cmd/internal/obj: optimize the function stacksplit on loong64

cmd/internal/obj: optimize the function stacksplit on loong64

In the process of stack split checking, loong64 uses the following
logic: if SP > stackguard then goto done, else morestack

The possible problem here is that the probability of morestack
execution is much lower than done, while static branch prediction
is more inclined to obtain morestack, which will cause a certain
probability of branch prediction error.

Change the logic here to:
if SP <= stackguard then goto morestack, else done

benchmarks on 3A6000:

goos: linux
goarch: loong64
pkg: fmt
cpu: Loongson-3A6000 @ 2500.00MHz
                              │  bench.old  │              bench.new              │
                              │   sec/op    │   sec/op     vs base                │
SprintfPadding                  418.3n ± 1%   387.0n ± 0%   -7.49% (p=0.000 n=20)
SprintfEmpty                    35.95n ± 0%   35.86n ± 0%   -0.25% (p=0.000 n=20)
SprintfString                   75.02n ± 1%   72.24n ± 0%   -3.71% (p=0.000 n=20)
SprintfTruncateString           165.7n ± 3%   139.9n ± 1%  -15.58% (p=0.000 n=20)
SprintfTruncateBytes            171.0n ± 0%   147.3n ± 0%  -13.83% (p=0.000 n=20)
SprintfSlowParsingPath          90.56n ± 0%   80.85n ± 0%  -10.72% (p=0.000 n=20)
SprintfQuoteString              560.2n ± 0%   509.7n ± 0%   -9.01% (p=0.000 n=20)
SprintfInt                      58.62n ± 0%   56.45n ± 0%   -3.70% (p=0.000 n=20)
SprintfIntInt                   141.7n ± 0%   122.2n ± 0%  -13.73% (p=0.000 n=20)
SprintfPrefixedInt              210.6n ± 0%   208.8n ± 0%   -0.88% (p=0.000 n=20)
SprintfFloat                    282.3n ± 0%   251.8n ± 1%  -10.80% (p=0.000 n=20)
SprintfComplex                  854.1n ± 0%   813.8n ± 0%   -4.71% (p=0.000 n=20)
SprintfBoolean                  76.32n ± 0%   71.14n ± 1%   -6.79% (p=0.000 n=20)
SprintfHexString                218.5n ± 0%   193.4n ± 0%  -11.51% (p=0.000 n=20)
SprintfHexBytes                 321.3n ± 0%   275.0n ± 0%  -14.42% (p=0.000 n=20)
SprintfBytes                    573.5n ± 0%   553.2n ± 1%   -3.54% (p=0.000 n=20)
SprintfStringer                 501.1n ± 1%   446.6n ± 0%  -10.86% (p=0.000 n=20)
SprintfStructure                1.793µ ± 0%   1.683µ ± 0%   -6.16% (p=0.000 n=20)
ManyArgs                        500.0n ± 0%   470.4n ± 0%   -5.92% (p=0.000 n=20)
FprintInt                       67.51n ± 0%   65.71n ± 0%   -2.66% (p=0.000 n=20)
FprintfBytes                    130.9n ± 0%   129.5n ± 1%   -1.11% (p=0.000 n=20)
FprintIntNoAlloc                67.55n ± 0%   65.80n ± 0%   -2.58% (p=0.000 n=20)
ScanInts                        386.3µ ± 0%   346.5µ ± 0%  -10.29% (p=0.000 n=20)
ScanRecursiveInt                25.97m ± 0%   25.93m ± 0%   -0.15% (p=0.038 n=20)
ScanRecursiveIntReaderWrapper   26.07m ± 0%   25.93m ± 0%   -0.53% (p=0.001 n=20)
geomean                         702.6n        653.7n        -6.96%

goos: linux
goarch: loong64
pkg: test/bench/go1
cpu: Loongson-3A6000 @ 2500.00MHz
                      │  bench.old   │              bench.new              │
                      │    sec/op    │   sec/op     vs base                │
BinaryTree17              7.688 ± 1%    7.724 ± 0%   +0.47% (p=0.040 n=20)
Fannkuch11                2.670 ± 0%    2.645 ± 0%   -0.94% (p=0.000 n=20)
FmtFprintfEmpty          35.93n ± 0%   37.50n ± 0%   +4.37% (p=0.000 n=20)
FmtFprintfString         56.32n ± 0%   59.74n ± 0%   +6.08% (p=0.000 n=20)
FmtFprintfInt            64.47n ± 0%   61.26n ± 0%   -4.98% (p=0.000 n=20)
FmtFprintfIntInt        100.30n ± 0%   99.67n ± 0%   -0.63% (p=0.000 n=20)
FmtFprintfPrefixedInt    116.7n ± 0%   119.3n ± 0%   +2.23% (p=0.000 n=20)
FmtFprintfFloat          234.1n ± 0%   203.4n ± 0%  -13.11% (p=0.000 n=20)
FmtManyArgs              503.0n ± 0%   467.9n ± 0%   -6.96% (p=0.000 n=20)
GobDecode                8.125m ± 0%   7.299m ± 0%  -10.17% (p=0.000 n=20)
GobEncode                8.930m ± 1%   8.581m ± 1%   -3.91% (p=0.000 n=20)
Gzip                     280.0m ± 0%   279.8m ± 0%   -0.10% (p=0.000 n=20)
Gunzip                   33.30m ± 0%   32.48m ± 0%   -2.49% (p=0.000 n=20)
HTTPClientServer         55.43µ ± 0%   54.10µ ± 1%   -2.41% (p=0.000 n=20)
JSONEncode              10.086m ± 0%   9.055m ± 0%  -10.22% (p=0.000 n=20)
JSONDecode               49.37m ± 1%   46.22m ± 1%   -6.40% (p=0.000 n=20)
Mandelbrot200            4.606m ± 0%   4.606m ± 0%        ~ (p=0.280 n=20)
GoParse                  5.010m ± 0%   4.855m ± 0%   -3.09% (p=0.000 n=20)
RegexpMatchEasy0_32      59.09n ± 0%   59.32n ± 0%   +0.39% (p=0.000 n=20)
RegexpMatchEasy0_1K      455.2n ± 0%   453.8n ± 0%   -0.31% (p=0.000 n=20)
RegexpMatchEasy1_32      59.24n ± 0%   60.11n ± 0%   +1.47% (p=0.000 n=20)
RegexpMatchEasy1_1K      555.2n ± 0%   553.9n ± 0%   -0.23% (p=0.000 n=20)
RegexpMatchMedium_32     845.7n ± 0%   775.6n ± 0%   -8.28% (p=0.000 n=20)
RegexpMatchMedium_1K     26.68µ ± 0%   26.48µ ± 0%   -0.78% (p=0.000 n=20)
RegexpMatchHard_32       1.317µ ± 0%   1.326µ ± 0%   +0.68% (p=0.000 n=20)
RegexpMatchHard_1K       41.35µ ± 0%   40.95µ ± 0%   -0.97% (p=0.000 n=20)
Revcomp                  463.0m ± 0%   473.0m ± 0%   +2.15% (p=0.000 n=20)
Template                 83.80m ± 0%   76.26m ± 1%   -9.00% (p=0.000 n=20)
TimeParse                283.3n ± 0%   260.8n ± 0%   -7.96% (p=0.000 n=20)
TimeFormat               307.2n ± 0%   290.5n ± 0%   -5.45% (p=0.000 n=20)
geomean                  53.16µ        51.67µ        -2.79%

Change-Id: Iaec2f50db18e9a2b405605f8b92af3683114ea34
Reviewed-on: https://go-review.googlesource.com/c/go/+/616035
Reviewed-by: Carlos Amedee <carlos@golang.org>
Reviewed-by: abner chenc <chenguoqi@loongson.cn>
Reviewed-by: David Chase <drchase@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>