ASCII fastpath for towupper and towlower.

This change elides unnecessary calls to __find_icu_symbol
for ASCII chars and improves PUBG mobile game loading time by 7% on
hikey620(Cortex-A53):

name                old time/op  new time/op  delta
PUBG_0.13.0_Launch   41.5s ± 2%   37.7s ± 3%  -9.24%  (p=0.008 n=5+5)

Below are the bionic benchmark results on a Pixel 2 XL for 64-bit,
showing a large speedup for ASCII and only a small slowdown for non-ASCII.

Before:

  BM_wctype_towlower_ascii_n         10.5 ns         10.4 ns     61973065
  BM_wctype_towlower_ascii_y         10.2 ns         10.2 ns     70158659
  BM_wctype_towlower_unicode_n       10.3 ns         10.3 ns     67719478
  BM_wctype_towlower_unicode_y       10.6 ns         10.5 ns     67841545
  BM_wctype_towupper_ascii_n         10.8 ns         10.8 ns     63456778
  BM_wctype_towupper_ascii_y         10.9 ns         10.9 ns     65116910
  BM_wctype_towupper_unicode_n       10.7 ns         10.7 ns     67463276
  BM_wctype_towupper_unicode_y       10.4 ns         10.4 ns     66467890

After:

  BM_wctype_towlower_ascii_n         3.35 ns         3.34 ns    205567652
  BM_wctype_towlower_ascii_y         3.30 ns         3.29 ns    214108746
  BM_wctype_towlower_unicode_n       10.9 ns         10.8 ns     65007743
  BM_wctype_towlower_unicode_y       10.6 ns         10.6 ns     63819060
  BM_wctype_towupper_ascii_n         3.53 ns         3.53 ns    195944444
  BM_wctype_towupper_ascii_y         3.48 ns         3.48 ns    199233248
  BM_wctype_towupper_unicode_n       11.1 ns         11.1 ns     62760216
  BM_wctype_towupper_unicode_y       11.0 ns         11.0 ns     61608872

Test: bionic unit tests on device
Test: bionic benchmarks on device
Signed-off-by: Balaram Makam <b.makam@samsung.com>
Change-Id: I77ab7efb66d7bcb35d00467663607535e5c1992f

0 files changed, 0 insertions, 0 deletions