We are catching a -Wmaybe-unitialized warning. We used Valgrind to determine its OK to suppress the warning. (No complaints about the warning itself; we'd rather know and be "better safe than sorry"). I'm having trouble determining when -Wmaybe-unitialized became available. The following is producing a warning hydra: // vmac.cpp:404:93: warning: ‘al2’ may be used uninitialized in this function // ... vmac.cpp:479:26: note: ‘al2’ was declared here // Valgrind cleared this finding. #if GCC_DIAGNOSTIC_AWARE # pragma GCC diagnostic push # pragma GCC diagnostic ignored "-Wmaybe-uninitialized" #endif and: c++ -DNDEBUG -g2 -O3 -fPIC -march=native -Wall -Wextra -pipe -c vmac.cpp vmac.cpp:457:33: warning: unknown warning group '-Wmaybe-uninitialized', ignored [-Wunknown-pragmas] # pragma GCC diagnostic ignored "-Wmaybe-uninitialized" ^ I checked the GCC release notes for 5, 4.9, 4.8. 4.7, 4.6, 4.5 and 4.4, but I did not see it discussed or mentioned. When did -Wmaybe-unitialized make its appearance?