gccgo: internal compiler error in start_function

[dvyukov]

gccgo crashes on the following input:

package a
func(interface{}F(t{

go1: internal compiler error: in start_function, at go/gofrontend/gogo.cc:1821
0x62819a Gogo::start_function(std::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, Function_type*, bool, Location)
    ../../gcc/go/gofrontend/gogo.cc:1821
0x647c2b Parse::function_decl(bool)
    ../../gcc/go/gofrontend/parse.cc:2333
0x648523 Parse::program()
    ../../gcc/go/gofrontend/parse.cc:5667
0x610411 go_parse_input_files(char const**, unsigned int, bool, bool)
    ../../gcc/go/gofrontend/go.cc:73
0x60c32f go_langhook_parse_file
    ../../gcc/go/go-lang.c:304

gcc version 6.0.0 2015070 (experimental) (GCC)

[dvyukov]

@paranoiacblack

[gopherbot]

CL https://golang.org/cl/12157 mentions this issue.