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Keith Randall authored
mapaccess{1,2} returns a pointer to the value. When the key is not in the map, it returns a pointer to zeroed memory. Currently, for large map values we have a complicated scheme which dynamically allocates zeroed memory for this purpose. It is ugly code and requires an atomic.Load in a bunch of places we'd rather not have it. Switch to a scheme where callsites of mapaccess{1,2} which expect large return values pass in a pointer to zeroed memory that mapaccess can return if the key is not found. This avoids the atomic.Load on all map accesses with a few extra instructions only for the large value acccesses, plus a bit of bss space. There was a time (1.4 & 1.5?) where we did something like this but all the tricks to make the right size zero value were done by the linker. That scheme broke in the presence of dyamic linking. The scheme in this CL works even when dynamic linking. Fixes #12337 Change-Id: Ic2d0319944af33bbb59785938d9ab80958d1b4b1 Reviewed-on: https://go-review.googlesource.com/22221 Run-TryBot: Keith Randall <khr@golang.org> TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by:
Michael Hudson-Doyle <michael.hudson@canonical.com>
60fd32a4
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