cmd/compile: split 3 operand LEA in late lower pass
On newer amd64 cpus 3 operand LEA instructions are slow, CL 114655 split
them to 2 LEA instructions in genssa.
This CL make late lower pass run after addressing modes, and split 3
operand LEA in late lower pass so that we can do common-subexpression
elimination for splited LEAs.
Updates #21735
Change-Id: Ied49139c7abab655e1a14a6fd793bdf9f987d1f1
Reviewed-on: https://go-review.googlesource.com/c/go/+/440035
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Wayne Zuo <wdvxdr@golangcn.org> Reviewed-by: Keith Randall <khr@golang.org> Reviewed-by: Keith Randall <khr@google.com> Reviewed-by: Joedian Reid <joedian@golang.org>