cmd/internal/obj/arm64: mark functions with small stacks NOSPLIT

This change omits the stack check on arm64 when the size of a stack
frame is less than obj.StackSmall.

The effect is not very significant, because CL 92040 has set the leaf
function with a framesize of 0 to NOFRAME, which makes the code
prologue on arm64 much closer to other architectures. But it is not
without effect, for example, it is effective for std library functions
such as runtime.usleep, fmt.isSpace, etc. Since this CL is very simple,
I think this optimization is worthwhile.

compilecmp results on linux/arm64:
name                      old time/op       new time/op       delta
Template                        284ms ± 1%        283ms ± 1%  -0.29%  (p=0.000 n=50+50)
Unicode                         125ms ± 2%        125ms ± 1%    ~     (p=0.445 n=49+49)
GoTypes                         1.70s ± 1%        1.69s ± 1%  -0.36%  (p=0.000 n=50+50)
Compiler                        124ms ± 1%        124ms ± 1%  -0.31%  (p=0.003 n=48+48)
SSA                             12.7s ± 1%        12.7s ± 1%    ~     (p=0.117 n=50+50)
Flate                           172ms ± 1%        171ms ± 1%  -0.55%  (p=0.000 n=50+50)
GoParser                        265ms ± 1%        264ms ± 1%  -0.23%  (p=0.000 n=47+48)
Reflect                         653ms ± 1%        646ms ± 1%  -1.12%  (p=0.000 n=48+50)
Tar                             246ms ± 1%        245ms ± 1%  -0.41%  (p=0.000 n=46+47)
XML                             328ms ± 1%        327ms ± 1%  -0.18%  (p=0.020 n=46+50)
LinkCompiler                    599ms ± 1%        598ms ± 1%    ~     (p=0.237 n=50+49)
ExternalLinkCompiler            1.87s ± 1%        1.87s ± 1%  -0.18%  (p=0.000 n=50+50)
LinkWithoutDebugCompiler        365ms ± 1%        364ms ± 2%    ~     (p=0.131 n=50+50)
[Geo mean]                      490ms             488ms       -0.32%

name                      old alloc/op      new alloc/op      delta
Template                       38.8MB ± 1%       38.8MB ± 1%  +0.16%  (p=0.013 n=47+49)
Unicode                        28.4MB ± 0%       28.4MB ± 0%    ~     (p=0.512 n=46+44)
GoTypes                         169MB ± 1%        169MB ± 1%    ~     (p=0.628 n=50+50)
Compiler                       23.2MB ± 1%       23.2MB ± 1%    ~     (p=0.424 n=46+44)
SSA                            1.55GB ± 0%       1.55GB ± 0%    ~     (p=0.603 n=48+50)
Flate                          23.7MB ± 1%       23.8MB ± 1%    ~     (p=0.797 n=50+50)
GoParser                       35.3MB ± 1%       35.3MB ± 1%    ~     (p=0.932 n=49+49)
Reflect                        85.0MB ± 0%       84.9MB ± 0%  -0.05%  (p=0.038 n=45+40)
Tar                            34.4MB ± 1%       34.5MB ± 1%    ~     (p=0.288 n=50+50)
XML                            43.8MB ± 2%       43.9MB ± 2%    ~     (p=0.798 n=46+49)
LinkCompiler                    136MB ± 0%        136MB ± 0%    ~     (p=0.750 n=50+50)
ExternalLinkCompiler            127MB ± 0%        127MB ± 0%    ~     (p=0.852 n=50+50)
LinkWithoutDebugCompiler       84.1MB ± 0%       84.1MB ± 0%    ~     (p=0.890 n=50+50)
[Geo mean]                     70.4MB            70.4MB       +0.01%

file      before    after     Δ       %
addr2line 4006004   4006012   +8      +0.000%
asm       4936863   4936919   +56     +0.001%
buildid   2594947   2594859   -88     -0.003%
cgo       4399702   4399806   +104    +0.002%
compile   22233139  22233107  -32     -0.000%
cover     4443681   4443785   +104    +0.002%
dist      3365902   3365806   -96     -0.003%
doc       3776175   3776231   +56     +0.001%
fix       3218624   3218552   -72     -0.002%
nm        3923345   3923329   -16     -0.000%
objdump   4295473   4295673   +200    +0.005%
pack      2390561   2390497   -64     -0.003%
pprof     12866419  12866275  -144    -0.001%
test2json 2587113   2587129   +16     +0.001%
trace     9609814   9609710   -104    -0.001%
vet       6790272   6791048   +776    +0.011%
total     106832751 106833455 +704    +0.001%

Updates #13379 (for arm64)

Change-Id: I07664ab0b978c66c0b18b8482222e9ba3772290d
Reviewed-on: https://go-review.googlesource.com/c/go/+/302853
Reviewed-by: eric fang <eric.fang@arm.com>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
Trust: eric fang <eric.fang@arm.com>
Run-TryBot: eric fang <eric.fang@arm.com>
TryBot-Result: Go Bot <gobot@golang.org>

src/cmd/internal/obj/arm64/obj7.go

@@ -539,6 +539,12 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
 				}
 			}
 
+			if p.Mark&LEAF != 0 && c.autosize < objabi.StackSmall {
+				// A leaf function with a small stack can be marked
+				// NOSPLIT, avoiding a stack check.
+				p.From.Sym.Set(obj.AttrNoSplit, true)
+			}
+
 			if !p.From.Sym.NoSplit() {
 				p = c.stacksplit(p, c.autosize) // emit split check
 			}