cmd/compile, runtime: emit only GC data for stack objects
Currently, for stack objects, the compiler emits metadata that
includes the offset and type descriptor for each object. The type
descriptor symbol has many fields, and it references many other
symbols, e.g. field/element types, equality functions, names.
Observe that what we actually need at runtime is only the GC
metadata that are needed to scan the object, and the GC metadata
are "leaf" symbols (which doesn't reference other symbols). Emit
only the GC data instead. This avoids bringing live the type
descriptor as well as things referenced by it (if it is not
otherwise live).
This reduces binary sizes:
old new
hello (println)
1187776 1133856 (-4.5%)
hello (fmt)
1902448 1844416 (-3.1%)
cmd/compile
22670432 22438576 (-1.0%)
cmd/link
6346272 6225408 (-1.9%)
No significant change in compiler speed.
name old time/op new time/op delta
Template 184ms ± 2% 186ms ± 5% ~ (p=0.905 n=9+10)
Unicode 78.4ms ± 5% 76.3ms ± 3% -2.60% (p=0.009 n=10+10)
GoTypes 1.09s ± 1% 1.08s ± 1% -0.73% (p=0.027 n=10+8)
Compiler 85.6ms ± 3% 84.6ms ± 4% ~ (p=0.143 n=10+10)
SSA 7.23s ± 1% 7.25s ± 1% ~ (p=0.780 n=10+9)
Flate 116ms ± 5% 115ms ± 6% ~ (p=0.912 n=10+10)
GoParser 201ms ± 4% 195ms ± 1% ~ (p=0.089 n=10+10)
Reflect 455ms ± 1% 458ms ± 2% ~ (p=0.050 n=9+9)
Tar 155ms ± 2% 155ms ± 3% ~ (p=0.436 n=10+10)
XML 202ms ± 2% 200ms ± 2% ~ (p=0.053 n=10+9)
Change-Id: I33a7f383d79afba1a482cac6da0cf5b7de9c0ec4
Reviewed-on: https://go-review.googlesource.com/c/go/+/313514
Trust: Cherry Zhang <cherryyz@google.com>
Reviewed-by: Than McIntosh <thanm@google.com>