cmd/compile: mark PCMPEQB as commutative

compilecmp linux/amd64:

internal/runtime/maps
internal/runtime/maps.(*table).Delete changed

internal/runtime/maps [cmd/compile]
internal/runtime/maps.(*Map).Delete changed
internal/runtime/maps.(*table).Delete changed

Change-Id: Ic3c95411c23cab7427e63105170de41e5766f809
Reviewed-on: https://go-review.googlesource.com/c/go/+/647935
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Dmitri Shuralyov <[email protected]>
Reviewed-by: Keith Randall <[email protected]>
Reviewed-by: Keith Randall <[email protected]>
Auto-Submit: Keith Randall <[email protected]>

Author: jake-ciolek

src/cmd/compile/internal/ssa/_gen/AMD64Ops.go

@@ -1156,7 +1156,7 @@ func init() {
 		//
 		// output[i] = input.
 		{name: "PSHUFBbroadcast", argLength: 1, reg: fp11, resultInArg0: true, asm: "PSHUFB"}, // PSHUFB with mask zero, (GOAMD64=v1)
-		{name: "VPBROADCASTB", argLength: 1, reg: gpfp, asm: "VPBROADCASTB"}, // Broadcast input byte from gp (GOAMD64=v3)
+		{name: "VPBROADCASTB", argLength: 1, reg: gpfp, asm: "VPBROADCASTB"},                  // Broadcast input byte from gp (GOAMD64=v3)
 
 		// Byte negate/zero/preserve (GOAMD64=v2).
 		//
@@ -1180,7 +1180,7 @@ func init() {
 		// } else {
 		//   output[i] = 0
 		// }
-		{name: "PCMPEQB", argLength: 2, reg: fp21, resultInArg0: true, asm: "PCMPEQB"},
+		{name: "PCMPEQB", argLength: 2, reg: fp21, resultInArg0: true, asm: "PCMPEQB", commutative: true},
 
 		// Byte sign mask. Output is a bitmap of sign bits from each input byte.
 		//