cmd/internal/obj/wasm: cache SP in a local

cmd/internal/obj/wasm: cache SP in a local

We use Wasm global variables extensively for simulating
registers, especially SP. V8 does not handle global variables
efficiently.

This CL reduces global variable accesses by caching the global SP
in a local variable in each function. The local cache is set on
function entry and updated after each call (where the stack could
have moved). Within a function, the SP access will use the local
variable.

Supersedes https://golang.org/cl/173979.

Running on Chrome Version 73.0.3683.103 on darwin/amd64:

name                   old time/op    new time/op     delta
BinaryTree17              15.3s ± 2%      14.5s ± 3%   -5.20%  (p=0.000 n=9+10)
Fannkuch11                8.91s ± 2%      9.48s ± 2%   +6.41%  (p=0.000 n=9+10)
FmtFprintfEmpty           197ns ± 5%      165ns ± 3%  -16.09%  (p=0.000 n=9+8)
FmtFprintfString          354ns ± 8%      325ns ± 7%   -8.33%  (p=0.001 n=10+10)
FmtFprintfInt             400ns ± 4%      368ns ± 6%   -8.01%  (p=0.000 n=10+10)
FmtFprintfIntInt          618ns ± 3%      587ns ± 6%   -4.97%  (p=0.001 n=10+10)
FmtFprintfPrefixedInt     637ns ± 4%      606ns ± 4%   -4.88%  (p=0.000 n=10+10)
FmtFprintfFloat           965ns ± 7%      898ns ± 4%   -6.97%  (p=0.000 n=10+10)
FmtManyArgs              2.34µs ± 1%     2.24µs ± 3%   -4.40%  (p=0.000 n=9+10)
GobDecode                29.8ms ± 3%     28.8ms ± 6%   -3.60%  (p=0.006 n=9+10)
GobEncode                20.5ms ± 8%     17.6ms ± 3%  -14.32%  (p=0.000 n=10+10)
Gzip                      714ms ± 3%      718ms ± 8%     ~     (p=0.971 n=10+10)
Gunzip                    148ms ± 3%      136ms ± 3%   -7.99%  (p=0.000 n=10+9)
HTTPClientServer          219µs ± 3%      215µs ± 4%     ~     (p=0.190 n=10+10)
JSONEncode               35.1ms ± 2%     31.8ms ±13%   -9.52%  (p=0.002 n=10+10)
JSONDecode                220ms ± 3%      207ms ± 5%   -5.87%  (p=0.000 n=10+10)
Mandelbrot200            5.22ms ± 1%     5.11ms ± 4%   -2.11%  (p=0.027 n=8+10)
GoParse                  17.2ms ± 6%     16.1ms ± 5%   -6.63%  (p=0.000 n=10+9)
RegexpMatchEasy0_32       375ns ± 3%      340ns ± 3%   -9.25%  (p=0.000 n=10+10)
RegexpMatchEasy0_1K      2.70µs ± 3%     2.65µs ± 4%     ~     (p=0.118 n=10+10)
RegexpMatchEasy1_32       341ns ± 2%      305ns ± 4%  -10.62%  (p=0.000 n=9+10)
RegexpMatchEasy1_1K      3.20µs ± 3%     2.99µs ± 3%   -6.35%  (p=0.000 n=10+10)
RegexpMatchMedium_32      520ns ± 3%      501ns ± 4%   -3.64%  (p=0.002 n=9+10)
RegexpMatchMedium_1K      145µs ± 7%      128µs ± 3%  -11.57%  (p=0.000 n=9+10)
RegexpMatchHard_32       7.88µs ± 3%     7.01µs ± 5%  -10.97%  (p=0.000 n=10+10)
RegexpMatchHard_1K        237µs ± 5%      207µs ± 4%  -12.71%  (p=0.000 n=9+10)
Revcomp                   2.34s ± 1%      2.31s ± 5%     ~     (p=0.230 n=7+10)
Template                  261ms ± 7%      246ms ± 5%   -5.93%  (p=0.007 n=10+10)
TimeParse                1.47µs ± 3%     1.39µs ± 5%   -5.75%  (p=0.000 n=9+10)
TimeFormat               1.52µs ± 3%     1.43µs ± 4%   -6.42%  (p=0.000 n=8+10)

name                   old speed      new speed       delta
GobDecode              25.7MB/s ± 3%   26.7MB/s ± 5%   +3.77%  (p=0.006 n=9+10)
GobEncode              37.5MB/s ± 8%   43.7MB/s ± 3%  +16.61%  (p=0.000 n=10+10)
Gzip                   27.2MB/s ± 3%   27.0MB/s ± 7%     ~     (p=0.971 n=10+10)
Gunzip                  131MB/s ± 3%    142MB/s ± 5%   +8.07%  (p=0.000 n=10+10)
JSONEncode             55.2MB/s ± 2%   61.2MB/s ±12%  +10.80%  (p=0.002 n=10+10)
JSONDecode             8.84MB/s ± 3%   9.39MB/s ± 5%   +6.28%  (p=0.000 n=10+10)
GoParse                3.37MB/s ± 6%   3.61MB/s ± 5%   +7.09%  (p=0.000 n=10+9)
RegexpMatchEasy0_32    85.3MB/s ± 3%   94.0MB/s ± 3%  +10.20%  (p=0.000 n=10+10)
RegexpMatchEasy0_1K     379MB/s ± 3%    387MB/s ± 4%     ~     (p=0.123 n=10+10)
RegexpMatchEasy1_32    93.9MB/s ± 2%  105.1MB/s ± 4%  +11.96%  (p=0.000 n=9+10)
RegexpMatchEasy1_1K     320MB/s ± 3%    342MB/s ± 3%   +6.79%  (p=0.000 n=10+10)
RegexpMatchMedium_32   1.92MB/s ± 2%   2.00MB/s ± 3%   +3.94%  (p=0.001 n=9+10)
RegexpMatchMedium_1K   7.09MB/s ± 6%   8.01MB/s ± 3%  +13.00%  (p=0.000 n=9+10)
RegexpMatchHard_32     4.06MB/s ± 3%   4.56MB/s ± 5%  +12.38%  (p=0.000 n=10+10)
RegexpMatchHard_1K     4.32MB/s ± 4%   4.96MB/s ± 4%  +14.60%  (p=0.000 n=9+10)
Revcomp                 109MB/s ± 1%    110MB/s ± 5%     ~     (p=0.219 n=7+10)
Template               7.44MB/s ± 8%   7.91MB/s ± 5%   +6.30%  (p=0.007 n=10+10)

Change-Id: I5828cf6b23ce104c02addc2642aba48dd6c48aab
Reviewed-on: https://go-review.googlesource.com/c/go/+/174062
Run-TryBot: Richard Musiol <neelance@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>