https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82524
Bug ID: 82524 Summary: expensive-optimizations produces wrong results Product: gcc Version: 7.2.1 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c++ Assignee: unassigned at gcc dot gnu.org Reporter: Vasilis.Vlachoudis at cern dot ch Target Milestone: --- Created attachment 42342 --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=42342&action=edit Bug example System: Fresh installation of Fedora Core 26 Compiler: g++ --version g++ (GCC) 7.2.1 20170915 (Red Hat 7.2.1-2) The attached file when compiled with/out the -fexpensive-optimization or fno-expensive-optimization flag produces different results $ g++ -O2 -fno-expensive-optimizations bug.cc; a.out A=00FFFFFF B=FFFFFFFF alphaBlend(A,B)=00FFFFFF $ g++ -O2 bug.cc; a.out A=00FFFFFF B=FFFFFFFF alphaBlend(A,B)=0000FFFF