cmd/compile: compiler panic in ssa.tighten

[unclejack]

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

go version go1.7.5 linux/amd64

Go was installed from the official amd64 tarball.

What operating system and processor architecture are you using (go env)?

GOARCH="amd64"
GOBIN="/opt/gopath/bin"
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/opt/gopath"
GORACE=""
GOROOT="/usr/local/go"
GOTOOLDIR="/usr/local/go/pkg/tool/linux_amd64"
CC="gcc"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build786142980=/tmp/go-build -gno-record-gcc-switches"
CXX="g++"
CGO_ENABLED="1"

What did you do?

I was compiling a project.

What did you expect to see?

I was expecting to see Go compile that project.

What did you see instead?

runtime error: invalid memory address or nil pointer dereference

goroutine 1 [running]:
cmd/compile/internal/ssa.Compile.func1(0xc424140d08, 0xc42325c0f0)
        /usr/local/go/src/cmd/compile/internal/ssa/compile.go:35 +0xc8
panic(0x8b82c0, 0xc42000e140)
        /usr/local/go/src/runtime/panic.go:458 +0x243
cmd/compile/internal/ssa.tighten(0xc42325c0f0)
        /usr/local/go/src/cmd/compile/internal/ssa/tighten.go:19 +0x64
cmd/compile/internal/ssa.Compile(0xc42325c0f0)
        /usr/local/go/src/cmd/compile/internal/ssa/compile.go:64 +0x321
cmd/compile/internal/gc.buildssa(0xc422a6c1b0, 0x0)
        /usr/local/go/src/cmd/compile/internal/gc/ssa.go:232 +0xc5f
cmd/compile/internal/gc.compile(0xc422a6c1b0)
        /usr/local/go/src/cmd/compile/internal/gc/pgen.go:405 +0x1377
cmd/compile/internal/gc.funccompile(0xc422a6c1b0)
        /usr/local/go/src/cmd/compile/internal/gc/dcl.go:1287 +0x186
cmd/compile/internal/gc.Main()
        /usr/local/go/src/cmd/compile/internal/gc/main.go:467 +0x19f8
cmd/compile/internal/amd64.Main()
        /usr/local/go/src/cmd/compile/internal/amd64/galign.go:93 +0x2fa
main.main()
        /usr/local/go/src/cmd/compile/main.go:33 +0x2a3



goroutine 1 [running]:
runtime/debug.Stack(0x0, 0x0, 0x0)
        /usr/local/go/src/runtime/debug/stack.go:24 +0x79
cmd/compile/internal/gc.Fatalf(0x90bf1b, 0x2c, 0xc423db3c40, 0x4, 0x4)
        /usr/local/go/src/cmd/compile/internal/gc/subr.go:165 +0x248
cmd/compile/internal/gc.(*ssaExport).Fatalf(0xb60d46, 0xbff, 0x90bf1b, 0x2c, 0xc423db3c40, 0x4, 0x4)
        /usr/local/go/src/cmd/compile/internal/gc/ssa.go:4437 +0x74
cmd/compile/internal/ssa.(*Config).Fatalf(0xc422f52000, 0xc400000bff, 0x90bf1b, 0x2c, 0xc423db3c40, 0x4, 0x4)
        /usr/local/go/src/cmd/compile/internal/ssa/config.go:200 +0x6e
cmd/compile/internal/ssa.(*Func).Fatalf(0xc42325c0f0, 0x90bf1b, 0x2c, 0xc423db3c40, 0x4, 0x4)
        /usr/local/go/src/cmd/compile/internal/ssa/func.go:397 +0x6b
cmd/compile/internal/ssa.Compile.func1(0xc424140d08, 0xc42325c0f0)
        /usr/local/go/src/cmd/compile/internal/ssa/compile.go:37 +0x25b
panic(0x8b82c0, 0xc42000e140)
        /usr/local/go/src/runtime/panic.go:458 +0x243
cmd/compile/internal/ssa.tighten(0xc42325c0f0)
        /usr/local/go/src/cmd/compile/internal/ssa/tighten.go:19 +0x64
cmd/compile/internal/ssa.Compile(0xc42325c0f0)
        /usr/local/go/src/cmd/compile/internal/ssa/compile.go:64 +0x321
cmd/compile/internal/gc.buildssa(0xc422a6c1b0, 0x0)
        /usr/local/go/src/cmd/compile/internal/gc/ssa.go:232 +0xc5f
cmd/compile/internal/gc.compile(0xc422a6c1b0)
        /usr/local/go/src/cmd/compile/internal/gc/pgen.go:405 +0x1377
cmd/compile/internal/gc.funccompile(0xc422a6c1b0)
        /usr/local/go/src/cmd/compile/internal/gc/dcl.go:1287 +0x186
cmd/compile/internal/gc.Main()
        /usr/local/go/src/cmd/compile/internal/gc/main.go:467 +0x19f8
cmd/compile/internal/amd64.Main()
        /usr/local/go/src/cmd/compile/internal/amd64/galign.go:93 +0x2fa
main.main()
        /usr/local/go/src/cmd/compile/main.go:33 +0x2a3

There was also something related to SSA tighthen pass at the top. I couldn't reproduce the issue to get that message again or this error above.

I've opened this issue in case there's some underlying bug. Please feel free to close this right away if it's a known issue or a duplicate.

[ianlancetaylor]

CC @randall77 @josharian

[josharian]

Looking at tighten.go at 1.7.5, that line is:

uses := make([]int32, f.NumValues())

f isn't nil; we can see from the stack trace. And we couldn't have gotten this far with a nil Func anyway.

NumValues is here:

https://github.com/golang/go/blob/release-branch.go1.7/src/cmd/compile/internal/ssa/func.go#L52
https://github.com/golang/go/blob/release-branch.go1.7/src/cmd/compile/internal/ssa/id.go#L26

I don't see anything there that could lead to a nil pointer dereference. This smells like memory corruption.

I'm not sure there's much to do if you can't reproduce it any more, even sporadically. I'll leave this open in case Keith has ideas, though.

[randall77]

I concur with Josh, I'm not seeing how this could happen.
I'm going to close for now, feel free to reopen if you see this again.