cmd/compile: SIGSEGV with 'go build'

[olivere]

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

$ go version
go version go1.17.6 darwin/arm64

Does this issue reproduce with the latest release?

Yes.

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

go env Output

$ go env
GO111MODULE=""
GOARCH="arm64"
GOBIN=""
GOCACHE="/Users/oliver/Library/Caches/go-build"
GOENV="/Users/oliver/Library/Application Support/go/env"
GOEXE=""
GOEXPERIMENT=""
GOFLAGS=""
GOHOSTARCH="arm64"
GOHOSTOS="darwin"
GOINSECURE=""
GOMODCACHE="/Users/oliver/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="darwin"
GOPATH="/Users/oliver"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/Users/oliver/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/Users/oliver/go/pkg/tool/darwin_arm64"
GOVCS=""
GOVERSION="go1.17.6"
GCCGO="gccgo"
AR="ar"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD="/Users/oliver/tmp/dict/go.mod"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -arch arm64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/tg/tvt4qm6d71q6p6v6g8dgbwc00000gn/T/go-build160318427=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

package main

import "fmt"

func main() {
	d := make(map[string]string)

	// I meant that to be:
	// for k, v := range d { ... }
	//
	// But I didn't expect it to crash a build, but get an error.
	for _, k, v := range d {
		fmt.Println(k, v)
	}
}

See code on Go Play.

What did you expect to see?

A proper build-time error.

What did you see instead?

A crash in the compiler:

$ go build
# dict.dev
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x2 addr=0x5c pc=0x104ca1da0]

goroutine 1 [running]:
cmd/compile/internal/types.(*Type).HasPointers(0x0)
	/usr/local/go/src/cmd/compile/internal/types/type.go:1592 +0x20
cmd/compile/internal/escape.(*escape).exprSkipInit(0x140000ea1c0, {0x14000381030, 0x0, 0x0, 0x0, 0x0}, {0x10558f668, 0x14000406ea0})
	/usr/local/go/src/cmd/compile/internal/escape/escape.go:584 +0x124
cmd/compile/internal/escape.(*escape).expr(0x140000ea1c0, {0x14000381030, 0x0, 0x0, 0x0, 0x0}, {0x10558f668, 0x14000406ea0})
	/usr/local/go/src/cmd/compile/internal/escape/escape.go:566 +0x78
cmd/compile/internal/escape.(*escape).assignList(0x140000ea1c0, {0x140000ea060, 0x2, 0x2}, {0x140000ea040, 0x2, 0x2}, {0x1053613da, 0xb}, {0x10558dca0, ...})
	/usr/local/go/src/cmd/compile/internal/escape/escape.go:972 +0x354
cmd/compile/internal/escape.(*escape).stmt(0x140000ea1c0, {0x10558dca0, 0x140000b0180})
	/usr/local/go/src/cmd/compile/internal/escape/escape.go:508 +0xc74
cmd/compile/internal/escape.(*escape).stmts(0x140000ea1c0, {0x14000444100, 0xe, 0x10})
	/usr/local/go/src/cmd/compile/internal/escape/escape.go:548 +0x74
cmd/compile/internal/escape.(*escape).stmt(0x140000ea1c0, {0x10558e088, 0x140000b2140})
	/usr/local/go/src/cmd/compile/internal/escape/escape.go:400 +0x9f8
cmd/compile/internal/escape.(*escape).stmts(0x140000ea1c0, {0x1400005c140, 0x1, 0x1})
	/usr/local/go/src/cmd/compile/internal/escape/escape.go:548 +0x74
cmd/compile/internal/escape.(*escape).block(...)
	/usr/local/go/src/cmd/compile/internal/escape/escape.go:555
cmd/compile/internal/escape.(*escape).stmt(0x140000ea1c0, {0x10558f988, 0x14000404360})
	/usr/local/go/src/cmd/compile/internal/escape/escape.go:457 +0x988
cmd/compile/internal/escape.(*escape).stmts(0x140000ea1c0, {0x14000068340, 0x2, 0x2})
	/usr/local/go/src/cmd/compile/internal/escape/escape.go:548 +0x74
cmd/compile/internal/escape.(*escape).block(0x140000ea1c0, {0x14000068340, 0x2, 0x2})
	/usr/local/go/src/cmd/compile/internal/escape/escape.go:555 +0x48
cmd/compile/internal/escape.(*batch).walkFunc(0x1400000a480, 0x14000400160)
	/usr/local/go/src/cmd/compile/internal/escape/escape.go:307 +0x118
cmd/compile/internal/escape.Batch({0x140000ae070, 0x1, 0x1}, 0x0)
	/usr/local/go/src/cmd/compile/internal/escape/escape.go:229 +0x1d4
cmd/compile/internal/ir.(*bottomUpVisitor).visit(0x14000098750, 0x14000400160)
	/usr/local/go/src/cmd/compile/internal/ir/scc.go:128 +0x3a8
cmd/compile/internal/ir.VisitFuncsBottomUp({0x14000068360, 0x2, 0x2}, 0x10556a6c8)
	/usr/local/go/src/cmd/compile/internal/ir/scc.go:60 +0x11c
cmd/compile/internal/escape.Funcs(...)
	/usr/local/go/src/cmd/compile/internal/escape/escape.go:1821
cmd/compile/internal/gc.Main(0x10556a630)
	/usr/local/go/src/cmd/compile/internal/gc/main.go:253 +0xef4
main.main()
	/usr/local/go/src/cmd/compile/main.go:55 +0x144

[bcmills]

Looks like this is fixed at head (https://go.dev/play/p/VGzVWkFnZNw?v=gotip):

./prog.go:12:12: range clause permits at most two iteration variables
./prog.go:13:18: undefined: v

[olivere]

Oh, I'm sorry I didn't try that.

[ianlancetaylor]

Thanks for reporting the bug.

Since this will be fixed in the 1.18 release, and since the code is invalid anyhow, I don't think it's worth backporting the fix. I'm going to close this issue.