strings,bytes: avoid allocations in Trim/TrimLeft/TrimRight

strings,bytes: avoid allocations in Trim/TrimLeft/TrimRight

There is evidence that the vast majority of uses for Trim* involve
cutsets with a single ASCII character, and the vast majority of
remaining uses involve cutsets with a small (<4) ASCII characters.
For this reason it makes sense to provide better fast paths for these
common cases.

Furthermore the current implementation needlessly allocates for unclear
benefits. This CL also replaces all paths to avoid allocations and, as
a side effect, it speeds up also the slow path.

strings:
name                    old time/op    new time/op    delta
Trim                      1.71µs ± 1%    0.70µs ± 0%   -58.93%  (p=0.008 n=5+5)
TrimASCII/1:1             6.43ns ± 0%    6.34ns ± 0%    -1.41%  (p=0.008 n=5+5)
TrimASCII/1:2             97.3ns ± 0%    18.2ns ± 1%   -81.34%  (p=0.008 n=5+5)
TrimASCII/1:4              101ns ± 0%      21ns ± 0%   -78.77%  (p=0.008 n=5+5)
TrimASCII/1:8              109ns ± 0%      29ns ± 0%   -73.60%  (p=0.008 n=5+5)
TrimASCII/1:16             124ns ± 0%      43ns ± 0%   -65.16%  (p=0.008 n=5+5)
TrimASCII/16:1            19.8ns ± 0%    18.6ns ± 0%    -5.90%  (p=0.008 n=5+5)
TrimASCII/16:2             167ns ± 0%      33ns ± 0%   -80.21%  (p=0.008 n=5+5)
TrimASCII/16:4             169ns ± 0%      35ns ± 0%   -79.01%  (p=0.008 n=5+5)
TrimASCII/16:8             177ns ± 0%      43ns ± 0%   -75.88%  (p=0.008 n=5+5)
TrimASCII/16:16            193ns ± 2%      57ns ± 1%   -70.30%  (p=0.008 n=5+5)
TrimASCII/256:1            232ns ± 0%     232ns ± 0%      ~     (p=1.000 n=5+5)
TrimASCII/256:2           1.28µs ± 1%    0.26µs ± 0%   -79.46%  (p=0.008 n=5+5)
TrimASCII/256:4           1.27µs ± 0%    0.27µs ± 0%   -78.95%  (p=0.008 n=5+5)
TrimASCII/256:8           1.28µs ± 0%    0.28µs ± 1%   -78.28%  (p=0.008 n=5+5)
TrimASCII/256:16          1.30µs ± 1%    0.29µs ± 0%   -77.49%  (p=0.008 n=5+5)
TrimASCII/4096:1          3.47µs ± 0%    3.47µs ± 0%    -0.14%  (p=0.008 n=5+5)
TrimASCII/4096:2          18.2µs ± 0%     3.9µs ± 0%   -78.53%  (p=0.008 n=5+5)
TrimASCII/4096:4          18.2µs ± 0%     3.9µs ± 0%   -78.55%  (p=0.008 n=5+5)
TrimASCII/4096:8          18.2µs ± 0%     3.9µs ± 0%   -78.49%  (p=0.008 n=5+5)
TrimASCII/4096:16         18.3µs ± 0%     3.9µs ± 0%   -78.44%  (p=0.008 n=5+5)
TrimByte                  10.6ns ± 1%    10.1ns ± 0%    -5.01%  (p=0.008 n=5+5)
TrimSpace/NoTrim          5.90ns ± 0%    5.89ns ± 0%      ~     (p=0.135 n=5+5)
TrimSpace/ASCII           10.6ns ± 0%     9.9ns ± 0%    -6.21%  (p=0.008 n=5+5)
TrimSpace/SomeNonASCII     127ns ± 0%     126ns ± 0%    -0.96%  (p=0.008 n=5+5)
TrimSpace/JustNonASCII     178ns ± 0%     178ns ± 0%      ~     (p=0.825 n=5+4)

name                    old alloc/op   new alloc/op   delta
Trim                        456B ± 0%        0B       -100.00%  (p=0.008 n=5+5)
TrimASCII/1:1              0.00B          0.00B           ~     (all equal)
TrimASCII/1:2              48.0B ± 0%      0.0B       -100.00%  (p=0.008 n=5+5)
TrimASCII/1:4              48.0B ± 0%      0.0B       -100.00%  (p=0.008 n=5+5)
TrimASCII/1:8              48.0B ± 0%      0.0B       -100.00%  (p=0.008 n=5+5)
TrimASCII/1:16             48.0B ± 0%      0.0B       -100.00%  (p=0.008 n=5+5)
TrimASCII/16:1             0.00B          0.00B           ~     (all equal)
TrimASCII/16:2             48.0B ± 0%      0.0B       -100.00%  (p=0.008 n=5+5)
TrimASCII/16:4             48.0B ± 0%      0.0B       -100.00%  (p=0.008 n=5+5)
TrimASCII/16:8             48.0B ± 0%      0.0B       -100.00%  (p=0.008 n=5+5)
TrimASCII/16:16            48.0B ± 0%      0.0B       -100.00%  (p=0.008 n=5+5)
TrimASCII/256:1            0.00B          0.00B           ~     (all equal)
TrimASCII/256:2            48.0B ± 0%      0.0B       -100.00%  (p=0.008 n=5+5)
TrimASCII/256:4            48.0B ± 0%      0.0B       -100.00%  (p=0.008 n=5+5)
TrimASCII/256:8            48.0B ± 0%      0.0B       -100.00%  (p=0.008 n=5+5)
TrimASCII/256:16           48.0B ± 0%      0.0B       -100.00%  (p=0.008 n=5+5)
TrimASCII/4096:1           0.00B          0.00B           ~     (all equal)
TrimASCII/4096:2           48.0B ± 0%      0.0B       -100.00%  (p=0.008 n=5+5)
TrimASCII/4096:4           48.0B ± 0%      0.0B       -100.00%  (p=0.008 n=5+5)
TrimASCII/4096:8           48.0B ± 0%      0.0B       -100.00%  (p=0.008 n=5+5)
TrimASCII/4096:16          48.0B ± 0%      0.0B           ~     (p=0.079 n=4+5)
TrimByte                   0.00B          0.00B           ~     (all equal)
TrimSpace/NoTrim           0.00B          0.00B           ~     (all equal)
TrimSpace/ASCII            0.00B          0.00B           ~     (all equal)
TrimSpace/SomeNonASCII     0.00B          0.00B           ~     (all equal)
TrimSpace/JustNonASCII     0.00B          0.00B           ~     (all equal)

name                    old allocs/op  new allocs/op  delta
Trim                        18.0 ± 0%       0.0       -100.00%  (p=0.008 n=5+5)
TrimASCII/1:1               0.00           0.00           ~     (all equal)
TrimASCII/1:2               2.00 ± 0%      0.00       -100.00%  (p=0.008 n=5+5)
TrimASCII/1:4               2.00 ± 0%      0.00       -100.00%  (p=0.008 n=5+5)
TrimASCII/1:8               2.00 ± 0%      0.00       -100.00%  (p=0.008 n=5+5)
TrimASCII/1:16              2.00 ± 0%      0.00       -100.00%  (p=0.008 n=5+5)
TrimASCII/16:1              0.00           0.00           ~     (all equal)
TrimASCII/16:2              2.00 ± 0%      0.00       -100.00%  (p=0.008 n=5+5)
TrimASCII/16:4              2.00 ± 0%      0.00       -100.00%  (p=0.008 n=5+5)
TrimASCII/16:8              2.00 ± 0%      0.00       -100.00%  (p=0.008 n=5+5)
TrimASCII/16:16             2.00 ± 0%      0.00       -100.00%  (p=0.008 n=5+5)
TrimASCII/256:1             0.00           0.00           ~     (all equal)
TrimASCII/256:2             2.00 ± 0%      0.00       -100.00%  (p=0.008 n=5+5)
TrimASCII/256:4             2.00 ± 0%      0.00       -100.00%  (p=0.008 n=5+5)
TrimASCII/256:8             2.00 ± 0%      0.00       -100.00%  (p=0.008 n=5+5)
TrimASCII/256:16            2.00 ± 0%      0.00       -100.00%  (p=0.008 n=5+5)
TrimASCII/4096:1            0.00           0.00           ~     (all equal)
TrimASCII/4096:2            2.00 ± 0%      0.00       -100.00%  (p=0.008 n=5+5)
TrimASCII/4096:4            2.00 ± 0%      0.00       -100.00%  (p=0.008 n=5+5)
TrimASCII/4096:8            2.00 ± 0%      0.00       -100.00%  (p=0.008 n=5+5)
TrimASCII/4096:16           2.00 ± 0%      0.00       -100.00%  (p=0.008 n=5+5)
TrimByte                    0.00           0.00           ~     (all equal)
TrimSpace/NoTrim            0.00           0.00           ~     (all equal)
TrimSpace/ASCII             0.00           0.00           ~     (all equal)
TrimSpace/SomeNonASCII      0.00           0.00           ~     (all equal)
TrimSpace/JustNonASCII      0.00           0.00           ~     (all equal)

bytes:
name                    old time/op    new time/op    delta
TrimSpace/NoTrim          5.89ns ± 0%    5.91ns ± 0%      ~     (p=0.095 n=5+4)
TrimSpace/ASCII           10.3ns ± 1%    10.2ns ± 0%      ~     (p=0.095 n=5+5)
TrimSpace/SomeNonASCII     120ns ± 1%     121ns ± 0%    +1.13%  (p=0.008 n=5+5)
TrimSpace/JustNonASCII     194ns ± 1%     195ns ± 0%      ~     (p=0.143 n=5+5)
TrimASCII/1:1             6.28ns ± 0%    5.95ns ± 0%    -5.26%  (p=0.008 n=5+5)
TrimASCII/1:2             95.8ns ± 1%    18.6ns ± 0%   -80.63%  (p=0.008 n=5+5)
TrimASCII/1:4             98.8ns ± 0%    22.1ns ± 0%   -77.62%  (p=0.008 n=5+5)
TrimASCII/1:8              107ns ± 0%      29ns ± 0%   -72.72%  (p=0.008 n=5+5)
TrimASCII/1:16             123ns ± 0%      44ns ± 1%   -64.30%  (p=0.008 n=5+5)
TrimASCII/16:1            13.2ns ± 0%    12.8ns ± 1%    -2.75%  (p=0.008 n=5+5)
TrimASCII/16:2             169ns ± 0%      33ns ± 0%   -80.33%  (p=0.008 n=5+5)
TrimASCII/16:4             173ns ± 0%      36ns ± 0%   -79.31%  (p=0.008 n=5+5)
TrimASCII/16:8             180ns ± 0%      43ns ± 0%   -76.02%  (p=0.008 n=5+5)
TrimASCII/16:16            197ns ± 2%      58ns ± 0%   -70.73%  (p=0.008 n=5+5)
TrimASCII/256:1            137ns ± 1%     136ns ± 0%    -0.82%  (p=0.016 n=5+5)
TrimASCII/256:2           1.40µs ± 0%    0.26µs ± 0%   -81.02%  (p=0.008 n=5+5)
TrimASCII/256:4           1.40µs ± 0%    0.27µs ± 0%   -80.83%  (p=0.008 n=5+5)
TrimASCII/256:8           1.41µs ± 0%    0.28µs ± 0%   -80.36%  (p=0.008 n=5+5)
TrimASCII/256:16          1.42µs ± 0%    0.29µs ± 0%   -79.48%  (p=0.008 n=5+5)
TrimASCII/4096:1          1.75µs ± 0%    1.75µs ± 0%      ~     (p=0.595 n=5+5)
TrimASCII/4096:2          20.9µs ± 0%     3.9µs ± 0%   -81.29%  (p=0.008 n=5+5)
TrimASCII/4096:4          20.9µs ± 0%     3.9µs ± 0%   -81.27%  (p=0.008 n=5+5)
TrimASCII/4096:8          20.9µs ± 0%     3.9µs ± 0%   -81.22%  (p=0.008 n=5+5)
TrimASCII/4096:16         20.9µs ± 0%     3.9µs ± 0%   -81.21%  (p=0.008 n=5+5)
TrimByte                  9.21ns ± 0%    9.30ns ± 0%    +0.91%  (p=0.008 n=5+5)

name                    old alloc/op   new alloc/op   delta
TrimSpace/NoTrim           0.00B          0.00B           ~     (all equal)
TrimSpace/ASCII            0.00B          0.00B           ~     (all equal)
TrimSpace/SomeNonASCII     0.00B          0.00B           ~     (all equal)
TrimSpace/JustNonASCII     0.00B          0.00B           ~     (all equal)
TrimASCII/1:1              0.00B          0.00B           ~     (all equal)
TrimASCII/1:2              48.0B ± 0%      0.0B       -100.00%  (p=0.008 n=5+5)
TrimASCII/1:4              48.0B ± 0%      0.0B       -100.00%  (p=0.008 n=5+5)
TrimASCII/1:8              48.0B ± 0%      0.0B       -100.00%  (p=0.008 n=5+5)
TrimASCII/1:16             48.0B ± 0%      0.0B       -100.00%  (p=0.008 n=5+5)
TrimASCII/16:1             0.00B          0.00B           ~     (all equal)
TrimASCII/16:2             48.0B ± 0%      0.0B       -100.00%  (p=0.008 n=5+5)
TrimASCII/16:4             48.0B ± 0%      0.0B       -100.00%  (p=0.008 n=5+5)
TrimASCII/16:8             48.0B ± 0%      0.0B       -100.00%  (p=0.008 n=5+5)
TrimASCII/16:16            48.0B ± 0%      0.0B       -100.00%  (p=0.008 n=5+5)
TrimASCII/256:1            0.00B          0.00B           ~     (all equal)
TrimASCII/256:2            48.0B ± 0%      0.0B       -100.00%  (p=0.008 n=5+5)
TrimASCII/256:4            48.0B ± 0%      0.0B       -100.00%  (p=0.008 n=5+5)
TrimASCII/256:8            48.0B ± 0%      0.0B       -100.00%  (p=0.008 n=5+5)
TrimASCII/256:16           48.0B ± 0%      0.0B       -100.00%  (p=0.008 n=5+5)
TrimASCII/4096:1           0.00B          0.00B           ~     (all equal)
TrimASCII/4096:2           48.0B ± 0%      0.0B       -100.00%  (p=0.008 n=5+5)
TrimASCII/4096:4           48.0B ± 0%      0.0B       -100.00%  (p=0.008 n=5+5)
TrimASCII/4096:8           48.0B ± 0%      0.0B       -100.00%  (p=0.008 n=5+5)
TrimASCII/4096:16          49.0B ± 0%      0.0B       -100.00%  (p=0.008 n=5+5)
TrimByte                   0.00B          0.00B           ~     (all equal)

name                    old allocs/op  new allocs/op  delta
TrimSpace/NoTrim            0.00           0.00           ~     (all equal)
TrimSpace/ASCII             0.00           0.00           ~     (all equal)
TrimSpace/SomeNonASCII      0.00           0.00           ~     (all equal)
TrimSpace/JustNonASCII      0.00           0.00           ~     (all equal)
TrimASCII/1:1               0.00           0.00           ~     (all equal)
TrimASCII/1:2               2.00 ± 0%      0.00       -100.00%  (p=0.008 n=5+5)
TrimASCII/1:4               2.00 ± 0%      0.00       -100.00%  (p=0.008 n=5+5)
TrimASCII/1:8               2.00 ± 0%      0.00       -100.00%  (p=0.008 n=5+5)
TrimASCII/1:16              2.00 ± 0%      0.00       -100.00%  (p=0.008 n=5+5)
TrimASCII/16:1              0.00           0.00           ~     (all equal)
TrimASCII/16:2              2.00 ± 0%      0.00       -100.00%  (p=0.008 n=5+5)
TrimASCII/16:4              2.00 ± 0%      0.00       -100.00%  (p=0.008 n=5+5)
TrimASCII/16:8              2.00 ± 0%      0.00       -100.00%  (p=0.008 n=5+5)
TrimASCII/16:16             2.00 ± 0%      0.00       -100.00%  (p=0.008 n=5+5)
TrimASCII/256:1             0.00           0.00           ~     (all equal)
TrimASCII/256:2             2.00 ± 0%      0.00       -100.00%  (p=0.008 n=5+5)
TrimASCII/256:4             2.00 ± 0%      0.00       -100.00%  (p=0.008 n=5+5)
TrimASCII/256:8             2.00 ± 0%      0.00       -100.00%  (p=0.008 n=5+5)
TrimASCII/256:16            2.00 ± 0%      0.00       -100.00%  (p=0.008 n=5+5)
TrimASCII/4096:1            0.00           0.00           ~     (all equal)
TrimASCII/4096:2            2.00 ± 0%      0.00       -100.00%  (p=0.008 n=5+5)
TrimASCII/4096:4            2.00 ± 0%      0.00       -100.00%  (p=0.008 n=5+5)
TrimASCII/4096:8            2.00 ± 0%      0.00       -100.00%  (p=0.008 n=5+5)
TrimASCII/4096:16           2.00 ± 0%      0.00       -100.00%  (p=0.008 n=5+5)
TrimByte                    0.00           0.00           ~     (all equal)

Fixes #46446

Change-Id: I9537c86f888af6285027f67bda4a97aeedb41d4a
Reviewed-on: https://go-review.googlesource.com/c/go/+/332771
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>
Reviewed-by: Joe Tsai <joetsai@digital-static.net>
Trust: Joe Tsai <joetsai@digital-static.net>
Trust: Than McIntosh <thanm@google.com>