vhdlpp: Support for std_logic_vector return type in functions.

VHDL does not allow to specify the size of returned std_logic_vector,
whereas Verilog requires the size to be known in advance. The size of
the vector is determined by checking the type of expression used in the
return statement.

vhdlpp/sequential.h

@@ -120,6 +120,8 @@ class ReturnStmt  : public SequentialStmt {
       int emit(ostream&out, Entity*entity, Architecture*arc);
       void dump(ostream&out, int indent) const;
 
+      const Expression*peek_expr() const { return val_; };
+
     private:
       Expression*val_;
 };

vhdlpp/subprogram.cc

@@ -21,6 +21,7 @@
 # include  "subprogram.h"
 # include  "entity.h"
 # include  "vtype.h"
+# include  "sequential.h"
 # include  "ivl_assert.h"
 
 using namespace std;
@@ -45,6 +46,7 @@ void Subprogram::set_program_body(list<SequentialStmt*>*stmt)
 {
       ivl_assert(*this, statements_==0);
       statements_ = stmt;
+      fix_return_type();
 }
 
 bool Subprogram::compare_specification(Subprogram*that) const
@@ -78,6 +80,32 @@ bool Subprogram::compare_specification(Subprogram*that) const
       return true;
 }
 
+void Subprogram::fix_return_type(void)
+{
+    if(!statements_)
+        return;
+
+    const ReturnStmt*ret = NULL;
+    const VType*t = NULL;
+
+    for (std::list<SequentialStmt*>::const_iterator s = statements_->begin()
+	; s != statements_->end(); ++s) {
+      if((ret = dynamic_cast<const ReturnStmt*>(*s))) {
+            const Expression*expr = ret->peek_expr();
+
+            if(const ExpName*n = dynamic_cast<const ExpName*>(expr)) {
+                if(Variable*v = find_variable(n->peek_name()))
+                    t = v->peek_type();
+            } else {
+                t = expr->peek_type();
+            }
+
+            if(t)
+                return_type_ = t;
+        }
+    }
+}
+
 void Subprogram::write_to_stream(ostream&fd) const
 {
       fd << "  function " << name_ << "(";

vhdlpp/subprogram.h

@@ -57,6 +57,10 @@ class Subprogram : public LineInfo, public ScopeBase {
       void dump(std::ostream&fd) const;
 
     private:
+	// Determines appropriate return type. Un case of std_logic_vector
+	// VHDL requires skipping its size in contrary to Verilog
+      void fix_return_type(void);
+
       perm_string name_;
       const ScopeBase*parent_;
       std::list<InterfacePort*>*ports_;