Optimise away empty (VHDL) processes

tgt-vhdl/process.cc

@@ -51,7 +51,11 @@ static int generate_vhdl_process(vhdl_entity *ent, ivl_process_t proc)
    // Initial processes are translated to VHDL processes with
    // no sensitivity list and and indefinite wait statement at
    // the end
-   if (ivl_process_type(proc) == IVL_PR_INITIAL) {
+   // However, if no statements were added to the container
+   // by draw_stmt, don't bother adding a wait as `emit'
+   // will optimise the process out of the output
+   if (ivl_process_type(proc) == IVL_PR_INITIAL
+       && !vhdl_proc->get_container()->empty()) {
       vhdl_wait_stmt *wait = new vhdl_wait_stmt();
       vhdl_proc->get_container()->add_stmt(wait);
    }

tgt-vhdl/vhdl_syntax.cc

@@ -218,6 +218,14 @@ bool vhdl_process::have_declared_var(const std::string &name) const
 
 void vhdl_process::emit(std::ofstream &of, int level) const
 {
+   // If there are no statements in the body, this process
+   // can't possibly do anything, so don't bother to emit it
+   if (stmts_.empty()) {
+      of << "-- Removed one empty process";
+      newline(of, level);
+      return;
+   }
+   
    emit_comment(of, level);
    if (name_.size() > 0)
       of << name_ << ": ";

tgt-vhdl/vhdl_syntax.hh

@@ -215,6 +215,7 @@ public:
    
    void add_stmt(vhdl_seq_stmt *stmt);
    void emit(std::ofstream &of, int level) const;
+   bool empty() const { return stmts_.empty(); }
 private:
    std::list<vhdl_seq_stmt*> stmts_;
 };