2014-08-21 18:04 ` uros at gcc dot gnu.org
2014-08-21 18:06 ` ubizjak at gmail dot com
2021-10-11 13:46 ` malincns at 163 dot com
11 siblings, 0 replies; 13+ messages in thread
From: uros at gcc dot gnu.org @ 2014-08-21 18:04 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62011
--- Comment #12 from uros at gcc dot gnu.org ---
Author: uros
Date: Thu Aug 21 18:03:49 2014
New Revision: 214279
URL: https://gcc.gnu.org/viewcvs?rev=214279&root=gcc&view=rev
Log:
Backport from mainline
2014-08-19 H.J. Lu <hongjiu.lu@intel.com>
* config/i386/i386.md (*ctz<mode>2_falsedep_1): Don't clear
destination if it is used in source.
(*clz<mode>2_lzcnt_falsedep_1): Likewise.
(*popcount<mode>2_falsedep_1): Likewise.
Backport from mainline
2014-08-18 Uros Bizjak <ubizjak@gmail.com>
PR target/62011
* config/i386/x86-tune.def (X86_TUNE_AVOID_FALSE_DEP_FOR_BMI):
New tune flag.
* config/i386/i386.h (TARGET_AVOID_FALSE_DEP_FOR_BMI): New define.
* config/i386/i386.md (unspec) <UNSPEC_INSN_FALSE_DEP>: New unspec.
(ffs<mode>2): Do not expand with tzcnt for
TARGET_AVOID_FALSE_DEP_FOR_BMI.
(ffssi2_no_cmove): Ditto.
(*tzcnt<mode>_1): Disable for TARGET_AVOID_FALSE_DEP_FOR_BMI.
(ctz<mode>2): New expander.
(*ctz<mode>2_falsedep_1): New insn_and_split pattern.
(*ctz<mode>2_falsedep): New insn.
(*ctz<mode>2): Rename from ctz<mode>2.
(clz<mode>2_lzcnt): New expander.
(*clz<mode>2_lzcnt_falsedep_1): New insn_and_split pattern.
(*clz<mode>2_lzcnt_falsedep): New insn.
(*clz<mode>2): Rename from ctz<mode>2.
(popcount<mode>2): New expander.
(*popcount<mode>2_falsedep_1): New insn_and_split pattern.
(*popcount<mode>2_falsedep): New insn.
(*popcount<mode>2): Rename from ctz<mode>2.
(*popcount<mode>2_cmp): Remove.
(*popcountsi2_cmp_zext): Ditto.
Modified:
branches/gcc-4_9-branch/gcc/ChangeLog
branches/gcc-4_9-branch/gcc/config/i386/i386.h
branches/gcc-4_9-branch/gcc/config/i386/i386.md
branches/gcc-4_9-branch/gcc/config/i386/x86-tune.def
^ permalink raw reply [flat|nested] 13+ messages in thread* [Bug target/62011] False Data Dependency in popcnt instruction
2014-08-04 14:29 [Bug rtl-optimization/62011] New: False Data Dependency in popcnt instruction debiandev at gmail dot com
` (9 preceding siblings ...)
2014-08-21 18:04 ` uros at gcc dot gnu.org
@ 2014-08-21 18:06 ` ubizjak at gmail dot com
2021-10-11 13:46 ` malincns at 163 dot com
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From: ubizjak at gmail dot com @ 2014-08-21 18:06 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62011
Uroš Bizjak <ubizjak at gmail dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |RESOLVED
Resolution|--- |FIXED
--- Comment #14 from Uroš Bizjak <ubizjak at gmail dot com> ---
.
>From gcc-bugs-return-458986-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Thu Aug 21 18:06:35 2014
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To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/62011] False Data Dependency in popcnt instruction
Date: Thu, 21 Aug 2014 18:06:00 -0000
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Uroš Bizjak <ubizjak at gmail dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Target Milestone|--- |4.9.2
--- Comment #13 from Uroš Bizjak <ubizjak at gmail dot com> ---
Fixed for 4.9.2+.
>From gcc-bugs-return-458988-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Thu Aug 21 18:32:27 2014
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From: "eric.niebler at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/62219] New: [c++11] Spurious error for lambda in a friend function of a class template with a default template parameters
Date: Thu, 21 Aug 2014 18:32:00 -0000
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Bug ID: 62219
Summary: [c++11] Spurious error for lambda in a friend function
of a class template with a default template parameters
Product: gcc
Version: 4.9.0
Status: UNCONFIRMED
Severity: normal
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Component: c++
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Reporter: eric.niebler at gmail dot com
This code:
template< class = void >
struct S
{
friend void foo( S )
{
[](){};
}
};
Gives me:
test.cpp: In function ‘void foo(S< <template-parameter-1-1> >)’:
test.cpp:6:8: error: default argument for template parameter for class
enclosing ‘foo(S< <template-parameter-1-1> >)::<lambda>’
[](){};
^
I'm not sure what the error is trying to tell me. FWIW, the code compiles
cleanly with clang.
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Subject: [Bug fortran/62214] [4.8/4.9/5 Regression] Problem with spread plus concatenation for characters
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--- Comment #3 from Thomas Koenig <tkoenig at gcc dot gnu.org> ---
Author: tkoenig
Date: Thu Aug 21 18:52:58 2014
New Revision: 214281
URL: https://gcc.gnu.org/viewcvs?rev!4281&root=gcc&view=rev
Log:
2014-08-21 Thomas Koenig <tkoenig@gcc.gnu.org>
PR fortran/62214
* frontend-passes.c (optimize_binop_array_assignment):
Do not try to optimize the array assignment for string
concatenation.
2014-08-21 Thomas Koenig <tkoenig@gcc.gnu.org>
PR fortran/62214
* gfortran.dg/array_assignment_5.f90: New test.
Added:
trunk/gcc/testsuite/gfortran.dg/array_assignment_5.f90
Modified:
trunk/gcc/fortran/ChangeLog
trunk/gcc/fortran/frontend-passes.c
trunk/gcc/testsuite/ChangeLog
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` (10 preceding siblings ...)
2014-08-21 18:06 ` ubizjak at gmail dot com
@ 2021-10-11 13:46 ` malincns at 163 dot com
11 siblings, 0 replies; 13+ messages in thread
From: malincns at 163 dot com @ 2021-10-11 13:46 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62011
Ma Lin <malincns at 163 dot com> changed:
What |Removed |Added
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CC| |malincns at 163 dot com
--- Comment #18 from Ma Lin <malincns at 163 dot com> ---
FYI, in Intel 10th/11th Generation Processor Errata Table, there is no popcnt
problem.
In 9th Generation Errata Table, this problem exists.
^ permalink raw reply [flat|nested] 13+ messages in thread