8000 Require compiler barrier support. · postgres/postgres@a011dc3 · GitHub
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Require compiler barrier support.
Previously we had a fallback implementation of pg_compiler_barrier() that called an empty function across a translation unit boundary so the compiler couldn't see what it did. That shouldn't be needed on any current systems, and might not even work with a link time optimizer. Since we now require compiler-specific knowledge of how to implement atomics, we should also know how to implement compiler barriers on a hypothetical new system. Reviewed-by: Heikki Linnakangas <hlinnaka@iki.fi> Suggested-by: Andres Freund <andres@anarazel.de> Discussion: https://postgr.es/m/721bf39a-ed8a-44b0-8b8e-be3bd81db748%40technowledgy.de Discussion: https://postgr.es/m/3351991.1697728588%40sss.pgh.pa.us
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‎src/backend/port/atomics.c

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@@ -40,14 +40,6 @@ pg_spinlock_barrier(void)
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}
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#endif
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#ifdef PG_HAVE_COMPILER_BARRIER_EMULATION
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void
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pg_extern_compiler_barrier(void)
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{
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/* do nothing */
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}
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#endif
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#ifdef PG_HAVE_ATOMIC_U64_SIMULATION
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‎src/include/port/atomics.h

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@@ -98,6 +98,9 @@
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#if !defined(PG_HAVE_ATOMIC_U32_SUPPORT)
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#error "could not find an implementation of pg_atomic_uint32"
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#endif
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#if !defined(pg_compiler_barrier_impl)
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#error "could not find an implementation of pg_compiler_barrier"
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#endif
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/*
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* Provide a spinlock-based implementation of the 64 bit variants, if

‎src/include/port/atomics/fallback.h

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@@ -33,21 +33,6 @@ extern void pg_spinlock_barrier(void);
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#define pg_memory_barrier_impl pg_spinlock_barrier
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#endif
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#ifndef pg_compiler_barrier_impl
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/*
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* If the compiler/arch combination does not provide compiler barriers,
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* provide a fallback. The fallback simply consists of a function call into
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* an externally defined function. That should guarantee compiler barrier
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* semantics except for compilers that do inter translation unit/global
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* optimization - those better provide an actual compiler barrier.
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*
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* A native compiler barrier for sure is a lot faster than this...
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*/
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#define PG_HAVE_COMPILER_BARRIER_EMULATION
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extern void pg_extern_compiler_barrier(void);
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#define pg_compiler_barrier_impl pg_extern_compiler_barrier
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#endif
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#if !defined(PG_HAVE_ATOMIC_U64_SUPPORT)
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