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I tried to compile KLayout with GCC 9 with as much warnings enables as possible.
I found next interesting occurrences:
src/db/db/dbDeepEdges.cc:594:67: warning: this condition has identical branches [-Wduplicated-branches] const db::Shapes &s = c->shapes (filter.requires_raw_input () ? edges.layer () : edges.layer ()); src/tl/tl/tlUri.cc:123:40: warning: this condition has identical branches [-Wduplicated-branches] if (ex.test ("//") || (ex.test ("/") ? prefer_authority : prefer_authority)) src/tl/tl/tlUri.cc:44:23: warning: logical ‘or’ of collectively exhaustive tests is always true [-Wlogical-op] else if (c >= 'a' || c < = 'f')