gccgo: internal compiler error in do_lower

[dvyukov]

gccgo crashes on the following program:

package a
var f=0<<6i

go1: internal compiler error: in do_lower, at go/gofrontend/expressions.cc:4881
0x5f86fc Binary_expression::do_lower(Gogo*, Named_object*, Statement_inserter*, int)
    ../../gcc/go/gofrontend/expressions.cc:4881
0x6108ae Expression::lower(Gogo*, Named_object*, Statement_inserter*, int)
    ../../gcc/go/gofrontend/expressions.h:801
0x6108ae Lower_parse_tree::expression(Expression**)
    ../../gcc/go/gofrontend/gogo.cc:2744
0x61245e Gogo::lower_expression(Named_object*, Statement_inserter*, Expression**)
    ../../gcc/go/gofrontend/gogo.cc:2783
0x61c0fc Variable::lower_init_expression(Gogo*, Named_object*, Statement_inserter*)
    ../../gcc/go/gofrontend/gogo.cc:6041
0x61c14c Lower_parse_tree::variable(Named_object*)
    ../../gcc/go/gofrontend/gogo.cc:2613
0x6169c9 Bindings::traverse(Traverse*, bool)
    ../../gcc/go/gofrontend/gogo.cc:7546
0x616b51 Gogo::traverse(Traverse*)
    ../../gcc/go/gofrontend/gogo.cc:2495
0x617047 Gogo::lower_parse_tree()
    ../../gcc/go/gofrontend/gogo.cc:2761
0x61042c go_parse_input_files(char const**, unsigned int, bool, bool)
    ../../gcc/go/gofrontend/go.cc:95
0x60c20f go_langhook_parse_file
    ../../gcc/go/go-lang.c:304

gofrontend is on commit 1d9d92ab09996d2f7795481d2876a21194502b89

[dvyukov]

@ianlancetaylor

[gopherbot]

CL https://golang.org/cl/14646 mentions this issue.