Switch statement optimization

[Paul Koning]

In switch statements with dense case values, the typical result is a jump table, which is fast.  If the values are sparse, a tree of compares is generated instead.

What if nearly all cases are dense but there are a few outliers?  An example appears in the NFS protocol parser, where you get a switch statement with cases for each of the opcode values.  All but one are small integers assigned in sequence, but one is 10044.  So the "sparse" case kicks in and a compare tree is generated for everything.

I can avoid this by putting in special case code for the 10044 case, then all the rest ends up being a jump table.  That brings up the question if GCC should recognize such scenarios and break up the switch statement into "dense parts" handled by a jump table, leaving the sorting between those as a compare tree.

	paul