https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86628
Bug ID: 86628 Summary: Missed simplification of division Product: gcc Version: tree-ssa Status: UNCONFIRMED Severity: normal Priority: P3 Component: c Assignee: unassigned at gcc dot gnu.org Reporter: david.bolvansky at gmail dot com Target Milestone: --- Hello, for code: int f(int x, int y, int z) { return (x * y * z) / (y * z); } GCC 8.1 (x86-64) with -O3 emits: f(int, int, int): mov eax, edi imul eax, esi imul esi, edx imul eax, edx cdq idiv esi ret but one multiplication can be removed, as Clang does it: f(int, int, int): imul esi, edx imul edi, esi mov eax, edi cdq idiv esi ret Also, for: unsigned f2(unsigned x, unsigned y, unsigned z) { return (x*z) / (y*z); } f2(unsigned int, unsigned int, unsigned int): mov eax, edi imul esi, edx imul eax, edx xor edx, edx div esi ret This could be simplified to "x/y". For a signed case it could be possible too, just z = -1 needs to be checked.