This patch adds a function that allows to directly properly size an xarray
when the size is known in advance.

3 places identified where this function can be used trivially.

The result is a reduction of 'realloc' operations in core
arena, and a small reduction in ttaux arena
(it is the nr of operations that decreases, the memory usage itself
stays the same (ignoring some 'rounding' effects).

E.g. for perf/bigcode 0, we change from
  core 1085742/ 216745904 totalloc-blocks/bytes,     1085733 searches
  ttaux 5348/   6732560 totalloc-blocks/bytes,        5326 searches
  core 712666/ 190998592 totalloc-blocks/bytes,      712657 searches
  ttaux 5319/   6731808 totalloc-blocks/bytes,        5296 searches

For bz2, we switch from
  core 50285/  32383664 totalloc-blocks/bytes,       50256 searches
  ttaux 670/    245160 totalloc-blocks/bytes,         669 searches
  core 32564/  29971984 totalloc-blocks/bytes,       32535 searches
  ttaux 605/    243280 totalloc-blocks/bytes,         604 searches

Performance wise, on amd64, this improves memcheck performance
on perf tests by 0.0, 0.1 or 0.2 seconds depending on the test.

git-svn-id: svn:// a5019735-40e9-0310-863c-91ae7b9d1cf9
4 files changed