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cmd/compile: internal compiler error: methods are too far away #16037

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dsnet opened this issue Jun 10, 2016 · 4 comments
Closed

cmd/compile: internal compiler error: methods are too far away #16037

dsnet opened this issue Jun 10, 2016 · 4 comments
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FrozenDueToAge NeedsFix The path to resolution is known, but the work has not been done.
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Go1.7

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@dsnet
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dsnet commented Jun 10, 2016 •
edited

Using go1.7beta1

Consider this generator code:

package main

import (
    "fmt"
    "html/template"
    "os"
)

var tmpl = template.Must(template.New("main").Parse(`
package main

type T struct {
{{range .Names}}
    {{.Name}} *string
{{end}}
}

{{range .Names}}
func (t *T) Get{{.Name}}() string {
    if t.{{.Name}} == nil {
        return ""
    }
    return *t.{{.Name}}
}
{{end}}

func main() {}
`))

func main() {
    const n = 5000

    type Name struct{ Name string }
    var t struct{ Names []Name }
    for i := 0; i < n; i++ {
        t.Names = append(t.Names, Name{Name: fmt.Sprintf("H%06X", i)})
    }
    tmpl.Execute(os.Stdout, t)
}

This program produces a giant struct with n fields, and n accessor methods to get at those fields and is similar to whats generated by large protobuf files.

Compiling the program produced by this generator crashes the compiler:

$ go run gen.go > main.go
$ go run main.go
# command-line-arguments
main.go:45011: internal compiler error: methods are too far away on T: 120008

goroutine 1 [running]:
runtime/debug.Stack(0x0, 0x0, 0x0)
    /go/src/runtime/debug/stack.go:24 +0x79
cmd/compile/internal/gc.Fatalf(0x4fffff, 0x22, 0xc420c6b340, 0x2, 0x2)
    /go/src/cmd/compile/internal/gc/subr.go:165 +0x248
cmd/compile/internal/gc.dextratype(0xc420e693b0, 0x54, 0xc420c40af0, 0x1d4c8, 0x50)
    /go/src/cmd/compile/internal/gc/reflect.go:613 +0x2db
cmd/compile/internal/gc.dtypesym(0xc420c40af0, 0xc420c40af0)
    /go/src/cmd/compile/internal/gc/reflect.go:1305 +0x103b
cmd/compile/internal/gc.dtypesym(0xc420c40c30, 0xc420c6ba20)
    /go/src/cmd/compile/internal/gc/reflect.go:1278 +0xd37
cmd/compile/internal/gc.dumptypestructs()
    /go/src/cmd/compile/internal/gc/reflect.go:1363 +0xcc
cmd/compile/internal/gc.dumpobj1(0x7fff5fbff451, 0x5b, 0x3)
    /go/src/cmd/compile/internal/gc/obj.go:133 +0x553
cmd/compile/internal/gc.dumpobj()
    /go/src/cmd/compile/internal/gc/obj.go:45 +0x52
cmd/compile/internal/gc.Main()
    /go/src/cmd/compile/internal/gc/main.go:488 +0x1a5d
cmd/compile/internal/amd64.Main()
    /go/src/cmd/compile/internal/amd64/galign.go:93 +0x2fa
main.main()
    /go/src/cmd/compile/main.go:33 +0x2a3

This did not fail with the Go1.6 compiler.

/cc @crawshaw @griesemer @ianlancetaylor @randall77
@dsnet dsnet added the NeedsFix The path to resolution is known, but the work has not been done. label Jun 10, 2016
@dsnet dsnet added this to the Go1.7 milestone Jun 10, 2016
@dsnet
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dsnet commented Jun 10, 2016

The error was introduced in 7d46917

@ianlancetaylor
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Hmmm, this does seem to be a problem. The overhaul of the reflection data structures assumed that all types are small. That appears not to be the case.

@crawshaw
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Even when the offset CL series is complete in 1.8 the space needed for each struct field on amd64 will be 16-bytes, so several thousand fields will overflow a uint16. So it looks like the moff field of uncommonType needs to be 4-bytes. For alignment, mcount should probably be pushed up to 4-bytes.

I'll do this tomorrow when I'm back from vacation.

@gopherbot
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CL https://golang.org/cl/24070 mentions this issue.

@golang golang locked and limited conversation to collaborators Jun 14, 2017
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