file-cache-filter-regexps

file-cache-filter-regexps is a variable defined in `filecache.el'.
Its value is

("~$" "\\.o$" "\\.exe$" "\\.a$" "\\.elc$" ",v$" "\\.output$" "\\.$" "#$" "\\.class$")

Documentation:
List of regular expressions used as filters by the file cache.
File names which match these expressions will not be added to the cache.
Note that the functions `file-cache-add-file' and `file-cache-add-file-list'
do not use this variable.

You can customize this variable.