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Replace xlc __fetch_and_add() with inline asm.

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PostgreSQL has been unusable when built with xlc 13 and newer, which are
incompatible with our use of __fetch_and_add().  Back-patch to 9.5,
which introduced pg_atomic_fetch_add_u32().

Reviewed by Tom Lane.

Discussion: https://postgr.es/m/20190831071157.GA3251746@rfd.leadboat.com
This commit is contained in:
Noah Misch 2019-09-13 19:34:06 -07:00
parent f380c51901
commit dd50f1a432
1 changed files with 35 additions and 4 deletions
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39
src/include/port/atomics/generic-xlc.h
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@ -73,11 +73,27 @@ pg_atomic_compare_exchange_u32_impl(volatile pg_atomic_uint32 *ptr,
static inline uint32
pg_atomic_fetch_add_u32_impl(volatile pg_atomic_uint32 *ptr, int32 add_)
{
uint32 _t;
uint32 res;
/*
* __fetch_and_add() emits a leading "sync" and trailing "isync", thereby
* providing sequential consistency. This is undocumented.
* xlc has a no-longer-documented __fetch_and_add() intrinsic. In xlc
* 12.01.0000.0000, it emits a leading "sync" and trailing "isync". In
* xlc 13.01.0003.0004, it emits neither. Hence, using the intrinsic
* would add redundant syncs on xlc 12.
*/
return __fetch_and_add((volatile int *)&ptr->value, add_);
__asm__ __volatile__(
" sync \n"
" lwarx %1,0,%4 \n"
" add %0,%1,%3 \n"
" stwcx. %0,0,%4 \n"
" bne $-12 \n" /* branch to lwarx */
" isync \n"
: "=&r"(_t), "=&r"(res), "+m"(ptr->value)
: "r"(add_), "r"(&ptr->value)
: "memory", "cc");
return res;
}
#ifdef PG_HAVE_ATOMIC_U64_SUPPORT
@ -103,7 +119,22 @@ pg_atomic_compare_exchange_u64_impl(volatile pg_atomic_uint64 *ptr,
static inline uint64
pg_atomic_fetch_add_u64_impl(volatile pg_atomic_uint64 *ptr, int64 add_)
{
return __fetch_and_addlp((volatile long *)&ptr->value, add_);
uint64 _t;
uint64 res;
/* Like u32, but s/lwarx/ldarx/; s/stwcx/stdcx/ */
__asm__ __volatile__(
" sync \n"
" ldarx %1,0,%4 \n"
" add %0,%1,%3 \n"
" stdcx. %0,0,%4 \n"
" bne $-12 \n" /* branch to ldarx */
" isync \n"
: "=&r"(_t), "=&r"(res), "+m"(ptr->value)
: "r"(add_), "r"(&ptr->value)
: "memory", "cc");
return res;
}
#endif /* PG_HAVE_ATOMIC_U64_SUPPORT */