cmd/compile: don't assume args are always zero-extended
On amd64, we always zero-extend when loading arguments from the stack.
On arm64, we extend based on the type. This causes problems with
zeroUpper*Bits, which reports the top bits are zero when they aren't.
Fix it to use the type to decide if the top bits are really zero.
For tests, only f32 currently fails on arm64. Added other tests
just for future-proofing.
Update #66066
Change-Id: I2f13fb47198e139ef13c9a34eb1edc932eea3ee3
Reviewed-on: https://go-review.googlesource.com/c/go/+/571135 Reviewed-by: Keith Randall <khr@google.com> Reviewed-by: Than McIntosh <thanm@google.com> Reviewed-by: Carlos Amedee <carlos@golang.org> Reviewed-by: David Chase <drchase@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>