cmd/compile: combine OR + NOT into ORN on PPC64

This shows up in a few crypto functions, and other
assorted places.

Change-Id: I5a7f4c25ddd4a6499dc295ef693b9fe43d2448ab
Reviewed-on: https://go-review.googlesource.com/c/go/+/404057
Run-TryBot: Paul Murphy <murp@ibm.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Lynn Boger <laboger@linux.vnet.ibm.com>
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Russ Cox <rsc@golang.org>

src/cmd/compile/internal/ssa/gen/PPC64.rules

@@ -381,8 +381,9 @@
 (OrB ...) => (OR ...)
 (Not x) => (XORconst [1] x)
 
-// Use ANDN for AND x NOT y
+// Merge logical operations
 (AND x (NOR y y)) => (ANDN x y)
+(OR x (NOR y y)) => (ORN x y)
 
 // Lowering comparisons
 (EqB x y)  => (ANDconst [1] (EQV x y))

src/cmd/compile/internal/ssa/rewritePPC64.go

@@ -11687,6 +11687,24 @@ func rewriteValuePPC64_OpPPC64OR(v *Value) bool {
 		}
 		break
 	}
+	// match: (OR x (NOR y y))
+	// result: (ORN x y)
+	for {
+		for _i0 := 0; _i0 <= 1; _i0, v_0, v_1 = _i0+1, v_1, v_0 {
+			x := v_0
+			if v_1.Op != OpPPC64NOR {
+				continue
+			}
+			y := v_1.Args[1]
+			if y != v_1.Args[0] {
+				continue
+			}
+			v.reset(OpPPC64ORN)
+			v.AddArg2(x, y)
+			return true
+		}
+		break
+	}
 	// match: (OR (MOVDconst [c]) (MOVDconst [d]))
 	// result: (MOVDconst [c|d])
 	for {

test/codegen/logic.go

@@ -22,3 +22,11 @@ func andWithUse(x, y int) int {
 	// use z by returning it
 	return z
 }
+
+// Verify (OR x (NOT y)) rewrites to (ORN x y) where supported
+func ornot(x, y int) int {
+	// ppc64:"ORN"
+	// ppc64le:"ORN"
+	z := x | ^y
+	return z
+}