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cmd/link: linker portion of dead map removal
This patch contains the linker changes needed to enable deadcoding of
large unreferenced map variables, in combination with a previous
compiler change. We add a new cleanup function that runs just after
deadcode that looks for relocations in "init" funcs that are weak, of
type R_CALL (and siblings), and are targeting an unreachable function.
If we find such a relocation, after checking to make sure it targets a
map.init.XXX helper, we redirect the relocation to a point to a no-op
routine ("mapinitnoop") in the runtime.
Compilebench results for this change:
│ out.base.txt │ out.wrap.txt │
│ sec/op │ sec/op vs base │
Template 218.6m ± 2% 221.1m ± 1% ~ (p=0.129 n=39)
Unicode 180.5m ± 1% 178.9m ± 1% -0.93% (p=0.006 n=39)
GoTypes 1.162 ± 1% 1.156 ± 1% ~ (p=0.850 n=39)
Compiler 143.6m ± 1% 142.6m ± 1% ~ (p=0.743 n=39)
SSA 8.698 ± 1% 8.719 ± 1% ~ (p=0.145 n=39)
Flate 142.6m ± 1% 143.9m ± 3% ~ (p=0.287 n=39)
GoParser 247.7m ± 1% 248.8m ± 1% ~ (p=0.265 n=39)
Reflect 588.0m ± 1% 590.4m ± 1% ~ (p=0.269 n=39)
Tar 198.5m ± 1% 201.3m ± 1% +1.38% (p=0.005 n=39)
XML 259.1m ± 1% 260.0m ± 1% ~ (p=0.376 n=39)
LinkCompiler 746.8m ± 2% 747.8m ± 1% ~ (p=0.706 n=39)
ExternalLinkCompiler 1.906 ± 0% 1.902 ± 1% ~ (p=0.207 n=40)
LinkWithoutDebugCompiler 522.4m ± 21% 471.1m ± 1% -9.81% (p=0.000 n=40)
StdCmd 21.32 ± 0% 21.39 ± 0% +0.32% (p=0.035 n=40)
geomean 609.2m 606.0m -0.53%
│ out.base.txt │ out.wrap.txt │
│ user-sec/op │ user-sec/op vs base │
Template 401.9m ± 3% 406.9m ± 2% ~ (p=0.291 n=39)
Unicode 191.9m ± 6% 196.1m ± 3% ~ (p=0.052 n=39)
GoTypes 3.967 ± 3% 4.056 ± 1% ~ (p=0.099 n=39)
Compiler 171.1m ± 3% 173.4m ± 3% ~ (p=0.415 n=39)
SSA 30.04 ± 4% 30.25 ± 4% ~ (p=0.106 n=39)
Flate 246.3m ± 3% 248.9m ± 4% ~ (p=0.499 n=39)
GoParser 518.7m ± 1% 520.6m ± 2% ~ (p=0.531 n=39)
Reflect 1.670 ± 1% 1.656 ± 2% ~ (p=0.137 n=39)
Tar 352.7m ± 2% 360.3m ± 2% ~ (p=0.117 n=39)
XML 528.8m ± 2% 521.1m ± 2% ~ (p=0.296 n=39)
LinkCompiler 1.128 ± 2% 1.140 ± 2% ~ (p=0.324 n=39)
ExternalLinkCompiler 2.165 ± 2% 2.147 ± 2% ~ (p=0.537 n=40)
LinkWithoutDebugCompiler 484.2m ± 4% 490.7m ± 3% ~ (p=0.897 n=40)
geomean 818.5m 825.1m +0.80%
│ out.base.txt │ out.wrap.txt │
│ text-bytes │ text-bytes vs base │
HelloSize 766.0Ki ± 0% 766.0Ki ± 0% ~ (p=1.000 n=40) ¹
CmdGoSize 10.02Mi ± 0% 10.02Mi ± 0% -0.03% (n=40)
geomean 2.738Mi 2.738Mi -0.01%
¹ all samples are equal
│ out.base.txt │ out.wrap.txt │
│ data-bytes │ data-bytes vs base │
HelloSize 14.17Ki ± 0% 14.17Ki ± 0% ~ (p=1.000 n=40) ¹
CmdGoSize 308.3Ki ± 0% 298.5Ki ± 0% -3.19% (n=40)
geomean 66.10Ki 65.04Ki -1.61%
¹ all samples are equal
│ out.base.txt │ out.wrap.txt │
│ bss-bytes │ bss-bytes vs base │
HelloSize 197.3Ki ± 0% 197.3Ki ± 0% ~ (p=1.000 n=40) ¹
CmdGoSize 228.2Ki ± 0% 228.1Ki ± 0% -0.01% (n=40)
geomean 212.2Ki 212.1Ki -0.01%
¹ all samples are equal
│ out.base.txt │ out.wrap.txt │
│ exe-bytes │ exe-bytes vs base │
HelloSize 1.192Mi ± 0% 1.192Mi ± 0% +0.00% (p=0.000 n=40)
CmdGoSize 14.85Mi ± 0% 14.83Mi ± 0% -0.09% (n=40)
geomean 4.207Mi 4.205Mi -0.05%
Also tested for any linker changes by benchmarking relink of k8s
"kubelet"; no changes to speak of there.
Updates #2559.
Updates #36021.
Updates #14840.
Change-Id: I4cc5370b3f20679a1065aaaf87bdf2881e257631
Reviewed-on: https://go-review.googlesource.com/c/go/+/463395
Run-TryBot: Than McIntosh <thanm@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
This commit is contained in:
Than McIntosh
parent
b46e44a399
commit
e2ca417ee7
@ -240,10 +240,6 @@ func RegisterMapInitLsym(s *obj.LSym) {
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// outlined global map initializer functions; if it finds any such
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// relocs, it flags them as R_WEAK.
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func weakenGlobalMapInitRelocs(fn *ir.Func) {
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// Disabled until next patch.
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if true {
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return
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}
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if globalMapInitLsyms == nil {
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return
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}
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@ -12,6 +12,7 @@ import (
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"cmd/link/internal/sym"
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"fmt"
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"internal/buildcfg"
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"strings"
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"unicode"
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)
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@ -29,6 +30,8 @@ type deadcodePass struct {
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dynlink bool
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methodsigstmp []methodsig // scratch buffer for decoding method signatures
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pkginits []loader.Sym
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mapinitnoop loader.Sym
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}
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func (d *deadcodePass) init() {
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@ -105,6 +108,11 @@ func (d *deadcodePass) init() {
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}
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d.mark(s, 0)
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}
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d.mapinitnoop = d.ldr.Lookup("runtime.mapinitnoop", abiInternalVer)
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if d.mapinitnoop == 0 {
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panic("could not look up runtime.mapinitnoop")
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}
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}
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func (d *deadcodePass) flood() {
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@ -229,6 +237,12 @@ func (d *deadcodePass) flood() {
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}
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d.mark(a.Sym(), symIdx)
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}
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// Record sym if package init func (here naux != 0 is a cheap way
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// to check first if it is a function symbol).
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if naux != 0 && d.ldr.IsPkgInit(symIdx) {
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d.pkginits = append(d.pkginits, symIdx)
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}
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// Some host object symbols have an outer object, which acts like a
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// "carrier" symbol, or it holds all the symbols for a particular
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// section. We need to mark all "referenced" symbols from that carrier,
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@ -262,6 +276,37 @@ func (d *deadcodePass) flood() {
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}
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}
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// mapinitcleanup walks all pkg init functions and looks for weak relocations
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// to mapinit symbols that are no longer reachable. It rewrites
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// the relocs to target a new no-op routine in the runtime.
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func (d *deadcodePass) mapinitcleanup() {
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for _, idx := range d.pkginits {
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relocs := d.ldr.Relocs(idx)
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var su *loader.SymbolBuilder
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for i := 0; i < relocs.Count(); i++ {
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r := relocs.At(i)
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rs := r.Sym()
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if r.Weak() && r.Type().IsDirectCall() && !d.ldr.AttrReachable(rs) {
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// double check to make sure target is indeed map.init
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rsn := d.ldr.SymName(rs)
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if !strings.Contains(rsn, "map.init") {
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panic(fmt.Sprintf("internal error: expected map.init sym for weak call reloc, got %s -> %s", d.ldr.SymName(idx), rsn))
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}
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d.ldr.SetAttrReachable(d.mapinitnoop, true)
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if d.ctxt.Debugvlog > 1 {
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d.ctxt.Logf("deadcode: %s rewrite %s ref to %s\n",
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d.ldr.SymName(idx), rsn,
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d.ldr.SymName(d.mapinitnoop))
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}
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if su == nil {
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su = d.ldr.MakeSymbolUpdater(idx)
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}
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su.SetRelocSym(i, d.mapinitnoop)
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}
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}
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}
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}
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func (d *deadcodePass) mark(symIdx, parent loader.Sym) {
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if symIdx != 0 && !d.ldr.AttrReachable(symIdx) {
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d.wq.push(symIdx)
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@ -370,6 +415,9 @@ func deadcode(ctxt *Link) {
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}
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d.flood()
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}
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if *flagPruneWeakMap {
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d.mapinitcleanup()
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}
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}
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// methodsig is a typed method signature (name + type).
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@ -19,14 +19,16 @@ func TestDeadcode(t *testing.T) {
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tests := []struct {
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src string
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pos, neg string // positive and negative patterns
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pos, neg []string // positive and negative patterns
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}{
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{"reflectcall", "", "main.T.M"},
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{"typedesc", "", "type:main.T"},
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{"ifacemethod", "", "main.T.M"},
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{"ifacemethod2", "main.T.M", ""},
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{"ifacemethod3", "main.S.M", ""},
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{"ifacemethod4", "", "main.T.M"},
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{"reflectcall", nil, []string{"main.T.M"}},
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{"typedesc", nil, []string{"type:main.T"}},
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{"ifacemethod", nil, []string{"main.T.M"}},
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{"ifacemethod2", []string{"main.T.M"}, nil},
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{"ifacemethod3", []string{"main.S.M"}, nil},
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{"ifacemethod4", nil, []string{"main.T.M"}},
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{"globalmap", []string{"main.small", "main.effect"},
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[]string{"main.large"}},
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}
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for _, test := range tests {
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test := test
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@ -39,11 +41,15 @@ func TestDeadcode(t *testing.T) {
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if err != nil {
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t.Fatalf("%v: %v:\n%s", cmd.Args, err, out)
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}
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if test.pos != "" && !bytes.Contains(out, []byte(test.pos+"\n")) {
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t.Errorf("%s should be reachable. Output:\n%s", test.pos, out)
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for _, pos := range test.pos {
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if !bytes.Contains(out, []byte(pos+"\n")) {
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t.Errorf("%s should be reachable. Output:\n%s", pos, out)
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}
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}
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if test.neg != "" && bytes.Contains(out, []byte(test.neg+"\n")) {
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t.Errorf("%s should not be reachable. Output:\n%s", test.neg, out)
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for _, neg := range test.neg {
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if bytes.Contains(out, []byte(neg+"\n")) {
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t.Errorf("%s should not be reachable. Output:\n%s", neg, out)
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}
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}
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})
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}
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@ -100,6 +100,7 @@ var (
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FlagRound = flag.Int("R", -1, "set address rounding `quantum`")
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FlagTextAddr = flag.Int64("T", -1, "set text segment `address`")
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flagEntrySymbol = flag.String("E", "", "set `entry` symbol name")
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flagPruneWeakMap = flag.Bool("pruneweakmap", true, "prune weak mapinit refs")
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cpuprofile = flag.String("cpuprofile", "", "write cpu profile to `file`")
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memprofile = flag.String("memprofile", "", "write memory profile to `file`")
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memprofilerate = flag.Int64("memprofilerate", 0, "set runtime.MemProfileRate to `rate`")
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26
src/cmd/link/internal/ld/testdata/deadcode/globalmap.go
vendored
Normal file
26
src/cmd/link/internal/ld/testdata/deadcode/globalmap.go
vendored
Normal file
@ -0,0 +1,26 @@
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package main
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import "os"
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// Too small to trigger deadcode (currently)
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var small = map[string]int{"foo": 1}
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// Has side effects, which prevent deadcode
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var effect = map[string]int{"foo": os.Getpid()}
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// Large and side-effect free
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var large = map[string]int{
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"11": 1, "12": 2, "13": 3, "14": 4, "15": 5, "16": 6, "17": 7, "18": 8, "19": 9, "110": 10,
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"21": 1, "22": 2, "23": 3, "24": 4, "25": 5, "26": 6, "27": 7, "28": 8, "29": 9, "210": 10,
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"31": 1, "32": 2, "33": 3, "34": 4, "35": 5, "36": 6, "37": 7, "38": 8, "39": 9, "310": 10,
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"41": 1, "42": 2, "43": 3, "44": 4, "45": 5, "46": 6, "47": 7, "48": 8, "49": 9, "410": 10,
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"51": 1, "52": 2, "53": 3, "54": 4, "55": 5, "56": 6, "57": 7, "58": 8, "59": 9, "510": 10,
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"61": 1, "62": 2, "63": 3, "64": 4, "65": 5, "66": 6, "67": 7, "68": 8, "69": 9, "610": 10,
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"71": 1, "72": 2, "73": 3, "74": 4, "75": 5, "76": 6, "77": 7, "78": 8, "79": 9, "710": 10,
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"81": 1, "82": 2, "83": 3, "84": 4, "85": 5, "86": 6, "87": 7, "88": 8, "89": 9, "810": 10,
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"91": 1, "92": 2, "93": 3, "94": 4, "95": 5, "96": 6, "97": 7, "98": 8, "99": 9, "910": 10,
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"101": 1, "102": 2, "103": 3, "104": 4, "105": 5, "106": 6, "107": 7, "108": 8, "109": 9, "1010": 10, "1021": 2,
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}
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func main() {
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}
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@ -8,3 +8,7 @@
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TEXT ·sigpanic0(SB),NOSPLIT,$0-0
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JMP ·sigpanic<ABIInternal>(SB)
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#endif
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// See map.go comment on the need for this routine.
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TEXT ·mapinitnoop<ABIInternal>(SB),NOSPLIT,$0-0
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RET
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@ -1422,3 +1422,10 @@ func reflectlite_maplen(h *hmap) int {
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const maxZero = 1024 // must match value in reflect/value.go:maxZero cmd/compile/internal/gc/walk.go:zeroValSize
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var zeroVal [maxZero]byte
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// mapinitnoop is a no-op function known the Go linker; if a given global
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// map (of the right size) is determined to be dead, the linker will
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// rewrite the relocation (from the package init func) from the outlined
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// map init function to this symbol. Defined in assembly so as to avoid
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// complications with instrumentation (coverage, etc).
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func mapinitnoop()
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