cmd/compile: building causes a panic: runtime error: index out of range [-1]

[renthraysk]

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

$ go version
go version go1.17 linux/amd64

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

What did you do?

package main

import (
	"io"
)

type Writer interface {
	io.Writer
	io.StringWriter
	io.ByteWriter
}

func writeString[T Writer](w T, s string) {
	w.WriteString(s)
}

func WriteString(w Writer, s string) {
	writeString[Writer](w, s)
}

func main() {
}

Attempting to build with go build -gcflags="-G=3" main.go

What did you expect to see?

No panic

What did you see instead?

# command-line-arguments
panic: runtime error: index out of range [-1]

goroutine 1 [running]:
cmd/compile/internal/ssagen.(*state).peekPos(...)
	/usr/local/go/src/cmd/compile/internal/ssagen/ssa.go:1061
cmd/compile/internal/ssagen.(*state).pushLine(0xc000150200, {0x44cb14, 0x0})
	/usr/local/go/src/cmd/compile/internal/ssagen/ssa.go:1043 +0x147
cmd/compile/internal/ssagen.buildssa(0xc00001eb00, 0x0)
	/usr/local/go/src/cmd/compile/internal/ssagen/ssa.go:420 +0x497
cmd/compile/internal/ssagen.Compile(0xc00001eb00, 0xc0000c6d00)
	/usr/local/go/src/cmd/compile/internal/ssagen/pgen.go:165 +0x4c
cmd/compile/internal/gc.compileFunctions.func4.1(0x1)
	/usr/local/go/src/cmd/compile/internal/gc/compile.go:153 +0x3a
cmd/compile/internal/gc.compileFunctions.func2(0x0)
	/usr/local/go/src/cmd/compile/internal/gc/compile.go:125 +0x1e
cmd/compile/internal/gc.compileFunctions.func4({0xc0000c6ca0, 0x4, 0x4})
	/usr/local/go/src/cmd/compile/internal/gc/compile.go:152 +0x53
cmd/compile/internal/gc.compileFunctions()
	/usr/local/go/src/cmd/compile/internal/gc/compile.go:163 +0x162
cmd/compile/internal/gc.Main(0xd16450)
	/usr/local/go/src/cmd/compile/internal/gc/main.go:287 +0xf3a
main.main()
	/usr/local/go/src/cmd/compile/main.go:55 +0xdd

[ALTree]

I don't think you're supposed to use -G=3 on 1.17. The dev.tyeparams branch was merged into master after the release. -G=3 in 1.17 has a lot of bugs and it's not supposed to be used at all, in general.

If you want to experiment with generics, use -G=3 with tip.

Anyway this is fixed on tip, so closing here.