.\" $NetBSD: __insn_barrier.3,v 1.2 2011/01/02 07:14:02 jruoho Exp $
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.Dd January 2, 2011
.Dt __INSN_BARRIER 3
.Os
.Sh NAME
.Nm __insn_barrier
.Nd compiler reorder barrier
.Sh SYNOPSIS
.In sys/cdefs.h
.Ft void
.Fn __insn_barrier
.Sh DESCRIPTION
The
.Fn __insn_barrier
macro prevents
.Tn GCC
from moving code across the barrier.
In other words, the compiler is not allowed to reorder read and write
commands below the barrier with the code preceding the barrier.
Like with the
.Em volatile
type qualifier,
.Fn __insn_barrier
may be necessary in some corner cases to prevent the compiler
from misoptimizing.
.Sh SEE ALSO
.Xr gcc 1 ,
.Xr cdefs 3 ,
.Xr mb 9
.Rs
.%A Paul E. McKenney
.%T Memory Barriers: a Hardware View for Software Hackers
.%D June 7, 2010
.%U http://www.rdrop.com/users/paulmck/scalability/paper/whymb.2010.06.07c.pdf
.Re
.Sh HISTORY
The
.Fn __insn_barrier
macro first appeared in
.Nx 2.0 .