Initial implementation of elaboration system tasks

(IEEE1800-2017 section 20.11)
This PR allows us to use $info/$warning/$error/$fatal **at elaboration time** within a generate block.
This is very useful to stop a synthesis of a parametrized block when an
illegal combination of parameters is chosen.

frontends/ast/ast.cc

@@ -154,6 +154,7 @@ std::string AST::type2str(AstNodeType type)
 	X(AST_GENIF)
 	X(AST_GENCASE)
 	X(AST_GENBLOCK)
+	X(AST_TECALL)
 	X(AST_POSEDGE)
 	X(AST_NEGEDGE)
 	X(AST_EDGE)

frontends/ast/ast.h

@@ -137,6 +137,7 @@ namespace AST
 		AST_GENIF,
 		AST_GENCASE,
 		AST_GENBLOCK,
+		AST_TECALL,
 		
 		AST_POSEDGE,
 		AST_NEGEDGE,
@@ -233,6 +234,7 @@ namespace AST
 		bool mem2reg_check(pool<AstNode*> &mem2reg_set);
 		void mem2reg_remove(pool<AstNode*> &mem2reg_set, vector<AstNode*> &delnodes);
 		void meminfo(int &mem_width, int &mem_size, int &addr_bits);
+		bool check_elab_tasks(void);
 
 		// additional functionality for evaluating constant functions
 		struct varinfo_t { RTLIL::Const val; int offset; bool is_signed; };

frontends/ast/genrtlil.cc

@@ -856,6 +856,7 @@ RTLIL::SigSpec AstNode::genRTLIL(int width_hint, bool sign_hint)
 	case AST_GENVAR:
 	case AST_GENFOR:
 	case AST_GENBLOCK:
+	case AST_TECALL:
 	case AST_GENIF:
 	case AST_GENCASE:
 	case AST_PACKAGE:

frontends/ast/simplify.cc

@@ -1146,6 +1146,7 @@ bool AstNode::simplify(bool const_fold, bool at_zero, bool in_lvalue, int stage,
 
 			if (type == AST_GENFOR) {
 				for (size_t i = 0; i < buf->children.size(); i++) {
+					if (!buf->children[i]->check_elab_tasks())
 						buf->children[i]->simplify(false, false, false, stage, -1, false, false);
 					current_ast_mod->children.push_back(buf->children[i]);
 				}
@@ -1261,6 +1262,7 @@ bool AstNode::simplify(bool const_fold, bool at_zero, bool in_lvalue, int stage,
 			}
 
 			for (size_t i = 0; i < buf->children.size(); i++) {
+				if (!buf->children[i]->check_elab_tasks())
 					buf->children[i]->simplify(false, false, false, stage, -1, false, false);
 				current_ast_mod->children.push_back(buf->children[i]);
 			}
@@ -1340,6 +1342,7 @@ bool AstNode::simplify(bool const_fold, bool at_zero, bool in_lvalue, int stage,
 			}
 
 			for (size_t i = 0; i < buf->children.size(); i++) {
+				if (!buf->children[i]->check_elab_tasks())
 					buf->children[i]->simplify(false, false, false, stage, -1, false, false);
 				current_ast_mod->children.push_back(buf->children[i]);
 			}
@@ -2969,6 +2972,44 @@ static void mark_memories_assign_lhs_complex(dict<AstNode*, pool<std::string>> &
 	}
 }
 
+// handle $info(), $warning(), $error(), $fatal()
+// we don't do that in simplify() because we don't know 
+bool AstNode::check_elab_tasks(void)
+{
+	if (type == AST_TECALL) {
+		int sz = children.size();
+		if (str == "$info") {
+			if (sz > 0)
+				log_file_info(filename, linenum, "%s.\n", children[0]->str.c_str());
+			else
+				log_file_info(filename, linenum, "\n");
+		} else if (str == "$warning") {
+			if (sz > 0)
+				log_file_warning(filename, linenum, "%s.\n", children[0]->str.c_str());
+			else
+				log_file_warning(filename, linenum, "\n");
+		} else if (str == "$error") {
+			if (sz > 0)
+				log_file_error(filename, linenum, "%s.\n", children[0]->str.c_str());
+			else
+				log_file_error(filename, linenum, "\n");
+		} else if (str == "$fatal") {
+			// TODO: 1st parameter, if exists, is 0,1 or 2, and passed to $finish()
+			// if no parameter is given, default value is 1
+			// dollar_finish(sz ? children[0] : 1);
+			// perhaps create & use log_file_fatal()
+			if (sz > 0)
+				log_file_error(filename, linenum, "FATAL: %s.\n", children[0]->str.c_str());
+			else
+				log_file_error(filename, linenum, "FATAL.\n");
+		} else {
+			log_file_error(filename, linenum, "Unknown elabortoon system task '%s'.\n", str.c_str());
+		}
+		return true;
+	}
+	return false;
+
+}
 // find memories that should be replaced by registers
 void AstNode::mem2reg_as_needed_pass1(dict<AstNode*, pool<std::string>> &mem2reg_places,
 		dict<AstNode*, uint32_t> &mem2reg_candidates, dict<AstNode*, uint32_t> &proc_flags, uint32_t &flags)

frontends/verilog/verilog_lexer.l

@@ -301,6 +301,11 @@ supply1 { return TOK_SUPPLY1; }
 	return TOK_ID;
 }
 
+"$"(info|warning|error|fatal) {
+	frontend_verilog_yylval.string = new std::string(yytext);
+	return TOK_ELAB_TASK;
+}
+
 "$signed"   { return TOK_TO_SIGNED; }
 "$unsigned" { return TOK_TO_UNSIGNED; }
 

frontends/verilog/verilog_parser.y

@@ -105,7 +105,7 @@ static void free_attr(std::map<std::string, AstNode*> *al)
 	bool boolean;
 }
 
-%token <string> TOK_STRING TOK_ID TOK_CONSTVAL TOK_REALVAL TOK_PRIMITIVE TOK_SVA_LABEL
+%token <string> TOK_STRING TOK_ID TOK_CONSTVAL TOK_REALVAL TOK_PRIMITIVE TOK_SVA_LABEL TOK_ELAB_TASK
 %token TOK_ASSERT TOK_ASSUME TOK_RESTRICT TOK_COVER
 %token ATTR_BEGIN ATTR_END DEFATTR_BEGIN DEFATTR_END
 %token TOK_MODULE TOK_ENDMODULE TOK_PARAMETER TOK_LOCALPARAM TOK_DEFPARAM
@@ -1869,6 +1869,15 @@ gen_stmt:
 		if ($6 != NULL)
 			delete $6;
 		ast_stack.pop_back();
+	} |
+	TOK_ELAB_TASK {
+		AstNode *node = new AstNode(AST_TECALL);
+		node->str = *$1;
+		delete $1;
+		ast_stack.back()->children.push_back(node);
+		ast_stack.push_back(node);
+	} opt_arg_list ';'{
+		ast_stack.pop_back();		
 	};
 
 gen_stmt_block:

kernel/log.cc

@@ -278,6 +278,17 @@ void log_file_warning(const std::string &filename, int lineno,
 	va_end(ap);
 }
 
+void log_file_info(const std::string &filename, int lineno,
+                      const char *format, ...)
+{
+	va_list ap;
+	va_start(ap, format);
+	std::string prefix = stringf("%s:%d: Info: ",
+				     filename.c_str(), lineno);
+	logv_warning_with_prefix(prefix.c_str(), format, ap);
+	va_end(ap);
+}
+
 YS_ATTRIBUTE(noreturn)
 static void logv_error_with_prefix(const char *prefix,
                                    const char *format, va_list ap)

kernel/log.h

@@ -80,6 +80,7 @@ void log_warning(const char *format, ...) YS_ATTRIBUTE(format(printf, 1, 2));
 
 // Log with filename to report a problem in a source file.
 void log_file_warning(const std::string &filename, int lineno, const char *format, ...) YS_ATTRIBUTE(format(printf, 3, 4));
+void log_file_info(const std::string &filename, int lineno, const char *format, ...) YS_ATTRIBUTE(format(printf, 3, 4));
 
 void log_warning_noprefix(const char *format, ...) YS_ATTRIBUTE(format(printf, 1, 2));
 YS_NORETURN void log_error(const char *format, ...) YS_ATTRIBUTE(format(printf, 1, 2), noreturn);

tests/various/elab_sys_tasks.sv

@@ -0,0 +1,30 @@
+module test;
+localparam X=1;
+genvar i;
+generate
+if (X == 1)
+  $info("X is 1");
+if (X == 1)
+  $warning("X is 1");
+else
+  $error("X is not 1");
+case (X)
+  1: $info("X is 1 in a case statement");
+endcase
+//case (X-1)
+//  1: $warn("X is 2");
+//  default: $warn("X might be anything in a case statement");
+//endcase
+for (i = 0; i < 3; i = i + 1)
+begin
+  case(i)
+    0: $info;
+    1: $warning;
+    default: $info("default case statemnent");
+  endcase
+end
+
+$info("This is a standalone $info(). Next $info has no parameters");
+$info;
+endgenerate
+endmodule

tests/various/elab_sys_tasks.ys

@@ -0,0 +1 @@
+read_verilog -sv elab_sys_tasks.sv