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cmd/compile: internal compiler error: panic: interface conversion: interface is nil, not ir.Node #61074

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nholstein opened this issue Jun 29, 2023 · 6 comments
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cmd/compile: internal compiler error: panic: interface conversion: interface is nil, not ir.Node #61074

nholstein opened this issue Jun 29, 2023 · 6 comments
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compiler/runtime Issues related to the Go compiler and/or runtime. NeedsDecision Feedback is required from experts, contributors, and/or the community before a change can be made.
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@nholstein
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What version of Go are you using (go version)?

I'm using 1.20.5 from https://pkg.go.dev/golang.org/dl/go1.20.5

$ go1.20.5 version
go version go1.20.5 darwin/arm64

Does this issue reproduce with the latest release?

Yes, with 1.20.5. It does not reproduce with 1.21rc2.

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

I'm running on darwin/arm64. I've also reproduced on linux/amd64.

go env Output
$ go1.20.5 env
GO111MODULE=""
GOARCH="arm64"
GOBIN=""
GOCACHE="/Users/ngh/Library/Caches/go-build"
GOENV="/Users/ngh/Library/Application Support/go/env"
GOEXE=""
GOEXPERIMENT=""
GOFLAGS=""
GOHOSTARCH="arm64"
GOHOSTOS="darwin"
GOINSECURE=""
GOMODCACHE="/Users/ngh/go/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="darwin"
GOPATH="/Users/ngh/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/Users/ngh/sdk/go1.20.5"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/Users/ngh/sdk/go1.20.5/pkg/tool/darwin_arm64"
GOVCS=""
GOVERSION="go1.20.5"
GCCGO="gccgo"
AR="ar"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD="/dev/null"
GOWORK=""
CGO_CFLAGS="-O2 -g"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-O2 -g"
CGO_FFLAGS="-O2 -g"
CGO_LDFLAGS="-O2 -g"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -arch arm64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/7q/4jtm00sd11d6vh2r7m59snmr0000gn/T/go-build2788118703=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

I was testing the new clear builtin on go1.21rc2, then ran the same code on go1.20.5. I expected the compilation to fail due to the undefined clear function; instead the compiler panicked. I minimized to the following program:

package main

func main() {
        var foo []string
        clear(foo)
}

And see the following error:

$ go1.20.5 run ./clear.go
# command-line-arguments
./clear.go:3:6: internal compiler error: panic: interface conversion: interface is nil, not ir.Node

Please file a bug report including a short program that triggers the error.
https://go.dev/issue/new

What did you expect to see?

A compilation error ("./clear.go:5:9: undefined: clear") on go1.20.5.

Successful compilation on go1.21rc2.

What did you see instead?

Successful compilation on go1.21rc2. 👍

An internal compiler error panic with go1.20.5:

./clear.go:3:6: internal compiler error: panic: interface conversion: interface is nil, not ir.Node
@nholstein
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It's worth noting the impact of this crash is limited; it only impacts valid Go 1.21 code using clear when compiled with go1.20.x. Older versions of Go behave as expected; go1.19.9 handles the erroneous source correctly:

$ go1.19.9 run ./clear.go
# command-line-arguments
./clear.go:5:9: undefined: clear

And with go1.20.5 any name other than clear doesn't crash. Additionally, if I change the type of var foo []string to a non-clearable type (var foo int), go1.20.5 doesn't panic and returns this error:

$ go1.20.5 run ./clear.go
# command-line-arguments
./clear.go:5:15: invalid argument: cannot clear foo (variable of type int): argument must be (or constrained by) map, slice, or array pointer

I've been testing by directly running the source file (go run ./clear.go); if module mode is enabled the compiler helpfully prints this error:

note: module requires Go 1.21

So I believe this will only impact code which correctly uses clear in 1.21 when compiled using a go1.20.x toolchain. One way this might occur is if a Go 1.20 module imports as 1.21 module.

@cuonglm
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cuonglm commented Jun 29, 2023

GOEXPERIMENT=nounified produces a better message, though still ICE:

$ GOEXPERIMENT=nounified go1.20.5 run main.go
# command-line-arguments
<unknown line number>: internal compiler error: failed to resolve builtin clear

cc @mdempsky @griesemer for decision.

@cuonglm cuonglm added the NeedsDecision Feedback is required from experts, contributors, and/or the community before a change can be made. label Jun 29, 2023
@griesemer
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go1.20 should report the error

clear requires go1.21 or later (-lang was set to go1.20; check go.mod)

(playground).

@cuonglm
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cuonglm commented Jun 29, 2023

go1.20 should report the error

clear requires go1.21 or later (-lang was set to go1.20; check go.mod)

(playground).

go1.20 and go1.20.x trigger ICE in my local, not sure why playground doesn't.

@mdempsky
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Playground autogenerates a 1.20 go.mod file I think. This repros it: https://go.dev/play/p/sbnZ28wE-s6

I think the issue is 1.20 typechecker understands clear and allows it sometimes, but the backend doesn't have it at all.

@mdempsky
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The problem here is basically just a worse error message: the Go 1.20 compiler is crashing and reporting an ICE instead of giving a standard error message when trying to compile Go 1.21 code.

We could backport a fix to report a nicer error message, but I don't think that really lives up to the standard we normally expect of backports. And it's not an issue with 1.21 or moving forward.

@bcmills bcmills added the compiler/runtime Issues related to the Go compiler and/or runtime. label Jun 29, 2023
@mknyszek mknyszek changed the title cmd/compile@1.20.5: internal compiler error: panic: interface conversion: interface is nil, not ir.Node cmd/compile: internal compiler error: panic: interface conversion: interface is nil, not ir.Node Jul 12, 2023
@mknyszek mknyszek added this to the Backlog milestone Jul 12, 2023
@mknyszek mknyszek closed this as not planned Won't fix, can't repro, duplicate, stale Jul 12, 2023
@mdempsky mdempsky mentioned this issue Jul 12, 2023
Closed
@randall77 randall77 mentioned this issue Jan 28, 2024
Closed
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@mdempsky @mknyszek @cuonglm @bcmills @griesemer @nholstein