compiler: Don't crash with self-referential types.

Fixes issue 6637.

From-SVN: r218199

gcc/go/gofrontend/expressions.cc

@@ -8735,7 +8735,11 @@ Call_expression::do_flatten(Gogo* gogo, Named_object*,
   // Add temporary variables for all arguments that require type
   // conversion.
   Function_type* fntype = this->get_function_type();
-  go_assert(fntype != NULL);
+  if (fntype == NULL)
+    {
+      go_assert(saw_errors());
+      return this;
+    }
   if (this->args_ != NULL && !this->args_->empty()
       && fntype->parameters() != NULL && !fntype->parameters()->empty())
     {
@@ -10901,9 +10905,8 @@ Interface_field_reference_expression::do_traverse(Traverse* traverse)
 // interface.  So introduce a temporary variable if necessary.
 
 Expression*
-Interface_field_reference_expression::do_lower(Gogo*, Named_object*,
-					       Statement_inserter* inserter,
-					       int)
+Interface_field_reference_expression::do_flatten(Gogo*, Named_object*,
+						 Statement_inserter* inserter)
 {
   if (!this->expr_->is_variable())
     {

gcc/go/gofrontend/expressions.h

@@ -2397,7 +2397,7 @@ class Interface_field_reference_expression : public Expression
   do_traverse(Traverse* traverse);
 
   Expression*
-  do_lower(Gogo*, Named_object*, Statement_inserter*, int);
+  do_flatten(Gogo*, Named_object*, Statement_inserter*);
 
   Type*
   do_type();

gcc/go/gofrontend/types.cc

@@ -6361,7 +6361,13 @@ Array_type::do_reflection(Gogo* gogo, std::string* ret) const
       unsigned long val;
       if (!this->length_->numeric_constant_value(&nc)
 	  || nc.to_unsigned_long(&val) != Numeric_constant::NC_UL_VALID)
+	{
+	  if (!this->issued_length_error_)
+	    {
 	      error_at(this->length_->location(), "invalid array length");
+	      this->issued_length_error_ = true;
+	    }
+	}
       else
 	{
 	  char buf[50];
@@ -6488,7 +6494,13 @@ Array_type::do_mangled_name(Gogo* gogo, std::string* ret) const
       unsigned long val;
       if (!this->length_->numeric_constant_value(&nc)
 	  || nc.to_unsigned_long(&val) != Numeric_constant::NC_UL_VALID)
+	{
+	  if (!this->issued_length_error_)
+	    {
 	      error_at(this->length_->location(), "invalid array length");
+	      this->issued_length_error_ = true;
+	    }
+	}
       else
 	{
 	  char buf[50];
@@ -10221,7 +10233,12 @@ Type*
 Forward_declaration_type::real_type()
 {
   if (this->is_defined())
+    {
+      Named_type* nt = this->named_object()->type_value();
+      if (!nt->is_valid())
+	return Type::make_error_type();
       return this->named_object()->type_value();
+    }
   else
     {
       this->warn();
@@ -10233,7 +10250,12 @@ const Type*
 Forward_declaration_type::real_type() const
 {
   if (this->is_defined())
+    {
+      const Named_type* nt = this->named_object()->type_value();
+      if (!nt->is_valid())
+	return Type::make_error_type();
       return this->named_object()->type_value();
+    }
   else
     {
       this->warn();

gcc/go/gofrontend/types.h

@@ -2360,7 +2360,8 @@ class Array_type : public Type
  public:
   Array_type(Type* element_type, Expression* length)
     : Type(TYPE_ARRAY),
-      element_type_(element_type), length_(length), blength_(NULL)
+      element_type_(element_type), length_(length), blength_(NULL),
+      issued_length_error_(false)
   { }
 
   // Return the element type.
@@ -2479,6 +2480,9 @@ class Array_type : public Type
   // The backend representation of the length.
   // We only want to compute this once.
   Bexpression* blength_;
+  // Whether or not an invalid length error has been issued for this type,
+  // to avoid knock-on errors.
+  mutable bool issued_length_error_;
 };
 
 // The type of a map.
@@ -2926,6 +2930,11 @@ class Named_type : public Type
   bool
   is_alias() const;
 
+  // Whether this named type is valid.  A recursive named type is invalid.
+  bool
+  is_valid() const
+  { return !this->is_error_; }
+
   // Whether this is a circular type: a pointer or function type that
   // refers to itself, which is not possible in C.
   bool