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 <and...@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
>From 03bf971d2dc701d473705fd00891028d140dd5ae Mon Sep 17 00:00:00 2001 From: Andres Freund <and...@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.ibdqmasoaunzj...@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
