This is inspired by
https://blog.cloudflare.com/go-dont-collect-my-garbage/
This CL adds allocation tracking and parallelizes p256-related benchmarks.
Amount of allocations can be significantly reduced by marking amd64 asm
functions as noescape. This exposes a bug in p256MovCond:
PANDN with memory argument will fault if memory is not aligned, so they
are replaced with MOVDQU (which is ok with unaligned memory) and
register version of PANDN.

Results on 88-thread machine (2x 22 cores) below:
crypto/elliptic:
name               old time/op    new time/op    delta
BaseMultP256-88      1.50µs ±11%    1.19µs ± 5%  -20.20%  (p=0.000 n=10+10)
ScalarMultP256-88    5.47µs ± 5%    3.63µs ±10%  -33.66%  (p=0.000 n=9+10)

name               old alloc/op   new alloc/op   delta
BaseMultP256-88        800B ± 0%      288B ± 0%  -64.00%  (p=0.000 n=10+10)
ScalarMultP256-88    2.59kB ± 0%    0.26kB ± 0%  -90.12%  (p=0.000 n=10+10)

name               old allocs/op  new allocs/op  delta
BaseMultP256-88        13.0 ± 0%       6.0 ± 0%  -53.85%  (p=0.000 n=10+10)
ScalarMultP256-88      16.0 ± 0%       5.0 ± 0%  -68.75%  (p=0.000 n=10+10)

crypto/ecdsa:
name              old time/op    new time/op    delta
SignP256-88         8.63µs ±37%    7.55µs ±38%     ~     (p=0.393 n=10+10)
VerifyP256-88       13.9µs ± 8%     7.0µs ± 7%  -49.29%  (p=0.000 n=10+9)
KeyGeneration-88    2.77µs ±11%    2.34µs ±11%  -15.57%  (p=0.000 n=10+10)

name              old alloc/op   new alloc/op   delta
SignP256-88         4.14kB ± 1%    2.98kB ± 2%  -27.94%  (p=0.000 n=10+10)
VerifyP256-88       4.47kB ± 0%    0.99kB ± 0%  -77.84%  (p=0.000 n=9+10)
KeyGeneration-88    1.21kB ± 0%    0.69kB ± 0%  -42.78%  (p=0.000 n=10+10)

name              old allocs/op  new allocs/op  delta
SignP256-88           47.0 ± 0%      34.0 ± 0%  -27.66%  (p=0.000 n=10+10)
VerifyP256-88         38.0 ± 0%      17.0 ± 0%  -55.26%  (p=0.000 n=10+10)
KeyGeneration-88      20.0 ± 0%      13.0 ± 0%  -35.00%  (p=0.000 n=10+10)

On machine with only 4 cores, results are much less impressive:
around 2% performance gain.

Change-Id: I8a2f8168f83d27ad9ace1b4b1a1e11cb83edf717
Reviewed-on: https://go-review.googlesource.com/80757
Run-TryBot: Ilya Tocar <ilya.tocar@intel.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>