The tables in the BSD tolower/toupper are slower for ASCII than just
doing the bit twiddling.
We can't actually remove the tables on LP32, so move them into the
"cruft" we keep around for backwards compatibility (but remove them for
LP64 where they were never exposed).
I noticed that the new bit-twiddling tolower(3) was performing better
on arm64 than toupper(3). The 0xdf constant was requiring an extra MOV,
and there isn't a BIC that takes an immediate value. Since we've already
done the comparison to check that we're in the right range (where the
bit is always set), though, we can EOR 0x20 to get the same result as
the missing BIC 0x20 in just one instruction.
I've applied that same optimization to towupper(3) too.
Before:
BM_ctype_tolower_n 3.30 ns 3.30 ns 212353035
BM_ctype_tolower_y 3.31 ns 3.30 ns 211234204
BM_ctype_toupper_n 3.30 ns 3.29 ns 214161246
BM_ctype_toupper_y 3.29 ns 3.28 ns 207643473
BM_wctype_towupper_ascii_n 3.53 ns 3.53 ns 195944444
BM_wctype_towupper_ascii_y 3.48 ns 3.48 ns 199233248
After:
BM_ctype_tolower_n 2.93 ns 2.92 ns 242373703
BM_ctype_tolower_y 2.88 ns 2.87 ns 245365309
BM_ctype_toupper_n 2.93 ns 2.93 ns 243049353
BM_ctype_toupper_y 2.89 ns 2.89 ns 245072521
BM_wctype_towupper_ascii_n 3.34 ns 3.33 ns 212951912
BM_wctype_towupper_ascii_y 3.29 ns 3.29 ns 214651254
(Why do both the "y" and "n" variants speed up with the EOR
change? Because the compiler transforms the code so that we
unconditionally do the bit twiddling and then use CSEL to decide whether
or not to actually use the result.)
We also save 1028 bytes of data in the LP64 libc.so.
Test: ran the bionic benchmarks and tests
Change-Id: I7829339f8cb89a58efe539c2a01c51807413aa2d
