gccgo: segmentation fault on invalid recursive type

[mdempsky]

Compiling this code with gccgo:

package p

import "unsafe"

type T struct {
        x int
        y int
        z [unsafe.Offsetof(T{}.y)]int
}

produces this crash:

x.go:5:6: error: invalid recursive type 'T'
 type T struct {
      ^
go1: internal compiler error: Segmentation fault

0xc133bf crash_signal
        /usr/local/google/tmp/go-build-release/gccgo-srcdir/gcc/toplev.c:326
0x7208dd Type::is_backend_type_size_known(Gogo*)
        /usr/local/google/tmp/go-build-release/gccgo-srcdir/gcc/go/gofrontend/types.cc:3382
0x725e58 Struct_type::backend_field_offset(Gogo*, unsigned int, long*)
        /usr/local/google/tmp/go-build-release/gccgo-srcdir/gcc/go/gofrontend/types.cc:6439
[...]

/cc @ianlancetaylor @thanm

(cmd/compile and go/types also reject the code, though each with slightly different error messages.)

[thanm]

I'll take a look

[gopherbot]

Change https://golang.org/cl/97855 mentions this issue: compiler: avoid crashing on bad self-referential type