cmd/compile: add testing-flag guard to package-is-collected assert
On advice of the department of garbage collection, forcing a garbage
collection generally does not improve performance. However,
this-data-is-now-unreachable is a good property to be able to test,
and that requires finalizers and a forced GC. So, to save build time,
this test was removed from the compiler itself, but to verify the
property, it was added to the fma_test (and the end-to-end dependence
on the flag was tested with an inserted failure in testing the
test).
TODO: also turn on the new -d=gccheck=1 debug flag on the ssacheck
builder.
Benchmarking reveals that it is profitable to avoid this GC,
with about 1.5% reduction in both user and wall time.
(48 p) https://perf.golang.org/search?q=upload:
20221103.3
(12 p) https://perf.golang.org/search?q=upload:
20221103.5
Change-Id: I4c4816d619735838a32388acf0cc5eb1cd5f0db5
Reviewed-on: https://go-review.googlesource.com/c/go/+/447359
Reviewed-by: Cherry Mui <cherryyz@google.com>
Run-TryBot: David Chase <drchase@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>