cmd/cgo,cmd/go: preallocate slices if they have known fixed capacities
This allows for more efficient use of memory.
Change-Id: I16f399a25c23b804e55289ca055fa83ea9862f16
GitHub-Last-Rev:
19bb96a7cf4d27c085cfdb074905c4bf34eb660d
GitHub-Pull-Request: golang/go#69841
Reviewed-on: https://go-review.googlesource.com/c/go/+/618960
Auto-Submit: Ian Lance Taylor <iant@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Michael Matloob <matloob@golang.org>