Merge pull request #2804 from smoogipoo/mania-keymod-optimisation

Don't compute keymod difficulties for mania-specific beatmap

osu.Game.Rulesets.Mania/Difficulty/ManiaDifficultyCalculator.cs

@@ -29,9 +29,12 @@ namespace osu.Game.Rulesets.Mania.Difficulty
         /// </summary>
         private const double decay_weight = 0.9;
 
+        private readonly bool isForCurrentRuleset;
+
         public ManiaDifficultyCalculator(Ruleset ruleset, WorkingBeatmap beatmap)
             : base(ruleset, beatmap)
         {
+            isForCurrentRuleset = beatmap.BeatmapInfo.Ruleset.Equals(ruleset.RulesetInfo);
         }
 
         protected override DifficultyAttributes Calculate(IBeatmap beatmap, Mod[] mods, double timeRate)
@@ -129,12 +132,24 @@ namespace osu.Game.Rulesets.Mania.Difficulty
             return difficulty;
         }
 
-        protected override Mod[] DifficultyAdjustmentMods => new Mod[]
+        protected override Mod[] DifficultyAdjustmentMods
+        {
+            get
+            {
+                var mods = new Mod[]
                 {
                     new ManiaModDoubleTime(),
                     new ManiaModHalfTime(),
                     new ManiaModEasy(),
                     new ManiaModHardRock(),
+                };
+
+                if (isForCurrentRuleset)
+                    return mods;
+
+                // if we are a convert, we can be played in any key mod.
+                return mods.Concat(new Mod[]
+                {
                     new ManiaModKey1(),
                     new ManiaModKey2(),
                     new ManiaModKey3(),
@@ -144,7 +159,8 @@ namespace osu.Game.Rulesets.Mania.Difficulty
                     new ManiaModKey7(),
                     new ManiaModKey8(),
                     new ManiaModKey9(),
-        };
+                }).ToArray();
-
+            }
+        }
     }
 }