Add some casts in tgt-vhdl to remove warnings.

The Cygwin compiler is a bit picky. This patch adds some casts
to remove compilation warnings. In the past I have had warnings
off because of problems with the STL, but we may as well get
rid of the warnings we can. It also does not recognize that an
assert(0) or assert(false) ends a routine so it complains about
no return at end of function or variables not being defined.
(cherry picked from commit 3f12a401eb)

tgt-vhdl/cast.cc

@@ -1,7 +1,7 @@
 /*
  *  Generate code to convert between VHDL types.
  *
- *  Copyright (C) 2008  Nick Gasson (nick@nickg.me.uk)
+ *  Copyright (C) 2008-2009  Nick Gasson (nick@nickg.me.uk)
  *
  *  This program is free software; you can redistribute it and/or modify
  *  it under the terms of the GNU General Public License as published by
@@ -60,6 +60,8 @@ vhdl_expr *vhdl_expr::cast(const vhdl_type *to)
          assert(false);
       }
    }
+   assert(false);
+   return NULL;
 }
 
 /*
@@ -140,9 +142,8 @@ vhdl_expr *vhdl_expr::to_boolean()
       conv->add_expr(this);
       return conv;
    }
-   else {
-      assert(false);
-   }
+   assert(false);
+   return NULL;
 }
 
 /*
@@ -180,8 +181,8 @@ vhdl_expr *vhdl_expr::to_std_logic()
 
       return ah;
    }
-   else
-      assert(false);
+   assert(false);
+   return NULL;
 }
 
 /*
@@ -274,8 +275,8 @@ vhdl_expr *vhdl_const_bits::to_vector(vhdl_type_name_t name, int w)
       value_.resize(w, sign_bit());  
       return this;
    }
-   else
-      assert(false);
+   assert(false);
+   return NULL;
 }
 
 vhdl_expr *vhdl_const_bits::to_integer()

tgt-vhdl/state.cc

@@ -139,6 +139,7 @@ ivl_signal_t find_signal_named(const std::string &name, const vhdl_scope *scope)
          return (*it).first;
    }
    assert(false);
+   return NULL;
 }
 
 // Compare the name of an entity against a string

tgt-vhdl/stmt.cc

@@ -239,9 +239,9 @@ assign_for(vhdl_decl::assign_type_t atype, vhdl_var_ref *lhs, vhdl_expr *rhs)
       return new vhdl_assign_stmt(lhs, rhs);
    case vhdl_decl::ASSIGN_NONBLOCK:
       return new vhdl_nbassign_stmt(lhs, rhs);
-   default:
-      assert(false);
    }   
+   assert(false);
+   return NULL;
 }
 
 /*

tgt-vhdl/support.cc

@@ -1,7 +1,7 @@
 /*
  *  Support functions for VHDL output.
  *
- *  Copyright (C) 2008  Nick Gasson (nick@nickg.me.uk)
+ *  Copyright (C) 2008-2009  Nick Gasson (nick@nickg.me.uk)
  *
  *  This program is free software; you can redistribute it and/or modify
  *  it under the terms of the GNU General Public License as published by
@@ -51,6 +51,7 @@ const char *support_function::function_name(support_function_t type)
    default:
       assert(false);
    }
+   return "Invalid";
 }
 
 vhdl_type *support_function::function_type(support_function_t type)
@@ -74,9 +75,9 @@ vhdl_type *support_function::function_type(support_function_t type)
       return new vhdl_type(VHDL_TYPE_UNSIGNED);
    case SF_LOGIC_TO_INTEGER:
       return vhdl_type::integer();
-   default:
-      assert(false);
    }
+   assert(false);
+   return vhdl_type::boolean();
 }
 
 void support_function::emit_ternary(std::ostream &of, int level) const

tgt-vhdl/vhdl_syntax.hh

@@ -571,7 +571,8 @@ public:
    // For some sorts of declarations it doesn't make sense
    // to assign to it so calling assignment_type just raises
    // an assertion failure
-   virtual assign_type_t assignment_type() const { assert(false); }
+   virtual assign_type_t assignment_type() const { assert(false);
+                                                   return ASSIGN_BLOCK; }
 
    // True if this declaration can be read from
    virtual bool is_readable() const { return true; }