cmd/compile: crash inlining function with FOR loop with labeled breaks/continues

[danscales]

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

Go tip

Does this issue reproduce with the latest release?

No, this is only on tip.

What did you do?

package main

func f(j int) {
loop:
	for i := 0; i < 4; i++ {
		if i == 1 {
			continue loop
		}
		println(j, i)
	}
}

func main() {
loop:
	for j := 0; j < 5; j++ {
		f(j)
		if j == 3 {
			break loop
		}
	}
}

What did you expect to see?

0 0
0 2
0 3
1 0
1 2
1 3
2 0
2 2
2 3
3 0
3 2
3 3

What did you see instead?

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x30 pc=0xa4eea1]

goroutine 1 [running]:
cmd/compile/internal/ssa.(*Block).AddEdgeTo(...)
go/src/cmd/compile/internal/ssa/block.go:274
cmd/compile/internal/ssagen.(*state).stmt(0xc0000e4700, {0xe43e50, 0xc0003dfad0})
go/src/cmd/compile/internal/ssagen/ssa.go:1731 +0x1461
cmd/compile/internal/ssagen.(*state).stmtList(0xc0000e4700, {0xc00006f3d0, 0x1, 0xc0004b7e00})
go/src/cmd/compile/internal/ssagen/ssa.go:1374 +0x5d
cmd/compile/internal/ssagen.(*state).stmt(0xc0000e4700, {0xe44b98, 0xc0003ef570})
go/src/cmd/compile/internal/ssagen/ssa.go:1678 +0x2d95
cmd/compile/internal/ssagen.(*state).stmtList(0xc0000e4700, {0xc0000e4200, 0x9, 0x4})
go/src/cmd/compile/internal/ssagen/ssa.go:1374 +0x5d
cmd/compile/internal/ssagen.(*state).stmt(0xc0000e4700, {0xe447b0, 0xc00036e3f0})
go/src/cmd/compile/internal/ssagen/ssa.go:1781 +0x20c9
cmd/compile/internal/ssagen.(*state).stmtList(0xc0000e4700, {0xc000418780, 0x4, 0x7ff37d75d768})
go/src/cmd/compile/internal/ssagen/ssa.go:1374 +0x5d
cmd/compile/internal/ssagen.buildssa(0xc000412c60, 0x0)
go/src/cmd/compile/internal/ssagen/ssa.go:567 +0x1d13
cmd/compile/internal/ssagen.Compile(0xc000412c60, 0xc000414ca0)
go/src/cmd/compile/internal/ssagen/pgen.go:183 +0x4c
cmd/compile/internal/gc.compileFunctions.func4.1(0x1)
go/src/cmd/compile/internal/gc/compile.go:153 +0x3a
cmd/compile/internal/gc.compileFunctions.func2(0x0)
go/src/cmd/compile/internal/gc/compile.go:125 +0x1e
cmd/compile/internal/gc.compileFunctions.func4({0xc00006f490, 0x2, 0x2})
go/src/cmd/compile/internal/gc/compile.go:152 +0x53
cmd/compile/internal/gc.compileFunctions()
go/src/cmd/compile/internal/gc/compile.go:163 +0x162
cmd/compile/internal/gc.Main(0xd13090)
go/src/cmd/compile/internal/gc/main.go:314 +0x1016
main.main()
go/src/cmd/compile/main.go:55 +0xdd

This is happening because of the identical labels between the inlined function and the outer function. We already have some code to make labels in inlined functions be unique, but we're not using it for labeled breaks/continues/for loops.

[gopherbot]

Change https://golang.org/cl/357649 mentions this issue: cmd/compile: fix inlining of labeled for loops