* [Bug target/58928] Different results from gcc when -mlzcnt is used
2013-10-30 20:05 [Bug c/58928] New: Different results from gcc when -mlzcnt is used mikeb01 at gmail dot com
@ 2013-12-10 7:06 ` gnome3fans at gmail dot com
2014-01-17 1:18 ` mikeb01 at gmail dot com
` (5 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: gnome3fans at gmail dot com @ 2013-12-10 7:06 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58928
chenjinzhi <gnome3fans at gmail dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |gnome3fans at gmail dot com
--- Comment #1 from chenjinzhi <gnome3fans at gmail dot com> ---
(In reply to Michael Barker from comment #0)
> Created attachment 31113 [details]
> Preprossed test.c code
>
> I have the following code:
>
> #include <stdint.h>
> #include <stdio.h>
> #include <x86intrin.h>
>
> long long lzcnt(long long l)
> {
> return __lzcnt64(l);
> }
>
> int main(int argc, char** argv)
> {
> printf("%lld\n", lzcnt(atoll(argv[1])));
> return 0;
> }
>
> If I compile and run with and without the -mlzcnt flag I get different
> results:
>
> $ gcc src/test.c -D__LZCNT__ -mlzcnt && ./a.out 2047
> 10
>
> $ gcc src/test.c -D__LZCNT__ && ./a.out 2047
> 53
>
> $ gcc -v
> Using built-in specs.
> COLLECT_GCC=gcc
> COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-redhat-linux/4.8.2/lto-wrapper
> Target: x86_64-redhat-linux
> Configured with: ../configure --prefix=/usr --mandir=/usr/share/man
> --infodir=/usr/share/info --with-bugurl=http://bugzilla.redhat.com/bugzilla
> --enable-bootstrap --enable-shared --enable-threads=posix
> --enable-checking=release --with-system-zlib --enable-__cxa_atexit
> --disable-libunwind-exceptions --enable-gnu-unique-object
> --enable-linker-build-id --with-linker-hash-style=gnu
> --enable-languages=c,c++,objc,obj-c++,java,fortran,ada,go,lto
> --enable-plugin --enable-initfini-array --enable-java-awt=gtk --disable-dssi
> --with-java-home=/usr/lib/jvm/java-1.5.0-gcj-1.5.0.0/jre
> --enable-libgcj-multifile --enable-java-maintainer-mode
> --with-ecj-jar=/usr/share/java/eclipse-ecj.jar --disable-libjava-multilib
> --with-isl=/builddir/build/BUILD/gcc-4.8.2-20131017/obj-x86_64-redhat-linux/
> isl-install
> --with-cloog=/builddir/build/BUILD/gcc-4.8.2-20131017/obj-x86_64-redhat-
> linux/cloog-install --with-tune=generic --with-arch_32=i686
> --build=x86_64-redhat-linux
> Thread model: posix
> gcc version 4.8.2 20131017 (Red Hat 4.8.2-1) (GCC)
>
> File test.i attached. It was the same for both compilations, so only one
> file attached.
I just test the code in my machine but the result is different from yours.
I compile and run with and without the -mlzcnt flag and get the same result:
53.
Here is my gcc -v output:
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-redhat-linux/4.8.2/lto-wrapper
Target: x86_64-redhat-linux
Configured with: ../configure --prefix=/usr --mandir=/usr/share/man
--infodir=/usr/share/info --with-bugurl=http://bugzilla.redhat.com/bugzilla
--enable-bootstrap --enable-shared --enable-threads=posix
--enable-checking=release --with-system-zlib --enable-__cxa_atexit
--disable-libunwind-exceptions --enable-gnu-unique-object
--enable-linker-build-id --with-linker-hash-style=gnu
--enable-languages=c,c++,objc,obj-c++,java,fortran,ada,go,lto --enable-plugin
--enable-initfini-array --enable-java-awt=gtk --disable-dssi
--with-java-home=/usr/lib/jvm/java-1.5.0-gcj-1.5.0.0/jre
--enable-libgcj-multifile --enable-java-maintainer-mode
--with-ecj-jar=/usr/share/java/eclipse-ecj.jar --disable-libjava-multilib
--with-isl=/builddir/build/BUILD/gcc-4.8.2-20131017/obj-x86_64-redhat-linux/isl-install
--with-cloog=/builddir/build/BUILD/gcc-4.8.2-20131017/obj-x86_64-redhat-linux/cloog-install
--with-tune=generic --with-arch_32=i686 --build=x86_64-redhat-linux
Thread model: posix
gcc version 4.8.2 20131017 (Red Hat 4.8.2-1) (GCC)
Hope helps
>From gcc-bugs-return-437156-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Tue Dec 10 07:06:05 2013
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From: "conradsand.arma at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/59364] C++11 extern thread_local breaks linking: undefined reference to TLS init function
Date: Tue, 10 Dec 2013 07:06:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?idY364
--- Comment #3 from Conrad <conradsand.arma at gmail dot com> ---
Reduced test case. Compile with:
g++ a.cpp -c -o a.o -std=c++11
g++ b.cpp -c -o b.o -std=c++11
g++ a.o b.o -o prog -std=c++11
file foo.hpp:
class foo
{
public:
inline foo() {}
inline ~foo() {}
inline double bar() { return 123.456; }
};
file a.cpp:
#include "foo.hpp"
thread_local foo foo_instance;
file b.cpp:
#include "foo.hpp"
extern thread_local foo foo_instance;
int main(int argc, char** argv)
{
double bar = foo_instance.bar();
return 0;
}
^ permalink raw reply [flat|nested] 8+ messages in thread* [Bug target/58928] Different results from gcc when -mlzcnt is used
2013-10-30 20:05 [Bug c/58928] New: Different results from gcc when -mlzcnt is used mikeb01 at gmail dot com
2013-12-10 7:06 ` [Bug target/58928] " gnome3fans at gmail dot com
@ 2014-01-17 1:18 ` mikeb01 at gmail dot com
2014-01-17 10:31 ` jtaylor.debian at googlemail dot com
` (4 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: mikeb01 at gmail dot com @ 2014-01-17 1:18 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58928
--- Comment #2 from Michael Barker <mikeb01 at gmail dot com> ---
> Hope helps
What hardware platform are you testing on? I'm running on Ivy Bridge:
Intel(R) Xeon(R) CPU E5620 @2.40GHz
Could you put the assembler that you see on the ticket:
With -mlzcnt:
0000000000400580 <lzcnt>:
400580: 55 push %rbp
400581: 48 89 e5 mov %rsp,%rbp
400584: 48 89 7d e8 mov %rdi,-0x18(%rbp)
400588: 48 8b 45 e8 mov -0x18(%rbp),%rax
40058c: 48 89 45 f8 mov %rax,-0x8(%rbp)
400590: f3 48 0f bd 45 f8 lzcnt -0x8(%rbp),%rax
400596: 48 98 cltq
400598: 5d pop %rbp
400599: c3 retq
Without -mlzcnt:
0000000000400580 <lzcnt>:
400580: 55 push %rbp
400581: 48 89 e5 mov %rsp,%rbp
400584: 48 89 7d e8 mov %rdi,-0x18(%rbp)
400588: 48 8b 45 e8 mov -0x18(%rbp),%rax
40058c: 48 89 45 f8 mov %rax,-0x8(%rbp)
400590: 48 0f bd 45 f8 bsr -0x8(%rbp),%rax
400595: 48 83 f0 3f xor $0x3f,%rax
400599: 48 98 cltq
40059b: 5d pop %rbp
40059c: c3 retq
^ permalink raw reply [flat|nested] 8+ messages in thread* [Bug target/58928] Different results from gcc when -mlzcnt is used
2013-10-30 20:05 [Bug c/58928] New: Different results from gcc when -mlzcnt is used mikeb01 at gmail dot com
2013-12-10 7:06 ` [Bug target/58928] " gnome3fans at gmail dot com
2014-01-17 1:18 ` mikeb01 at gmail dot com
@ 2014-01-17 10:31 ` jtaylor.debian at googlemail dot com
2014-01-17 11:16 ` jakub at gcc dot gnu.org
` (3 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: jtaylor.debian at googlemail dot com @ 2014-01-17 10:31 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58928
Julian Taylor <jtaylor.debian at googlemail dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |jtaylor.debian at googlemail dot c
| |om
--- Comment #3 from Julian Taylor <jtaylor.debian at googlemail dot com> ---
the result will be different depending on running on amd or intel cpu.
lzcnt encoding maps to some other instruction (bsr) on intel cpus, see
http://code.google.com/p/corkami/wiki/x86oddities#lzcnt
^ permalink raw reply [flat|nested] 8+ messages in thread* [Bug target/58928] Different results from gcc when -mlzcnt is used
2013-10-30 20:05 [Bug c/58928] New: Different results from gcc when -mlzcnt is used mikeb01 at gmail dot com
` (2 preceding siblings ...)
2014-01-17 10:31 ` jtaylor.debian at googlemail dot com
@ 2014-01-17 11:16 ` jakub at gcc dot gnu.org
2014-01-19 0:44 ` mikeb01 at gmail dot com
` (2 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: jakub at gcc dot gnu.org @ 2014-01-17 11:16 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58928
Jakub Jelinek <jakub at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |jakub at gcc dot gnu.org
--- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Intel(R) Xeon(R) CPU E5620 @2.40GHz
is not IvyBridge, plus even IvyBridge doesn't support lzcnt insn, only Haswell
or some recent AMD CPUs. So, this looks like user error, you shouldn't compile
code you intend to run on non-lzcnt CPUs with -mlzcnt.
^ permalink raw reply [flat|nested] 8+ messages in thread* [Bug target/58928] Different results from gcc when -mlzcnt is used
2013-10-30 20:05 [Bug c/58928] New: Different results from gcc when -mlzcnt is used mikeb01 at gmail dot com
` (3 preceding siblings ...)
2014-01-17 11:16 ` jakub at gcc dot gnu.org
@ 2014-01-19 0:44 ` mikeb01 at gmail dot com
2014-01-20 23:48 ` mikeb01 at gmail dot com
2014-01-20 23:48 ` mikeb01 at gmail dot com
6 siblings, 0 replies; 8+ messages in thread
From: mikeb01 at gmail dot com @ 2014-01-19 0:44 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58928
--- Comment #5 from Michael Barker <mikeb01 at gmail dot com> ---
(In reply to Jakub Jelinek from comment #4)
> Intel(R) Xeon(R) CPU E5620 @2.40GHz
> is not IvyBridge, plus even IvyBridge doesn't support lzcnt insn, only
> Haswell or some recent AMD CPUs. So, this looks like user error, you
> shouldn't compile code you intend to run on non-lzcnt CPUs with -mlzcnt.
Sorry, shelled into the wrong machine when running the command. Actual model
number is (i7-3770). Happy with the explanation, please close.
There is a further issue that the bug.c code won't compile under g++, due to a
missing builtin.
/.../lzcntintrin.h:38:29: error: ‘__builtin_clzs’ was not declared in this
scope
return __builtin_clzs (__X);
However I will raise a separate bug for that.
>From gcc-bugs-return-440872-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Sun Jan 19 00:59:55 2014
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From: "mikeb01 at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/59874] New: Missing builtin (__builtin_clzs) when compiling with g++
Date: Sun, 19 Jan 2014 00:59:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59874
Bug ID: 59874
Summary: Missing builtin (__builtin_clzs) when compiling with
g++
Product: gcc
Version: 4.8.2
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: mikeb01 at gmail dot com
Created attachment 31888
--> http://gcc.gnu.org/bugzilla/attachment.cgi?id=31888&action=edit
Preprocessed version of bug.cc
The following code:
#include <x86intrin.h>
int main(int argc, char** argv)
{
return __lzcnt32(2047);
}
Fails to compile using g++ (works fine with gcc). It will compile if the
-mlzcnt switch is used, but on some platforms that will generate incorrect
code.
The __builtin_clzs does not appear to be defined when using the c++ compiler.
If I hand modify the lzcntintrin.h file and comment out the whole definition of
the __lzcnt16 intrinsic it works okay and generates the expected code.
$ g++ -v -save-temps -D__LZCNT__ bug.cc
Using built-in specs.
COLLECT_GCC=g++
COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-redhat-linux/4.8.2/lto-wrapper
Target: x86_64-redhat-linux
Configured with: ../configure --prefix=/usr --mandir=/usr/share/man
--infodir=/usr/share/info --with-bugurl=http://bugzilla.redhat.com/bugzilla
--enable-bootstrap --enable-shared --enable-threads=posix
--enable-checking=release --with-system-zlib --enable-__cxa_atexit
--disable-libunwind-exceptions --enable-gnu-unique-object
--enable-linker-build-id --with-linker-hash-style=gnu
--enable-languages=c,c++,objc,obj-c++,java,fortran,ada,go,lto --enable-plugin
--enable-initfini-array --enable-java-awt=gtk --disable-dssi
--with-java-home=/usr/lib/jvm/java-1.5.0-gcj-1.5.0.0/jre
--enable-libgcj-multifile --enable-java-maintainer-mode
--with-ecj-jar=/usr/share/java/eclipse-ecj.jar --disable-libjava-multilib
--with-isl=/builddir/build/BUILD/gcc-4.8.2-20131212/obj-x86_64-redhat-linux/isl-install
--with-cloog=/builddir/build/BUILD/gcc-4.8.2-20131212/obj-x86_64-redhat-linux/cloog-install
--with-tune=generic --with-arch_32=i686 --build=x86_64-redhat-linux
Thread model: posix
gcc version 4.8.2 20131212 (Red Hat 4.8.2-7) (GCC)
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-D' '__LZCNT__' '-shared-libgcc'
'-mtune=generic' '-march=x86-64'
/usr/libexec/gcc/x86_64-redhat-linux/4.8.2/cc1plus -E -quiet -v -D_GNU_SOURCE
-D __LZCNT__ bug.cc -mtune=generic -march=x86-64 -fpch-preprocess -o bug.ii
ignoring nonexistent directory
"/usr/lib/gcc/x86_64-redhat-linux/4.8.2/include-fixed"
ignoring nonexistent directory
"/usr/lib/gcc/x86_64-redhat-linux/4.8.2/../../../../x86_64-redhat-linux/include"
#include "..." search starts here:
#include <...> search starts here:
/usr/lib/gcc/x86_64-redhat-linux/4.8.2/../../../../include/c++/4.8.2
/usr/lib/gcc/x86_64-redhat-linux/4.8.2/../../../../include/c++/4.8.2/x86_64-redhat-linux
/usr/lib/gcc/x86_64-redhat-linux/4.8.2/../../../../include/c++/4.8.2/backward
/usr/lib/gcc/x86_64-redhat-linux/4.8.2/include
/usr/local/include
/usr/include
End of search list.
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-D' '__LZCNT__' '-shared-libgcc'
'-mtune=generic' '-march=x86-64'
/usr/libexec/gcc/x86_64-redhat-linux/4.8.2/cc1plus -fpreprocessed bug.ii
-quiet -dumpbase bug.cc -mtune=generic -march=x86-64 -auxbase bug -version -o
bug.s
GNU C++ (GCC) version 4.8.2 20131212 (Red Hat 4.8.2-7) (x86_64-redhat-linux)
compiled by GNU C version 4.8.2 20131212 (Red Hat 4.8.2-7), GMP version
5.1.1, MPFR version 3.1.1, MPC version 1.0.1
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
GNU C++ (GCC) version 4.8.2 20131212 (Red Hat 4.8.2-7) (x86_64-redhat-linux)
compiled by GNU C version 4.8.2 20131212 (Red Hat 4.8.2-7), GMP version
5.1.1, MPFR version 3.1.1, MPC version 1.0.1
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
Compiler executable checksum: 489f772b6d0264e1e4c03fca513f7a0d
In file included from
/usr/lib/gcc/x86_64-redhat-linux/4.8.2/include/immintrin.h:64:0,
from
/usr/lib/gcc/x86_64-redhat-linux/4.8.2/include/x86intrin.h:62,
from bug.cc:1:
/usr/lib/gcc/x86_64-redhat-linux/4.8.2/include/lzcntintrin.h: In function
‘short unsigned int __lzcnt16(short unsigned int)’:
/usr/lib/gcc/x86_64-redhat-linux/4.8.2/include/lzcntintrin.h:38:29: error:
‘__builtin_clzs’ was not declared in this scope
return __builtin_clzs (__X);
>From gcc-bugs-return-440873-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Sun Jan 19 02:45:09 2014
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From: "josephlawrie at hotmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/59875] New: Weak symbols in glibc prevent optimizations
Date: Sun, 19 Jan 2014 02:45:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59875
Bug ID: 59875
Summary: Weak symbols in glibc prevent optimizations
Product: gcc
Version: 4.8.1
Status: UNCONFIRMED
Severity: trivial
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: josephlawrie at hotmail dot com
The following (weird) code changed from a stackoverflow post demonstrates the
problem:
#include <array>
#include <cassert>
#include <cstdlib>
/*
void * operator new(std::size_t n) throw(std::bad_alloc)
{
return malloc(n);
}
void operator delete(void * p) throw()
{
if(p != nullptr)
free(p);
}
/*
class P {
public:
P() : _value(nullptr) {}
~P() { delete _value; }
private:
char *_value;
};
void foo() {
if(std::array<P, 4>().size() != 4)
assert(false);
}
(compiled with g++ -std=c++11 -O3 -fno-weak -static -Wa,-alh test.cpp -o test)
The result of delete _value cannot be eliminated (and hence neither can array
construction, etc) even though the standard says something to the effect of
"The value of the first argument supplied to a deallocation function may be a
null pointer value; if so, and if the deallocation function is one supplied in
the standard library, the call has no effect." i.e, delete should do nothing.
I thought this has something to do with the fallback to glibc's free which can
be hooked (and hence the delete's side effect are unknown). The uncommented
version however still contains a call to free, so it is possibly just a
constant propagation thing.
>From gcc-bugs-return-440874-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Sun Jan 19 04:22:04 2014
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From: "3dw4rd at verizon dot net" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/59867] Template string literal loses first symbol
Date: Sun, 19 Jan 2014 04:22:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?idY867
--- Comment #8 from Ed Smith-Rowland <3dw4rd at verizon dot net> ---
I put this in a while back because it looked like it was going into C++14. I
jumped to gun. Unfortunately, I am not on a place where I can look at this
until Tuesday.
It should only be activated for -std=c++1y.
^ permalink raw reply [flat|nested] 8+ messages in thread* [Bug target/58928] Different results from gcc when -mlzcnt is used
2013-10-30 20:05 [Bug c/58928] New: Different results from gcc when -mlzcnt is used mikeb01 at gmail dot com
` (4 preceding siblings ...)
2014-01-19 0:44 ` mikeb01 at gmail dot com
@ 2014-01-20 23:48 ` mikeb01 at gmail dot com
2014-01-20 23:48 ` mikeb01 at gmail dot com
6 siblings, 0 replies; 8+ messages in thread
From: mikeb01 at gmail dot com @ 2014-01-20 23:48 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58928
Michael Barker <mikeb01 at gmail dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Resolution|FIXED |INVALID
^ permalink raw reply [flat|nested] 8+ messages in thread* [Bug target/58928] Different results from gcc when -mlzcnt is used
2013-10-30 20:05 [Bug c/58928] New: Different results from gcc when -mlzcnt is used mikeb01 at gmail dot com
` (5 preceding siblings ...)
2014-01-20 23:48 ` mikeb01 at gmail dot com
@ 2014-01-20 23:48 ` mikeb01 at gmail dot com
6 siblings, 0 replies; 8+ messages in thread
From: mikeb01 at gmail dot com @ 2014-01-20 23:48 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58928
Michael Barker <mikeb01 at gmail dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |RESOLVED
Resolution|--- |FIXED
--- Comment #6 from Michael Barker <mikeb01 at gmail dot com> ---
Not a bug, closed by reporter.
^ permalink raw reply [flat|nested] 8+ messages in thread