[dev.link] cmd/link: reduce memory usage for storing symbol section information
Currently, we use a dense array to store symbol's sections. The
array element is a *sym.Section, which takes 8 bytes per symbol
on a 64-bit machine. And the array is created upfront.
To reduce memory usage, use a 16-bit index for sections, so we
store 2 bytes per symbol. The array is pointerless, reducing GC
work. Also create the array lazily.
This reduces some memory usage: linking cmd/compile,
name old alloc/op new alloc/op delta
Loadlib_GC 42.1MB ± 0% 36.2MB ± 0% -14.01% (p=0.008 n=5+5)
name old live-B new live-B delta
Loadlib_GC 16.8M ± 0% 15.4M ± 0% -8.36% (p=0.008 n=5+5)
Archive_GC 98.2M ± 0% 97.2M ± 0% -1.02% (p=0.008 n=5+5) # at the end
Change-Id: If8c41eded8859660bca648c5e6fdf5830810fbf6
Reviewed-on: https://go-review.googlesource.com/c/go/+/229306 Reviewed-by: Than McIntosh <thanm@google.com> Reviewed-by: Jeremy Faller <jeremy@golang.org>