static cast: support changing size and signedness

Support SystemVerilog Static Cast
- size
- signedness
- (type is not supposted yet)

Fix #535

frontends/ast/ast.cc

@@ -95,6 +95,7 @@ std::string AST::type2str(AstNodeType type)
 	X(AST_TO_SIGNED)
 	X(AST_TO_UNSIGNED)
 	X(AST_SELFSZ)
+	X(AST_CAST_SIZE)
 	X(AST_CONCAT)
 	X(AST_REPLICATE)
 	X(AST_BIT_NOT)

frontends/ast/ast.h

@@ -76,6 +76,7 @@ namespace AST
 		AST_TO_SIGNED,
 		AST_TO_UNSIGNED,
 		AST_SELFSZ,
+		AST_CAST_SIZE,
 		AST_CONCAT,
 		AST_REPLICATE,
 		AST_BIT_NOT,

frontends/ast/genrtlil.cc

@@ -814,6 +814,16 @@ void AstNode::detectSignWidthWorker(int &width_hint, bool &sign_hint, bool *foun
 		children.at(0)->detectSignWidthWorker(sub_width_hint, sign_hint);
 		break;
 
+	case AST_CAST_SIZE:
+		while (children.at(0)->simplify(true, false, false, 1, -1, false, false)) { }
+		if (children.at(0)->type != AST_CONSTANT)
+			log_file_error(filename, location.first_line, "Static cast with non constant expression!\n");
+		children.at(1)->detectSignWidthWorker(width_hint, sign_hint);
+		width_hint = children.at(0)->bitsAsConst().as_int();
+		if (width_hint <= 0)
+			log_file_error(filename, location.first_line, "Static cast with zero or negative size!\n");
+		break;
+
 	case AST_CONCAT:
 		for (auto child : children) {
 			sub_width_hint = 0;
@@ -1289,6 +1299,20 @@ RTLIL::SigSpec AstNode::genRTLIL(int width_hint, bool sign_hint)
 			return sig;
 	}
 
+	// changing the size of signal can be done directly using RTLIL::SigSpec
+	case AST_CAST_SIZE: {
+			RTLIL::SigSpec size = children[0]->genRTLIL();
+			RTLIL::SigSpec sig = children[1]->genRTLIL();
+			if (!size.is_fully_const())
+				log_file_error(filename, location.first_line, "Static cast with non constant expression!\n");
+			int width = size.as_int();
+			if (width <= 0)
+				log_file_error(filename, location.first_line, "Static cast with zero or negative size!\n");
+			sig.extend_u0(width, sign_hint);
+			is_signed = sign_hint;
+			return sig;
+		}
+
 	// concatenation of signals can be done directly using RTLIL::SigSpec
 	case AST_CONCAT: {
 			RTLIL::SigSpec sig;

frontends/ast/simplify.cc

@@ -950,6 +950,7 @@ bool AstNode::simplify(bool const_fold, bool at_zero, bool in_lvalue, int stage,
 	case AST_TO_SIGNED:
 	case AST_TO_UNSIGNED:
 	case AST_SELFSZ:
+	case AST_CAST_SIZE:
 	case AST_CONCAT:
 	case AST_REPLICATE:
 	case AST_REDUCE_AND:

frontends/verilog/verilog_lexer.l

@@ -517,6 +517,8 @@ import[ \t\r\n]+\"(DPI|DPI-C)\"[ \t\r\n]+function[ \t\r\n]+ {
 "<<<" { return OP_SSHL; }
 ">>>" { return OP_SSHR; }
 
+"'" { return OP_CAST; }
+
 "::"  { return TOK_PACKAGESEP; }
 "++"  { return TOK_INCREMENT; }
 "--"  { return TOK_DECREMENT; }

frontends/verilog/verilog_parser.y

@@ -298,6 +298,7 @@ static void rewriteAsMemoryNode(AstNode *node, AstNode *rangeNode)
 %left '+' '-'
 %left '*' '/' '%'
 %left OP_POW
+%left OP_CAST
 %right UNARY_OPS
 
 %define parse.error verbose
@@ -3001,6 +3002,24 @@ basic_expr:
 		$$ = new AstNode(AST_LOGIC_NOT, $3);
 		SET_AST_NODE_LOC($$, @1, @3);
 		append_attr($$, $2);
+	} |
+	TOK_SIGNED OP_CAST '(' expr ')' {
+		if (!sv_mode)
+			frontend_verilog_yyerror("Static cast is only supported in SystemVerilog mode.");
+		$$ = new AstNode(AST_TO_SIGNED, $4);
+		SET_AST_NODE_LOC($$, @1, @4);
+	} |
+	TOK_UNSIGNED OP_CAST '(' expr ')' {
+		if (!sv_mode)
+			frontend_verilog_yyerror("Static cast is only supported in SystemVerilog mode.");
+		$$ = new AstNode(AST_TO_UNSIGNED, $4);
+		SET_AST_NODE_LOC($$, @1, @4);
+	} |
+	basic_expr OP_CAST '(' expr ')' {
+		if (!sv_mode)
+			frontend_verilog_yyerror("Static cast is only supported in SystemVerilog mode.");
+		$$ = new AstNode(AST_CAST_SIZE, $1, $4);
+		SET_AST_NODE_LOC($$, @1, @4);
 	};
 
 concat_list: