cmd/compile: add rule to use ANDN for a&^b on ppc64x

Adds a rule to generate ANDN for AND x ^y.

Fixes #17567

Change-Id: I3b978058d5663f32c42b1af19bb207eac5622615
Reviewed-on: https://go-review.googlesource.com/31769
Run-TryBot: Lynn Boger <laboger@linux.vnet.ibm.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>

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

@@ -267,6 +267,9 @@
 (OrB x y) -> (OR x y)
 (Not x) -> (XORconst [1] x)
 
+// Use ANDN for AND x NOT y
+(AND x (XORconst [-1] y)) -> (ANDN x y)
+
 // Lowering comparisons
 (EqB x y)  -> (ANDconst [1] (EQV x y))
 // Sign extension dependence on operand sign sets up for sign/zero-extension elision later

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

@@ -4471,6 +4471,24 @@ func rewriteValuePPC64_OpPPC64ADDconst(v *Value, config *Config) bool {
 func rewriteValuePPC64_OpPPC64AND(v *Value, config *Config) bool {
 	b := v.Block
 	_ = b
+	// match: (AND x (XORconst [-1] y))
+	// cond:
+	// result: (ANDN x y)
+	for {
+		x := v.Args[0]
+		v_1 := v.Args[1]
+		if v_1.Op != OpPPC64XORconst {
+			break
+		}
+		if v_1.AuxInt != -1 {
+			break
+		}
+		y := v_1.Args[0]
+		v.reset(OpPPC64ANDN)
+		v.AddArg(x)
+		v.AddArg(y)
+		return true
+	}
 	// match: (AND (MOVDconst [c]) (MOVDconst [d]))
 	// cond:
 	// result: (MOVDconst [c&d])