cmd/compile: add De Morgan's rewrite rule

Adds rules that rewrites statements such as ~P&~Q as ~(P|Q) and ~P|~Q as ~(P&Q), removing an extraneous instruction.

Change-Id: Icedb97df741680ddf9799df79df78657173aa500
GitHub-Last-Rev: f22e2350c95e9052e990b2351c3c2b0af810e381
GitHub-Pull-Request: golang/go#60018
Reviewed-on: https://go-review.googlesource.com/c/go/+/493175
Reviewed-by: Keith Randall <khr@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Stefan M <st3f4nm4d4@gmail.com>
Reviewed-by: Keith Randall <khr@google.com>
Run-TryBot: Cherry Mui <cherryyz@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>

1 files changed, 14 insertions, 0 deletions

diff --git a/test/codegen/logic.go b/test/codegen/logic.go
index 748c639d6b..ac33f91dad 100644
--- a/test/codegen/logic.go
+++ b/test/codegen/logic.go
@@ -25,3 +25,17 @@ func ornot(x, y int) int {
 	z := x | ^y
 	return z
 }
+
+// Verify that (OR (NOT x) (NOT y)) rewrites to (NOT (AND x y))
+func orDemorgans(x, y int) int {
+	// amd64:"AND",-"OR"
+	z := ^x | ^y
+	return z
+}
+
+// Verify that (AND (NOT x) (NOT y)) rewrites to (NOT (OR x y))
+func andDemorgans(x, y int) int {
+	// amd64:"OR",-"AND"
+	z := ^x & ^y
+	return z
+}