Documentation/memory-barriers.txt: Need barriers() for some control dependencies

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Current compilers can "speculate" stores in the case where both legs
of the "if" statement start with identical stores.  Because the stores
are identical, the compiler knows that the store will unconditionally
execute regardless of the "if" condition, and so the compiler is within
its rights to hoist the store to precede the condition.  Such hoisting
destroys the control-dependency ordering.  This ordering can be restored
by placing a barrier() at the beginning of each leg of the "if" statement.
This commit adds this requirement to the control-dependencies section.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

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Paul E. McKenney 2014-02-12 20:19:47 -08:00

parent bbf393b0d5

commit 9b2b3bf531

1 changed files with 19 additions and 7 deletions

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Documentation/memory-barriers.txt

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