tgt-vhdl: Fix shift2 test regression

Caused by translate_select emitting a logical instead of arithmetic
shift for signed arguments.

tgt-vhdl/expr.cc

@@ -473,8 +473,18 @@ static vhdl_expr *translate_select(ivl_expr_t e)
          // We can't directly select bits from something that's not
          // a variable reference in VHDL, but we can emulate the
          // effect with a shift and a resize
-         return new vhdl_binop_expr(from, VHDL_BINOP_SR, base->to_integer(),
+
-                                    new vhdl_type(*from->get_type()));
+         if (ivl_expr_signed(ivl_expr_oper1(e))) {
+            vhdl_fcall *sra = new vhdl_fcall("shift_right", from->get_type());
+            sra->add_expr(from);
+            sra->add_expr(base->to_integer());
+
+            return sra;
+         }
+         else
+            return new vhdl_binop_expr(from, VHDL_BINOP_SR, base->to_integer(),
+                                       from->get_type());
+
       }
       else if (from_var_ref->get_type()->get_name() != VHDL_TYPE_STD_LOGIC) {
          // We can use the more idiomatic VHDL slice notation on a

tgt-vhdl/vhdl_syntax.cc

@@ -923,7 +923,7 @@ void vhdl_unaryop_expr::emit(std::ostream &of, int level) const
 }
 
 vhdl_binop_expr::vhdl_binop_expr(vhdl_expr *left, vhdl_binop_t op,
-                                 vhdl_expr *right, vhdl_type *type)
+                                 vhdl_expr *right, const vhdl_type *type)
    : vhdl_expr(type), op_(op)
 {
    add_expr(left);

tgt-vhdl/vhdl_syntax.hh

@@ -119,10 +119,10 @@ enum vhdl_binop_t {
  */
 class vhdl_binop_expr : public vhdl_expr {
 public:
-   vhdl_binop_expr(vhdl_binop_t op, vhdl_type *type)
+   vhdl_binop_expr(vhdl_binop_t op, const vhdl_type *type)
       : vhdl_expr(type), op_(op) {}
    vhdl_binop_expr(vhdl_expr *left, vhdl_binop_t op,
-                   vhdl_expr *right, vhdl_type *type);
+                   vhdl_expr *right, const vhdl_type *type);
    ~vhdl_binop_expr();
 
    void add_expr(vhdl_expr *e);
@@ -271,7 +271,7 @@ private:
  */
 class vhdl_fcall : public vhdl_expr {
 public:
-   vhdl_fcall(const string& name, vhdl_type *rtype)
+   vhdl_fcall(const string& name, const vhdl_type *rtype)
       : vhdl_expr(rtype), name_(name) {};
    ~vhdl_fcall() {}