internal/runtime/maps: hash copy of key instead of key itself
Hashing the key means we have to take the address of it. That inhibits
subsequent optimizations on the key variable.
By hashing a copy, we incur an extra store at the hash callsite, but
we no longer need a load of the key in the inner loop. It can live
in a register throughout. (Technically, it gets spilled around
the call to the hasher, but it gets restored outside the loop.)
Maybe one day we can have special hash functions that take
int64/int32/string instead of *int64/*int32/*string.
Change-Id: Iba3133f6e82328f53c0abcb5eec13ee47c4969d1
Reviewed-on: https://go-review.googlesource.com/c/go/+/629419 Reviewed-by: Russ Cox <rsc@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: Michael Pratt <mpratt@google.com>