http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52041
--- Comment #10 from Iain Sandoe <iains at gcc dot gnu.org> 2012-01-30 18:22:12 UTC --- the stage3 tree-ssa-strlen.o fails with -fcompare-debug "failure (length)". An incomplete analysis ... run out of time... The first mismatched tree dump is 18t.ssa -- with differences like # DEBUG x => y but also there are some differences in temporary var numbers. ==== Looking at the asm, there seem to be differences like + movl al,%eax cmp $xxx, %eax and cltq in stage2 missing in stage 3 -- so size changing instructions.