http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46900
--- Comment #6 from Tobias Burnus <burnus at gcc dot gnu.org> 2010-12-16 15:23:40 UTC --- I think that the files passed to lto1 are the same - but I get different command-line options: a) Two-step compile with "-fexternal-blas -flto -Ofast -march=native" x86_64-unknown-linux-gnu/4.6.0/lto1 -march=k8-sse3 -msahf --param l1-cache-size=64 --param l1-cache-line-size=64 --param l2-cache-size=1024 -mtune=k8 b) Single-step compile: x86_64-unknown-linux-gnu/4.6.0/lto1 -quiet -dumpbase ccmRjX1L.ltrans0.o -mtune=generic -march=x86-64 Thus, the "-march=native" somehow gets lost in the single-step compile.
