RFR(xs): 8211387: [Zero] atomic_copy64: Use ldrexd for atomic reads on ARMv7

[Andrew Haley]

On 10/05/2018 03:18 PM, Andrew Haley wrote:
> 
> There's no CLREX, and no-one ever reported any problem. CLREX could be
> a performance boost because it takes the cache line out of exclusive
> state back to shared state, reducing later bus traffic.

One more thing: LoadExclusive and StoreExclusive must be executed in
program order with the same address. CLREX is essential in interrupt
code because you might return to a StoreExclusive instruction and in
that case the StoreExclusive must fail: the CLREX guarantees that.

-- 
Andrew Haley
Java Platform Lead Engineer
Red Hat UK Ltd. <https://www.redhat.com>
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