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runtime: handle 3 and 4 bytes separately in memclrNoHeapPointers? #23930

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josharian opened this issue Feb 19, 2018 · 2 comments

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commented Feb 19, 2018

In memcpy, we separated the 3 and 4 byte cases on amd64 to allow load/store forwarding. Should we do the same in memclrNoHeapPointers? Should we generally audit the two routines to make sure they're in sync as needed, and cross-reference in docs?

Somewhat related: #23306

cc @randall77 @TocarIP

@josharian josharian added this to the Go1.11 milestone Feb 19, 2018

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commented Mar 26, 2018

I don't think so. I've tried recreating Issue18740 for memclr, but it proved to be quite difficult, memory is either cleared in bulk before allocation or memclr is inlined into single MOVL. More generally speaking it makes sense to have different implementation of memmove and memclr (at least for larger sizes), due to different memory access pattern. E. g. memmove will trash 2x cache and will stop fitting into uop cache earlier, because it needs 2x uops (extra read per each write)

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commented Mar 28, 2018

Thanks for looking into it, Ilya. Closing.

@josharian josharian closed this Mar 28, 2018

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