From 7acad64c09776c18a090cc89e49ee4302fae3764 Mon Sep 17 00:00:00 2001 From: Taylor R Campbell <riastradh@NetBSD.org> Date: Wed, 30 Mar 2022 20:55:02 +0000 Subject: [PATCH 04/49] x86: Omit needless store in membar_producer/exit. On x86, every store is a store-release, so there is no need for any barrier. But this wasn't a barrier anyway; it was just a store, which was redundant with the store of the return address to the stack implied by CALL even if issuing a store made a difference. --- common/lib/libc/arch/i386/atomic/atomic.S | 7 +++++-- common/lib/libc/arch/x86_64/atomic/atomic.S | 7 +++++-- 2 files changed, 10 insertions(+), 4 deletions(-) diff --git a/common/lib/libc/arch/i386/atomic/atomic.S b/common/lib/libc/arch/i386/atomic/atomic.S index 3dea25c1ce90..d929dd25024d 100644 --- a/common/lib/libc/arch/i386/atomic/atomic.S +++ b/common/lib/libc/arch/i386/atomic/atomic.S @@ -188,8 +188,11 @@ ENTRY(_membar_consumer) END(_membar_consumer) ENTRY(_membar_producer) - /* A store is enough */ - movl $0, -4(%esp) + /* + * Every store to normal memory is a store-release on x86, so + * there is never any need for explicit barriers to order + * anything-before-store. + */ ret END(_membar_producer) diff --git a/common/lib/libc/arch/x86_64/atomic/atomic.S b/common/lib/libc/arch/x86_64/atomic/atomic.S index a483aa98de1d..02554cd00edd 100644 --- a/common/lib/libc/arch/x86_64/atomic/atomic.S +++ b/common/lib/libc/arch/x86_64/atomic/atomic.S @@ -263,8 +263,11 @@ ENTRY(_membar_consumer) END(_membar_consumer) ENTRY(_membar_producer) - /* A store is enough */ - movq $0, -8(%rsp) + /* + * Every store to normal memory is a store-release on x86, so + * there is never any need for explicit barriers to order + * anything-before-store. + */ ret END(_membar_producer) -- 2.33.0