Allow attributes on individual switch cases in RTLIL.

The parser changes are slightly awkward. Consider the following IL:

    process $0
      <point 1>
      switch \foo
        <point 2>
        case 1'1
          assign \bar \baz
          <point 3>
          ...
        case
      end
    end

Before this commit, attributes are valid in <point 1>, and <point 3>
iff it is immediately followed by a `switch`. (They are essentially
attached to the switch.) But, after this commit, and because switch
cases do not have an ending delimiter, <point 3> becomes ambiguous:
the attribute could attach to either the following `case`, or to
the following `switch`. This isn't expressible in LALR(1) and results
in a reduce/reduce conflict.

To address this, attributes inside processes are now valid anywhere
inside the process: in <point 1> and <point 3> a part of case body,
and in <point 2> as a separate rule. As a consequence, attributes
can now precede `assign`s, which is made illegal in the same way it
is illegal to attach attributes to `connect`.

Attributes are tracked separately from the parser state, so this
does not affect collection of attributes at all, other than allowing
them on `case`s. The grammar change serves purely to allow attributes
in more syntactic places.

backends/ilang/ilang_backend.cc

@@ -204,6 +204,11 @@ void ILANG_BACKEND::dump_proc_switch(std::ostream &f, std::string indent, const
 
 	for (auto it = sw->cases.begin(); it != sw->cases.end(); ++it)
 	{
+		for (auto ait = (*it)->attributes.begin(); ait != (*it)->attributes.end(); ++ait) {
+			f << stringf("%s  attribute %s ", indent.c_str(), ait->first.c_str());
+			dump_const(f, ait->second);
+			f << stringf("\n");
+		}
 		f << stringf("%s  case ", indent.c_str());
 		for (size_t i = 0; i < (*it)->compare.size(); i++) {
 			if (i > 0)

frontends/ilang/ilang_parser.y

@@ -282,14 +282,14 @@ proc_stmt:
 	} case_body sync_list TOK_END EOL;
 
 switch_stmt:
-	attr_list TOK_SWITCH sigspec EOL {
+	TOK_SWITCH sigspec EOL {
 		RTLIL::SwitchRule *rule = new RTLIL::SwitchRule;
-		rule->signal = *$3;
+		rule->signal = *$2;
 		rule->attributes = attrbuf;
 		switch_stack.back()->push_back(rule);
 		attrbuf.clear();
-		delete $3;
-	} switch_body TOK_END EOL;
+		delete $2;
+	} attr_list switch_body TOK_END EOL;
 
 attr_list:
 	/* empty */ |
@@ -298,9 +298,11 @@ attr_list:
 switch_body:
 	switch_body TOK_CASE {
 		RTLIL::CaseRule *rule = new RTLIL::CaseRule;
+		rule->attributes = attrbuf;
 		switch_stack.back()->back()->cases.push_back(rule);
 		switch_stack.push_back(&rule->switches);
 		case_stack.push_back(rule);
+		attrbuf.clear();
 	} compare_list EOL case_body {
 		switch_stack.pop_back();
 		case_stack.pop_back();
@@ -319,12 +321,15 @@ compare_list:
 	/* empty */;
 
 case_body:
+	case_body attr_stmt |
 	case_body switch_stmt |
 	case_body assign_stmt |
 	/* empty */;
 
 assign_stmt:
 	TOK_ASSIGN sigspec sigspec EOL {
+		if (attrbuf.size() != 0)
+			rtlil_frontend_ilang_yyerror("dangling attribute");
 		case_stack.back()->actions.push_back(RTLIL::SigSig(*$2, *$3));
 		delete $2;
 		delete $3;

kernel/rtlil.h

@@ -1327,7 +1327,7 @@ public:
 #endif
 };
 
-struct RTLIL::CaseRule
+struct RTLIL::CaseRule : public RTLIL::AttrObject
 {
 	std::vector<RTLIL::SigSpec> compare;
 	std::vector<RTLIL::SigSig> actions;