http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46186
--- Comment #12 from pinskia at gmail dot com <pinskia at gmail dot com> 2010-10-26 15:56:20 UTC --- On Oct 26, 2010, at 7:30 AM, "j...@jak-linux.org" <gcc-bugzi...@gcc.gnu.org > wrote: > http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46186 > > --- Comment #1 from Julian Andres Klode <j...@jak-linux.org> > 2010-10-26 14:30:24 UTC --- > Created attachment 22162 > --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=22162 > Clang's assember This multiplication transformation is incorrect if the loop wraps (unsigned always wraps; never overflows). Gcc is correct in its speed. Though -O3 is faster but not because of multiplication but rather constant propatagtion. So this bug is invalid and some one should report a bug to llvm folks about this. > > Attaching the assembler output from clang, it should help understand > which > optimizations clang does (and improve gcc to do them as well).
