<div>
-<p>SequentiallyConsistent (<code>seq_cst</code> in IR) provides Acquire and/or
- Release semantics, and in addition guarantees a total ordering exists with
- all other SequentiallyConsistent operations.
+<p>SequentiallyConsistent (<code>seq_cst</code> in IR) provides
+ Acquire semantics for loads and Release semantics for
+ stores. Additionally, it guarantees that a total ordering exists
+ between all SequentiallyConsistent operations.
<dl>
<dt>Relevant standard</dt>
reason about for the programmer than other kinds of operations, and using
them is generally a practical performance tradeoff.</dd>
<dt>Notes for optimizers</dt>
- <dd>In general, optimizers should treat this like a nothrow call; the
- the possible optimizations are usually not interesting.</dd>
+ <dd>In general, optimizers should treat this like a nothrow call.
+ However, optimizers may improve performance by reordering a
+ store followed by a load unless both operations are sequentially
+ consistent.</dd>
<dt>Notes for code generation</dt>
- <dd>SequentiallyConsistent operations generally require the strongest
- barriers supported by the architecture.</dd>
+ <dd>SequentiallyConsistent loads minimally require the same barriers
+ as Acquire operations and SequeuentiallyConsistent stores require
+ Release barriers. Additionally, the code generator must enforce
+ ordering between SequeuentiallyConsistent stores followed by
+ SequeuentiallyConsistent loads. On common architectures, this
+ requires emitting a full fence after SequeuentiallyConsistent stores.</dd>
</dl>
</div>