Make use of the newly-enabled limited midstack inlining.
Similar changes will be done in followup CLs.

name                    old time/op  new time/op  delta
MutexUncontended        19.3ns ± 1%  18.9ns ± 0%   -1.92%  (p=0.000 n=20+19)
MutexUncontended-4      5.24ns ± 0%  4.75ns ± 1%   -9.25%  (p=0.000 n=20+20)
MutexUncontended-16     2.10ns ± 0%  2.05ns ± 0%   -2.38%  (p=0.000 n=15+19)
Mutex                   19.6ns ± 0%  19.3ns ± 1%   -1.92%  (p=0.000 n=20+17)
Mutex-4                 54.6ns ± 5%  52.4ns ± 4%   -4.09%  (p=0.000 n=20+20)
Mutex-16                 133ns ± 5%   139ns ± 2%   +4.23%  (p=0.000 n=20+16)
MutexSlack              33.4ns ± 2%  18.9ns ± 1%  -43.56%  (p=0.000 n=19+20)
MutexSlack-4             206ns ± 5%   225ns ± 8%   +9.12%  (p=0.000 n=20+18)
MutexSlack-16           89.4ns ± 1%  98.4ns ± 1%  +10.10%  (p=0.000 n=18+17)
MutexWork               60.5ns ± 0%  58.2ns ± 3%   -3.75%  (p=0.000 n=12+20)
MutexWork-4              105ns ± 5%   103ns ± 7%   -1.68%  (p=0.007 n=20+20)
MutexWork-16             157ns ± 1%   163ns ± 2%   +3.90%  (p=0.000 n=18+18)
MutexWorkSlack          70.2ns ± 5%  57.7ns ± 1%  -17.81%  (p=0.000 n=19+20)
MutexWorkSlack-4         277ns ±13%   276ns ±13%     ~     (p=0.682 n=20+19)
MutexWorkSlack-16        156ns ± 0%   147ns ± 0%   -5.62%  (p=0.000 n=16+14)
MutexNoSpin              966ns ± 0%   968ns ± 0%   +0.11%  (p=0.029 n=15+20)
MutexNoSpin-4            269ns ± 4%   270ns ± 2%     ~     (p=0.807 n=20+19)
MutexNoSpin-16           122ns ± 0%   120ns ± 4%   -1.63%  (p=0.000 n=19+19)
MutexSpin               3.13µs ± 0%  3.13µs ± 1%   +0.16%  (p=0.004 n=18+20)
MutexSpin-4              826ns ± 1%   832ns ± 2%   +0.74%  (p=0.000 n=19+16)
MutexSpin-16             397ns ± 1%   395ns ± 0%   -0.50%  (p=0.000 n=19+17)
RWMutexUncontended      71.4ns ± 0%  69.5ns ± 0%   -2.72%  (p=0.000 n=16+20)
RWMutexUncontended-4    18.4ns ± 4%  17.5ns ± 0%   -4.92%  (p=0.000 n=20+18)
RWMutexUncontended-16   8.01ns ± 0%  7.92ns ± 0%   -1.15%  (p=0.000 n=18+18)
RWMutexWrite100         24.9ns ± 0%  24.9ns ± 1%     ~     (p=0.099 n=19+20)
RWMutexWrite100-4       46.5ns ± 3%  46.2ns ± 4%     ~     (p=0.253 n=17+19)
RWMutexWrite100-16      68.9ns ± 3%  69.9ns ± 5%   +1.46%  (p=0.012 n=18+20)
RWMutexWrite10          27.1ns ± 0%  27.0ns ± 2%     ~     (p=0.128 n=17+20)
RWMutexWrite10-4        34.8ns ± 1%  34.7ns ± 2%     ~     (p=0.180 n=20+18)
RWMutexWrite10-16       37.5ns ± 2%  37.2ns ± 4%   -0.89%  (p=0.023 n=20+20)
RWMutexWorkWrite100      164ns ± 0%   164ns ± 0%     ~     (p=0.106 n=12+20)
RWMutexWorkWrite100-4    186ns ± 3%   193ns ± 3%   +3.46%  (p=0.000 n=20+20)
RWMutexWorkWrite100-16   204ns ± 2%   210ns ± 3%   +2.96%  (p=0.000 n=18+20)
RWMutexWorkWrite10       153ns ± 0%   153ns ± 0%   -0.20%  (p=0.017 n=20+19)
RWMutexWorkWrite10-4     179ns ± 1%   178ns ± 2%     ~     (p=0.215 n=19+20)
RWMutexWorkWrite10-16    191ns ± 1%   192ns ± 2%     ~     (p=0.166 n=15+19)

linux/amd64 bin/go 14630572 (previous commit 14605947, +24625/+0.17%)

Change-Id: I3f9d1765801fe0b8deb1bc2728b8bba8a7508e23
Reviewed-on: https://go-review.googlesource.com/c/go/+/148958Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>