In reference to this on the wiki.
Bitmaps, also called sparse bit sets, are implemented
using a linked list with a cache. This is probably not
the most time-efficient representation, and it is not
unusual for bitmap functions to show up high on the
execution profile. Bitmaps are used for many things,
such as for live register sets at the entry and exit
of basic blocks in RTL, or for a great number of data
flow problems. See bitmap.c (and sbitmap.c for GCC's
simple bitmap implementation).
Can someone point me to a testcase where bitmap
functions show up high on the profile?
Can anyone give me some background on the use of
bitmaps in gcc?
Are they assumed to be sparse?
How critical is the memory consumption of bitsets?
What operations are the most speed critical?
Would it be desirable to merge bitmap and sbitmap into
one datastructure?
Anyone have good ideas for improvements?
Anything else anyone would want to add?
I think I may take a look at this. Once I figure out
the requirments maybe we can speed it up a bit.
Brian N. Makin
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