Make the for_step of for loops optional

In IEEE Std 1800-2017 A.6.8: the for_step part of the for loop
is optional. If missing, it is assumed that the programmer known
what they are doing.

design_dump.cc

@@ -1388,6 +1388,7 @@ void NetForLoop::dump(ostream&fd, unsigned ind) const
 	    fd << "<nil>";
       fd << endl;
       statement_->dump(fd, ind+4);
+      if (step_statement_)
 	    step_statement_->dump(fd, ind+4);
 }
 

elaborate.cc

@@ -5457,7 +5457,7 @@ NetProc* PForeach::elaborate_static_array_(Design*des, NetScope*scope,
  *  - index variable (name1_)  (optional)
  *  - initial value (expr1_)   (only if name1_ is present)
  *  - condition expression (cond_)
- *  - step statement (step_)
+ *  - step statement (step_)   (optional)
  *  - sub-statement (statement_)
  *
  * The rules that lead to the PForStatment look like:
@@ -5526,9 +5526,12 @@ NetProc* PForStatement::elaborate(Design*des, NetScope*scope) const
       // Now elaborate the for_step statement. I really should do
       // some error checking here to make sure the step statement
       // really does step the variable.
-      NetProc*step = step_->elaborate(des, scope);
+      NetProc*step = nullptr;
+      if (step_) {
+	    step = step_->elaborate(des, scope);
 	    if (!step)
 		  error_flag = true;
+      }
 
       // Elaborate the condition expression. Try to evaluate it too,
       // in case it is a constant. This is an interesting case
@@ -5544,10 +5547,10 @@ NetProc* PForStatement::elaborate(Design*des, NetScope*scope) const
       // Error recovery - if we failed to elaborate any of the loop
       // expressions, give up now. Error counts where handled elsewhere.
       if (error_flag) {
-	    delete initial_expr;
+	    if (initial_expr) delete initial_expr;
-	    delete ce;
+	    if (ce) delete ce;
-	    delete step;
+	    if (step) delete step;
-	    delete sub;
+	    if (sub) delete sub;
 	    return 0;
       }
 

net_proc.cc

@@ -212,7 +212,7 @@ void NetForLoop::wrap_up()
       // statement. This can happen for example with statments like this:
       //   for ( ; <condition> ; <step> ) <statement> ;
       // If the index_ and init_expr_ are present, then generate the
-      // inital assignment and push it into the sequential block
+      // inital assignment and push it into the sequential block.
       if (index_ || init_expr_) {
 	    top->set_line(*this);
 	    NetAssign_*lv = new NetAssign_(index_);
@@ -225,6 +225,10 @@ void NetForLoop::wrap_up()
       internal_block->set_line(*this);
 
       if (statement_) internal_block->append(statement_);
+
+      // The step statement is optional. If missing, it is assumed that
+      // the programmer has added it to the regular statement. Hopefully.
+      if (step_statement_)
 	    internal_block->append(step_statement_);
 
       NetWhile*wloop = new NetWhile(condition_, internal_block);

parse.y

@@ -675,7 +675,7 @@ static void current_function_set_statement(const YYLTYPE&loc, std::vector<Statem
 %type <event_statement> event_control
 %type <statement> statement statement_item statement_or_null
 %type <statement> compressed_statement
-%type <statement> loop_statement for_step jump_statement
+%type <statement> loop_statement for_step for_step_opt jump_statement
 %type <statement> concurrent_assertion_statement
 %type <statement> deferred_immediate_assertion_statement
 %type <statement> simple_immediate_assertion_statement
@@ -1418,6 +1418,10 @@ for_step /* IEEE1800-2005: A.6.8 */
       { $$ = $1; }
   ;
 
+for_step_opt
+  : for_step { $$ = $1; }
+  | { $$ = nullptr; }
+  ;
 
   /* The function declaration rule matches the function declaration
      header, then pushes the function scope. This causes the
@@ -1616,7 +1620,7 @@ lifetime_opt /* IEEE1800-2005: A.2.1.3 */
   /* Loop statements are kinds of statements. */
 
 loop_statement /* IEEE1800-2005: A.6.8 */
-  : K_for '(' lpvalue '=' expression ';' expression ';' for_step ')'
+  : K_for '(' lpvalue '=' expression ';' expression ';' for_step_opt ')'
     statement_or_null
       { PForStatement*tmp = new PForStatement($3, $5, $7, $9, $11);
 	FILE_NAME(tmp, @1);
@@ -1624,7 +1628,7 @@ loop_statement /* IEEE1800-2005: A.6.8 */
       }
 
       // The initialization statement is optional.
-  | K_for '(' ';' expression ';' for_step ')'
+  | K_for '(' ';' expression ';' for_step_opt ')'
     statement_or_null
       { PForStatement*tmp = new PForStatement(nullptr, nullptr, $4, $6, $8);
 	FILE_NAME(tmp, @1);
@@ -1635,7 +1639,7 @@ loop_statement /* IEEE1800-2005: A.6.8 */
       // statement in a synthetic named block. We can name the block
       // after the variable that we are creating, that identifier is
       // safe in the controlling scope.
-  | K_for '(' K_var_opt data_type IDENTIFIER '=' expression ';' expression ';' for_step ')'
+  | K_for '(' K_var_opt data_type IDENTIFIER '=' expression ';' expression ';' for_step_opt ')'
       { static unsigned for_counter = 0;
 	char for_block_name [64];
 	snprintf(for_block_name, sizeof for_block_name, "$ivl_for_loop%u", for_counter);
@@ -1726,7 +1730,7 @@ loop_statement /* IEEE1800-2005: A.6.8 */
 	yyerror(@1, "error: Error in for loop step assignment.");
       }
 
-  | K_for '(' lpvalue '=' expression ';' error ';' for_step ')'
+  | K_for '(' lpvalue '=' expression ';' error ';' for_step_opt ')'
     statement_or_null
       { $$ = 0;
 	yyerror(@1, "error: Error in for loop condition expression.");

pform_dump.cc

@@ -1158,7 +1158,10 @@ void PForStatement::dump(ostream&out, unsigned ind) const
       else
 	    out << "<no-cond>";
       out << "; <for_step>)" << endl;
+      if (step_)
 	    step_->dump(out, ind+6);
+      else
+	    out << setw(ind+6) << "" << "<no for_step statement>" << endl;
       if (statement_)
 	    statement_->dump(out, ind+3);
       else

synth2.cc

@@ -1458,6 +1458,11 @@ bool NetForLoop::synth_async(Design*des, NetScope*scope,
 	    return false;
       }
 
+      if (!step_statement_) {
+	    cerr << get_fileline() << ": sorry: Unable to synthesize for-loop without for_step statement." << endl;
+	    return false;
+      }
+
       ivl_assert(*this, index_ && init_expr_);
       if (debug_synth2) {
 	    cerr << get_fileline() << ": NetForLoop::synth_async: "