Hammer Compile Freezes
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The compile has likely not actually frozen, it's actually just taking a very long time for your map to compile. Although complex maps can often take a long time to compile fully, this is usually the sign of an poorly optimized map. In general, long VVIS compile times are much easier to reduce than VRAD.
See Controlling Geometry Visibility and Compile Times for suggestions of ways to optimize your map and decrease compile times.
See Lightmap to reduce compile times.
