Optimize IsTileSafe

Add dungeon flags for Fire/Lightning Wall and use them to check if the
monster considers the tile safe.

Source/levels/gendung.h

@@ -84,16 +84,17 @@ enum lvl_entry : uint8_t {
 
 enum class DungeonFlag : uint8_t {
 	// clang-format off
-	None        = 0, // Only used by lighting/automap
-	Missile     = 1 << 0,
-	Visible     = 1 << 1,
-	DeadPlayer  = 1 << 2,
-	Populated   = 1 << 3,
-	// 1 << 4 and 1 << 5 were used as workarounds for a bug with horizontal movement (relative to the screen) for monsters and players respectively
-	Lit         = 1 << 6,
-	Explored    = 1 << 7,
-	SavedFlags  = (Populated | Lit | Explored), // ~(Missile | Visible | DeadPlayer)
-	LoadedFlags = (Missile | Visible | DeadPlayer | Populated | Lit | Explored)
+	None                  = 0, // Only used by lighting/automap
+	Missile               = 1 << 0,
+	Visible               = 1 << 1,
+	DeadPlayer            = 1 << 2,
+	Populated             = 1 << 3,
+	MissileFireWall       = 1 << 4,
+	MissileLightningWall  = 1 << 5,
+	Lit                   = 1 << 6,
+	Explored              = 1 << 7,
+	SavedFlags            = (Populated | Lit | Explored), // ~(Missile | Visible | DeadPlayer)
+	LoadedFlags           = (Missile | Visible | DeadPlayer | Populated | Lit | Explored)
 	// clang-format on
 };
 use_enum_as_flags(DungeonFlag);

Source/missiles.cpp

@@ -131,7 +131,12 @@ void PutMissile(Missile &missile)
 		return;
 	}
 
-	dFlags[position.x][position.y] |= DungeonFlag::Missile;
+	DungeonFlag &flags = dFlags[position.x][position.y];
+	flags |= DungeonFlag::Missile;
+	if (missile._mitype == MIS_FIREWALL)
+		flags |= DungeonFlag::MissileFireWall;
+	if (missile._mitype == MIS_LIGHTWALL)
+		flags |= DungeonFlag::MissileLightningWall;
 
 	if (missile._miPreFlag)
 		MissilePreFlag = true;
@@ -1107,7 +1112,7 @@ void InitMissiles()
 	Missiles.clear();
 	for (int j = 0; j < MAXDUNY; j++) {
 		for (int i = 0; i < MAXDUNX; i++) { // NOLINT(modernize-loop-convert)
-			dFlags[i][j] &= ~DungeonFlag::Missile;
+			dFlags[i][j] &= ~(DungeonFlag::Missile | DungeonFlag::MissileFireWall | DungeonFlag::MissileLightningWall);
 		}
 	}
 }
@@ -4070,7 +4075,7 @@ void ProcessMissiles()
 	for (auto &missile : Missiles) {
 		const auto &position = missile.position.tile;
 		if (InDungeonBounds(position)) {
-			dFlags[position.x][position.y] &= ~DungeonFlag::Missile;
+			dFlags[position.x][position.y] &= ~(DungeonFlag::Missile | DungeonFlag::MissileFireWall | DungeonFlag::MissileLightningWall);
 		} else {
 			missile._miDelFlag = true;
 		}

Source/monster.cpp

@@ -1685,25 +1685,14 @@ bool RandomWalk2(Monster &monster, Direction md)
  */
 bool IsTileSafe(const Monster &monster, Point position)
 {
-	if (!TileContainsMissile(position)) {
-		return true;
-	}
+	if (!InDungeonBounds(position))
+		return false;
 
-	bool fearsFire = (monster.resistance & IMMUNE_FIRE) == 0 || monster.type().type == MT_DIABLO;
-	bool fearsLightning = (monster.resistance & IMMUNE_LIGHTNING) == 0 || monster.type().type == MT_DIABLO;
+	const bool fearsFire = (monster.resistance & IMMUNE_FIRE) == 0 || monster.type().type == MT_DIABLO;
+	const bool fearsLightning = (monster.resistance & IMMUNE_LIGHTNING) == 0 || monster.type().type == MT_DIABLO;
 
-	for (auto &missile : Missiles) {
-		if (missile.position.tile == position) {
-			if (fearsFire && missile._mitype == MIS_FIREWALL) {
-				return false;
-			}
-			if (fearsLightning && missile._mitype == MIS_LIGHTWALL) {
-				return false;
-			}
-		}
-	}
-
-	return true;
+	return !(fearsFire && HasAnyOf(dFlags[position.x][position.y], DungeonFlag::MissileFireWall))
+	    && !(fearsLightning && HasAnyOf(dFlags[position.x][position.y], DungeonFlag::MissileLightningWall));
 }
 
 /**