cpluspluscheck complains about use of register
Hi,
When running cpluspluscheck I get many many complaints like
In file included from /tmp/pg-test-repo/src/include/port/atomics.h:70,
from /tmp/pg-test-repo/src/include/utils/dsa.h:17,
from /tmp/pg-test-repo/src/include/nodes/tidbitmap.h:26,
from /tmp/pg-test-repo/src/include/nodes/execnodes.h:24,
from /tmp/pg-test-repo/src/include/commands/trigger.h:17,
from /tmp/pg-test-repo/src/pl/plpgsql/src/plpgsql.h:21,
from /tmp/cpluspluscheck.qOi18T/test.cpp:3:
/tmp/pg-test-repo/src/include/port/atomics/arch-x86.h: In function ‘bool pg_atomic_test_set_flag_impl(volatile pg_atomic_flag*)’:
/tmp/pg-test-repo/src/include/port/atomics/arch-x86.h:143:23: warning: ISO C++17 does not allow ‘register’ storage class specifier [-Wregister]
143 | register char _res = 1;
| ^~~~
It seems we should just remove the use of register? It's currently only used
in
src/include/storage/s_lock.h
src/include/port/atomics/arch-x86.h
From what I understand compilers essentially have been ignoring it for quite a
while...
Greetings,
Andres Freund
Andres Freund <andres@anarazel.de> writes:
When running cpluspluscheck I get many many complaints like
/tmp/pg-test-repo/src/include/port/atomics/arch-x86.h:143:23: warning: ISO C++17 does not allow ‘register’ storage class specifier [-Wregister]
Interesting, I don't see that here.
It seems we should just remove the use of register?
I have a vague idea that it was once important to say "register" if
you are going to use the variable in an asm snippet that requires it
to be in a register. That might be wrong, or it might be obsolete
even if once true. We could try taking these out and seeing if the
buildfarm complains. (If so, maybe -Wno-register would help?)
regards, tom lane
Hi,
On 2022-03-08 13:46:36 -0500, Tom Lane wrote:
Andres Freund <andres@anarazel.de> writes:
When running cpluspluscheck I get many many complaints like
/tmp/pg-test-repo/src/include/port/atomics/arch-x86.h:143:23: warning: ISO C++17 does not allow ‘register’ storage class specifier [-Wregister]Interesting, I don't see that here.
Probably a question of the gcc version. I think starting with 11 g++ defaults
to C++ 17.
It seems we should just remove the use of register?
I have a vague idea that it was once important to say "register" if
you are going to use the variable in an asm snippet that requires it
to be in a register. That might be wrong, or it might be obsolete
even if once true. We could try taking these out and seeing if the
buildfarm complains.
We have several inline asm statements not using register despite using
variables in a register (e.g. pg_atomic_compare_exchange_u32_impl()), so I
wouldn't expect a problem with compilers we support.
Should we make configure test for -Wregister? There's at least one additional
use of register that we'd have to change (pg_regexec).
(If so, maybe -Wno-register would help?)
That's what I did to work around the flood of warnings locally, so it'd
work.
Greetings,
Andres Freund
It seems we should just remove the use of register?
I have a vague idea that it was once important to say "register" if
you are going to use the variable in an asm snippet that requires it
to be in a register. That might be wrong, or it might be obsolete
even if once true. We could try taking these out and seeing if the
buildfarm complains.We have several inline asm statements not using register despite using
variables in a register (e.g. pg_atomic_compare_exchange_u32_impl()), so I
wouldn't expect a problem with compilers we support.Should we make configure test for -Wregister? There's at least one additional
use of register that we'd have to change (pg_regexec).
From a compilation perspective, "register" tells the compiler that you
cannot have a pointer on a variable, i.e. it generates an error if someone
adds something like:
void * p = ®ister_variable;
Removing the "register" declaration means that such protection would be
removed, and creating such a pointer could reduce drastically compiler
optimization opportunities.
--
Fabien.
Hi,
On 2022-03-08 10:59:02 -0800, Andres Freund wrote:
On 2022-03-08 13:46:36 -0500, Tom Lane wrote:
Andres Freund <andres@anarazel.de> writes:
When running cpluspluscheck I get many many complaints like
/tmp/pg-test-repo/src/include/port/atomics/arch-x86.h:143:23: warning: ISO C++17 does not allow ‘register’ storage class specifier [-Wregister]Interesting, I don't see that here.
Probably a question of the gcc version. I think starting with 11 g++ defaults
to C++ 17.It seems we should just remove the use of register?
I have a vague idea that it was once important to say "register" if
you are going to use the variable in an asm snippet that requires it
to be in a register. That might be wrong, or it might be obsolete
even if once true. We could try taking these out and seeing if the
buildfarm complains.We have several inline asm statements not using register despite using
variables in a register (e.g. pg_atomic_compare_exchange_u32_impl()), so I
wouldn't expect a problem with compilers we support.Should we make configure test for -Wregister? There's at least one additional
use of register that we'd have to change (pg_regexec).(If so, maybe -Wno-register would help?)
That's what I did to work around the flood of warnings locally, so it'd
work.
I hit this again while porting cplupluscheck to be invoked by meson as
well. ISTM that we should just remove the uses of register. Yes, some very old
compilers might generate worse code without register, but I don't think we
need to care about peak efficiency with neolithic compilers.
Fabien raised the concern that removing register might lead to accidentally
adding pointers to such variables - I don't find that convincing, because a)
such code is typically inside a helper inline anyway b) we don't use register
widely enough to ensure this.
Attached is a patch removing uses of register. The use in regexec.c could
remain, since we only try to keep headers C++ clean. But there really doesn't
seem to be a good reason to use register in that spot.
I tried to use -Wregister to keep us honest going forward, but unfortunately
it only works with a C++ compiler...
I tested this by redefining register to something else, and I grepped for
non-comment uses of register. Entirely possible that I missed something.
Greetings,
Andres Freund
Attachments:
v1-0001-Remove-uses-of-register-due-to-incompatibility-wi.patchtext/x-diff; charset=us-asciiDownload
From 03bf971d2dc701d473705fd00891028d140dd5ae Mon Sep 17 00:00:00 2001
From: Andres Freund <andres@anarazel.de>
Date: Sat, 24 Sep 2022 12:01:06 -0700
Subject: [PATCH v1] Remove uses of register due to incompatibility with C++17
and up
The use in regexec.c could remain, since we only try to keep headers C++
clean. But there really doesn't seem to be a good reason to use register in
that spot.
Discussion: https://postgr.es/m/20220308185902.ibdqmasoaunzjrfc@alap3.anarazel.de
---
src/include/port/atomics/arch-x86.h | 2 +-
src/include/storage/s_lock.h | 14 +++++++-------
src/backend/regex/regexec.c | 2 +-
.cirrus.yml | 4 +---
4 files changed, 10 insertions(+), 12 deletions(-)
diff --git a/src/include/port/atomics/arch-x86.h b/src/include/port/atomics/arch-x86.h
index cef1ba724c9..6c0b917f12e 100644
--- a/src/include/port/atomics/arch-x86.h
+++ b/src/include/port/atomics/arch-x86.h
@@ -140,7 +140,7 @@ pg_spin_delay_impl(void)
static inline bool
pg_atomic_test_set_flag_impl(volatile pg_atomic_flag *ptr)
{
- register char _res = 1;
+ char _res = 1;
__asm__ __volatile__(
" lock \n"
diff --git a/src/include/storage/s_lock.h b/src/include/storage/s_lock.h
index 65aa66c5984..4225d9b7fc3 100644
--- a/src/include/storage/s_lock.h
+++ b/src/include/storage/s_lock.h
@@ -142,7 +142,7 @@ typedef unsigned char slock_t;
static __inline__ int
tas(volatile slock_t *lock)
{
- register slock_t _res = 1;
+ slock_t _res = 1;
/*
* Use a non-locking test before asserting the bus lock. Note that the
@@ -223,7 +223,7 @@ typedef unsigned char slock_t;
static __inline__ int
tas(volatile slock_t *lock)
{
- register slock_t _res = 1;
+ slock_t _res = 1;
__asm__ __volatile__(
" lock \n"
@@ -356,7 +356,7 @@ typedef unsigned char slock_t;
static __inline__ int
tas(volatile slock_t *lock)
{
- register slock_t _res;
+ slock_t _res;
/*
* See comment in src/backend/port/tas/sunstudio_sparc.s for why this
@@ -511,9 +511,9 @@ typedef unsigned int slock_t;
static __inline__ int
tas(volatile slock_t *lock)
{
- register volatile slock_t *_l = lock;
- register int _res;
- register int _tmp;
+ volatile slock_t *_l = lock;
+ int _res;
+ int _tmp;
__asm__ __volatile__(
" .set push \n"
@@ -574,7 +574,7 @@ static __inline__ int
tas(volatile slock_t *lock)
{
volatile int *lockword = TAS_ACTIVE_WORD(lock);
- register int lockval;
+ int lockval;
/*
* The LDCWX instruction atomically clears the target word and
diff --git a/src/backend/regex/regexec.c b/src/backend/regex/regexec.c
index 29c364f3db1..3d9ff2e6079 100644
--- a/src/backend/regex/regexec.c
+++ b/src/backend/regex/regexec.c
@@ -192,7 +192,7 @@ pg_regexec(regex_t *re,
int flags)
{
struct vars var;
- register struct vars *v = &var;
+ struct vars *v = &var;
int st;
size_t n;
size_t i;
diff --git a/.cirrus.yml b/.cirrus.yml
index 0e3b2d42681..7b5cb021027 100644
--- a/.cirrus.yml
+++ b/.cirrus.yml
@@ -556,8 +556,6 @@ task:
# - Use -fmax-errors, as particularly cpluspluscheck can be very verbose
# - XXX have to disable ICU to avoid errors:
# https://postgr.es/m/20220323002024.f2g6tivduzrktgfa%40alap3.anarazel.de
- # - XXX: the -Wno-register avoids verbose warnings:
- # https://postgr.es/m/20220308181837.aun3tdtdvao4vb7o%40alap3.anarazel.de
###
always:
headers_headerscheck_script: |
@@ -569,7 +567,7 @@ task:
make -s -j${BUILD_JOBS} clean
time make -s headerscheck EXTRAFLAGS='-fmax-errors=10'
headers_cpluspluscheck_script: |
- time make -s cpluspluscheck EXTRAFLAGS='-Wno-register -fmax-errors=10'
+ time make -s cpluspluscheck EXTRAFLAGS='-fmax-errors=10'
always:
upload_caches: ccache
--
2.37.3.542.gdd3f6c4cae
On Sat, Sep 24, 2022 at 12:11 PM Andres Freund <andres@anarazel.de> wrote:
I hit this again while porting cplupluscheck to be invoked by meson as
well. ISTM that we should just remove the uses of register. Yes, some very old
compilers might generate worse code without register, but I don't think we
need to care about peak efficiency with neolithic compilers.
+1. I seem to recall reading that the register keyword was basically
useless as long as 15 years ago.
--
Peter Geoghegan
Andres Freund <andres@anarazel.de> writes:
I hit this again while porting cplupluscheck to be invoked by meson as
well. ISTM that we should just remove the uses of register.
OK by me.
I tried to use -Wregister to keep us honest going forward, but unfortunately
it only works with a C++ compiler...
I think we only really care about stuff that cpluspluscheck would spot,
so I don't feel a need to mess with the standard compilation flags.
regards, tom lane
Hi,
On 2022-09-24 16:01:25 -0400, Tom Lane wrote:
Andres Freund <andres@anarazel.de> writes:
I hit this again while porting cplupluscheck to be invoked by meson as
well. ISTM that we should just remove the uses of register.OK by me.
Done. Thanks Tom, Peter.
Re: Tom Lane
I hit this again while porting cplupluscheck to be invoked by meson as
well. ISTM that we should just remove the uses of register.OK by me.
I tried to use -Wregister to keep us honest going forward, but unfortunately
it only works with a C++ compiler...I think we only really care about stuff that cpluspluscheck would spot,
so I don't feel a need to mess with the standard compilation flags.
This has started to hurt: postgresql-debversion (a Debian version number
data type written in C++) failed to build against Postgresql <= 15 on
Ubuntu's next LTS release (24.04):
In file included from /usr/include/postgresql/15/server/port/atomics.h:70:
/usr/include/postgresql/15/server/port/atomics/arch-x86.h:143:2: error: ISO C++17 does not allow 'register' storage class specifier [-Wregister]
143 | register char _res = 1;
I managed to work around it by putting `#define register` before
including the PG headers.
Should the removal of "register" be backported to support that better?
Christoph
Christoph Berg <myon@debian.org> writes:
Should the removal of "register" be backported to support that better?
Perhaps. It's early days yet, but nobody has complained that that
broke anything in v16, so I'm guessing it'd be fine.
regards, tom lane
On Fri Oct 25, 2024 at 3:04 PM CDT, Tom Lane wrote:
Christoph Berg <myon@debian.org> writes:
Should the removal of "register" be backported to support that better?
Perhaps. It's early days yet, but nobody has complained that that
broke anything in v16, so I'm guessing it'd be fine.
FWIW, I ran into this compiling an extension written in C++ for v15, so
I'll throw my support for backpatching this if that is still on the
table. Understandable if not, though.
--
Tristan Partin
Neon (https://neon.tech)
"Tristan Partin" <tristan@partin.io> writes:
FWIW, I ran into this compiling an extension written in C++ for v15, so
I'll throw my support for backpatching this if that is still on the
table. Understandable if not, though.
I'm inclined to think "too late". Even if we back-patched to v15
and earlier now, your extension would probably still want to be
compilable against earlier minor releases, so the back-patch
would not help you a lot. Christoph's workaround of
"#define register" is probably the best answer for old PG versions,
or you can compile with "-Wno-register".
regards, tom lane
On Fri Oct 25, 2024 at 3:19 PM CDT, Tom Lane wrote:
"Tristan Partin" <tristan@partin.io> writes:
FWIW, I ran into this compiling an extension written in C++ for v15, so
I'll throw my support for backpatching this if that is still on the
table. Understandable if not, though.I'm inclined to think "too late". Even if we back-patched to v15
and earlier now, your extension would probably still want to be
compilable against earlier minor releases, so the back-patch
would not help you a lot. Christoph's workaround of
"#define register" is probably the best answer for old PG versions,
or you can compile with "-Wno-register".
For my purposes, I only need to support the latest minor releases of PG
versions, so a backpatch would be useful come December (?). I do
understand the "too late" argument though.
We did indeed fix the problem with "-Wno-register," though it's always
nice to not have the manual fix. But hey, Postgres is a C project, so
it's all good 😄. Thanks for getting back to me, Tom.
--
Tristan Partin
Neon (https://neon.tech)