http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50088
H.J. Lu <hjl.tools at gmail dot com> changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |hjl.tools at gmail dot com --- Comment #3 from H.J. Lu <hjl.tools at gmail dot com> 2011-08-15 14:47:51 UTC --- It is done on purpose: /* X86_TUNE_MOVX: Enable to zero extend integer registers to avoid partial dependencies. */ m_PPRO | m_P4_NOCONA | m_CORE2I7 | m_ATOM | m_GEODE | m_AMD_MULTIPLE | m_GENERIC, You can remove m_ATOM to see its performance impact with -mtune=atom on Atom.