Silence warning in select.cc

With GCC 9.3, at least, compiling select.cc spits out a warning about
an implausible bound being passed to strncmp. This comes from inlining
IdString::compare(): it turns out that passing std::string::npos as a
bound to strncmp triggers it.

This patch replaces the compare call with a memcmp with the same
effect. The repeated calls to IdString::c_str are slightly
inefficient, but I'll address that in a follow-up commit.

diff --git a/passes/cmds/select.cc b/passes/cmds/select.cc
index 6e728c16f5148ff09c6d803007cdf94fa4681f84..c5ef72b1c1acecf8d22c251abc2942863b20c7f1 100644 (file)
--- a/passes/cmds/select.cc
+++ b/passes/cmds/select.cc
@@ -34,7 +34,10 @@ static bool match_ids(RTLIL::IdString id, std::string pattern)
 {
        if (id == pattern)
                return true;
-       if (id.size() > 0 && id[0] == '\\' && id.compare(1, std::string::npos, pattern.c_str()) == 0)
+       const char *id_c = id.c_str();
+       if (*id_c == '\\' &&
+           id.size() == 1 + pattern.size() &&
+           memcmp(id_c + 1, pattern.c_str(), pattern.size()) == 0)
                return true;
        if (patmatch(pattern.c_str(), id.c_str()))
                return true;