VHDL: ensure with-select statement choices completely cover input space

Newer versions of GHDL seem to be stricter when checking this than
older versions. ModelSim still accepts an incomplete with-select,
however.

This patch makes the output 'U' if none of the conditions match.
(cherry picked from commit 9c568d8f47)

tgt-vhdl/logic.cc

@@ -145,6 +145,10 @@ static void comb_udp_logic(vhdl_arch *arch, ivl_net_logic_t log)
    vhdl_var_ref *out = nexus_to_var_ref(arch->get_scope(), output_nex);
    vhdl_with_select_stmt *ws =
       new vhdl_with_select_stmt(new vhdl_var_ref(*tmp_ref), out);
+
+   // Ensure the select statement completely covers the input space
+   // or some strict VHDL compilers will complain
+   ws->add_default(new vhdl_const_bit('X'));
    
    int nrows = ivl_udp_rows(udp);
    for (int i = 0; i < nrows; i++) {

tgt-vhdl/vhdl_syntax.cc

@@ -1005,13 +1005,18 @@ void vhdl_with_select_stmt::emit(std::ostream &of, int level) const
       of << " when ";
       (*it).cond->emit(of, level);
       
-      if (++it != whens_.end()) {
+      if (++it != whens_.end() || others_ != NULL) {
          of << ",";
          newline(of, indent(level));
       }
       else
          of << ";";
    }
+
+   if (others_) {
+      others_->emit(of, level);
+      of << " when others;";
+   }
 }
 
 void vhdl_with_select_stmt::add_condition(vhdl_expr *value, vhdl_expr *cond, vhdl_expr *delay)
@@ -1019,3 +1024,8 @@ void vhdl_with_select_stmt::add_condition(vhdl_expr *value, vhdl_expr *cond, vhd
    when_part_t when = { value, cond, delay };
    whens_.push_back(when);
 }
+
+void vhdl_with_select_stmt::add_default(vhdl_expr* value)
+{
+   others_ = value;
+}

tgt-vhdl/vhdl_syntax.hh

@@ -311,15 +311,17 @@ private:
 class vhdl_with_select_stmt : public vhdl_conc_stmt {
 public:
    vhdl_with_select_stmt(vhdl_expr *test, vhdl_var_ref *out)
-      : test_(test), out_(out) {}
+      : test_(test), out_(out), others_(NULL) {}
    ~vhdl_with_select_stmt();
    
    void emit(std::ostream &of, int level) const;
    void add_condition(vhdl_expr *value, vhdl_expr *cond, vhdl_expr *delay=NULL);
+   void add_default(vhdl_expr* value);
 private:
    vhdl_expr *test_;
    vhdl_var_ref *out_;
    when_list_t whens_;
+   vhdl_expr* others_;
 };