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cmd/compile: internal error autotmp_3 (type *int) recorded as live on entry, p.Pc=0 #15091

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gyuho opened this issue Apr 4, 2016 · 8 comments
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cmd/compile: internal error autotmp_3 (type *int) recorded as live on entry, p.Pc=0 #15091

gyuho opened this issue Apr 4, 2016 · 8 comments
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Go1.7

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@gyuho
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gyuho commented Apr 4, 2016

This was first reported here russross/blackfriday#251, but it looks like a Go compiler issue.

What version of Go are you using (go version)?

go version devel +59fc42b Fri Apr 1 22:23:13 2016 +0000 linux/amd64

What operating system and processor architecture are you using (go env)?
GOARCH="amd64"
GOBIN=""
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/home/gyuho/go"
GORACE=""
GOROOT="/home/gyuho/go-master/go"
GOTOOLDIR="/home/gyuho/go-master/go/pkg/tool/linux_amd64"
CC="gcc"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build999228004=/tmp/go-build -gno-record-gcc-switches"
CXX="g++"
CGO_ENABLED="1"
What did you do?

I just run go build -race to reproduce:

package sample

type Html struct {
    headerIDs map[string]int
}

func (options *Html) header(id string) string {
    for count, found := options.headerIDs[id]; found; count, found = options.headerIDs[id] {
        _ = count
    }
    return ""
}
What did you expect to see?

No error message.

What did you see instead?
./sample.go:7: internal error: (*Html).header autotmp_3 (type *int) recorded as live on entry, p.Pc=0

Thank you all!
@bradfitz bradfitz added this to the Go1.7 milestone Apr 4, 2016
@bradfitz
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bradfitz commented Apr 4, 2016

/cc @randall77 @brtzsnr @josharian

@josharian
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git bisect implicates e99dd52

/cc @dr2chase

@josharian
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Although I don't really see how

@josharian
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Oh. Because I was using a script with git bisect, and that version fails make.bash. Sigh. Trying again with a better script...

@josharian
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Actually, that revision might be the actual culprit. From the description: "Add convert op for proper liveness in presence of uintptr to/from unsafe.Pointer conversions." And I forgot that this gets triggered via the race detector, which plays fast and loose with types internally.

@josharian josharian mentioned this issue Apr 8, 2016
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@dr2chase
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dr2chase commented Apr 8, 2016

Unclear whether race detector is inserting bad code or if this is a fumbled conversion.
autotmp_3 appears after "walk", target of an assignment:

.   .   .   .   .   AS u(1) l(8) tc(1)
.   .   .   .   .   .   NAME-sample.autotmp_3 u(1) a(true) l(8) x(0+0) class(PAUTO) esc(N) tc(1) used(true) PTR64-*int
.   .   .   .   .   .   INDREG-SP a(true) l(8) x(32+0) tc(1) runtime.val·1 PTR64-*int

Race detector inserts what looks like a use before initialization, though we could have botched the conversions, too:

.   .   .   CALLFUNC u(100) l(8) tc(1)
.   .   .   .   NAME-runtime.raceread u(1) a(true) x(0+0) class(PFUNC) tc(1) used(true) FUNC-func(uintptr)
.   .   .   CALLFUNC-list
.   .   .   .   AS u(2) l(8) tc(1)
.   .   .   .   .   INDREG-SP a(true) l(8) x(0+0) tc(1) uintptr
.   .   .   .   .   CONVNOP u(2) l(8) tc(1) uintptr
.   .   .   .   .   .   CONVNOP u(2) l(8) tc(1) TUNSAFEPTR-unsafe.Pointer
.   .   .   .   .   .   .   ADDR u(2) l(8) tc(1) PTR64-*int
.   .   .   .   .   .   .   .   IND u(2) l(8) tc(1) addrtaken int
.   .   .   .   .   .   .   .   .   NAME-sample.autotmp_3 u(1) a(true) l(8) x(0+0) class(PAUTO) esc(N) tc(1) used(true) PTR64-*int

For reasons not 100% clear, this ends up with autotmp_3 treated as if it were an argument to the function, which ultimately fails because of course it isn't.

Any insights into what the race detector is doing here would be welcome, I am going to look both at that and at the convert op code.

@gopherbot
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CL https://golang.org/cl/21771 mentions this issue.

@dr2chase dr2chase self-assigned this Apr 8, 2016
@gyuho
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gyuho commented Apr 8, 2016

Awesome. Confirmed that it's fixed. Thanks all!

@gyuho gyuho mentioned this issue Apr 8, 2016
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@dr2chase dr2chase mentioned this issue Jun 10, 2016
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