cmd/compile/internal/ssa: optimize (AND (MOVDconst [-1] x)) on PPC64
This sequence can show up in the lowering pass on PPC64. If it
makes it to the latelower pass, it will cause an error because
it looks like it can be turned into RLDICL, but -1 isn't an
accepted mask.
Also, print more debug info if panic is called from
encodePPC64RotateMask.
Fixes #62698
Change-Id: I0f3322e2205357abe7fc28f96e05e3f7ad65567c
Reviewed-on: https://go-review.googlesource.com/c/go/+/529195 Reviewed-by: Lynn Boger <laboger@linux.vnet.ibm.com>
Run-TryBot: Paul Murphy <murp@ibm.com>
TryBot-Result: Gopher Robot <gobot@golang.org> Reviewed-by: Matthew Dempsky <mdempsky@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: Cherry Mui <cherryyz@google.com>