cmd/compile: Add some CMP and CMN optimization rules on arm64
This CL adds some optimizaion rules:
1, Converts CMP to CMN, or vice versa, when comparing with a negative
number.
2, For equal and not equal comparisons, CMP can be converted to CMN in
some cases. In theory we could do the same optimization for LT, LE, GT
and GE, but need to account for overflow, this CL doesn't handle them.
There are no noticeable performance changes.
Change-Id: Ia49266c019ab7908ebc9510c2f02e121b1607869
Reviewed-on: https://go-review.googlesource.com/c/go/+/429795 Reviewed-by: Keith Randall <khr@golang.org> Reviewed-by: Keith Randall <khr@google.com> Reviewed-by: Cherry Mui <cherryyz@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Eric Fang <eric.fang@arm.com>