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Remove duplicate reads from the inner loops in generic atomic ops.

The pg_atomic_compare_exchange_xxx functions are defined to update*expected to whatever they read from the target variable. Therefore,there's no need to do additional explicit reads after we've initializedthe "old" variable. The actual benefit of this is somewhat debatable,but it seems fairly unlikely to hurt anything, especially since wewill override the generic implementations in most performance-sensitivecases.Yura Sokolov, reviewed by Jesper Pedersen and myselfDiscussion:https://postgr.es/m/7f65886daca545067f82bf2b463b218d@postgrespro.ru

1 parent34ae182 commite530be9Copy full SHA for e530be9

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+24

-48

lines changed

src/include/port/atomics
- generic.h

1 file changed

+24

-48

lines changed

`‎src/include/port/atomics/generic.h`

Lines changed: 24 additions & 48 deletions

Original file line number	Diff line number	Diff line change
`@@ -170,12 +170,9 @@ static inline uint32`
`170`	`170`	`pg_atomic_exchange_u32_impl(volatilepg_atomic_uint32*ptr,uint32xchg_)`
`171`	`171`	`{`
`172`	`172`	`uint32old;`
`173`		`-while (true)`
`174`		`-{`
`175`		`-old=pg_atomic_read_u32_impl(ptr);`
`176`		`-if (pg_atomic_compare_exchange_u32_impl(ptr,&old,xchg_))`
`177`		`-break;`
`178`		`-}`
	`173`	`+old=pg_atomic_read_u32_impl(ptr);`
	`174`	`+while (!pg_atomic_compare_exchange_u32_impl(ptr,&old,xchg_))`
	`175`	`+/* skip */;`
`179`	`176`	`returnold;`
`180`	`177`	`}`
`181`	`178`	`#endif`
`@@ -186,12 +183,9 @@ static inline uint32`
`186`	`183`	`pg_atomic_fetch_add_u32_impl(volatilepg_atomic_uint32*ptr,int32add_)`
`187`	`184`	`{`
`188`	`185`	`uint32old;`
`189`		`-while (true)`
`190`		`-{`
`191`		`-old=pg_atomic_read_u32_impl(ptr);`
`192`		`-if (pg_atomic_compare_exchange_u32_impl(ptr,&old,old+add_))`
`193`		`-break;`
`194`		`-}`
	`186`	`+old=pg_atomic_read_u32_impl(ptr);`
	`187`	`+while (!pg_atomic_compare_exchange_u32_impl(ptr,&old,old+add_))`
	`188`	`+/* skip */;`
`195`	`189`	`returnold;`
`196`	`190`	`}`
`197`	`191`	`#endif`
`@@ -211,12 +205,9 @@ static inline uint32`
`211`	`205`	`pg_atomic_fetch_and_u32_impl(volatilepg_atomic_uint32*ptr,uint32and_)`
`212`	`206`	`{`
`213`	`207`	`uint32old;`
`214`		`-while (true)`
`215`		`-{`
`216`		`-old=pg_atomic_read_u32_impl(ptr);`
`217`		`-if (pg_atomic_compare_exchange_u32_impl(ptr,&old,old&and_))`
`218`		`-break;`
`219`		`-}`
	`208`	`+old=pg_atomic_read_u32_impl(ptr);`
	`209`	`+while (!pg_atomic_compare_exchange_u32_impl(ptr,&old,old&and_))`
	`210`	`+/* skip */;`
`220`	`211`	`returnold;`
`221`	`212`	`}`
`222`	`213`	`#endif`
`@@ -227,12 +218,9 @@ static inline uint32`
`227`	`218`	`pg_atomic_fetch_or_u32_impl(volatilepg_atomic_uint32*ptr,uint32or_)`
`228`	`219`	`{`
`229`	`220`	`uint32old;`
`230`		`-while (true)`
`231`		`-{`
`232`		`-old=pg_atomic_read_u32_impl(ptr);`
`233`		`-if (pg_atomic_compare_exchange_u32_impl(ptr,&old,old \|or_))`
`234`		`-break;`
`235`		`-}`
	`221`	`+old=pg_atomic_read_u32_impl(ptr);`
	`222`	`+while (!pg_atomic_compare_exchange_u32_impl(ptr,&old,old \|or_))`
	`223`	`+/* skip */;`
`236`	`224`	`returnold;`
`237`	`225`	`}`
`238`	`226`	`#endif`
`@@ -261,12 +249,9 @@ static inline uint64`
`261`	`249`	`pg_atomic_exchange_u64_impl(volatilepg_atomic_uint64*ptr,uint64xchg_)`
`262`	`250`	`{`
`263`	`251`	`uint64old;`
`264`		`-while (true)`
`265`		`-{`
`266`		`-old=ptr->value;`
`267`		`-if (pg_atomic_compare_exchange_u64_impl(ptr,&old,xchg_))`
`268`		`-break;`
`269`		`-}`
	`252`	`+old=ptr->value;`
	`253`	`+while (!pg_atomic_compare_exchange_u64_impl(ptr,&old,xchg_))`
	`254`	`+/* skip */;`
`270`	`255`	`returnold;`
`271`	`256`	`}`
`272`	`257`	`#endif`
`@@ -357,12 +342,9 @@ static inline uint64`
`357`	`342`	`pg_atomic_fetch_add_u64_impl(volatilepg_atomic_uint64*ptr,int64add_)`
`358`	`343`	`{`
`359`	`344`	`uint64old;`
`360`		`-while (true)`
`361`		`-{`
`362`		`-old=pg_atomic_read_u64_impl(ptr);`
`363`		`-if (pg_atomic_compare_exchange_u64_impl(ptr,&old,old+add_))`
`364`		`-break;`
`365`		`-}`
	`345`	`+old=pg_atomic_read_u64_impl(ptr);`
	`346`	`+while (!pg_atomic_compare_exchange_u64_impl(ptr,&old,old+add_))`
	`347`	`+/* skip */;`
`366`	`348`	`returnold;`
`367`	`349`	`}`
`368`	`350`	`#endif`
`@@ -382,12 +364,9 @@ static inline uint64`
`382`	`364`	`pg_atomic_fetch_and_u64_impl(volatilepg_atomic_uint64*ptr,uint64and_)`
`383`	`365`	`{`
`384`	`366`	`uint64old;`
`385`		`-while (true)`
`386`		`-{`
`387`		`-old=pg_atomic_read_u64_impl(ptr);`
`388`		`-if (pg_atomic_compare_exchange_u64_impl(ptr,&old,old&and_))`
`389`		`-break;`
`390`		`-}`
	`367`	`+old=pg_atomic_read_u64_impl(ptr);`
	`368`	`+while (!pg_atomic_compare_exchange_u64_impl(ptr,&old,old&and_))`
	`369`	`+/* skip */;`
`391`	`370`	`returnold;`
`392`	`371`	`}`
`393`	`372`	`#endif`
`@@ -398,12 +377,9 @@ static inline uint64`
`398`	`377`	`pg_atomic_fetch_or_u64_impl(volatilepg_atomic_uint64*ptr,uint64or_)`
`399`	`378`	`{`
`400`	`379`	`uint64old;`
`401`		`-while (true)`
`402`		`-{`
`403`		`-old=pg_atomic_read_u64_impl(ptr);`
`404`		`-if (pg_atomic_compare_exchange_u64_impl(ptr,&old,old \|or_))`
`405`		`-break;`
`406`		`-}`
	`380`	`+old=pg_atomic_read_u64_impl(ptr);`
	`381`	`+while (!pg_atomic_compare_exchange_u64_impl(ptr,&old,old \|or_))`
	`382`	`+/* skip */;`
`407`	`383`	`returnold;`
`408`	`384`	`}`
`409`	`385`	`#endif`

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`‎src/include/port/atomics/generic.h`

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