[concurrency-interest] If LoadLoad barrier is reduced to no-op, why lfence?

Lei Zhao leizhao833 at gmail.com
Fri Jul 27 12:57:11 EDT 2012


Hello Everyone,

  I am currently reading the JMM cookbook (
http://gee.cs.oswego.edu/dl/jmm/cookbook.html) and have a (maybe hardware
related) question about barrier instructions: if the LoadLoad barrier is
going to be no-op on x86-TSO, why does lfence instruction exist at all?
(similarly StoreStore and sfence). I am a little confused about whether
x86-TSO intrinsically guarantees load-load ordering or not. Thank you.

- Lei
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