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Remove configurability of PPC spinlock assembly code.

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Assume that we can use LWARX hint flags and the LWSYNC instruction
on any PPC machine.  The check on the assembler's behavior was only
needed for Apple's old assembler, which is no longer of interest
now that we've de-supported all PPC-era versions of macOS (thanks
to them not having clock_gettime()).  Also, given an up-to-date
assembler these instructions work even on Apple's old hardware.
It seems quite unlikely that anyone would be interested in running
current Postgres on PPC hardware that's so old as to not have
these instructions.

Hence, rip out associated configure test and manual configuration
options, and just use the modernized instructions all the time.
Also, update atomics/arch-ppc.h to use these instructions as well.
(It was already using LWSYNC unconditionally in another place,
providing further proof that nobody is using PG on hardware old
enough to have a problem with that.)

Discussion: https://postgr.es/m/166622.1660323391@sss.pgh.pa.us
This commit is contained in:
Tom Lane
2022-08-13 13:36:39 -04:00
parent adee0df127
commit 8ded65682b
7 changed files with 26 additions and 115 deletions
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34
configure vendored
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@ -15349,39 +15349,7 @@ $as_echo "#define HAVE_X86_64_POPCNTQ 1" >>confdefs.h
fi
;;
ppc*|powerpc*)
# On PPC, check if assembler supports LWARX instruction's mutex hint bit
{ $as_echo "$as_me:${as_lineno-$LINENO}: checking whether assembler supports lwarx hint bit" >&5
$as_echo_n "checking whether assembler supports lwarx hint bit... " >&6; }
if ${pgac_cv_have_ppc_mutex_hint+:} false; then :
$as_echo_n "(cached) " >&6
else
cat confdefs.h - <<_ACEOF >conftest.$ac_ext
/* end confdefs.h. */
int
main ()
{
int a = 0; int *p = &a; int r;
__asm__ __volatile__ (" lwarx %0,0,%1,1\n" : "=&r"(r) : "r"(p));
;
return 0;
}
_ACEOF
if ac_fn_c_try_compile "$LINENO"; then :
pgac_cv_have_ppc_mutex_hint=yes
else
pgac_cv_have_ppc_mutex_hint=no
fi
rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
fi
{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $pgac_cv_have_ppc_mutex_hint" >&5
$as_echo "$pgac_cv_have_ppc_mutex_hint" >&6; }
if test x"$pgac_cv_have_ppc_mutex_hint" = xyes ; then
$as_echo "#define HAVE_PPC_LWARX_MUTEX_HINT 1" >>confdefs.h
fi
# Check if compiler accepts "i"(x) when __builtin_constant_p(x).
# On PPC, check if compiler accepts "i"(x) when __builtin_constant_p(x).
{ $as_echo "$as_me:${as_lineno-$LINENO}: checking whether __builtin_constant_p(x) implies \"i\"(x) acceptance" >&5
$as_echo_n "checking whether __builtin_constant_p(x) implies \"i\"(x) acceptance... " >&6; }
if ${pgac_cv_have_i_constraint__builtin_constant_p+:} false; then :