From: "Bryan O'Sullivan" <bos@xxxxxxxxxxxxx>
This copy routine is memcpy-compatible, but on some architectures will use
cache-bypassing loads to avoid bringing the source data into the cache.
One case where this is useful is when a device issues a DMA to a memory
region, and the CPU must copy the DMAed data elsewhere before doing any work
with it. Since the source data is read-once, write-never from the CPU's
perspective, caching the data at those addresses can only evict potentially
useful data.
We provide an x86_64 implementation that uses SSE non-temporal loads, and a
generic version that falls back to plain memcpy.
+ movq %r11, 56(%rdi)
+ addq %rcx, %rdi
+ cmpq %rdx, %rcx /* is rdx >= 64? */
+ jbe .L42
+ sfence
+ orl %edx, %edx
+ je .L33