tree 652724a2410e05b7ce359770405b476feaa536c1
parent 4f21e8a96366a3e1708a4fdc25bcb6a80fe15cf4
author Jorropo <jorropo.pgm@gmail.com> 1786596094 +0200
committer Jorropo <jorropo.pgm@gmail.com> 1788329640 -0700

cmd/compile: teach known bits to remove no-op or

This does not trigger when building the std nor cmd.

This code looks very 1:1 with code already existing in prove's
simplifyValue method.
However known bits can catch cases prove misses because prove doesn't
support the 1 | ? entry (where ? is the no-op argument being removed).

This is important as it allows to optimize no-op ors when neither
argument is const, but where one argument is completely shadowed.

Prove's blind spot exists because prove will never have a known
LSB after an unkown MSB.
This means the 0 | ? case can never be proven by prove since it
implies either both arguments are const (will be handled by
generic.rules) or there must be a ? | ? case at the LSB.

Change-Id: I33b3631774341beb62d5235c8bc82a6f2504d824
Reviewed-on: https://go-review.googlesource.com/c/go/+/814341
LUCI-TryBot-Result: golang-scoped@luci-project-accounts.iam.gserviceaccount.com <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Michael Pratt <mpratt@google.com>