Fixed cstr_buf for std::string with small string optimization

backends/blif/blif.cc

@@ -61,7 +61,7 @@ struct BlifDumper
 	{
 	}
 
-	std::vector<std::string> cstr_buf;
+	vector<shared_str> cstr_buf;
 
 	const char *cstr(RTLIL::IdString id)
 	{

backends/btor/btor.cc

@@ -155,7 +155,7 @@ struct BtorDumper
 		 
 	}
 	
-	std::vector<std::string> cstr_buf;
+	vector<shared_str> cstr_buf;
 
 	const char *cstr(const RTLIL::IdString id)
 	{

kernel/log.cc

@@ -52,7 +52,7 @@ string log_last_error;
 
 vector<int> header_count;
 pool<RTLIL::IdString> log_id_cache;
-vector<string> string_buf;
+vector<shared_str> string_buf;
 int string_buf_index = -1;
 
 static struct timeval initial_tv = { 0, 0 };

kernel/yosys.h

@@ -140,6 +140,17 @@ using std::vector;
 using std::string;
 using std::pair;
 
+// A primitive shared string implementation that does not
+// move its .c_str() when the object is copied or moved.
+struct shared_str {
+	std::shared_ptr<string> content;
+	shared_str() { }
+	shared_str(string s) { content = std::shared_ptr<string>(new string(s)); }
+	shared_str(const char *s) { content = std::shared_ptr<string>(new string(s)); }
+	const char *c_str() { return content->c_str(); }
+	const string &str() { return *content; }
+};
+
 using hashlib::mkhash;
 using hashlib::mkhash_init;
 using hashlib::mkhash_add;

passes/cmds/show.cc

@@ -41,7 +41,7 @@ struct ShowWorker
 {
 	CellTypes ct;
 
-	std::vector<std::string> dot_escape_store;
+	vector<shared_str> dot_escape_store;
 	std::map<RTLIL::IdString, int> dot_id2num_store;
 	std::map<RTLIL::IdString, int> autonames;
 	int single_idx_count;