http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51821
--- Comment #11 from Uros Bizjak <ubizjak at gmail dot com> 2012-01-12 08:04:13 UTC --- I think that DF is OK, the problem is in recog.c/peep2_find_free_register, with this loop: while (from != to) { HARD_REG_SET this_live; from = peep2_buf_position (from + 1); gcc_assert (peep2_insn_data[from].insn != NULL_RTX); REG_SET_TO_HARD_REG_SET (this_live, peep2_insn_data[from].live_before); IOR_HARD_REG_SET (live, this_live); } Here we need to analyse the insn patterns for ALL sets and clobbers, not only track live registers through the insn stream.