target-sh4: optimize swap.w

It's possible swap the two 16-bit words of a 32-bit register using a
rotation. If the TCG target doesn't implement rotation, the replacement
code is similar to the previously implemented code.
Signed-off-by: NAurelien Jarno <aurelien@aurel32.net>

target-sh4/translate.c

@@ -732,17 +732,7 @@ static void _decode_opc(DisasContext * ctx)
 	}
 	return;
     case 0x6009:		/* swap.w Rm,Rn */
-	{
-	    TCGv high, low;
-	    high = tcg_temp_new();
-	    tcg_gen_shli_i32(high, REG(B7_4), 16);
-	    low = tcg_temp_new();
-	    tcg_gen_shri_i32(low, REG(B7_4), 16);
-	    tcg_gen_ext16u_i32(low, low);
-	    tcg_gen_or_i32(REG(B11_8), high, low);
-	    tcg_temp_free(low);
-	    tcg_temp_free(high);
-	}
+        tcg_gen_rotli_i32(REG(B11_8), REG(B7_4), 16);
 	return;
     case 0x200d:		/* xtrct Rm,Rn */
 	{